Customer Application Brief
Paint and Coatings
Filtration in the Phosphate and Electrodeposition Processes
Of an Automotive Assembly Plant
Introduction
Automotive assembly is the process of assembling the parts of an
automobile that comprise the outer body of the vehicle. This process, which is highly automated, includes coating (or painting) the
vehicle. However, prior to coating the vehicle, removal of
particulates from the vehicle body is necessary. This is
accomplished by a number of pre-treatment steps, which
include rinsing and washing the vehicle body. These steps are
a critical part of the automotive coating process, as inadequate
pretreatment can result in a defective coating.
This Customer Application Brief (CAB) presents the benefits
of using a filter system that demonstrates efficient reduction
of particulates and provides significant life advantage in the
phosphate and electrodeposition (ED) processes.
The Process
During the fabrication of the automobile body parts, a number
of stamping, machining and welding operations are performed.
Upon completion of the body assembly, it is inspected and sanded as needed to remove irregularities from the surface, such as scratches
and weld splatter. The result of these operations is a dirty vehicle, covered with particulates such as weld balls, grease, dust and fine grit.
All of these particulates must be reduced prior to coating the vehicle.
The pretreatment process is comprised of several stages, including spray rinsing and caustic washing the vehicle, followed by a pretreatment step, commonly referred to as ‘phosphate’. The phosphate wash reduces surface roughness, retards iron and steel rusting, and
improves adhesion between the metal and the paint. The caustic wash removes oil and particulates, including weld balls.
After the phosphate stage, the next step is the electro deposition (ED) process. Historically, rust would originate in the interior recesses
of the vehicle body. The use of the ED paint coats the entire automobile body, inside and out, to protect these surfaces. The ED paint also
improves adhesion of the subsequent primers, top coats and clear coats, thereby reducing the level of paint chipping or peeling.
Description of the Application
The process begins with a thorough washing of the vehicle body. This is accomplished in a several stages, which includes rinsing, caustic
washing, and additional rinsing. The first (washing) stage can be accomplished by spray, immersion or a combination of both. This will reduce
the bulk of the contaminant from the automobile body.
The next step of the process is the zinc phosphate treatment stage. This prepares the surface prior to the ED process. The zinc phosphate
system is applied via immersion of the vehicle body into the phosphate solution.
The final rinse stage consists of a pure, deionized (DI) water spray. The entire process utilizes a cascade system where a portion of the
water from each step is purposely diverted to the previous washing station, while fresh make-up DI water enters the cleanest or latest
stage, of the washing system. This, along with filtration, allows for control of the overall water cleanliness for the entire vehicle body
washing process.
Once the vehicle body has been thoroughly washed, it is ready to receive the ED coating. The ED paint is applied when the vehicle body
is immersed into a paint bath where direct current is applied between the part and a counter electrode. Paint is attracted and deposited
onto the vehicle body by the electric field. The vehicle is then removed from the bath and rinsed to reclaim undeposited, or excess paint.
Like the phosphate system, the ED system utilizes a cascade system. This ensures that the cleanest DI water is used to rinse the paint in
the final stage of the ED system. A proper filtration system is critical in maintaining the integrity of the ED system.
Rinse
Wash
Phosphate
Rinse
DuoFLO
Filters
To ED
Water
Figure 1. - General Automotive Washing Process Showing Typical Filter Locations
The Problem:
If the body is not thoroughly washed and free of debris and oil, the particulates will interfere with the coating application and the vehicle
paint quality will be compromised. Typical contaminants include, but are not limited to, sludge, oil, weld balls, metal fines, fibers and
micro-organisms. These particulates are present as a result of the fabrication and assembly operations, and other environmental factors,
such as clothing fibers on operations personnel and dust in the atmosphere. Since the pre-treatment fluids are recycled, removal of
particulates from the fluids is critical to ensure proper washing of the vehicle body. This is accomplished through filtration of the process
water, detergent solutions and zinc phosphate solution.
