The difference between vacuum furnace and non-vacuum furnace

The difference between vacuum furnace and non-vacuum furnace

The electric heater is an important part of the vacuum furnace, which determines the working capacity and working period of the furnace. The electric heater is composed of electric heating elements. The working conditions of the electric heating elements in the vacuum furnace have the following differences compared with the non-vacuum furnace.

1. The heat transfer form of the electric heating element to the workpiece is different

The electric heating element of the vacuum furnace transfers heat to the workpiece through radiation, so under the same other conditions, the temperature of the vacuum furnace is higher than that of the non-vacuum furnace. However, the temperature difference is only significant in the low-temperature furnace.

2, the conditions for the interaction between the electric heating element and the atmosphere in the furnace are different

The working conditions of the electric heating element in the vacuum furnace are better than other conditions, especially much better than the non-vacuum furnace with an oxidizing atmosphere in the furnace. Therefore, the heating element does not require high oxidation resistance in a vacuum state. In addition to the chemical reaction between the atmosphere in the furnace and the electric heating element, some electric heating materials, especially rare metals, become brittle and easily damaged by absorbing a large amount of gas during heating. In the state, these metals can work reliably for a longer period of time.

3, the volatilization speed of heating element materials is different

The electric heating material is easy to volatilize in the vacuum furnace. As the temperature of the electric heating element increases, its vapor pressure also increases, so the service life is reduced. From this point of view, vacuum also has an adverse effect on electric heating elements.

For low and medium temperature vacuum furnaces (use temperature not higher than 1000℃), nickel-chromium alloys and iron-chromium aluminum alloys are generally used as electric heating elements; for high-temperature vacuum furnaces, especially those with a temperature greater than 1200℃, the electric heating used The components are pure metals such as aluminum, tungsten, tantalum, and graphite. Non-metallic electric heating materials, such as silicon carbide, will decompose the bonding agent under vacuum, and aluminum silicide will soften when it exceeds 1300°C under vacuum. Therefore, vacuum furnaces rarely use these two electric heating materials.