On 2018-08-08 14:48:54
Vacuum heat treatment technology of precision bearing
For small and micro precision bearings, the chemical composition, original structure, machining level, heat treatment process and processing equipment of raw materials may greatly affect the service life of bearings.
Around 1968, vacuum quenching oil and water quenchant were developed by American company and Japanese vacuum Research Institute. The heat treatment of bearing steel began to adopt vacuum heat treatment, and vacuum technology also developed rapidly in the heat treatment industry. From single chamber furnace to multi chamber combined machine group, from general vacuum heat treatment to high pressure gas quenching, vacuum water quenching, vacuum carburizing, vacuum carbonitriding and multi-element carburizing. After decades of efforts, the production quality and level of domestic vacuum furnace have been greatly improved, the production cost of the user has been reduced, and the application scope of vacuum heat treatment has been expanded rapidly.
At present, vacuum heat treatment has been applied to heat treatment of various tool steel, stainless steel, high-speed steel, bearing steel and all important parts such as carbon steel and alloy steel.
Vacuum heat treatment advantages
(1) It can realize bright heat treatment. When the workpiece is heated under the pressure lower than atmospheric pressure, it will not contact with air or change the surface. When the furnace is vacuumized to 0.1-1pa, the impurity content in the workpiece can be reduced to 1.5ppm (1ppm = 0.0001%), so the workpiece can be cleaned and bright quenched.
(2) The distortion of workpiece after vacuum quenching is small. For example, the ovality of 9Cr18 radial bearing rings with an outer diameter of 65mm and a wall thickness of 2mm is reduced to 1 / 8-1 / 9 after vacuum quenching compared with that of ordinary heat treatment.
(3) It has the function of degassing and improves the mechanical properties and service life of the processed workpiece. Because iron and steel will inhale air (H2, N2, Co, etc.) during smelting, resulting in tiny pores and hydrogen embrittlement. With vacuum technology, the impure gas such as water in the workpiece can be pumped out, making the workpiece surface clean and bright, and not prone to hydrogen embrittlement. Due to the improvement of surface quality and wear resistance of workpieces, the service life of workpieces can be increased by 30% ~ 120%.
(4) It can reduce the machining allowance after heat treatment. After vacuum heat treatment, there is no oxidation and decarbonization, and the distortion is very small, so the machining can be reduced or even avoided after heat treatment.
(5) Decomposition of oxides. When the true void is lower than the decomposition pressure of the corresponding oxide of metal or alloy, the oxide will decompose, forming free oxygen to discharge, further improving the surface quality of the workpiece, and activating the workpiece surface.
(6) The utility model has the advantages of clean operating environment, simple and automatic operation, and belongs to the clean heat treatment of pollution-free and pollution-free.