Tech Talk
What are the critical considerations for coolant when using superabrasives?
The type of coolant and its concentration depends on the material, abrasive, and grinding process. For example, when grinding with diamond the need for lubricity is not as critical (exceptions to exist) as it is when grinding with CBN. Using CBN,I have ground with straight sulfur chlorinated oil and with water soluble oil as low as 3 percent concentration, experiencing little difference in cutting ability. Regarding synthetics, my experience has not been very successful with CBN but, quite acceptable for conventional and some diamond application. The decision on coolant type should be made using a coolant expert as a team member, reviewing your process and options
Coolant flow, coolant pressure, tank size, and filtration are among the most important issues regarding optimizing of your grinding system. First, the coolant flow should, in almost all cases, exceed the velocity of the wheel. This can be accomplished with knowing the actual GPM (gallons per minute) at the nozzle exit and designing the nozzle with an opening that will allow the flow velocity of the coolant to equl the velocity of the wheel.
Streamlining the pluming and installing the correct pump designed for the proper line pressure will assure this flow. The nozzle should be designed with a laminar nose to direct the flow in a straight line between the wheel and work piece. This will reduce the amount of misting and create a “fluid horsepower” allowing you to increase stock removal without burning. The nozzle opening is sometimes as small as 0.020” (0.5mm) and will need good filtration on the coolant return to maintain particle distribution small enough not to disrupt the flow of the coolant from the nozzle.
The tank size will need to be at least 5 times the GPM. This allows for enough time for the coolant to circulate and reach room temperature. If oil is used sometimes a chiller will be needed. Temperature variations can cause inconsistencies in part geometry due to thermal properties of the material being ground.
High pressure is a relative term but is not the term that should be used for this process. For the most part pressures less than 250 PSI are used. However is a scrubber is needed then high pressure (between 1000 and 2000 PSI) is utilized. The scrubber would be utilized for long chip material that would have tendency to attach to the abrasive particles or get caught in the pores of the wheel.
What is accomplished with all of this is increased wheel life, better finishes, decreased cycle times and better control of your processes.
