Burnout furnace for jewellery casting: the burnout cycle and how to choose a furnace

In lost-wax casting, the burnout furnace turns a flask full of investment and wax into a clean, empty mould ready for metal. Many casting problems start here: rough surfaces, black specks and porosity often come from a rushed or uneven burnout. This guide explains the burnout cycle and what to look for in a furnace.

What happens during burnout

1. Wax removal. At low temperature, most of the wax melts and runs out of the flask.
2. Drying and slow heating. Water in the investment leaves gradually, so the mould does not crack.
3. Burning off the rest. At the highest temperature, any wax left behind burns away completely.
4. Cooling to casting temperature. The flask is brought down to the temperature right for your metal and design.

A typical cycle

Exact figures depend on your investment powder and flask size, so always follow the burnout chart from your investment maker. As an example, published cycles for gypsum investments used with gold and silver commonly:

• ramp slowly to around 300 °C and hold;
• ramp to a peak of around 730 °C and hold for a few hours;
• then cool the flask to the casting temperature, which depends on the alloy and how thin the pieces are.

Larger flasks need longer holds, because the inside of the flask takes time to catch up with the furnace. The inside of a flask can lag the display by 30 to 60 minutes.

Signs your burnout is the problem

• Rough or pitted surfaces: heating too fast in the first hour, so the wax boiled.
• Black specks or gas holes: wax or ash not fully burnt away. A complete burnout leaves the inside of the flask clean white.
• Fins and cracks in the casting: the investment cracked from heating too fast.
• Different results from flask to flask: uneven heat inside the furnace, or flasks cast before they reached temperature.

Using 3D printed resin patterns? They need their own burnout care. See our guide to castable resin casting problems.

What to look for in a burnout furnace

• A programmable controller that runs the ramps and holds automatically.
• Even heat throughout the chamber, so every flask gets the same treatment.
• The right chamber size for the number and size of flasks you cast at once.
• Good ventilation for the smoke and fumes from burning wax.
• A suitable power supply for your workshop.

Burnout furnaces from Semsons Tech

We supply burnout furnaces for jewellery casting, as well as the melting and casting machines that follow, such as our induction melting and vacuum casting machines.

Where to see and buy it

These are the Semsons Tech machines for this job. The store links let you book online; the other links open the full specifications or a quotation request.

Tell us your flask size and how many you cast a day, and we will suggest the right furnace. Book a demonstration or call +91 98216 12340.