US Patent 7645727 Gear cutting oil

Metalworking fluids contain active sulfur, a certain kind of inactive sulfur called “available sulfur”, and fat in a base oil of a lubricating viscosity. The metalworking fluids are chlorine free and phosphorous free. Boundary lubrication is provided by the fat, while extreme pressure lubrication is provided by the sulfur. Available sulfur is inactive sulfur minus any contribution of inactive sulfur from sulfurized saturated fats. Active sulfur and available sulfur are present in balanced proportions, while fat is present at an amount effective to provide boundary lubrication. Use of the fluids reduces tool wear over a long period of action and over a variety of boundary and extreme pressure conditions.