SECTOR FOCUS: REGULATION
Developing a new seal test under ISO 1817 for use with metalworking fluids
Dr. Stephan Baumgärtel, Verband Schmierstoff - Industrie e.V.
Metalworking fluids (MWFs) are used in workshops worldwide for the cutting and forming of metals. Their main purposes are to cool and lubricate cutting heads, workpieces and machine tools, inhibit corrosion and remove fine filings of metal, known as swarf, from the cutting work area.
MWFs can consist of a variety of base oils and additives to best fulfill the above tasks depending on the application. In addition, MWFs should not pose a health risk. Less attention is often paid to the interaction between machine tools and MWF. There is a huge range of various elastomers available on the market. In a single lathe, dozens of different materials can be found.
Some chemicals used for blending MWF are known to be critical components for sealing materials. As a general rule, polar additives, additives in which the molecules are oppositely charged, dissolve better in rather polar sealing compounds when compared with non-polar additives on which the the molecules are equally charged. Similarly base oils used in metalworking fluids dissolve better in non-polar sealing materials. However, although this is a useful rule of thumb, it does not replace a compatibility test.
Some combinations of various MWFs and elastomers can result in more or less severe change of elastomer properties, sometimes resulting in the complete destruction of the test materials (Figure 1).
In several new formulation technologies, especially in so-called “high pH” or strong alkaline products, a number of problems with seal compatibility were observed. Seals and paints were strongly attacked causing their corrosion and failure even though
20 LUBE MAGAZINE NO.170 AUGUST 2022
these fluids were often said to have “excellent hydrolysis resistance” by the
manufacturers.as well as, “resistance to microorganisms”, “excellent resistance to oils, greases and many solvents“ and “resistance to lubricants, moisture and chemicals”.
Figure 1: Test bar after storage in “unsuitable” MWF.
As already mentioned, modern tool machines contain a wide variety of elastomers and sometimes even the original equipment manufacturer (OEM) don’t know which materials are used, especially for compounds delivered from 3rd party suppliers.
The behaviour of elastomers towards cutting fluids is difficult to predict, because of the wide variety of formulations of both additives and base oils. In general, the compatibility for generic chemicals and generic elastomers is known, but not necessarily for newer mixtures and recently developed elastomers. Compatibility testing is usually laboratory-specific; that is to say, many lubricant manufacturers have their own “in house” testing procedures, with limited read across to other laboratories.
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