In this paper, finite element analysis and performance comparison of 7 common failures reason of industrial cardan shaft are comprehensively analyzed, and the comprehensive performance of industrial cardan shaft is designed and improved.
1. Oblique Embossing of Shaft Journal Is Serious
We observed from failure piece that oblique embossing of cross shaft journal is serious, and the inner wall of the bearing ring also produces corresponding embossing, but depth is lighter than the cross shaft. After analysis, forbearing mounted on universal joint assembly, when total circumferential clearance of bearing is large, needle roller is prone to skew, causing cross shaft journal to produce an embossing at an angle to the axis. When embossing depth is deepened, the needle can not rotate, thus increasing frictional resistance and accelerating extension of indentation. Appropriate total circumferential clearance should be controlled within the range of 0.1 to 0.4 mm, and total circumferential clearance given in JB/T3232 is not more than 0.5 mm.
2. The Industrial Cardan Shaft Internal Wear is Serious
In use state where industrial cardan shaft swing angle is small, the inner diameter of needle bearing on universal joint assembly, and cross shaft journal will repeatedly oscillate within a small angle range. When the radial clearance of cross shaft and bearing expands with wear, product load is concentrated, and fatigue indentation occurs prematurely in a place where the load is large, thereby developing a large-scale peeling. Especially at crosshead of the cross shaft, due to the influence of stress concentration, the chamfer of the loaded part is almost completely collapsed, and in severe cases, sintering occurs at a high temperature.
3. The Seal on The Industrial Cardan Shaft lacks lubricant
Failure to fill lubricating oil on time or bearing seal on the universal joint may cause oil loss in the early stage of bearing and material of dust cover is not resistant to low temperature. The oil seal lip will produce aging cracks in cold winter weather, making grease early loss. In addition, an industrial cardan shaft assembly generates high temperatures due to lack of oil during operation, causing bearing and shaft diameter to bite, causing the needle to break and seal and dustproof cover to be damaged, and the surface of the ferrule has ablation marks. It is an abnormal failure form.
4. Industrial Cardan Shaft Needle Roller Failure
In failure samples of the cardan shaft assembly, most needle roller surfaces have pitting, pit, and large area fatigue peeling, a few needle heads are broken, and a few needles have a large pit at about 1.5 mm from the head of a needle. And the phenomenon of bruises, most of the needle breakage is also broken from here, the occurrence of this situation is mainly related to bearing structure size parameters and circumferential total gap design.
5. Industrial Cardan Shaft Gasket Failure
The shim is the first component to fail in gimbal assembly. Gasket failure is in the form of nylon gasket breakage and wear. We carefully analyzed the failed gasket samples and found that there were obvious cracks and debris on the periphery of the gasket. Obviously, the periphery of the gasket is where the stress is concentrated by the gasket. Once the gasket is damaged, the axial force will be fully absorbed by the remaining gasket, and force per unit area of gasket will increase. The film will be destroyed. Therefore, it is necessary to design a reasonable gasket shape and bearing structure. At the same time, since the failure of the gasket is accompanied by wear failure, gasket material must be selected from materials with high strength and wear resistance.
6. The Cross Shaft of the Industrial Cardan Shaft breaks
The break of the cross shaft is generally caused under the condition that the user is seriously overloaded or under abnormal conditions. Although industrial cardan shaft is designed to fully comply with a standard safety factor of 2.5 times static joint strength of industrial cardan shaft in JB/T8925-2008, the proportion of faults occurring during the three-package period of main engine factory still accounts for 2% to 5% of total faults. Although this situation is sudden, it is inevitable. Static torsional strength matching of industrial cardan shaft must be more than three times the maximum output torque of the engine to avoid the occurrence of sudden failure caused by special overload.
7. Metallographic Analysis of The Industrial Cardan Shaft
Physical and chemical analysis of failed parts, select characteristic position in typical parts of the cross shaft, ferrule and a needle roller, cut test piece, and take a metallographic sample along the longitudinal section, and metallographic structure level is qualified. In order to determine the hardness of the core of cross shaft, ferrule, and a needle roller, Vickers's hardness gradient distribution was measured by microhardness tester, and the hardness of parts was basically consistent with hardness distribution law. Take cross shaft of industrial cardan shaft, an outer ring test piece, and several needle test pieces, heat them to 70~80 °C in 50% hydrochloric acid aqueous solution, heat for about 1h, check for hot pickling and find that parts are burns in the use. This kind of burn phenomenon is judged to be due to poor sealing performance of industrial cardan shaft and oil loss and poor grease performance, resulting in premature burn failure of various parts after joint of the industrial cardan shaft.