This section provides overview, applications, and principles of vacuum furnaces. Also, please take a look at the list of 10 vacuum furnace manufacturers and their company rankings.
A vacuum furnace is a furnace capable of vacuum heat treatment processing. Since the object is heated in a vacuum inside the furnace, the surface of the object can be processed without oxidizing it. Decarburization can be prevented and the luster of stainless steel and other materials can be maintained after heat treatment. The high surface cleanliness of the surface also allows for the joining of dissimilar metals, and the gradual cooling process from heating to cooling reduces distortion.
This treatment method emits less carbon dioxide and reduces variation in dimensions and hardness. In some cases, heat treatment is performed in a vacuum furnace while nitrogen gas or other gases are flowing.
Metals treated in vacuum furnaces are characterized by high luminosity, and surface oxidation and impurities can be reduced. Vacuum furnaces are used for quenching and tempering, sintering, brazing of evaporators, etc., and annealing. Instead of ordinary metals, high-grade steels such as cemented carbide tools and metals that require special functions such as magnets, capacitors, automotive parts, and industrial machine parts are fabricated in vacuum furnaces.
Although vacuum furnaces offer many advantages, they are also expensive to maintain, and large furnaces are particularly costly.
Vacuum furnaces use a combination of oil rotary pumps and turbomolecular pumps to exhaust the air inside the furnace and maintain a high vacuum. Heating in the absence of oxygen in a high vacuum prevents oxidation.
The furnace vessel is mainly made of stainless steel, capable of heating from 1000°C to 2300°C, and heated by metal heaters such as tungsten, molybdenum, and silicon carbide.
Smaller furnaces include tubular furnaces, in which the object is heated in an alumina or quartz glass tube. Kanthal wire is used as the heater material, and the furnace can heat from 700°C to 1600°C. The furnace can be cooled by natural cooling or gas cooling.
Cooling methods include natural cooling, gas cooling, and oil cooling. For high temperatures, the vessel is double-layered and water-cooled.
For measuring high temperatures, radiation temperature is measured externally. Almer-Chromel thermocouples or platinum-rhodium alloy thermocouples are used.
In a standard vacuum furnaces, heating and cooling are performed in the same chamber.
Vacuum furnaces heat treat products through the three processes of conveyance, heating, and cooling, and are broadly classified into two types of structures, one chamber type and multi-chamber type, depending on the type, number, and purpose of heat-treated parts.
In the "one-chamber type" furnace, there is no transfer mechanism, and the operator transfers and places the product to be treated in the furnace, where it is heated and cooled in a single chamber. Since the heating and cooling processes are performed in the same chamber, the furnace must be able to withstand rapid temperature differences, and heat-resistant stainless steel or carbon materials are used for the heater and structural members. Because of the simplicity of the structure, the lineup of furnaces is extensive, ranging from small-scale experimental furnaces to large-scale mass-production furnaces.
For cooling, natural cooling or gas cooling with inert gas such as nitrogen is used to prevent contamination of the furnace and heat-treated products. Uniform and contamination-free cooling is possible by controlling the number and position of cooling gas outlets and the flow and retention of cooling gas using an agitating fan.
Therefore, the structure is suitable for processing products that are sensitive to surface contamination or deformation. On the other hand, the cooling speed is slow, and the next product to be heat-treated cannot be loaded until the previous treatment is completed, which is a disadvantage of low productivity.
The "multi-chamber type" has a structure in which the transfer, heating, and cooling processes are performed in two or more chambers. The basic advantage is that heating and cooling can be completed automatically as set once the product is fed into the transfer chamber, and productivity can be improved by controlling the temperature in each zone, such as before, during, and after, and by staggering the processing time in multiple small batch heating chambers.
By using a separate cooling chamber, liquid refrigerants with high cooling capacity, such as oil, can be selected. Furthermore, since the cooling chamber is not heated, high cooling capacity can be maintained, and even metal materials with low hardenability and sensitive to cooling rates can perform well. On the other hand, it is necessary to be aware of disadvantages such as the need for cleaning after heat treatment due to contamination of the treated material by the refrigerant, and the occurrence of distortion and cracking due to the high cooling rate.
Carbon materials such as carbon graphite and C/C composite are used in vacuum furnaces as heating elements, structural materials, and heat treatment jigs.
Carbon materials are characterized by high heat resistance up to 3,000°C, light weight, low coefficient of thermal expansion, low deformation due to thermal fatigue, and low heat capacity.
Its light weight allows for increased loading capacity of heat-treated products and reduced setup load, and its low deformation resistance leads to lower running costs. The low heat capacity also has an energy-saving effect, which has many productivity-enhancing benefits.
On the other hand, there are disadvantages such as contamination of the furnace interior and heat-treated parts due to the volatile nature of carbon during heating, and the fact that gas cooling is the only method used.
*Including some distributors, etc.
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