Studies and researches concerning the tribological behaviour of friction couple functioning with selective transfer

The actual tendency to separate lubricants from the oxidation products and to stabilize them in a meta-stable phase on one side, and on the other side to use lubricants in friction couples which accelerations the oxidation processes when they heat, leads to their mechanical destruction and to and to a catalytic and electrochemical effect of the friction surfaces. perimental researches on different lubricated friction couples confirmed that it is utility to realize processes thermodynamic instability inside the lubricant and on the friction couples surfaces in the first stage of friction process. This supposes that in functioning conditions must take place physic-chemical processes that are favorable to the friction, such as: polymerized, formation of active substances at the contact surface, formation of colloids and of other substances (compounds with low resistance to shear stress). on in such conditions is called selective transfer and it is used only where the friction of mixed and adherence layers are not safe enough or the durability friction couples is not ensured. This transfer uses the positive effect of friction through physical chemical processes that take place in the contact areas of the friction couples, which ensures a thermodynamic instability of the lubricant and allow the transfer of some elements of the material from one surface to another, forming a thin, superficial layer, having superior properties at friction and minimal wear. ctive transfer can be certainly performed in a friction couple lubricated with glycerine or a special lubricant, if in the friction zone there is a material made of an alloy based on copper. e paper analyzed the physic-chemical factors and the proper processes for initiation and realising the selective transfer for a couple of materials (steel/bronze), which in optimal conditions of forms in the contact zones a thin layer of copper, being able to function in the conditions of a selective transfer and presents some studies and researches concerning the tribological behaviour of a friction couple with linear contact (cylinder/plane) which is functioning with selective transfer, tested on the Timken installation.