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Wenger Corporation
Saves Over $93,000 by Reducing Powder Paint Use and Rework
Fine-tuning
the Automatic Paint Spraying System
| Company |
Wenger
Corporation
Owatonna, Minnesota |
| Results |
Decreased
paint use by increasing transfer efficiency from
75 to 93 percent, saving over 12,000 pounds of powder
and over $81,000 annually. Cost for rework has dropped
by an estimated $12,500 annually. |
|
Process
Background
Wenger Corporation supplies equipment and technology for music
education and performing arts. Wenger coats nearly 800 different
parts with dimensions that range from a few inches to 10 feet.
In
1999, Wenger decided to bring its powder coating in-house
to gain greater control over lead time and to reduce costs.
The company purchased an automatic powder coat painting system.
One of two spray booths are rolled online, depending on whether
light or dark colors are being sprayed. Powder reclamation
cyclones remove powder from the spray booth and return usable
powder to the feed hopper.
Each
automatic booth has two banks of six oscillating guns. Two
manual touchup guns are located before the automatics. Painters
touch up hard to get areas before the parts pass the automatic
guns. The automatic system was designed to powder coat 90
percent of parts without requiring additional touch up. The
automatic guns are programmed to adjust the gun-to-part distances
according to part dimensions and to trigger when parts move
into position.
Incentives
for Change
Wenger needed to fine tune its new powder coating system.
The automatic spray system was not performing as anticipated
and used more powder than projected. Manual touchup and the
number of reject parts was higher than Wenger expected. The
company wanted to reduce powder use and the cost of waste
by 25 percent.
A
MnTAP intern reviewed the programming and set up of
the automatic spray guns. He investigated other improvements
to the painting system as well.
Powder
Hopper
For each major color used, Wenger had purchased a 250-pound
capacity main hopper which fluidizes the powder, creating
the appropriate consistency for spraying. The automatic level
control keeps a constant amount of powder in the hopper to
provide continuous powder flow to the spray guns. Virgin and
reclaimed powder are fed into the main hopper in a ratio that
allows for uniform powder properties.
These
large-capacity hoppers were prototypes. The intern discovered
that the fluidizing membrane was not supported well and bowed.
The bowing caused the air flow holes in the membrane to pinch
closed, resulting in the need for higher pressure to fluidize
the powder. Because of the bowing, powder was inconsistently
fluidized in the hopper leading to puffing and surging when
the guns were triggered. Powder would splatter or be too light
on the parts, resulting in rejects. The increased pressure
also blew out seals on the hoppers, causing loss of powder
and compressed air. Line time was lost while repairs were
made and the mess was cleaned up.
Results.
To help the powder fluidize better, the intern made changes
to increase air delivery to the membrane. After this temporary
fix, the manufacturer redesigned the membrane supports and
the base of the hopper to better suit the large volume of
powder. Wenger then purchased hoppers for all colors used
in the automatic booths. Now these colors are reclaimed with
no spray-to-waste, boosting the total transfer efficiency.
Increased
Transfer Efficiency
First pass transfer efficiency. The automatic guns
were not functioning correctly so operators disabled their
control program, leaving guns to operate with limited movement
and without being triggered off as desired. In this mode,
distance-to-part was not optimized and powder continued to
spray even when parts were not in front of the gun, reducing
first pass transfer efficiency. The intern investigated the
variables used in programming the automatic guns.
Reclaiming
powder. Cyclones control the amount of powder returned
to the hopper by sorting out the smaller particles as waste.
When cyclone pressure was set at 22 to 25 pounds per square
inch (PSI), 25 percent of all powder was going to waste. Each
time powder is reclaimed through the system, the fine particle
portion is separated and removed from the process by the cyclones.
Wastes can also be reduced by improving the first pass transfer
efficiency of the system. Waste powder was weighed and its
dollar value was tracked.
Result.
Cyclone pressure was reduced to 20 PSI. Reprogramming gun
movement, distances to the parts and triggering timing, along
with reductions in gun pressures, helped achieve a higher
first pass transfer efficiency. Powder waste decreased to
seven percent, saving over 12,000 pounds of powder and $38,400
annually.
Coating
Thickness Testing
Wenger had difficulty achieving a consistent coating, or mil,
thickness. The system started out providing inadequate powder
coverage. When it was adjusted the powder became too thick
on some areas of the part, wasting powder. Manual touchup
was done on both the top and bottom of parts. To spray under
a part, painters opened the booth doors, affecting the air
flow of the spray booths.
