Greenkote thermal diffusion coatings protect automotive lock parts

  • 14-Dec-2009 11:59 EST
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Greenkote TD patented PM coatings work by thermo-chemical surface modification.

The automotive industry faces some of the strictest regulations when it comes to meeting environmental and safety standards regarding materials and parts for vehicles. Those restrictions became even more challenging for automakers when the European Commission adopted the end-of-life-vehicles (ELV) directive in 1997.

Put in place as a means to make vehicle dismantling and recycling more environmentally friendly, the ELV and other regulatory EU directives force automakers to search for ways to maintain the highest level of quality for metal finished parts while meeting the growing demands for environmentally safe materials.

Greenkote GmbH is a provider of thermal diffusion coatings services for the automotive and fastener industries. With the opening last fall of a new coatings plant near Munich, in Sauerlach, Germany, the company believes it has improved its ability to serve European auto manufacturers and their Tier 1 suppliers. The facility has over 2000 m2 (21,000 ft2) of operations and office space.

Greenkote is a thermal diffusion coatings process that modifies and improves the basic surface characteristics of metals and is thus applicable to metal finished parts. Because the coatings do not contain any hazardous heavy metals, this green technology is an appropriate choice to help meet the demanding specifications of the automotive industry in the EU market.

Greenkote developed PM-10 and PM-21 coatings mainly as a base for corrosion protection and low-friction topcoats. PM-10 is zinc-aluminum and PM-21 is zinc-aluminum-magnesium. Duplex coating PM-10 with e-coating is approved by various auto manufacturers including Volkswagen, Audi, and General Motors Co.

In January 2009, Greenkote started coatings production for Audi’s Tier 1 suppliers. The Greenkote PM-10 plus e-coat topcoat meets VW specification TL-196, delivering improved protection for Audi’s automotive lock parts.

Greenkote PM zinc TD (thermal diffusion) coatings meet the ELV directive because no hazardous materials are used. Also, the process used produces neither hazardous air pollutants nor industrial wastewater discharge.

The Greenkote coatings are purchased and processed as a dry powder, so there are no solvents or water to be removed during the coating process. The little water used for post rinsing can be totally recycled.

In addition to its green aspects, Greenkote zinc TD coatings offer a high level of corrosion protection due to their adhesion properties for paint, e-coat, and powder coatings topcoats. The sacrificial zinc layer in the thermal diffusion basecoat is another reason for good performance against corrosion.

In most automotive applications, there is a need for a topcoat over the Greenkote process. Currently, the best topcoat combination is a black electro-coat, commonly called “e-coat,” or “KTL” in Europe. The Greenkote PM-10 coating paired with e-coat offers several synergies and is a solid replacement for zinc-nickel plating with e-coat. Greenkote duplex coatings protect all sorts of lock parts including base plates, strikers, and latches.

Greenkote PM coatings provide high-performance corrosion protection at a competitive cost when compared to other zinc coatings such as zinc plating, hot-dip galvanizing, and zinc metal flake coatings, according to the company. With zinc TD coatings, there is no hydrogen embrittlement, which can be a concern with electroplating.

Additionally, Greenkote PM coatings provide good rubber-to-metal bonding surfaces and eliminate porosity in sinter metals while producing a thin, uniform thickness on threads, blind holes, and even tube interior walls. They also provide a hard, wear-resistant surface. Wear testing on striker wire loops shows normal wear and gouging after 5000 cycles with another duplex coating, while the Greenkote PM and e-coat barely shows any signs of wear after 10,000 cycles.

Greenkote TD patented PM coatings work by thermo-chemical surface modification. Carbon steel, cast iron, and sintered metal parts can be coated with zinc TD coatings. The coating temperatures range between 360 and 410ºC (680 and 770ºF).

The coating layer forms in steps:

1)    Zinc in the coating diffuses into aluminum in the coating and into the iron in the substrate.

2)    Iron in the substrate forms intermetallics of Zn-Fe-Al.

3)    Aluminum inclusions are formed on the coating surface.

The thermo-chemical process forms a protective layer that partially diffuses into the substrate and cannot be separated by physical or environmental testing. The aluminum inclusions on the surface are a key in healing any micro cracks or porosity in the coating while the zinc provides a sacrificial layer.

Dan Riter, Director of Engineering at Greenkote Plc wrote this article for Automotive Engineering.

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