Typically, bag filters have been used in this application, since they are relatively cheap and easy to replace. However, conventional bag
filters have limitations in this application, allowing contaminants to remain in the effluent, and ultimately on the vehicle. Contamination
in the phosphate system can carry over to the ED system, causing coating defects and ruining the appearance of the paint, up to and
including, the final clear coat. The manufacturer is then forced to address coating defects or poor paint quality in one of four ways:
•
Choose not to repair the problem area and hope it does not present any future problem Minor sanding of defect area in the paint and
repainting as needed
•
Sand and repaint the entire panel
•
Sand and repaint the entire automobile body
Any one of the above options will have a negative impact on the automotive manufacturer, either from quality reputation, lower productivity or higher operating expenses. The cost of defects and rework is a major concern in an assembly plant, and can exceed $5,000,000
per year. For this reason, extensive efforts are undertaken to maintain the cleanliness of both the phosphate and ED systems. This is
primarily addressed with filtration.
The filter must meet two criteria to be effective.
•
The filter must reduce the contaminants found in the wash water, rinse water, and paint.
•
The filter must exhibit sufficient life to be cost effective.
Typically, cheap, bag filters are used in these automotive assembly processes. However, if the bags are being changed frequently, productivity can be negatively impacted. As a result, the cost effectiveness of a typical bag filtration system should be evaluated. The total
filtration cost should be determined, taking into consideration all costs associated with maintenance of the system, such as purchase price
of the filter, labor for installation and change out, disposal costs, employee exposure, cost of defects and other system components.
2
The Solution
Manufacturing a vehicle with a defect-free coating starts with the integrity of the phosphate and ED systems. There are three major
requirements of these systems include:
•
Water and chemicals must be free of contaminants when introduced into the system.
•
Holding tanks must be routinely cleaned following a regimented maintenance system.
•
Filtration system must be cost effective and designed to maintain cleanliness of wash water and cleaning solutions to extend fluid
service life.
3M Purification has developed an advanced filtration system which can meet
or exceed all of the above requirements. The system, developed using 3M
Purification’s extensive filtration experience, and is now available to users of
standard bag type filters and housings.
The 3M™ DF series filtration system is an advanced alternative to standard
bag filters which are commonly used in the automotive assembly process. The
3M DF series filter media features a true graded-porosity structure combined
with a 62% increase in filter surface area, as compared to standard filter bags.
The 3M DF series system incorporates a unique design which includes the filter
element, coupled with a stainless steel support basket, to provide for 100%,3
dimensional support of the 3M DF series filter. This eliminates potential for
filter element rupture and the resulting gross contamination of the downstream
effluent. Additionally, the hold-up volume of a 3M DF series filter is reduced by
67%, as compared to standard filter bags, which minimizes worker exposure to
process fluids.
3M™ DF Series Filter Systems
Phosphate Wash - The 3M DF series filter system has been successfully applied (as shown in Figure 1) in all stages of the pre-treatment
process at customer locations worldwide with a significant portion in the phosphate wash stage of automotive assembly. In fact,
customers have realized up to 7.4 times increased dirt holding capacity using a 3M DF series filter versus the standard bag filter.
Phosphate Conditioning - 3M DF series filters have also been applied in the phosphate conditioning stage of the pre-treatment process
providing up to 63 % greater dirt holding capacity than bag filters, while extending filter life by up to 40 % . Graphs 1A and 1B show the
average results of a comparison of the 3M DF series filer system and standard filter bags in the phosphate conditioning stage for two sets
of filters.
Graphs 1A
Graphs 1B
100%
100%
Dirt
Holding
capacity
Filter life at
equivalent
pressure
differential
Set 1
Set 2
Set 1
Set 2
Competitor
3M™ DF Series
Competitor
3M™ DF Series
Graphs 1A and 1B. - 3M™ DF Series Filter Advantage in Phosphate Conditioning Stage
Electro Deposition - Applied in the electro deposition stage of the automotive assembly process, the 3M DF series filter (10 micron)
was compared to standard filter bags (10 micron) in 5 multi-element housings. The filters were changed at a fixed differential pressure of
18 psid. The 3M DF series elements required replacement an average of 1.5 times per month, while the competitive bag filters required
change out 7-8 times per month (Graph 2). This equates to an 80% decrease in filter usage when applying the 3M DF series filtration
system.
