When the connecting rod nut of a diesel generator breaks during operation, it will not only damage the cylinder head and cylinder liner, but also cause the connecting rod to deform and bend, damage the casing, twist the crankshaft, and other serious economic losses. During maintenance, in order to avoid the cylinder ramming accident caused by the fracture of the connecting rod nut, special attention should be paid to the following matters:
1. The connecting rod nut of the diesel generator has a large impact alternating load and is an important part of the equipment. High-quality alloy steel is selected, quenched and tempered and precision processed, with high strength and impact resistance, and cannot replace ordinary nuts and inferior parts. Bolt materials, heat treatment technology, and processing accuracy do not meet the technical requirements, and insufficient mechanical strength will cause deformation and fracture accidents.
2. Check carefully before assembly. If you notice that the nut has scratches, sliding buckles, cracks, dents, necking or cracks (using oil immersion method or magnetic flaw detection method), or the nut and the nut do not match, or the nut and the nut hole do not fit closely, or use the contrast method observe that the length of the nut is 2% longer than the new standard nut and should be replaced.
3. Check the matching clearance between the connecting rod bearing and the connecting rod journal. If the gap is too large, it is easy to cause the connecting rod nut to break. At this time, new connecting rod bearings must be replaced or additional bearings must be selected or repaired.
4. Check whether the connecting rod nut or nut is in contact with the supporting surface of the connecting rod end cover. If there are burrs or unevenness, the connecting rod nut will be affected by the additional torque and easily break.
5. During the assembly process, use a torque wrench to alternately connect the nuts (generally divided into 3 or 4 times), and evenly screw in the specified torque. If the tightening torque is insufficient, there will be a gap between the connecting rod joint surface during work, and the nut is easy to break or break when subjected to impact, the nut is elongated and deformed, the strength is reduced, and it is easy to break and damage after being stressed.
The connecting rod nut of the diesel generator connecting rod nut machine has different prescribed torques. When the technical data is insufficient, the safe torque range of the nut can be estimated based on the diameter of the nut. M10 nuts, such as class 12.9, have a safety torque of 60-80N.m. M12 nuts, with a torque of 80-100N.m. M14 nuts, with a torque of 100-120N.m.
6. When tightening the nut, if you notice that the torque of a certain nut on the same connecting rod exceeds the specified value, you should loosen the two nuts on the connecting rod, and then tighten them alternately to make the two nuts tighten. It is only allowed to loosen the screw that is overtightened, otherwise the nut will generate additional bending stress, which will easily lead to fatigue and fracture.
7. When tightening the connecting rod nut, try to rotate the crankshaft to check whether it rotates freely. If the crankshaft is difficult to rotate after the nut is tightened, the cause should be found. Do not let go of the connecting rod nut to allow the crankshaft to rotate.
8. In order to prevent the connecting rod nut or nut from falling off, a new cotter pin, iron wire or lock piece should be used for locking, if the notch on the nut and the nut hole are incorrect, in principle, it can only be aligned with the tightening direction. The used overhead, iron wire or lock piece, etc. shall not be used anymore.
9. Periodically check the tightening of the connecting rod nut during use, find out the reason, if it is falling off, check whether the nut is damaged, and then tighten it with a torque wrench according to the specified torque.
10. When the diesel generator is running, when the connecting rod nut falls off or elongates, because the connecting rod bearing falls off, there will be a loud knocking sound and vibration before the whole falls off and breaks. At this point, you should stop immediately to avoid a bigger accident.
11. When a connecting rod nut is slipped, cracked or broken, the two connecting rod nuts on the same connecting rod should be replaced in pairs and cannot be matched with the old and the new.
12. When the diesel generator burns ceramic tiles many times or burns ceramic tiles severely at one time, the connecting rod bolt material is affected by high temperature annealing, the metallographic structure changes, and the mechanical strength decreases, so it should be replaced.
13. In case of accidents such as runaway, biting, or overturning of the diesel generator, check the connecting rod nut and replace it immediately if it is found to be deformed or cracked.
14. In order to prevent the fatigue fracture and damage of the connecting rod nut, when the diesel generator has been running for 6000-7000 hours or the diesel generator is accidentally damaged and repaired, even if the surface of the nut is not obviously damaged, new parts should be replaced.
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