Vacuum Casting Machines for Jewellery, Gold and Silver
A vacuum casting machine for jewellery melts metal by induction inside a sealed chamber, evacuates the air from that chamber and from the investment flask, and then fills the mould while no atmosphere is present to be trapped in the metal. The result is a casting with less gas porosity, less oxide inclusion and sharper detail reproduction than open-air pouring gives. OPDEL supplies vacuum and pressure-over-vacuum casting equipment for jewellery manufacturers, precious metal refiners, sample and assay laboratories, and casting houses working in gold, silver, platinum, palladium, brass and bronze.
How vacuum casting works
Lost-wax casting fails in three predictable ways: gas trapped as the metal front closes around it, oxide skin dragged into the cavity, and thin sections that freeze before they fill. Vacuum casting addresses all three by changing the atmosphere rather than the alloy.
The metal is melted by induction in a graphite or ceramic crucible. The flask sits below on a lifting device, sealed against the chamber. A pump evacuates the chamber so the mould cavity and the porous investment are under negative pressure. The metal is then released — by gravity through a stopper rod, by centrifugal acceleration, or by gas pressure applied above the melt. Because the cavity is evacuated, the investment itself becomes a vent: air ahead of the metal front escapes through the mould wall instead of being compressed into a bubble at the top of a stone setting.
Argon or nitrogen is normally admitted over the melt during heating. That inert cover is what protects the alloy from re-oxidising while it sits at temperature, and it is why the deoxidiser dose can usually be reduced.
Vacuum-assisted, pressure-over-vacuum, and centrifugal
Three mechanisms are in use, and the right one depends on section thickness, alloy and batch size.
Pressure-over-vacuum
The flask is evacuated, then the melt chamber is pressurised so metal is pushed into the mould rather than only drawn. This is the standard route for stone-in-place work and for fine filigree, because fill is completed before the leading edge chills.
The OPPRSCast Mini pressure-over-vacuum casting machine casts at up to 2.5 bar with a manual flask lift and an external vacuum pump, and takes a 1 kg gold or 0.5 kg silver crucible (90 cm³). The larger OPPressCast OP3 and OP5 dual-chamber casting systems cast at up to 6 bar with a pneumatic flask lift and an integrated vacuum pump rated 100 mbar at 40 m³/hr, in 3 kg Au and 5 kg Au crucible sizes. Both use a central graphite stopper rod with the thermocouple embedded in the sealing rod, so the temperature is read at the metal rather than at the coil.
Vacuum with centrifugal injection
Where the alloy is high-melting — platinum, palladium, titanium — acceleration does the filling and vacuum plus inert gas does the protection. The OPSPRCast D universal casting machine with the patented Rotating Coil System keeps the coil rotating with the arm and flask so the metal stays liquid through injection. The OPCS Digital centrifugal casting system covers higher-volume production up to 1.3 kg Au, and the compact OPCast D centrifugal casting machine suits boutique studios, with the vacuum pump and inert gas circuit present on the OPC-12 variant only. For assay and quality-control sample work rather than production, the OPSPR Pro sample casting system is the relevant machine.
Gravity vacuum casting for lost wax
The OPC A03 lost-wax vacuum casting machine casts by vacuum with automatic programmable gas pressure on a fully automatic cycle, with argon protection and a pneumatic flask lift. The smaller OPC F1000 and F2000 casting machines run the same vacuum-with-gas-pressure principle on a manually sequenced cycle for 1–2 kg melts.
Vacuum chamber as an add-on
If a static melting furnace is already installed, a separate chamber can be added instead of a complete machine. The VAC vacuum casting chamber is a trolley-mounted chamber and pump connected by a large-section tube, used with an ST series static induction melting furnace to cast lost-wax flasks alongside the furnace. It accepts flanged cylinders with reducing discs.
