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How are flumes designed?
| To return spent metal removal fluid and chips
generated by the machining operations, central systems utilize trenches (flumes) in the
plant floor. For better MRF and chip flow, the trenches are sloped down to the filter
tank. Flush nozzles piped from the MRF system pumps are used to assist in carrying the
chips through the flumes. Flumes are installed so the top surface of the liners and the
cover plate are flush with the surrounding floor or deck. |
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| Flumes should be located immediately below the machine discharge chute and
should be wide enough to contain the chip and MRF discharge. Flumes are usually supplied
in standard widths of 9", 12", 15", 18", 24" and 36". Flume
width should also be based on the quantity of MRF flowing through the flumes. Flumes
should be sized and pitched to maintain an MRF velocity of 6-10 ft./sec., depending on the
material being machined. |
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| Most flume systems are installed with a 1/8" per foot slope to the
filter tank. Flush nozzles are installed at intervals (usually every 20-32 feet, depending
on the application) throughout the flume system to move chips and maintain MRF velocity.
The flume sections at these nozzles are built so the flow from the nozzle is discharged
below the MRF flowing through the flume. Each of these step-flush boxes results in a
2" to 2-1/2" drop in trench elevation. |
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| The pitch of the flumes, number of step-flush nozzles, and length of the
trench runs will determine the depth of the metal removal fluid pit. The pit construction
cost increases significantly with increased depth. Deep pits usually require sheet piling
and de-watering. Pit depth can be minimized if the pit can be located in the center of
long trench runs rather than at the end. |
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| Flumes are constructed in approximately 20-foot sections of a 10-gauge
steel liner formed into a "U" shape. The "U" type construction should
transition from a round cross-section, to a half-round, to a rectangular cross-section at
all changes in direction. Changes in direction should be accomplished with 3-foot (inside)
radius turns. Flume sections should be welded watertight (no stitch welding), including
curb angles. Section joints should be ground to provide smooth MRF flow. |
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| Flume cover plates are required in all areas not covered by machines.
Covers should be made from 3/8", 1/2" or 5/8" thick non-slip
("Slip-Not," "E-Z Weld," etc.) safety plate capable of supporting 250
PSF. When crossing an aisle, the top of the trench should be recessed 8 inches and a
10-gauge cover welded to the liner. Reinforced concrete is then poured over the trench to
complete the aisle. |
| The use of flume systems to move chips should be minimized. While flumes
and other sources of aerosol generation should be covered, an enclosed flume spillway can
cause the mechanically generated mist to be blown back at the machine operator. Venting
the flume to the metal removal fluid reservoir, if it’s practical to do so, will
reduce this problem. |
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Are there different types
of flume systems?
| When engineering flumes for a central system, the primary consideration is
the type of material being machined. Flume systems are usually classified as aluminum,
cast iron, or steel. Each material has its own characteristics and related
problems. There are different requirements and considerations. The following sections show
typical requirements and considerations for each material. |
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Aluminum
| Aluminum chips are light and, therefore, easier to transport through the
flumes. While aluminum turning operations produce some long, stringy chips, they usually
do not form large springy bundles. |
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| Metal removal fluid velocity should be maintained at 6-8 ft./sec. Flush
nozzles are usually spaced at 30-foot intervals, with a trench slope of 1/16" to
1/8"/ft. MRF required for trench flush is approximately 1-1/2 to 2 GPM/ft. of trench.
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Cast Iron
| Cast iron and nodular iron break up into small, heavy granular chips that
move readily through the trench if MRF velocity is adequate. |
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| MRF velocity should be maintained at approximately 10 ft./sec. MRF
required for trench flush is approximately 2 to 2-1/2 GPM/ft. of trench. Normal spacing
for flush nozzles is approximately 20 feet. |
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Steel
| Steel chips can vary in size and shape, from very small granular pieces to
long, stringy curls on turning operations. It is the long, stringy curls that intertwine
and collect to form large bundles, which are very difficult to move through the trench.
The problem with bundles usually starts with the machine not discharging the chips
efficiently. Often, long, stringy chips are hung up in the machine discharge and are
allowed to accumulate there from a number of parts before the operator manually clears the
machine. The operator usually uses a stick or rake to push the accumulated bundle through
the machine into the trench. When the bundle is forced through the machine discharge, it
compresses until it enters the trench, where it springs back out. At that point, it may
become lodged in the trench. The trench should be wide enough to accept the bundles as
they spring back out after being compressed. |
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| MRF velocity should be maintained at 10 ft./sec. through the trench. MRF
flow required for trench flush is 2-1/2 to 5 GPM/ft. of trench, depending on the type of
chips expected. Flush nozzles are usually spaced every 20 feet but should be located near
operations where bundles are expected. |
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The table below summarizes the different requirements for the different metals.
Flume Requirements
| |
MRF Velocity |
MRF Flow |
Nozzle Spacing |
Other |
Aluminum |
6-8
ft./sec. |
1-1/2 to 2
GPM/ft |
30-foot
intervals |
trench
slope of 1/16" to 1/8"/ft |
Cast Iron |
10
ft./sec. |
2 to 2-1/2
GPM/ft |
20 feet |
|
Steel |
10
ft./sec |
2-1/2 to 5
GPM/ft |
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place nozzles where
bundles expected |
| The above discussion centers on flume systems that use stepped flushes and flush
nozzles. However, recently another kind has been used for aluminum machining and ferrous
fine grinding operations: high-volume/low-pressure trench flushing. |
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What is high-volume/low-pressure
trench flushing?
| These systems have only high-volume MRF supply pipes at the shallow end of each trench
run; there are no intermediate flush nozzles. The trench slope is varied from 0 to
3/8"/ft. throughout the system to maintain 6 ft./sec. MRF velocity. These systems
have performed well to date. |
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There are some advantages to this type of flushing:
 | easier trench installation and fabrication |
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| lower mist generation |
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| lower piping costs because there are few flush drops |
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| less expensive trench liners—no step flush boxes to fabricate |
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| lower energy consumption |
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| The only disadvantage is that if problems moving the chips are encountered at certain
operations, there are no intermediate nozzles where flow can be increased. |
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Contact Chris Roman, 