- Email: [email protected]
Two-coat electrocoat, a breakthrough technology
Two-Coat Technology by Lisa Merlo PPG Industries,
Electrocoat, and John
Springdale,
Motley
Pa.
0
ver the past few years significant advances in polymer chemistry have led to the next generation of finishing technology. Extensive R&D efforts have created new polymers that have in turn facilitated breakthrough electrocoating processes that permit a second coat to be applied via electrocoat. Today, manufacturers who require highperformance coatings can benefit from the productivity, cost reduction, and reduced environmental impact offered by the electrocoat (E-coat) process. Markets that have already benefited from this breakthrough technology include automotive OEMs, electrical generators, transformers, and even outboard motorboats. The breakthrough comes at a time when all industries are required to lower operating costs, reduce air and waste emissions, but also increase product quality and performance. The benefits of electrocoating and the new two-coat processes can help many companies meet these increasingly difficult requirements. A FORTY-VEAR
THE
ELECTROCOAT
PROCESS
The fundamental principle of electrocoating is that opposites attract. An electrocoating system applies a DC charge to a metal part immersed in a bath of oppositely charged paint molecules. The molecules form a uniform, continuous film over its entire surface. (See Fig. 1.) The process is highly effective. Since the substrate is dipped in a charged bath, the molecules are attracted to the entire surface without fail and the process assures precise film control. In a single-coat system the combination of polymer chemistry and a specific electrical charge creates a point in the process where the coating film insulates the part, ending the coating process. No more coating can be applied and every charged surface, no matter how complex the geometry, is covered.
Cathode
Anode
JOURNEY
It has long been recognized that E-coat processes are less expensive, are environmentally friendly, and can reduce manpower needs. In addition coatings applied by the E-coat process perform at very high levels in some of the most difficult user environments. PPG Industries introduced anodic technology in 1961, allowing primer coats to be applied to substrates through an electrodeposition for the first time. The technology was revolutionary and found immediate uses in automotive and industrial markets. In the following years the technology was refined continually with new chemistries and treating processes that expanded the products that could be coated and the industries that could utilize E-coat. In 1971 cathodic technology was introduced and in 1976 cathodic primers for automobiles were introduced. By the 1980s high-build, super-smooth primers and high-performance acrylic systems were developed, expanding the use of E-coat. By almost any standard E-coat technology became the coating process by which all others are compared. September
A Breakthrough
2000
I 1) t
H2
00 0 ii 0 0
Figure
1. Principle
of electrocoating
(opposites
attract).
59
THE
BENEFITS
E-coat technology following benefits.
has long been recognized
for the
Coating Efficiency E-coat systems are the most efficient coating technology. E-coat provides precise film control with variances of only 0.1 to 0.2 mil across the painted surface. Film thickness for spray systems can vary 0.5 to 2.0 mil. As a result the technology prevents runs, sags, and drips leading to a high-quality finish and reduced rework costs and material usage. A closed-loop rinse system recovers and returns dragout paint solids and rinse liquids to a E-coat tank, boosting paint usage and transfer efficiency to 95 to 99%. Line Productivity The immersion process generates two main productivity benefits: dense line loading and fast line speeds. E-coat lines are automated and it is not uncommon for them to have rack densities of 2.5 to 5 ft2 of ware per cubic foot of ware package area. Parts can be hung densely because parts are immersed rather than set up for spray application. Automotive body E-coat lines can easily process up to 100 vehicles an hour. Since E-coat systems are automated, the human error factor is greatly minimized. One line operator can run the average E-coat tank. Environmental Advantages E-coat systems are clean systems. Electrocoatings (primers and topcoats) are water-based. This means there are no or very low levels of VOCs and HAPS and they are also free of heavy metals. In fact HAPfree formulas are now available in response to the Clean Air Act of 1990. E-coat systems substantially reduce the exposure of workers to hazardous materials, they reduced fire hazards, and there is minimal waste discharge. An ultrafilter/recycled rinse system can all but eliminate wastewater and the associated treatment and disposal costs. TWO-COAT
