How to prevent connecting rod bolt breaking accide

How to prevent the fracture accident of connecting rod bolts

the fracture of connecting rod bolts during operation will lead to serious cylinder tamping accidents, which will not only damage the cylinder head and cylinder liner, deform and bend the connecting rod, but also cause major economic losses such as crushing the body and breaking the crankshaft. In order to avoid the cylinder tamping accident caused by the fracture of connecting rod bolts, the following points should be paid attention to in the use and maintenance:

1. Connecting rod bolts bear a large alternating impact load during the operation of the engine. They are important parts of the engine. They are made of high-quality alloy steel through quenching and tempering treatment and precision machining, and have high strength and impact toughness. They cannot be replaced by ordinary bolts or inferior parts. If the bolt material, heat treatment and machining accuracy do not meet the technical requirements, it will lead to insufficient mechanical strength and deformation and fracture accidents

2. Check carefully before assembly. If the bolt is found to be scratched, buckled, cracked, dented, necked or cracked (inspected by oil immersion method or magnetic flaw detection), or the bolt and nut fit loosely, or the bolt cannot fit closely with the bolt hole, or the bolt length is 2% longer than the new standard bolt length by comparison method, it should be replaced

3. check the fitting clearance between the connecting rod bearing and the connecting rod journal when the operator places the sample with the cleaned surface on the rotary table. If the clearance is too large, it is easy to cause the fracture accident of the connecting rod bolt. At this time, replace the connecting rod bearing with a new one or enlarge the bearing, and select or scrape it

4. check the connection between the connecting rod bolt or nut and the bearing surface of the connecting rod end cap shoulder support. If there is burr or unevenness, it should be polished, otherwise the connecting rod bolt is easy to break under the action of additional torque

5. During assembly, use a torque wrench to tighten the connecting rod bolts alternately in several times (generally three to four times) and gradually and evenly to the specified torque. If the tightening torque is insufficient, the joint surface of the connecting rod in China's plastic machinery market will produce cracks, and the bolt is easy to be pulled or cut when subjected to impact force; If it is tightened too tightly, the bolt will stretch and deform, and its strength will be reduced. It is easy to break and damage after being stressed. The specified torque of connecting rod bolts of various types of engines is different. In the absence of technical data, the range of safety torque can be estimated according to the bolt diameter. For example, the safety torque of Mu connecting rod bolts is 60-80nm; M12 bolt, its torque is 80-100nm; M14 bolt, its torque is 100-120nmo

6. If the torque of a bolt on the same connecting rod exceeds the specified value too much, loosen all the connecting rod bolts on the connecting rod and tighten them alternately in several times, and make the tightness of the two bolts consistent. It is not allowed to just loosen the over tightened bolt, otherwise 3 Torque measurement range: 1% ⑴ 00% bolts produce additional bending stress, which is easy to fatigue fracture