The aim of the present work is to introduce new self-lubricating polymeric materials for bearing applications, where external lubricant such as oil or grease can be excluded and the design can be simplified and maintenance cost can be reduced. The proposed polymeric composites are consisting of polyamide (PA6) filled by different types of vegetables oils such as (almond oil, camphor oil, castor oil, cress oil, flaxseed oil, habetelbaraka oil, lettuce oil, olive oil, sesame oil, and sunflower oil) in concentration up to 10 wet. %. The friction coefficient of the proposed composites is investigated at different value of applied load. Based on the experimental results, it was found that, as the oil content increases friction coefficient decreases. It seems that friction decrease was displayed due to oil transfer from the specimen to the counterface forming a thin layer which was responsible for the friction decrease. The adhesion of oil molecules into the sliding surfaces depends on the polarity of oil molecules. Polar molecules will form multilayer which strengthened the adhesion of oil into the solid surface. Polarity of oil influences the thickness of oil film. As the normal load increases friction coefficient decreases. This behavior may be related to increase of exiting oil from test specimens covering the contact area. The minimum value of friction coefficient (0.15) was observed at PA6 and flaxseed oil specimens, at oil content 10 wt. % and 30 N normal load. It seems that friction decrease was displayed due to oil transfer from the specimen to the counterface forming a thin layer, which was responsible for the friction decrease. The decrease of friction coefficient is attributed to the adhesion of oil molecules into the sliding surfaces.
Ali et al. (Tue,) studied this question.