bearing heat treatment development course and technology

---

Development of heat treatment
(1) cleaning heat treatment
Waste water, waste gas, waste salt, dust, noise and electromagnetic radiation from heat treatment production will cause pollution to the environment. To solve the environmental pollution of heat treatment and to implement clean heat treatment (or green heat treatment) is one of the development directions of heat treatment technology in developed countries. In order to reduce the emission of SO2, Co, CO2, dust and cinder, the use of coal as fuel has been basically eliminated, and the use of heavy oil is becoming less and less. The majority of light oil is used, and natural gas is still the most ideal fuel.
The waste heat utilization of combustion furnace has reached a high level. The optimization of burner structure and strict control of air-fuel ratio ensure the reasonable combustion and minimize NOx and Co. gas carburizing, carbonitriding and vacuum heat treatment technology are used instead of salt bath treatment to reduce the pollution of waste salt and CN containing toxic substances to water source. Water soluble synthetic quenching oil is used instead of partial quenching In order to reduce oil pollution, bio degradable vegetable oil is used instead of some mineral oil.

(2) precision heat treatment
Precision heat treatment has two meanings: on the one hand, according to the use requirements of parts, materials, structural dimensions, using the knowledge of physical metallurgy and advanced computer simulation and detection technology, optimizing process parameters to achieve the required performance or maximize the potential of materials; on the other hand, fully ensuring the stability of optimization process and realizing the small dispersion of product quality（ Or zero) and heat treatment distortion is zero.

(3) energy saving heat treatment
Scientific production and energy management are the most potential factors for the effective utilization of energy. The choice of scientific management is to establish a professional heat treatment plant to ensure full load production and give full play to equipment capacity. In terms of energy structure of heat treatment, primary energy is preferred; waste heat and waste heat are fully utilized; processes with low energy consumption and short cycle are used instead of those with long cycle and large energy consumption.

(4) less non oxidation heat treatment
The performance of parts after heat treatment is improved, the defects such as decarburization and cracks are greatly reduced, the amount of finishing allowance after heat treatment is reduced, and the utilization rate of materials and machining efficiency are improved. Vacuum heating gas quenching, vacuum or low pressure carburizing, nitriding, nitrocarburizing and boronizing can obviously improve the quality, reduce distortion and improve the service life.

Application effect of heat treatment technology
(1) the scope of application of GCr15 steel is expanded. Generally, the effective wall thickness of ferrule is less than 12mm when GCr15 steel is quenched by m, but due to the strong cooling ability of nitrate salt when BL is quenched, if the measures such as stirring, series movement and water addition are adopted, the effective wall thickness of ferrule can be expanded to about 28mm.

(2) stable hardness and good uniformity
Because BL transformation is a slow process, generally speaking, GCr15 steel needs 4h, GCr18Mo steel needs 5h, the ferrule is isothermal in nitrates for a long time, and the structure transformation of the surface and the center is almost simultaneous, so the hardness is stable and the uniformity is good. Generally, the hardness of GCr15 steel after BL quenching is 59 ~ 61hrc, and the uniformity is ≤ 1 HRC, which is different from the problems of low hardness, soft spot, poor uniformity and so on when the ferrule wall thickness is slightly larger during quenching.

(3) reduce quenching and grinding cracks
In the production of railway and rolling mill bearings, due to the large size and heavy weight of the ferrule and the brittleness of the m-structure during oil quenching, in order to obtain high hardness after quenching, strong cooling measures are often taken, which results in quenching microcracks; while in BL quenching, because the toughness of the BL structure is much better than that of the m-structure, at the same time, the surface pressure stress of – 400 ~ – 500MPa is formed, which greatly reduces the tendency of quenching cracks; in grinding The working time surface compressive stress counteracts part of the grinding stress, which reduces the overall stress level and greatly reduces the grinding cracks.

(4) improvement of bearing service life
For the railway and rolling mill bearings which bear large impact load, the main failure mode after m-quenching is: the inner sleeve cracks during assembly, the outer ring flange falls off and the inner ring breaks during use, while the inner sleeve cracks during assembly due to the good impact toughness and surface pressure stress of the isothermal quenching bearing, or the outer sleeve flange falls off and the inner sleeve breaks heavily during use It can reduce the edge stress concentration of roller. Therefore, the average life and reliability after isothermal quenching are higher than that after M quenching.

vacuum oil quenching furnace