1 Abstract This paper proposes specific measures for the prevention of the failure of the square axis and the use of cyclical repair. The boundary 4 excavator square shaft is a precious large alloy steel forging. During work, there was a breakage. For this reason, a macroscopic analysis of the fracture of the other axis was made and an improvement plan was proposed. 1 Fracture Analysis of Square Axis Apart from tensioning the track shoes, the square shaft mainly serves as a support. Since the square shaft is fixed in the square hole of the track frame, the tension wheel walks on the large rock with foundation, and forms a right-angled angle with the support wheel of the other track frame, supporting the entire weight of the excavator. Excavate at this time. The side of the shaft on the side of the rock. To share the pressure of the total weight of the equipment. In addition to the uneven road stope, the structural design of the square shaft journal also has some questions. Such as 02 and 23, the transition fillet at the ruler 8 is too small; its surface roughness is 6.3 is too low, there are knife marks; stiffness is too large and other reasons, all create conditions for fatigue fracture of the square shaft. The bending stress of the square shaft journal is higher than the fatigue limit. Under the square shaft, ie, the bending stress side, a certain plastic deformation will occur on the square shaft for each overload period. These crystal slip lines are getting deeper and deeper, wider and wider, and the fatigue source is generated from the transition fillet 88 at 021 and square 23,1. These tiny cracks continue to expand and form microscopic cracks under the action of peak loads. Due to the fact that the square shaft also has to tighten the track shoes to facilitate walking by the excavator. So it is also subject to lateral bending stress. Therefore, micro cracks continue to expand toward the lower front of the square axis. A macroscopic crack has formed. This area can be a source of fatigue. The excavator walks and works on the uneven stope, and the square shaft is also continuously subjected to longitudinal and lateral bending stress. This kind of bending stress is a long-term complicated irregular side, which causes the fatigue source to continue to expand and form a fatigue expansion zone. Due to the tensile stress state of the material at the crack tip, plastic deformation is less likely to occur than the one-way tensile stress, so that the fatigue crack is more rapidly expanded. Therefore, the fracture is very rough, unplanned, and accompanied by hills and pits caused by material tear. When the effective area of ​​the journal is continuously reduced and peak bending stress occurs, the fracture reaches a new unstable state, and the new rapid static load breaks again. This is repeated alternately until the next remaining effective cross section fails to withstand the maximum load, and instantaneous breakage occurs immediately. This area is an instantaneous breaking area. Due to bending fatigue cracks, the fracture surface of this journal is not a plane but a definite curved surface. Called a one-way type fracture. Preventing breakage of the square shaft To prevent the breakage of the square shaft and improve the service life of the square shaft, the following measures have been taken. 023, the bending fatigue strength can be increased by 1.6 times, and the stiffness ratio can be reduced by changing the journal transition fillet ruler 8 to only 12. The journal 023 can be tangent to the square 23, 1 to produce a transition plane of about 32 mm. It can be considered as an infinitely large transition radius R. The effective stress concentration factor Ka is reduced from 2.1 to 1. Eased the stress, avoiding the appearance of fatigue sources. The roughness 6.3 of the fillet ruler 12 is changed to 1.6. The surface quality coefficient can be increased from 84 to 0.94. Due to bolder journals, not only the square shaft sleeves were eliminated. Moreover, it also saves processing man-hours and makes full use of the advantages of good structural steel strength and hardness. In order to reduce the wear of square shafts and copper bushes and avoid blockage of oil lines, the single oil passages were changed to upper and lower dual oil passages, and upper and lower double curve oil passages were added. In this way, a large amount of oil can be supplied in the non-loaded area, and oil supply can also be assisted in the heavy load area. Practice has proved that the oil path is smooth and well-lubricated. However, as the excavator walks and works, irregular peak loads often appear at the ends of the square shaft, causing the copper sleeve to undergo severe plastic deformation. In particular, the equipment near the large and medium repairs, in the maintenance of production in the non-load zone, the axial clearance between the square shaft journal and the copper sleeve is often around 512 1, so that the gravel and mud continues to enter the interior, so that the square shaft The neck produces mechanical wear and plastic deformation. However, all of them are within the range of 1.22.51. According to the wear