Keishi Matsumoto

Tribological Properties of Water Glass Lubricant for Hot Metalworking

Tribological properties of water glass (sodium silicate aqueous solution) with graphite powders, a lubricant for hot metalworking, were studied by means of pin-on-disk type tribotesting at a wide variety of temperature ranges. The lubricant is a water suspension consisting of water glass with graphite powders at room temperature. It becomes solid or a suspension state consisting of solid or liquid glass with the graphite powders owing to evaporation of the water inside. The frictional behavior of the lubricant over 100°C was strongly affected by the state of the glass, which is a factor of temperature, and was categorized into the following three regions in accordance with the state of the glass: solid film lubrication by the powder glass and the graphite (Region I), fluid film lubrication by the viscous liquid glass (Region II), and fluid film lubrication by the low-viscosity liquid glass and solid film lubrication by the graphite (Region III). The lowest friction coefficient was obtained in Region III.