Fastener knowledge: several points should be paid attention to to prevent connecting rod bolts from breaking

The connecting rod bolts are broken during operation. If you don't notice it, it may cause a series of accidents. In order to avoid accidents, we need to carry out maintenance of the connecting rod bolts.

The knowledge of fasteners, the following points should be paid attention to to prevent the connecting rod bolt from breaking:

1. The connecting rod bolt bears a great alternating impact load during engine operation. It is an important part of the engine. It is made of high-quality alloy steel after quenching and tempering treatment and precision processing. It has high strength and resistance. The impact toughness can not be replaced by ordinary lugui or inferior parts. If the bolt material, heat treatment, and machining accuracy do not meet the technical requirements, it will cause insufficient mechanical strength and cause deformation and fracture accidents.

2. Check carefully before assembly. When it is found that there are scratches, sliding buckles, cracks, dents, necking or cracks on the bolts (application of oil immersion method or magnetic inspection), or the bolts and nuts are loose, or the bolts cannot be closely matched with the bolt holes, or use According to the comparison method, the bolts whose length is 2% longer than the new standard bolt length should be replaced.

3. Check the matching clearance between the connecting rod bearing and the connecting rod journal. If the clearance is too large, it will easily lead to the fracture of the connecting rod bolt. At this time, replace the new connecting rod bearing or enlarge the bearing, and select or scrape it. (Guide: Where are the advantages of aluminum alloy threaded fasteners)

4. Check the fit of the connecting rod bolt or nut with the bearing surface of the connecting rod end cap shoulder. If there is burr or unevenness, it should be trimmed, otherwise the connecting rod bolt is easily broken due to additional torque.

5. When assembling, use a torque wrench to twist the connecting rod bolts alternately (generally 34 times) gradually and evenly to the specified torque. If the tightening button torque is insufficient, the connecting rod joint surface will have a gap during work, and the bolt will be easily broken or sheared when subjected to impact force; if it is tightened too tightly, the bolt will elongate and deform, reduce the strength, and easily break and damage after being stressed. The specified torque of the connecting rod bolts of various types of engines is not the same. In the absence of technical data, the safety torque range can be estimated based on the bolt diameter. For example, the safety torque of the MU connecting rod bolt is 6080Nm; the M12 bolt has a safety torque of 6080Nm. Torque is 80100Nm; M14 bolt, its torque is 100120Nmo.

6. If it is found that the torque of a bolt on the same connecting rod exceeds the specified value during bolting, all the two connecting rod bolts on the connecting rod should be loosened and then re-tightened alternately, and make the two The bolts are tight and tight. It is not allowed to loosen only the bolt that is over-tightened, otherwise the bolt will produce additional bending stress and be easy to fatigue and fracture.

7. In the process of tightening the connecting rod bolts, try to rotate the crankshaft to check whether it rotates freely. If the crankshaft is difficult to rotate after the bolts are tightened, you should find the reason. Never loosen the connecting rod bolts to rotate the crankshaft.

8. In order to prevent the connecting rod bolt or nut from loosening during work, a new anti-loose device such as a split pin, iron wire or lock piece should be used to lock; if the notch on the nut is aligned with the end of the hole on the bolt, principle The upper can only be turned inward to align; used cotter pins, iron wires or lock plates must not be reused.

9. During use, check the tightness of the connecting rod bolts regularly, and find out the reason when loosening is found, check whether the bolts are damaged, and then use a power wrench to tighten the bolts to the specified value in stages according to the specified torque.

10. When the connecting rod bolt is loosened or elongated during work, before the connecting rod bearing is completely loosened or broken, there will be a loud knocking sound and vibration due to the loosening of the connecting rod bearing. At this time, you should stop immediately , So as to avoid bigger accidents.

11. When a connecting rod bolt is slippery, cracked or broken, the two connecting rod bolts on the same connecting rod should be replaced in pairs, and the old and new ones must not be used together.

12. When the engine burns several times or burns severely once, the connecting rod bolt material is subjected to high temperature annealing, the metallographic structure changes, the mechanical strength decreases, and the load-bearing capacity decreases, so it should be replaced.

13. When the engine has a runaway, cylinder bite or rollover accident, you must not ignore the careful inspection of the connecting rod bolts. When the bolts are found to be deformed or cracked, they should be replaced in time.

14. In order to prevent the fatigue fracture and damage of the connecting rod bolts, after the engine has been working for 60007000 hours, even if the bolts are obviously damaged, they should be replaced.

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