Effects of Porous Surface Layer on Lubrication Evaluated by Ring Compression Friction Test

Lubrication is an important parameter in cold working of steels. Metal soap on phosphate coating is the most commonly used lubrication system in industries at present, but the technique is less productive and environmentally hazardous. The authors proposed an alternative lubrication process which makes use of porous layer formed on the surface of the workpiece by oxidization and chemical reduction in the previous paper. The technique, due to the porous layer, enables to hold more liquid lubricant on the surface and consequently to decrease the friction. This research expands the range of application of this technique. The porous layer is applied to three types of steels containing different levels of carbon and its effects are analyzed under three lubrication conditions; unlubricated, machine oil and grease, by ring-compression test. Another important condition, compression speed is investigated by using two types of equipments, a hydraulic press (low speed) or a mechanical press (high speed). This study proves that the porous layer technique is applicable to a range of types of steels reducing the friction coefficient, and at the same time provides some insights to explain the mechanics of the technique. The lubrication effects are explained by the thickness of lubricant held at the interface between the die and the surface of workpiece.