Investigation for the Ejection Property of the Conventional Lubricants Used in Powder Metallurgy Process

Zinc stearate (ZnSt) and N,N’-ethylene bis (stearamide) (EBS) are conventional lubricants for powder metallurgy. While an iron powder mixture containing ZnSt exhibits excellent flowability, its ejection property was found to be inferior to that of a mixture containing EBS. The main purpose of this study was to identify the reason why EBS is superior to ZnSt in the ejection property. To achieve this objective, we attempted to evaluate the “lubricity” and “extrusive property” of the two lubricants separately, as these properties appear to determine their ejection properties. Lubricity was investigated by sliding tests on a uniform lubricant film. The friction coefficient of EBS obtained in this test was larger than that of ZnSt. The extrusive property, which means the ability to fill the gap between the compact and the die wall, was evaluated by an X-ray analysis of the compact surfaces. The results of those measurements indicated that the extrusive property of EBS was greater than that of ZnSt, resulting in the better ejection property.