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Quality defects of imported bearings supporting the selection and heat treatment

A: imported bearing matching selection:
The shaft is supported in the radial and axial with two bearings imported bearing, at this time, the side of the fixed side bearing is called, it bear radial and axial load two, up the relative axial displacement between the fixed shaft and bearing box function. The other side is called the free side, only bear radial load, axial can move relatively, in order to solve interval error caused by the temperature change of the axis of the telescopic part questions and the installation of bearings.
For the fixed side bearing, just choose the available rolling surface in the axial direction (such as cylindrical roller bearing) or by fitting surface mobile (such as radial ball bearing) bearing. In a relatively short shaft, the fixed side and free side without any other conditions, using bearings only one-way fixed axial movement (such as radial thrust ball bearing)
Two: the quality defects of imported bearings after heat treatment:
1 the quenching crack
Crack of bearing parts in the quenching cooling process by internal stress formed by quenching crack. The cause of crack formation are: because the quenching heating temperature is exorbitant or cooling too quickly, the thermal stress of anti fracture strength and quality of the metal volume change when the tissue stress greater than steel; shortcomings task appearance (such as micro crack or scratch appearance) or steel external defects (such as slag, major non metal dopant, white spots, shrinkage surplus) formed in the quenching stress concentration; major appearance of decarburization and carbide segregation; parts after quenching and tempering is lack or not timely tempering; behind the process forming cold punching stress is too large, forging folding, deep turning marks, sharp edges and other oil groove. In short, the cause 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 crack. The quenching crack is deep and long, straight fracture, fracture surface without oxide color. It is often in the bearing rings on the longitudinal crack straight or circular crack; in ball bearings on the shape of S shape, T shape or a ring. Organizational characteristics of quenching crack is a crack on both sides without decarburization scene, significant differences in data and forging cracks and crack.
2 overheating
From the import bearing parts can be inspected to coarse mouth after quenching microstructure in the overheated, but to really determine its overheating levels must inspect the microstructure. If the emergence of coarse acicular martensite in the quenched structure in GCr15 steel, quenching overheating organization for. The cause can be formed through high temperature quenching heating or heating and heat preservation time is too long the formation of one-sided overheating; also can be due to the original organization banded carbide major, low carbon zones in between the two belts forming part of coarse martensite acicular, overheating formation. The increase of residual austenite overheating organization, size stability of landing. Because the quenching microstructure in the overheated, crystal thick steel, landing will lead to parts of the landing impact resistance, toughness, and the service life of the bearings are landing. Overheating major and even the formation of quenching crack.
3 surface decarburization
Imported bearing parts in the thermal solution process, if it is heated in the oxidizing medium appearance will attack oxidation makes the mass fraction of parts appearance increase of carbon, the formation of the appearance of decarburization. The appearance of decarburized layer depth beyond the final machining allowance will cause parts scrapped. Determination of the appearance of depth of decarburized layer in metallographic test available metallography and microhardness method. With the micro hardness of surface layer distribution curve measuring method for quasi, do arbitration criterion.
To solve the 4 thermal deformation
Imported bearing parts in the thermal solution, there is the thermal stress and structural stress, the stress can be superimposed on each other or partial cancellation, is complex, because it can with heating temperature, heating rate, cooling method, cooling speed, the shape of a part and size change and change, so the heat settlement deformation is unavoidable. Familiar with and control its change rule can cause deformation of bearing parts (such as ring ellipse and dimension expansion etc.) in controllable size, good consumption. Of course, in the heat to solve mechanical collision course in also in part episodes of deformation, but the deformation can be increased by improved operation and prevent.

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