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Managing MRF
Facilities & Equipment
Health Issues
Employers/Employees
Management Plan
Introduction
What are metal removal fluids?
| Metal removal fluids (MRFs), collectively, are one of four fluids that are
known broadly as metalworking fluids as outlined in Figure 1. Other
metalworking fluids include those used for metal forming, metal protecting,
and metal treating. In this guide, we will focus on the metal removal fluids,
a broad range of products that include those products designed for machining, grinding,
broaching, honing or any other process in which metal is removed to obtain the final
product. The four basic types of metal removal fluids and the corresponding U.S.
usage is shown in Figure 2. |
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| Purposes of MRF |
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cooling |
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lubrication |
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| Why use metal removal fluids? |
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| Metal removal fluids have two primary functions: to cool
and to lubricate. |
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| The metal removal process—regardless of its
type—generates a tremendous amount of heat. This heat must be reduced in order to
achieve productivity and part quality. The cooling effect provided by a metal removal
fluid gives the cutting tool or grinding wheel a longer life and helps to prevent burning
and smoking. |
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| At the point where the tool is in contact with the part,
lubrication is necessary to reduce friction between the tool and the part. Lubrication may
be physical, boundary, or chemical. |
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| Physical lubrication is provided by a thin film of
lubricating component. Boundary lubrication occurs when a specially included
component attaches itself to the surface of the metallic part being machined, such as an
aluminum casting. Chemical lubrication occurs when a component of the machining
or grinding fluid reacts with the metallic component being machined, resulting in improved
tool life, better finishes, or both. |
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corrosion
protection |
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removal of chips |
| Besides the primary functions of cooling and lubricating, metal removal
fluids have a number of secondary functions: |
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 | to provide corrosion protection for the part and the machine |
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| to assist in the removal of chips or swarf (an accumulation of fine metal and abrasive
particles) from the machining or grinding of the part |
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| in central systems, to transport the chips and swarf away from the machine tool |
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| to lubricate the machine tool itself |
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For example, almost all machine tools include at least
some amount of steel, aluminum or brass, which could rust or corrode. For that reason, water-miscible metal removal fluid
formulations (those fluids that are meant to be diluted with water) include components
that slow or prevent such corrosion. Additionally, every metal removal operation involves
formation of at least some swarf or metal chips that must be removed from the cutting
zone. Metal removal fluids—and the circulating systems, which carry the fluid within
the machine tool or from machine tool to a central filter—are designed to carry swarf
or chips to a device that will filter out most, if not all, of these metal particles
before the fluid is recirculated back to the machine tool. |
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| straight oil
soluble oil
semisynthetic
synthetic |
| What are the types of
metal removal fluids? |
| Metal removal fluids are commonly identified as one of four types:
straight or neat oils, soluble oils, semisynthetics, and synthetics. |
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| Straight
oil is a metal removal fluid that is mostly mineral or vegetable oils. The
mineral (petroleum) oils used for these fluids today are "severely solvent
refined" or "severely hydrotreated." These processes remove possible
cancer-causing substances (read additional information on the cancer risk of petroleum oils). Other oils of animal,
marine or synthetic origin may also be used in these fluids. Additives to improve
performance and increase the useful life of the fluids are usually present. |
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| Straight oil MRFs are generally used for processes that require
lubrication rather than cooling (slow cut speeds, high metal-to-metal contact) or with
older machines designed for use only with straight oils. |
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| Straight oil MRF systems require larger filters and may require fire
protection, making them more costly than soluble oil systems. Straight oil MRF is usually
more costly per gallon than soluble oil and water mixtures. |
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| For further information about what additives are used in straight oils,
see Table 1. |
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| Soluble
oil (or emulsifiable oil) is a combination of 30-85% of severely refined
mineral oil, as described above, and emulsifiers to help disperse the oil in water. The
fluid concentrate usually includes other additives to improve performance and lengthen the
life of the fluid. Soluble oil products are supplied as concentrates that are diluted with
water to obtain the working fluid. Depending on the fluid and the application, the
concentrate may be diluted one part concentrate to five parts of water up to one part
concentrate to forty parts of water (17% to 2.4%). |
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| Soluble oils as a class provide good lubrication. In addition, they
provide improved cooling as compared to straight oils. On the other hand, soluble oils
sometimes have poor corrosion control, are sometimes "dirty" (i.e., machine tool
surfaces and nearby areas become covered with oil or difficult-to-remove product
residues), may smoke (they may not cool as well as semisynthetics and synthetics), and may
have poor mix stability or short sump life. |
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| We need to point out that there is a difference between
"commodity" soluble oils, which contain few, if any, additives for improving
performance, and "premium" soluble oils, which offer high performance and
a longer fluid life. |
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| For further information on the ingredients of soluble oil MRF, see Table 2. |
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| Semisynthetic
metal removal fluids contain a detergent package to lower the surface tension of water and
aid in "wetting" of the part. Semisynthetic fluids are similar to the true
synthetic fluids. However, they do contain some petroleum oil, perhaps 5-30% in the
concentrate. Like all fluid types, they contain additives to improve performance and
increase fluid life. |
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| The concentrates of these products are transparent, and typically after
dilution they are transparent or translucent. They are diluted with five to forty parts
water (17% to 2.4%). Semisynthetics are perhaps the most complex of metal removal fluid
formulations. They offer good lubrication, good heat reduction, good rust control, have
longer sump life and are cleaner than soluble oils. On the negative side, this class of
products has a greater tendency to foam in soft water and can be unstable in hard water. |
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| For further information on the components of semisynthetic MRF, see Table 3. |
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| Synthetic
metal removal formulations do not contain any petroleum oil. They contain detergent-like
components to help "wet" the part and other additives to improve performance.
Synthetic fluids are diluted with water the same way soluble oils and semisynthetic fluids
are. |
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| Among the four types of fluids, these are the cleanest, offer the best
heat reduction, have excellent rust control, offer longer sump life, are transparent
(allowing the operator to see his or her work), and are largely unaffected by hard water.
On the other hand, some synthetics offer poor physical lubrication and can foam in some
applications. |
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| Most synthetic MRFs form true solutions with water (unlike emulsions,
which are not solutions) that are difficult to break down for disposal. However, there is
a small sub-class of synthetics, called emulsifiable synthetics, that contain insoluble
esters in place of oil. These fluids have the milky appearance of soluble oils and provide
good lubrication. |
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| For further information on what's in synthetic MRF, see Table 4. |
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Contact Chris Roman, 