Coolant Maintenance
Good coolant maintenance programs will include regular laboratory testing of the coolant, either in-house or by the coolant manufacturer. This section contains suggestions for proper maintenance and control of coolant that the customer can perform. Implementing these suggestions is not as straightforward as it seems. Control and maintenance of coolant is difficult, particularly in small systems or individual sumps.
Frequent testing and adjustment of coolant is feasible on large central systems where the cost of these procedures is easily justified in the control of thousands of gallons of coolant. It is not as easy to justify detailed analysis of a 100 gallon sump. Unfortunately small systems are subject to much more rapid changes and greater fluctuations and therefore actually should be checked more frequently than large sumps to maintain good control. These factors make the choice of coolant particularly critical for small sumps.
Small coolant systems normally use less effective equipment for filtration and oil separation than those found on central systems. This requires that the coolant in small systems be more tolerant of contamination from metal fines, tramp oils and other materials.
COOLANT LIFE:
Many factors are involved in the success or failure of a metalworking coolant. This brochure will attempt to address the most frequently encountered factors, and also offer tips and techniques for maximizing the performance of your fluid. These guidelines should be strictly adhered to for optimum results.
The DuraKut product line of coolants has been formulated using state-of-the-art components selected for their resistance to bacterial attack and subsequent deterioration. As such they will give a service life far greater than that of conventional water-soluble coolants. There are steps that can be taken to improve the longevity of these coolants even further.
PREPARING THE MACHINE:
Most important in maximizing coolant life is to start with a clean sump. Any bacteria, dirt and/or sludge left from the previous coolant can decrease the life of the new fluid. A thorough cleaning with a good machine cleaner, (DuraKlean Machine Cleaner) is highly recommended before the introduction of any new coolant.
MACHINE CLEAN OUT PROCEDURE:
If the system is severely contaminated or rancid, an appropriate amount of conditioner approved for use in metalworking fluids should be added and allowed to circulate per manufacturer’s instructions before initiating cleanout procedures. Drain sump or system as well as possible. Remove any solids from the sump or system. Add 1 gallon of DuraKlean Machine Cleaner for each 20 gallons of coolant capacity.Fill the sump with tap water up to the normal operating level and allow the fluid to circulate for at least four hours. While the fluid is circulating, use a rag or brush to remove stubborn deposits on machine surfaces and in the troughs. Allow the fluid to wash the material into the machine sump. Remove the fluid from the sump. Remove any further solids or sludge from the sump. Fill the sump to normal operation level with tap water, add 1 gallon of DuraKlean Machine Cleaner to each 100 gallons of water and allow the fluid to circulate for at least ½ hour as a final rinse. Drain this solution from the machine sump. Immediately recharge the machine with the a DuraKut metalworking fluid at the manufactures recommended dilution radio and allow the fluid to circulate for a least ½ hour to ensure the machine is protected against corrosion.
ALTERNATIVE CLEANING PROCEDURE: (Minimal down time)
When production absolutely cannot be interrupted for the period of time required for the previous procedure, the following method may be substituted:
1. Add DuraKlean Machine Cleaner directly to the old coolant at 1-3% of volume of sump.
2. Run production for 1-2 shifts.
3. Drain system and remove all solids.
4. Rinse sump and flush coolant lines.
5. Remove rinse water.
6. Recharge with fresh coolant…
7. Add a coolant conditioner if bacteria or fungus is a problem.
MACHINE CLEANING PROCEDURE:
Use the following method to recharge a freshly cleaned machine with metalworking fluid:
1. Fill machine sump with water to a level where sump pump will circulate water.
2. With pump running add the required amount of coolant concentrate.
3. Continue to add coolant and water until a uniform mixture is obtained.
4. Check concentration with refractometer and make necessary corrections before machining.
Note: The high detergency of many of the fluids in the DuraKut product line will continue to clean a sump and system after the initial charge. This may result in:
A. Temporary flush of odors from loosened deposits.
B. A temporary spike in bacteria levels.
C. The appearance of floating masses of sludge which have been dislodged from the more inaccessible areas of the sump and system
This is considered normal and will usually occur within the first two weeks of use of a fresh charge. Once removed these floating masses should not reappear.
