Spherical plain bearing is Sliding Bearing,
It has one outer ring. one inner ring and spherical sliding face. It is applied
to operation with not very quick turning and slewing, and can accommodate to
larger surface pressure.
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From the point of view of oxidative decarburization on both sides of the gear crack after quenching, the crack occurs before quenching and non-heat treatment quenching. This is also confirmed from the cracking of the gear that has not been quenched. The crack depth is shallow, mostly in the carburized layer, and a few terminate in the transition layer, indicating that the crack occurred after carburizing. From the characteristics of the crack, this is a crack in a very special case, and there are many influencing factors. The main reason is that there is a large tensile stress in the surface layer, and at the same time, the secondary surface layer is in the state of compressive stress, and the presence of local defects such as machining marks will cause cracks in the weak surface, and the crack will expand to the compressive stress region. Will not continue to go deeper.
After carburizing with chrome molybdenum steel, the cooling rate is appropriate (approximate air cooling). When cooled to 690-600 °C, the surface of the layer is unstable, and the transformation of austenite to pearlite occurs to form fine pearlite and carbide. The decrease in temperature causes austenite to bainite or martensite transformation in the secondary surface layer, accompanied by a sharp expansion of the volume, causing a large change in the structural stress and causing surface cracking. The reason is that when a carbon atom penetrates into the C phase and reaches a certain concentration, the Cr and Mo elements in the C phase combine with the carbon atoms to form an alloy carbide, so that the solid solution amount of the alloy in the austenite is lowered, thus making the continuous The cooling transition curve shifts to the left, the stability of austenite decreases, and decomposition is easy to occur, and pearlite and carbide are obtained. In the subsurface layer (near the transition layer), the concentration of carbon infiltrated is lower than that of the surface layer, and no carbide is formed, that is, the content of carbon elements and alloying elements in the subsurface austenite is higher, which improves the stability of austenite. The continuous cooling curve is shifted to the right, and it is easy to transform into a mixed structure of martensite or bainite when air-cooled. This abnormal tissue transformation leads to a change in tissue stress, which causes the surface pearlite to generate a large tensile stress.