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2022-08-06

Failure Analysis Of Excavator Bucket Teeth

Failure Analysis Of Excavator Bucket Teeth

The quality of the excavator bucket is now more and more important in our lives, there are many friends to buy excavator bucket will encounter some misunderstandings, one is the introduction of coal mining machine production excavator bucket quality skills identification. Determine the quality of the bucket to determine the production process, because the production process of the bucket is complex, including cutting, milling, drilling, grinding, molding, welding, painting and other work, each step should be carried out in the operation of the bucket, bucket, if a step failure will affect the bucket.

1. Failure Form

The bucket teeth are subjected to different degrees of wear and impact under different operating conditions and fail to different degrees and in different forms. The bucket teeth failed after only 3 days of use (about 36h) under normal working conditions, which is not in line with the requirements from both economic and service perspectives. From the macroscopic photos of the failed parts, it can be seen that the front working surface of the bucket tooth has more obvious furrow-like scratches, a small amount of plastic deformation at the tip, no cracks, and the front working surface (the surface in contact with the ground) is thin, about 4mm, and the rear working surface is about 8mm.

2. Analysis And Discussion

  • (1) Force analysis The working surface of the bucket tooth is in contact with the excavated material, and the force is different in different working stages of a complete excavation process. When the tip of the tooth first contacts the surface of the material, the tip of the bucket tooth is subjected to a strong impact due to the high speed. If the yield strength of the bucket tooth is low, plastic deformation will occur at the tip. As the digging depth increases, the force on the bucket teeth will change. When the bucket teeth cut the material, the relative movement between the bucket teeth and the material produces a large positive squeezing pressure on the surface, which generates a large friction between the working surface of the bucket teeth and the material. If the material is hard rock, concrete, etc., the friction force will be very large. As a result of this process, different degrees of surface wear are generated on the working surface of the bucket teeth, resulting in deep and large furrows. The positive pressure on the front working surface is significantly greater than that on the rear working surface, and the front working surface is severely worn. It can be judged that the positive pressure and friction are the main external mechanical factors of bucket tooth failure, and play a major role in the process of failure.
  • (2) Process analysis Two specimens were taken from the front and rear working surfaces and ground flat for hardness testing. It was found that the hardness on the same specimen varied greatly, and the initial judgment was that the material was not uniform. The specimens were ground, polished and etched, and it was found that there were obvious boundaries on each specimen, only the boundary parts were different. From the macroscopic point of view, the surrounding area is light gray, the middle part of the color is darker, indicating that the piece is likely to be inlaid castings, from the surface, the part surrounded by the block should also be inlaid. In the HRS-150 digital Rockwell hardness tester and MHV-2000 digital micro hardness tester on both sides of the boundary line respectively hardness test, found that the difference is obvious. The above analysis confirmed that the bucket tooth is a block structure. The closed part is the inlay and the surrounding part is the matrix. The mechanical properties of the metal material depend on the composition of the material and the heat treatment process. The similar composition and the difference in hardness indicate that the bucket teeth were put into use without heat treatment after casting. The later tissue observation also proved this point.
  • (3) Organizational analysis of the metallographic observation shows that the matrix is mainly black fine lamellar tissue. The block organization consists of two parts: white block and black fine flake, and the white block organization is more in the area far from the cross section. Further microhardness tests showed that the white massive tissue was ferrite and the black flake tissue was a mixture of brittlenite or brittlenite and pearlite. The formation of large blocks of ferrite in the inlay is similar to the formation of a partial phase transformation zone in the heat-affected zone of welding. By the thermal action of the metal fluid during casting, this region is in the austenite and ferrite two-phase zone, in which the ferrite grows sufficiently and its tissue form is maintained to room temperature. Due to the relatively thin wall of the bucket tooth and the large size of the insert, the temperature of the middle part of the insert is low and no large ferrite is formed.
  • (4) Performance analysis by the wear test on the MLD-10 wear tester shows that the wear resistance of both the matrix and the inlay under small impact abrasive wear test conditions is better than that of quenched 45 steel. At the same time, there is a difference in the wear resistance of the matrix and the inlay, with the matrix being more wear resistant than the inlay. The composition of both sides of the matrix and inlay is close to each other, so it can be seen that the inlay in the bucket teeth mainly plays the role of cold iron. During the casting process, the matrix grains are refined to improve its strength and wear resistance. Due to the influence of the casting heat of the inlay produces a similar organization to the heat-affected zone of welding, which does not play a role in enhancing wear resistance. If proper heat treatment is carried out after casting to improve the organization of the matrix and inlay, the wear resistance and service life of the bucket teeth will be significantly improved.

3. Conclusion

  • (1) The bucket tooth material is low-alloy wear-resistant steel, which is suitable for the bucket tooth. However, due to the lack of necessary heat treatment, the organization of the bucket tooth is not uniform, the insert does not play its proper role, and the overall wear resistance of the bucket tooth is poor, leading to early failure.
  • (2) It is recommended that after casting, the castings be properly normalized to improve the organization and performance and service life. After proper heat treatment of the casting, the service life of the bucket teeth was increased by nearly two times under the same working conditions.

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