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Selection of imported bearings and quality defects after heat treatment

A: imported bearings matching selection:

Shaft is in two bearings in radial and axial support, this time, the side of the imported bearings said fixed side bearing, it is subjected to both radial and axial load, play the role of the fixed shaft between the bearing box and the relative axial displacement. The other side is called the free side, only to bear the radial load, the axial direction can be relatively moved, in order to solve the temperature change caused by the axis of the expansion of the problem and the installation of the bearing gap error.

For the fixed side bearing, the rolling surface can be used in the axial movement (such as cylindrical roller bearings) or assembly surface movement (such as radial ball bearings) bearing. In a relatively short axis, the fixed side and the free side of the no other case, the use of only one-way fixed axial movement of the bearing (such as the radial thrust ball bearing)

Two: the quality defects of imported bearings after heat treatment:

1 quenching crack

In the course of quenching and cooling, the bearing part is formed by the internal stress of the crack, which is called the quenching crack. Formation causes of the cracks are: because the quenching heating temperature is too high or cooling too quickly transition, thermal stress and quality of metal volume change of tissue stress greater than steel anti fracture strength; task appearance of the original disadvantages (such as surface micro crack or scratch) or steel external defects (such as slag, major non metal dopants, flakes, shrinkage holes remaining, etc.) in quenching stress concentration; major surface decarburization and carbide segregation; parts after quenching tempering lack or not timely tempering; behind the process of cold punching, too, folded forging, deep turning marks, the oil groove sharp edges and corners, such as the stress. In short, the cause of the formation of quenching cracks can be one or more of the above factors, the existence of internal stress is an important cause of the formation of quenching cracks. The quenching crack is deep and long, the fracture is straight, and the broken section is not oxidized. It is often in bearing rings on the longitudinal crack straight or circular crack; in ball bearings on the shape of a s shape, T shape or a ring. The organizational characteristics of quenching crack is on both sides of the crack without decarburization scene, significant difference with the forging crack and crack data.

2 overheating

From parts of imported bearings coarse mouth may inspect to the quenching microstructure of overheating, but to really determine overheating levels required to inspect the microstructure. If there are coarse needle like martensite in the quenched microstructure of GCr15 steel, then the quenching. Formation reasons can is too high or heating and heat preservation time is too long to form the one-sided overheating quenching heating temperature Du; also can be significant due to the original banded carbides, between the two zones of low carbon zones formed part of martensite acicular thick, forming part of overheating. Increase of retained austenite and stable size of the. Because the quenching microstructure overheating, steel crystal is coarse, will lead to the toughness of the part of the fall, the impact resistance performance, bearing life also landed. Overheating is important and even the formation of quenching cracks.

3 surface decarburization

Imported bearing parts of the thermal settling process, if it is in the oxidation medium heating, surface oxidation attack increases the parts on the outside of the carbon mass fraction, forming surface decarburization. The appearance of decarburized layer depth beyond the last machining allowance will make parts scrapped. Determination of surface decarburization depth in metallographic test by metallographic and micro hardness method. The method of measuring the micro hardness distribution curve of the outer layer is the standard, and can be used as the criterion of arbitration.

4 thermal solution deformation

Imported bearing parts to solve the thermal, thermal stress and organizational stress, the internal stress can be superimposed on each other or partial cancellation is complex, because it can with heating temperature, heating rate, cooling method, cooling rate, part shape and size change and change, so the heat to solve the deformation is unavoidable. Familiar with and control its change law can make the bearing parts of the deformation (such as ring ellipse, size is swollen etc.) under control of scale, is advantageous to the consumer. Of course, the mechanical impact of the thermal solution will also cause the parts to attack, but this deformation is to be able to use the improved operation to increase and prevent the.