TECHNOLOGY
Considering the benefits attributed to E-coat technology, being able to utilize the E-coat process to apply a second primer is an attractive proposition. The fundamental obstacle to developing two-coat technology was the chemical nature of the initial coat. Normally, the first coat creates an insulating barrier once the desired depth is achieved and the coating process is stopped. To achieve a two-coat process the initial coating had to contain properties that would control the electrodeposition process as the first coat is applied yet could be made conductive 60
again in order to accept a second coat. Research led to new formulations of epoxy and acrylic primers that are able to achieve that goal. The two-coat system relies upon a polymer that, when fully cured, becomes conductive enough to accept a subsequent coat of primer. It’s the chemistry of the E-coat primer that allows that process to take place. When the primer is partially cured at a temperature between 130 to 175°C (266-347°F) it reaches a conductivity of approximately lo-l2 mhos/cm or more. That is required to effectively bond a second electrodeposited composition. The second layer is then cured to a thermoset film coating. The two-coat process is able to deposit a variety of primer combinations. In the vast majority of cases, the initial primer coat is an epoxy product that has proven to provide superior corrosion protection; however, epoxy is susceptible to damage from ultraviolet rays and must be protected. Normally, an acrylic product performs this function. These combinations are available from current two-coat systems: Epoxy/Epoxy This system is the ultimate in corrosion protection. Salt spray results in excess of 3,000 hours are capable with this combination. Epoxy/Acrylic A combination of two distinct coatings (epoxy and acrylic) gives the benefits of both corrosion and UV durability. Acrylic/Acrylic This system is the ultimate in UV durability. When applying a conductive black acrylic primer, with a second coat of acrylic, we can achieve excellent UV durability with E-coat. Epoxy/Urethane This system (Power-Prime) offers better resistance to corrosion and chipping from stones. The first coat is an epoxy corrosion inhibitor. The second coat is the primer surfacer. Two-coat E-coats are being used wherever a highperformance paint film is required. The first to take advantage of the breakthrough process were the electric transformer, electric generator, and marine industries. (See Table I.) The second electrodepositable coating in these markets consists of an acrylic and is usually used as a final topcoat. This combination of an epoxy first coat and acrylic second coat results in excellent corrosion and UV resistance. The acrylic protects the epoxy from the degradation that would occur if it were exposed to the weather. The two-coat system is Metal
Finishing
Table
I. Two-Coat
Applications
of Electrocoat
in the
Industrial
Marketplace
End Use Agricultural implements (equipment) Aluminum trim Generator housings Heating, ventilation, and cooling Heavy-duty maintenance Lawn and garden Marine engines Railway Structural steel Transformers Truck market Wheels
Corrosion Aesthetic Corrosion Corrosion Corrosion Corrosion Corrosion Corrosion Corrosion Corrosion Corrosion Corrosion
Prime system at the DaimlerChrysler plant in Campo Largo, Brazil, the first commercial primer/ surfacer to be applied via E-coat, a process that improves coating application and performance. In the year since this plant used two-coat E-coat, it has experienced reduced sanding, improved appearance, increased performance, and reduced VOC emissions over conventional primer. (See Figs. 4 and 5.) Two-coat E-coat is in the process of being introduced into the truck trailer market. Wabash National will start protection with the Powecron twocoat E-coat process to coat platform trailers, thereby substantially raising the performance of coatings used in this market.
