Vacuum Ingot Casting Machine

— Vacuum Ingot Casting Machine: Vacuum Level and Mold Design

A vacuum ingot casting machine is a sealed induction melting and casting unit that turns a weighed gold or silver charge into a bar of declared weight and surface. The chamber is evacuated to 0.001–0.01 mbar and proved by a leak-rate hold test, then backfilled with 99.99% argon or nitrogen and held above ambient while the metal freezes, feeding the shrinking last liquid. Silver is harder: it holds about twenty times its own volume of oxygen, so air-cast silver spits. Pour temperature is a superheat above melting: 1,064 °C gold, 961.78 °C silver. The cavity is cut to the bar envelope with its contraction allowance, draft angle and feed head; weight follows from the charge. Big-cavity programmes anchor to Good Delivery weights: 400 troy ounces of gold (12.44 kg), 1,000 of silver (31.10 kg). A cycle runs twelve to twenty minutes on a stored PLC programme, directional cooling leaving a dense, ripple-free mirror bar. Casting carries fineness through, not up; the machine is engineered to your bar programme.

Product Overview

A vacuum ingot casting machine is the last piece of equipment in a precious metal flow rather than the first. Everything upstream — the leach, the precipitation, the electrolysis cell, the refining and purification circuit, the granulator and the dryer — is trying to deliver a metal that is already at the right fineness and in a form that can be handled. What that flow cannot deliver is a finished bar: sponge and crystal have to be melted, and metal that is melted in air takes oxygen and hydrogen into solution, forms an oxide skin on the surface, loses volatile alloying elements, and freezes with gas porosity and a shrinkage pipe where the last liquid collapsed. This machine exists to do that melting and that freezing inside a sealed chamber, and the whole of its engineering is in two questions — how completely the chamber is emptied of air, and how the metal is fed while it contracts.

The first question is the vacuum, and it is routinely under-specified in the market. A vacuum pump removes air, and with it the oxygen that would oxidise the melt and the nitrogen and water vapour that would contribute hydrogen, but the useful part of the specification is not the pressure a pump can reach on a closed valve — it is how quickly the chamber reaches pressure with a charge in it and how well it holds that pressure once the pump is isolated. Those are three different figures, and a machine described only as a vacuum machine has stated none of them. A chamber that reaches a good ultimate pressure and then leaks back to atmosphere has achieved an inert atmosphere by purging rather than by evacuation, and the difference shows up as a residual oxide skin and as a scatter in the assay of the cast bar rather than as an obvious defect.

The second question is the contraction, and it is the reason the chamber is pressurised rather than merely evacuated. Gold and silver both occupy less volume as solids than as liquids, and an ingot freezes from the mold wall inwards, so the last metal to solidify is the metal in the middle and just under the top surface. If there is nothing above it to replace the volume it loses, that metal pulls away from the already-solid shell and forms a pipe or a dispersed porosity — and in an investment bar, where the surface is the product, a pipe is not a metallurgical curiosity, it is a rejected bar. Filling the chamber with inert gas to a controlled positive pressure above ambient and holding that pressure through solidification supplies the reservoir, closes the pipe, and does it without introducing oxygen. Vacuum and overpressure are therefore not alternatives to each other; they are the first and second halves of one cycle.

The metals decide how the two halves are weighted. Silver is the more demanding of the two, because molten silver dissolves a very large volume of oxygen — of the order of twenty times its own volume close to the melting point — and because that solubility collapses as the metal freezes, the gas comes out of solution suddenly and violently. Cast silver in air spits, erupts and blisters, and the resulting ingot has a pitted crown and an uneven surface even when its assay is correct. Degassing under vacuum before the pour removes the dissolved gas while the metal is still liquid, and the inert atmosphere prevents it from being taken up again before the metal freezes. Gold takes up far less gas, so the vacuum matters more in gold work for the oxide-free surface and for the control of volatile alloying elements in karat alloys, and it matters at its most acute in the alloys, where zinc at a boiling point of 907 °C and other volatile constituents will leave the melt if the metal is held hot in air.

The third factor, and the one that decides whether a good cast can be repeated, is the mold. The cavity sets the bar envelope and the bar weight, the wall finish sets the as-cast surface, the draft angle sets whether the bar releases without being pulled, the feed head gives the contraction somewhere to draw from, and the preheat temperature decides whether the first metal into the cavity chills on contact or fills the corner. A mold that is correct for a 1 kg gold bar is not correct for a 12.5 kg one, and neither is correct for silver, because the contraction allowance, the thermal mass and the freezing range are all different. The cavity therefore belongs in the process design package alongside the chamber, and the drawings are issued against the bar the customer intends to sell.

Around those three factors sits the rest of the machine, and it is unremarkable in the best sense: an induction power supply and coil that put the heat inside the charge, a crucible that does not contaminate the melt, a pour mechanism that tilts or inverts the crucible on a controlled profile rather than dumping it, a gas handling set that evacuates, backfills and holds, a cooling circuit that takes the heat out of the coil and the mold, and a control system that runs the whole sequence from a stored programme with the interlocks, alarms and event log a continuous shift needs. What is not unremarkable is the sealing: a chamber that is opened and closed once per cycle, for years, in a shop where a leak costs a whole bar, is a machine designed around its seal faces and its lid mechanism rather than around its electronics.

Because bar weights, bar envelopes, metal mixes and monthly programmes differ so widely between a mint, a bullion refinery and a jewellery alloy house, the machine is engineered from your declared numbers rather than selected from a model list. The cavity count and layout follow from the bar programme; the chamber working volume follows from the mold block and the pour mechanism; the induction power and frequency follow from the metal mix and the mass to be melted inside the evacuation and melt windows the cycle allows; the vacuum system follows from the chamber volume and the leak-rate criterion; the inert-gas handling follows from the chamber volume and the number of evacuation and backfill cycles per hour; and the cooling duty follows from the heat that has to leave the coil, the mold and the ingot in the intervals between casts. Those figures are stated in the process design package, and we would rather revise the bar programme than supply a machine whose chamber cannot hold the vacuum its own cycle depends on.

Product Core Selling Points

The vacuum specification is issued as pressure, time and leak rate together. Most published machine descriptions quote the vacuum as a word and nothing else. This machine is quoted as three figures — the absolute pressure the chamber reaches, the evacuation window the cycle allows, and the leak rate the chamber holds after the pump is isolated — because a chamber that reaches a good pressure and then leaks back up has not degassed anything, and the hold test is the one item a buyer can repeat on site with the pump valved off.
Pressurised solidification is treated as a process stage, not as a safety fill. Inert gas is backfilled to a controlled positive overpressure and held while the ingot freezes, which is what feeds the contraction of the last liquid to solidify. The pressure is a set point in the casting programme with a hold time attached to it, not a purge that is opened once the pour is finished.
The mold cavity is dimensioned in the open, with the contraction allowance stated. The cavity is cut to the ordered bar envelope plus the allowance for the metal being cast, with a draft angle, a feed head and a machined wall finish. Because the allowance is written down, a buyer can check the mold drawing against the bar the machine is expected to deliver.
Bar weight is set by the pre-weighed charge, which is why a declared weight holds. The metal is weighed before it enters the chamber and the cavity accepts that charge with its shrinkage allowance, so the ingot weight is a consequence of the charge rather than of how full the mold happened to be. The weight is verified on the ingot and reconciled against the charge at the end of the cycle.
The nine-stage cycle is issued as a time budget. Evacuation, melting and degassing, superheat dwell, backfill, pour, pressurised hold, controlled cooling, venting and discharge each carry their own interval, and the budget is what shows which intervals are quality-critical — the degassing dwell and the pressurised hold — and which are simply throughput.
Purity is carried through, not created, and the page says so. The chamber removes dissolved gas and excludes oxygen from the melt surface; it does not remove base metals or separate one precious metal from another. Stating that boundary is what lets a refinery plan the machine behind its refining or electrolysis route rather than in place of it.
Loss is accounted as a closed budget with a return loop. Crucible skull, runner and rejected ingot return to the next charge, and only the vapour and fine dust deposited on the chamber wall are irrecoverable. Because the two figures are separated, a per-cycle metal loss measured on the shop floor is not mistaken for metal that has left the plant.
The chamber is sealed by design, not by gasket replacement. Sealing faces are machined, lapped and inspected, the lid is a backed and guided assembly rather than a lid dropped onto a gasket, and the seal condition is checked against the leak-rate test at each campaign rather than discovered when a programme pulls a poor vacuum.
No flame anywhere in the cycle. Induction heating puts the energy inside the charge and the pour happens inside a sealed chamber, so there is no torch, no flux, no open crucible and no operator standing over molten metal — which is the difference in acceptable risk between this machine and a bench casting setup.
Karat gold and silver are treated as different casting problems. Volatile alloying elements such as zinc, which boils at 907 °C, are held in the melt by melting under vacuum with a controlled superheat dwell and a short time at temperature, so the fineness of a karat alloy stays on target; silver is degassed for the opposite reason, because it holds oxygen in solution and rejects it on freezing.
Multi-cavity and single-cavity layouts are both first-class configurations. A single-cavity mold for a 12.5 kg Good Delivery weight bar and a multi-cavity mold set producing several 1 kg bars per cycle are engineered from the same chamber, with the cavity layout, the pour path and the thermal uniformity of the mold block treated as design outputs rather than as mould options.
Cooling is a controlled programme, not an open door. The ingot cools inside the sealed chamber on a set profile with the chamber still under inert gas, and the mold is brought to a stated temperature before discharge, so the surface is bright and the cast structure is even rather than quenched at the surface and loose in the middle.
The machine is built to run continuously and to be operated by one person. The whole cycle runs from a stored programme, the operating sequence is a single start command with the chamber state and the metal temperature displayed through the cycle, and the control system carries the interlocks and the alarm and event log that a shift pattern needs when the unit is running around the clock.
Cavity, chamber, power and programme engineered to your production. Cavity count and layout, bar envelope and weight, chamber working volume, induction power and frequency, vacuum system, inert-gas handling, cooling duty, cycle programme and utilities are stated in the process design package against your declared bar weights, metal mix, feed fineness and monthly programme.

