Fastener knowledge: factors that often break connecting rod bolts

Connecting rod bolts are a common connection part in fasteners. It is mainly composed of two parts, a head and a screw. In use, it needs to be matched with a nut for fastening the two through holes. However, the connecting rod bolts used in diesel engines are prone to breakage when they are repeatedly used. What is the reason? The author will share with you several major factors that often break the connecting rod bolts.

1. When assembling, the tightening torque is too large and the force is uneven. Since there is no strict torque wrench in the assembly, the specific tightening torque is not well understood, and the tighter the better; the longer the afterburner is used to fasten the connecting rod bolts, the tightening torque is too large, and exceeds the bolt material The yield limit causes the connecting rod bolts to yield deformation, causing them to break due to excessive elongation under the action of impact load. It should be emphasized that the connecting rod bolts must be tightened according to the standard. Do not think that the tighter and the greater the strength, the better. (Guide: Six measures to prevent stainless steel screws from locking)

2. The connecting rod of the diesel engine is divided into multiple levels, and it should be noted that the connecting rod of different levels cannot be changed during the maintenance. If the connecting rod cover is carelessly messed up or installed incorrectly during maintenance, it will cause the coupling surface of the connecting rod big end to not fit tightly, which will cause the connecting rod cover to loosen during engine operation and cause the connecting rod bolt to break. The big end of the connecting rod of WD615 series diesel engine is of the oblique cut type, and the bevel angle is 45°. The connecting surface of the connecting rod cover and the big end of the connecting rod adopts a 60° sawtooth positioning structure. This structure has a tight fit, accurate positioning, reliable, and compact structure. specialty. If the connecting rod cover is messed up or installed incorrectly during maintenance, it will inevitably lead to poor positioning of the serrations of the joint surface, which will easily cause the connecting rod cover to loosen during the engine work, and cause the connecting rod bolt to break.

3. When the diesel engine is running, there is a runaway fault or the piston burns to death in the cylinder, and the connecting rod bolt is broken. If the engine has a runaway failure during use, a comprehensive inspection of the engine should be carried out, and it is best to replace the connecting rod bolt; if a certain cylinder has serious cylinder pull during operation, the connecting rod should also be replaced when replacing the cylinder piston assembly Bolt replacement.

4. Material problems, processing defects and heat treatment process problems can also cause connecting rod bolts to break during engine operation.

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