Metal Working Fluid Analysis–More Than Looking at Bugs and Gunk
by Michael Holloway, CLS, OMA I
National Sales Manager

Working metal requires cutting metal. When there is metal to metal contact a parts get hot. If it is just one pass then the part or tool (bit or blade) can cool but if there are many parts being worked there is little if any time to cool the tool – enter metal working fluids. Grinding, sawing, milling drilling, reaming, boring, tapping or threading will require a stream or bath of fluid to keep the part and tool cool. The fluid will also extend tool life by reducing friction as well as protection against corrosion. Metal working fluids also are designed to carry away chips (AKA swarf). The fluids can be 100% mineral oil based, an oil water mixture (either an oil water emulsion or a soluble solution), or synthetic. The type of fluid used depends on the type of work. Each fluid has its own characteristics and design features yet they all experience many of the same problems. Often the fluid has a direct influence on tool life and part quality yet many machine shops do not correct the problem until it is too late. This results in lower production rates, increased tool usage, lower part quality and in some cases operator safety.

Fluid analysis can provide invaluable information about a system. It conveys information without having to stop the process. There are several tests that are run on metal working fluids that provide insight into the health of the fluid but also provide an explanation of production issues. The following table covers several production issues, why they might be occurring and what to test for to confirm.

Issue Why? What To Test For
Poor Part Finish If an oil, it needs more extreme pressure performance, if it is a water/oil emulsion it needs remixing. In oil, look for the proper sulfur content but too much sulfur in the formula can stain copper, brass and bronze. Chlorine content is important as well because of the high synergistic effect it has with sulfur. Phosphorous is a common extreme pressure compound used but it breaks down at lower temperatures. The concentration of sulfur, chlorine or phosphorous compounds are too lean. Look to compare the sample against a reference.
Lower than Normal Tool Life
If an oil, it needs less extreme pressure additive in oil, if it is a water / oil emulsion it needs remixing.

In oils, the concentration of sulfur, chlorine or phosphorous compounds are too rich. Look to compare the sample against a reference.
Part is Discolored or Stained
If an oil, water is the main culprit. If a water soluble fluids, the pH may be out of balance or there is bacteria in the system. The part may not be getting enough coolant or in a water soluble fluids, the oil part of the ratio may be too low.
Test for water if using an oil. Test for proper pH and bacteria if a water mixture. Test for the proper concentration balance of water to oil.
There is Excessive Smoke
If an oil, slow down the feed rates, if a water mixture there may be tramp oil in the system.
For oil system test for viscosity – compare to reference. If water mixture test for tramp oil.
The Fluid Foams
If an oil, water is the main culprit. If using a water soluble fluids, check fluid levels and adjust mixture to the proper water oil ratio. For oil test for water. For water soluble fluids, test refractive index to determine if the proper mix ratio is being used.
Skin Rashes In both oils and water soluble fluids, metallic fines and bacteria will create dermatitis. Test for fines, bacteria and ICP for Cobalt.

The following table looks at preventing problems by testing.

Fluid Properties Test Reason
Water Oil Mix Ratio
Refractometer, Alkalinity

If the balance is off, fluid and tool life as well as part finish can be affected.

Rust and Corrosion Protection Copper, iron Coupon Test, HPLC to test for additive concentration

If the active ingredients are reduced, fluid and tool life as well as part finish can be affected.

Water Hardness in Water Soluble fluids Water Hardness

Hardness > 200ppm can produce mix stability issues,
Hardness < 50 ppm can lead to foaming.

Chlorine Content Chlorine Titration Chloride > 50 ppm can inhibit rust prevention.
Sulfate Content Sulfate Sulfate > 100 ppm can promote corrosion & microbes.
pH for Water Soluble Fluids pH The pH between 8.5 – 9.5 (7-8 for aluminum) is the optimum for fluid, tool and part life.
Tramp Oil Babcock Bottles and Centrifuge Tramp oil in the system will shorten fluid and tool life as well as part finish can be affected.
Biological Growth Culture Fluid for direct response

Bacteria in the system will shorten fluid and tool life, part finish can be affected.

Bacteria can cause dermatitis and a foul smell.

ALS offers a unique service in the industry. There are no other dedicated commercial metalworking labs with the service scope and technical expertise that ALS has in North America. The laboratory is state of the art with staff whose expertise rests in testing metalworking fluids. ALS provides unmatched service for blenders, distributors and end users.

ALS Tribology prides itself on being able to solve the most complicated metal working fluid issues. We challenge you to bring us a metal working fluid problem we can’t figure out how to solve.