Conversion Coatings & Phosphating
Alocrom (chromic conversion coating) can be applied either locally or all over via a dip process. It utilises hexavalent chrome (either chromic acid in the case of the dip Alocrom, or sodium/potassium dichromate in the case of local Alocrom) to convert the surface of aluminium components to greatly enhance their protection from subsequent corrosion. If applied all over Alocrom can be applied in a light (more electrically conductive) coating, or a heavier (more corrosion resistant) coating, but in either case is negligible in terms of thickness, as it is not a coating as such, but a chemical conversion of the surface. Typically it is applied to bonding points (eg. spot faces round bolt holes), under paint in a similar way to anodising, or to cover bare patches left by processing, such as left by jig marks.
Iridite NCP is one of the first hexavalent chrome alternatives to Alocrom (Specifically Alocrom 1000) which came on to the market offering an environmentally preferable REACH compliant method of converting the surface of commercial aluminium components to enhance corrosion protection. It is often used as a stand alone finish.
Phosphating is the application of a porous crystalline coating usually applied to ferrous based materials. The process is non electrolytic with the phosphate layer being produced by catalytic action between the component material and the Phosphating solution. This catalytic action producing an exceptionally strong bond of the phosphate layer to the component surface.
The coating produced is crystalline and porous and forms a very good base for subsequent applications. As an undercoat for paints it dramatically improves adhesion of the painted layer, and the application of specialised oils and greases will enhance the corrosion performance of the component, or provide lubricity for subsequent manufacturing operations.
Although most commonly applied to ferrous materials, it can also be applied to zinc or zinc plated bases where, prior to subsequent painting operations, both corrosion performance and adhesion are considerably improved.
Ashton & Moore Ltd. offers four types of Phosphating, Zinc Phosphate which gives a finer grain with a wider range of thicknesses being achievable, or Manganese Phosphate which is limited to heavier films, The Manganese phosphate coating also has different crystalline structure to zinc phosphate, this structure is laminar rather than columnar, compressive, and imparts greater corrosion resistance and lubricity without the need for additional coating, although these can be specified if required. Manganese phosphate is particularly good for components where “wearing/running in” is required, and because it is a compressive, coating continues to offer lubricative properties for extended life.
We also offer low temperature phosphate used on components sensitive to high temperature (>45’C), such as those with swaged bands packed with grease and calcium modified phosphate which offers a super fine grain finish smoother than the more traditional Zinc phosphate. The calcium modified phosphate used in the automotive and defence industries has the additional advantage of being able to employ a zirconium based post rinse, rather than the traditional hexavalent chrome one, making it REACH compliant.