Studies on friction in ball joint lubricated by lithium grease with Sio2 nanoparticles

The aim of the work was to study the effect of addition of SiO2 nanoparticles to a lithium grease and of contact pressure on the friction coefficient COF during reciprocating rotational movement in the contact zone between a ball stud and its bearing in the ball joint. The studies were carried out using a tribotester with reciprocating friction torque in the contact between the ball stud and its bearing. Ball stud was fixed and the holder with the bearing rotated reversibly around ball stud axis at a constant frequency. The ball stud was loaded by a force increasing in a stepwise manner for the consecutive series. The contact zone was lubricated with a pure lithium grease or with the lithium grease with dispersed SiO2 nanoparticles. The friction coefficient decreased with increase of the contact pressure for the pure lithium grease. For the concentration ☐=6 wt.% of SiO2 nanoparticles the COF value decreased further. However, for the concentration ☐=2 wt.% it increased with increase of the contact pressure.