Specifications
| Model | Max power | Supply | Max melt temp | Crucible capacity | Max flask D×H | Vacuum pump |
|---|---|---|---|---|---|---|
| OPPRSCast Mini | 5 kW | 230 V ±10%, 1 ph | 1300 °C | 1 kg Au / 0.5 kg Ag | 4″ × 8″ with flange | External |
| OPPRSCast OP3 | 11.0 kW, 6 kHz | 400 V ±10%, 3 ph (230 V optional) | 1300 °C | 3 kg Au (208 cm³) | 120 × 300 mm | Included |
| OPPRSCast OP5 | 11.0 kW, 6 kHz | 400 V ±10%, 3 ph (230 V optional) | 1300 °C | 5 kg Au (430 cm³) | 120 × 300 mm | Included |
| OPSPRCast Lite D4 | 4.0 kW | 230 V ±10%, 1 ph | 2000 °C | 200 g Pt / 170 g Au / 80 g Ag | 80 × 75 mm | Included |
| OPSPRCast Plus D5-T | 5.0 kW | 230 V ±10%, 1 ph | 2000 °C | 200 g Pt / 170 g Au / 80 g Ti / 80 g Ag | 90 × 90 mm | Included |
| OPCS3-D | 10.0 kW | 400 V ±10%, 3 ph | 2000 °C | 1 kg Pt / 1.3 kg Au | 150 × 180 mm | Included |
| OPCast D (OPC-12) | 3.0 kW | 230 V ±10%, 1 ph | 2000 °C | 150 g Pt / 150 g Au / 80 g Ag | 80 × 75 mm | Included |
| OPC A03 | — | — | 1150 °C | 4.2 kg Au 18kt / 2.9 kg Ag 925 | — | Vacuum with programmable gas pressure |
| OPC F1000 / F2000 | 4.5 / 5.0 kW | — | 1150 °C | 1.5 / 2.3 kg Au 18kt | ø100 × 250 mm | Vacuum with gas pressure |
Cooling and gas: OPPRSCast OP3 and OP5 require external water at 5.8 L/min minimum with inlet water no warmer than 35 °C, and argon to a maximum of 60 L at 2 bar per casting. The OPCS Digital range needs 2 L/min minimum. Chamber-pressure and vacuum-level figures beyond those listed are .
What this changes on the shop floor
- Yield. Fewer rejected trees means less metal cycling back through remelt, and each remelt carries its own loss. Reduced oxidation under argon also means less dross skimmed off.
- Finishing labour. Cleaner surfaces and fewer subsurface pores cut the polishing hours per piece, which is usually the larger of the two savings in a labour-costed shop.
- Stone-in-place. Filling at pressure lets stones be set in wax rather than after casting, removing a whole setting operation on suitable designs.
- Repeatability. Programmable cycles mean the same result from the second-shift operator as from the first. OPPRSCast machines store up to 10 cycles with 10 adjustable parameters each.
- Safety. A sealed chamber with an interlocked lid keeps the operator away from molten metal at pour.
Who uses these machines
Jewellery manufacturers casting rings, chains, bangles and pendants; refiners casting recovered gold and silver into feedstock; sample-preparation and assay laboratories; dental laboratories; and art and limited-edition metal casting. Suitability for medical or aerospace components depends on the qualification standard being worked to — .
Consumables and support
Crucible life is the main running cost after power. Graphite inserts and ceramic crucibles are consumable items and should be ordered with the machine: see graphite crucibles and casting components and the wider casting consumables range. Downstream of casting, an investment cleaner removes the mould from the tree before finishing.
Frequently asked questions
Which capacity should I buy? Size from the heaviest single tree you cast, not from monthly output — the crucible has to hold one flask’s worth of metal plus sprue and button in one melt. A 1 kg gold crucible covers a small studio; 3 kg and 5 kg crucibles cover production shops. If your tree weight is close to a crucible limit, take the next size up rather than running the machine at its ceiling.
What power supply do I need? It varies by model. The OPPRSCast Mini, OPSPRCast D, OPCast D and OPSPR Pro run on 230 V single phase; OPPRSCast OP3 and OP5 and the OPCS Digital range run on 400 V three phase with a 230 V option. Confirm the supply at your site before ordering, since retrofitting three-phase is usually the longest lead item in an installation.
What else does the machine need to run? External cooling water at the stated flow with inlet temperature no higher than 35 °C, and a cylinder of argon or nitrogen. A closed-loop chiller is worth budgeting for if you cast continuously — .
Can I use my existing flasks and crucibles? Only if the diameters and flange type match. Each model has a defined minimum and maximum flask size, and the pressure machines need perforated flasks with a flange; reducing rings exist for smaller flasks. Send your current flask dimensions with your enquiry and they can be checked against the model before you order.
Is training included, and how long does commissioning take?
What is the lead time?
What warranty and spare parts backup is there?
Can I add vacuum casting to a furnace I already own? Often yes. A VAC chamber can be paired with an ST series static furnace, and the ST specification lists a casting chamber vacuum as an applicable option with a stated maximum cylinder size . Whether a specific installed furnace can be retrofitted is .
Is vacuum casting worth it over centrifugal alone? If you cast thin sections, filigree, or stones in place, the reject reduction usually pays for the difference. If you cast heavy, simple sections in silver, a centrifugal machine without vacuum may be enough. The comparison to run is rejects plus polishing hours per 100 pieces, not machine price.
Request a quotation
Tell us the alloys you cast, your heaviest tree weight, your flask sizes and your available power supply, and we will recommend the model and quote it. Reach the OPDEL team through the contact page, or by phone or email using the details listed there. Company registration details: . Model naming across literature is inconsistent — .