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What is the main factor affecting the FAG bearing grinding metamorphic layer? - bearing knowledge

by:Waxing     2020-06-03
According to FAG formation mechanism of grinding badness layer of bearings working surface, the main factors influencing the FAG bearing grinding metamorphic layer is a function of grinding and grinding force. 1, the grinding heat in the grinding, grinding wheel and workpiece contact zone, consume large amounts of energy, to produce a large number of grinding heat, local transient high temperature caused by grinding area. On the basis of the theory of linear motion heat source heat transfer formula derivation, calculation or by the method of infrared ray and measured experiment under the condition of instantaneous temperature thermocouple method, can be found in 0. 1 to 0. The grinding area within 001 ms instantaneous temperature up to 1000 ~ 1500 ℃. The instantaneous high temperature, which would have made certain depth on the surface of the work surface to produce high temperature oxidation, amorphous group, high temperature tempering, secondary hardening, and even burn cracking and other changes. ( 1) Surface under the action of transient high temperature oxide layer of the surface of the steel and the oxygen in the air, rises into extremely thin ( 20~30nm) The iron oxide thin layer. It is worth noting that the oxide layer thickness and surface grinding metamorphic layer is the total thickness test results in corresponding relation. This shows that the thickness of oxide layer, is directly related to the grinding process is an important symbol of grinding quality. ( 2) Amorphous layer organization grinding the instantaneous high temperature makes the workpiece surface reach a molten state, molten metal molecular flow is evenly coated to the work surface, and the matrix metal cooling at breakneck speed, formed a very thin layer of amorphous tissue layers. It has high hardness and toughness, but it is only about 10 nm, it is easy to be removed in the precision grinding processing. ( 3) High temperature tempering instantaneous high temperature can make the surface layer of grinding zone certain depth ( 10 ~ 100海里) Be heated to a temperature higher than the workpiece temperature tempering heat. In the absence of austenitizing temperature reached, with the improvement of heated temperature, the surface will produce one by one and heating temperature corresponding to the organization transformation, or high temperature tempering tempering hardness. The higher the heating temperature and hardness of the decline is more severe. ( 4) Transient high temperature quenching layer when the grinding area on the second floor heat the workpiece surface layer to the austenitizing temperature ( Ac1) Above, the layer of austenitizing group in the subsequent cooling process, the quenching into martensite structure anew. Where the secondary hardening burns of workpiece, the second time hardening layer must be under very low temperature tempering hardness layer. ( 5) Grinding crack two quenching burns will make workpiece surface layer stress changes. Secondary hardening zone is in compression state, the high temperature materials back to the fire area underneath there are the largest tensile stress, this is the place where the most likely to occur crack core. Crack is the most easily spread along the original austenite grain boundary. Serious burns can lead to crack of the grinding surface ( Formed a crack) Artifacts caused by scrapping. 2, grinding force formation of the metamorphic layer in the process of grinding, the workpiece surface layer will be grinding wheel cutting force, compression force and friction force. And, in particular, the role of the latter two, make the workpiece surface layer formed directional strong plastic deformation and strain hardening layer. The metamorphic layer is bound to affect the surface residual stress changes. ( 1) Cold plastic deformation layer in the process of grinding, every moment of abrasive is equivalent to a cutting edge. But in many cases, the rake Angle of cutting edge negative, in addition to abrasive cutting action, is to make the workpiece surface under compression ( The plough) That left obvious plastic deformation of workpiece surface layer. The deformation layer deformation degree as the degree of grinding wheel dull increases and grinding feed. ( 2) Thermoplastic deformation ( Or high temperature deformation) Layer of grinding heat in the transient temperature of the work surface formation, makes a certain depth of the workpiece surface layer elastic limit fell sharply, even to the point of elastic disappear. The work surface on the grinding force, especially under the action of compression force and friction force, caused by free stretch, subject to the conditions of the matrix metal, the surface is compressed ( More plough) , cause the plastic deformation in the surface layer. High temperature plastic deformation under the condition of the grinding process is constant, with the temperature increasing of workpiece surface. ( 3) Sometimes work hardening layer microhardness and metallographic method can be found that caused by the machining deformation of surface hardness. In addition to grinding machining, casting and heat treatment heating caused by the surface decarburized layer, if again later processing has not been completely removed, residual on the workpiece surface will cause surface softening metamorphism, contribute to FAG bearing early failure.
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