capable of providing long-term exterior durability and corrosion resistance in excess of one thousand salt spray hours. (See Table II.) Two-coat E-coat was introduced first into the transformer market in the early 1990s. The transformer industry needs a two-layer system that will provide 3 mil or 75 microns minimum film thickness, will coat hot-rolled carbon steel, adjust to variations in product geometry, and withstand long-term environmental exposure-from salt and humidity to industrial pollutants. Until the two-coat E-coat process was developed transformers were spray coated, a process that had difficulty reaching into recessed areas, especially within fins. (See Fig. 2.) The two-coat E-coat combination is also being used in the generator industry where it has been found to provide a coating system that is extremely corrosion resistant and has improved weatherability and chemical resistance as compared to other traditional coating systems. (See Fig. 3.) The outboard-motor industry has used two-coat E-coat to provide superior protection against sun, saltwater, and sand. The initial primer delivers a corrosion and chip-resistant epoxy followed by an acrylic layer than provides protection from W rays. Now, the two-coat process is being utilized by the automotive industry. PPG introduced the PowerTable
II. Film
Properties
for
Cationic
Epoxy
Lead-Free
TWO-COAT
September
based
2000
Acrylic
Topcoat
Performance All colors Primer: 0.5-2.5 mil Topcoat: 1.0-1.2 mil 15580% 3H+ 95-100% 1,000 + hours l,OOO+ hours 250+ hours Pass: 10 minutes
-
Gloss, 60” Pencil hardness Crosshatch adhesion Salt spray Humidity Water soak Steam alkali properties
PROCESS
Test Method
Color Film thickness
Film
ELECTROCOAT
Any conductive substrate can be coated with twocoat E-coat. A system used to E-coat conductive substrates incorporates material handling, metal cleaning and pretreatment, dual electrocoating and curing, and wastewater treatment. (See Fig. 6.) After fabrication, parts are loaded on a conveyor. The conveyor first transfers the parts through an 8- to ll-stage cleaning and pretreatment system. It is customary to pretreat the substrate with a phosphate conversion coating, either zinc or iron phosphate, followed by a rinse, which seals the conver-
PrimerKationic
Property
Major Requirements resistance, color control, and weatherability quality and corrosion resistance resistance and weatherability resistance, color control, and weatherability resistance, color control, and weatherability resistance and weatherability resistance and weatherability and chip resistance, weatherability resistance and weatherability resistance and weatherability and chip resistance, weatherability and chip resistance, weatherability
ASTM ASTM ASTM ASTM ASTM ASTM on iron
phosphate
pretreatment
with
D D D B D D
chrome
-
523-89 3363-92A 3359-95 117-95 1735-92 870-92 seal.
Formulation
is lead-free
ad chrome-free.
61
Figure ABB.)
Sethcs Bearing-free CPVC or PVDF Vertic l
l l l l l
l l
New one piece molded pump design for increased body strength and extended pump life. New models to 7-l/2 HP, 185 GPM. No bearings, no seals and no wearing parts. Can run dry indefinetely without pump damage. Easily mounts inside or outside of tank. Unique twin impeller design for high volume circulation and leakproof operation. Large selection of CPVC or PVDF filter chambers. immediate delivery on all models.
2. Typical
transformer
with
fins.
(Photo
courtesy
sion coating. After pretreatment, the parts move on to the E-coat system, which is either a monorail or index hoist system. Counterflowing design allows rinsewater to be reused multiple times to cut back on wastewater discharge. Parts are carried down into the first E-coat tank where a black cathodic epoxy primer is applied. Next the parts proceed through a dehydration oven, which removes moisture trapped between lap seams that would otherwise boil out during curing and cause flaws in the film. The parts then proceed to the cure oven where it is heated and baked at least to give partial curing of the deposited composition. The curing operation is usually carried out at a temperature sufficient to make the coating conductive, such as a temperature greater than 300”F, for a period of time ranging from 10 to 60 minutes. Once the primer is cured and made conductive, a cationic acrylic or urethane coat is applied in the
P.O. Box 12128, Hauppauge, New York 11788-0843 Tel: l-800-645-0500 l Fax: 631-435-0654 Website: www.met-pro.com/sethco.html e-mail: sethcosalesQmindspring.com West
Coast
Office: 230 N. Crescent Way, Unit I, Anaheam. Tel: 714-991-0270 . Fax: 714-991-8107
Circle 62
057 on reader
information
CA 92801
of
Figure 3. Two-coat E-coat provides and weatherability for the generator of Cummings Power Generation.)
high corrosion resistance industry. (Photo courtesy
card Metal
Finishing
Figure let.
4. First
coat
of primer/surfacer
applied
at DaimletChtys-
second E-coat tank. The second E-coat uses the substrate with the first electrodeposited coating as the cathode. The film thickness of the electrodeposited coating is not particularly restricted and can vary largely depending upon the application of finished products, etc. The baking and curing temperature of the coating film is 212 to 410°F (loo-210°C). Following each E-coat step is an immersion rinse, a second spray rinse, and a final immersion rinse. Permeate from the ultrafilters is returned to the third postrinse with the overflow from each rinse counterflowing towards the E-coat processing tank. This is one of the things that make E-coat so efficient. The excess E-coat is rinsed off the parts and ultimately returned to the processing tanks and reused.
