aluminum oxide polymer composite layers
what is hard anodizing?
Hard anodizing is the term used to describe the functional refinement of aluminum components as anode in special, cold electrolytes. This process is sometimes also referred to as hard coat anodizing. Hard anodizing creates very thin, non-metallic conversion coatings. Parts of the base material become fully integrated with the coating, which results in an extremely high bonding strength of the anodic layers. Aalberts surface treatment offers two hard anodizing processes: CompCote® and HART-COAT®.
hard anodizing with CompCote®
CompCote® stands for hard-anodized aluminum oxide-polymer composite coatings. The coating process has been patented, among others, in Europe and in the USA.
hard anodizing with HART-COAT®
One of our core competencies, HART-COAT® laid the foundation for hard anodizing in Germany as early as at the beginning of the 1960s. Today, we serve customers from all key industries. Every year, more than 500 million components are finished with our reliable hard anodizing processes.
The advantages you benefit from when partnering with Aalberts surface technologies:
- Cutting-edge process technology for aluminum components in lengths of up to eight meters
- Great variety of processes for individual component properties
- Maximum precision with our own electrolytes
- HART-COAT® conforms to the ISO 10074 standard
- We are the market leader for hard anodizing processes in Germany and, thanks to many locations in Europe and China, we are well positioned when it comes to the implementation of international projects
When materials are finished with CompCote®, the base material is transformed into hard-anodized layers through anodic oxidation and the aluminum oxide layer’s simultaneous molecular bonding to polymers. This process creates an ideal bond between the coating and the base material. Due to the molecular polymer content, CompCote® offers chemical bond bridges when combined with specifically matched top coats so that an excellent bonding strength is created here as well.
Thanks to the very hard aluminum oxide, the CompCote® surface treatment technique scores with high, alloy- and process-dependent strength. When subjected to abrasion resistance testing (Taber Abraser test), the coating excels with outstanding resistance to wear. Often, it scores better than conventional, anodized coatings. CompCote® coatings have high corrosion resistance. When subjected to notched-bar impact testing, they show a fibrous fracture pattern, whereas conventional oxide layers burst in a brittle way similar to glass.
CompCote® creates an optimized micro structure on the surface: In friction pairings and friction tests, the composite layers show excellent gliding properties – so-called “seizures” as a result of poor lubrication could be excluded. Apart from that, CompCote® coatings can be easily dyed. Our standard colors include black, titan grey, blue, red, gold and green. The colored surfaces are more resistant to light than dyed conventional anodized coatings. CompCote®-H is the variant to go for when it comes to special requirements. This coating is even harder and offers even better wear and corrosion protection.
CompCote® is suitable for almost all aluminum alloys.
Hard anodizing is a surface coating process for the functional refinement of aluminum materials. Using electric current, we transform the workpiece surface into a hard, ceramic-like aluminum oxide layer. The new layer is created in the form of regular, hexagonal cells which, like honeycombs, are perpendicular to the workpiece surface. This columnar arrangement creates a particularly stable cell structure; each cell has a pore channel. As a result, HART-COAT® protects workpieces against wear and corrosion. Available in different variants and suitable for many post-treatment processes, HART COAT® is a very versatile type of coating.
As a result of the aluminum oxide’s metamorphosis, HART-COAT® coatings are extremely hard and wear-resistant. During the hard anodizing process, half of the oxide grows into the base material, whereas the other half grows out of it. This creates a particularly strong bond between the coating and the base material. The ceramic-like HART-COAT® layer is electrically insulating. It has low thermal conductivity and high dielectric strength. With increasing coating thickness, the dielectric strength increases, but not proportionally. When applied as a protective layer to the bottom ends of motor pistons, it is able to withstand extremely high temperatures for a short time. Depending on the requirements profile, special post-treatment processes can be implemented to further increase the wear and corrosion resistance or the gliding behavior.
|Temperature in °C||Heat conductivity in W/m·K|
Be it wrought alloys, cast alloys or die-cast alloys, almost all technically interesting aluminum alloys may receive a finishing with HART-COAT® coatings. Where possible, the following must be observed should you decide to have your components coated by us:
- No material, processing or surface defects
- No oil residues
- Protective, parts-specific packaging
- Machining before coating
- No foreign particles on the workpiece surface
- Thoroughly deburred and, if possible, rounded edges
- End distances must be taken into account
- Bleeder holes might become necessary
fields of application for materials coated with CompCote®
The combination of low-density aluminum and CompCote® opens up new possibilities when it comes to technical and decorative applications with increased quality requirements. CompCote® does not affect the base material’s flexural fatigue strength, which makes it particularly interesting for applications in the aviation sector.
further areas of application in which CompCote® excels:
- Electrical engineering
- Mechanical engineering
- Medical technology
- Packaging machines
fields of use of hard-coated materials
Thanks to its good wear resistance, hard-coated aluminum can replace more expensive, wear-resistant steel or other corrosion-resistant materials.
