Bearing layers causes deterioration grinding, grinding deterioration affecting SUNTHAI bearing layer of the main factors is the grinding heat and grinding force.
1 grinding heat
In grinding, the grinding wheel and workpiece contacted, consume a large amount of energy, resulting in a lot of grinding heat, causing the local instantaneous grinding zone temperature. The use of linear motion equations derived heat the heat transfer theory, the calculation method or application of infrared and thermocouple method under the experimental conditions measured the instantaneous temperature, can be found in the 0.1 ~ 0.001ms instantaneous temperature within the grinding zone can be as high as 1000 ~ 1500 ℃. This instantaneous high temperature, sufficient to work a certain depth of the surface layer of the surface of high temperature oxidation, amorphous tissue, high-temperature tempering, secondary hardening, cracking or burn a variety of changes.
(1) the surface oxide layer
Instantaneous high temperature, steel surface and the role of oxygen in the air or into very thin (20 ~ 30nm) thin layer of iron oxide. It is noteworthy that the surface oxide layer thickness and the total layer thickness of grinding deterioration test results showed a corresponding relationship. This shows that the oxide layer thickness and is directly related to the grinding process, grinding is an important indicator of quality.
(2) amorphous tissue layer
Grinding area transient surface temperature to reach the molten state, the molecular flow of molten **l has been evenly coated on the work surface, and is the base **l at great speed cooling, forming a thin layer of amorphous tissue layer. It has high hardness and toughness, but it is only about 10nm, it is easy to be removed in precision grinding.
(3) high-temperature tempering layer
Grinding area transient surface temperature can make a certain depth (10 ~ 100nm) of the workpiece is heated to above the tempering temperature of heating. Austenitizing temperature is not reached in the case, as the heating temperature was increased, the surface layer will result in corresponding with the heating temperature to return fire or changes in the organization of high-temperature tempering, the hardness is lower. The higher the heating temperature, the hardness decreased and the more powerful.
(4) two-story hardened layer
When the grinding area of the instantaneous heat the workpiece surface layer heated to austenitizing temperature (Ac1) above, the layer of tissue in the subsequent austenite during cooling, has been re-hardened into martensite. Where there are secondary quenching the workpiece burn, the secondary hardness of hardened layer must be very low under high-temperature tempering layers.
(5) grinding cracks
Secondary hardening the surface layer will burn stress. Secondary hardening in compression zone, the area below the high-temperature tempering material existence of the maximum tensile stress, this is most likely crack the core of the place. Most likely to crack along the original austenite grain boundaries spread. Severe burns may cause the entire grinding surface cracks (mostly crack) caused parts scrapped.
(2) the formation of the **morphic layer of the grinding force
In the grinding process, the surface layer by grinding the cutting force, compression force and the friction effect. In particular the role of the latter two, the direction of the workpiece surface layer to form a strong layer of plastic deformation and work hardening layer. These **morphic layer will inevitably affect the surface layer of residual stress changes.
(1) cold plastic deformation layer
In the grinding process, every moment is equivalent to a cutting abrasive blade. However, in many cases, the cutting edge of the rake angle is negative, abrasive cutting action in addition to outside, is to make the surface under compression (plow effect), so that the workpiece surface, leaving a clear layer of plastic deformation. The deformation of this layer will be deformed as the wheel and the grinding of blunt feed rate increases.
(2) thermoplastic deformation (or high-temperature deformation) layer
Grinding heat in the working surface of the instantaneous temperature, the surface layer of a certain depth of the elastic limit of a sharp decline, even to the degree of flexibility disappear. At this point the surface layer in grinding work force, particularly the role of compression and friction, the cause of freedom stretching limited by the base **l, the surface is compressed (more plow), resulting in the surface layer of plastic deformation. High-temperature plastic deformation in the grinding process unchanged, with the surface temperature increases.
(3) hardening layer
Sometimes microhardness method and **llographic method can be found, due to deformation caused by surface processing layer hardness increased.
In addition to grinding, the casting and heat caused by heating the surface decarburized layer, and then later processed in place, if not completely, remaining on the surface of the workpiece surface will also cause the softening of deterioration, led to early failure of bearings MSRHK.
