The vacuum instrument of vacuum brazing furnace is within the scope of validity. After leak detection by leak detector, the protection valve at the vacuum gauge has air leakage problem, so the valve is replaced.
1. Through the inspection, the gap between the rotor and the rotor and the inner wall of the pump cavity is within the allowable range. The gear wear is very small and there is no need to replace it, but the bearing is seriously worn. Therefore, the bearing is replaced. The shaft head seal ring of roots pump leaked oil. The seal ring of shaft head was replaced and the lubricating oil at both ends of roots pump was replaced. After the roots pump is repaired, there is no air leakage at the seal. The limit vacuum degree of roots pump can reach 3 × 10-2 PA.
2. Through the external leak detection of the furnace body and vacuum pumping system of the vacuum brazing furnace, it is found that the main valve stem seal, pre extraction valve, air release valve, pneumatic ball valve and furnace door seal have different degrees of air leakage. After decomposition and inspection, it was found that the seal of the main valve stem and the seal ring of the furnace door were seriously aged, and there was a problem of air leakage due to cracks. Therefore, the corresponding sealing rings were replaced. When replacing the sealing ring of the main valve stem, considering the influence of high temperature, the sealing ring is simple aging, so the material selected is fluororubber.
Fluororubber is a very good sealing material with high temperature resistance and various media resistance. It has small outgassing volume and incomparable superior performance of other sealing materials, thus providing necessary guarantee for the sealing here. At the same time, it was found that the valve core of pre extraction valve, vent valve, pneumatic ball valve stem and valve core were seriously worn, so these three valves were replaced.
When detecting the leakage at the metal head of thermocouple, because of the long response time of leakage detection, if there are very small air leakage points near the metal head of thermocouple, it is particularly simple to misjudge. To solve this problem, a special method is adopted: first, wrap the sealing part of the coupling wire with a plastic bag, and then the helium gas is put into the plastic bag for leak detection. Through the detection of the above methods, it is found that there is air leakage in the self sealing part of the thermocouple, so the new thermocouple is replaced.