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| Cleanliness is essential to the proper function of metal removal
fluids. During use, metal removal fluid becomes contaminated with debris ranging from
large chips to microscopic metal or abrasive particles. |
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| The largest material is removed by separation
techniques such as settling. Smaller particles can also be removed by settling if the
system allows sufficient time without agitation of the fluid. But the smallest particles
are not effectively removed by separation techniques. If the very small particles need to
be removed for proper machine performance, then filtration
methods are needed. Filtration uses different techniques to clean the fluid, depending
on what type of particle needs to be removed and how clean the fluid must be.. |
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How should a filtration system be designed?
 | The plant layout should provide space for maintenance (drum and pump removal, etc.),
media replacement, and chip handling |
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| New system design should include a reserve capacity of a minimum of 25% over machining
and flush requirements. |
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| The process engineer should supply the metal removal fluids engineer with complete
foundation, utility, and MRF requirements, as well as machine and layout drawings. |
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| When high-pressure MRF is required for special operations on a machining line, the
machine tool supplier should furnish all necessary pumps, valves, secondary filtration,
piping, etc. to increase the pressure from the system MRF supply |
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| Central systems can be equipped with a liquid level indicator—float, bubbler or
electronic. Automatic high/low alarms with automatic water make-up are recommended. |
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| The process tooling and MRF engineers should work together to prevent chip bundles that
can block the machine discharge or trench. |
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| Standardizing pump and motor selection throughout the facility helps reduce parts
inventory and maintenance training, so it’s a good idea to coordinate with facilities
engineering and maintenance. |
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| System pumps should be selected to operate in the most efficient range on the
manufacturer's pump curve. For energy conservation, variable-speed pump controls should be
considered for all new central systems over 2000 GPM. |
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Find out how to size a central system.
| Important considerations for a metal removal fluid filtration system are,
of course, the filter media and filters. |
How is the type of filtration for a system selected?
| Just as in flume design,
each of the various metals being machined—aluminum, cast or nodular iron, and
steel—has characteristics that affect the decision as to the type of filtration and
chip handling to be used for a specific manufacturing process. |
Aluminum
| Most aluminum used is cast aluminum alloys ranging from SAE 308 to
SAE 390. The type of chip generated depends on the type of operation (turning, boring,
milling, etc.). Most aluminum chips do not present major handling problems, although
ductile aluminum may form bundles in turning operations. Water-soluble MRF is normally
used when machining aluminum. The most notable exception is when a light mineral oil is
used to aid in holding micro-finish and critical tolerances. Due to the light weight of
aluminum, the use of settling tanks is ineffective, as the aluminum chips tend to float or
stay in suspension. To remove heavy aluminum chip loads prior to filtration, a
flow-through wedge-wire tank with a drag conveyor is required. |
Cast iron/nodular iron
| Water-soluble MRF is used for most cast iron machining. Cast iron
breaks up into small, heavy granular chips that settle out readily. An overflowing
settling tank with a drag conveyor is used to remove heavy chip loads prior to filtration. |
Steel
| Most steel machining is done with a water-soluble MRF. Some operations (especially
gear machining) are done with a mineral oil to provide lubrication for heavy stock
removal. Steel, when machined, produces a wide range of chips, depending on the type of
machining being done and material composition. Turning and boring usually produce a long,
stringy chip, which is the most difficult to handle. Often stringy chips will entangle and
form large bundles that are difficult to move through the flumes. The use of a chip
breaker at the tool may help prevent the formation of large bundles. An overflowing hinge
pan or screw conveyor can be used to remove the large bundles and strings prior to the
main filter. If long, stringy chips are not expected, an overflowing settling tank with drag conveyor can be used prior to the
filter. |
Why do grinding operations create different problems for filtration?
| Grinding operations performed on all three materials (aluminum, cast iron and steel)
present different problems than machining operations, which generate large chips. Rough
grinding can produce a chip large enough to build a filter cake on the medium through
which finer filtration can be obtained. Finish grinding and honing usually produce chips
that are too fine to form a good filter cake. Instead, they blind off (plug or coat) the
pores in the medium. Without a filter cake, the pore size of the medium determines the
clarity of the MRF: the smaller the pore size, the more particles are removed and the
greater the clarity. Grinding also produces "swarf," an accumulation of fine
chips and fine abrasive particles and bonding material from the grinding wheel. Swarf
consists of very fine particles that tend to float and collect on the surface. Swarf will
be carried out by the medium or can be manually skimmed |
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Contact Chris Roman, 