Once a new coolant is in, concentration control is the most important parameter for a coolant user to monitor. It is imperative for long coolant and tool life!
Low concentration is the most common cause of coolant problems that customers experience. DuraKut coolants have been formulated to operate at a minimum concentration of 4% (25:1). A lower concentration than this, even for a short period, could lead to problems such as machine and workpiece corrosion, poor tool life and rancidity of the working solution.
A refractometer, designed for measuring the concentration of an aqueous solution, can be used for checking cutting and grinding fluids, drawing and stamping fluids, and rust preventatives concentrations. A hand held refractometer is useful for day-to-day control of concentration and is much faster than the laboratory procedure. To use a refractometer, you simply place one or two drops of the coolant solution onto the prism surface, close the cover plate, look through the eyepiece (facing the light) and read the scale. It is important to ensure that your refractometer reads zero with water alone. This is accomplished by placing a drop of water on the prism and reading the results normally. The reading must be zero, an adjustment screw must be turned to calibrate the refractometer.
ADVANTAGES OF RICH MIXTURES:
-Best corrosion protection for workpiece and machine tool.
-Excellent lubricity for tough machining operations.
-Better resistance to rancidity for long sump life.
-Cushion of protection in case extra water is added.
DISADVANTAGES OF RICH MIXTURES:
-Higher tendency to foam, due to rich mixture.
-Stronger solutions can be more irritating to skin.
-Heavier coating on machine could lead to buildup.
-Greater coolant usage.
-Could lead to smoking or thermal damage to workpiece.
ADVANTAGES OF LEANER MIXTURES:
-Excellent cooling for grinding or high-speed machining.
-Least irritating to workers’ skin, eyes and lungs.
-Minimal foam levels.
-Lightest residual film.
-Most coolant mix for the money.
DISADVANTAGES OF LEANER MIXTURES:
-Little margin for error. A small amount more of water, may result in a coolant mixture too lean for corrosion control.
-Less effective rancidity resistance.
-Less lubricity may result in poor finished and/or shortened tool life.
CONTAMINATION:
After concentration, the next most important factor in coolant control is the prevention of contamination by extraneous materials. Coolant sumps and systems have a tendency to become repositories for everything from cigarette butts and coffee to sandwiches, rodents, tobacco juice, floor cleaners/sweepings and even urine! All of these materials provide a source of food for bacteria and hence can impart some pretty foul odors to the coolant. While the coolant itself may not be affected by this contamination, the odors produced may lead one to believe that the fluid has gone sour. With the appropriate operator training and the provision of screens, covers and/or garbage receptacles, these problems can be eliminated.
MICROBES IN THE COOLANT:
Microscopic organisms (microbes) such as bacteria and fungus are naturally present in and on machine surfaces and live in the air we breathe and water we drink. The vast majority is not a pathogen (disease causing) and does not cause problems in metalworking coolants. However some are ideally suited for life in the warm, damp and dark environment of a fluid sump and can eventually lead to problems such as odors, plugged lines causing poor coolant flow, corrosion and emulsion instability.
Bacteria levels of 10(4) to 10(6) colonies per milliliter are normal and actually desirable in machine coolant systems. Since bacteria and fungus compete for the same food sources, the growth of fungus is kept under control by healthy bacteria colonies. When fluids like DuraKut biostable products are in use, the bacteria count rises to a moderate level and remains there because the components of the fluid are not available as food sources. The more aggressive bacteria colonies then consume fungal colonies keeping their numbers in check.
If biocides are used indiscriminately and bacteria colonies are eliminated or drastically lowered (10(2) or less colonies per milliliter), fungus colonies will grow rapidly. Because they form large stringy rubbery masses, fungi can clog filters and fluid transfer lines, causing poor cooling and burning of parts.
TRAMP OILS:
Another importance factor in coolant life is control of tramp oils. This refers to any oils which are not part of the original coolant formulation, including way lubes, hydraulic fluids, gear lubes, etc. which find their way into the coolants.
These tramp oils carry their own contaminants, such as sulfur, phosphorous or solvents, which can be detrimental to the coolant, either directly by destabilizing the emulsion or indirectly by providing food for bacteria. If excessive tramp oils are allowed to cover and “seal off” the surface of the coolant in the sump, oxygen will rapidly deplete and allow anaerobic bacteria (bacteria which live in the absence of oxygen) to grow and multiply, producing hydrogen sulfide, which is responsible for the “rotten egg” odor familiar to many machinists. Keeping the level of floating oils to a minimum will prevent the surface of the sump from “sealing off.”
