The scraper machines produced by our company are mainly buried scraper conveyor and U-shaped scraper conveyor. The models of buried scraper conveyor are tgss16 ~ tgss100, and the output is 22.5 ~ 1200t / h. The U-shaped scraper conveyor has tgsu16 ~ tgsu63, and the output is 22.5 ~ 260t / h. (with wheat) ρ= 0.75t/m3). In order to better serve customers and improve their own production and manufacturing quality, our company summarizes experience and makes the following analysis on the chain breaking accident of scraper conveyor:
1、 Accidental chain break
1. Manufacturing quality problems. The poor manufacturing quality of ring chain is one of the reasons for chain breakage. First, brittle fracture. There are several reasons for the occurrence of brittle fracture: first, at the welded joint, the superposition of tensile residual stress and working stress promotes the occurrence and propagation of brittle fracture. Second, welding angular deformation and misalignment. In welding construction, due to manufacturing error and staggered angle deformation, local stress concentration is caused, additional parameter moment is generated, fracture stress is reduced, and brittle fracture occurs in the structure. Third, the effect of welding thermal cycle increases the hardness and reduces the plasticity of the joint, which is easy to cause brittle fracture. Brittle fracture is caused by tensile stress. The brittle fracture of ring chain usually occurs near the welded joint. Second, plastic fracture. Plastic fracture is mainly caused by poor plasticity and low shear strength of base metal. Plastic fracture is caused by shear force. Similarly, the poor quality of the pin of the sleeve roller chain is also one of the reasons for the chain breaking. Brittle fracture will occur due to improper heat treatment; The superposition of residual stress at the welded joint will promote the occurrence of brittle fracture.
2. I-pin drive. When using die forging chains, i-pins are used to connect the rings. In use, the die forging chain is easy to lose the position surface due to the rotation of I-pin, resulting in the disconnection of chain links and fracture.
3. Jumping teeth. Tooth skipping refers to the chain link falling off from the sprocket of the scraper conveyor head. Tooth skipping will cause the chain link to have an impact on the head shaft and sprocket teeth. Under normal circumstances, due to the large design safety load, it is not easy to break the chain under impact, but when the chain link is corroded and worn and the tensile strength is reduced, it will be easy to break in case of impact.
4. Too many materials are loaded or arched materials squeeze the scraper conveyor. The scraper chain is started or frequently started when it is fully loaded or overloaded, which increases the dynamic tension borne by the chain. When it exceeds the limit or the chain is corroded and worn, it is very easy to break.
5. Unequal pitch. After the scraper chain works for a period of time, it will form unequal pitch for various reasons, and the unequal pitch of the two chains will concentrate all the load on one chain. Fracture may occur when heavy load starting or chain corrosion occurs.
6. The chute is worn. The chute with severe wear is easy to jam the scraper at the joint of the lower chute, resulting in a sudden increase in the load of the chain. When the tension exceeds the limit or the chain is corroded and worn, it is possible to break the chain.
7. The slot is not straight. On the one hand, the machine slot is not straight, which makes the force on the two chains uneven. In serious cases, the chain tension is concentrated on one side; When the tension exceeds the limit or the chain is corroded and worn, it is possible to break the chain.
8. The chain is too tight. Chain over tightening is usually caused when tightening the chain. Due to the excessive adjustment of the initial tension during chain tightening, it not only affects the normal operation of the scraper conveyor and shortens the service life, but also has no buffer room when the scraper chain is stuck, which increases the tension load of the chain link. When it exceeds the limit value, it is possible to break the chain.
9. Some materials remain in the machine slot. This situation makes the scraper conveyor increase the friction at the next start-up, and this load start-up also increases the tension load of the chain link, which is easy to break the chain at the start-up.
2、 Natural chain break
Due to the complex working environment of scraper conveyor, the natural damage of scraper chain is inevitable. There are three common natural damage modes: dynamic load, corrosion and wear:
① Dynamic load. When the chain works normally, there is dynamic load. Because the speed of the head sprocket changes when driving the chain, there is acceleration or deceleration, so there is alternating load acting on the chain. Although this dynamic load is much smaller than the sudden impact force, the cyclic alternating action is also a main cause of chain fatigue fracture.
② Corrosion. Because some materials transported will have some corrosivity, these substances are very easy to corrode the chain and cause the chain plate to rust and peel, so as to reduce the effective section and strength of the chain plate and make the chain plate easy to break.
③ Wear and tear. Due to the contact friction between the chain and the machine slot and materials during operation, at the same time, the driving sprocket and the scraper chain will slide relatively when engaged, and there is friction between each section of the chain. Various reasons lead to the wear of the chain during operation.
Based on the above factors that may cause the fracture of scraper chain, combined with the actual situation of our company, prevent the fracture of scraper chain from the following aspects: first, strictly control the quality so that the purchased scraper chain can meet the relevant national manufacturing standards and the basic strength of transported materials; The second is to achieve the whole process control in the process of equipment installation, ensure the complete engagement between the master-slave sprocket and the chain, and make the lower plane of the machine slot on the same horizontal plane; Finally, strengthen the daily production and maintenance, and solve the problems in time, so as to prolong the service life of the equipment as much as possible.