Application Scenarios

Bullion refineries finishing their own gold and silver. A refinery that already produces 99.99% gold or silver crystal and needs to deliver a bar rather than a powder, at a declared weight, with a surface a buyer will accept without question.
Mints and coin blank producers. Operations that cast bar or strip stock as the input to a minting or rolling line, where the as-cast surface and the internal soundness decide how much rolling and polishing the stock needs downstream.
Precious metal refineries with an electrolysis route upstream. Plants where a gold electrolysis cell or a silver electrolysis line delivers crystal that has to be melted and cast, and where the casting step is the last chance to lose the fineness that the cell achieved.
Jewellery alloy houses casting karat gold. Operations making 18K, 22K or colour-controlled alloys, where the volatile alloying elements have to be held in the melt and the fineness of a declared alloy has to be reproducible from bar to bar.
Precious metal recovery and e-waste refining plants. Operations recovering gold and silver from printed circuit boards, contacts, catalysts and plating residues, where the recovered metal is cast into a saleable bar at the end of the route.
Silver producers working from doré or fire-refined silver. Sites where silver is melted and cast into Good Delivery weight bars, and where the silver oxide and the spitting behaviour of molten silver are the governing problems rather than the assay.
Operations casting to Good Delivery weight for the first time. Producers who need the 12.5 kg gold and 31 kg silver bars that the London market recognises, and who need a mold and a casting programme that reproduce those weights rather than approximate them.
Refineries casting copper and copper alloy ingots. Where copper recovered from a leach, an electrolysis bleed or a plating operation is melted and cast into an ingot for sale, remelting or anode casting.
Hallmarking and assay laboratories. Small, well-characterised casting work where the requirement is a documented weight, a documented fineness and a bar that can be tested and retained as a reference.
Platinum group metal processors. Where the melting and superheat duty is specified for the platinum group metals and their alloys, and where the chamber, crucible and mold materials are selected for the higher temperatures involved.
Plants replacing an open crucible and a torch. Operations still melting in an open crucible with a gas torch or a resistance furnace and pouring into an open mold, where the problems are oxide skin, gas porosity and an operator standing over molten metal.
Plants whose bars are rejected on weight or on surface. Producers whose rejection rate is driven by under-weight bars, surface ripples or porosity found at assay, and where the fix is a fixed cavity volume and a controlled freeze rather than more inspection.
Operations casting several bar sizes from one machine. Mints and refineries running 100 g, 1 kg, 10 oz and 12.5 kg programmes, where the mold set is changed on a schedule and the casting programme is recalled from the control system rather than re-invented.
Small and pilot plants. Reduced-volume casting cells built from a single chamber upward, where the same cavity dimensioning and the same vacuum criteria scale down rather than being replaced by a different concept.

Applicable Raw Materials

The chamber accepts metallic precious metal feed that has been dried and weighed, and every feed below enters the machine as a pre-weighed charge placed in the crucible or the mold. Material that is already coarse and clean is charged directly; sponge, powder and fine crystal are consolidated by granulation, briquetting or pre-melting rather than charged loose, because a fine charge that is drawn out of the crucible by the pump is metal that will be found on the chamber wall; and material that is wet, oily or contaminated with an element that would volatilise into the chamber is dried or refined before it is charged. Output is stated for each feed.

Gold sponge and precipitated gold powder. The classical feed from an oxalate, sulphur dioxide or ferrous sulphate reduction, dried and usually granulated before charging so that the charge does not carry fines into the vacuum line. Output: a cast gold bar at the fineness of the feed.
Electrolytic gold crystal from a gold electrolysis cell. Coarse crystalline gold stripped from the cathode, washed, dried and charged directly, with the fineness already established by the cell. Output: a cast bar at 99.99% or better, at the weight of the charge.
Gold granules and shot from a granulator. Metal converted to a free-flowing granule by a shot-making or granulating unit, which is the form the crucible handles most easily and the form that reassures the charge weight. Output: a cast bar from a uniformly charged, weighable feed.
Karat gold and colour-controlled gold alloys. 18K, 22K and formulated alloys charged against a written composition, where the volatile constituents have to be held in the melt and the fineness of the finished bar has to match the declaration. Output: a cast alloy bar at the declared fineness and colour.
Silver crystal from a silver electrolysis line. The main feed into silver bar production, coarse crystal from a silver nitrate cell, washed free of entrained electrolyte and dried before charging. Output: a cast silver bar at the fineness of the crystal.
Silver doré and fire-refined silver. Bars or granules that have been through a smelting step and carry residual base metal, charged where the fineness is acceptable and the residual load is known. Output: a cast silver bar at the declared fineness of the feed.
Silver cement and reduced silver powder. Silver precipitated from solution with zinc, copper or a reductant, washed and dried, and granulated before charging because the powder is too fine to place in a crucible without loss. Output: a cast silver bar from a consolidated charge.
Recovered gold and silver from electronic and industrial scrap. Metal recovered from printed circuit boards, connectors, contacts, plating residues and spent catalysts, refined to a declared fineness upstream and cast here. Output: a cast bar at the fineness the recovery route achieved.
Copper and copper alloy ingot feed. Copper recovered from a leach, an electrolysis bleed or a plating operation, melted and cast into an ingot for sale, remelting or anode casting. Output: a cast copper or copper alloy ingot.
Platinum group metals and their alloys. Where the melting and superheat duty is specified for them, charged with a crucible and a mold selected for the higher temperature and for the lower tolerance of these metals to contamination. Output: a cast platinum group metal bar or alloy bar at the declared composition.
Returned, rejected and part-processed ingots. Bars that failed a weight, a surface or an assay check, cut and recharged rather than sold at a discount, with the rejection reason recorded against the lot so the cause can be found. Output: a re-cast bar at the declared weight and fineness.
Skull, runner and crucible residue reclaimed from the previous campaign. The metal that solidified in the crucible, in the pour path or in the feed head, recovered and returned to the next charge so that it circulates inside the plant rather than leaving it. Output: recovered metal returned to the next charge.
Bar croppings and offcuts from downstream operations. Trimmed ends, punched centres and machining swarf from minting, rolling and finishing, dried and degreased before charging. Output: cast bar feed with the oil and moisture removed first.
Feed that must not be charged. Wet or oil-contaminated scrap, which will pull water vapour into the chamber and defeat the vacuum; material containing mercury, cadmium or other volatile contaminants, which will leave the melt and deposit in the vacuum line; sealed or hollow components, which will outgas in the chamber; and metal whose fineness is unknown, because casting carries a fineness through rather than establishing one — these are routed to drying, refining or dismantling before they reach the machine. Output: a documented rejection or a re-route to the correct upstream step.

Finished Products

The machine is configured around the bar programme the customer sells and the point at which the customer takes delivery of it. Where the customer already operates a granulator, a dryer, an assay laboratory and a stamping and packaging line, the machine is supplied as the chamber with its vacuum system, mold set, cooling circuit and control system; where it does not, granulation, drying, weighing, marking and packaging are included with it.

Good Delivery weight gold bars. The 400 troy ounce bar, about 12.44 kg, cast in a single-cavity mold to the envelope and the weight the London market recognises, which is the reference point the large-cavity programmes are dimensioned against. Output: a cast gold bar at about 12.44 kg with its cast weight recorded.
Good Delivery weight silver bars. The 1,000 troy ounce bar, about 31.10 kg, cast in a single-cavity mold, and the reason a silver programme runs a larger chamber and a larger mold block than a gold programme of the same throughput. Output: a cast silver bar at about 31.10 kg with its cast weight recorded.
Kilogram gold bars. The 1 kg investment bar, either cast singly or as a multi-cavity set producing several bars in one cycle, and the most common bullion weight in both gold and silver. Output: cast 1 kg bars at the declared weight, in single or multi-cavity sets.
Small bullion bars. 100 g, 50 g and 10 troy ounce programmes run in multi-cavity molds, where the cavity count and the mold thermal uniformity decide whether every cavity fills and freezes identically. Output: cast small bars with the cavity-to-cavity weight spread recorded.
Karat and alloy bars. 18K, 22K and formulated colour alloys cast to a declared composition, at the fineness the alloy specification names rather than at a bullion fineness. Output: cast alloy bars at the declared fineness and colour.
Copper and base metal ingots. Copper and copper alloy ingots cast for sale, remelting or anode casting, where the chamber is used for surface quality and gas removal rather than for fineness. Output: cast ingots with the surface free of oxide scale.
Platinum group metal bars. Where the melting duty is specified for them, cast bars and alloy bars at the declared composition, with the crucible and the mold selected for the higher temperature. Output: cast bars at the declared composition.
As-cast surface with no oxide skin. The ingot leaves the mold free of oxide, with the mold wall finish reproduced on the surface and without the water-wave ripple that an open pour produces, so the bar either needs no finishing at all or needs only a light polish before marking. Output: an as-cast bright surface, with the bar released against a surface standard agreed before manufacture.
Ingots with no gas porosity and no shrinkage pipe. The result of degassing under vacuum and holding an inert-gas overpressure through solidification, giving a bar that is dense through its section rather than sound only at the surface, which is what a density check or a section through a rejected bar is looking for. Output: a dense ingot with the shrinkage allowance consumed inside the feed head rather than inside the bar.
Declared bar weights held to a stated tolerance. The weight is set by the pre-weighed charge, verified on the ingot and reconciled against the charge at the end of the cycle, with the tolerance stated in the contract rather than left to the mold. Output: bars at the declared weight with the cast weight recorded against the lot.
Marked and traced bars. Weight, fineness, manufacturer’s mark and a serial or lot number applied to the bar, with the cast record carrying the charge weight, the mold and cavity number, the programme used, the vacuum figures recorded through the cycle and the assay result. Output: a marked bar and a lot record that stands behind it.
Assay results from the cast bar. Fineness declared by fire assay, X-ray fluorescence or inductively coupled plasma analysis, run on the bar or on a sample taken from the charge, with the method and the laboratory agreed before manufacture so that acceptance does not depend on how the figure was produced. Output: an assay certificate for the lot.
Recovered skull, runner and feed-head metal. The metal that solidified in the crucible, the pour path and the feed head, recovered, weighed and returned to the next charge rather than written off. Output: recovered metal returned to the next charge with its weight recorded.
A reconciliation for every lot. Charge weight in, bar weight out, recovered metal returned, and the difference stated as the loss for that cycle, so that the irrecoverable fraction is visible and any drift is caught on the next cast rather than at the month end. Output: a closed charge-and-product reconciliation with the loss declared.

