Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
metal removal fluid. Gear oils, for example, are very high viscosity versus a lower viscosity oil in the base metal removal fluid.
4. Loss of pH. The emulsifier packages in most emulsifiable oils and semisynthetic are designed to operate at pH ranges between 9.0 and 9.5. For non-ferrous metals, the pH would best not exceed 9.2 to avoid staining the base metal. Over time in very dry conditions, the amine packages in the metal removal fluid can selectively evaporate causing a drop in pH. Bacteria growing in and on surfaces of the machine tool and fluid sump can release acids that also lower the pH. Some steel rolling mills coat their products with “slushing oils” that may have a weak acid present that also lowers the pH.
Small pH drops from 9.3 to 8.9 may be acceptable and will not cause significant fluid damage. However, if the pH drops below 8.0, irreversible damage to the emulsifier package may occur, which will be impossible to restore.
Control plan for pH:
Discuss the acceptable ranges of pH with the manufacturer. Their typical ranges may be between 9.0 and 9.3. The use of primary and tertiary alkanolamines (MEA, TEA) may be added sump side. Less aggressive amines such as Monoisopropanolamine (MIPA), and amino-methyl propanol (AMP) may be added if there is a risk of ammonia release from the fluid.
Caution Avoid using inorganic bases such as sodium or potassium hydroxides. These reactive bases have minimal buffering and can result in overshooting the high range of pH. (9.3). Excessively high fluid pH can be irritating to the worker, or worse, can cause severe chemical burns, as can be seen in Figure 4.
36 LUBE MAGAZINE NO.174 APRIL 2023
No.145 page 5
Figure 4: Failure Mechanism #4 - Lack of pH Control. .
In all cases, add the pH-correcting fluid in small doses to prevent overshooting. Always use a calibrated (2 point, 7 & 10 ) pH meter and not pH paper. pH paper is difficult to read in the narrow ranges of 9.0 to 9.3, and the reactive pH surfaces of the paper lose sensitivity over time. This is especially true in high humidity conditions.
5. Effects from microorganisms (bacteria and fungus).
Bacteria and fungi can have an extremely detrimental impact on the useful life of a metal removal fluid.
Bacteria can grow rapidly, produce acids that lower pH, cause corrosion, and produce foul odors. Some types of bacteria can cause health problems such as hypersensitivity pneumonitis (HP). Bacteria can grow in the fluid and consume certain additives. They can grow on machine surfaces in the form of biofilms. They can enter metal removal systems from the water source, residues on parts, and airborne contaminants.
Fungi typically (but not exclusively) grow on the machine tool and support surfaces such as filters and associated piping. They can produce foul odors such as “sweaty socks”. They can grow in lengths of more than one meter and break away, clogging filters and piping systems. They are dimensionally “thick” (centimeters or more) and are difficult to kill with fungicides.
Control plan for bacteria and fungus: The best approach would entail the use of biostable/
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