The application of vacuum pump in vacuum induction melting machine, the design idea of vacuum system, the main configuration and precautions of vacuum system, the selection and calculation of vacuum pump are mainly introduced. It has reference value for the development of similar vacuum furnaces and the application of vacuum pumps. By strictly checking the R & D links, cleaning, degassing and baking according to the ultra-high vacuum specification, the ultimate pressure of the vacuum furnace reached 2 × 10-7pa, extending the conventional ultimate pressure of the vacuum furnace to an order of magnitude. In recent years, oil-free vacuum pump has been introduced and widely used in semiconductor industry. Thus, the oil-free ultra-high vacuum acquisition system represented by roots vacuum pump and dry pump has been widely used in semiconductor electronic technology, optical coating system and aerospace field.
If the temperature of the extraction surface is reduced to below 20 K by low temperature medium, the gas with lower boiling point can be condensed on the extraction surface, and a large number of gas can be extracted. This kind of air pump which condenses the gas by using the low temperature air extraction surface is called low temperature pump or condensation pump. It is a device that condenses, adsorbs or condenses + adsorbs the gas after the surface temperature is reduced by using low-temperature medium, which will reduce the pressure of the space to be pumped, and obtain vacuum or maintain vacuum state.
As a complete pumping system, the vacuum pump is composed of two parts, the main body is the vacuum pump body, and the second part is the compressor. Now widely used are refrigerator vacuum pumps, the core of which is the cryocooler. The basic working process is as follows: firstly, helium is compressed to high temperature and pressure state; then it is cooled to normal temperature helium through heat exchanger; finally, the purified high-purity helium is adiabatic expanded through cylinder to become low temperature helium. As a result, helium is constantly cooled and becomes the refrigeration medium – low temperature helium.
The advantages of choosing roots vacuum pump are as follows:
1. It is clean, oil-free and has a wide range of air extraction. It can quickly obtain an ideal ultra-high vacuum environment;
2. Compared with other vacuum pumps with the same caliber, roots vacuum pump has a larger pumping speed, especially the ability of pumping water vapor;
3. There is no choice for the extracted gas, and the impurity particles do not affect the system operation;
4. It can be installed at any angle, without moving parts, without the need for the front pump, so the cost of operation and maintenance is low;
5. The air exposure has little impact on the system. The compressor can be self-protection after water cut-off, so it can be unattended.
Design of vacuum system of vacuum induction melting machine:
The biggest problem is to solve the heat load when the roots vacuum pump system is used in the vacuum furnace. The heat load in vacuum furnace mainly comes from three aspects:
1. Heat radiation from the side of furnace body;
2. In viscous flow, gas molecules carry away heat;
3. Heat conduction and radiation from the pump outlet pipe.
In order to obtain the ideal ultra-high vacuum, and at the same time using the redundancy technology, we designed the vacuum system of molecular pump unit and roots true pump in parallel. The molecular pump unit can be used as the pre pumping of the system, so that when the vacuum pump cools down, it can work directly in the molecular flow state.
In addition, when the outgassing volume of vacuum chamber is large, it can be switched to molecular pump in time, which can not only prolong the saturation time of vacuum pump, but also save the regeneration time. Molecular pump and vacuum pump are connected with the vacuum chamber through pneumatic ultra-high vacuum gate valve. In order to ensure that the system is clean and oil-free, and at the same time give full play to the pumping advantage of low-temperature pump, pure oil-free magnetic suspension molecular pump is selected, and the scroll type dry pump is selected for the front pump, and the dry pump is also used for pumping when the pump is regenerated.
Main configuration of vacuum system
When the molecular pump unit and the compressor are started at the same time, the secondary cold head of the vacuum pump drops from room temperature to below 15 k after about 120 min (the valve of the low-temperature pump can be opened), at this time, the vacuum degree of the vacuum system of the vacuum induction melting machine can reach 10-5pa, so that the vacuum pump can directly start pumping from the high vacuum.
This set of equipment is a typical vacuum induction melting machine, which is used in diffusion welding process under ultra-high vacuum conditions. Its heat capacity and surface area are larger than that of heat treatment furnace of the same specification, with high degree of automation. It can give full play to its significant advantages when equipped with roots vacuum pump.
Vacuum pump for vacuum induction melting machine
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