A vacuum sintering furnace is a specialized device for producing alloys (such as permanent magnetic materials) and serves as an ideal alternative to traditional ingot casting processes. It uses vacuum induction melting, where a crucible is sealed inside a vacuum chamber. Electromagnetic induction generates eddy currents as the heat source, which melts and degasses the alloy or conductive material under vacuum or inert gas. The molten alloy is poured using a tilting crucible system, rapidly solidified on water-cooled rollers to form thin sheets, and then slowly cooled on water-cooled plates while being stirred. This produces large, uniform alloy sheets with controlled thickness.
The heat treatment process in a vacuum sintering furnace generally consists of three stages:
- Heating – The most important step. Early heating methods included charcoal and coal, later evolving to liquid or gaseous fuels. Modern furnaces commonly use electric heating, which is easier to control and environmentally friendly. Heating can be direct (applied to the metal) or indirect (through molten salt, metal, or suspended particles).
- Holding (Soaking) – Maintaining the material at a set temperature to ensure uniform thermal penetration and achieve the desired microstructure.
- Cooling – Controlled cooling to prevent stress, distortion, or undesirable microstructural changes. In some cases, only heating and cooling are required without an extended holding stage.
Key Process Parameter:
- Heating temperature is critical. It must be chosen and controlled according to the material type and heat treatment purpose, generally above the phase transformation temperature to obtain the desired high-temperature microstructure.