3
In addition, several customers have applied the 3M™ DF
series system to upgrade their filtration systems (from 25 to
10 microns), realizing an average of 1.7 times dirt holding
capacity, while maintaining filter life.
•
•
•
•
Reduction in number of weld balls and fine metal particles
More than 3 times more efficient removal of oils
Trapped (cellulosic) fibers
Reduction in micro organisms
These advantages result in a better quality coating, with fewer
defects, and less rework for the customer. One customer
estimates that using 3M DF series filters will significantly
reduce the number of cars reworked, with a potential cost
savings of $1.75 million per year.
Another automotive assembly customer calculated an annual
cost savings of $34-40K per year after switching to 3M
DF series filters. This does not include savings realized by
reduction in rework, which is estimated to be $1.5-2 million
per year. In this particular case, the customer was able to
significantly reduce the tank cleaning frequency each year. An
itemization of the savings estimates are shown in Table 2.
Conclusion
Efficient filtration is essential for proper maintenance of the
phosphate wash and ED systems in automotive assembly. The
application of 3M DF series filters in place of standard bags has
been successful at all of the major automotive manufacturers
in the world, reducing rework and allowing for significant
operational cost savings. The 3M DF series filtration system is
ideally suited for automotive assembly applications, as well as
a number of other industrial applications, when compared to
standard bag filters.
8
7
Number of Filter Changeouts
Other advantages observed by automotive assembly customers
upon conversion to 3M DF series filtration system include:
3M™ DF Series Filters vs Bag Filters in Electrodeposition Line
9
6
5
— Bag Filters
4
— 3M DF Series
3
2
1
0
1
2
3
4
5
Month
Graph 2. - Filter Changeout Frequency
Item
Cost savings (%)
Reduction in number bags used
5-7/year
Reduction in labor for tank cleaning
10-20/year
Tank cleaning/maintenance chemicals
1-3/year
DI water makeup
1-3/year
Solid waste disposal
3-5/year
Waste water disposal
1-2/year
Utilities
1-5/year
Table 2. - Filter bag system vs. DuoFLO Filters
Important Notice
The information described in this literature is accurate to the best of our knowledge. A variety of factors, however, can affect the performance of the Product(s) in a particular
application, some of which are uniquely within your knowledge and control. INFORMATION IS SUPPLIED UPON THE CONDITION THAT THE PERSONS RECEIVING THE
SAME WILL MAKE THEIR OWN DETERMINATION AS TO ITS SUITABILITY FOR THEIR USE. IN NO EVENT WILL 3M PURIFICATION INC. BE RESPONSIBLE FOR DAMAGES
OF ANY NATURE WHATSOEVER RESULTING FROM THE USE OF OR RELIANCE UPON INFORMATION.
It is your responsibility to determine if additional testing or information is required and if this product is fit for a particular purpose and suitable in your specific application.
3M PURIFICATION INC. MAKES NO REPRESENTATIONS OR WARRANTIES, EITHER EXPRESS OR IMPLIED INCLUDING WITHOUT LIMITATION ANY WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR OF ANY OTHER NATURE HEREUNDER WITH RESPECT TO INFORMATION OR THE PRODUCT TO WHICH
INFORMATION REFERS.
Limitation of Liability
3M Purification Inc. will not be liable for any loss or damage arising from the use of the Product(s), whether direct, indirect, special, incidental, or consequential, regardless of
the legal theory asserted, including warranty, contract, negligence or strict liability. Some states do not allow the exclusion or limitation of incidental or consequential damages,
so the above limitation may not apply to you.
3M Purification Inc.
400 Research Parkway
Meriden, CT 06450
U.S.A.
Phone (800) 243-6894
(203) 237-5541
Fax
(203) 630-4530
www.3Mpurification.com
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