Accessa free “purchasingagent”to submitRFQls,2417 Receivecompetingquotationsfrom supplierswarldwide Savetimeandeffort negotiatingwith suppliersandshippers Learnaboutnew products,services, and industryevents
ReceiveRFQ’sfrom buyerslookingfor productsor services Respondconfidentiallyto RF& with the termstheydetermine Savemoneyofl salespersonnet,travel, adve~~s~ng, etc. Link website,company,and productinformation
Figure 5. Second Chrysler.
coat
of primer/surfacer
applied
at DaimlerCircle
September
2000
.’
109 on reader
information
card 63
Figure
6. System
schematic
COST
EFFECTWENESS
for application
of two-coat
E-coat.
sions and minimal hazardous handling costs can translate ings .
The gains demonstrated by the two-coat system clearly duplicate those that have been recorded for the one-coat process since electrodeposition was introduced in 1961. In every industry where E-coat technology has been utilized the results are a system that increases efficiently and productivity while reducing environmental problems while producing a high-performing product. Economic studies and real-world experience indicates that manufacturers using a Power-Prime system may realize significant cost savings over conventional finishing systems. These cost reductions are due to increased automation, less sanding and rework costs, and possibly lower capital and depreciation costs. In addition the benefits of lower emis-
waste generation into quantifiable
and sav-
CONCLUSlON
E-coat technology has become the industry standard for providing a high-performance, low-cost paint film in the 35 years since it was first introduced and commercialized by PPG. Through extensive research and development PPG has further improved and refined the process to take it to even higher levels of performance. Today, with the advent of two-coat E-coat technology, end users can improve the performance of their products, decrease the impact that their finishing operation has on the enviMF ronment, and reduce their bottom line.
RELIABLE pH/ORP CONTROL complete unit for automatic pH or ORP control and treatment supplied with controller, indicator, pump, probe and buffers uni-directional proportional control * adjustable bellows pump for acid/alkali service
l
+ indicator can be upgraded to a recorder * panel or NEMA mount
l
l
v
l-800-635-5580 ,..probes,
repairs
and
-
more!
Circle September
2000
www.analyticaImeasurements.com 621
004 on reader
Ramsey
information
Ave.
Hillside,
NJ 07205
card 65
Electrocoat, and John
Springdale,
Motley
Pa.
0
ver the past few years significant advances in polymer chemistry have led to the next generation of finishing technology. Extensive R&D efforts have created new polymers that have in turn facilitated breakthrough electrocoating processes that permit a second coat to be applied via electrocoat. Today, manufacturers who require highperformance coatings can benefit from the productivity, cost reduction, and reduced environmental impact offered by the electrocoat (E-coat) process. Markets that have already benefited from this breakthrough technology include automotive OEMs, electrical generators, transformers, and even outboard motorboats. The breakthrough comes at a time when all industries are required to lower operating costs, reduce air and waste emissions, but also increase product quality and performance. The benefits of electrocoating and the new two-coat processes can help many companies meet these increasingly difficult requirements. A FORTY-VEAR
THE
ELECTROCOAT
PROCESS
The fundamental principle of electrocoating is that opposites attract. An electrocoating system applies a DC charge to a metal part immersed in a bath of oppositely charged paint molecules. The molecules form a uniform, continuous film over its entire surface. (See Fig. 1.) The process is highly effective. Since the substrate is dipped in a charged bath, the molecules are attracted to the entire surface without fail and the process assures precise film control. In a single-coat system the combination of polymer chemistry and a specific electrical charge creates a point in the process where the coating film insulates the part, ending the coating process. No more coating can be applied and every charged surface, no matter how complex the geometry, is covered.
Cathode
Anode
JOURNEY
It has long been recognized that E-coat processes are less expensive, are environmentally friendly, and can reduce manpower needs. In addition coatings applied by the E-coat process perform at very high levels in some of the most difficult user environments. PPG Industries introduced anodic technology in 1961, allowing primer coats to be applied to substrates through an electrodeposition for the first time. The technology was revolutionary and found immediate uses in automotive and industrial markets. In the following years the technology was refined continually with new chemistries and treating processes that expanded the products that could be coated and the industries that could utilize E-coat. In 1971 cathodic technology was introduced and in 1976 cathodic primers for automobiles were introduced. By the 1980s high-build, super-smooth primers and high-performance acrylic systems were developed, expanding the use of E-coat. By almost any standard E-coat technology became the coating process by which all others are compared. September
A Breakthrough
2000
I 1) t
H2
00 0 ii 0 0
Figure
1. Principle
of electrocoating
(opposites
attract).
