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NEWS |
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| Excavator bucket teeth failure reason analysis |
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Open bucket teeth of excavator in use because of serious wear and early failure, the one tooth, analysis of failure mode and failure of tooth surface, and puts forward improving measures.
Failure mode
The failure form of bucket teeth in different working conditions of service are subject to different degrees of wear and impact failure occurs in different degree, different forms of. The bucket teeth under normal working conditions using only 3 days (approximately 36h) will fail, whether from the economic point of view or from the point of view, are not in line with the requirements of. From the macro photos of the number of failed parts visible, bucket teeth of the working surface has obvious scratches furrow shaped, apex with a small amount of plastic deformation, no crack, front face (contact with the ground surface) of the thin, about 4mm, after the working face is about 8mm.
Analysis and discussion
A: the stress analysis of bucket teeth working face and the mining phase contact, different working stages in a complete process of digging the force of different. Tooth tip of first contact material surface, due to the fast, the bucket tooth part is strong impact. If the bucket teeth of low yield strength, will produce plastic deformation at the tip. With the increase of mining depth, tooth stress will change. When the bucket tooth cutting material, and the relative motion between the bucket tooth material, produce positive pressure in the surface, resulting in larger friction between tooth surface and materials. If the material is relatively hard rock, concrete, friction will be great. This process is repeated action results in the surface wear of different degrees in the bucket tooth working surface, resulting in greater depth. Bucket teeth composition is good effect to the bucket tooth length of life, the bucket teeth of course more careful nitwit sell bucket teeth his bucket teeth I have used, the effect is good! Before the positive pressure was significantly greater than after working surface, working surface wear, can judge the positive pressure and the friction force is the main external mechanical tooth failure factors, play a major role in the process of failure in the.
Two: process analysis were used, the working face after each take two specimens, polished hardness test. Find the same block specimen hardness difference is very big, preliminary judgment is inhomogeneous materials. The samples were ground, polished, corrosion, obvious boundaries are each sample, only boundary in different parts of. From the macro perspective, the surrounding light gray, the middle part is dark, the member may be inserted casting, look from the surface, was surrounded by section should also be insert. In the HRS-150 digital Rockwell hardness tester and MHV-2000 digital micro hardness on both sides of the border are hardness testing, found significantly different (see Table 1). Through the above analysis confirmed that the tooth is insert block structure. The sealing part is inserted, the surrounding part matrix. The two component approach, alloying with Cr, Mn, Si and other elements, the main composition of the alloy (mass fraction,%) of 0.38C, 0.91Cr, 0.83Mn, 0.92Si. Composition and heat treatment process on the mechanical properties of metal materials depends on the material. Similar composition and hardness are different, the bucket teeth after casting without heat treatment is put into use. Observation of tissue behind the also proved this point.
Three: analysis of metallographic observation shows that the matrix organization, mainly black fine lamellar tissue, insert organized by the white block and black strips are composed of two parts, and far away from the more white massive tissue (cross-sectional area, further microhardness test, white massive microstructure is ferrite, black fine flake troostite or flexion martensite and pearlite mixed organization. Insert bulk ferrite forming part of phase transformation zone body formation and welding heat affected zone of similar. The process of casting liquid metal heat effect, in the region of austenite and ferrite two-phase region, fully grown in the zone of ferrite, maintain its organization form to room temperature. Because the bucket tooth wall is thin, and insert large volume, low temperature insert center, has not formed the bulk of ferrite.
Four: Performance Analysis Based on MLD-10 wear test machine shows, matrix and insert in the small impact abrasive wear resistance wear test conditions than the quenched 45 steel. There are differences in the matrix and the wear resistance of the insert, insert block matrix than wear (see Table 2). Matrix and inserts on both sides of the composition approaches, visible tooth insert in the mainly played the role of cold iron. In the process of casting fine matrix grain, increase the strength and wear resistance. Because of the influence of insert casting heat generated by similar to the microstructure of heat affected zone, not to enhance the wear resistance of. If the appropriate heat treatment of after casting to improve matrix and tissue block, will significantly improve the wear resistance and the service life of bucket tooth.
Conclusion
A: the tooth material for low alloy wear resistant steel, is more appropriate for bucket tooth. But due to the lack of necessary after heat treatment, tooth tissue is not uniform, insert and did not play its due role, the wear resistance of bucket teeth difference, leading to early failure.
Two: the proposal after casting, proper normalizing on Microstructure and properties of casting, to improve, improve service life. For reasonable heat treatment process on casting, under the same conditions, the bucket teeth of service life is increased by nearly 2 times. |
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