Vacuum Ingot Casting Machine Process Flow

The nine stages below are the working cycle of one vacuum ingot casting machine, from the bar programme that fixes the mold through to the ingot being weighed and the charge reconciled. It is written at machine level rather than at plant level on purpose: this is the sequence a casting engineer works through when the question is how a cavity is dimensioned, how the chamber is proved tight and what has to be held while the metal freezes. Cavity count and layout, bar envelope and weight, chamber working volume, induction power and frequency, vacuum system, inert-gas handling, cooling duty and utilities are fixed during process design against your own bar programme, metal mix and site.

Vacuum ingot casting machine working cycle — from the bar programme that dimensions the cavity through evacuation, melting, degassing and pressurised solidification to a weighed, assayed ingot, with the skull, the runner and every rejected bar returned to the next charge.

Steps 1 — Ingot Programme Review and Mold Cavity Dimensioning. The mold is dimensioned before the chamber is built, and the arithmetic runs from the bar the customer sells. The declared bar weight sets the charge weight; the bar envelope sets the cavity footprint; the contraction of the metal between the liquid and the solid state sets the allowance by which the cavity is cut larger than the finished bar; a draft angle on the cavity walls is what allows the ingot to be lifted without being pulled; and a feed head above the cavity gives the last liquid somewhere to draw from as it freezes, so that the pipe forms in the feed head rather than in the bar. Every one of those is a drawing dimension rather than a mould-shop judgement, and the cavity drawing is issued with the process design package so that the bar it will produce can be checked on paper before the first cast. The metal mix is the input that governs the rest: gold, silver, karat alloy and copper have different melting points, different contraction and different behaviour towards dissolved gas, and the cavity, the superheat and the mould material all follow from it. Reagent and utility input: declared bar weight and envelope, metal mix and target fineness, bar count per cycle, monthly programme, existing assay and weighing practice. Output: a mold cavity drawing with the contraction allowance, draft angle and feed head stated, a cavity count and layout, and the chamber, induction, vacuum, gas and cooling duties that follow from it.

Steps 2 — Mold Preparation, Release Coating and Preheat. The mold block is cleaned, inspected for a scored or eroded cavity wall, and brought to a controlled preheat temperature before the charge is placed. The preheat matters because the first metal into a cold cavity chills against the wall and freezes before the cavity has filled, which shows on the finished bar as a lap, a cold shut or a short corner; a cavity at the wrong temperature at the other extreme gives a coarse cast structure and a surface that picks up mould material. Where a release coating is used it is applied thin and evenly and allowed to dry, because a thick or patchy coating transfers its own texture to the bar and can flake into the melt. The mold is then set in the chamber on its locating feature, so that the pour path and the cavity orientation are the same at every cast and the cavity number recorded against the lot means something. Reagent and utility input: machined graphite or ceramic mold block, cavity inspection gauge, controlled preheat source, release coating where specified, mold setting and locating fixture. Output: a clean, correctly preheated mold set at its locating feature with the cavity number recorded against the campaign.

Steps 3 — Charge Weighing, Loading and Chamber Sealing. The charge is weighed on a calibrated balance and placed in the crucible, and the weighed figure is the number the finished bar will be reconciled against. The charge form matters as much as its weight: granule and coarse crystal sit in the crucible and melt down predictably, whereas sponge and fine powder are granulated or briquetted first, because fines are drawn towards the vacuum port and end up on the chamber wall as an assay-known but unrecovered loss. The crucible is inspected for a cracked or glazed wall and for metal from the previous campaign, and the charge is placed so that the induction coil couples to the whole mass rather than to one side of it. The lid is then closed on its guide, the seal faces are checked for metal spatter and for the condition of the gasket, and the lid is locked — because the seal is the one part of the machine that has to work on every single cycle for years, and it is inspected every time rather than replaced when a programme pulls a poor vacuum. Reagent and utility input: calibrated balance, dried and granulated charge, inspected crucible, clean seal faces and gasket, guided and locked lid. Output: a weighed charge in a sealed chamber with the charge weight and the cavity number written into the cycle record.

Steps 4 — Chamber Evacuation and Leak-Rate Hold Test. The pump is started and the chamber is evacuated, and this stage carries the whole of the vacuum specification rather than a single number. Three figures matter and they are recorded separately: the absolute pressure the chamber reaches with the charge in it, the time the evacuation takes, and the rate at which the pressure rises once the pump is valued off. The third figure is the one that decides whether the machine is actually working in an inert atmosphere. A chamber that reaches a good pressure and then leaks back up is being purged rather than evacuated, and the consequence is a residual oxide skin and a scatter in the assay of the cast bar rather than a visible defect — which is exactly why the hold test is written into the cycle as a stage rather than left as a commissioning check. The shell vents and the pump exhaust are verified as part of the same stage, so that the gas leaving the chamber leaves the building through the duct rather than into the shop. Reagent and utility input: vacuum pump, isolation valve, vacuum gauge or transducer, calibrated leak-rate timing, chamber and pump exhaust venting. Output: a chamber evacuated to the set pressure inside the evacuation window and demonstrated to hold it against the leak-rate criterion, with all three figures written into the cycle record.

Steps 5 — Vacuum Induction Melting and Gas Removal. The induction supply is energised and the charge is heated from inside by the eddy currents the coil induces in the metal itself, which is why there is no element, no flame and no combustion product in contact with the melt. Melting under vacuum does two things at once: it keeps oxygen away from the surface so that no oxide skin forms, and it lowers the partial pressure above the melt so that dissolved gas leaves the metal and is carried out by the pump. This is the stage that matters most for silver, where the melt holds a very large volume of oxygen in solution — of the order of twenty times its own volume near the melting point — and where that gas would otherwise come out of solution abruptly as the metal freezes, throwing metal out of the mold as the spitting and blistering that air-cast silver is known for. For gold the stage is quieter but not idle, because a gold melt still takes up gas and because the same reduced pressure is what keeps an oxidising atmosphere off the melt surface. The melt is brought to temperature at a rate the charge and the crucible allow rather than at the maximum the supply can deliver, because a violent melt throws fines. Reagent and utility input: induction power supply and coil, crucible, vacuum system holding the set pressure, cooling water to the coil, chamber pressure and metal temperature instrumentation. Output: a fully molten, degassed charge at the melting temperature with the chamber still under vacuum.

Steps 6 — Superheat Dwell and Alloy Homogenisation. The melt is taken above its melting point — gold melts at 1,064 °C and silver at 961.78 °C, and the pour temperature is set as a superheat above that figure so that the same setting transfers between metals — and then held for a dwell at temperature. The superheat is what carries the metal into the far corners of the cavity and what feeds the contraction while the ingot freezes, and a pour that is too cold shows as a short fill or a cold shut while one that is too hot coarsens the cast structure and attacks the mould cavity. The dwell is where an alloy becomes uniform, and it is also the interval that has to be kept short in karat work, because volatile constituents leave the melt at temperature: zinc boils at 907 °C, well below the temperature a karat gold melt actually reaches, so an alloy held hot in an oxidising atmosphere loses zinc and drifts off its declared composition. Melting under vacuum with a controlled dwell and a defined time at temperature is what holds the fineness of a declared alloy. Reagent and utility input: induction power control, immersion or optical temperature measurement, dwell timer, vacuum system holding the set pressure, alloy composition specification. Output: a melt at the set superheat, homogeneous in composition, with the dwell time and the maximum temperature recorded against the lot.

Steps 7 — Inert Gas Backfill and Pressurised Solidification. Inert gas — argon or nitrogen at 99.99% purity or better — is admitted to the chamber to a controlled positive overpressure above ambient, and then the crucible is tilted or inverted on a controlled profile so that the metal enters the cavity from the feed head as a smooth stream rather than being dropped into it. Two things are happening at once and both matter. The inert gas has displaced the vacuum, so the melt surface and the freezing ingot are never in contact with oxygen, which is what keeps the bar free of an oxide skin. And the chamber is held at a pressure above ambient while the metal freezes, which is what supplies the reservoir that feeds the contraction of the last liquid to solidify. Gold and silver both occupy less volume as solids than as liquids and freeze from the mould wall inwards, so without that reservoir the last metal pulls away from the solid shell and forms a pipe or a dispersed porosity below the surface — a defect that is invisible on a perfect surface and fatal at a density check. Holding the overpressure through solidification is the stage that closes it, and the pressure is a set point with a hold time attached rather than a purge opened after the pour. Reagent and utility input: argon or nitrogen at 99.99% purity or better, pressure regulator and control valve, chamber pressure instrumentation, tilt or invert pour mechanism with a controlled profile, mould at its preheat temperature. Output: a cavity filled from the feed head, an ingot freezing under inert gas at a controlled overpressure, and the backfill pressure, the pour profile and the pressure hold time recorded against the lot.

Steps 8 — Controlled Cooling, Venting and Ingot Discharge. The ingot cools inside the sealed chamber on a set profile rather than by opening the door, because the cooling rate is what decides the cast structure and the surface: cooled too fast the bar is quenched at the skin and loose in the middle, cooled too slowly the cycle is extended for nothing. The mould and the ingot are brought to a stated temperature before the chamber is vented, which is the point at which the inert atmosphere is released and the lid can be opened; venting through a filter rather than straight to the shop keeps the metal dust that has deposited in the chamber where it can be collected and weighed. The mould is opened on its guide, the ingot is lifted or the mould is inverted on its own fixture rather than levered, and the feed head and the runner are separated from the bar. The mould is inspected for erosion and for metal that has adhered to the cavity wall, because a cavity that has changed shape will produce a bar that has changed weight. Reagent and utility input: cooling circuit and cooling programme, mould and ingot temperature measurement, filtered vent line, mould opening fixture and ingot lift, cavity inspection gauge. Output: a cooled, discharged ingot and a separated feed head and runner, with the mould inspected and returned to the set for the next cast.

