Uniform coating of complex parts with cavities is a major performance feature of the Aquence process.
Chemical instead of electrical action
The Aquence process also differs from classic e-coating in that it
requires no metal pretreatment and no electricity to form the
coating. Through a chemical reaction in a bath of polymer emulsion, an organic layer is formed on the degreased metal surface.
A mild acid releases divalent iron ions, which then combine with
the paint particles in the solution and re-bond with the surface
of the substrate so that each ferrous area of the component is
uniformly coated in the desired thickness, while leaving plastic
parts uncoated. This makes it possible not only to coat complex
structures evenly inside and out, but also to process complete assemblies consisting of different materials.
The immersion coating line has now been in operation at the
Räckers production site in Ahaus, Germany, for more than a year,
and its performance in terms of corrosion protection and toughness has completely convinced Mr. Räckers.
“In our lab tests, the process easily achieved 1,000 hours in
the neutral salt spray test,” he said.
Scanning electron microscopy images show a uniform, dense
wet film before curing, and consistent coating thickness even on
sharp-edged geometries.
Co-cure; after application, the powder coating and the primer cure
together in the same oven.
Perfect performance on all corners and edges
This process for coating ferrous metals is purely chemical and
offers a number of decisive advantages over classic e-coating.
“Foremost among these is the absolutely uniform one-hundred
percent coating of components or assemblies, which simply cannot be achieved with electrodeposition,” said Claus Räckers,
CEO of Räckers.
Even poorly accessible areas, cavities or sharp corners and
edges can be provided with a continuous layer of corrosion-protection. With Aquence, there are none of the restrictions associated with the Faraday effect.
“As a component manufacturer for commercial vehicles, full
corrosion protection on all exterior and interior surfaces is a crucial performance feature for us and our customers,” said Mr.
Räckers, explaining why the decision went in favor of the Aquence autodeposition process.
At Räckers, it is used to provide long-term corrosion protection on complex tubular and preassembled components with intricate geometries and lengths of up to eight meters.
Seven steps to optimal results
The robust and simple coating concept comprises just seven
baths. After a four-stage cleaning and rinsing sequence, chemical
deposition takes place in the Aquence bath directly on the degreased substrates. The two-stage post-rinse removes any chemical residues from the parts.
“Compared to the e-coat process, the investment costs are
about 20 percent lower,” said Eric Ardourel, technology man-
ager Europe at Henkel. “At the same time, the line has a smaller
shop floor footprint, partly because the usual phosphating or
chromating steps are not required and also because the oven size
can be much smaller than for e-coating.”
The environmentally responsible process is therefore free of any
toxic heavy metals such as zinc or nickel and also generates practi-
cally no volatile organic compounds (VOC) or hazardous sludge, all
of which significantly reduces waste generation and disposal costs.
Co-cure process
Another positive effect on the overall process costs is the fact
that it consumes less energy. Besides needing no electricity to produce the reaction in the coating bath, energy savings are also
achieved due to the lower bake temperature in the subsequent
two-zone ovens.
“Unlike e-coating, which needs a cure temperature of about
190 degrees centigrade due to the high VOC content, the coated
components are first dried at just 60 degrees centigrade, then
briefly pre-baked at 140 degrees centigrade. This naturally also
shortens the time it takes the parts to cool down before the topcoat is applied,” said Mr. Ardourel.
About 95 percent of all parts at Räckers are powder coated.
Crosslinking of the Aquence primer and the powder coating is
performed in the same oven, also at a reduced temperature of
some 170 degrees centigrade.
www.coatingsworld.com
February 2012
