The appliance industry has long relied on surface treatment chemistries such as zinc phosphate and electro-coating technologies to properly clean, conversion coat, and paint metal substrates. These surface treatments create and sustain a lasting quality finish and help prevent corrosion to enhance the aesthetics of finished goods and the working life of inner components.

A new multi-functional coating technology has recently been introduced to the appliance industry. Electroceramic coating allows manufactures and suppliers to achieve a combination of chemical, corrosion, temperature, and abrasion resistance many times greater than those of traditional coatings. Along with increased performance results, this technology can aid manufacturers in reducing parts and processing costs associated with creating a lasting finish. This new coating process extends the life of parts exposed to harsh operating conditions. It delivers a ceramic toughness that is flexible and durable and one that can lower part and system costs.

Introduced by Henkel Corp. as Alodine® EC2™ , the electroceramic coating technology is designed to work on most light metal surfaces such as aluminum, aluminum alloys, titanium, titanium alloys, and aluminized, aluminum-plated and IVD or Ion Vapor Deposition aluminum substrates. The coating is also suitable for aluminized ferrous materials.

Based on a titanium analog of electrodeposited oxides, electroceramic coating forms a protective layer of titanium oxide ceramic that resists corrosion, increases wear resistance, and reduces surface friction of the finished coated surface. As the ceramic layer of this coating provides a smooth finish, parts generally have a soft feel similar to that of a finished ground surface.

Enlarge this picture Fig. 2. Performance data on salt spray testing results for corrosion.

Naturally flexible and tough, electroceramic coating provides a protective barrier that resists chips and flakes. As tested with a gravelometer, electroceramic coating protection is far superior to the protection of e-coat and paint. The finish itself appears light metallic grey in color and is aesthetically pleasing, requiring no post-application chemical, thermal or infrared cure.

For end use applications where color choices are required, electroceramic coating technology is compatible with most typical powder paint finishes. The coating provides an excellent base for paints, adhesives, sealants, and thermal spray coatings, and dramatically improves the adhesion of spray-applied materials.

Traditional cleaning and shot blast preparation are not required prior to thermal spray application. Fig.1 shows the appearance of the coating on a range of different parts and components.

In electroceramic coating, an electrolytic process deposits a specially formulated ceramic layer onto the surface of a metal substrate. The thickness of this layer ranges from 3 to 15 microns of transition metal oxide using the titanium analog as the focus. The coating has a hardness of 637 to 800 Vickers, as tested with a nano-indenter, yet is extremely flexible. The coating’s roughness is less than 0.07 microns with a coefficient of friction of 0.2, resulting in a smooth finished surface.

Enlarge this picture Fig. 3. Steps required for electroceramic coating process versus traditional coating processes.

When a metal substrate is coated with an electroceramic coating, the surface resists abrasion and provides increased wear resistance. (Tested to 2,000 Taber cycles, C-17 Wheel, with no wear-through on a coating thickness of 12 microns.) Unlike traditional finish coatings, electroceramic coating is highly flexible and exhibits a pass rating for flexibility of 1-2 T bend, per the ASTM D 4145 test method.

In addition, the electroceramic coating will coat the metal substrate in any area that is wet with the chemistry, so that internal passageways, crevices and holes can benefit from the coating technology as well as exteriors.

Electroceramic coating is stable at extremely high temperatures up to 900 DegC, well beyond the melting temperature of aluminum. In applications where thermal resistance is critical, electroceramic coating will remain intact during thermal events where substrates themselves may fail, as can be experienced in pumps, compressors, and engines.

The mechanical, chemical, and life cycle requirements of the finished appliance dictate the substrates selected for use in an assembly. Designers, engineers, and process professionals go to great lengths to select the appropriate material for the end use environment and the forces that are experienced by the appliance.

Enlarge this picture Fig. 4. Electroceramic coating does not require pretreatment conversion coatings or seals.

Both the material’s cost and its appropriateness for an application strongly factor into substrate selection. For parts such as pumps, valves, tanks and hoses, chosen substrates have included stainless steel, brass and certain plastics that resist chemical wear and corrosion. Stainless steel, however, is more expensive than aluminized steel. Cast brass costs more than aluminum. And plastics prices have been on the rise, as they are closely tied to the petroleum market.

With new electroceramic coating technology, engineers can consider potentially cost-saving alternative substrates for their particular applications. By treating substitute materials with electroceramic coatings, less expensive substrates can perform at levels meeting or exceeding the levels required by the industry. (See Fig. 2.)

By using less dense materials — such as aluminum versus brass — manufacturers can potentially reduce the weight of individual parts and of the final assembly. Through material substitution — for example using aluminized steel in place of stainless steel, manufacturers can reduce overall materials costs without sacrificing performance or working part life. As substitute materials are readily available in the market, manufacturers minimize purchasing complexity and lower overall costs.

The electroceramic coating process is much less complex than traditional surface treatment chemistries. Given that it requires fewer processing steps, electroceramic coating allows for faster process speeds and reduced processing costs. (See Fig. 3.)

Compared to traditional methods such as paint finishing, anodizing or electro-coating, electroceramic coating processes require a smaller footprint in the plant, and less time to apply the coating in order to get a final finish. By reducing the necessary steps and processes to complete the electroceramic coating, manufacturers can save facility space.

Electroceramic coating does not require pretreatment conversion coatings or seals. Chromate and solvents are eliminated from the surface treatment steps. The overall process is just six steps, compared to 16 steps for traditional surface treatment finishing processes.

In order to apply electroceramic coating technology, parts go through the following series of steps:

Parts enter a cleaning stage to remove any soil contaminants found on the surface of the metal.
1. Parts go through first rinse stage.
2. Parts go through second rinse stage in preparation for the coating stage.
3. In the electroceramic coating tank, parts are charged to create a plasma field that deposits the titanium oxide coating from the solution onto the surface, creating the finished ceramic coating.
4. Parts go through one to two final rinses.
5. Parts are dried and moved to their next process in the manufacturing plant.

Another virtue of the electroceramic coating is that it can be easily repaired. Performing such repair requires only that the part goes through the application process an additional time in order for the elecroceramic coating to deposit itself back on the area that was previously damaged. Unlike many traditional coatings, electroceramic coating does not have to be stripped off or sanded down prior to reprocessing. When parts undergo a subsequent application, the functional coating that is applied builds itself on the area that is bare and evens itself out to a uniform layer with the original deposited coating.

Electroceramic coatings provide a surface that is ready to be painted, bonded to, and finish coated. The final surface is thousands of times harder than paint, yet is as flexible as paint.

While the coating is inherently a final finish, electroceramic coating can accept most paints for improved aesthetics and greater customer choice. Parts treated with electroceramic coatings require no additional primers prior to bonding with most adhesives. Once the electroceramic coating has been applied to a substrate, the part can be treated with Teflon, Kynar, and other thermal spray coatings as required by the manufacturer.

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