Fri, 06 Jul 2018 02:34:30 +0000
vacuum in heat treatment furnace of application
1. Principle and characteristics of vacuum heat treatment vacuum heat treatment is a special heat treatment process for quenching, annealing, tempering, sintering and solderless brazing of workpieces under vacuum conditions. Because this process has the function of vacuum protection and easy removal of adsorbents on the workpiece surface, it also has the function of degassing and evaporation on the workpiece. Therefore, this heat treatment process has developed rapidly in recent years, and its main features are:
(1) the workpiece can obtain high-quality surface tissue in the vacuum of the protective atmosphere, with bright surface, no decarbonization, no carbon increase, no hydrogen brittleness and nitrogen brittleness.
(2) the workpiece is heated in a vacuum with good degassing performance, thus improving the mechanical performance of the workpiece, improving the strength and abrasion resistance of the workpiece, and extending the service life of the workpiece.
(3) the vacuum heat treatment process compared with other method, small deformation, after processing can cancel or reduce the procedure of processing capacity, particularly for titanium and other active metal, including aluminum, drilling, such as heat resistant material, can use the other party for you to heat treatment.
(4) the production environment of vacuum heat treatment furnace is clean, without producing oil mist and smell, without explosion risk, which can greatly reduce pollution and pollution.
2. Vacuum system of vacuum heat treatment furnace several common vacuum systems of vacuum heat treatment furnace. The problem that these vacuum systems should pay attention to in the work is that the rotary vane vacuum pump should be started at the beginning of the work to carry out the pre-pumping of the furnace body and the main pump. The main pump can only be started when the main pump and the front pressure reach or are less than their maximum front pressure. 1. Several kinds of vacuum system furnace body of vacuum heat treatment furnace; 2- air charging valve; 3- pipe stop valve; 4-lutz pump; 5 – the hose; 6- mechanical pump: 7-high vacuum valve; 8-baffle: 9-oil booster pump; 10 – diffusion pump
3. Several problems in the design of vacuum system of vacuum heat treatment furnace
3.1 design requirements of the vacuum system from the perspective of “vacuum” :
(1) in order to improve the pass-through capacity of the system, the pipes between the vacuum parts should be thick and short, and the diameter between the main pump and the furnace body should be no less than the diameter of the air outlet. (2) the system shall combine the pumping procedures of each pump according to the principle that series can improve the ultimate vacuum and parallel connection can improve the pumping efficiency.
(3) in order to ensure the sealing performance of the system, the total ownership rate of the system must be limited to the allowable range. In order to facilitate the detection of leakage in different sections, measurement points should be set for each sealing interval to facilitate the elimination of leakage points.
(4) in order to prevent vibration and return of oil of mechanical pump at the entry date of mechanical pump; A shock – retarding hose is arranged between the roots pump and the main pump vent. In order to save energy, prepump and maintenance pump should be set up in large vacuum system.
3.2 the selection and calculation of the main pump shall directly refer to the pump of heat treatment pumping as the main pump, and the juice calculation of the pumping system shall generally start from the main pump. The type of main pump shall be determined according to the limit vacuum reached by the cold drawing pair of heat treatment furnace and the type, component, miscellaneous and dust in the gas, etc.
3.3 after the main pump is selected, the pre-stage pump shall be selected according to the following provisions:
(1) the front-stage pump shall ensure that the gas flow discharged by the main pump is always and timely eliminated.
(2) the pressure caused by the front stage pump at the outlet of the main pump should be lower than the maximum exhaust pressure of the main pump. The relevant calculation methods can be referred to the literature “.
3.4 the center of the vacuum system design problem in the first place, considering the problem is that the vacuum properties of materials, should choose good air-tightness, little hole no crack surface, the chemical stability is good, not easy to oxidation and corrosion, good thermal stability, within the scope of work humidity vacuum performance and mechanical properties without changing the material. Therefore, stainless steel materials, such as stainless steel plate, stainless steel pipe, are good vacuum structural materials. The surface of components in the vacuum chamber should be smooth, such as electroplating, polishing and oxidation treatment, so as to reduce the adsorption gas on the surface of structural materials. Secondly, it is the sealing performance of the structure, reducing the leakage of the system, reasonably designing the weld structure, reducing the weld seam and reasonably designing the static seal and dynamic seal structure.