Some tribological and environmental aspects in metal drawing

The methods of soap powder lubrication in dry drawing of metals are compared with a novel solid film lubrication. Concerning powder lubrication the required lubricant carrier or conversion treatments of the forming material surface are also considered. Both the tribological as well as the environmental aspects indicate the high potential of solid film lubrication. By means of examples the problem of aqueous dispersion stability of calcium soap systems is dealt with, which is one of the main problems in developing suitable coating systems. After coating, the adhesive and rheological behaviour of the dried solid soap layers on the wire or rod surface enable an excellent hydrodynamic pressure to be built up during the drawing process. When using a double die pressure tool, the pressure development is substantially controlled by the inlet die. In applying the solid soap film lubrication some environmental advantages with respect to soap powder lubrication become obvious. Chemically aggressive substances, such as lubricant carriers and conversion chemicals or acid pickling solutions, can be minimized or even eliminated. Moreover, rinsing water pollution and lubricant dust are reduced.