59
THE
BENEFITS
E-coat technology following benefits.
has long been recognized
for the
Coating Efficiency E-coat systems are the most efficient coating technology. E-coat provides precise film control with variances of only 0.1 to 0.2 mil across the painted surface. Film thickness for spray systems can vary 0.5 to 2.0 mil. As a result the technology prevents runs, sags, and drips leading to a high-quality finish and reduced rework costs and material usage. A closed-loop rinse system recovers and returns dragout paint solids and rinse liquids to a E-coat tank, boosting paint usage and transfer efficiency to 95 to 99%. Line Productivity The immersion process generates two main productivity benefits: dense line loading and fast line speeds. E-coat lines are automated and it is not uncommon for them to have rack densities of 2.5 to 5 ft2 of ware per cubic foot of ware package area. Parts can be hung densely because parts are immersed rather than set up for spray application. Automotive body E-coat lines can easily process up to 100 vehicles an hour. Since E-coat systems are automated, the human error factor is greatly minimized. One line operator can run the average E-coat tank. Environmental Advantages E-coat systems are clean systems. Electrocoatings (primers and topcoats) are water-based. This means there are no or very low levels of VOCs and HAPS and they are also free of heavy metals. In fact HAPfree formulas are now available in response to the Clean Air Act of 1990. E-coat systems substantially reduce the exposure of workers to hazardous materials, they reduced fire hazards, and there is minimal waste discharge. An ultrafilter/recycled rinse system can all but eliminate wastewater and the associated treatment and disposal costs. TWO-COAT
TECHNOLOGY
Considering the benefits attributed to E-coat technology, being able to utilize the E-coat process to apply a second primer is an attractive proposition. The fundamental obstacle to developing two-coat technology was the chemical nature of the initial coat. Normally, the first coat creates an insulating barrier once the desired depth is achieved and the coating process is stopped. To achieve a two-coat process the initial coating had to contain properties that would control the electrodeposition process as the first coat is applied yet could be made conductive 60
again in order to accept a second coat. Research led to new formulations of epoxy and acrylic primers that are able to achieve that goal. The two-coat system relies upon a polymer that, when fully cured, becomes conductive enough to accept a subsequent coat of primer. It’s the chemistry of the E-coat primer that allows that process to take place. When the primer is partially cured at a temperature between 130 to 175°C (266-347°F) it reaches a conductivity of approximately lo-l2 mhos/cm or more. That is required to effectively bond a second electrodeposited composition. The second layer is then cured to a thermoset film coating. The two-coat process is able to deposit a variety of primer combinations. In the vast majority of cases, the initial primer coat is an epoxy product that has proven to provide superior corrosion protection; however, epoxy is susceptible to damage from ultraviolet rays and must be protected. Normally, an acrylic product performs this function. These combinations are available from current two-coat systems: Epoxy/Epoxy This system is the ultimate in corrosion protection. Salt spray results in excess of 3,000 hours are capable with this combination. Epoxy/Acrylic A combination of two distinct coatings (epoxy and acrylic) gives the benefits of both corrosion and UV durability. Acrylic/Acrylic This system is the ultimate in UV durability. When applying a conductive black acrylic primer, with a second coat of acrylic, we can achieve excellent UV durability with E-coat. Epoxy/Urethane This system (Power-Prime) offers better resistance to corrosion and chipping from stones. The first coat is an epoxy corrosion inhibitor. The second coat is the primer surfacer. Two-coat E-coats are being used wherever a highperformance paint film is required. The first to take advantage of the breakthrough process were the electric transformer, electric generator, and marine industries. (See Table I.) The second electrodepositable coating in these markets consists of an acrylic and is usually used as a final topcoat. This combination of an epoxy first coat and acrylic second coat results in excellent corrosion and UV resistance. The acrylic protects the epoxy from the degradation that would occur if it were exposed to the weather. The two-coat system is Metal
Finishing
Table
I. Two-Coat
Applications
of Electrocoat
in the
Industrial
Marketplace
End Use Agricultural implements (equipment) Aluminum trim Generator housings Heating, ventilation, and cooling Heavy-duty maintenance Lawn and garden Marine engines Railway Structural steel Transformers Truck market Wheels
Corrosion Aesthetic Corrosion Corrosion Corrosion Corrosion Corrosion Corrosion Corrosion Corrosion Corrosion Corrosion
Prime system at the DaimlerChrysler plant in Campo Largo, Brazil, the first commercial primer/ surfacer to be applied via E-coat, a process that improves coating application and performance. In the year since this plant used two-coat E-coat, it has experienced reduced sanding, improved appearance, increased performance, and reduced VOC emissions over conventional primer. (See Figs. 4 and 5.) Two-coat E-coat is in the process of being introduced into the truck trailer market. Wabash National will start protection with the Powecron twocoat E-coat process to coat platform trailers, thereby substantially raising the performance of coatings used in this market.