Steps 9 — Ingot Weighing, Assay and Charge Reconciliation. Every bar is weighed against the charge weight it was cast from, because that comparison is the check that the cavity volume and the pour practice are still producing the declared bar; a bar that has drifted off its weight points at a worn cavity or a short fill long before a customer finds it. The fineness is declared by fire assay, X-ray fluorescence or inductively coupled plasma analysis on the bar or on a sample from the charge, by the method and the laboratory agreed in the contract. The bar is then marked with its weight, its fineness, the manufacturer’s mark and a serial or lot number, and the cast record is closed: charge weight in, bar weight out, skull and runner recovered and weighed, and the difference declared as the loss for that cycle. That reconciliation is what separates the metal that never left the plant from metal that has actually gone — the skull, the runner and any rejected bar go back into the next charge, while the vapour and the fine dust deposited on the chamber wall do not, and only the second figure belongs in the plant’s metal balance. Reagent and utility input: calibrated balance, assay sample and laboratory method, marking punches or laser, chamber wall clean-down and dust collection, recovered metal returned to the charge store. Output: a weighed, assayed and marked ingot at the declared weight and fineness; recovered skull, runner and rejected bars returned to the next charge; and a closed charge-and-product reconciliation with the cycle loss declared.

Product Structure (Main Equipment)

The machine is assembled from the three equipment groups below. Materials are selected item by item: sealed chamber and lid in stainless steel with a machined and lapped sealing face, sight glass and elastomeric or metal gasket selected against the working temperature and the number of cycles per shift; crucible in high-purity graphite, with ceramic and coated options for metals that react with carbon; mold blocks in fine-grain high-density graphite, with ceramic and steel options where the metal, the temperature or the production volume calls for them; and 316L stainless steel or non-ferrous wetted parts in the gas, cooling and venting lines.

Chamber, sealing and vacuum containment

Sealed casting chamber with a guided lid. A stainless steel chamber sized from the mold block, the crucible and the pour mechanism, with a machined and lapped sealing face and a lid that is guided and locked rather than dropped onto a gasket, because the seal has to work on every cycle for years with molten metal in the vessel. Output: a chamber that holds its pressure against the leak-rate criterion throughout its service life.
Sealing face, gasket and seal inspection access. The sealing face and the gasket are the two wear items in the pressure envelope and are treated as such, with the face accessible for inspection and re-lapping and the gasket selected against the working temperature and the cycle count rather than against first cost. Output: a seal that can be inspected and renewed rather than only replaced.
Sight glass and illumination. A sight glass on the chamber and lighting inside it, so that the pour and the freeze can be watched and recorded rather than inferred from the instruments, and so that a casting fault can be seen at the cycle it occurred in. Output: a visible and recordable pour, with the glass also serving the optical temperature measurement where one is fitted.
Vacuum pump, isolation valve and gauging. A pump specified by the displacement needed to bring the chamber volume to the set pressure inside the evacuation window the cycle allows, an isolation valve for the leak-rate hold test, and pressure measurement taken in the chamber rather than at the pump. Output: a chamber evacuated to a stated pressure inside a stated time and proved against a stated leak rate.
Gas handling set — backfill, overpressure control and venting. A regulator and control valve on the argon or nitrogen supply, chamber pressure instrumentation, and a filtered vent line, delivering the inert gas at the purity and the controlled positive overpressure the casting programme requires and releasing it through a filter when the cycle ends. Output: an inert atmosphere at a stated purity and a held overpressure through solidification, with the vented dust captured rather than released.
Chamber clean-down and dust collection. Access to the chamber wall and to the vacuum line for the periodic collection of metal dust, because that dust is assay-known metal and belongs in the reconciliation rather than in a rag. Output: recoverable chamber dust returned to the charge store with its weight recorded.
Sealed exhaust and shop ventilation interface. The pump exhaust and the chamber vent are ducted to a defined discharge point rather than into the shop, with the duct interface and the extraction volume agreed with the site. Output: chamber gases leaving the building at a defined point, with the duct connection inside the supply scope at the interface.

Induction melting, crucible and pour mechanism

Induction power supply and coil. An induction supply and a water-cooled coil sized on the mass to be melted inside the melt window the cycle allows and on the metal mix, so that the heat is generated inside the charge rather than conducted into it from a surface, and so that the same coil can follow the programme through the melt into the superheat. Output: a charge melted and brought to superheat inside the intervals the cycle budget allows.
Crucible and crucible seating. High-purity graphite crucibles with ceramic and coated options for metals that react with carbon, seated so that the coil couples to the whole charge uniformly and so that the pour path is fixed rather than improvised. Output: a melt held in a crucible that does not contaminate it, with the pour path fixed at every cast.
Tilt or invert pour mechanism. A mechanism that tilts or inverts the crucible on a controlled profile so that the metal enters the mold at a smooth rate from the feed head, rather than being dumped into the cavity where it would entrain gas and splash the mold wall. Output: a controlled, repeatable pour with the profile stored against the bar programme.
Coil and crucible cooling circuit. A closed cooling circuit on the coil and the power supply, with the duty set from the heat that has to leave the coil during a melt and the heat that has to leave the machine between casts, and with flow and temperature protection interlocked to the supply. Output: a coil and a power supply held inside their temperature limits at the duty the programme requires.
Charge handling and weighing station. The balance, the granulation or briquetting step where fines have to be consolidated, and the charging tools, treated as part of the machine because the charge weight is what the finished bar weight is reconciled against. Output: a weighed, uniformly prepared charge with the weight recorded against the cycle.
Mold handling, setting and changing fixtures. Locating features, handling fixtures and setting gauges for the mold block, so that a cavity change is a scheduled operation with the position verified rather than a trial-and-error adjustment. Output: a mold set at its locating feature, with the cavity number recorded against the lot.

Mold set, instrumentation and control

Single-cavity and multi-cavity graphite mold blocks. Fine-grain high-density graphite blocks machined with the cavity, the contraction allowance, the draft angle and the feed head as drawing dimensions, in single-cavity form for large bars and multi-cavity form for small bars produced several to a cycle. Output: a mold set that produces the declared bar weight and envelope, in the cavity count the programme calls for.
Ceramic and steel mold options. Ceramic and steel molds for metals and temperatures where graphite is not the right cavity material and for higher-volume duties where a longer mold life is worth the different thermal behaviour. Output: a cavity material matched to the metal and the production volume rather than to a single house standard.
Mold preheat and temperature control. A controlled preheat source and temperature measurement on the mold block, so that the cavity is at its set temperature before the pour and the same temperature is reproduced at every cast. Output: a cavity at its set preheat temperature, recorded against the cycle.
Chamber pressure, gas and metal temperature instrumentation. Chamber pressure measurement for the evacuation and hold stages, supply and chamber pressure measurement for the backfill and overpressure stages, and metal temperature measurement taken on the melt rather than on the crucible wall. Output: a cycle whose vacuum, overpressure and metal temperature are all recorded rather than inferred.
Ingot and mold temperature monitoring through the cooling stage. Temperature measurement carried through the controlled cooling interval, so that the vent and discharge steps happen at the intended ingot and mold temperature rather than at a fixed delay. Output: a cooling profile followed to a measured end point rather than to a timer.
PLC control with stored casting programmes. A PLC and operator interface holding the whole sequence — evacuation, leak test, melt ramp, superheat dwell, backfill, pour profile, pressure hold, cooling profile, vent and discharge — as a stored programme recalled by bar programme, with the interlocks that prevent a pour before the vacuum and the temperature are satisfied. Output: a repeatable cycle run from a stored programme rather than from an operator’s memory.
Alarm annunciation and event logging. Alarms for a failed leak test, an evacuation over time, a power or cooling fault, an over-temperature melt, a gas supply loss and an interlock breach, with an event log that records the cycle against the lot number along with the charge weight and the recorded vacuum, overpressure and temperature figures. Output: a machine that reports its own cycle state and a record that stands behind the lot.

