Nanotechnology offers metalworking businesses great potential for more efficient and environmently friendlier pre-treatment processes. New nanoceramic conversion treatments like Henkel’s Bonderite NT score highly over traditional processes through leaner process management, lower energy costs and considerably reduced maintenance effort.
   
The current global ecological situation calls for the responsible and intelligent use of the available resources. The demand for and use of environmentally benign manufacturing technologies have therefore rocketed in the last few years. One example is De Dietrich Thermique based in Mertzwiller in Alsace, France. As one of the leading manufacturers of heating systems in Europe, the company produces over 200,000 heating boilers and hot water storage units at the site per year—about 80 percent of these are coated. In 2009, the company switched from the conventional iron phosphating metal pre-treatment method to nanoceramic conversion protection with Bonderite NT.
   
“After the old production facility was totally destroyed in a fire, one of Europe’s most advanced coating lines has now been built here. True to our company philosophy, a top design priority was the use of environmentally benign process technologies, without compromising on quality,” said Pascal Kern, technical manager at De Dietrich. The company’s high quality aspirations are obvious from a glance at its list of references. Be it at Hungary’s National Museum in Budapest, the luxury Ermitage hotel in Geneva or the IMKB stock exchange in Istanbul, heating systems from De Dietrich are in operation all over the world. Its famous post horn logo dating back to 1778 is considered the oldest in the industry.
   
In its quest for an alternative, environmentally sound pre-treatment process, the company finally opted for Henkel and its Bonderite NT surface treatment to replace traditional iron phosphating before the application of the paint finish. On the metal surface, the novel process generates a nanoceramic conversion layer that gives long-term protection from corrosion creep and improves paint adhesion. What makes it special is that its formulation contains no toxic heavy metals such as chromium and nickel, and no eutrophication-inducing phosphates or organic compounds. As neither toxic heavy metals nor phosphates have to be disposed of, the process has a high sustainability profile from the ecological point of view. However, it also brings major benefits to the pre-treatment process in terms of quality and economy.
   
Meanwhile, Bonderite NT has been in successful use at De Dietrich for a year and has demonstrated its suitability for the task at the site. Supplied as finished parts, up to 3,000 iron housings have to be prepared for powder coating every day. Mr. Kern estimates that costs would be 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 metals were deliberately rejected in the product’s development. This means that the process no longer generates sludge, and the time and expense required for maintenance 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 uncongested, and we need fewer replacement parts,” Mr. Kern said.
   
Cost savings of some €250,000 are achieved in this way. The site’s additional own purification system for treating the process water is now no longer needed.
   
“To ensure a high level of corrosion protection, we used to have to replace the conversion bath three times per year. Today, the water remains in the new, resource-efficient process,” Mr. Kern said. The Bonderite NT bath is controlled and topped up simply and quickly on the basis of the pH.

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.
   
“In the past we used to have great difficulty passing our specification with iron phosphating,” said Mr. Kern.
   
The nanoceramic coating is also superior as far as paint adhesion is concerned. Bonderite NT creates a continuous, high-density inorganic layer of nanoceramics, according to Bernard Claveau, sales representative at Henkel, explaining the principle of this modern technology. The coating increases the surface area of the metal, offering a greater surface for paint adhesion than what can be achieved with iron phosphating. The golden shimmer of the part surfaces pretreated with Bonderite NT also facilitates visual inspection of the process. More than steel, Bonderite NT can also treat aluminium and zinc.
   
“The implementation of Bonderite NT has enabled us to achieve significant improvements in metal pre-treatment over the previously used iron phosphating method,” said Mr. Kern. “The nanoceramic coating delivers outstanding quality and points the way forward ecologically and economically.”