Too much mist in the air.
Too much mist from the spray system creating a fog is typically a result of too much atomizing air flow through the nozzle. Ideally, the proper amount of atomizing air flow is just enough to propel the fluid to the cutting tool. Settings are dependent on many factors including the length of tubing from the pump to the nozzle, fluid viscosity, and the machining operation. For systems that use a metering screw to regulate atomizing air flow, a good starting point is 1/2 to 3/4 of a turn open from fully closed. Other systems use various regulators and proportional valves to control atomizing air flow and must be adjusted on a case-by-case basis.
It may take some trial and error to get the atomizing air flow dialed in. A piece of cardboard or paper held at the cutting tool while the nozzle sprays against it is a good visual indicator of fluid output from the nozzle. Longer tubing lengths from the pump to the nozzle may require a greater air flow adjustment starting point due to pressure loss through the longer tubing run. Thicker, more viscous fluids may also require more air flow to properly atomize the fluid.