Gun
variables. To identify the spray variables in need of
tweaking, the intern ran a series of 72-inch vertical flat
panels through the system. Mil thickness measurements were
taken at various points on the panels. Gun variables for spacing
between guns, distance to part and up-and-down stroke rate,
charge to the powder, as well as powder flow rates were adjusted
through eight different tests.
Results.
Adjusting the guns greatly improved the consistency of the
mil thickness and improved quality. Providing a consistent,
even thickness on the part from top to bottom allowed Wenger
to reduce overall coating use by 15 percent during the course
of the summer. This will result in an annual savings of $25,900.
Stationary
guns. The panel test also showed that the top and bottom
of parts could not be automatically coated to the correct
thickness when parts were placed within the top or bottom
12 inches of the operational window. Even when optimal gun
settings were used, the tests showed that parts in this top
and bottom range were inadequately coated. The oscillators
could not overlap at the extreme top and bottom. Parts at
the top had the thinnest coating because the powder is affected
by gravity and air flow from the opening for the conveyor.
Results.
Placing two stationary guns at the top of the booth gave the
desired film thickness and eliminated a great deal of manual
touchup. Adding two stationary guns at the bottom eliminated
the need for painters to go into the booth to paint under
a part. The manual touchup openings in the booths could now
used as they were designed. Air flow through the booth improved,
lessening the amount of paint that escapes and becomes waste.
A total of eight additional stationary guns were added between
the two booths, costing $36,000.
Maintenance/process
control. Equipment ages over time—seals fatigue and
gun tips wear out. Moving equipment—like oscillating
guns—can cause parts to loosen and change alignment.
Testing with flat panels or standard products periodically
will help assure that your spray system is operating within
the desired parameters or will help you find trouble spots.
Procedures
Deviating from procedures can impact a system’s efficiency.
Operators at Wenger were not cutting powder delivery hoses
to the optimal lengths. When they were too long extra pressure
was required. Hoses were also routed improperly and not always
secured as designed. These errors often caused the hoses to
be pinched by the gun movers, restricting air flow or pulling
hoses loose, wasting powder. When the air was restricted,
powder flow was disrupted, causing defect parts due to sputtering
and insufficient coating.
Operators
at Wenger thought they were being efficient by quickly cleaning
the booths between colors. In their efficiency, they rearranged
the order of operations and did not always keep the booth
in “run” mode to allow the cyclones to reclaim the
most powder possible while the hoses were blown out, guns
were blown off, and floor and ceiling swept. Following changeover
procedures—in order—can save up to five pounds of
powder per color change. For Wenger, this could can save $1,800
a month.
During
color changes, powder delivery hoses are changed out with
the hoppers. The hoses that are run under the spray booths
were suspended by a series of support clips. The intern installed
a PVC pipe that operators now simply feed the hoses through,
making the process easier and more efficient during changeovers.
Overall
Results
With the help of a MnTAP intern, Wenger decreased paint use
by increasing transfer efficiency from 75 to 93 percent, saving
over 12,000 pounds of powder and over $81,000 annually. Cost
for rework has dropped by an estimated $12,500 annually.
Wenger
would have improved the performance of its automatic paint
spraying system on its own. But with the assistance of a MnTAP
intern, the company was able to get a jump on troubleshooting
and have its system tweaked much sooner. MnTAP was able to
offer Wenger a staff person dedicated to solving this waste-related
problem.
New
Equipment Reminders
Your purchase contract should document the expectations for
the system and the type of technical support that will be
provided. The equipment supplier is the expert on any new
equipment. Be sure that new equipment purchases include ongoing
or follow-up training of operators and their supervisors.
Once
in place, most new systems need a little tweaking to ensure
they meet operating expectations. Owners and vendors share
responsibility in getting the system to run efficiently. Allow
time for troubleshooting and be sure to collect data on how
the system is operating so adjustments can be made. Systems
need the same attention to fine tuning when the product mix
changes.
More
Information
MnTAP has a variety of technical assistance services available
to help Minnesota companies reduce and manage their industrial
waste. If you would like assistance or more information about
MnTAP’s Intern Program, call 612.624.1300
or 800.247.0015 from greater Minnesota.
This project was conducted in 2000
by MnTAP intern Tom Paitrick, a chemical engineering junior
at the University of Minnesota.
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