A study of solid lubricants used to prevent wear and friction in powder metallurgy production
This research continues the earlier researches on wear friction and lubrication and its application to the powder metallurgy industries. A detailed study of the parameters involved in wear and friction has been made by using the "Pin and Disc" machine with cross cylinders technique. One iron powder was chosen and compacted over a range of densities with a series of metallic stearates as admixed lubricants for the purpose of examinations. These compacts were used as the "pins" for the wear and friction apparatus, the "disc" was made from high carbon high chromium steel which is one of the steels normally used in punches and dies in the powder metallurgy industries. The wear behaviour of these compacts was studied in relation to the following parameters: applied load between compact (or pin) and disc, sliding speed, travelled distance, density and hardness of compact. These were examined for a range of stearate lubricants and the wear rates determined, these data were then related to the possible industrial life for punches and dies in powder metallurgy presses. Besides wear rate, friction forces between the compact (or pin) and disc were measured and these forces of friction were translated into coefficients of friction for each type of lubricant. The thesis presents the results of these investigations with a survey of current theories on wear and friction of metallic systems relevant to powder metallurgy. Conclusions have been drawn and suggestions made on the most useful solid lubricant necessary in the pressing of metallic powders to reduce wear and friction in production presses. Calculations have been carried out using the data collected to estimate the possible press tool wear and accordingly a possible tool life was determined for pressing with each type of ~tearate lubricant. The overall conclusion was that zinc stearate is the best solid lubricant in the five metallic stearates (Al, Na, Mg, Ca and Zn) for use in iron powder compaction.