The present work discusses the friction and wear of polyethylene as bearing materials scratched by steel insert in the presence of magnetic field. Tests were carried out at dry and oil lubricated surfaces. Paraffin, fenugreek, camphor, cress and Habet El-Baraka oils were used as lubricants. The friction coefficient and wear of the tested composites were investigated using a tribometer designed and manufactured for that purpose. It was found that, at dry sliding, friction coefficient displayed the highest values, where a value of 1.5 was approached. Application of magnetic field on the sliding surface caused significant friction decrease. As the intensity of the magnetic field increases, friction coefficient decreased. Wear of polyethylene increased with increasing applied load, and significantly increased under the application of the magnetic field. Lubricating the sliding surface by paraffin oil significantly decreased friction coefficient, while magnetic field significantly decreased friction and increased wear. Friction coefficient displayed by fenugreek oil represented relatively higher values indicating the weak lubricating properties of that oil. As the magnetic field was applied, friction coefficient decreased. Wear in the presence of magnetic field significantly decreased. Camphor oil displayed relatively lower friction and wear values than that observed for fenugreek oil. Application of magnetic field on the sliding surface caused significant friction and wear reduction. Besides, friction coefficient and wear displayed by cress oil decreased as a result of the magnetic field. Finally, Habit El-Baraka oil displayed the lowest values of friction coefficient among the tested oils. The wear resistance observed was quite good.

The effect of magnetic field and electric current on the friction coefficient displayed by rolling bearing greased by lithium grease dispersed by solid lubricants such as graphite, molybdenum disulphide, talc and polymeric particles is investigated. It was shown that the magnetic field had no effect on friction coefficient observed for lithium grease without additives. Addition of talc showed significant increase in friction coefficient. This increase was influenced by magnetic field. No significant effect on friction coefficient was observed for grease dispersed by molybdenum disulphide. Generally molybdenum disulphide displayed relatively lower friction coefficient than graphite and talc. Copper particles dispersed in grease displayed the lowest friction values. Friction coefficient displayed by grease significantly decreased with increasing electric voltage due to decrease of grease viscosity as the voltage increased. In the presence of graphite and talc, friction coefficient increased up to maximum then decreased with increasing voltage. Slight friction increase was observed for grease dispersed by copper. The lowest friction coefficient was displayed by molybdenum disulphide dispersing grease. The highest friction coefficient was displayed by grease dispersed by graphite and talc, while the lowest friction was shown for molybdenum disulphide dispersing grease. Grease dispersed by high density polyethylene showed friction decrease. The lowest friction reduction was observed for polymethyl methacrylate. The strong adhesion of polytetrafluroethylene particles into the sliding surfaces significantly increased friction coefficient. It seems that polytetrafluroethylene particles were adhered to surfaces of inner and outer races as well as the balls. Changing the terminal of the voltage applied to the rotating shaft cased significant friction decrease for polymethyl methacrylate. Viscosity of the grease decreased with increasing the voltage. Friction coefficient decreased for high density polyethylene and polytetrafluroethylene. The lowest friction values were observed at 6 volts which indicated that increasing voltage across the sliding surface could significantly decrease friction coefficient.

The present work investigates the influence of magnetic field on the friction coefficient displayed by sliding of steel pin on polyamide disc lubricated by paraffin oil and dispersed by different lubricant additives such as zinc dialkyldithiophosphates (ZDDP), molybdenum disulphide (MoS2), heteropolar organic based additive (CMOC), graphite (C), detergent additive (calcium sulphonate) (DA), polytetrafluroethylene (PTFE) and polymethyl methacrylate (PMMA). Based on the experiments carried out in the present work, it was found that, at surfaces lubricated by paraffinic molecules friction coefficient decreased with increasing applied load. As the magnetic field increased friction coefficient increased. When the oil was dispersed by ZDDP additive significant decrease of friction was observed. The performance of ZDDP additive was not affected by application of the magnetic field. Dispersing Mo S2 or C in the lubricating oil caused significant friction increase. The effect of magnetic field on performance of MoS2 was insignificant, while magnetic field caused slight friction reduction in the presence of C. Magnetic field decreased friction coefficient when the oil was dispersed by CMOC. Under the action of magnetic field the force of adhesion significantly increased causing proper surface coating which caused the friction decrease. Oil dispersed by calcium sulphonate showed significant friction decrease due to the polarity of its molecules. Application of magnetic field caused further friction decrease. As a result of the quite good response of DA additive with magnetic field based on the values of friction coefficient observed for the oil dispersed by DA additive, it can be recommended to use this additive when magnetic field is applied. The good lubricating properties observed for PTFE additive can be from its ability to form a layer on the sliding surfaces. PTFE particles dispersed in the oil were much influenced by magnetic field, where the lowest value was displayed at the highest intensity of magnetic field. The same trend of friction decrease was observed for PMMA particles dispersed in oil.

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