Nozzles are often used to supply coolant during grinding or machining operations to control workpiece temperature, keep the grinding wheel or tool clean and open for chip flow, enable extreme pressure additives in the coolant to do their job, and flush chips away from the cutting area. Popular configurations include rigid, bent metal tubes and conformable plastic versions with many joints. Plastic nozzles are designed for low pressure (approximately 30 psi) and can stray out of position at higher pressure. They are easy to aim, but need to be placed close to the workpiece because they generate wide, dispersed jets that entrain air into the coolant stream. Rigid metal tubes are stiffer, but they also deliver dispersed coolant jets. Re-aiming them requires frequent bending that ultimately leads to fracture. Plus, their close proximity to the tool can result in damaged nozzle tips and reduced jet quality.
During the past 20 years, I have demonstrated that coherent-jet nozzles are more effective than plastic and rigid tube nozzles for coolant delivery. Their internal nozzle geometry creates a tight, coherent jet when the coolant exits. This is especially important for grinding, because most of the heat goes into the part, not away with the chips.
Grinding wheel speeds of 6,000 sfpm or higher generate a boundary layer of air that stops low-pressure coolant from wetting the wheel surface...read more