Loader dual filter bolt fracture analysis of the causes

Loader dual variable filter 2020 - bolt fracture reason analysis 12 - 18 chih-peng liu dragon workers ( Shanghai) Machinery manufacturing co. , LTD. 1 loader technology center. Fault phenomenon one use 3 months of ZL50C loader, in the case of no precursors, hex bolts on the double variable filter suddenly fracture. The loader dual variable filter is mainly composed of core and shell, shell including cover and barrel, both for the cast quality. Cover and cylinder four through eight. 8 hex bolt together, as shown in figure 1. Maintenance personnel reflect, the type of loader when working in harsh working conditions, appear too much within double variable filter hex bolt fracture phenomenon, caused by the separation, torque converter shell and cover oil spills, cause the loader cannot continue to use. 2. Cause analysis and dismantling after the double variable filter found its cylinder in good condition, in case of damage. Fracture surface basic straight, perpendicular to the bolt axis, no obvious plastic deformation fracture, fracture bolt two fracture can be up, down, bolt hardness is taller. The bolt fracture shape as shown in figure 2. ( 1) Analysis of bolt fracture bolt right after installation, the threaded connection button 1 of about 25% of the total load, under 2 buckle under 19% of the total load, so the bolt fracture were 60% ~ 65% is located in the root of screw thread connection button 1. Fracture of the double variable filter bolt is happened in 1 button thread root, thus the bolt button 1 thread position does bear a larger load, excessive load is the main cause of the bolt fracture. ( 2) Analysis of bolt fracture from the bolt fracture, we found that the fracture formation area is very obvious, can clearly see the fatigue crack extension area source, fatigue and brittle fracture zone. On the basis of analysis, bolt bearing pre-tightening force and the double variable for a long time in the oil filter oil pulse impact of alternating load, first crack at fatigue crack source, and the fatigue crack extension. When the rest is not enough to bear the pre-tightening force and the alternating load, eventually led to the bolt fracture. The bolt fracture is shown in figure 3. ( 3) Above to identify the cause of the fracture analysis, while it is possible to determine the bolts was caused by fatigue fracture, but not exactly it is concluded that the causes of fatigue fracture. We examined multiple fracture of the bolt double oil filter, the bolt fracture research found that no matter which position the bolt fracture, fracture of the bolt fatigue crack source near heart always located in the cylinder, the fatigue extension area, brittle fracture area is always located in the cylinder far end. All bolts which can be concluded that under the direction of the arrows in figure 4 bending moment, and the bending moment as alternating load, easy to cause the bolt fracture. Bolts under bending moment was the cause of double variable filter stiffness on the cover, in the process of loader work, due to the continuous oil shock pulse, cause periodic deformation, cover to cover the center to produce continuous bump, recovery, convex alternate deformation, the bolt under continue, alternating bending load, and the stress concentration area of initial fatigue crack source, increase and gradually expanded, eventually occurs brittle fracture. 3. Improved method analysis by above knowable, pure increase bolt diameter, improve their level of strength, can not fundamentally eliminate the bolt fatigue fracture. For this, we will double the thickness of the filter cover increased by 2 mm, in order to improve the stiffness of the upper cover and reduce its deformation in work, avoid bolts under bending load. The improvement has solved the double variable filter hex bolt fatigue fracture. Source: engineering machinery and maintenance 2017, 03