Product Features

The vacuum is specified as pressure, evacuation time and leak rate together. A single pressure figure describes what the pump can do on a closed valve; the three figures together describe what the chamber does with a charge in it, and only the leak-rate hold test can be repeated by a buyer on site with the pump isolated.
Melting and inert-gas protection are engineered as two stages of one cycle. The chamber is evacuated to degas the melt and to keep oxygen out of it, and it is then backfilled to a controlled positive overpressure; a machine that performs only the first is a vacuum melter, not a vacuum ingot casting machine.
Solidification under overpressure, held to a set point and a hold time. Both gold and silver contract as they freeze and the last liquid to solidify sits below the surface with no reservoir above it, so the chamber is held above ambient pressure until the ingot has frozen — which is what collapses the shrinkage pipe that a vacuum-released chamber leaves behind.
Cavity dimensioned from the bar, with the contraction allowance on the drawing. Cavity footprint, contraction allowance, draft angle and feed head are drawing dimensions issued with the process design package, so the bar a mold will produce can be checked before the first cast rather than after the first rejection.
Bar weight set by the pre-weighed charge and reconciled on the ingot. Because the cavity accepts a weighed charge with its shrinkage allowance, a declared bar weight is reproducible, and the comparison of charge weight against cast weight is the check that the cavity is still what it was.
Degassing aimed at the metal that actually holds gas. Silver dissolves a very large volume of oxygen in the melt — of the order of twenty times its own volume near the melting point — and rejects it as it freezes, which is why vacuum degassing is the difference between a bright bar and a spitting, blistered one; gold takes up less, so the vacuum in gold work is carried by the oxide-free surface and by the volatile elements in karat alloys.
Superheat expressed relative to the melting point rather than as a fixed pouring temperature. Gold melts at 1,064 °C and silver at 961.78 °C, so the pour temperature is set as a superheat above the metal’s own melting point, which is why the same programme transfers between metals and why a cold pour shows as a short fill rather than as a low reading.
Volatile alloying elements held in the melt by a controlled dwell. Zinc boils at 907 °C, below the temperature a karat gold melt reaches, so a karat alloy held hot in air drifts off its declared composition; vacuum melting with a defined dwell and a short time at temperature is what holds the fineness of a declared alloy.
No flame, no flux and no open crucible. The heat is induced directly in the charge and the pour happens inside a sealed chamber, so there is no torch flame, no flux addition and no operator standing over an open vessel of molten metal.
Sealing treated as the primary wear item. Machined and lapped sealing faces, a guided and locked lid, an accessible seal for inspection and re-lapping, and a gasket selected against the working temperature and the cycle count — because a shop that opens the chamber once a cycle needs the seal to be maintainable, not merely replaceable.
Cooling as a controlled profile with a measured end point. The ingot cools inside the sealed chamber under inert gas on a set profile, and the chamber is vented at a measured ingot and mold temperature rather than after a fixed delay, so the cast structure and the surface are a consequence of a programme rather than of the shop temperature.
Multi-cavity and single-cavity programmes from one chamber. A single 12.44 kg Good Delivery gold bar and a set of 1 kg bullion bars are both engineered from the same chamber, with the cavity layout, the pour path and the thermal uniformity of the mold block treated as design outputs.
Weight anchors taken from the market the bars are sold into. The 400 troy ounce gold bar at about 12.44 kg and the 1,000 troy ounce silver bar at about 31.10 kg are the reference points the large-cavity programmes are dimensioned against, and 1 kg, 100 g and 10 oz are the common small weights, so the machine is specified against a bar that exists rather than against an arbitrary size.
Purity carried through, with the boundary stated. The chamber cannot remove a base metal or separate one precious metal from another; fineness is established upstream and the machine is specified for the fineness of the feed it will be given, which is what lets the casting step sit behind a refining route rather than be asked to replace one.
Metal loss split into what returns and what leaves. Crucible skull, runner and rejected bars are recovered and recharged; only vapour and chamber-wall dust are irrecoverable. Separating those two figures is what stops a per-cycle loss measured on the shop floor being read as metal that has left the plant.
Continuous duty from a stored programme with one operator. The full sequence runs from a recalled programme with the chamber state, the metal temperature and the pressures displayed through the cycle, and the alarm and event log carries the cycle record against the lot for a plant running the machine around the clock.

Technical Parameters And Specifications

Vacuum ingot casting machine technical parameters. Bar weights, bar envelope, cavity count, chamber working volume and the melting duty are engineered to your declared bar programme and metal mix; the figures below are the design values the machine is specified against.

Parameter	Specification
Primary function	Vacuum induction melting and casting of precious metals in a sealed chamber, producing a cast bar with no oxide skin, no gas porosity and no shrinkage pipe, in which the metal is melted under vacuum, degassed, poured into a machined mold and solidified under a controlled inert-gas overpressure
Machine type	Chamber-based batch casting unit: charge, evacuate, melt, superheat, backfill, pour, hold pressure through solidification, cool, vent, discharge, weigh and reconcile
Working principle	The charge is melted by eddy currents induced in the metal itself by a water-cooled coil, so no flame or combustion product contacts the melt; the chamber is evacuated to remove dissolved and entrained gas and to exclude oxygen; and the chamber is then held above ambient pressure with inert gas while the ingot freezes so that the contraction of the last liquid to solidify is fed from a reservoir rather than forming a pipe
Bars per cycle	One cavity for large Good Delivery weights, and multi-cavity mold sets for small bars; the cavity count and layout are engineered to your bar programme
Bar weight range	From a few grams up to the Good Delivery weights, with 100 g, 10 troy oz, 1 kg and 12.5 kg gold and 1 kg, 100 oz and 31 kg silver as the common programmes; the working range is engineered to your declared bar weights
Good Delivery gold weight	400 troy ounces, about 12.44 kg, the reference weight the single-cavity large-bar programme is dimensioned against
Good Delivery silver weight	1,000 troy ounces, about 31.10 kg, the reference weight the large silver-cavity programme is dimensioned against
Troy ounce basis	1 troy ounce equals 31.1035 g, which is the conversion used to state a bar weight against the Good Delivery figures
Bar weight tolerance	Set by the pre-weighed charge and the fixed cavity volume, verified by weighing the cast bar and reconciling it against the charge weight, and stated in the contract as a tolerance against the declared weight
Metals cast	Gold, karat gold and colour-controlled gold alloys, silver, and copper; the platinum group metals where the melting and superheat duty is specified for them
Melting point — gold	1,064 °C, used as the datum the gold superheat is set above
Melting point — silver	961.78 °C, used as the datum the silver superheat is set above
Melting point — copper	1,085 °C, used as the datum the copper superheat is set above
Pour temperature basis	Expressed as a superheat above the melting point of the metal being cast rather than as an absolute pouring temperature, so that the same casting programme transfers between metals and the setting stays meaningful when the metal mix changes
Superheat control	Induction power ramped to the set superheat and held for a defined dwell, with the metal temperature measured on the melt rather than on the crucible wall
Melting and superheat duty	Engineered to your metal mix and to the mass to be melted inside the melt and superheat intervals the cycle allows
Crucible	High-purity graphite, seated so that the coil couples to the whole charge uniformly, with ceramic and coated options for metals that react with carbon
Chamber working volume	Sized from the mold block, the crucible and the pour mechanism with the freeboard the pour and the melt need, and stated in the process design package rather than as a nominal figure
Chamber construction	Stainless steel vessel with a machined and lapped sealing face, a guided and locked lid, a sight glass and internal illumination, a gas inlet, a pump port, a filtered vent and the instrumentation ports
Seal and gasket	Machined and lapped sealing face with an accessible inspection and re-lapping route, and an elastomeric or metal gasket selected against the working temperature and the number of cycles per shift
Chamber vacuum — pressure	The absolute pressure the chamber reaches with a charge in it, stated together with the measurement point rather than as a pump specification on a closed valve
Chamber vacuum — evacuation time	The interval allowed to bring the chamber volume to the set pressure, which is the figure that fixes the pump displacement together with the chamber volume
Chamber vacuum — leak rate	The rate at which chamber pressure rises once the pump is isolated, stated as a criterion and verified by a hold test at every campaign through an isolation valve, and the only part of the vacuum specification a buyer can repeat on site
Vacuum pump	Specified by the displacement needed to bring the chamber volume to the set pressure inside the evacuation window the cycle allows, with the pump exhaust ducted out of the building rather than discharged into the shop
Inert gas	Argon or nitrogen at 99.99% purity or better, selected against the metal and the site, admitted through a regulator and a control valve to the chamber
Inert gas overpressure	A controlled positive pressure above ambient, stated as a set point in the casting programme and held while the ingot solidifies so that the contraction of the last liquid to solidify is fed from a reservoir rather than forming a shrinkage pipe
Pressure hold time	The interval the overpressure is held through solidification, recorded against the lot together with the backfill pressure and the pour profile
Gas handling and venting	Regulator, control valve, chamber pressure instrumentation and a filtered vent line, so that the chamber vents through a filter and the metal dust it carries is collected rather than released
Vacuum and gas instrumentation	Chamber pressure measurement for the evacuation and hold stages, supply and chamber pressure measurement for the backfill and overpressure stages, and metal temperature measurement on the melt
Mold material	Fine-grain high-density machined graphite as standard, with ceramic and steel options for metals and temperatures where graphite is not the right cavity material and for duties where a longer mold life is wanted
Mold cavity dimensioning	Cavity footprint from the ordered bar envelope, cut larger than the finished bar by the contraction allowance for the metal, with a draft angle on the cavity walls and a feed head above the cavity so that the shrinkage pipe forms in the feed head rather than in the bar
Draft angle and feed head	A draft angle on the cavity walls so the ingot lifts without being pulled, and a feed head sized from the contraction demand of the bar so it has somewhere to draw from while the metal freezes
Mold preheat	The mold block is brought to a controlled temperature before the pour so that the first metal into the cavity does not chill against the wall and freeze before the cavity fills, with the temperature set by the metal and the cavity wall and recorded against the cycle
Release coating	Applied thin and evenly where a coating is used, then dried, because a thick or patchy coating transfers its own texture to the bar and can flake into the melt
As-cast surface	Free of oxide skin and free of the water-wave ripple an open pour produces, reproducing the mold wall finish, with the bar either needing no finishing or needing only a light polish before marking
Internal soundness	Dense through the section as a result of vacuum degassing and a held inert-gas overpressure, with the shrinkage allowance consumed inside the feed head rather than inside the bar
Purity	Carried through from the feed rather than created by the machine; the chamber removes dissolved gas and excludes oxygen, and cannot remove a base metal or separate one precious metal from another, so fineness is established upstream and the machine is specified for the fineness of the feed it will be given
Casting cycle	A stage-by-stage budget covering evacuation, the leak-rate hold test, melting, the superheat dwell, backfill, pour, the pressure hold, controlled cooling, venting and discharge, with a 1 kg class programme typically completing in about twelve to twenty minutes from lid close to lid open
Quality-critical intervals	The degassing dwell during evacuation and melting, and the pressurised hold through solidification, are the two intervals that decide ingot quality; the remaining intervals decide throughput
Deoxidation and fluxing	Not used; there is no flux addition and no deoxidising agent in the melt, because the atmosphere rather than an additive is what keeps oxygen away from the metal
Metal loss	Split into a recoverable fraction and an irrecoverable fraction: crucible skull, runner and rejected bars are weighed and returned to the next charge, while vapour and the fine dust deposited on the chamber wall are the irrecoverable loss
Charge reconciliation	Every cycle closes on charge weight in, cast bar weight out, recovered metal returned, and the difference declared as the loss for that cycle
Control system	PLC with a stored casting programme for each bar programme, covering the evacuation and hold sequence, the melt ramp, the superheat dwell, the backfill, the pour profile, the pressure hold, the cooling profile and the vent and discharge sequence
Interlocks	Pour prevented until the vacuum and the metal temperature satisfy the programme, backfill prevented before the evacuation and the hold test are complete, and the induction supply and the cooling circuit interlocked against a cooling fault
Alarms and records	Alarms for a failed leak test, an evacuation over time, a power or cooling fault, an over-temperature melt, a gas supply loss and an interlock breach, with an event log recording the cycle against the lot number along with the charge weight and the recorded vacuum, overpressure and temperature figures
Operator requirement	One operator per machine; the sequence runs from the stored programme and the chamber state, the metal temperature and the pressures are displayed through the cycle, so the unit can be run on a shift pattern with a documented procedure rather than with a specialist caster
Materials of construction — chamber and gas lines	Stainless steel for the chamber, the lid and the sealing face; 316L stainless steel or non-ferrous wetted parts in the gas, cooling and venting lines; the gasket selected against the working temperature and the cycle count
Cooling	A closed circuit on the coil and the power supply sized from the heat that has to leave the coil during a melt and between casts, plus a controlled cooling programme on the mold and the ingot inside the sealed chamber with a measured end point before venting
Marking and traceability	Weight, fineness, manufacturer’s mark and a serial or lot number applied to the bar, with the lot record carrying the charge weight, the mold and cavity number, the programme used and the recorded vacuum, overpressure and temperature figures
Assay	Fineness declared by fire assay, X-ray fluorescence or inductively coupled plasma analysis, on the bar or on a sample taken from the charge, with the method and the laboratory agreed in the contract before manufacture
Capacity, batch throughput, power, footprint and utilities	Engineered to your declared bar weights, bar envelope, metal mix, cavity count and monthly programme, and stated in the process design package rather than taken from a fixed model list
Installation	Indoor, on a level floor with the services and the exhaust duct connection shown on the layout drawing, with the pump exhaust and the chamber vent taken to a defined discharge point
Verification	Chamber leak-rate hold test repeated at every campaign, cast weight reconciled against the charge weight for every lot, and fineness declared by the agreed assay method, with surface and internal soundness released against a standard agreed before manufacture

