Coatings World - November 2010

Water consumption has been dramatically reduced as a result of the new pre-treatment process.

The typical golden shimmer of the Bonderite NT coating facilitates visual inspection of parts. Pascal Kern of De Dietrich and Bernard Claveau of Henkel worked hand in hand to put the new pre-treatment process in place.

two to three times higher if the entire coating process were outsourced to an external service provider. Moreover, having the process in-house allows the company to respond flexibly when it comes to choosing colors. Mr. Kern is responsible at De Dietrich Thermique for the entire painting process and hence also for the use of the new Bonderite NT pre-treatment technology, which is applied by spraying.

IMPORTANT CONTRIBUTION TO
RESOURCE-EFFICIENT MANUFACTURING

The continuous spraying line for pre-treatment comprises a total of four process steps. The first two steps are alkaline degreasing followed by a three-stage rinse. Then the Bonderite NT conversion coating is applied and the surfaces are rinsed with deionized water in the final step. The advantages of the new process have impressed Mr. Kern.

“The new process from Henkel has worked perfectly from the start and the results have exceeded our expectations,” he said.

The elimination of the previously necessary passivation stage not only makes the entire process shorter but brings other benefits as well. A big advantage is also that there is no need to heat the system to 55°C, as required in the old phosphating zone, since the new conversion process operates at room temperature. Mr. Kern estimates the energy savings to be around 30 percent compared to the previously used iron phosphating. Last but not least, the shorter contact time of 45 seconds creates basic potential for accelerating throughput on the pre-treatment line still further. However, this advantage is not currently exploited at De Dietrich Thermique because of the slower downstream powder coating process.

Better results have also been achieved in terms of
water consumption, cleanliness and disposal. What
makes a big difference is that phosphates and heavy met-
als were deliberately rejected in the product’s develop-
ment. This means that the process no longer generates
sludge, and the time and expense required for mainte-
nance and disposal have thus been dramatically reduced.
“We no longer have to remove the sludge from the tank
every day, the pipes and spray nozzles remain uncongest-
ed, and we need fewer replacement parts,” Mr. Kern said.

BETTER CORROSION PROTECTION
COMBINED WITH OPTIMAL PAINT ADHESION

Before it was introduced in this pre-treatment line, the Bonderite NT process was extensively tested in the Henkel labs and had successfully completed trials on another coating line. Comparative measurements were carried out over a period of months until the final approval was granted.

Although the inorganic nanoceramic layer is just 20 to 30 nanometers thick and hence much thinner than an iron phosphate coating, the extensive preliminary tests showed significantly better results for corrosion protection and paint adhesion than those achieved with the conventional process. In the ISO 9227 salt spray test on painted steel panels, for example, De Dietrich Thermique’s specification of 300 hours with less than 1 mm corrosion creep from the scribe were not only achieved but also exceeded with a pass performance at 600 hours.