The front and rear axle blocks of the bicycle are fatigued and peeled off, and the high-frequency induction heating machine can easily deal with it.

The front and rear axle blocks of bicycles are key parts of the rotating part of the bicycle. The standard stipulates that after working for 60 minutes under the operating conditions of 2000N and 2000r/min, it must be inspected. There must be no peeling or collapse on the raceway, and it is a qualified part. The front and rear axle blocks are made of 15Cr or 20 steel. The production and processing procedures are: drawing (diameter 14-diameter 13mm) - annealing - pickling - phosphating - cold heading forming - arc hole machining - ball track calendering - tapping - milling - carburizing or carbonitriding One is quenched, one is tempered, one is polished and one is blackened. During production, it was found that the main failure modes of workpieces are fatigue spalling failure and collapse, and most of them are fatigue spalling failures. After analyzing the causes of the defects, it was found that heat treatment using a high-frequency heating machine can effectively avoid the occurrence of such defects.

When inspecting and analyzing the fatigue spalling performance of the workpiece, it was found that carbides in the workpiece structure have an important impact on the fatigue spalling performance. When the martensite matrix deforms, the carbides gradually separate from the martensite matrix, causing the carbides to fall off, pinholes appearing on the ball track, and a pitted peeling morphology. The carbide on the ball track has an irregular shape. When external force is applied, stress concentration occurs in the contact area between the carbide tip and martensite. When the stress exceeds the strength of martensite, microcracks will initiate and fatigue sources will appear. Under the action of stress, cracks propagate and eventually fatigue spalling damage occurs.

Inspection and analysis pointed out that if the martensite structure is coarse, the fatigue spalling of the shaft block is mainly due to the expansion and extension of microcracks under fatigue stress, eventually causing local detachment damage; if the martensite is fine and there are many carbides on the surface, Fatigue spalling in the workpiece is mainly caused by carbide spalling, or due to stress concentration at the sharp corners of carbides, cracks initiate and expand at the stress concentration, and finally cause fatigue spalling damage.

Analysis shows that the high hardness and high strength of the front and rear axle block surfaces are the main properties of the workpiece to resist external forces and enable the workpiece to operate safely. Production and inspection show that when the workpiece hardness is greater than 80HRA, the failure rate of front and rear axle block parts decreases. This production practice law is consistent with the above-mentioned law of the influence of carbide and martensite structure thickness on contact fatigue.

Production practice and test work summarize the main measures to improve the performance of front and rear axle blocks and prevent fatigue spalling as follows:

(1) The workpiece should ensure high surface hardness and use a high-frequency heating machine for heat treatment so that the workpiece has good fatigue spalling resistance. The best hardness is 80-83HRA.

(2) The front and rear shaft blocks are required to have no decarburization layer and no obvious carbide on the surface after quenching and tempering. This can greatly reduce the risk of surface fatigue spalling damage on the workpiece and extend the service life of the workpiece.