Throw the paint brushes away, Ron Prouse reckons the real way to colour your case involves lots of noxious chemicals.
Anodize or -dise - vb. To coat (a metal, such as aluminium) with a protective oxide film by electrolysis. - Collins English Dictionary.
The subject of this Modjitsu tutorial started one Friday night when I called a friend, Scott, to ask him a couple of questions about another matter. 'What are you up to at the moment?' I asked innocently. The answer had me reaching for my car keys, 'I'm just gold anodising some stuff out in the shed ....'
Anodising? At home? I have to get in on this action!The truth is that DIY anodising is surprisingly easy. Sure, there is the matter of highly toxic chemicals such as sulphuric acid, and the real possibility of experiencing a hydrogen gas explosion, but the process itself is easily within the realm of most computer modders.
When you are aware of them, and take precautions, the dangers just add to the fun of doing something that most people wouldn't attempt.
Aluminium is a reactive metal, but it doesn't corrode as quickly as most ferrous products. This is because an oxide layer quickly forms on it's surface, protecting the base metal underneath. When aluminium oxide forms in air the result is a white powdery layer that can be easily scraped off. Conversely, anodising is an electro-chemical process that forms a structured, crystalline 'surface skin', which is extremely durable. There are several variations to the anodising process; however this tutorial will focus on creating a decorative layer that can be coloured.
What can be anodised? Basically any aluminium can be treated, however this process is most successful with flat-sheet or turned products - so, if you have an aluminium case that you want to change the colour of, this is how to do it!
ABOVE: Prepare the container.
Step one is to prepare the container -- turning it into an effective cathode. It is important to note that any metal immersed in the acid should only consist of lead or aluminium. I'm using lead cathodes, to lessen the volume of aluminium sulphate being released into the acid solution. Cut the sheet lead into shape, drill 3/16" holes through the container and lead and bolt them together. The nuts should be on the outside of the container so they can be used as the power connectors.
ABOVE: Keep solution under 2/3rds capacity.
The bolt holes should be kept as high as possible to avoid acid seeping out of the them, and the volume of the solution should be no more than 2/3rds of the container's capacity. The reason for using two cathodes is to ensure that the anodising process occurs more evenly over the surface of the work-piece ... a lead-lined tank would be perfect, as long as there was no 'metal-to-metal' contact resulting in short circuits.
ABOVE: Dilute acid slowly to avoid 'boiling'.
The most easily procured form of sulphuric acid is from a battery wholesaler, and will be 35% strength (WW) with a Specific Gravity (SG) of 1.28. Actually this is overkill, with 10% WW / 1.2SG being enough to get a good oxide layer, however I have been using the stronger concentration with good results. If using acid concerns you, you can dilute down to a ratio of 2:1 water/acid, but add the acid to the water slowly so the resultant thermal reaction doesn't cause the solution to 'boil' over.
ABOVE: Positive and negative connections.
Hook up the lead plates with a length of 30A wire, using spade connectors under the external nuts. This is the cathode pole, and will be connected to the negative lead from the battery charger (or suitable 12V DC power supply). The aluminium bar across the tank is the anode pole, and is attached to the positive connection. As mentioned, everything in the tank should be either aluminium or lead, and external connections should be copper - to avoid sparks from arcing.
ABOVE: A potentially explosive situation.
When the tank is connected and working correctly, there will be a 'sheet' of hydrogen bubbles generated across the lead sheet by the electrolysis action. With good ventilation this is not a major issue, but if it occurs in a confined space then the build up of highly flammable hydrogen gas over several hours is an explosive situation. Especially if the explosion then sprays sulphuric acid all over the place ... so there are a few rules worth following.
ABOVE: Prepare the aluminium for treatment.
With the tank constructed the next step is to prepare the aluminium for treatment. If the components are in clean, non-corroded condition then they can be anodised without any pre-treatment - if not, then a caustic solution of Sodium Hydroxide (Diggers drain cleaner) at about 15% WW can be used as a dip to brighten the metal. Important note: keep the acid and alkali baths well separated!
During anodising it is normal to see small bubbles forming on the work-piece, but if large bubbles form in the one spot there is a chance that th
Issue: 137 | June, 2012