First of all, we can look at the bearing ring defect fracture reasons are:
First, raw material inclusion, loose, brittle element segregation or carbide liquid analysis, mesh, strip, uneven polarization and other defects are not eliminated or improved in the processing, will cause stress concentration, weaken the basic strength of the ring, become the source of crack.
Treatment method: preventive measures are to adhere to the main channel supply, as far as possible to purchase stable and reliable quality of steel, strengthen the purchase of steel warehousing inspection, from the source of the close.
Two, there are cracks in the grinding process
Treatment method: strengthen the monitoring of the grinding process. Grinding burns and grinding cracks are not allowed on the finished bearing rings, especially on the matching surface with the inner ring taper changed.If the rings are pickled, they should be fully inspected and burned products should be removed. Severe burns that cannot be repaired or unqualified should be scrapped. The rings with grinding burns are not allowed to enter the assembly process.
Three, improper heat treatment
Treatment method: in order to solve the soft spot and other defects of medium and large varieties of bearing ring, the composition and performance of quenching oil should be determined. If it is not satisfactory, it should be replaced by fast quenching oil in advance, so as to enhance the quenching ability of quenching as medium and improve quenching and cooling conditions.Strict tempering process.In view of the varieties with many fracture phenomena, secondary tempering is carried out after rough grinding of the rings, which can further stabilize the structure and size of the rings, reduce the grinding stress, and improve the performance of the grinding metamorphism layer.
Bearing rings often fracture in the use of the phenomenon, which mainly has three forms, respectively: fatigue fracture, overload fracture and thermal fracture.
1, fatigue fracture
Bearing ring (especially the outer ring) under alternating load and impact load, the stress it bears constantly exceeds the fatigue strength limit of the material, leading to the fatigue crack, and the crack eventually expands to a certain extent, leading to the fracture at the maximum stress of the parts.Generally occurs in the bearing area of the outer ring of the bearing, because the outer ring usually fits with the bearing box hole for clearance, and the bearing box body is a variable and elliptical part, which is easy to cause fatigue fracture under alternating load and impact load.
2. Overload fracture
Similar to fatigue fracture, when the stress on the bearing is greater than the tensile strength of the material, the inner ring cracks, usually due to improper installation, such as bearing installation tilt, resulting in partial load of the bearing, resulting in partial overload of the bearing caused by fracture;In addition, improper striking during installation caused bearing cracking and falling blocks, which is also classified as overload cracking.Most common interference when installation, and bearing fit size can also lead to large amount of interference of bearing ring crack (mainly has four row cylindrical bearing inner ring interference fit), interference is too big lead to inner ring stress is larger, especially thin cross section thickness (thickness of section < 12 mm) of inner ring, too much interference often leads to inner ring axial crack.
3. Thermal fracture
Fracture is mainly due to the hot and bearing ring end face with sliding friction between parts, under the action of axial force, frictional heat, producing the end face burned with color changing conditions, such as friction and heat that causes bearing ring end face crack, crack characteristics is perpendicular to the direction of friction work, also transverse crack of cross section thickness thinner (thickness of section < 12 mm) had a greater influence on the inner ring, especially overloaded high or medium speed mill roller bearing.
Here, we should pay attention to the fatigue fracture and overload fracture of bearing rings may occur at the same time, especially for bearings with poor service conditions (such as 22328, etc.).The research on the phenomenon of ring fracture should not only consider from the point of view of the defects produced in the material and production process, but also study and analyze the structural size of bearing parts, processing measurement means, processing technology, bearing service conditions and other factors.
1. Bearing structure and service conditions.Different structures are suitable for different service conditions;The processing technology of bearing parts is not the same with different structures, which affects its quality.Therefore, we should develop new structural products to adapt to different service conditions, and can indicate its suitable service conditions or performance on the bearing instructions, in order to facilitate the choice of customers.
2. Strengthen process research, improve processing technology, improve processing quality, and reduce the possibility of defects in processing.For example, on the heat treatment, for the larger varieties of inner and outer rings, try to use the lower limit quenching heating temperature, adapt to extend the insulation time, to improve the alloying concentration, increase the breaking strength of martensite, and on the premise of ensuring the quality of high tempering temperature to enhance the impact toughness of the workpiece.
3, improve the processing monitoring means, promote the improvement of processing quality.For example, the monitoring of the curvature position of the flow channel is improved to improve the overall performance of the bearing after assembly and improve the working condition of the bearing.
Bearing ring fracture occurs more, has always been one of the serious problems in the quality of bearing, China bearing network share the definition of fracture under here: used as the stress on the bearing ring, is greater than the tensile strength of material or material fatigue strength limit, to cause ring crack, crack extended to a certain degree eventually lead to part of the spare parts for complete separation, called a crack or break.