Technical Advantages

The vacuum specification can be checked by the buyer, not just believed. Pressure, evacuation time and leak rate are three separate figures, and the leak-rate hold test is performed with the pump isolated at every campaign. A machine quoted on a pressure alone cannot be verified on site, and a chamber that leaks back up is purging rather than evacuating however good its pump is.
Degassing is aimed at the metal that actually holds gas. Silver in the melt dissolves a very large volume of oxygen, of the order of twenty times its own volume near the melting point, and rejects it as the metal freezes. That is the mechanism behind the spitting, blistering and pitted crown of air-cast silver, and removing the gas while the metal is still liquid under vacuum is what stops it — a claim a machine that only purges with inert gas cannot make.
Solidification under a held overpressure is what produces a sound bar. Gold and silver both contract on freezing and freeze from the mold wall inwards, so the last liquid to solidify has no reservoir above it unless the chamber supplies one. Holding inert gas above ambient pressure through solidification collapses the pipe and the dispersed porosity that would otherwise sit invisibly under a perfect surface.
Cavity dimensions are issued as a drawing, with the contraction allowance written down. Footprint, contraction allowance, draft angle and feed head are stated, so the bar a mold will produce can be checked on paper before the first cast, and a worn cavity can be identified from a weight drift rather than from a rejected delivery.
Bar weight is a consequence of the charge, which is why it repeats. The charge is weighed before it enters the chamber and the cavity accepts it with its shrinkage allowance, so the declared weight does not depend on how full the mold happened to be, and the charge-against-cast comparison at the end of every cycle is a free process control.
Superheat is stated against the metal, so the programme transfers. Gold melts at 1,064 °C and silver at 961.78 °C, and the pour temperature is set as a superheat above the metal’s own melting point rather than as an absolute figure. That is what makes a cold pour show up as a short fill and a hot pour as a coarse structure, instead of both looking like a number on a display.
Volatile alloying elements are held by controlling the dwell, not by accepting the loss. Zinc boils at 907 °C, below the temperature a karat gold melt reaches, so an alloy held hot in an oxidising atmosphere drifts off its declared composition. Melting under vacuum with a defined dwell and a short time at temperature is what keeps a declared karat on target.
Energy is induced in the charge, so there is no flame and no combustion product. The coil heats the metal from inside; there is no element, no torch and no flux, which removes the flame, the oxide from combustion and the operator standing over an open crucible from the process.
Loss is published as two figures rather than one. The skull, the runner and rejected bars return to the next charge; only vapour and chamber-wall dust leave the plant. Separating them is what stops a shop-floor loss reading being mistaken for metal that has gone, and what makes the metal balance close.
The seal is engineered as a wear item. Machined and lapped faces, a guided and locked lid, accessible inspection and re-lapping, and a gasket selected against the working temperature and the cycle count — because a machine that opens once a cycle for years lives or dies on its seal faces.
Cooling ends on a measured temperature rather than on a timer. The ingot cools inside the sealed chamber on a set profile and the chamber is vented at a measured ingot and mold temperature, so the cast structure and the surface follow the programme instead of the shop temperature and the operator’s patience.
The machine is specified against a bar that exists in the market. The 400 troy ounce gold bar at about 12.44 kg and the 1,000 troy ounce silver bar at about 31.10 kg are the anchors for the large-cavity programmes, and 1 kg, 100 g and 10 oz cover the small bullion weights, so the cavity, the chamber and the pour path are dimensioned against a real product rather than against a nominal size.
The boundary of what casting can do is stated rather than implied. The chamber removes gas and excludes oxygen; it does not refine. A refinery can therefore place this machine behind its electrolysis or refining route with confidence, and a buyer whose problem is a contaminated feed is told that the answer is upstream rather than sold a casting machine that cannot solve it.
Configuration stated in writing before manufacture. Cavity count and layout, bar envelope and weight, chamber working volume, induction power and frequency, vacuum system, inert-gas handling, cooling duty, cycle programme and utilities are engineered from your bar programme and metal mix and issued as a process design package rather than discovered at commissioning.

Service Process

Step 1 — Bar Programme and Feed Consultation. Send the bar weights and envelopes you intend to sell, the metal mix and the fineness of the feed you will charge, the bar count per cycle you want and the monthly programme, together with a representative sample or a typical analysis of the metal. Our metallurgical team confirms the fineness of the feed and the elements that will behave differently under vacuum — the volatile alloying constituents in a karat alloy, the gas-holding behaviour of the silver, and any element that would report to the chamber wall — and sets out the bar programme the machine will be dimensioned against. Output: assay report and a preliminary machine proposal with the cavity count, the bar weights achievable and the batch pattern.

Step 2 — Laboratory Casting Trials and Machine Design. Bench and pilot casts confirm the cavity dimensioning and the contraction allowance against the actual bar envelope, the superheat and the dwell that suit your metal, the vacuum and hold figures that keep the cast free of oxide and gas porosity, the mold material and preheat, the pour profile and the pressure hold time. The results are converted into the chamber working volume and lid arrangement, the crucible and coil, the induction power and frequency, the vacuum system against the pressure, evacuation and leak-rate figures, the inert-gas handling, the cooling duty, a layout and a utility schedule against your programme and site. Output: trial cast report and bar samples, a machine design package with the cavity drawings and the cycle budget, and a firm quotation.

Step 3 — Chamber, Mold and Machine Fabrication. The chamber is fabricated and the sealing faces are machined and lapped; the lid assembly, the pour mechanism and the mold locating features are produced; the mold blocks are machined to the cavity drawings with the contraction allowance, draft angle and feed head cut in; the gas handling set, the pump set, the cooling circuit and the instrumentation are assembled; and the control system is loaded with the casting programmes. Output: assembled, pre-piped and pre-instrumented machine modules with the cavity drawings released against the bar programme.

Step 4 — Factory Assembly, Testing and Acceptance. The chamber is leak-tested and the leak-rate criterion is measured and recorded; the mold blocks are checked dimensionally against the cavity drawings; a trial cast is made on the customer’s own metal or an agreed substitute and the cast bar is weighed against the charge, examined for surface and section soundness and assayed; the interlocks and the alarm set are function-tested; and the customer is invited to attend the factory acceptance test and to witness the leak test and the trial cast. Output: a FAT-approved machine with its leak-test record, cavity dimensional record and trial cast report.

Step 5 — Shipping, Installation and Commissioning. We supervise the site services interface, the setting and levelling of the machine, the exhaust duct connection, the electrical tie-in and the cooling circuit, then run an instrumented commissioning campaign on your own metal until the declared bar weight, the as-cast surface and the fineness are demonstrated on successive casts and the recorded vacuum, overpressure and cycle figures are confirmed against the design. Output: a producing vacuum ingot casting machine at contracted performance with its commissioning record.

Step 6 — Operator Training and Handover. On-site training covers charge weighing, granulation and drying practice, crucible inspection and loading, seal face inspection and lid closing, the evacuation and leak-rate hold test, the melt and superheat programme, the backfill and pressure hold, the pour profile, the cooling and venting sequence, ingot discharge and mold handling, cavity inspection, weighing and reconciliation, sample taking and marking, and the alarm and event log, supported by standard operating procedures and a full handover dossier. Output: a trained crew and complete documentation.

Step 7 — Process Optimisation and Ongoing Support. Remote troubleshooting, crucible, mold block and gasket supply, periodic performance audits in which the cast weights, the assay results, the cycle timings, the recorded vacuum figures and the metal loss are reviewed against the design, and cavity or programme upgrade paths as your bar programme changes. Output: sustained performance and spare-part continuity.