limit specified in the maintenance regulations, they can be used for large or medium-sized repairs. When it is turned over during installation 180, the surface of the journal originally subjected to bending and tensile stress is changed into a bending compressive stress. This avoids the appearance of fatigue sources and extends the life of the square shaft. The three-axis circulatory repair is completed through two mid-repair periods, and the shaft pedestal with 40-axis square shaft journals has become elliptical. In order to prevent uneven hardness during surfacing, the elliptical journal on the lathe was 022,225,1 cylindrical journal. There are 20,1 thick ancient coin support wheels at both ends of the square shaft, artificial rolling, flame preheating with a gas torch 300., preferably in the summer room, with about 102.0% baking stainless steel rod, continuous longitudinal pile Welding, slow-rolling and timely hammering with a hammer to eliminate welding stress; then processing, the first rough car fine car and then fine-grinding wheels on the knife holder grinding 023, journal. And cooling with cutting fluid, and finally with a long block of wood nails, emery cloth, coated with mechanical oil polishing, up to 1.6 roughness is better. Because stainless steel contains, and more, wear resistance is higher than the original spindle material 40CrMnMo or 35CrM0. So the service life of the repaired square shaft is higher than the new square shaft. This type of surfacing repair can be performed several times. However, after the second repair, the elliptical 023,1 journals do not have to be used. After the diesel engine is cleaned, it can be directly preheated. For square shafts with multiple surfacing repairs, it is not good to be 0200mmX43Omm. This way, even if there is a source of fatigue to be driven by the car, the transition fillets of squares 23, and 023 should be 12. If both ends are 2 feet, 04 and 201 nipples With oil plug screw thread has been flattened, you can make the car into a light hole, insert into the steel core and re-thread the thread to restore the original function. After the improved square shaft steel sleeves, add the upper and lower double channel oil grooves at the shaft neck, square 23, and 02,7, and use a fillet ruler of 15 at the transition point, and then kiss. The inner hole and the journal are used together, and they are tightly closed after being hot-mounted. For the early change of the front of the fracture of the square axis, or change the back axis of the 021 journal wear over the limit, you can use five old square shaft, out of the four new square shaft. The hole shaft interference fit. The short section preheat 200 hits the short section and the long section assembly on the platform with a hammer. This not only limits the welding deformation, but also complements the weld strength. There are 25 angle slopes on both sides of the weld, and there are 10,1 empty bottoms in the middle. When welding, the electrode can be fully welded to the bottom of the weld to avoid incomplete penetration. The square shaft material is 40CrMnMo or 35CrMo. This medium carbon alloy steel has poor welding performance, so the welding end must be preheated in the annealing furnace 3 about 200300. After the heat is put on the ancient coin support wheel, slow rolling welding, like In the overheated area of ​​the weld seam, coarse austenite grain structure is easily generated, plasticity is reduced by 1015, impact is reduced, and the property is reduced by 2530, which is a great hazard to the quality of the weld seam. In order to avoid this phenomenon, use 15, 15, 1 stainless steel electrode for drying. Because the nickel alloy can improve the weld edge edge flexibility and plasticity, but also because the stainless steel is not sensitive to thermal cycling, no cracks. Then use 300. Drying 1 of the 05, 5, 7 electrode DC anti-welding. Two or more welders of Class 5 or more were employed for welding. It is advisable to use short arcs and narrow lanes. There must be no cracks inside the weld, such as cracks, shrinkage holes, etc. The welding temperature should be maintained at 2002801. The residual stress after square shaft welding is quite large. Must be put into the pit immediately. After 3 hours, the temperature rises by 500 tons, and the temperature is kept for 12 hours. The sealed furnace mouth is slowly cooled to room temperature with the furnace. Then the axle journals are made and the welding port is planed and processed to the finished product. After welding the stainless steel electrode, it is then turned to the finished product. After several welding repairs, the vehicle can be fitted with a steel sleeve with a small journal 021. After a few years of use, it can be over-limited. It can also use five old square shafts to connect four new square shafts and then resume the 0231 axis. Neck, this cycle of using large alloy steel is more reasonable. 1Material Mechanics, Zhejiang University, 1979 1979 2. Metal Fracture Analysis Shanghai Jiaotong University, 1979. Authors Sun Fengxi Anshan Iron and Steel Group Anshan Mining Co., Ltd. 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