Fri, 07 Sep 2018 05:57:22 +0000
vacuum braze furnace
1. Vacuum brazing furnace and its application characteristics
Vacuum brazing furnace is one of the most important furnace types in vacuum equipment. Vacuum brazing furnace has successfully played an increasingly important role in the thermal process of iron and steel, non-ferrous metals, composite materials, non-metallic materials, etc. Vacuum equipment manufacturing technology is now more advanced and flexible configuration, can adapt to both the process and product more complex and personalized requirements. According to incomplete statistics, there are only 4800 vacuum heat treatment furnaces in China, 90% of which are made in China. This shows that China has caught up with or is approaching the world’s leading level in the development of vacuum equipment manufacturing and vacuum heat treatment technology. As an important process of material heat treatment, vacuum heat treatment can realize vacuum atmospheric pressure, vacuum negative pressure, vacuum positive pressure, high pressure gas quenching, vacuum oil quenching, vacuum grading and so on. Temperature and other quenching process requirements. The development of vacuum heat treatment furnaces embodies the characteristics of high pressure and large vacuum chambers. Large vacuum brazing furnaces have emerged which can handle 100 tons of workpieces. Compared with resistance furnaces and salt furnaces, vacuum heat treatment furnaces have great advantages.
It has the advantages of no oxidation, no decarbonization, no carburization and vacuum degassing. Bright quenching can be realized. The surface quality of workpiece or product after treatment is good, but also toughness and thermal fatigue can be improved.
2) Vacuum heat treatment is pollution-free and pollution-free. It does not need sewage and dirty gas treatment, especially avoiding the volatilization and discharge of gases such as R salt bath furnace. It is beneficial to improve the working environment and physical and mental health of workers.
3) Vacuum brazing furnaces are controlled by computer, and the degree of automation and so on. The process repeatability is good, the quality of heat treatment is stable, the labor intensity of R operator is greatly reduced, and the labor productivity is improved.
4) Vacuum heat treatment has small deformation and is not easy to crack. For complex workpieces and large complex dies, it can realize heat treatment of finished products or heat treatment of small machining allowance, and can improve the quality and grade.
2, vacuum brazing furnace vacuum system leakage analysis and Countermeasures
One of the most important performance indicators of vacuum furnace is whether it can meet the vacuum requirement of the process. Vacuum furnace leak detection and solving the problem of leak is one of the technical difficulties encountered in vacuum heat treatment. This paper compares and discusses if the vacuum equipment can not reach the vacuum degree, the general use of the system valve and vacuum gauge for leak source analysis.
Set up: the vacuum chamber of the equipment is pumped for a long time to reach the pressure P, and the limit pressure of the pump is P, then there are two possibilities as follows:
P1 > P0 (2)
Type (1) indicates that the vacuum system is well sealed and has no air leakage.
Formula (2) indicates that there may be three situations.
A has poor performance in vacuum pumping.
The B system is deflated, that is, the vacuum system itself or material parts and so on.
C system leaks. Leak hole exists.
Which of the three cases is a, b, c, that is, in the analysis of the leakage source, the common method is to pump the vacuum system to a stable specific pressure. Close the valve to isolate the system, while measuring the vacuum and time, draw pressure-time (P-t) curve, as shown in Figure 1.
In Figure 1:
Line 1 indicates poor pumping performance of the vacuum system does not leak nor vent should be analyzed pump problems, troubleshooting.
Curve 2 shows the phenomenon of degassing, indicating that the vacuum chamber or system parts, material degassing, that is, water vapor, oil, condensate gas re-evaporation degassing. Generally speaking, the gas release rate decreases with the increase of time and pressure, and the leakage rate tends to be stable after a long time of pumping.
Diagonal line 3 shows that there is a leak in the vacuum system, that is, the air outside the system through the leak into the system to increase the pressure is mainly due to poor manufacturing and assembly.
Curve 4 indicates deflation and leakage. The characteristic of the curve is that the front section is a curve, the rear section is a diagonal line, the curve part indicates the phenomenon of gas release, the diagonal part indicates the method of gas leakage part placement is the main judgment means of the vacuum system leakage source, but find out the reason, take different measures according to different conditions, so as to achieve the effect of solving the problem with half the effort.
3. common parameters and leak rate requirements for leak detection in vacuum brazing furnace
1) leakage rate
Usually, the leakage rate is used to indicate the size of the leak, which is defined as: air with dew point below – 25 C, standard atmospheric pressure at inlet pressure level, outlet pressure below 103Pa, and air flow through the leak at (23 3) C is the leakage rate of the leak, in Pa. m3 / s. If the test fails to meet the above requirements, the calculated leakage rate must be corrected.
2) maximum permissible leakage rate
Maximum allowable leakage rate for static sealed vacuum devices
Formula: V- device volume, L, t- device life, h;
Pmax- maximum allowable working pressure, Pa;
The working pressure in the P0- device is Pa.
Maximum allowable leakage rate of dynamic sealed vacuum devices
Medium: S- pump effective pumping speed of the container, L/s.
Maximum allowable leakage rate for multiple dynamic sealed vacuum devices
If the dynamic system consists of multiple parts with X welds and Y detachable seals between the parts, the maximum allowable leakage rate of each part before assembly and assembly is: