Illustrate bearing ring grinding deformation specific reasons and improvement measure

The quality control of bearing parts in the machinery industry is very strict, also often occurs because of serious deformation caused by bearing to scrap, many vendors in the process of bearing parts manufactured for coarse grinding roll, serious elliptical disguised in the outer diameter, lead to bearing can't normal use to scrap. According to this problem, the following 崋 bearing in the network (for short ） To share some experimental examples to get to know the specific reason for the deformation of the bearing ring grinding. Take one, bearing ring samples 1, deformation detection: the physical and chemical inspection from 100 randomly selected 4500 parts of bearing ring is used to detect the diameter change quantity, ratio are shown in table 1, can be seen from table 1 deformation is more consistent on both ends of the bearing ring, the deformation mostly in 0. 15 ~ 0. Between 20 mm. 2, hardness testing: random 6 bearing ring, testing its end surface hardness, the readings are shown in table 2. Can be seen from table 2, each bearing ring end face has low hardness point of minimum hardness up to 44. 5HRC。 3, burns detection: randomly selected 30 pieces of bearing ring with 4% nitric acid alcohol corrosion groove and end face, all have burned. As shown in figure 1, figure 2. End face than race severe burns, and appear secondary hardening burns. Take 1 piece of pickling through analyzing anatomical parts, sampling position in grinding burns, as shown in figure 3. Measured the burned layer about 1. 4 mm, shape as shown in figure 4. Preparing metallographic specimen, the burn condition of 50 times and 500 times respectively as shown in figure 5 and figure 6. Can be seen from the figure 5, figure 6 sample has serious secondary hardening area and the high temperature back to the fire area. 4, tempering stability test: from the hardness of face detection data ( See table 2) As you can see, the same parts surface hardness difference is too big, can't use the ring to tempering stability test, only sample after tempering stability test, randomly selected 3 piece circle line, from the sample shown in figure 7. In the heat treatment production line, Roller hearth furnace chamber salt bath fire line) Tempering, performed on the original tempering process: 170 c x4h. Near the original hardness after tempering hardness test, the test results are shown in table 3. According to standard JB/T 1255 - 2014 rolling bearing conditions of high carbon chromium bearing steel parts heat treatment technology, before and after tempering hardness difference is not greater than 1 HRC tempering stability is unqualified, can be seen from table 3 data: the number of tempering heat treatment stability of qualified products. 5, microstructure examination, metallographic specimen, according to standard JB/T 12552014 rolling bearing conditions of high carbon chromium bearing steel parts heat treatment technology, the components of the microstructure of martensite level 3, heat treatment quality qualification. Tempered structure shown in figure 8. Second, through the analysis of the bearing ring sampling inspection are discussed, from figure 1 ~ figure 6, you can see that in the process of bearing ring grinding burn is serious, grinding, grinding burn is a result of parts grinding surface friction force by the grinding wheel, cutting force and grinding force, make the parts surface produces plastic deformation, producing a large number of grinding heat, grinding heat can make the grinding area of local instantaneous temperature above 1000 ℃, so a lot of grinding heat as not being taken away by cutting fluid in time, can make the grinding surface layer of organization change, namely the formation of a surface metamorphic layer. When grinding heat caused by the phase change of the workpiece surface temperature lower than that of bearing steel, the surface of the metamorphic layer for high temperature tempering, the cold black after pickling, as shown in figure 2, figure 5, and its hardness decreases, forming high temperature tempering burns. When the surface temperature is higher than the phase transition point, is it the surface layer of tissue from tempered martensite transformation to austenite, and then due to the interaction between the quenching of cutting fluid and the secondary hardening, get quenching martensite structure ', the formation of secondary quenching burns, as shown in figure 2, figure 5 in the gray area. 2, as can be seen in table 1, bearing ring deformation is bigger, deformation is more consistent on both ends of the ring, the deformation mostly in 0. 15 ~ 0. Between 20 mm. This is because in the process of grinding, ring surface layer under the action of cutting force and cutting heat, also can produce different degree of plastic deformation and volume change caused by metal organizational change, make the workpiece surface layer produces internal stress. Again after processing, internal stress redistribution, deformation '. 3, from table 2, according to the bearing ring end face hardness value deviation is larger, the highest hardness value of 64 HRC, min. 44. 5 HRC, local low hardness of bearing ring grinding burns. In addition, the tempering stability test results in table 3 shows that after heat treatment, most of the residual stress has been eliminated, not enough to cause the waste of grinding process produces a large amount of deformation. Three, through discussion come to the conclusion that bearing ring grinding deformation causes and improving measures 1, the deformation of the bearing ring is serious when dry grinding of grinding burn ( High temperature tempering burns + secondary hardening burns) Caused by. 2, to avoid grinding bearing ring grinding burns, can undertake improvement measures from the following aspects: the reasonable selection and low grinding wheel dressing; To ensure the cutting fluid spray into the grinding zone, increased cutting fluid flow, improve the cutting fluid pressure; Appropriate decrease grinding depth, reduce feed; Low as possible to reduce grinding allowance, etc.