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Controlled Spraying and Laser Touch
in the Fiber Reinforced Plastics Industry
Controlled spraying significantly
reduces styrene emissions from open mold fiber reinforced
plastic application processes. This pollution prevention
technique benefits employee health, the manufacturing
operation and the natural environment, by increasing material
transfer efficiency, which reduces styrene emissions.
Transfer efficiency is the amount
of material adhering to the mold compared to the amount
of material sprayed. Increase transfer efficiency in
your FRP shop by minimizing resin atomization and reducing
overspray loss—material that misses the mold during
spray application. Both atomization and overspray expose
the surface area of resin and gelcoat particles to air,
increasing styrene emissions.
A study by the Indiana Clean Manufacturing
Technology and Safe Materials Institute, Purdue University,
showed that styrene emissions from gelcoat and resin
application could be reduced by 20 percent or more through
controlled spraying. American Composites Manufactures
Association (ACMA) tests show that styrene emissions
are directly related to the exposed surface area and
are independent of the film/layer's thickness. According
to ACMA's Controlled
Spraying Handbook, three major elements work
together to reduce emissions:
- Spray gun
settings
- Capturing
overspray at the mold perimeter
- Training
operators
Spray Gun Settings
Spray guns transfer resin or gelcoat from bulk containers
to the mold. Sprayed in a fan shaped pattern material
efficiently covers the mold. In the case of externally
mixed spray equipment—mixing catalyst and resin
after they exit the spray gun—the finely divided
liquid droplets of the fan pattern aid in mixing the
catalyst with the resin or gelcoat. Proper mixing is
required to adequately cure the laminate.
Calibrate Pressure
The amount of atomization depends on a variety of characteristics,
including resin temperature and properties, type of
spray gun, gun-to-mold spray distance and mold shape.
Each set of characteristics has an acceptable amount
of atomization. To minimize atomization use the lowest
gun fluid tip-pressure that gives an effective fan pattern
and insures adequate mixing of the catalyst and resin
or gelcoat. Maintain a pressure calibration log so you
can track if operators are monitoring atomization. More
details are available in chapter 4 of ACMA's Controlled
Spraying Handbook.
Control the
Fan Pattern
Select a fan pattern that allows operators to work efficiently
while maintaining control over the resin or gelcoat's
placement and thickness. Match orifice size and tip
angle to the resin's characteristics and to the size
and shape of the mold. Use wide spray patterns for wide
parts and narrow spray patterns for narrow parts. Because
spray equipment varies, consult the manufacturer to
determine the best operating pressure for a given set
of conditions. In general, as tip pressure increases
the fan pattern moves from a circular pattern to an
erratically elongated pattern to a “clean”
elliptical pattern. At higher pressures, an undesirable
larger elliptical pattern forms. Ideal conditions are
usually at the lowest pressure that yields an elliptical
pattern. This distributes material evenly across the
fan, providing uniform coverage.
Capturing Overspray
To minimize the amount of material that hits the floor,
capture overspray as close to the mold's edge as possible.
This will reduce styrene emissions. Capture overspray
by:
- Widening the mold's flange
- Incorporating a removable flange
extension
- Using wide disposable masking
Operator Spray Technique
Spray technique has a significant impact on the amount
of waste generated in open mold processes. Inefficient
technique results in excess material use, reduced transfer
efficiency and increased amounts of overspray. Train
operators to maximize your operation's efficiency.
Thoroughly train operators on proper
spray techniques. Explain the need for controlled spraying,
including how overspray impacts material use and styrene
emissions. Also, explain the importance of proper spray
equipment setup and spray technique.
Proper Spray
Techniques
- Spray gun orientation. Hold the
gun perpendicular to the mold surface as material
is applied. A more even mil thickness and the least
overspray is produced the closer the gun's angle is
to 90 degrees.
- Spray pattern. Establish a pattern
that gives the proper coverage. Use smooth, long parallel
strokes. Start at the area of the mold closest to
the operator and follow the mold's contour as closely
as possible. Keep the stroke rate, gun-to-part distance
and gun angle constant.
- Mold perimeter. Spray the mold's
perimeter first, keeping overspray within the containment
flange. Next, work from the mold's interior out to
the perimeter, stopping short of the mold's edge.
- Corners. Spray inside and outside
corners at a 45 degree angle.
- Large molds. A large mold may make
it difficult for an operator to keep the gun angle
at 90 degrees near the mold's center. In this case,
add material starting from the outer edge working
to the interior. At the center of the mold deviating
the angle from perpendicular is less of a problem
because material is likely to fall on the mold's surface
and not become overspray.
- Gun operation. Do not trigger the
spray gun on and off. This could make the catalyst
and resin ratio inconsistent.
- Mil thickness monitoring. Operators
should use a mil thickness gauge to monitor laminate
buildup. This check helps ensure that they hit the
target weight for parts and keep overall emissions
minimal. Or, use equipment that monitors the amount
of material dispensed to achieve tighter control over
part weights.
Laser Touch Improves Spray Technique
and Reduces Waste
Adequate training increases the
efficiency of material use. Spray performance can improve
further when a properly trained spray operator is assisted
by Laser Touch technology. Mounted on a spray gun, the
Laser Touch unit has two laser beams that converge into
one when the gun is properly positioned. The visual
signal of both lasers coming together on a part lets
operators instantly know if they have proper aim, gun-to-part
distances and gun angle. Improved accuracy and consistency
ensures material placement, maximizing transfer efficiency.
