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Crossed roller bearings are a kind of bearings that are used more in machinery, especially in industrial machines. Of course, when we use them, we want to have better performance of crossed roller bearings and ensure that the crossed roller bearings have better performance. Various properties, then we need to heat treatment its processing materials, why heat treatment, and what is the effect of heat treatment on crossed roller bearing materials? Let's find out together!
The distribution of residual stress on the surface of bearing steel after quenching is largely affected by the cooling rate and quenching medium. For the material used in crossed roller bearings, after heating to 840 ° C and quenching in oil, the axial stress and shear stress The distribution characteristics of the stress along the section are roughly the same, and the magnitudes are similar. There is tensile stress near the inner and outer surfaces, and compressive stress at the center of the section. If the material and quenching process are different, the surface stress distribution law is different, or even reversed.
(1) Two types of quenching cracks will appear after the bearing is quenched: deep cracks and surface cracks. Deep cracks are caused by stresses related to temperature gradients; surface cracks are related to surface decarburization. Another reason for cracks is mainly due to the reduction of the brittle fracture strength of the formed martensite due to the higher quenching temperature. Increasing the quenching temperature will reduce the number of quenching cracks; ℃, can make it more stable.
(2) If it is taken out from the hot oil and cleaned immediately, it will induce cracks, and even the mixture of a small amount of water in the quenching oil will significantly increase the risk of cracks; if there is insufficient intermediate annealing, or decarburization is not removed. The layer is subjected to secondary quenching, which also increases the possibility of cracks. Surface quenching cracks caused by decarburization are largely related to the depth of the tool marks on the surface after machining, which causes stress concentration. The greater the depth of the tool marks before quenching, the longer the cracks after quenching.
During heat treatment, oxidation and decarburization on the surface of the ferrule are inevitable, and the thickness of these oxidation and decarburization layers is called the heat treatment metamorphic layer. However, by using the protective atmosphere heat treatment method, the thickness of the metamorphic layer can be minimized, thereby reducing metal waste and grinding consumption.
There are three main reasons for the dimensional change of crossed roller bearing materials during heat treatment: volume reasons, plastic reasons and elastic reasons.
(1) Volume reason: During heat treatment, the structural change of the steel causes the volume change, and the volume change causes the dimensional change.
(2) Plastic reason: The plastic reason is caused by plastic deformation under the action of instantaneous stress generated during quenching and cooling.
(3) Elastic reason: The elastic reason is caused by the surface residual stress, which is mainly related to the elastic modulus and Poisson's ratio of the material.The above is the whole content of the influence of heat treatment on the material of the crossed roller bearing. I believe that everyone has an understanding of the above content, and it is not difficult to see that the influence of heat treatment on the material of the crossed roller bearing is still very important, and it will also directly affect the bearing. Therefore, it is necessary to carry out strict quality control during heat treatment. Only in this way can the quality and safety of the crossed roller bearing be guaranteed, which must be paid attention to.
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