However, many grinding machines have self-contained grinding fluid systems. Several methods are used for grinding fluid cleaning. Cleaning of the fluid should be carefully done and monitored. A fundamental technique is settling. Grinding fluid is pumped to the settling tank, where swarf settles out by gravity. Settling tanks should have a series of baffles and enough capacity to allow time for swarf to settle. Because settling is slow, filtering may also be used. The filtering material is changed periodically. The type of filter used is limited as to the size of particles that can be trapped. Many of these systems use paper filtration instead of cloth because of disposal regulations. Another recent development that circumvents the use of disposable filters is microscreen filtration. The microscreen is a thin, preciseaperture stainless steel filter, produced by electrodeposition, that in turn is fusion bonded to a perforated backing plate.
In addition, a diamond-based filter has been developed for this purpose. Other grinding fluid cleaning methods include the centrifugal separator (Figure L-71), in which grinding fluid is processed by a rapidly rotating centrifuge. Swarf is spun to the outside, and clean coolant remains in the center.
The cyclonic separator (Figure L-72) also uses centrifugal force. Clean grinding fluid exits out the top, and swarf goes to the bottom. The magnetic separator (Figure L-73) will remove Figure L-73 The magnetic separator removes iron and steel chips from water-soluble oils and cutting oils. The magnets are located in the roll visible just past the electrical control box. Chips picked up by the roll are scraped off onto the slide and go down into the sludge box (Barnes International, Inc.). iron and steel grindings. A magnetic drum rotates in the grinding fluid and attracts the grinding swarf, which is later scraped off and removed. A general rule of thumb for grinding fluid filtration is that the filtration should remove particles larger than between and of the grain size of the selected grinding wheel. For superabrasive applications using resinoid bonds, filtration to is necessary, because recirculating abrasive material heavily erodes the wheel bonding, prematurely releasing still-sharp and effective abrasive grains.
Environmental Concerns The Environmental Protection Agency (EPA) is paying increased attention to the hazards of placing grinding sludge into landfills because of potential contamination of soil and groundwater. Many states have classified grinding sludge as “special waste,” which occupies a place in the system of regulation between general refuse and hazardous waste. Grinding is a dirty process compared with hard turning, for example. The residuals from hard turning are fully recyclable. The use of superabrasives can materially reduce
the volume of grinding sludge, as a much smaller amount of abrasive particles is discharged. Creep-feed grinding also produces chips resembling steel wool that can be recycled. It is important to be aware of the potential environmental hazards in machining processes and take steps to minimize these hazards at every level.