Four-ball assessment of drawing soap efficiency and the effect of dilution

Abstract

Four-ball and cup-drawing tests have been performed on a commercial soap-type drawing compound diluted with varying quantities of water. The results from both tests are explained in terms of a predominant surface adsorption or chemisorption boundary lubrication mechanism. Data which depend on the soap film coverage ( i.e. the peak cup-drawing load and a four-ball parameter which gives the wear scar size as a function of load) show an inverse correlation. The peak cup-drawing load increases linearly with dilution as the adsorbed soap film coverage diminishes. The four-ball wear parameter, on the other hand, decreases with dilution, since the higher sliding speed and more severe conditions in the four-ball test activate chemical attack of the surface by the adsorbed molecules, which decreases with dilution, other factors being constant. The drawing efficiency of the soap solutions could be estimated from the four-ball wear tests to within 0.2%. Application of these findings to press shop trials is discussed. While initial trials may still be necessary, especially for difficult shapes, they can now be conducted on a known scientific basis and reduced to a minimum.