Water-based fluids were a great breakthrough for the machining market. As speeds and feeds of the machines were increased, the need for cooling became essential. However, with the introduction of water-based products new challenges arose.
Water-based fluids have a finite life. This means that no matter how good your fluid maintenance program is, the fluid will eventually need to be drained and disposed. There are numerous reasons for this: biological growth, pH drift, corrosion issues, emulsion split, and introduction of tramp oil. All of these failure factors are intertwined with one another. In the beginning, as use of water-based fluids increased, these fluids were being dumped and re-charged on a weekly basis. Fluid maintenance was not even a thought at that time.
There were two major events that drove the industry towards development of fluid maintenance practices. First, major manufacturers wanted to minimize downtime and maximize output. This could be done by extending the drain intervals for the fluid. Second, metalworking waste was characterized as a hazardous waste and needed to be handled and disposed of as such. Extending the fluid life in the sump would decrease disposal costs that this introduced.
Practices were put into place to monitor the important characteristics of the fluids, helping to reveal when a fluid might be degrading so that operators can treat the sump before it fails. Fluid manufacturers recognized that in addition to monitoring providing longer life fluids by introducing antimicrobial and buffering agents would also help increase the sump life of the fluid.
Fast forward to today: although metalworking fluids have greatly improved fluid life across the board thanks to both fluid monitoring practices and long-life fluid properties, the extended sump life comes with it’s own challenges that need to be addressed in the machining process to keep manufacturing up and running smoothly.
With extended fluid life came the following concerns:
- Hard water increases through evaporation and machining process.
- Negatives: emulsion split, hard water soap build up in the system, corrosion.
- Depletion of specific additives through filtering.
- Antifoam is typically filtered out of the fluid at a greater level than reintroduced via fluid top-off. As antifoam is depleted, foaming issues increase. Negatives: foam overs leading to messes and downtime and reduced lubricity from the entrapped air which decreases tool-life and product finish.
- Depletion of specific additives through chemistry.
- Antimicrobials: in a system that is highly contaminated bacteria as you charge new fluid or has been allowed to become highly contaminated via lack of maintenance will use up the antimicrobials faster than they can be replenished with fluid top-off. This will cause a sump to go rancid much quicker. Negatives: foul smell, grey sump, exposure of bacteria and endotoxins to operators, decrease in pH, and increase in corrosion.
- Buffering additives: in a system that is highly contaminated with bacteria as you charge new fluid or has been allowed to become highly contaminated via lack of maintenance will use up the buffering faster than then can be replenished with fluid top-off. This is because bacteria produce acidic by-products as they metabolize food. Buffering agents are added to metalworking fluids because they are designed to hold a specific pH even as more and more acid is added. However, they all have a breakpoint so as more acid is produced, it is a strain on the buffering additives. Negatives: decrease pH, increased corrosion, bacteria growth (metalworking fluids are designed to provide an inhospitable environment by keeping the pH higher, as the pH falls bacteria will thrive).
- Accumulation of tramp oils.
- Negatives: increase anaerobic bacteria (tramp oil will float and sit on the top of the fluid especially during shutdowns), emulsion split.
- Accumulation of chips and swarf (metal ‘dust’)
- Negatives: increase surface area for bacterial growth and metal pitting/corrosion.
With extended fluid life came the following positives:
- Sustainability by reducing fluid waste and practicing proper disposal.
- Cost savings by reducing fluid waste and downtime between sump change overs.
- Increase profits by increasing throughput thanks to a decrease in downtime
Conclusion: Not all metalworking fluids are created equally
Modern metalworking fluids have been designed to include multifunctional additives to help extend the life of the fluid. They build in buffering agents that can maintain a pH that is inhospitable to bacteria making it difficult for them to reproduce. Maintaining pH also helps protect the metal from corrosion by decreasing the acidic by-products produced by the bacteria. They often contain wetting agents that carry chips and swarf to filters as the fluid is being recirculated so there is less build-up on machine surfaces. Often these fluids will have a higher cost per gallon than traditional fluids. However, it must be taken into account that if they last longer, lead to less disposal costs, and protect both the machine and finished parts from corrosion the overall cost to the machine shop is less.
Typical long-life fluids:
- Synthetic fluids
- Do not contain bacteria ‘food’ such as oil and emulsifiers
- Semi-synthetic fluids
- Built in buffering additives
- Emulsifiable oils
- If they are fortified with properly utilized antimicrobial products
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