Warranty And After-Sales Service

Warranty period. Twelve months from commissioning or eighteen months from shipment, whichever falls first, covering design, materials and workmanship of the equipment supplied, with the terms and the excluded wear parts stated in the contract.
Wear part and consumable clarity. Crucibles, mold blocks, gaskets, seal faces, sight glass, coating materials and pump service kits are identified as consumables with their expected service intervals declared up front, so the operating cost of the machine is visible before it is commissioned rather than after.
Mold and cavity service. Cavity inspection, re-machining and refurbishment, new cavity sets as your bar programme changes, and dimensional verification against the cavity drawings, so the bar weight can be held against a maintained mold rather than against a worn one.
Cavity and bar weight verification. Periodic verification of the cast bar weight against the charge weight and against the cavity drawings, so a drift in bar weight points at the cavity or the pour practice rather than at the assay. Output: verification report against the lot records.
Crucible and seal supply. Crucibles, seal faces, gaskets and sight glasses supplied as service items with lead times stated at order, so a campaign is not stopped by a consumable that has to be re-sourced.
Spare parts availability. A recommended commissioning and first-year spares set is quoted with the machine, and spare parts remain available through the equipment’s service life with lead times stated at order.
Remote support. Telephone, email and messaging support for operating questions, alarm interpretation, a vacuum that will not hold, a cast surface that has changed, an assay that has drifted and cycle timing problems while your casting cell is running. Output: same-day response on operating issues.
On-site service. Engineer attendance for warranty faults, process problems and periodical check-ups, with response and attendance times agreed in the contract according to your location. Output: on-site intervention and a service report.
Seal face re-lapping and chamber overhaul support. Assistance with seal inspection and re-lapping, chamber overhaul, gas and cooling circuit service and the re-setting of the mold and pour geometry, so that a mid-life overhaul is planned rather than reactive. Output: a documented overhaul with the machine returned to drawing tolerance.
Assay and metal balance verification service. Periodic verification of the cast weight reconciliation, the assay results and the recovered metal against your own laboratory and weighbridge records, so that the irrecoverable loss is tracked over time rather than assumed from commissioning. Output: verification report against the cycle records.
Operator retraining and refresher visits. Additional training, refresher sessions and process optimisation visits as your bar programme, metal mix or product requirement changes. Output: updated training and revised procedures.
Documentation set. Operation and maintenance manuals, cavity and mold drawings, chamber and sealing drawings, gas and vacuum schematics, cooling and electrical drawings, layout, spare parts catalogue, safety data for the gases used, and the emergency response plan covering a molten metal spill, a gas release and an electrical isolation. Output: complete documentation handover.
Compliance support. Assistance with exhaust and emission parameter declarations, gas storage and handling requirements, and the handling, storage and recovery of the metal-bearing dust collected from the chamber and the vent filter. Output: technical data for your permit applications.
Lifetime technical support. The cavity drawings and the casting programmes remain yours, and our engineering team remains available for modification and programme-change advice for the operating life of the machine. Output: long-term engineering continuity.

Frequently Asked Questions

What is a vacuum ingot casting machine?

A vacuum ingot casting machine is a sealed chamber in which a weighed charge of gold, silver or alloy is melted by induction under vacuum, held at a superheat so that the dissolved gas leaves the melt and no oxide can form, and then poured into a machined mold inside the same chamber while the chamber is held at a controlled inert-gas pressure above ambient. The vacuum does one job and the overpressure does another. Evacuation removes the oxygen that would oxidise the melt and the gas that is dissolved in the metal, which matters most in silver because molten silver holds a very large volume of oxygen and releases it as it freezes, throwing metal out of the mold and leaving a blistered and pitted surface. The overpressure does the opposite job: gold and silver both contract as they freeze and freeze from the mold wall inwards, so the last metal to solidify has no reservoir above it unless the chamber supplies one, and holding inert gas above ambient pressure through solidification feeds that contraction and collapses the shrinkage pipe that would otherwise form invisibly below a perfect surface. The machine therefore consists of a sealed chamber with a guided lid and a lapped sealing face, an induction coil and crucible, a vacuum pump with an isolation valve and pressure measurement, a gas handling set that backfills and holds pressure, a machined mold with its cavity dimensioned from the ordered bar, a cooling circuit and a controlled cooling programme, and a PLC that runs the whole cycle from a stored programme.

How does a vacuum ingot casting machine differ from an open crucible and a torch?

By what the metal is exposed to at the two moments that decide the bar. In an open crucible melted with a torch or a resistance furnace, the melt surface is in contact with air throughout, so an oxide skin forms and has to be removed with a flux or a reducing agent, gas from the atmosphere dissolves in the metal and comes out again during freezing as porosity, and a pour into an open mold leaves the metal open to the air at exactly the moment when it is hottest and most reactive. In the sealed machine the melt never sees air, so there is no oxide skin, no flux and no deoxidising addition; the dissolved gas is removed under reduced pressure rather than simply not added; and the pour and the whole of the freeze happen in an inert atmosphere at a controlled pressure. The differences that a customer sees are an as-cast surface that needs no acid treatment or scraping, a section that is dense rather than porous, and a bar weight that is a consequence of the pre-weighed charge and a fixed cavity rather than of how carefully the operator poured. The difference the operator sees is that there is no flame and no open vessel of molten metal.

Why is inert gas used after the chamber has been evacuated?

Because the vacuum removes the gas and the inert gas then keeps it out, and those are two stages of the same idea. Evacuating the chamber removes oxygen, nitrogen and water vapour from the space around the melt, which stops oxidation and withdraws dissolved gas from the liquid metal. But a vacuum cannot be maintained while the crucible is tilted and the metal pours, and a vacuum alone gives the freezing ingot no reservoir to draw from as it contracts. So once the melt is degassed the chamber is backfilled with argon or nitrogen at a controlled pressure above ambient. The inert gas does two things: it keeps oxygen away from the melt surface and the freezing ingot so that no oxide skin forms, and its positive pressure supplies the reservoir that feeds the contraction of the last liquid to solidify. That is why a machine that evacuates and then simply releases to atmosphere is not doing the same job as one that backfills and holds. Purity matters because any oxygen carried in with the gas is oxygen at the melt surface: argon or nitrogen at 99.99% or better is the specification.

What vacuum level does the machine pull, and how is it verified?

It should not be answered with one number, and a machine quoted that way has not been specified. Three figures describe a casting vacuum and they are different in kind. The first is the absolute pressure the chamber reaches with a charge in it, which is the figure usually quoted and which says nothing about how long it takes to get there or whether it stays. The second is the evacuation time, the interval allowed to bring the chamber volume down to that pressure, which is what actually sizes the pump: a pump displacement means nothing until it is stated against a chamber volume and a time. The third is the leak rate, the rate at which chamber pressure rises once the pump is isolated, and it is the most important of the three, because a chamber that reaches a good pressure and then leaks back up is being purged rather than evacuated and the consequence is a residual oxide skin and a scatter in the assay rather than an obvious defect. The leak rate is verified by a hold test through an isolation valve, and it is the one part of the vacuum specification a buyer can repeat on site, which is why it is written into the cycle as a stage rather than left as a commissioning check.

Why does silver need vacuum degassing more than gold?

Because molten silver dissolves far more oxygen than molten gold does. Silver in the liquid state takes up a very large volume of oxygen, of the order of twenty times its own volume close to the melting point, and that solubility collapses as the metal freezes. The gas therefore comes out of solution suddenly, at the moment when the metal is already partly solid and can no longer flow, which throws metal out of the mold and leaves the characteristic pitted, blistered crown that air-cast silver is known for. It is a gas problem rather than an oxidation problem, and it cannot be solved by covering the melt with a flux or a reducing atmosphere, because the oxygen is already in solution rather than on the surface. Removing it requires holding the melt under reduced pressure long enough for the gas to leave while the metal is still liquid, which is exactly what the evacuation and melt stages do. Gold takes up much less gas, so in gold work the vacuum is carried by the oxide-free surface and by the need to control volatile alloying elements in karat alloys rather than by a degassing requirement of the same magnitude.

What ingot weights and bar sizes can the machine cast?

The machine is engineered to a declared bar programme rather than sold against a fixed list, and the working range runs from bars of a few grams up to the Good Delivery weights. The large-cavity programme is anchored to the two weights the London market recognises: the 400 troy ounce gold bar, which is about 12.44 kg, and the 1,000 troy ounce silver bar, which is about 31.10 kg. Those are cast one to a mold, because a single cavity that size has to be filled from a feed head and cooled on a controlled profile. The small-bar programme runs multi-cavity molds, with 100 g, 50 g, 10 troy ounce and 1 kg as the common bullion weights, several cavities to a cycle, and with the cavity layout and the thermal uniformity of the mold block treated as design outputs because every cavity has to fill and freeze identically. Karat gold and colour-controlled alloys are cast in the same range against a declared composition. What sets the real limit is the melting duty rather than the cavity: the chamber, the coil and the cooling circuit are sized on the mass that has to be melted and brought to superheat inside the intervals the cycle allows, so the answer to how large a bar the machine can cast is the answer to how much metal it can melt in the time available.

Is the machine LBMA Good Delivery compliant?

The machine casts to the weight and the envelope that the Good Delivery standard specifies, which is a statement about the bar and not about the machine. The standard fixes the bar weights at 400 troy ounces, about 12.44 kg, for gold and 1,000 troy ounces, about 31.10 kg, for silver, with an acceptable range around those weights and dimensional requirements on the bar. A casting machine reaches those weights by being built with a single cavity of the right size, a feed head that gives the contraction somewhere to draw from, and a pre-weighed charge that sets the bar weight, and by being able to hold its vacuum and its overpressure so that the bar comes out sound and with a declared fineness. What the machine cannot do is qualify a refinery: Good Delivery accreditation belongs to the refiner and to its assay and provenance procedures, and a machine is one of the tools a refinery uses to meet them. We therefore quote the bar weights, the envelope, the weight tolerance and the assay method, and state plainly that the accreditation is the customer’s, supported by the documentation we supply for the lot.

How long does one casting cycle take?

A 1 kg class programme typically completes in about twelve to twenty minutes from lid close to lid open, and the split across the stages matters more than the total. Evacuation and the leak-rate hold test take the first interval, and this is not dead time: it is where the dissolved gas leaves the melt and where the chamber is proved tight, so shortening it is the fastest way to a blistered bar. Melting and the superheat dwell take the next, and the dwell is the interval where an alloy becomes uniform and where a karat alloy’s volatile constituents are either held or lost. The backfill, the pour and the pressure hold follow, and the pressure hold is the second quality-critical interval because it is what feeds the contraction while the ingot freezes. Controlled cooling, venting and discharge take the last interval, ending on a measured ingot and mold temperature rather than on a timer. Throughput follows from the bar weight, the cavity count and the cycle time together, so a machine with eight small cavities and a machine with one large cavity can have quite different outputs from the same cycle length, and the batch throughput for your programme is therefore stated in the process design package rather than quoted as a single figure.

