Paint Recycling at the DaimlerChrysler Plant in Dusseldorf, Germany:
19 August 1999
Paint Recycling at the DaimlerChrysler Plant in Dusseldorf, Germany:
* A milestone on the road to environmentally friendly vehicle painting
* The recycling and reuse of paint
* Paint sludge waste but by about 70 percent
AUBURN HILLS, Mich. and STUTTGART, Germany, Aug. 19 -- The
DaimlerChrysler plant in Dusseldorf, Germany, has, for the first
time, succeeded in completely recycling and reusing vehicle paint material.
The paint particles that land beside the body as overspray during the
application of the second coat are reprocessed and used for painting the
bodies of the Mercedes-Benz van called Sprinter.
The recycling operation is integrated into the normal painting process.
By this means, DaimlerChrysler not only reduces its requirement for new paint
by 12 percent per year -- 30 metric tons on this paint line -- but also
decreases the amount of paint sludge that has to be disposed of by 70 percent
(50 metric tons on this line). In addition, the transportation and disposal
processes are eliminated.
The process developed in Dusseldorf demonstrates again that environmental
stewardship and good business need not be contrary goals. Investment in
integrated, sustainable environmental protection also brings about a mid- and
long-term reduction in costs. Because less new paint is required and the need
to dispose of the sludge is eliminated, the roughly $380,000 invested in the
new facility will have been completely amortized after three and a half years.
The new facility has been functioning smoothly for one year now, thereby
proving its suitability. Such success has encouraged engineers to go even
further. However, first it will be necessary to completely overhaul the
second coat application process on the Dusseldorf paint line.
Three coats of paint -- three functions
Each of the three coats of paint is applied in a separate painting
process. During the first step, the bare steel body of the vehicle is
submerged in a pool filled with an anticorrosive primer, primed and
subsequently rinsed with a washing solution. After the body has been rinsed,
the ultra-filtrate containing the remaining paint particles flows back into
the basin. In this manner, the priming facility operates without producing
waste water.
The second coat of paint is known as the filler. It protects against
paint chipping and smoothes minor imperfections in the sheet metal. In the
method used previously for this process, air atomized applicators sprayed the
paint onto the body. However, as a result of this process, half of the paint
remained as undesired overspray, which had to be disposed of as coagulated and
dehydrated sludge for $270 per metric ton. By switching to an electrostatic
method, the engineers have been able to reduce these losses by about 80
percent. The new procedure imparts a positive electrostatic charge to the
paint particles, thereby causing the negatively charged body to attract them.
After the conversion to the new paint application method, the old paint,
which consists of up to 50 percent solvent, was replaced with a new filler
paint consisting of 43 percent water and only seven percent organic solvent.
The emissions have been reduced by 80 percent.
An additional benefit for the environment: Because of its high water
content, this new filler paint is recyclable in a closed cycle for the first
time. This includes the filler paint from the fully automatic spray booths
and the overspray from the manual painting in the few areas which automation
can not reach.
After the white filler has covered the gray primer, a final application of
a third coat of paint gives the body the desired color. This surface film
also protects the vehicle against the elements.
Because of a special circumstance, engineers at the DaimlerChrysler plant
in Dusseldorf can make the painting process even more environmentally
friendly. The reason is that 70 percent of the customers order Mercedes-Benz
Sprinter vans in white -- a very practical color which forms the background
for advertisements on vans. As the recycling method is suitable for all new
installations using monochromatic water paint systems and the experiences to
date have been very positive, the engineers in Dusseldorf are now also
planning to integrate the technology into the third coating process after it
has been overhauled. White, water-based top coat should be sealing more than
70 percent of all Sprinters by 2002. The overspray will be completely
recycled and reused in the painting process.
Improved paint quality by means of membranes
In order to spray the paint particles a second time, they have to be
constantly dissolved in water. To achieve this, temperature-controlled and
humid air blow the overspray mist through a grating in the floor into the
flowing water beneath. The airflow rate is 130 million gallons per hour. In
the fully automated booth, the water absorbs 100 percent of the overspray.
During the preceding manual paint application, flakes of dry paint rubbed off
shoes and pieces of dirt from the conveyor belt also enter the water. This is
why 30 percent of the overspray needs to be disposed of by the usual method of
flocculation and drying via an additional, specially constructed water
circuit.
The actual recycling process in the ultrafiltration plant concentrates the
highly diluted paint particles, forming a substance that initially consists of
equal amounts of water and solids. The water flows through several membranes
that, like a sieve, filter the larger particles of pigment out from the
smaller water molecules flowing through. Finally, in a procedure identical to
that used for new paint, the engineers check technological parameters such as
adhesiveness, resistance to chipping, and behavior under varying climatic
conditions. These checks are carried out before each application of a new
coat in the paint booth.