Energy can be saved by enhancing the service life of machinery and by designing lighter units. These design changes enable, for example, lower fuel consumption and larger payloads. The implementation of this kind of solutions, however, requires development of better wear resistant materials. In this study, the wear resistance of a structural steel and three grades of wear resistant steel was evaluated with granite abrasive in tests simulating the conditions in heavy machinery in mining and transportation. Two high-stress abrasion and one impact-abrasion wear testing methods were used. In all tests, higher hardness led to decreased mass loss, but in impact-abrasion the hardness dependence was smaller than in the heavy abrasion tests. This may, however, at least partly result from deformation of softer materials over the sample edges, which is not shown as mass loss. Wear surfaces of structural steel samples exhibited the highest degree of plastic deformation due to their lower hardness and higher ductility compared to the wear resistant steels. On the other hand, in harder materials the scratches were more visible, indicating a change in wear mechanism. Both differences and similarities in the behavior and wear mechanisms of the selected steels were observed in the applied conditions.
Generally synthetic gear oils have superior oxidation stability compared to mineral gear oils, although there is a concern that the oil life may depend on the sludge formation during its oxidation process. In the methods of ASTM D2893 or ASTM D5763 which are commonly used as oxidation tests of gear oils, the test duration for degradation is specified 312 hours. Considering the evaluation to select synthetic gear oils, the test duration is too short to find the significant difference since the degradation of synthetic gear oils would be minimal. The authors provide a new method, in which gear oils are oxidized and degraded by modified dry-TOST (dry-Turbine Oil Oxidation Stability Test) method without catalysts, and use the RPVOT (Rotating Pressure Vessel Oxidation Test) residual ratio as the newly introduced degradation index. This study shows the RPVOT residual ratio has a correlation with changes of kinematic viscosity or acid number which are generally used as the degradation index, and also presents that degradation tendency of the gear oils can be classified by the relationship graph between RPVOT residual ratio and sludge quantity.
Existence of thin lubricating film in inlet zone at the die and billet interface in hydrostatic extrusion process prevents metal-to-metal contacts in contact zone, which leads to reduction in interfacial solid friction. This enhances both the tooling life and surface quality of the products in addition to efficient extrusion operation. Hence, accurate prediction of the minimum film thickness of the lubricating oil in the inlet zone at the die and billet interface and its maintenance during the extrusion process in terms of operating parameters are vital issues from the operation and design point of views. Therefore, the objective of this work is to accurately analyze the inlet zone of extrusion operation for minimum film thickness considering the viscous heat dissipation in the lubricating film for proposing a handy empirical relation for minimum film thickness in terms of operating parameters for use in design and operation of extrusion process. Coupled solution of Reynolds equation, energy equation, and rheological relations are obtained for the minimum film thickness computations as functions of extrusion speed, material parameter, extrusion pressure, and die semi-angle.
Theoretical study was carried out to investigate the frictional property of belt wrapped three times around a circular shaft. A belt equation of fractional expression was derived. The self-locking mechanism was investigated theoretically by the equation. The discriminant of self-locking condition was clarified. The necessary conditions for self-locking are μb < μ and sufficient wrapping angle of the belt, where μ is the coefficient of friction between the belt and shaft and μb is the coefficient of friction between the belt and belt. According to the formula derived, self-locking occurs even under a realistic condition. It occurs when the ratio of belt tensions becomes 0 or negative. Providing the coefficient of friction μ and the ratio of the coefficients of friction κ = μb/μ, some critical over-wrapping angles for self-locking were calculated numerically. Furthermore some normal force distributions in self-locking conditions were calculated theoretically.
Electrolytic in-Process Dressing (ELID) has been found to have wide application especially in superfine grinding, but its mechanism is still unclarified yet. Simulation experiments were conducted by using an electrolysis friction test machine, which is a ball-on-disk friction machine equipped with an electrolyzing system. Copper, which is one of the most widely used metal bond materials of super abrasive wheels, and iron, one of the most widely used bond materials in ELID, were tested in three different types of electrolyte: tap water, electrolyzed water, and solution of CG-7 to tap water. Experimental results showed that there was almost no detectable wear for both copper and iron when electrolysis was not implemented, and also the material removal was little when only electrolysis was applied. Strong synergistic effect between electrolysis and friction was observed for copper in both tap water and electrolyzed water, and for iron in electrolyzed water and CG-7 solution. The friction coefficient of Si3N4 ball against iron disk was lower than that against copper disk.