Force analysis bucket tooth working face and the excavated object contact, in a complete excavation process in different working stages of its different stress conditions.When the tooth tip first touches the material surface, the bucket tooth tip is impacted strongly due to its fast speed.If the yield strength of bucket teeth is low, plastic deformation will occur at the tip.With the increase of digging depth, the stress of bucket teeth will change.When the bucket tooth cutting material, the bucket tooth and the material occur relative movement, produces the very big positive extrusion pressure on the surface, thus produces the big friction force between the bucket tooth working face and the material.If the material is hard rock, concrete, etc., friction will be very large.The result of the repeated action of this process produces different degrees of surface wear on the bucket tooth working face, and then produces the furrow with greater depth.Bucket tooth composition good affect the length of the service life of bucket teeth, choose bucket teeth of course more careful daddus sell bucket teeth I also used his bucket teeth, the effect is good!The positive pressure on the front working face is obviously greater than that on the back working face, and the front working face is badly worn. It can be judged that the positive pressure and friction force are the main external mechanical factors for the failure of bucket teeth, which play a major role in the failure process.
Process analysis: take two samples from the front and back working faces respectively, and grind them flat for hardness test.It is found that the hardness of the same sample is very different, and the preliminary judgment is that the material is not uniform.The samples were ground, polished and corroded, and it was found that there were obvious boundaries on each sample, but the boundaries were different.From the macro point of view, the surrounding part is light gray and the middle part is dark, indicating that the piece is probably an inlaid casting. On the surface, the enclosed part should also be an inlaid block.The hardness tests on both sides of the boundary were carried out on hrs-150 digital display rockwell hardness tester and mhv-2000 digital display microhardness tester, and significant differences were found.The enclosed part is an insert block and the surrounding part is a matrix.The composition of the two is similar. The main alloy composition (mass fraction, %) is 0.38c, 0.91cr, 0.83mn and 0.92si.The mechanical properties of metal materials depend on their composition and heat treatment process.The similar composition and the difference of hardness indicate that the bucket teeth were put into use without heat treatment after casting.Subsequent tissue observations confirm this.
Organization analysis of metallographic observation showed that the substrate is mainly black fine lamellar structure, set piece of tissue consists of two parts, fritter white block and black, and white block away from the cross section area organization more (and further microhardness test proves that the organization for the ferrite white patches, black fine lamellar structure of troostite or troostite and pearlite hybrid organization.The formation of the bulk ferrite in the insert is similar to that of some phase transition zones in the heat affected zone of welding.Under the action of metal liquid heat during casting, this region is in austenite and ferrite two-phase zone, where the ferrite is fully grown and its microstructure is maintained to room temperature.Because the bucket tooth wall is relatively thin and the insert block volume is large, the central part of the insert block temperature is low, no large ferrite is formed
The wear test on mld-10 wear test machine shows that the wear resistance of matrix and insert is better than that of quenched 45 steel under the condition of small impact wear test.Meanwhile, the wear resistance of the matrix and the insert is different, and the matrix is more wear-resistant than the insert (see table 2).The composition on both sides of the matrix and the insert is close, so it can be seen that the insert in the bucket teeth mainly ACTS as a chiller.In the process of casting, the matrix grain is refined to improve its strength and wear resistance.Due to the influence of casting heat, the structure of the insert is similar to that of the welding heat affected zone.If proper heat treatment is carried out after casting to improve the structure of matrix and insert, the wear resistance and service life of bucket teeth will be obviously improved.
Post time: Apr-15-2019