Coolant’s primary purpose is to lubricate and cool the work surface enabling the machining of metals without welding everything together. Each coolant works best for a given application at a recommended concentration of coolant to water. Refer to your coolant’s product data to determine what ratio is best for your application. Maintaining this correct concentration prevents raw material waste and health concerns, as well as prematurely-worn tooling, poor surface finishes, and rust.
Check concentration on the initial sump charge, of course. Also monitor each day, as evaporation takes place. This means water is lost, but concentrate is left behind. It’s also important to create a good oil/water mixture, or emulsion. Always mix coolant into water, and not water into coolant. Mixing equipment will aide in this process as well as establish a proper proportion without laborious measurement.
Everyone has heard of hard water. If you’ve showered with hard water, you know it’s difficult to create a good lather. Hard water means the water contains minerals, and these minerals prevent soap from lathering. These minerals include calcium and magnesium carbonates.
Coolant emulsions also work best when only a certain amount of minerals is present. Low hardness helps create foam, and high hardness splits the coolant emulsion rendering it useless for proper lubrication and cooling. Since coolant is mixed with up to 95% water, it’s important to verify against the coolant product data what mineral levels are best. It’s recommended to check the hardness of the water supply for the initial coolant charge. Then monitor at the sump level at least once a week since evaporation can take place, which will remove water, leaving the minerals behind. You can see evidence of this mineral ‘scale’ on your own water faucets at home.
Do you know anyone who doesn’t use deodorant? Especially on a hot summer day? Deodorant works because it is has high pH, or alkalinity, neutralizing the acidity of perspiration.
Coolants are also designed to be alkaline, to neutralize the acidity of bacteria that enter the fluid pool via the water, work material, and our skin. Just like the bacteria under our arms, the ones we fight in coolant are the anaerobic kind, which do not like oxygen. When the machine pump isn’t circulating the coolant, the coolant stagnates, creating a breeding ground for bacteria. These bacteria then feed on tramp oil left on the surface, colonize, and emit acids.
Aerating the fluid and skimming tramp oil are the best defense, especially when the machine is not circulating the coolant.
If the pH of the fluid goes below its minimum value, the coolant emulsion will emit odors and may even split, just as when hardness levels are too high. Monitor pH weekly so action can be taken before problems arise.
Manage Tramp Oil
The best food source for bacteria is tramp oil since it has organic nutrients. It must be skimmed to prevent excessive bacterial growth. When tramp oil is left in the fluid pool, bacteria colonize and create a slimy layer known as biofilm. This biofilm inhibits oil removal via a mechanical skimmer since it is not attracted, like true oil, to the pick-up device. Tramp oils can also emulsify into the coolant as it circulates through the machine pump and eventually will not separate via gravity for skimming. This emulsified oil creates shop mist and reduces the cooling capacity of the fluid.
Skim tramp oil every day the machine runs.
The metals we machine are also minerals, and may affect the coolant emulsion. The most damaging materials are iron, aluminum, and magnesium. Leaving chips in the fluid pool also creates a nesting ground for bacteria, and the small chips recirculate causing worn tooling and poor surface finishes.
Removing these metal chips is crucial to preventing problems associated with hardness, and to keep tooling performing at its best. They should be removed on a daily basis.