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Part Placement, Spray Adjustment and Overspray
Reuse Increase Transfer Efficiency
| Company |
Medallion
Kitchens
Waconia, Minnesota
|
| Results |
Reclaim 11.5 gallons
of sealer overspray daily, saving $23,000 per year.
Waste sludge reduced 50 percent saving $30,000 annually. |
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Medallion Kitchens
is a leading woodworking company manufacturing a variety of
kitchen cabinets and bathroom vanities at a daily rate of
approximately 900 cabinets. Wooden cabinet parts are stained
and then finished with a solvent-based catalyzed sealer and
topcoat before they are assembled into completed cabinets.
The process of spraying the sealer and topcoat finishes onto
the cabinets is automated; a central computer controls a conveyor
belt system, two water-wash spray booths and two drying ovens.
Sensor-automated spray guns apply coatings to cabinet parts
in each booth.
Overspray, the finish that misses cabinet
parts during application, is wasted raw material. Overspray
generates waste by (1) volatilizing, which releases volatile
organic compounds (VOCs); (2) landing on conveyor bands, which
then must be cleaned off and disposed of as hazardous sludge;
or (3) falling into a tank containing recirculating water;
which collects and floats in the water until manually removed
and disposed of as hazardous sludge. Before any changes were
made, this application process used approximately 75 gallons
of sealer per day in the sealer spray booth, and generated
approximately 50 gallons per day of hazardous waste sludge.
Approximately 50 percent of the sludge content consisted of
water.
Incentives for Change
Medallion Kitchens was interested in: 1) reducing solvent
emissions because future air quality regulations promise to
reduce the allowable VOC emission levels; 2) reusing the sealer
and topcoat overspray to reduce raw material costs; and 3)
minimizing sludge waste to reduce hazardous waste disposal
costs, along with liabilities after the sludge leaves the
facility; and 4) reducing labor costs associated with sludge
removal, dewatering and handling.
Intern Activities
A system for reclaiming and reusing overspray material was
designed by Medallion Kitchens and installed in the sealer
spray booth. The system consists of two collection trays,
a holding reservoir, copper piping, and a pump. The MnTAP
intern tested the new system, and examined ways to improve
transfer efficiency through adjusting spray timing and part
placement.
Spray timing adjustment. One source of overspray
came from the spray guns starting too early or remaining on
too long. To determine the actual area covered with finish,
a piece of paper the size of an average part was taped to
Plexiglas and sent through the spray booth. The photo-electric
cell ignored the clear surface and sprayed the paper. Overspray
that collected on the clear surface was measured to determine
the areas and amounts of overspray. This test method was used
to adjust the spray gun timing to minimize overspray.
Part placement. During the application of
spray coatings, the spray system was unable to turn off and
on fast enough to avoid spraying the empty spaces inside the
cabinet frames. This resulted in another source of overspray.
Attempts were made to place smaller parts (doors or drawer
fronts) within the internal areas of the frame to improve
transfer efficiency.
Results
Overspray reclamation and reuse. The reclamation system was
built for $2,500 and is currently operating in the sealer
spray booth at Medallion Kitchens. An average of 11.5 gallons
of sealer is reclaimed daily, resulting in raw material cost
savings of $92 per day or $23,000 per year. Waste sludge generated
in the sealer spray booth was reduced by 50 percent to an
average of 25 gallons per day. Hazardous waste disposal costs
for the sealer booth were also reduced by 50 percent, saving
$30,000 annually.
Spray gun timing. During testing of spray
gun timing, the overspray pattern on the Plexiglas had
dimensions of 15 centimeters by 16 centimeters. This showed
that regardless of part size, the spray guns were being triggered
on at a distance of 16 centimeters from the parts and spraying
15 centimeters past the edge of parts. By adjusting the timing
of the spray gun controller, overspray dimensions were reduced
to 10 centimeters by 11 centimeters. Further reduction was
not possible because of the need to “wrap” the edges
of parts with spray. Transfer efficiency calculated for an
average part measuring one foot by one foot improved from
44 percent to 55 percent after adjusting the spray controller
timing. However, the increase in transfer efficiency was less
for larger parts.
Part placement in frames. A problem with
placing parts within the frames occurred during the conveyor
transfer of the parts from the spray booth to the drying oven.
The sudden change in speed during this transfer caused the
parts to shift, touch each other, and stick together resulting
in an unacceptable finish. To remedy this situation, an electronic
control was installed to gradually accelerate the conveyor
as parts enter the oven. Gradual acceleration prevents the
smaller parts from sliding into the frames.
Although changing the acceleration rate
allows parts to flow through the system without touching,
other concerns must be resolved before implementation. Part
scheduling will need to be altered to coordinate frames with
smaller parts, and another worker may be needed to assist
with added duties during part placement, sanding, and unloading.
In addition, quality could suffer if parts were placed too
close to each other which could prevent the edges from being
sprayed.
For More Information
MnTAP has a variety of technical assistance services available to help Minnesota businesses implement industry-tailored solutions that maximize resource efficiency, prevent pollution, increase energy efficiency, and reduce costs.Our information resources are available online. Or,
call MnTAP at 612.624.1300 or 800.247.0015 from greater Minnesota
for personal assistance.
This project was conducted in 1992 by MnTAP
intern John Sipple, a mechanical engineering student at the
University of Minnesota.
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