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Figure 3. Cobalt leaching capacity of different EP-, anti-wear and friction modifying additives

The accumulation of cobalt in metalworking fluids can be significantly reduced by using suitable inhibitors. To prevent the accumulation for the long-term it is additionally necessary to select any component of the metalworking fluid with a low potential to leach and accumulate cobalt. This is not only important for water-mixed MWF where the different kinds of amines are the main perpetrators of cobalt leaching. Unsuitable additives are also able to increase the cobalt content of metalworking oils to more than 1000 ppm. Particularly anti-wear additives based on acidic or neutralised phosphoric acid partial esters can accumulate high concentrations of cobalt (figure 3).

By combining suitable additives and base oils it was e.g. possible to develop a special grinding oil for the production of cutting tools made of cemented carbide. After a field test period of more than 20 months the cobalt concentration in the grinding oil was still below 2 ppm which was also the measuring accuracy of the analytical method.

Nickel: Nickel is the main component of many high performing metal alloys like Monel, Nimonic or Inconel. It is also an important alloying element in many types of stainless steel, providing toughness and increased tensile strength. Dissolved in aqueous solutions or neat oils it forms ions which can cause heavy allergic reactions. The accumulation of nickel in water or neat oil metalworking fluids can be effectively reduced by suitable inhibitors.

Other heavy metals: Lead, chromium, zinc, copper or manganese are also regularly used as alloying elements for several types of steel or non-ferrous alloys. Due to their

toxicological or ecotoxicological effects limits for the exposure at the workplace or into the environment are already existing or expected within a short time. Therefore it is an important task of the lubricant and lubricant additive manufacturers to develop suitable products which prevent the release into and accumulation of heavy metals in metalworking fluids at best.


The political, technological and economic conditions for the use of additives in metalworking fluids will certainly become more tight and demanding in future. As a result of the technical progress the requirements on materials and machining processes as well as on the protection of human health and the environment are continuously increasing.

In order to meet those demands, there is a clear need for an adjustment of existing additives, respectively a development of appropriate new additives which provide high performance for challenging metalworking processes. Furthermore, it will become indispensable for all new additives and metalworking fluids to comply with requirements on low toxicity towards machine operators and low ecotoxicity. Therefore, a successful adaption of metalworking fluids to future requirements needs a much closer cooperation between the developers of new production processes and new materials, the lubricant formulators, base oil suppliers and the additive manufacturers.




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