Leakage Detection Method of Plasma Nitriding Furnaces

Plasma nitriding furnaces belongs to the category of low vacuum equipment. Usually, after a period of use of equipment, air leakage will exist. In the case of slight leakage, the leakage generally does not have a great impact on the nitriding quality of the workpiece (except stainless steel series), but if the leakage of the equipment is serious, it will affect the nitriding quality of the workpiece, and must be repaired.

Leak detection of vacuum equipment is relatively difficult, usually using the "section" inspection method, that is, a section of the inspection.

The first step is to separate the furnace body from the gas supply system in order to distinguish whether the leakage is caused by the furnace body or by the gas supply system.

Separate the intake pipe from the bell jar and seal the intake joint (using the special plug or vacuum mud I provided). Start the vacuum pump to vacuum, after pumping to a higher vacuum (such as about 30 Pa or higher), close the butterfly valve, pause for a period of time (15-30 minutes), observe the leakage of the equipment.

Step 2: After the first step of work, if the furnace body leaks, the sealing parts (including observation window, inflatable device, bell cover lower sealing flange surface, large sealing ring on chassis, pressure measuring part sealing part, cathode part sealing part, butterfly valve and connecting flange surface between the exhaust pipeline) that may leak should be inspected one by one until the furnace body is basically free of air leakage.

Note: When implementing the following inspection steps, we should follow the principle of "sectional" inspection method, that is, one step at a time. After each inspection step is completed, vacuum is used to observe the inspection effect. If the problem of air leakage is solved, no other inspection will be carried out. Otherwise, check in turn (check steps can be disorderly).

1. Check whether the glass mirror of the observation window is broken or not. If it is broken, it should be replaced.

2. Check whether the inner hexagonal screw of the fastening glass mirror on the observation window is loose or not. If it is loose, it should be tightened, but it must be symmetrically and evenly tightened, and the force should not be excessive, so as to avoid crushing the glass.

3. Check whether the inner and outer sealing rings (white) of the windows are ageing. If they are ageing, new sealing rings need to be replaced.

4. Remove the automatic charging device on the base of the furnace body, remove the sealing rubber and ash on the air-filled sealing surface with a clean rag stained with gasoline, and install it as it is.

5. Check the sealing condition of the pressure measuring place on the furnace chassis. If the fastening nut is loosened, it should be replaced if the sealing ring is damaged.

6. Check the sealing condition of cathode parts. If the fastening nut is loose, it should be tightened. If the sealing ring is damaged, it should be replaced.

7. Check the bottom sealing flange of the bell cover of the furnace body. If there are rusts, pits and other damages, they should be dealt with in time. (Note: After lifting the bell cover each time, it should be placed on rubber board, wood or other soft support to prevent damage to the sealing flange surface.)

8. Check the large sealing ring on the chassis of the furnace body. If there is any damage, it should be repaired or replaced in time. (Note: After lifting the bell cover each time, before putting the bell cover on again, clean the ash on the chassis and big sealing ring with a clean brush, then wipe off the ash on the sealing flange and big sealing ring with a clean rag stained with gasoline, in order to prevent the ash from leaking into the big sealing ring.)

9. Check the tightening of the flange surfaces of each connection of the hard elbow for suction. If it is loose, it should be tightened evenly. If the seal ring is damaged, it should be replaced in time.

10. Check whether there is any ash on the inner seal ring of the disc valve. If there is ash, it may cause the butterfly valve tube not to die and leak. If such a situation is found, it should be cleaned up in time with a clean rag stained with gasoline and then coated with vacuum grease. Note: When cleaning the seal ring of butterfly valve, do not soak the seal ring with gasoline, otherwise the seal ring will increase and the butterfly valve will not be able to switch.

Step 3: After the completion of the first step, if the furnace body does not leak, all the sealing parts of the furnace body are in good condition. Then slowly open the butterfly valve, which may occur in the following two cases.

1. Vacuum degree decreases slightly at the moment of opening butterfly valve, but it does not continue to decrease afterwards (i.e. the pressure rise rate is within the range specified by the equipment or within the range permitted by the process), which indicates that stainless steel suction hose, solenoid valve and their connecting parts are in good condition.

2. If the vacuum decreases continuously after the butterfly valve is opened, it indicates that there may be air leakage at the connecting sealing parts of the electromagnetic vacuum belt inflatable valve, the stainless steel corrugated hose or the hose ends. If this happens, leak detection can be carried out according to the following procedures.

(1) First check the sealing parts at both ends of bellows. If the sealing flange is loose, it should be tightened evenly. If the sealing ring is damaged, it should be replaced in time.

(2) Then check whether the sealing ring inside the solenoid valve is adhered to ash, if there is ash, it may cause air leakage. It is found that such a situation exists, and the ash can be cleaned up with a clean rag stained with gasoline.

(3) Finally check the corrugated hose. The inspection can be carried out by sealing pressure (pressure is 0.1 MPa). After pressurization, the pipe body is immersed in water in stages and the leakage position is observed. (Bellows should be avoided when pressurizing)

Step 4: After completing the first three steps, having solved the problem of furnace body leakage or confirmed that the leakage is not caused by the furnace body, the intake pipe separated from the furnace body in the first step is connected to the bell cover of the furnace body again (and the sealing at the joint is ensured to be intact). First, the flowmeters are shut down, and then the vacuum pump is started to vacuum the furnace body. The purpose of this step is to check the leakage of the air supply system.

If it is found that there is air leakage in the equipment, the sealing condition of the intake joint, the gas pipe and the connection of all kinds of gas flow confluence tees can be checked until the problem of air leakage is eliminated.

(1) Check the sealing condition at the joint of intake pipe and intake pipe and the outlet of flowmeter. If air leakage is suspected, the joint can be sealed with vacuum sealing mud.

(2) Check whether the flowmeter can be shut down. The method is to block the inlet end of the flowmeter and compare the difference between blocking and closing only the leakage of the flowmeter. If the flowmeter is not dead, it needs to be repaired or replaced.

(3) Check whether the ammonia hose leaks or not. If aging leaks are found, the hose should be replaced.

Usually, after completing the inspection of the above steps, the problem of gas leakage in the furnace body can be solved.

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