| Assuming that the right fluid was selected in the first place, there are
many possible signs that a fluid is not performing well. Signs might include one or more
of the following: |
 | rust or corrosion of the machine tool or of the part produced |
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| foul odor (rancidity) of the fluid due to oxidation or bacterial growth (especially
important for water-miscible
formulations) |
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| tool failure due to loss of performance additives |
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| growth of fungi that block fluid flow |
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| failure at the workpiece-tool interface (for example, burning of a ground part due to
excessive heat build-up) |
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| excessive foam |
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To understand why fluids fail, it is essential to understand that metal removal fluids
in use change over time. The composition of an "in-use"
MRF will be different from the MRF in its "as-received"
state—its state as it comes from the supplier.
Why do metal removal fluids change over time?
As used in the shop, MRFs are affected by both their environment and their use. Because
the characteristics of MRF systems vary widely, the same product used in two systems may
have very different compositions after a period of use.
These changes stem from two main causes:
- decreases or increases of different components of the fluid
- contamination of the systems
Some components of the MRF become more concentrated in use, while others tend to be
used up as parts and chips carry them away. For example, materials such as alkanolamines
and inorganic salts tend to concentrate as water evaporates from a system, while more
surface-active chemicals and biocides tend to be used up as parts and chips carry them
away.
In general, adding the MRF concentrate on a routine basis will keep fluid components in
balance. These product additions should be based on a regular program of chemical testing.
Such testing can indicate whether fluid concentrate or specific components need to be
added to the fluid.
Process contaminants also affect the performance of an in-use fluid. The machining
process can add chips, graphite fines, grinding wheel debris, and dissolved metals.
Lubricants used as hydraulic oils, spindle oils, slideway lubes, greases, and gear
lubricants can find their way into the fluid as tramp
oil. Without proper filtration and tramp oil removal systems, these process
contaminants can build up over time and decrease the performance of a metal removal fluid.
Unwanted microorganisms can grow in all water-miscible metal removal fluids.Many fluid
components can act as food sources for these microorganisms. However, contaminants that
have nothing to do with the machining process, such as shop rags, food waste, mop water,
cigarette butts and other materials, often find their way into the fluid system. They
bring microorganisms with them, and they also provide food for these microorganisms. As
bacteria grow in a fluid system, they can remove needed components and produce odors,
rust, performance problems, and product instability. The growth of fungus can clog pipes
and nozzles.
Microorganisms usually aren't a problem with straight oils. But straight oil MRF can
still deteriorate and produce undesirable effects. Straight oils still need to be tested
using a regular program of laboratory analysis.
Contamination reduces the performance and effective life of metal removal fluids.
Contamination can also contribute to adverse health effects for those who work with
metal removal fluids. Recently, endotoxins, a by-product of Gram-negative bacterial
growth, have been identified as a potential health risk.
The metal removal process itself can produce metallic contaminants, such as nickel and
cobalt, which have adverse health effects. These possible effects are discussed more fully
in Health Issues.
See Managing MRF to find out
how to make sure the metal removal fluid is kept in good condition.
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Contact Chris Roman, 