Excavator bucket teeth is an important component excavators, also wearing parts, is a combination of bucket teeth and tips from the tooth base composition, both by pin connections. Since bucket teeth wear failure partly prongs, as long as you can replace with a tip. An open-air excavator bucket teeth during use due to the heavy wear and early failure, criticism against the tooth, failure modes and failure analysis of the reasons for fighting tooth surface, and proposed improvement measures.
Failure mode
Bucket teeth in different operating conditions of service are subject to different degrees of abrasion and impact and in different degrees, different forms of failure. The bucket teeth under normal operating conditions only three days (about 36h or so) will fail, both from an economic point of view or from the use of point of view, it is not desirable. Failure pieces from the batch macro picture shows the front surface of the bucket teeth work more visible furrow scribe, the tip of a small amount of plastic deformation, cracks and former Face (contact with the ground surface) thinnest, about 4mm, after Face approximately 8mm.
Analysis and Discussion
Stress Analysis of bucket teeth Face with the excavated material in contact with an entire mining process in different stages of their work force situation is different. When parts of the prongs first contact with the material surface, due to the faster, fighting tooth tip part by relatively strong impact. If the yield strength of the bucket teeth low, will produce plastic deformation at the tip. With mining depth increased, bucket teeth will change by force. When the bucket teeth cutting materials, bucket teeth relative motion with the material to produce large positive extrusion pressure at the surface, resulting in a greater friction between the bucket teeth Face and materials. If the material is harder pieces of rock, concrete, etc., friction will be great. The results of this process repeated the role in fighting tooth face in different degrees of surface wear, and produce a greater depth of the furrows. Positive pressure front face significantly greater than after Face, Face badly worn before, can determine the main factors are external mechanical pressure and friction are fighting tooth failure, play a major role in the failures generated.
Process analysis were before, after two samples from each working face, polished hardness testing. Found that the same piece of sample hardness varies widely, preliminary judgment is uneven material. The samples were grinding, polishing, etching, we found that there are obvious boundaries on each sample, just different parts of the boundary. From a macro perspective, around the pale gray, darker middle part, indicating that the member is likely to be insert casting, on the surface, partially surrounded should also be insert. On the HRS-150 Digital Rockwell hardness tester and MHV-2000 digital micro hardness tester for hardness testing on both sides of the line were found significant differences. Through the above analysis confirmed that the insert is fighting tooth structure. Wherein the closure part is the inserts, surrounding part is the substrate. Both components close to Cr, Mn, Si and other alloying elements, the main alloy composition (mass fraction,%) of 0.38C, 0.91Cr, 0.83Mn, 0.92Si. Mechanical properties of metallic materials depends on the material composition and heat treatment process. Composition similar difference exists hardness, indicating that bucket teeth without heat treatment after casting is put into use. Organization later observed also proved this point.
Tissue analysis optical microscopy showed that the matrix is mainly black fine lamellar structure. Insert organization consists of two massive white and black thin slices, and away from the cross-sectional area larger white granular structure. Further microhardness tests show that white granular structure of ferrite, black fine flake organization troostite or troostite and mixed structure of pearlite. Forming insert large blocks of ferrite in the weld heat affected zone forming part of the phase transition region is similar. By liquid metal thermal effect of the casting process, the region is in the austenite and ferrite two-phase region, fully grown in the region of ferrite, its organizational shape retention to room temperature. Since bucket teeth wall is thin, and larger inserts, inserts the central part of the low temperature, not the formation of large ferrite.
Performance Analysis by the MLD-10 abrasion test machine wear test showed that wear resistance of the substrate and insert a small impact than hardened abrasive wear of 45 steel under test conditions better. At the same time there are differences abrasion matrix and inserts, the substrate than the insert wear. Components on both sides of the substrate and insert close fighting tooth visible in insert is mainly played the role of cold iron. During casting matrix grain refinement to improve their strength and wear resistance. Since the insert casting heat generation affected tissue similar weld heat-affected zone, did not play a role in enhancing the wear resistance. If after casting appropriate heat treatment to improve the matrix and tissue inserts will significantly improve wear resistance and service life of bucket teeth.
In conclusion
The fight tooth material is low alloy wear-resistant steel for bucket teeth is more appropriate. But because without the necessary heat treatment, bucket teeth inhomogeneity, insert did not play its due role, bucket teeth overall poor wear resistance, leading to early failure.
Recommendation after casting molding, casting normalizing appropriate to improve the organization and performance, improve life. After the casting proper heat treatment, under the same working conditions, the life of the bucket teeth increased nearly 2-fold.
Heavy Equpiment Parts 