All Metalworking Fluids Will Fail

By Jonathan Sowers, CLS

ALL METALWORKING FLUIDS WILL FAIL AT SOME POINT.  You may experience this sooner than you expected if the fluid is not properly maintained.  Proper metalworking fluid maintenance includes correct maintenance practices, housekeeping in the plant, and also appropriate routine laboratory testing.  Staveley Services Fluids Analysis offers a full slate of testing capabilities specifically designed for metalworking fluids.  With a dedicated Metalworking Fluids Laboratory located at our Glendale Heights, Illinois facility (a suburb of Chicago), we have the right tests, experienced technicians, and analysts to help you get the most out of your metalworking fluids.

Why are metalworking fluids necessary?  The metal working process creates much friction and heat.  If the heat and friction are not reduced, the tools used in the process are quickly damaged or destroyed and the quality of the product is diminished.  Metalworking fluids reduce friction at the tool/substrate interface and transfer heat away from the tools and materials being processed.  They also keep the work area clean by constant removal of metal chips and tramp oil. This reduces the time to process, improves the quality of workmanship, and increases tool life.  The ability to transfer heat away from the metal working process is why metalworking fluids are often called coolants.

Oils are natural lubricants and provide lubricity to metalworking fluids that are petroleum-based. Other metalworking fluids use additives to reduce friction. During the metal working process heat diffuses into the metalworking fluid. The “heated” fluid flows off the work area into a collection container or sump, where it cools off and then enters the cycle again. Water has excellent cooling characteristics and many metalworking fluids contain water to cool the machining process. Soluble oils and semi-synthetic oils have both water and oil components. Metalworking fluids containing both oil and water require surfactants to form and maintain emulsions, a mixture of the oil and water, so that both properties work together, without separating into their individual components.

Other desirable performance characteristics to look for in your metalworking fluid include:

Each brand and type of coolant has been formulated to work within a specific concentration range.  If used outside that range, problems will occur, and usually hard and fast!  If the coolant concentration is too low, there may not be enough additive at work to maintain the mixture and its ecology, and tooling will break prematurely or cause bad finishes.  If too high a concentration is used, it is expensive, and may develop into a health hazard.  A low pH may indicate that the concentration is too low or that there is bacterial contamination or both.  Keeping your metalworking fluid at the high end of the range is the best practice, as it will enhance rust and corrosion inhibitors, but, not too high, as this may cause adverse health issues. 

The effectiveness of a metalworking fluid for heat transfer and as a lubricant decreases for a number of reasons.  Fluids break down in process; they accumulate foreign substances including tramp oil, swarf, dissolved minerals, and/or dirt from the process.  These substances prevent the metalworking fluid from working.  Selective depletion of a fluid component could also reduce effectiveness.  For example, swarf is particulate metal created during the grinding or cutting of metals.  The presence of swarf creates friction, defeating both the lubricating ability and cooling ability of the fluid.  The increased concentration of tramp oil similarly interferes. 

In addition, the heat of the operation and the chemical reactivity of swarf fines initiate degradation of the metalworking fluid.  These particles chemically interact with the oils in emulsions, weakening the emulsion and breaking it apart.  Swarf also facilitates the growth of bacteria and fungi that feed on the fluid by providing a substrate for them to grow on, causing what is called coolant spoilage.

The number one problem with most metalworking fluids is microbial contamination. Bacteria and other microbial organisms thrive in the environment created by the impurities in the metalworking fluid.  They feed on minerals oils, fatty acids, emulsifiers, corrosion inhibitors, other additives and waxes in metalworking fluids.  Bacterial growth can produce noxious byproducts such as hydrogen sulfide, commonly referred to as the Monday morning odor. These are just a few areas where Staveley Service Fluids Analysis can help you to monitor and control your fluids.

There are four primary metalworking fluid types in use today.  They are generally categorized and contain the additives and constituents listed here.

Staveley Services Fluids Analysis has specific test packages designed for each type of fluid, depending on its basestock and additive makeup. In addition to the types of Metalworking Fluids above, Staveley has additional testing available for Quench Oils and offers extensive testing for specific additives and concentrates to ensure the product you are using is within manufacturers’ specifications. The right combination of testing supplies you with valuable information to help you maintain the highest level of fluid performance and long fluid life.

For more information on Staveley’s Metalworking test capabilities please click here.