Combining proven filtration systems with new technologies helps shops clean up water-soluble coolant and reduce costs.
This typical central coolant filtration system has absorbent cartridges located just upstream of machine tools.
This Parker Hannifin portable filter cart can be used to treat new fluids, transfer and condition fluids in use, or complement an existing filtration system.
Off- line filtration is installed totally independent of the main coolant system and may include an optional cooling loop.
A properly sized, installed, and maintained water-soluble coolant filtration system should not only remove contaminants like swarf and oil, but also reduce operating costs. Yet, balancing the benefits of filtration against the cost of purchasing filters, replacing elements, and maintaining filtration equipment can be tricky. That's why careful filtration system design and component selection is critical.
Unfortunately, even the most efficient filtration system cannot completely remove traces of tramp oil and entrained fine solid particles in coolants. In fact, there are several types of coolant contamination that challenge the capabilities of standard filtration systems.
For instance, intentional contamination — such as the chips and fines created during the metalworking process — is the most obvious kind of coolant contamination. Unintentional contamination, on the other hand, is anything that enters coolant from the environment. This includes plant debris, airborne solids, and foreign liquids that enter the coolant either through the reservoir or as it cascades over machine components and flows through return lines. It is also the contamination created by component wear in a manner similar to what happens when hydraulic and lubrication systems degrade.
Additionally, tramp oil is a significant contaminant in water-based coolants. This is lubricating oil washed off workpieces and machine parts and hydraulic oil from fluid-power systems. These oils may mix with metalworking coolants for a variety of reasons, including component leakage, maintenance practices, poor housekeeping, and faulty system design.
Biological contamination is another problem. The water, oil, and warm temperature of metalworking coolants provide an environment where microbes grow rapidly. Air whipped into the coolant can also increase the rate of bacterial growth and may cause foaming that impairs coolant functions. Excessively high temperatures accelerate the deterioration of coolant additives and speed up evaporation, resulting in higher contaminant concentration.
Blending the old with the new
Although single, standard filtration systems may have trouble removing all of these contaminants alone, combining them with new polymeric technology can result in extremely low levels of coolant contamination. Cartridge separators, which use polymeric absorbents, reduce hydrocarbons in water-soluble coolants to a negligible part-per-million level.
Polymeric absorption is not a filtration technology but, rather, uses chemical forces to attract hydrocarbons to the media, which are then permanently bound within its structure. Polymeric absorbent cartridges remove free, emulsified, and dissolved oils, grease, and a multitude of organic solvents. They will not, however, strip coolants of desirable lubricants, anti-rust, or anti-foaming agents. The cartridges are nonhazardous, incinerable, and cost effective.
Coolant polishing
Polymeric absorptive cartridges can be used as a pretreatment separator to protect water-soluble coolant treatment systems that may be damaged or impaired by hydrocarbon contamination. When installed at point-of-use just upstream from a cutting tool, an absorbent cartridge removes trace hydrocarbons from the coolant to increase machine tool life. Absorbent cartridges also reduce coolant hydrocarbon contamination to extremely low levels when used in conjunction with upstream oil skimmers and sediment filters (such as bag or pleated cartridge filters). This combination removes gross amounts of oil and fines produced by metalworking operations.
The affinity of the polymeric absorbent for hydrocarbon contaminants is so strong that accelerated testing — Toxic Characteristics Leachate Procedure (TCLP) — indicates the effluent hydrocarbon level in water to be below current and proposed EPA limits.
The modified polymer is formulated to control the speed of hydrocarbon absorption by eliminating the potential for skin formation at the polymer/hydro-carbon interface. Consequently, this polymer, when incorporated into a radial-flow design cartridge, ensures maximum utilization of surface area. Absorbent cartridge efficiency depends upon the residence time of the fluid within the cartridge, which is a function of the volumetric flow rate.
Flow rate capability: A maximum flow rate of 1.0 gpm per 10- in. cartridge length is recommended for the most effective removal of trace hydrocarbon contamination.
Hydrocarbon removal efficiency: At an equivalent flowrate of 1.0 gpm per 10-in. length of cartridge, a representative absorbent cartridge typically reduces trace hydrocarbon contaminants in excess of 95% in a single pass. This efficiency level can be maintained only to a net differential pressure of 10 psi. Series or multipass filtration can virtually eliminate hydrocarbon contamination.
Hydrocarbon absorbent capacity: A typical 10 in. absorbent cartridge medium has the potential to remove up to 250 gm (about one-half pint) of low density hydrocarbon contaminant from a water-soluble coolant.
Off-line filtration
Even with the best filter system, contaminant ingression rates can easily exceed removal rates. Simply changing filters or replacing the coolant are expensive options, but these remedies will not eliminate the contamination overload problem. It is necessary to have an off-line filtration loop totally independent of the equipment's coolant system. Off-line filtration, also called recirculating, kidney-loop, or auxiliary filtration, consists of a pump, filter, electric motor, and appropriate hardware connections. Fluid is continuously pumped out of the reservoir, through the filter, and back to the reservoir.
Off-line filtration keeps the contamination level within the coolant at a constant level. This type of system maintains overall cleanliness, but does not provide protection for specific components. An off-line filtration loop has the added advantage of being relatively easy to retrofit on an existing system that has inadequate filtration. Also, the filter can be serviced without shutting down the main system.
Most major manufacturers offer a number of off-line filtration options. For example, Parker Hannifin's portable filter carts use high-capacity filter or absorbent cartridges for long service life and better system protection. The first-stage filter captures larger particles to protect the pump. The second-stage vessel can use a high-capacity sediment cartridge or an absorbent cartridge if trace hydrocarbons or tramp oil are at an undesirable level. Portable filter carts and hand-held pump/motor/filter units are effective for prefiltering and transferring fluids into reservoirs or to clean up existing systems.
