Question: Can you anodise castings ?
Answer : Some alloy types yes. the process only anodises the aluminium content of the alloy. castings usually have other elements like zinc, silicone etc added to allow the molten metal to flow into the mould. This means that the surface after anodising can be dark grey and patchy, but quite often can be covered by dying black before sealing. a satin finish ie bead blasting before anodising also helps mask this effect. high zinc content alloys fizz and dissolve in the acid bath (carbs etc) .
Question : why do some components have silver edges without any colour ?
Answer 1 : anodise only grows perpendicular to the surface, with sharp corners the anodise grows 90 degrees from both surfaces, consequently there will be an area between the sides of both layers that doesnt have any anodic pores to absorb dye. parts should be tumbled and de-burred to put a radius on all edges to stop this happening, this is a manufacturing fault and not a fault of the anodic process
Answer 2: this can also happen on mirror polished items where excessive heat can oxidise the edges if the buffing wheel catches them. This will only become apparent once the part has been anodised and dyed. the only solution is to strip the anodise and re-polish the component BY HAND and re-anodise. to stop this happening in the first place, heavy etching of the component will remove the oxidisation, but also any mirror shine.
Question : Whats the score with free machining alloys ?
Answer : FMA aluminium is a high strength alloy best suited for fast automated machining. it has a high copper content which like castings creates surface finish issues. a satin or matt finish works best
Question : Do you do "Hard anodising " ?
Answer : No. Hard anodising or Type 3 hardcoat is usually only required on moving parts where metal against metal protection is required ie . chain wheels and sprockets. its also done to cookware to achieve a non stick coating. type 2 (which is what i do) is normally sufficient for most components and will comply with any salt spray corrosion testing.
Question : Can 6082 mirror polished be anodised and keep its shine ?
Answer : it is one of the better alloys for this, but isnt the best. during the anodising process, the surface will go cloudy due to the inpurities within the alloy . a wipe with oil after cleaning will reveal a deep gloss shine. on a scale of 1-10, expect no more than a 8.
Answer : it is one of the better alloys for this, but isnt the best. during the anodising process, the surface will go cloudy due to the inpurities within the alloy . a wipe with oil after cleaning will reveal a deep gloss shine. on a scale of 1-10, expect no more than a 8.