Water Mix Grinding Fluids - Management And Control
Water Mix Grinding Fluids come in many guise’s and bring with them their own unique set of issues when considering the most effective way to use and care for them. Coolant management and control play a key part in the production process and should always be on the production manager's radar.
Generally, water mix grinding fluids come in two types, either oil based or synthetic. Oil based grinding fluids form a milky emulsion when mixed while synthetic coolants mostly form a solution. Synthetic coolants are usually recognisable in use because they often remain transparent as they have no emulsifiers to absorb tramp oil.
Choosing the right grinding fluid will have implications for productivity and cost reduction. Properly applied water mix grinding coolants reduce friction by lubrication with the water phase delivering good cooling properties to the grinding wheel and work piece. The grinding operation and wheel choice is key in choosing the fluid type. Aluminium Oxide wheels coarsely dressed for heavy stock removal point the way to a water-based coolant. Alternatively, in super finishing grinding operations using a CBN grinding wheel, a neat grinding oil may be selected.
However, partly due to more stringent H&S rules, water-based coolants are usually preferred to neat oil products where they can be proved to be as effective. Water mix coolants also find more favour with operators.
Modern grinding machine tools often use high pressure delivery systems. Coolant velocity is just as important as coolant volume. Good final part quality relies on the fluid getting to the point of cut and at the proper velocity and dilution. High pressure delivery systems allow the fluid to quickly wet the wheel and the work piece while providing the correct lubricity.
Coolant Mixing, Distribution and Contamination
To obtain optimum performance for any grinding application the grinding concentrate has to be mixed properly. It's ability to remove heat from the process means inevitably that water will evaporate every day. If not monitored and corrected grinding performance will be lost with the corresponding detrimental effects on product quality. Lower concentrations due to water loss can cause poor surface finish and lead to more frequent wheel dressing. Daily checks and distributing different top-up dilutions at each machines is a tedious activity multiplied by the number of machines in the shop.
Contamination from the grinding process is inevitable. Grinding chips and fines from the wheel and wheel dressing will increase with stock removal. Recirculating grinding fines contribute to poor surface finish, component reworks and scrap. It is imperative that grinding coolants delivered to the grinding zone contain as few particles as possible. Traditional systems include hydro cyclones, magnetic filters and more often paper-band filters. However paper-band must be continually purchased and supplied. The paper waste is also difficult to separate contributing heavily to the waste pile and disposal cost.
Tramp oil from the machine slide-ways, spindles and work pieces collect in the coolant blinding the grinding wheel and often causing wheel chatter. Increasing levels of contamination, if not brought under control, will allow bacteria to grow causing premature coolant failure. Deposits from the fluid left on machine table and beds can be difficult to remove, this can be an issue with some fully synthetic coolants.
Taking Control - Centralise Every Function
Water mix grinding fluids work better and last longer when they are used and maintained exactly as the supplier intended. Centralised coolant management systems not only control every aspect of fluid top-up and delivery they also remove contamination from the process, depositing all waste in one place for removal or recycling. Each system is designed for the overall flow rate needed in a grinding machine shop but what is common to all of them is that zero consumable media is used.
Providing clean coolant at the right dilution directly to the point of use allows the grinding process to continue as intended – without the issues caused by contaminated product at the grinding wheel. Additionally existing standalone filtration equipment, such as paper-band filters at each machine, can be removed along with the consumable cost and maintenance associated with them. Freeing up space in a crowed machine shop may produce other benefits of their own. Often grinding machine filtration equipment takes up as much, if not more space, than the machine it serves.
Grinding process can also be improved with the addition of high pressure systems where they may have been none before, these can easily be retrofitted. Grinding waste from the process is easily collected and discharged at the central plant by scraper. Coolant recovery through a de-watering process or briquetting provide more cost savings along with easier waste disposal. Where swarf and grinding waste has an intrinsic value the briquetting process is particularly useful and can be included with the central filter unit.
DinoFilter Working Principle
Every grinding machine in the machine shop is installed with a return pump station which replaces all existing filtration equipment. Contaminated coolant returning to the DinoFilter is processed through the filter tank which contains several filter drums with exchangeable stainless filter cloth. Coolant is pumped from the inside of each drum, the decompression causes grinding fines to build as a filter cake on the outside of the filter mesh.
The drums are self cleaning, periodically each drum will turn against a stationary brush to remove the filter cake to the bottom of the DinoFilter tank to be removed by scraper. Clean grinding coolant is automatically supplied to each grinding machine in the machine shop at the correct dilution. Loss from the the system from evaporation and drag out is made up as required by the topping up and coolant mixer system.
The DinoFilter central system is recommended for machine shops where centralised coolant management forms a key element in the manufacturing process. With flow rates climbing to 100,000 litres/min these units are just as at home delivering coolant flows of hundreds of litres/min. Each DinoFilter is designed to the exact requirements of the grinding process.
There is no 'one size fits all' solution although the functionality of each unit is exactly the same.
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The Pygmer is a stand alone media free grinding fluid filtration system following similar design parameters to the DinoFilter. Ideal as a replacement for filter systems using consumable media particularly, paper band systems the unit has a small footprint, is self cleaning and is suitable for machine flow rates up to 500 litres/minute
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