DIY Home Aluminum Anodizing

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  • Large scale DIY anodising with battery acid

    If you have been doing some DIY anodising with a small anodising bath, there is always a desire to scale things up to enable you to anodising larger and larger parts. The principle problem here is where to get the acid and where to keep it.

    Online retailers are now very reluctant to sell concentrated sulphuric acid to private individuals, so you have to resort to battery acid.

    Battery acid can be purchased online in various quantities and is normally quite easy to find. Shipping costs will not make this route cheap, so it is often wise to ask around local garages, especially motor cycle garages to see if they can supply some. Get ready for some strange looks and questions. One online retailer I have seen will sell you a 25 litre batch of battery acid for next day delivery!

    Battery acid is usually 33% sulphuric acid. To anodise aluminium we need a 20% sulphuric acid solution. Therefore to every 1 litre of battery acid, we need to add 650ml of de-ionised water. Of course, we should never add water to acid always add the acid to the water. Do this a bit at a time because it is an extremely exothermic reaction you dont want a vat of boiling acid!

    The other worry is what to keep it in!

    One approach is to use plastic picnic cool boxes. These are a nice square shape and fairly strong. The downside is that they are insulated! Anodising large parts will heat up the anodising bath, and we need it to cool down, not be kept in an insulated box! The next downside is that they do not have an air tight lid. Finally, how many times have you need a crack in the inner plastic of a cool box? Lots of times! The inner plastic liner is not that thick, and Id worry that youd puncture it if you dropped a sharp edged part. Cool boxes are not actually designed to hold liquids.

    The best thing is a 5 gallon wine and beer making fermenting bucket. These are made from thick food grade plastic and usually have a lid that closes with a mechanical seal no rubber parts to perish in the rubber. These buckets are designed to hold liquid they are designed to hold boiling liquids. The plastic is usually quite thick and designed to hold 25 kilos of water with 6 kilos of sugar dissolved in it. All wine and beer is acidic, so they cope well with acidity. They also have handled suited to take that weight! Best of all they usually cost about a tenner!

    Go to your local home brew shop and choose the thickest and heaviest bucket they have with a lid, preferably the type without a hole for an airlock. I suggest half filling with acid, about 10-15 litres of solution. For this you need around 2 gallons of battery acid.

    Use this bucket to hold the acid for your anodising bath with no fear that it is going to leak.

    For extra protection, go and get a plastic storage crate from the DIY store and place the bucket in the plastic crate. If the bucket does leak, you have a second backup! All that remains is to find somewhere to keep the bucket of acid. Having so much acid stored in the house is a little worrying, but most of us have a shed we can keep it in. It is worth making a wooden case for the whole anodising bath and putting a lock on it, along with the correct chemical warning symbols.

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