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Analysis and Research on a New Type of Anti-Slow Bolt in Preventing Bolt Activities
It is commonly believed that network-like cracks in electroplated surfaces are influenced by the current intensity during plating and the temperature of the electrolyte. We have discussed this issue with the factory, but their explanations were not very convincing. In our view, this remains an unresolved technical challenge. Similar to the chrome-plated cylinder liners with a honeycomb pattern, such a structure can enhance oil retention on the journal surface, particularly during engine startup and load conditions. The oil film stored in the mesh pattern provides better protection for the journal. However, the mesh grooves formed during chrome plating of the cylinder liner differ from the iron plating patterns on the journal. Practical experience has shown that cracks in damaged journals (typically over 2mm in length) tend to grow significantly after a mid-term repair. The extent of crack propagation depends on its initial condition. At this point, the crankshaft becomes unsuitable for further use. As a result, the presence of these reticular cracks limits the service life of a repaired crankshaft to approximately one mid-term repair cycle, with only a few being able to continue operating. If this issue can be resolved, non-etching iron plating technology could offer great potential for repairing high-volume, mass-produced diesel engine crankshafts. Otherwise, from an economic standpoint, the value of repairing damaged crankshafts in diesel locomotives may be questionable.
To address this problem, we believe new bolt anti-loosening technology must be implemented. Based on this, we developed and manufactured a new type of anti-slip bolt. The working principle of this new bolt relies on a nylon sleeve. Unlike traditional bolts, the nylon sleeve is unthreaded. When the bolt is tightened into the housing, the housing's threads act as a die, forcing the nylon sleeve to deform and create an interference fit. This is achieved through the elasticity of nylon and its high friction coefficient, effectively preventing loosening. After implementing this new bolt system, we conducted a loading test on locomotive No. 4020 in May 2000. During the mid-term repair period, the motor was replaced several times, but none of the axle bolts loosened or failed. In total, we repaired 78 bolts, and only 6 experienced plastic deformation of the nylon thread. The integrity rate reached 92.13%, with 71.7% of the bolts being reusable after replacing the nylon sleeves. This solution proved to be both effective and cost-efficient, significantly improving the reliability of the axle bolts.