Analysis of the reasons for the detachment of the bearing bush alloy layer
Thread Content
The faulty machine suffered an incident last November involving a break in the secondary piston ring, which led to collision with the cylinder head and bending of the connecting rod. During maintenance, it was found that the screws securing the crosshead shutoff plates were broken and that the axial clearance at the small end of the connecting rod was too large. During repairs, I applied red grease and carried out bearing scraping on the large end of the connecting rod (the scraping is not yet complete). The manager brought in technicians from another factory to provide on-site guidance; while adjusting the clearances, I noticed that the contact surface between the shaft bearings was too small. The technicians explained that since these are standard components, there is no need for bearing scraping and they can be installed directly. After replacing the crosshead components and adjusting the clearances, it took some effort to turn the engine manually, but it operated normally once started. On April 13, the machine experienced abnormal vibration, with the entire unit shaking from side to side. Inspection revealed pitting on the crankshaft bearings and the loss of the alloy layer in the bearing shells. I believe that the small clearance and contact surface of the bearing bushes are to blame for the shedding of the alloy layer; these shed particles enter the bearing and cause pitting. I hope all fellow netizens and teachers can help analyze it; thank you.
If such a serious issue occurs with the equipment, it should be disassembled and the relevant parts inspected, such as the clearance between the crankshaft pulleys at different angles, and whether the bolts used to connect the components have been stretched or deformed. It is necessary to measure whether the bearing shells need to be fitted and lapped during installation. Is it necessary to scrape the oil lines from the lower tile? No one can decide how it should be. There are two possible explanations for the phenomenon in the photo: one is a quality issue with the tiles used, and the other is that the gap is too large, causing the black tiles to fall off due to vibrations. It is recommended that all bearings be thoroughly inspected. All the above checks have been completed. For reference. One more thing to add is that the issues related to equipment management require serious reflection. This is exactly why things shouldn’t get so serious.
Measure the concentricity and levelness of the crosshead slide relative to the cylinder; after connecting the connecting rod, move the big end bearing cap to check if there is any resistance.
I’m ashamed – I was in the process of scraping the tiles when a technician came to the site to give guidance; he said it wasn’t necessary to continue with scraping, so I stopped. Speaking of equipment management, it’s a long story. I started working at that factory on November 18th last year. When the accident occurred, my supervisor and I were on site; the machine suddenly started running more slowly and made a muffled sound. Instinctively, I checked the oil pressure gauge, and it showed 1.2 kilograms of pressure. Thinking that there was not enough oil and that this could cause the shaft to seize, I immediately asked the staff on duty to add about 4-5 liters of oil before stopping the machine. However, subsequent checks revealed that there wasn’t actually a lack of oil – it was just that the oil pressure gauge fluctuated from time to time. Despite the fact that oil was added, the incident was classified by the management (internally) as being caused by a lack of oil. There are only three people responsible for equipment maintenance; I am the team leader, and the other two colleagues are in their fifties. They are the kind of people who neither know how to do the work nor want to do it – they have an attitude of thinking it doesn’t concern them whether the equipment runs or not, and they just waste time. After I established a record-keeping system and management procedures for maintenance based on operating hours, I was advised not to stand out, so I didn’t implement those measures. Due to the impact of the pandemic, I decided to just get things done for now. The floor of the machine room is a mess with oil stains, and the cooling towers have been taped up. . . The valve is rusted shut and cannot be turned either.
If the foundation is weak, even a slight disturbance can cause chaos; the conditions are indeed tough
After seeing the pictures, all I can think is: the equipment and surrounding areas are fully equipped with leaks, dirt, and mess
I worked on the crankshaft bearings all day yet still didn’t manage to remove them; several of the jacks are broken. . . One of the crankshaft cranks is loose; it’s this that causes the abnormal vibration and shaking of the entire machine. Fortunately, the senior manager was there to help, otherwise it would have been extremely exhausting.
Even if the piston ring breaks, it shouldn’t be able to get between the piston and the cylinder head, right? Aren’t piston rings quite thick? The gap between the piston and the cylinder liner is very small; it should be impossible to get through!
The guide ring has been worn to the point where it’s about to scrape against the cylinder; there are around 6 gaps on the piston, and the piston rings pass through these gaps into the clearance area. The clearance is only 2.0. This machine has experienced an incident where the cylinder head was damaged – not because the shaft was bent, but because the cylinder head was crushed. . . .