capable of providing long-term exterior durability and corrosion resistance in excess of one thousand salt spray hours. (See Table II.) Two-coat E-coat was introduced first into the transformer market in the early 1990s. The transformer industry needs a two-layer system that will provide 3 mil or 75 microns minimum film thickness, will coat hot-rolled carbon steel, adjust to variations in product geometry, and withstand long-term environmental exposure-from salt and humidity to industrial pollutants. Until the two-coat E-coat process was developed transformers were spray coated, a process that had difficulty reaching into recessed areas, especially within fins. (See Fig. 2.) The two-coat E-coat combination is also being used in the generator industry where it has been found to provide a coating system that is extremely corrosion resistant and has improved weatherability and chemical resistance as compared to other traditional coating systems. (See Fig. 3.) The outboard-motor industry has used two-coat E-coat to provide superior protection against sun, saltwater, and sand. The initial primer delivers a corrosion and chip-resistant epoxy followed by an acrylic layer than provides protection from W rays. Now, the two-coat process is being utilized by the automotive industry. PPG introduced the PowerTable
II. Film
Properties
for
Cationic
Epoxy
Lead-Free
TWO-COAT
September
based
2000
Acrylic
Topcoat
Performance All colors Primer: 0.5-2.5 mil Topcoat: 1.0-1.2 mil 15580% 3H+ 95-100% 1,000 + hours l,OOO+ hours 250+ hours Pass: 10 minutes
-
Gloss, 60” Pencil hardness Crosshatch adhesion Salt spray Humidity Water soak Steam alkali properties
PROCESS
Test Method
Color Film thickness
Film
ELECTROCOAT
Any conductive substrate can be coated with twocoat E-coat. A system used to E-coat conductive substrates incorporates material handling, metal cleaning and pretreatment, dual electrocoating and curing, and wastewater treatment. (See Fig. 6.) After fabrication, parts are loaded on a conveyor. The conveyor first transfers the parts through an 8- to ll-stage cleaning and pretreatment system. It is customary to pretreat the substrate with a phosphate conversion coating, either zinc or iron phosphate, followed by a rinse, which seals the conver-
PrimerKationic
Property
Major Requirements resistance, color control, and weatherability quality and corrosion resistance resistance and weatherability resistance, color control, and weatherability resistance, color control, and weatherability resistance and weatherability resistance and weatherability and chip resistance, weatherability resistance and weatherability resistance and weatherability and chip resistance, weatherability and chip resistance, weatherability
ASTM ASTM ASTM ASTM ASTM ASTM on iron
phosphate
pretreatment
with
D D D B D D
chrome
-
523-89 3363-92A 3359-95 117-95 1735-92 870-92 seal.
Formulation
is lead-free
ad chrome-free.
61
Figure ABB.)
Sethcs Bearing-free CPVC or PVDF Vertic l
l l l l l
l l
New one piece molded pump design for increased body strength and extended pump life. New models to 7-l/2 HP, 185 GPM. No bearings, no seals and no wearing parts. Can run dry indefinetely without pump damage. Easily mounts inside or outside of tank. Unique twin impeller design for high volume circulation and leakproof operation. Large selection of CPVC or PVDF filter chambers. immediate delivery on all models.
2. Typical
transformer
with
fins.