The increased performance is seen as less waste is produced.
Fiberglas Fabricators
Tests Laser Touch
A MnTAP intern studied the effectiveness of Laser Touch
at Fiberglas Fabricators, in Le Center, Minnesota. The
company manufactures electric utility enclosures of
varying sizes and shapes. The parts are rectangular
and have a depth of one foot or more. The base of each
part is cut out, creating a large source of waste. Trim
and overspray are the other major waste sources.
The intern tested Laser Touch on a
variety of parts in an average day’s production.
An initial waste assessment was performed to set baseline
waste numbers. The amount of gelcoat applied to the
mold was determined by weighing the mold before and
after application. Filled resin, catalyst and chopped
glass inputs were monitored by Technology for Manufacturers
(TFM) material monitoring device. Woven glass was weighed
on a scale. Before the part was allowed to cure, the
waste from the mold edge—trim waste—was removed
and weighed. After the part was removed from the mold,
edge finishing and cut out wastes were weighed. Overspray
waste was the difference between the inputs and the
cut out and trim wastes. Parts were carefully monitored
throughout the process and the same spray operator performed
all the tests. The application equipment used was the
Magnum fluid impingement technology (FIT). Styrene emissions
were not included in the analysis.
Using the CFA’s Controlled Spray
Program as the guide, the operator for this study was
trained on proper spray technique. The Laser Touch was
installed and set for the desired gun-to-part distance.
Materials used and waste generated were determined as
described above.
Data and Results
Tables 1 and 2 represent data for a variety of different
parts. Identical parts are represented in each trial,
but direct comparisons cannot be made between tables.
The average waste rate was 14.5 percent before using
Laser Touch versus 10.6 percent after. The Laser Touch
device and the controlled spray training resulted in
nearly a 27 percent reduction in the solid waste generated.
| Table 1. Baseline
material use and waste data for a variety of parts
in typical production. |
 |
| Part |
Materials used*
(pounds) |
Waste generated
(pounds) |
Percent waste |
| 1 |
62.8 |
10.7 |
17.0 |
| 2 |
62.5 |
8.6 |
13.8 |
| 3 |
62.2 |
7.45 |
12.0 |
| 4 |
59.8 |
9.1 |
15.2 |
| 5 |
59.35 |
12.65 |
21.3 |
| 6 |
58.8 |
10.9 |
18.5 |
| 7 |
134.4 |
13.4 |
10.0 |
| 8 |
137.1 |
21.5 |
15.7 |
| 9 |
136.5 |
13.5 |
9.9 |
| 10 |
126.1 |
21.1 |
1.7 |
| 11 |
126.6 |
15.6 |
12.3 |
| 12 |
60.55 |
11.2 |
18.5 |
| 13 |
60.15 |
10.3 |
17.1 |
| |
|
|
|
| Total |
1147.0 lbs. |
166.0 lbs. |
Average 14.5% |
|
| *Materials used is
total amount of catalyzed filled resin, gelcoat,
chopped and woven glass that is applied. |
| Table 2. Material
use and waste data for a variety of parts using
the Laser Touch device. |
|
| Part |
Materials used*
(pounds) |
Waste generated
(pounds) |
Percent waste |
| 1 |
58.85 |
7.0 |
11.9 |
| 2 |
62.7 |
6.9 |
11.0 |
| 3 |
129.4 |
9.9 |
7.7 |
| 4 |
129.9 |
10.6 |
8.2 |
| 5 |
63.9 |
5.6 |
8.8 |
| 6 |
66.15 |
5.0 |
7.6 |
| 7 |
62.7 |
8.5 |
13.6 |
| 8 |
63 |
7.1 |
11.3 |
| 9 |
68.3 |
9.0 |
13.2 |
| 10 |
70.2 |
12.2 |
17.4 |
| |
|
|
|
| Total |
775.0 lbs. |
82.0 lbs. |
Average 10.6% |
|
| *Materials used is
total amount of catalyzed filled resin, gelcoat,
chopped and woven glass that is applied. |
Table 3 represents a before and after
comparison for identical parts. Large and small parts
are represented in the sample. The large part averaged
a 22 percent decrease in waste while smaller parts averaged
a 33 percent decrease.
| Table 3. Before
and after Laser Touch comparisons of waste data
for identical parts. |
|
| Part |
Waste
(pounds per 100 pounds input*) |
Percent
decrease |
| |
Before |
After |
|
| A |
12.9 |
8.8 |
32 |
| B |
11.9 |
7.9 |
34 |
| C |
17.8 |
13.9 |
22 |
|
| *Input equals the
sum of resin, glass, catalyst and gelcoat into part. |
Economics
Because of the quick payback,
Fiberglas Fabricators will consider purchasing Laser
Touch if it does not move to robotic spray up.
| Table 4. Economic
justification for implementing controlled spray
using the Laser Touch |
|
| Annual
savings in materials if scrap rate dropped from
14.5 to 10.6 percent |
$23,700 |
| |
|
| Decrease in landfill
disposal costs |
20 percent |
| |
|
|
Savings associated with decreased
landfill costs
|
$2,600 |
| |
|
|
Total annual economic benefit
|
$26,300 |
| |
|
Cost of Laser Touch
(4 units at $1,000 each, including installation)
|
$4,000 |
| |
|
| Payback period |
< 2 months |
|
For More Information
Other MnTAP publications for
the FRP industry:
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.
The Laser Touch study was conducted
in 2001 by MnTAP.
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