Hard-anodized aluminum is used to prevent contact corrosion, improve the gliding properties and increase the electrical or thermal insulation.
The density of aluminum alloys is equal to one third of the value of common iron materials and non-ferrous metals. When switching from steel or brass to aluminum, it is possible to significantly reduce the inertial forces of fast spinning machine parts. This results in new constructive possibilities and energy cost savings. HART-COAT® creates the required surface resistance.
examples of components which can be finished with HART-COAT®:
|Iron bottoms||Bearing shells|
|Surgical instruments||Baffle plates|
|Damping chambers||Guide rollers|
|Guided cylinders||Cam discs|
|Housings||Pneumatic and hydraulics cylinders|
|Holders and fixtures||Rollers|
|Heating plates||Transport levers|
|Camera parts||Compressor wheels|
|Rocker arms||Toothed wheels and racks|
|Clutch parts||Cylinder liners|
HART-COAT®-GLATT - especially smooth and wear-resistant
HART-COAT®-GLATT (HC-GL) is a process variant of HART-COAT® that produces very smooth and highly wear-resistant coatings on aluminum materials. HC-GL coatings are formed by anodic oxidation in a cooled acid electrolyte of special composition. We offer the process at our sites in Kerpen, Weiterstadt, Kirchheim as well as Göppingen-Voralb.
|Temperature in °C||Heat conductivity in W/m·K|
HC-PLUS surface treatment with PTFE
The anti-friction and corrosion behavior of HART-COAT® layers can be improved with the use of PTFE
(polytetrafluorethylene). The PTFE particles are applied to the HART-COAT® layer in a secondary process. This supplies optimum dry-lubricated performance, and the anti-adhesive properties of the surface and the anti-adhesive properties facilitate the cleaning of the surface.
Our HART-COAT-H2® (HC-H2®) is a hard-anodic coating that was specially developed for hydrogen technology applications.
The anodic layer is particularly suitable for several aluminum components in the hydrogen path of fuel cells. Due to the dense and homogeneous layer structure as well as the only slight increase in roughness by the anodization process, there is a high general corrosion resistance. This higher resistance leads to longer durability of the electrically non-conductive anodic layer, which also increase the resistance to crevice corrosion or under-surface corrosion on sealing surfaces. The still intact aluminum oxide layer maintains the continuous barrier effect against hydrogen which is another advantage using HC-H2® instead of classic (hard) anodic layers.
- Anode recirculation blower (ARB)
- Hydrogen gas injector (HGI)
- Anode block as carrier module for ARB and HGI
- Hydrogen supplier module (HSM)
- Rails or manifolds for hydrogen distribution (from filler via pressure vessel to stack)
- Typical operating conditions for fuel cells range in temperature between -40 °C and +120 °C with a pressure load of up to 20 bar
- High requirements for corrosion resistance and impermeability in this area
- Test procedures for individual stresses (temperature change, impermeability and corrosion) or superimposed stresses (cyclical complex stresses) specified by OEMs and suppliers have been passed successfully
- Typical layer thicknesses range between 10 to 25 μm (+/- 5) with a typical layer hardness of > 450 HV 0.025
industries we serve
frequently asked questions
Yes, given that the aluminum alloy has the right mechanical properties.
The aluminum component’s mechanical properties (such as the tensile strength) must be suitable for the respective application.
Compared to steel, aluminum offers the following advantages:
- Aluminum is about two thirds lighter than steel
- Use of aluminum components in vehicles
- Fuel savings and thus less pollutant emissions
- Realisation of higher payloads
- Increased driving ranges of electric vehicles
- Aluminum is a good thermal conductor (Al: 170-220 W/mK, steel: 47-58 W/mK)
- Aluminum can be processed and shaped in countless ways
Usually, oil and residues compromise the quality of the coating. They can have an insulating effect that prevents the formation of a layer. Since hard-anodised coatings are conversion coatings, residues may later be visible on the surface. When oil or other residues come off during the coating process, the anodizing bath becomes soiled. Oil and residues inside the bath may reattach to the components when these are being removed from the bath.
Hard anodizing improves the wear and corrosion resistance of aluminum components. Hard-anodized coatings are thermal and electric insulators. Since they are electrically insulating, they can be used for electrical isolation. Components treated with hard anodizing may be temporarily exposed to high thermal loads. As the high temperatures reach the base material evenly and with delays only, they will not damage the components. Hard anodizing is the finishing method to go for when it comes to aluminum components for mass applications.
The maximum weight depends on the capabilities of the coating plant. As aluminum has a low density, it is not the weight, but rather the dimensions of the component which have to be considered.
These coatings are so-called conversion coatings. Parts of the base material become fully integrated with the coating, which results in an extremely high bonding strength of the anodic layers.
Any questions? Contact us directly or select a process location near you.