Hard anodising

The technical hard anodising process is a combination of physics and chemistry. The hard and dense layers have an extremely high resistance - especially to abrasive stress. Hard anodised parts can be used wherever abrasive stresses occur. Due to the density and structure of the layer, hard anodised layers also have a high corrosion resistance. The dielectric strength per µm is 20 to 30 V per base material. Hard anodised coatings can also be impregnated with Teflon, which improves the sliding properties.

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In principle, hard anodising is the same process as anodising. Here, the aluminium is converted into an oxide. The main differences lie in the parameters of acid concentration, current density and temperature with which the electrolyte is operated. The layer thicknesses achieved are many times greater and, depending on the alloy, can be up to 100 µm. In addition, the anodised pores are smaller in diameter, which leads to higher hardness. A disadvantage of hard anodising is its colouring capacity. Since these layers have a dark surface, they can only be dyed to a limited extent. The colouring of hard anodised components in black is no problem. Other colours are only possible to a limited extent. The most frequent areas of application for this process are in the production of components that must have a high degree of hardness and thus good wear protection.

Due to the combination of the layer structure and the high layer thickness, a hardness of approx. 500 HV and a current-insulating layer with a dielectric strength of 20 to 30 V per um are achieved. Furthermore, hard anodised coatings have a very good corrosion resistance. In addition, the layers can be Teflonimpregnated to improve the sliding properties. These properties enable a wide variety of applications, e.g. in medicine and defence technology, aerospace, offshore, etc. All aluminium alloys with a copper content of less than 2% can be hard anodised. The layer thickness is half of the layer thickness, whereby the other half diffuses into the base material.

Grey, Black, Nature

Summary

  • With hard anodising, colouring is not possible with every colour, and the appearance also differs from the anodising process. We will be happy to advise you.
  • Our baths allow us to process workpieces with dimensions up to 105 x 295 cm. Uncoloured components, as well as black and RAL 8000 are possible in these dimensions.
  • Much higher layer thicknesses are achieved, which can be up to 100 µm due to the alloy. In addition, the diameter of the anodised pores is smaller, which leads to higher hardnesses.
  • High copper alloys with more than 2% copper content cannot be hard anodised.
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Advantages

  • High corrosion protection
  • High abrasion resistance
  • High hardness due to alloy of approx. 500HV
  • High dielectric strength of 20-30 V per µm layer thickness
  • Dimensional accuracy of your workpiece. It should be noted that only 50% of the generated layer thickness is noticeable as a "job". 50% of the layer diffuses into the base material. Please note this for fitting parts!
Anodising layers Hard anodising

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