How much metal is lost in a vacuum casting cycle?

Two different figures are involved and they should not be mixed. The irrecoverable loss is the metal that leaves the melt as vapour and the fine dust that deposits on the chamber wall and in the vent filter, and it is a small fraction of a percent. Because the chamber is sealed and the gas leaves through a filter rather than into the shop, that dust can be collected, weighed and assayed, and it is assay-known metal rather than waste. The recoverable loss is everything that solidified somewhere other than as a finished bar: the skull left in the crucible, the metal in the runner and the feed head, any metal that adhered to the mold cavity, and any bar that failed a weight, surface or assay check. Every one of those is weighed and returned to the next charge rather than written off. A per-cycle loss measured on the shop floor is therefore larger than the metal the plant has actually lost, and the two are separated by closing the reconciliation at the end of every cycle: charge weight in, cast bar weight out, recovered metal returned and weighed, and the difference declared. That reconciliation is what makes the drift visible on the next cast instead of at the month end.

What is the mold made of, and how is the cavity dimensioned?

The standard cavity material is a fine-grain high-density machined graphite block, with ceramic and steel options where the metal, the temperature or the production volume makes a different cavity material the better answer. The cavity itself is a drawing rather than a mould-room judgement, and four dimensions carry most of the result. The footprint comes from the ordered bar envelope. The cavity is cut larger than the finished bar by the contraction allowance for the metal being cast, because gold and silver both occupy less volume as solids than as liquids and the ingot therefore shrinks away from the wall as it freezes. A draft angle on the cavity walls lets the ingot lift without being pulled, which matters more on the long faces of a large bar than on a small one. And a feed head above the cavity gives the contraction somewhere to draw from, so that the pipe forms in the feed head and is cut off with the runner instead of sitting inside the bar. One cavity is correct for one bar in one metal: a mold that suits a 1 kg gold bar does not suit a 12.5 kg one and does not suit silver, because the contraction allowance, the thermal mass and the freezing behaviour all differ.

Why is the mold preheated before the pour?

Because the first metal into a cold cavity chills against the wall and freezes before the cavity has filled. The consequences are visible on the finished bar as a lap line, a cold shut where two streams of metal met without fusing, or a short corner where the metal never arrived, and none of them can be corrected afterwards because they are inside the bar as well as on its surface. Preheating the mold block to a controlled temperature gives the metal a wall that does not immediately extract its heat, so the cavity fills completely and the ingot then freezes progressively from the wall inwards on the cooling profile rather than all at once at the surface. The temperature is a set point rather than a rule of thumb, and it is measured on the mold block and recorded against the cycle, because a mold at the wrong temperature at the hot end also produces a coarse cast structure and can pick up mold material on the bar surface. Preheating is one half of the same control: the other half is holding the inert-gas overpressure while the metal freezes, and the two together are what produce a bar that is sound through its section rather than only at its surface.

What controls shrinkage porosity and pipe in the ingot?

A reservoir above the metal while it freezes, held at a pressure that pushes metal into the cavity as the volume is lost. Gold and silver both occupy less volume as solids than as liquids, and an ingot freezes from the mold wall inwards, so the last metal to solidify is the metal in the middle and just below the top surface. If nothing replaces the volume that metal loses, it pulls away from the already solid shell and forms a pipe, a single cavity running down from the top, or a dispersed porosity distributed through the last region to freeze. Both are invisible on a perfect as-cast surface and both are fatal at a density check or a section through a rejected bar. A feed head above the cavity gives the pipe somewhere else to form and lets it be cut off with the runner. Holding the chamber at a controlled pressure above ambient while the ingot freezes supplies the driving force that feeds the contraction from that reservoir. And controlling the cooling profile so that the ingot freezes directionally from the far end towards the feed head keeps the last liquid where the reservoir can still reach it. A vacuum that is pulled and then simply released gives none of those three, which is why the overpressure is a stage of the cycle rather than a purge at the end of it.

Can the machine cast karat gold and alloys without losing the fineness?

Yes, provided the dwell at temperature is controlled, and the element to watch is zinc. Zinc boils at 907 °C, which is below the temperature a karat gold melt actually reaches, so an alloy held hot in an oxidising atmosphere loses zinc preferentially, and since zinc is what carries both the colour and much of the hardness in many yellow and rose alloys, the bar drifts off its declared composition as well as off its colour. Melting under vacuum removes the oxidising atmosphere and pulls the vapour away from the melt surface, and a defined superheat with a short controlled dwell limits how much time the alloy spends hot. The alloy is then cast in the same chamber, so it is not re-exposed to air between melting and freezing. The declaration that matters is the fineness or composition the customer sells against, and it is verified by the agreed assay method on the bar or on a sample from the charge. It is worth being clear about the boundary: the machine holds a declared composition through the melt, and it does not correct one. If an alloy arrives with the wrong zinc or the wrong copper, casting it will faithfully reproduce the error.

Does the machine need a vacuum pump and a chiller, and what utilities does it require?

Yes to the pump, and the cooling depends on the site. The vacuum pump is part of the machine, specified by the displacement needed to bring the chamber volume down to the set pressure inside the evacuation window the cycle allows, with an isolation valve for the leak-rate hold test and pressure measurement taken on the chamber rather than at the pump. For a chamber in the 1 to 2 kg bar class, the 63 cubic metres per hour displacement that most published machines of this size specify is a reasonable indication of the order of magnitude, but the number is a consequence of the chamber volume and the time allowed rather than a figure worth specifying on its own. On cooling, the coil and the power supply need a closed cooling circuit, which is normally supplied with the machine and can be served either by a chiller or by an existing site cooling water circuit with the right temperature and flow. What cannot be left to the site is the exhaust: the pump exhaust and the chamber vent are ducted to a defined discharge point, and the vent line is filtered so that the metal-bearing dust is collected rather than released. Electrical supply, compressed air if the lid or the pour mechanism is air-actuated, and the gas supply with its regulator and its storage arrangements all follow the local standard, and the whole utility schedule is issued with the layout drawing once the bar programme is fixed.

What surface finish and dimensional tolerance does the ingot come out with?

The bar comes out of the mold reproducing the cavity wall finish, free of oxide skin, and free of the water-wave ripple that an open pour produces, and in most bullion programmes that is the finished surface: it needs no acid treatment, no scraping and no buffing, and it may need only a light polish before marking. That is a consequence of three things rather than of a finishing step: the melt never sees oxygen, so there is no oxide to remove; the pour is made by tilting or inverting the crucible on a controlled profile so the metal enters the cavity smoothly instead of splashing, which is what produces the wave pattern on an open pour; and the cavity wall finish is machined and maintained, so the texture on the bar is the texture of the mold. Where a bar is to be minted, rolled or stamped downstream, the as-cast surface matters differently, because the rolling reduction will remove it and the requirement becomes internal soundness and a consistent section instead. On dimensional tolerance, the cavity fixes the envelope and the contraction allowance sets the difference between the cold cavity and the cold bar, so the as-cast dimensions are a consequence of the mold drawing. What is normally contracted and verified is the bar weight against the declared weight, which is measured on every bar and reconciled against the charge, and the surface standard, which is agreed before manufacture so that acceptance does not depend on an opinion formed at delivery.

Can the machine run continuously, and who can operate it?

Yes to continuous running, and the operating requirement is a trained operator rather than a casting specialist. The whole sequence runs from a stored programme recalled by bar programme, covering the evacuation and the hold test, the melt ramp, the superheat dwell, the backfill, the pour profile, the pressure hold, the cooling profile and the vent and discharge, and the operator’s job through the cycle is to have prepared the charge and the mold correctly and to read the chamber state, the metal temperature and the pressures as they are displayed. The interlocks are what make that safe on a shift pattern: the pour cannot start until the vacuum and the metal temperature satisfy the programme, the backfill cannot start until the evacuation and the hold test are complete, and the induction supply and the cooling circuit are interlocked against a cooling fault. Between casts the workload is the practical work that decides whether the next bar is good: inspecting and weighing the charge, checking the seal faces and the gasket, inspecting the cavity, changing the mold on its locating feature, and closing and locking the lid. The machine carries alarms for a failed leak test, an evacuation over time, a power or cooling fault, an over-temperature melt, a gas supply loss and an interlock breach, and the event log records the cycle against the lot number along with the recorded vacuum, overpressure and temperature figures, which is what allows a fault found on the bar to be traced to the cycle it came from.

What is verified before the machine is accepted?

Three things are verified in the factory and three on site, and the methods are agreed in the contract before manufacture so that acceptance does not depend on how the figures are produced. In the factory the chamber is leak-tested and the leak rate is measured and recorded against the criterion, because that single figure is what the whole inert-atmosphere claim rests on; the mold blocks are checked dimensionally against the cavity drawings, since the cavity is what sets the bar weight and the bar envelope; and a trial cast is made on the customer’s own metal or an agreed substitute, with the bar weighed against the charge, examined for surface and section soundness, and assayed by the agreed method. The interlocks, the alarm set and the event log are function-tested at the same time, and the customer is invited to attend and to witness the leak test and the trial cast. On site the services interface, the levelling, the exhaust duct connection and the electrical and cooling tie-ins are verified, and an instrumented commissioning campaign runs on the customer’s own metal until successive casts demonstrate the declared bar weight, the agreed as-cast surface and the declared fineness, with the recorded vacuum, overpressure and cycle figures confirmed against the design. The acceptance package carries the leak-test record, the cavity dimensional record, the trial cast report and the commissioning report, and every subsequent lot is released against a cast weight reconciliation, an assay certificate and a lot record.

Vacuum Ingot Casting Machine

Product Overview

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Application Scenarios

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Finished Products

Vacuum Ingot Casting Machine Process Flow

Product Structure (Main Equipment)

Chamber, sealing and vacuum containment

Induction melting, crucible and pour mechanism

Mold set, instrumentation and control

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