the glass used as a lubricant in the hot extrusion of metals. At the high pressures and temperatures generated during extrusion, the glass melts and acquires the properties of a good lubricant with a low coefficient of friction. Glass lubricant is significantly more effective than the lubricants ordinarily used at high temperatures, such as graphite. The best lubricating properties are characteristic of the glass having a viscosity of approximately 90 newtons-sec/m2 (900 poises) at the temperature at which the metal deforms. Glass lubricant is used in the extrusion of pipe and solid and hollow shapes. Glass in powder form based on Na2O—CaO—SiO2 systems with additions of B2O3, Al2O3, MgO, BaO, and K2O is the preferred type.
Glass lubricant serves to improve the extrusion process and protect the metals from oxidation.