Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
Figure 2b: Failure Mechanism #1 - Cation Attack.
Control plan for metals being machined: Remove the reactive chips from the fluid as soon as possible, typically within 48 hours of the chip generation. Cations will continue to be released from chips as long as they are in contact with the fluid. Use full-flow, not side-stream filtration during the metal cutting process. When choosing your filtration media, start at 30 micron. For emulsions, do not go below 10 micron, or there is a possibility of stripping out desirable components of the metal removal fluid. Defoamers will be removed first.
Use polyester filter media instead of polypropylene. Polyester media does not have an affinity to adsorb oil, therefore it will not remove the oil phase of the fluid. If the fluid is saturated with tramp oil, polypropylene media can be used, but only for a short time or until the tramp oil is at a manageable level.
1b. Attack by positively charged contaminants: water hardness Water harness typically consists of calcium and/or magnesium ions, and a limited amount of iron ions. The same failure effect described in 1a above is the same failure effect of water hardness releasing cations of calcium and magnesium. The failure reaction of hard water cations from water occurs in a matter of a few minutes. Since water in the manufacturing metal removal area evaporates preferentially, the cation load from the water increases over time. Metal removal systems generate a significant amount of heat (such as in a grinding operation), and evaporate the water phase rapidly, leading to an increased rate of fluid failure.
34 LUBE MAGAZINE NO.174 APRIL 2023
No.145 page 3
Between the cations released from the metal cut or the water supplied for dilution, the effect can be devastating on the fluid stability as well as the metal removal process.
Table 1 depicts how various cations interact in hard water, the metal removal process, and in wastewater treatment to split emulsions.
2. Effects of negatively charged contaminants There are 5 primary anions of concern: chlorides, sulfates, phosphates, nitrites/nitrates, and carbonates.
Note that as anions build in the fluid, the fluid itself does not fail directly. It is how the fluid performs in the metal removal system that fails, either by corrosion or increased bacteria and fungus growth. Table 2 is a summary of the effect of these anions.
Control plan for water-related issues: Purify the water by either reverse osmosis (RO) or de-ionisation (DI). Although these two methods are dissimilar in how they purify water, the final result on the fluid is essentially the same. The target level for water purity is a total dissolved solids (TDS)
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