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Is acid etching before anodizing useful?

hello...
I have 2 questions (related to each other)
1-) we use acid etching for 5 months but I have not glade bath performance so there is some negative parts; for example; mud is main problem, fluoride harms filtering system, environmental problems (although waste-water treatment system), reworks e.t.c
so, is there anybody to glad acid etching bath?

2-) are fluoride ions (in aqueous form) harmful for anodizing bath and before-later (anodizing bath) rinse baths? especially sometimes in bright parts' surface occur like pits. So I wonder is there relationship fluoride's negative effect (in anodizing or another rinse baths)
thanks...

Alaattin Tuna
engineer - Sakarya, Turkey
July 15, 2011

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I know anodisers prefer wire brushing machine to eliminate extrusion lines, handling marks, preparing the surface of aluminium extrusion for receiving very uniform and good-looking matte finish, with economical caustic etching in anodising line.

Matt appearance by acid etching is quite different than that of caustic etch to European market. Fluoride is a harmful substance for using in bath formulation and waste treatment. That is why acid etching is not preferred by European anodisers.

Erol Deniz
- Istanbul, Turkey
July 27, 2011

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July 28, 2011

We need more details on your etch process to advise you properly. It would also be useful to know which industry you are working in as the rules about what you can and can't use is dependent on the product lines you are producing.

So, can you let us know what your current bath make up is, the immersion times and temperatures, any pre- and post- etch process steps and what you are trying to achieve (is it a matte finish or bright one, is it dyed or natural anodising and which anodising are you doing, chromic, sulfuric, modified sulfuric, phosphoric, other).

In my industry the majority of anodisers in the UK will use a proprietary acid etch solution. This is not for turning a surface matt but for the removal of amorphous oxides and leaving a very clean and active surface.

Brian Terry
Aerospace - Yeovil, Somerset, UK