(Photo
courtesy
sion coating. After pretreatment, the parts move on to the E-coat system, which is either a monorail or index hoist system. Counterflowing design allows rinsewater to be reused multiple times to cut back on wastewater discharge. Parts are carried down into the first E-coat tank where a black cathodic epoxy primer is applied. Next the parts proceed through a dehydration oven, which removes moisture trapped between lap seams that would otherwise boil out during curing and cause flaws in the film. The parts then proceed to the cure oven where it is heated and baked at least to give partial curing of the deposited composition. The curing operation is usually carried out at a temperature sufficient to make the coating conductive, such as a temperature greater than 300”F, for a period of time ranging from 10 to 60 minutes. Once the primer is cured and made conductive, a cationic acrylic or urethane coat is applied in the
P.O. Box 12128, Hauppauge, New York 11788-0843 Tel: l-800-645-0500 l Fax: 631-435-0654 Website: www.met-pro.com/sethco.html e-mail: sethcosalesQmindspring.com West
Coast
Office: 230 N. Crescent Way, Unit I, Anaheam. Tel: 714-991-0270 . Fax: 714-991-8107
Circle 62
057 on reader
information
CA 92801
of
Figure 3. Two-coat E-coat provides and weatherability for the generator of Cummings Power Generation.)
high corrosion resistance industry. (Photo courtesy
card Metal
Finishing
Figure let.
4. First
coat
of primer/surfacer
applied
at DaimletChtys-
second E-coat tank. The second E-coat uses the substrate with the first electrodeposited coating as the cathode. The film thickness of the electrodeposited coating is not particularly restricted and can vary largely depending upon the application of finished products, etc. The baking and curing temperature of the coating film is 212 to 410°F (loo-210°C). Following each E-coat step is an immersion rinse, a second spray rinse, and a final immersion rinse. Permeate from the ultrafilters is returned to the third postrinse with the overflow from each rinse counterflowing towards the E-coat processing tank. This is one of the things that make E-coat so efficient. The excess E-coat is rinsed off the parts and ultimately returned to the processing tanks and reused.
Accessa free “purchasingagent”to submitRFQls,2417 Receivecompetingquotationsfrom supplierswarldwide Savetimeandeffort negotiatingwith suppliersandshippers Learnaboutnew products,services, and industryevents
ReceiveRFQ’sfrom buyerslookingfor productsor services Respondconfidentiallyto RF& with the termstheydetermine Savemoneyofl salespersonnet,travel, adve~~s~ng, etc. Link website,company,and productinformation
Figure 5. Second Chrysler.
coat
of primer/surfacer
applied
at DaimlerCircle
September
2000
.’
109 on reader
information
card 63
Figure
6. System
schematic
COST
EFFECTWENESS
for application
of two-coat
E-coat.
sions and minimal hazardous handling costs can translate ings .
The gains demonstrated by the two-coat system clearly duplicate those that have been recorded for the one-coat process since electrodeposition was introduced in 1961. In every industry where E-coat technology has been utilized the results are a system that increases efficiently and productivity while reducing environmental problems while producing a high-performing product. Economic studies and real-world experience indicates that manufacturers using a Power-Prime system may realize significant cost savings over conventional finishing systems. These cost reductions are due to increased automation, less sanding and rework costs, and possibly lower capital and depreciation costs. In addition the benefits of lower emis-
waste generation into quantifiable
and sav-
CONCLUSlON
E-coat technology has become the industry standard for providing a high-performance, low-cost paint film in the 35 years since it was first introduced and commercialized by PPG. Through extensive research and development PPG has further improved and refined the process to take it to even higher levels of performance. Today, with the advent of two-coat E-coat technology, end users can improve the performance of their products, decrease the impact that their finishing operation has on the enviMF ronment, and reduce their bottom line.
RELIABLE pH/ORP CONTROL complete unit for automatic pH or ORP control and treatment supplied with controller, indicator, pump, probe and buffers uni-directional proportional control * adjustable bellows pump for acid/alkali service
l
+ indicator can be upgraded to a recorder * panel or NEMA mount
l
l
v
l-800-635-5580 ,..probes,
repairs
and
-
more!
Circle September
2000
www.analyticaImeasurements.com 621
004 on reader
Ramsey
information
Ave.
Hillside,
NJ 07205
card 65