A study on wear rates of 100Cr6 steel running against sintered steel surfaces under dry and starved lubrication

This paper investigates the tribological behavior of 100Cr6 steel pin running against sintered steel bearing material used in hermetic compressors. Tests were conducted under dry and starved lubrication sliding conditions in air at room temperature. Although porous structure acts as crack initiation sites thus limiting the wear resistance of sintered iron in dry sliding conditions under high contact stresses, it is believed to be beneficial in lubricated sliding conditions as it absorbs a large amount of lubricant. Wear tests without lubrication show that these pores are completely filled by abrasive particles in the initial stages of the test and no longer maintain their oil absorption capability. Initial results show that oxidation of frictional surfaces by flash temperature in dry conditions reduces weight loss volume by decreasing the coefficient of friction

Effect of R600a on tribological behaviour of sintered steel under starved lubrication

This study aims to develop and characterize wear resistant and low friction tribopairs that are compatible with new ozone-friendly Isobutane refrigerant to run at hermetic compressor bearings. The tribological behavior of 100Cr6 steel pin is investigated under starved lubrication condition in air and R600a environments when running against sintered steel with and without steam treatment. EDS and SEM are carried out on pin and plate samples after wear tests. The results indicate that durability distance is lower for the tests with R600a than those with air. The adverse effect of R600a on wear rate is linked to the change in the viscosity and foaming characteristics of the oil in the presence of R600a as well as the lack of oxides. Kemal Sariibrahimoglu1, Huseyin Kizil1*, Mahmut F. Aksit2, Ihsan Efeoglu3, and Husnu Kerpicci

Wear performance of titanium and niobium added MOS2 coatings under isobutane exposure

As conventional refrigerants phased out, Hydrocarbons such as Isobutane emerged as the main alternative in refrigeration industry. However, compatibility of these new ozone friendly refrigerants with compressor oils and bearing materials need to be evaluated. This study investigates wear performance of Titanium and Niobium added MoS2 coatings running against 100Cr6 steel under isobutane exposure. Wear performance is established under starved lubrication condition by comparing the maximum achieved sliding distance before the sudden increase and fluctuation of the friction curve. Sinter steel samples were coated with MoS2, MoS2-Ti, MoS2-Nb thin films by magnetron sputtering. The concept of durability distance has been defined as the distance until a sudden fluctuation of the friction curve is observed. It was found that addition of Titanium and Niobium adversely affects wear performance of the MoS2 coatings under isobutane exposure. This can be attributed to the possible degradation of MoS2 lamellar structure that acts as solid lubricant under such exposure

Tribological behavior of sintered steel under starved lubrication in R600A environment

This study aims to develop and characterize wear resistant and low coefficient of friction material pairs at hermetic compressors bearings, compatible with new environmentally acceptable R600a (Isobutane) refrigerant. However, the long term wear and durability of compressors using R600a is unknown. The tribological behavior of 100Cr6 steel pin running against untreated and steam treated sintered steel under starved lubrication in air and R600a environments were investigated. Tests were conducted at a constant load of 50 N and the sliding speed of 0.8 m/s. Mineral oil was misted into the sample at the beginning of the each wear test. Energy dispersive X-ray analysis and SEM were carried out on pin and plate samples after wear tests. The concept of durability distance had been established for starved lubrication sliding; it was expressed as the distance necessary for the generation of the very first wear track marking, as correlated to the first fluctuation of the corresponding friction curve. It was found that durability distance is lower for the tests in R600a than those of in air. Adverse effect of R600a on wear is thought to be due to change in viscosity and foaming characteristics of the oil in the presence of R600a

Efficacy of treating segmental bone defects through endochondral ossification: 3D printed designs and bone metabolic activities

Three-dimensional printing (3D printing) is a promising technique for producing scaffolds for bone tissue engineering applications. Porous scaffolds can be printed directly, and the design, shape and porosity can be controlled. 3D synthetic biodegradable polymeric scaffolds intended for in situ bone regeneration must meet stringent criteria, primarily appropriate mechanical properties, good 3D design, adequate biocompatibility and the ability to enhance bone formation. In this study, healing of critical-sized (5 ​mm) femur defects of rats was enhanced by implanting two different designs of 3D printed poly(l-lactide-co-ε-caprolactone) (poly(LA-co-CL)) scaffolds seeded with rat bone marrow mesenchymal stem cells (rBMSC), which had been pre-differentiated in vitro into cartilage-forming chondrocytes. Depending on the design, the scaffolds had an interconnected porous structure of 300–500 ​μm and porosity of 50–65%. According to a computational simulation, the internal force distribution was consistent with scaffold designs and comparable between the two designs. Moreover, the defects treated with 3D-printed scaffolds seeded with chondrocyte-like cells exhibited significantly increased bone formation up to 15 weeks compared with empty defects. In all experimental animals, bone metabolic activity was monitored by positron emission tomography 1, 3, 5, 7, 11 and 14 weeks after surgery. This demonstrated a time-dependent relationship between scaffold design and metabolic activity. This confirmed that successful regeneration was highly reproducible. The in vitro and in vivo data indicated that the experimental setups had promising outcomes and could facilitate new bone formation through endochondral ossification.publishedVersio