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Aluminum Foundry Replaces TCA with
Waterbased Coatings
| Company |
Progress Casting
Group, Inc., Plymouth, MN |
| Industry |
Aluminum
foundry |
| Waste |
111-trichloroethane
(TCA) used as a carrier in the core wash. |
| Change |
Replaced
TCA with water- and isopropyl alcohol (IPA)-based
coatings. |
| Cost |
$27,500 for custom-made drip tanks and
infrared heater for use with waterbased
coatings. $5,000 for exhaust hood and sprinklers
for use with IPA-based coatings.
|
| Savings |
Eliminated
TCA usage (35,000 pounds in 1993), resulting
in cost savings of $59,000 in TCA purchase
costs. Met consumer demand to eliminate use
of ozone-depleting chemicals (TCA). Met goals
set through participation in the U.S. EPA’s
33/50 Program. |
|
Background
Progress Casting Group, Inc., located in Plymouth, Minnesota,
is an aluminum foundry that casts parts for use in a
variety of applications, including: food processing
equipment, motorcycles and airplanes.
In 1993, Progress Casting used approximately
35,000 pounds of 111-trichloroethane (TCA) as a carrier
in the wash used to coat sand cores. After sand cores
are dipped into the wash, the TCA quickly evaporated
leaving a protective coating on the cores. The coating
prevented molten metal from penetrating the cores during
the parts-casting process and left a smooth finish on
the casting surface. TCA was used as a wash carrier
because it held other wash components in suspension,
dried quickly to give a consistent coating thickness,
and ensured adequate tensile strength to prevent the
coating from chipping.
Incentives
for Change
The
following factors contributed to Progress Casting’s
interest in finding alternatives to TCA:
- Environmental
commitment. Progress Casting made a commitment to
prevent pollution by participating in the US Environmental
Protection Agency’s (EPA) 33/50 toxic chemical
use reduction program. Its goal was to reduce TCA
use by 30 percent in 1992, and eliminate TCA use by
January 1994.
- Economics.
Economics was an important factor in eliminating TCA
use. TCA costs were increasing due to excise taxes
and phasing-down of TCA production, as mandated by
the 1990 Clean Air Act Amendments (CAAA). In 1992,
Progress Casting spent $44,250 on TCA purchases. In
1993, the same volume of TCA cost $59,000.
- Customer
demand. Customers demanded that Progress Casting stop
using TCA because of new product-labeling rules mandated
by the CAAA. These rules require that products made
with ozone-depleting chemicals (ODC) be labeled stating
that ODCs were used in the production of the product.
Alternatives
to TCA
Progress Casting evaluated a variety of water- and IPA-based
coatings as alternatives to TCA. Each coating was tested
for its ability to provide a uniform coating thickness
and quality without damaging the sand cores.
Implementation
Problems
Progress Casting uses a low-pressure permanent molding
technique to cast some of its parts. The pressure can
cause molten metal to burn into the sand core
if the coating is inadequate; therefore, the coating
selected had to withstand the pressure and protect the
core.
Other problems with using waterbased
coatings included:
- Keeping solid components suspended
in the mixing tank.
- Developing dipping techniques that
provided even coating thickness.
- Finding drying methods that dried
fast enough to leave a strong coating on the sand
cores.
The primary problem with using an
IPA-based coating was the fire hazard caused by IPA’s
high flash point.
Drying Requirements
The waterbased coatings required significantly more
time to dry than TCA; therefore, Progress Casting had
to determine the appropriate drying time and temperature
requirements. In addition, vendors could not supply
“turn-key” equipment that would work with
the washes for all the core sizes used at Progress Casting.
Consequently, Progress Casting evaluated four different
drying techniques to determine which one would work
best. These included: high intensity lights, microwave,
drying tunnels, and infrared ovens.
The high intensity lights and drying
tunnels did not dry fast enough to prevent coatings
from dripping and losing thickness uniformity. Microwave
drying used nonselective heat that penetrated the sand
cores and caused them to disintegrate. Infrared ovens,
however, quickly dried the coatings without damaging
the sand cores.
Customized
Equipment
All the waterbased coatings tested required numerous
dips of the sand cores into the corewash slurry (TCA
coated adequately after only one dip). To accommodate
this requirement, Progress Casting worked with vendors
to design custom equipment to automate dipping and drying
the smaller sand cores. Automation is a key factor in
producing consistent coating thickness and quality.
 |
| Part-dipping
Process |
The equipment layout was designed
for efficiency and consists of: a dip tank containing
a continuously recirculating waterbased slurry; two
separate infrared ovens; and four rotating racks used
to hold the cores and lower them into the dip tank and
ovens. First, a row of sand cores is placed on one of
the racks, and then lowered into the dip tank containing
continuously recirculating corewash and held in the
coating solution for approximately one minute. With
the corewash forced upward in the tank, the counter-current
effect facilitates wetting of the core surface and helps
ensure uniform coating. The aeration action also minimizes
bacterial growth in the corewash.
After dipping, cores are then lifted
out of the tank and rotated into place over one of the
infrared ovens as the operator adds another row of cores
to the second rack. The racks then simultaneously lower
the cores into either the dip tank or the infrared oven.
By having four racks, two sections of cores are simultaneously
dipped into either the slurry tank or the infrared ovens
as the operator removes one row of cores and adds another
row. Each core is dipped and dried twice.
When the automated dipping/drying
equipment was first tested, Progress Casting evaluated
core coating quality to determine the right ratio of
dipping and drying times required to get a uniform,
quality coating. Other problems with using this equipment
included: fungal growth in the slurry mix, which was
resolved by the core wash vendor; and curdling or separating
of the corewash, which was resolved by adjusting the
mixer speed in the dip tank.
 |
| Dipping/Drying
Equipment Layout |
Safety concerns. IPA has a flashpoint
of 53°F; therefore, using IPA in a foundry situation
can be extremely dangerous. To reduce the fire hazard,
Progress Casting installed an exhaust hood in the work
area to remove the IPA from the plant floor as it is
sprayed onto parts. In addition, a sprinkler system
was also installed in the work area.
IPA was almost a “drop in”
substitute for TCA, except for the fire hazard and a
slightly longer drying time. Through testing, Progress
Casting found that the IPA can be sprayed onto a part
and then hand rubbed into the surface. No heating of
the part is required to set the IPA surface coating.
Results
As of October 1994, Progress Casting has completely
eliminated TCA use by substituting water- and IPA-based
coatings for the TCA. As a result, Progress Casting
has eliminated $59,000 in TCA purchase costs. Approximately
35,000 pounds of water- and IPA-based coatings are purchased
at an annual cost of $14,500. The net annual cost savings
resulting from eliminating TCA is $44,500.
In addition to the economic benefits,
Progress Casting has satisfied customer demands to eliminate
TCA use; thereby, eliminating the ODC use labeling requirement
mandated by the CAAA.
Progress Casting has also achieved
its 33/50 Program goals by first reducing and them completely
eliminating its use of TCA.
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 publication was created with
the assistance of Progress Casting Group employees,
Joe Teff and Randy Oehrlein.
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