Self-aligning ball bearing cage surface morphology and the reasons of the white spot defects

Bearing manufacturers in the production of self-aligning ball bearing cage, often to surface treatment of bearing retainer, the process, if after pickling corrosion, will find self-aligning ball bearing cage bright white speckles appears on the surface, this is a kind of surface treatment of defects, why the surface appeared a lot of white speckles of the bearing cage? The bearing network ( Referred to as ') According to the understanding of the knowledge of bearing, cut heart to share the ball bearing cage white spot defects of concrete surface morphology as well as relevant. 1, self-aligning ball bearing cage surface morphology of white spot defect features we look at first, with white spot defects cage and normal maintains a small claws, big claw the appearance of the surface topography, as shown in figure 1, 2. We can see from the picture: maintains a rough surface with a white spot defects, orange peel shaped, with bright white spots, and around the perimeter of the spots is mainly distributed in large claw and over the entire surface of small claws; The normal maintains a smooth surface, uniform color appearance. Figure 1 maintains a small claw tutu 2 maintains a large claw surface morphology of surface topography in figure 2, self-aligning ball bearing cage defect internal macro cage and normal cage big claws, small claws to set samples, and then get metallographic specimen and grinding on the cold acid corrosion. After grinding sample appearance appearance as shown in figure 3. Can be seen from figure 3 a, after cold acid corrosion defects into cage of the surface of the sample can still be seen clear bright white spots, which shows that bright white spots, not only exist in the surface, exist within the retainers, too bright white spots. As can be seen from the figure 3 b, into normal cage of the surface of the specimen after cold acid corrosion colour and lustre is uniform, found no similar spots. Figure 3 big, small claws pickling sample photos 3, self-aligning ball bearing cage grain observation analysis for normal cage and defect cage big claws, small claws microstructure ( Grain size) Observations and analyses research respectively, the morphology of grain size chart as shown in figure 4. Figure 4 big and small claw grain sample tissue contrast can be seen from the figure 4 a, the normal sample grain size is small, uniform, and have certain tropism. Grain is a tropism is because the cage is steel plate after gear cutting and forming, plastic processing, produce plastic deformation under the action of impact, orientation and deformation of the grain direction is roughly same, according to GB/T6394 - 2002 'standard metal average grain size determination method', the grain size is 8. Level 5; And the core area of the grain fine, uniform and consistent with normal cage, as can be seen from the figure 4 d, uneven heart defect sample small claw grain, grain size of coarse grains area small claw to 0. 2) Grain size and the relationship of uniformity and white spot defects due to the grain boundary of material gathered a lot of impurities, as a result, than inside the grain boundary corrosion. Fine grain area compared with bulky grain area, the former grain boundary density is big, the total area of the grain boundary is much, will inevitably reduce the corrosion resistant performance. When pickling for defect cage, due to its uneven grain size, small claws and the edge of the large claw is corrosion of rough grain area, therefore, show bright white after pickling, without corrosion resistance of the fine grain zone in dark gray. Rough uneven grain causes and formation of white spot test verifies the machining process of the cage is: cut, cut material circle - teeth - recrystallization annealing to clean up - forming - plastic, pickling and oil. The surface normal cage without recrystallization annealing, grain size is very uniform. , research shows that the shape of white spots and surface defect frame can be used with other batch of steel plate type cage has after recrystallization annealing, but maintain the surface does not appear white spots. Thus, keep the surface appear white spots has nothing to do with the quality of steel plate, also proved that if the cage using normal recrystallization annealing process, also won't appear white spots. In order to further analyze the genesis of cage surface shape of white spots, not in 3 after recrystallization annealing of cage with higher than normal recrystallization annealing temperature annealing experiment was carried out. Normal recrystallization annealing process is: heated to 640 ℃, the heat preservation 3 ~ 4 h, from air cooling. This experiment selected the annealing temperature is respectively 700680 and 660 ℃, holding time is 3. 5 h, then empty out cold. Pickling corrosion, photo as shown in figure 5. Can see clearly from the table, the three pieces of cage surface there are white spots, and the higher the heating temperature, the more serious the shape of white spots. This batch of 08 al maintains a material, the microstructure is mainly composed of ferrite grain, in the cage for corrosion inspection, found that the coarse grain area than the fine grain area more resistant to corrosion. Figure 5 different annealing temperature of the surface of the cage photos can be seen through the above analysis, keep the surface of bright white spots, is due to the number of cage during recrystallization annealing treatment caused by coarse grains caused by the heating temperature is too high. Advise recrystallization annealing process in production to strictly according to the technological requirements, on a regular basis to calibration of furnace temperature and furnace temperature uniformity, and regularly identify thermocouple and temperature control table, etc. , in order to avoid similar situation occur.