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Metalworking Fluids 101: How to Control Bacterial and Fungi Growth

Controlling bacterial and fungi growth in metalworking fluids is important to maintain performance and prevent contamination in the machining environment.

Here are some standard practices for managing bacterial and fungal growth:

  1. Regular Maintenance: Regular maintenance of the metalworking fluid system, including filtering and topping up, help remove contaminants and maintain fluid quality.
  2. Chemical Additives: Biocides or fungicides can be added to the fluid to control bacterial or fungal growth. These additives should be carefully selected and implemented following the manufacturer’s recommendations. This avoids adverse effects on fluid performance and the environment.
  3. Storage: Proper storage of metalworking fluids includes keeping containers sealed and protected from contamination. This helps prevent bacterial or fungal growth.
  4. Proper Temperature Control: Reduce bacterial and fungal growth by maintaining fluid temperatures within a specific range. Achieve this through appropriate system design and temperature control, such as cooling systems or heat exchangers.
  5. Regular Testing: Testing of your fluid identifies any changes in quality, such as bacterial or fungal growth. This allows prompt corrective action.
    Establishing and following a comprehensive maintenance program is essential to maintain fluid quality.

Here are a few tips to keep your fluids working longer for you:

Clean Your System Before Introducing Fresh Metalworking Fluid

Cleaning a metalworking fluid (MWF) system before introducing fresh coolant is vital to ensure that the new coolant performs effectively and prevents contamination. Keeping the MWF delivery system running cannot be ignored; otherwise, you are exposing the new fluid to the same conditions that force you to change the fluid in the first place. By draining the sump only, you are disposing of most of the bacteria/fungi, but as long as there is some residual MWF in the system, there will be some residual bacteria/fungi.

These bacteria/fungi consume the metalworking fluid’s organic components (oil and other additives). You provide a free food supply by allowing them to come into contact with fresh fluid. Due to the abundance of food, they will rapidly multiply. Within a short period, you will find yourself pumping out the machine tool sump again.

The proper addition of biocide should kill existing bacteria and fungi, and then the coolant should be pumped out and discarded. Use a suitable cleaner and circulate it through the system. Then, remove the cleaner and rinse before refilling with fresh MWF.

Bacterial and Fungi Growth Cleaning Tips

Here are some reasons why cleaning the system is essential:

  1. Removes Contaminants: Cleaning the system removes any accumulated debris, oil residues, or other contaminants, improving fluid performance and extending fluid life.
  2. Prevents Cross-Contamination: Cleaning the system before introducing fresh fluid helps prevent cross-contamination from previous fluids, which could affect the performance of the new fluid and create machine issues.
  3. Improves Surface Finish: Cleaning the system helps remove any buildup of debris or residue on machined parts, improving surface finish and reducing post-processing requirements.
  4.  Maintaining System Efficiency: Cleaning the system helps maintain system efficiency, reducing the amount of fluid required and maintenance costs.
    The method of cleaning a metalworking fluid system will depend on the specific requirements of the system and the type of fluid. However, following the manufacturer’s recommendations and taking proper safety precautions when cleaning the system is essential.

Operate the System at the Correct Concentration

All water-based metalworking fluids are designed to be operated at a given concentration dissolved or emulsified with water. The correct concentration, measured with a refractometer, is vital to provide the cutting operation with optimal lubricity and cooling, corrosion protection, and resistance to bacteria and fungus. Operating a system at a low concentration may decrease tool life, create bacteria and/or fungus problems, possible corrosion, and eventual unplanned downtime. Conversely, operating the system at too high a concentration may result in dermatitis, foaming, and heavy residues.

Installation of a venturi mixer or a proportioning pump is critical to maintaining consistent fluid values such as pH. It will aid in the elimination of metalworking fluid and concentration-related problems.

Premix the MWF concentrate with pure water at your manufacturer’s recommended values for the initial charge. To maintain the recommended range, machine concentration must be checked frequently and adjusted with pure water, concentrate, or premixed fluid.

Ensure Makeup Water Is of Adequate Quality

The quality of makeup water is another point to take into consideration for bacterial and fungi growth. A simple thing such as the hardness factor can impact quality. Test your water hardness using hardness test strips.

Water used for making MWF mixtures should be as pure as possible. This is the most economical and trouble-free solution. Minerals in metalworking fluid water can corrode machine tools and machined parts. It can also aggravate the deposition of residues on machine tools. This increases the rate at which bacteria and fungi grow in the metalworking fluid.

Water that contains specific dissolved ions such as calcium and magnesium are considered “hard”. It forms a scale with evaporation and will form insoluble soap scum when mixed with many MWFs. Again, always test your water with hardness test strips.

Other minerals, such as sulfates, are detrimental. This is because they promote the growth of sulfate-reducing bacteria that produce a “rotten egg” odor. Eliminate the odor with odor control tablets. These have no impact on the properties of the MWF solution.

Additionally, chlorides and minerals can be corrosive to metal and contribute to rust. The more concentrated these minerals are, the faster they build up and cause adverse effects. Therefore, the purer the water for making MWF mixtures, the longer the fluid can remain in production before issues develop.

One method of removing minerals is to run them through a zeolite softener followed by a reverse osmosis filter. Purified water can also be produced by deionization, eliminating most dissolved minerals, thus creating a higher-quality water.

Incorporate Biocides

The incorporation of effective biocides is also helpful in preventing degradation caused by bacterial action. These compounds may be incorporated as components in formulated MWFs or may be added to MWFs before and during use. Biocidal activity should be broad enough to suppress the growth of a highly diverse contaminant population. Over time, chemical and biological demands may consume the biocides. This causes the concentrations to fall below those needed to inhibit microbial growth. Therefore, biocides should be added judiciously to prevent microbial growth or to arrest modest growth. Some biocides that function very well in cleaning products can serve as food for the various types of bacteria found in water-miscible fluids that are so easily contaminated.

Grossly contaminated fluids should be treated if necessary with biocide just before being pumped out as part of the overall cleaning procedure. However, this should be done after operators have ceased working with the fluid (i.e., off shift). Consistant monitoring and prevention of microbial growth is the best approach. This prevents the buildup of endotoxins and other hazardous biological substances. You then preserve your fluid quality and function.

Miscellaneous Factors

A good filtration system should be in place to avoid repetitive problems related to bacterial and fungi growth. Metalworking fluid is subjected to the metal chips and fines of the process. Also airborne contamination from cascading fluid over a part and the machine. Pay attention to machine leakages, residues left on the parts from previous operations, water, operators, and other factors. Whenever possible, minimize contaminants.

The buildup of chips and metal fines in the metalworking delivery system provides an excellent “nesting” area for bacteria. In large systems, these chip beds may extend for many yards in sluices and pipes. The associated biomass will be too large for simple treatment with biocides to be effective. The periodic removal of this debris minimizes the potential for bacteria growth and extends MWF life.

Following these recommendations will help you maintain your MWF. If you have other questions about the bacterial and fungal growth in metalworking fluids, don’t hesitate to reach out to our specialists. We are happy to help you!

 

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