The DuraKut line of metalworking fluids are formulated to reject rather then emulsify these oils, making removal a simple job. They can be skimmed from the surface of the sump by any of a variety of methods, such as oil wheels, rope-type skimmers, coalescing units, absorbent pads or even shop vacuums.
SOLIDS CONTAMINATION:
Another area for concern is the level of chips, fines or swarf in the sump. Quantities of these small particles can provide an enormous surface area for bacteria to attach themselves to while at the same time creating “dead areas” where coolant cannot circulate. There are many methods available for removal of these particulates such as magnetic wheels, conveyors or indexable filters. In general, the less solid material in the sump or system, the better.
WATER QUALITY:
Due to ordinary evaporation, a metalworking sump acts like a still and any minerals in the water will remain behind as the water evaporates. Over time the mineral build-up can result in poor emulsion (mix) stability, heavy residue on machine surfaces, corrosion problems and a host of undesirable conditions. Leander Lubricants can perform analysis of customer’s water for hardness and conductivity and to determine compatibility with DuraKut products. A good rule of thumb is to use tap water for the initial charge and the purest water available for makeup solutions, thus minimizing the level of mineral buildup. (A certain amount of water hardness can help keep foam levels down.)
The “allowable” hardness will depend on specific formulations. Hardness is typically expressed as ppm as CaCo3 or grains per gallon as CaCo3 (17ppm ~ 1 gpg). Typically you have little control over the lower limit (if tap water is used) and foam can be expected in water softer than 50-75 ppm. If treated water (DI or RO) is available it is not normally recommended for a fresh coolant charge due to the likeliness of foam, typically tap water (or a blend of tap and DI to ~100-150 ppm) is recommended for fresh charge and DI recommended for make-up. The high range can be empirically derived, test the product in hard water to establish where performance is no longer acceptable for a particular formula (emulsion stability unacceptable, corrosion protection unacceptable, etc). Typical soluble oils are fine to maybe 400-500 ppm, some maybe 700-1000 ppm (but specifically formulated for very hard water). Certainly if the customer is in a hard water area (>250 ppm) the extra cost for using DI water for make-up will pay for itself in extended sump life. This is normally the case even in softer water areas (100-250) although maybe harder to quantify.
Solution synthetics generally are not foam problems except in the softest waters (<50 ppm?). As with soluble oils hard water tolerance is a function of the particular formula.
Chloride content is also hard to pin down a specific allowable level, but we used the guideline that if the tap water contains >50ppm chloride (particularly if high hardness) it may be worth considering using DI water for make-up to extend the life of the coolant before rust becomes a problem.
pH:
pH (acidity/alkalinity) can give a good indication of the overall system condition. All water extendible coolants are designed to operate in the alkaline range (above 7.0 pH). Alkalinity helps control rusting and minimized microbial growth. A regular pH check using tape, strips or pens can spot trends before problems become severe. Typically pH should be between 8.5 and 9.4.
COOLANT MANAGEMENT:
1. Run oil skimmers or coalesces to remove excess tramp oil from coolant. A wet/dry vacuum can be used on small sumps. Dispose of as waste oils according to all local, state and federal regulations.
2. Circulate coolant and check concentration with a refractometer. Maintain fluid level. Add premixed coolant at lower concentration level to balance loss of water.
3. Check pH using pH color sticks (If pH starts to fall, add coolant to bring up concentration. If pH does not stabilize, it is time to replace coolant. If coolant needs to be replaced, dump old coolant, clean machine using a machine cleaner and immediately charge with fresh coolant.).
4. Record data on a machine check sheet (See attached example). This can be used to determine trends of a particular machine.
5. Check all filters, chip strainers and canister filters.
6. Provide aeration of coolant during extended periods of idle time. An air lance with 5 psi pressure allowed to bubble gently in an idle sump is often sufficient to prevent excessive anaerobic bacteria formation.
In summary, if you start with a clean sump, keep concentration up and prevent contamination, your coolant will enjoy a long, productive life!
