A vacuum furnace is a type of furnace that can heat materials to very high temperatures. The function is to carry out processes such as heat treatment, sintering or brazing. The area where the heat is produced is called a hot zone.
The hot zone is by far the most critical component of your vacuum furnace as it is the functional core. Hot zone designs and internal supports and hardware need to be designed with consideration to low mass and specific heat wherever possible to avoid hot zone energy absorption. Considerations in selecting a particular type of hot zone include maximum temperature range of operation, types of cycles to be performed, expected holding times at elevated temperatures, peak power concerns and overall operating power costs. All of these factors relate to hot zone construction and its related power losses.
Since the early development of the vacuum furnace, engineers and thermal experts have tried to improve the insulating characteristics and the performance of the components inside the hot zone. The most acceptable types of hot zones manufactured today use graphite in the form of sheets, felt or board for insulating purposes as well as graphite components such as heating elements, connectors and furnace bases.
Choosing the correct materials will result in controlled atmosphere and vacuum furnaces capable of running at uniform temperatures up to 5250°F+ with low contamination and minimizing power losses.
As graphite emerged as a highly engineered advance material, the use of this material in manufacturing hot zone components increased. Graphite hot zone components allow for intricate part designs that can be manufactured fast and reliably.
The graphite wafer is an excellent material. It allows operation at very high temperatures (up to 3000°C based on the vacuum level), has low density, reduced weight and modest thermal capacity. It creates the ideal black body conditions (emissivity about 1) inside the heating chamber for obtaining high uniformity.
Graphite hot zones are easily repairable and suitable expedients can be applied to guarantee a long life. These include applying a sacrificial layer made of CFC or with a graphite laminate, protecting the wafer both against the effects of the high temperature (deformation – expansion), and gas erosion during the load cooling phase. Wafer thickness depends on the maximum operating temperature.
A furnace with this type of heating chamber is the best solution at least for the more conventional vacuum treatments. On the downside, there are also less positive aspects regarding graphite’s capacity to adsorb vapors. A graphite’s property which we should take into account when it is time to decide on the right technology for the vacuum furnace hot zone design.
Utilizing the appropriate materials to place in service is of key importance and will change with each particular application. XRD Graphite developed a complete range of materials for high temperature vacuum furnaces, offer the end user a wide selection of advanced materials options. Here is our graphite Component for Vacuum Furnace:
- Heating chamber
- Heating pipes
- Conductive rod joint parts
- Graphite tray
- Graphite box for sintering
- Graphite plate
- Electrode connectors
Here is physical and chemical index of graphite material：http://www.graphitemachining.cn/materials