Bearing machining heat treatment process and technology
Heat Treatment Development History
(1) Clean Heat Treatment
Heat production of the formation of wastewater, waste gas, waste salt, dust, noise and electromagnetic radiation Dengjun causes environmental pollution. Solution heat treatment of the pollution problems, the implementation of clean heat treatment (or green heat treatment) is the developed countries, the direction of one of the heat treatment technology. In order to reduce SO2, CO, CO2, emissions of dust and cinders, has basically put an end to the use of coal as fuel, the use of heavy oil less and less in favor of mostly light oil, natural gas remains the most desirable fuel.
Burning furnace waste heat utilization has reached a high degree of structural optimization burner and air - fuel ratio of strict control to ensure a reasonable premise of combustion, so that NOX and CO reduced to a minimum; use of gas carburizing, carbonitriding and vacuum heat treatment technology alternatives to reduce the waste with molten salt treatment with CN-salt and toxic contamination of water sources; use of synthetic water-soluble quenching oil to replace part of the quenching oil, use of bio-degradable vegetable oil instead of part of mineral oil to reduce oil pollution.
(2) Precision Heat Treatment
Precision heat treatment has two meanings: one is based on the use of spare parts requirements, materials, structure, size, the use of physical metallurgy knowledge and advanced computer simulation and testing technology, optimize the process parameters, to achieve the required performance or to maximize the material potential; the other hand, fully guarantee the stability of process optimization to achieve product quality and dispersion of small (or zero), and heat distortion is zero.
(3) energy-saving heat treatment
Scientific production and energy management is the most efficient use of energy potential factors, a professional heat treatment plant in order to ensure full capacity, the ability to give full play equipment, scientific management choice. In the heat energy structure, the preferred choice of primary energy; make full use of waste heat, waste heat; use of low-energy, short cycle process instead of a long cycle, energy-intensive large crafts.
(4) less non-oxidative heat treatment
The use of protective atmosphere, heated by an alternative oxidizing atmosphere heated to precise control of carbon potential, nitrogen potential of the controlled atmosphere heating, heat treatment to improve the performance of spare parts, heat treatment defects such as decarbonization, cracks, etc. greatly reduced after heat treatment to reduce the amount of finishing to stay to improve the material utilization and machine processing efficiency. Vacuum plus hot quenching, vacuum or low pressure carburizing, nitriding, nitrocarburizing and boride, etc. can significantly improve quality, reduce distortion, increased life expectancy.
Effect of Heat Treatment Technology
(1) expanded the scope of application GCr15 steel, in general, M quenching GCr15 steel rings 12mm below the effective wall thickness, but the BL quenching cooling ability due to nitrate, the use of a stirring, string action, add water and other measures, ferrule Effective wall thickness can be extended to around 28mm.
(2) hardness, stability, uniformity is better
As the BL change is a slow process, the general GCr15 steel required to 4h, GCr18Mo steel required to 5h, ring in the nitrate in the long isothermal surface, changes in heart almost at the same time organized by the Department, so the hardness and stability, uniformity is good, the general GCr15 steel BL quenching hardness 59 ~ 61HRC, uniformity ≤ 1HRC, not like the quenching ring thickness appeared slightly larger number of low hardness, soft points, and poor uniformity problems.
(3) reduction of quenching, grinding cracks
The railway, rolling mill bearing production, because the ring size of large, weight, oil-quenching when the brittleness M organizations, in order to obtain high hardness after quenching cooling measures are taken frequently, resulting in quenching microcracks; while BL quenching, due to BL organizational structure, toughness is much better than the M, while the surface of up to -400 ~-500MPa compressive stress, which greatly reduces the tendency of quenching cracks; in grinding the surface when the compressive stress offset some of the grinding stress, so that the overall stress level down, greatly reducing the grinding cracks.
4) increase bearing life
To withstand large impact loads for the railway, rolling mill bearings, etc., when used by the M after quenching the main failure in the form of: when the inner sleeve assembly cracking, using the process off by the impact of outer wall blocks, inner ring fragmentation, while austempering bearing As the impact toughness is good, the surface compressive stress, both sets of cracks within the assembly, or the use of the process of coat ribs off blocks, sets of fragmentation within a greatly reduced bias, and can reduce the roller edge stress concentration. Therefore, the isothermal M after quenching than after quenching the average life expectancy and increased reliability.
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