We usually don’t think of coolant maintenance as mechanical, but this is the most important aspect, which keeps the the chemistry and biology in proper order. There is a direct link between what we do (or don’t do) at the mechanical level to what goes on at the microscopic level. By mechanics we are specificaly referring to keeping the fluids moving and removing foreign contaminants. These contaminants include tramp oils, emulsified oils, particulates created from the machining process, and any other thing that may end up in the sump.
Remove the Oil Layer
This layer is what seals off the air supply to the sump and provides nutrients for the bacteria. By keeping oxygen from the coolant, anaerobic bacteria will thrive. These types of bacteria are more dangerous to the chemical components of the coolant than any other types. The oil acts as their food source and they combine with it to create a biofilm, which forms somewhat of a skin on the surface. These biofilms are difficult to remove, and once they are formed, only lead to contamination of the entire machine.
The simplest method to remove floating oils are a variety of mechanical skimmers, which mount to the sump, pull off the oil layer with some type of media (disk, belt, or tube), and drain it to a collection container. Some of this variety are also equipped with a mini separation tank so there is no wasted coolant, as it may be picked up during the process since most coolant contains some mineral oil. There are also coalescers, which pull the oil off via a collection apparatus, and transfer it to a drum or tank for separation. The de-oiled coolant then is introduced back the sump. This type of unit is the best type, since it requires very little maintenance and keeps the fluid in circulation. Some of this variety also incorporate additional aeration devices and can filter small floating particulates.
Keep the Fluids Moving
Circulation of the sump is as important as any other mechanical method since it keeps things moving, forcing oxygen into the system. Oils have a harder time pooling on the surface, which helps to prevent bacterial biofilms. If you have any doubt about this strategy, think about how an aquarium works, and why ponds can go stagnant.
It may not be feasible to leave the coolant pump on at all times, so instead, a small centrifugal pump can be introduced to the sump to keep the coolant from remaining in a static state. If the machine sump is divided, all baffles should be agitated. Small aerators can also perform this function if the sump holds 50 gallons or less.
Keep in mind any coolant that pools in the lines is affected by the same forces in play. When machine sumps are emptied, cleaned, and recharged, these lines are usually overlooked, and bacterial contamination still exists within the system.
Finally, both floating and sinking chips should be removed so they do not interact with the chemical components of the fluid to cause premature failure. Although most of the material sinks the bottom, even if a conveyor is in operation, they will interact with any fluids that they touch. A shovel or industrial vacuum may be used to remove the larger, sinking chips. A general filtration system should be used regularly to remove all others. Some floating chips may be filtered via a coalescing unit with this capability, however, very fine chips, such as 5-25µ in size, should be removed after the oil has separated, or re-emulsion can occur.