Earlier on this year someone raised the topic of electrolytic de-rusting, and when I mentioned I had been doing some anodising I was asked to post something.
In about December 2008 I decided to fit a variable pressure fuel regulator, and the only way I could see to mount it was to turn up some spacers to fix on the end of the fuel rail. I thought about steel, but expected it would interact with the aluminium nearby, and besides it would tend to rust. I didn't have any stainless the right size, so the obvious answer was some aluminium - the only problem was engine heat and spray etc was going to mean it would go from bright and shiny to dull fairly quickly, and not being a great one for polishing I hit on the idea of anodising it. This turned out to be easy as I already had all the ingredients.
Anodising is the electrolytic formation of a thick oxide film, that protects the surface from further corrosion. It is basically a four stage process once you have your pristine aluminium part :
First, remove the existing oxide film in a sodium hydroxide solution (this can be used to remove earlier anodising attempts too)
Second, create a thick oxide film in an electrolytic bath with battery acid (50% diluted) as the electrolyte, lead as the cathode, and a battery charger as the voltage source
Third, dye the item using Dylon or some other fabric dye
Fourth, seal the oxide layer in steam or boiling water.
Now I won't waste my time repeating the instruction to be found on the web (e.g. Home anodising and More and others), but I will raise a few points :
I managed OK with acid from dead batteries (which I keep in a wine makers flagon), and I managed OK with good old tap water and not distilled - but then I wasn't looking for a show finish.
When diluting acid always add acid to water, not the other way round, and this stuff really is acid - so will burn holes in skin, clothes and who knows what. So will the sodium hydroxide solution. You have been warned!
It is a bit tricky to make and keep a good electrical contact with the item being anodised - I had some success using aluminium MIG wire forced in thread holes - but if it can jiggle, then the anodising will make an insulating oxide layer as quick as you like. So, given you are only allowed aluminium in the bath, this can take some thought.
I also had trouble getting the parts to take dye - and one of the key factors is the size of the pores in the oxide. At winter temperatures the anodising will tend to be a bit cold and so the pores are too small to take the dye - though the size of dye molecules does vary with colour. If the electrolyte is more like 20 to 25C then you stand a far batter chance of dyeing it. If you are at the boundary then it can be rather blotchy (this can also occur if it is not kept clean and immediately anodised after coming out of the hydroxide bath and rinsing). The type of anodising that doesn't take a dye is often called hard anodising, and is still just as effective at keeping corrosion at bay.
So how did the parts last the year ? Well I am very pleased. They have survived without being cleaned and still look the same silvery grey they started. If I can find the time I will experiment some more, using a warmer solution to enable better dyeing - but right now I have some more important issues to deal with - electrical gremlins !
Steve
In about December 2008 I decided to fit a variable pressure fuel regulator, and the only way I could see to mount it was to turn up some spacers to fix on the end of the fuel rail. I thought about steel, but expected it would interact with the aluminium nearby, and besides it would tend to rust. I didn't have any stainless the right size, so the obvious answer was some aluminium - the only problem was engine heat and spray etc was going to mean it would go from bright and shiny to dull fairly quickly, and not being a great one for polishing I hit on the idea of anodising it. This turned out to be easy as I already had all the ingredients.
Anodising is the electrolytic formation of a thick oxide film, that protects the surface from further corrosion. It is basically a four stage process once you have your pristine aluminium part :
First, remove the existing oxide film in a sodium hydroxide solution (this can be used to remove earlier anodising attempts too)
Second, create a thick oxide film in an electrolytic bath with battery acid (50% diluted) as the electrolyte, lead as the cathode, and a battery charger as the voltage source
Third, dye the item using Dylon or some other fabric dye
Fourth, seal the oxide layer in steam or boiling water.
Now I won't waste my time repeating the instruction to be found on the web (e.g. Home anodising and More and others), but I will raise a few points :
I managed OK with acid from dead batteries (which I keep in a wine makers flagon), and I managed OK with good old tap water and not distilled - but then I wasn't looking for a show finish.
When diluting acid always add acid to water, not the other way round, and this stuff really is acid - so will burn holes in skin, clothes and who knows what. So will the sodium hydroxide solution. You have been warned!
It is a bit tricky to make and keep a good electrical contact with the item being anodised - I had some success using aluminium MIG wire forced in thread holes - but if it can jiggle, then the anodising will make an insulating oxide layer as quick as you like. So, given you are only allowed aluminium in the bath, this can take some thought.
I also had trouble getting the parts to take dye - and one of the key factors is the size of the pores in the oxide. At winter temperatures the anodising will tend to be a bit cold and so the pores are too small to take the dye - though the size of dye molecules does vary with colour. If the electrolyte is more like 20 to 25C then you stand a far batter chance of dyeing it. If you are at the boundary then it can be rather blotchy (this can also occur if it is not kept clean and immediately anodised after coming out of the hydroxide bath and rinsing). The type of anodising that doesn't take a dye is often called hard anodising, and is still just as effective at keeping corrosion at bay.
So how did the parts last the year ? Well I am very pleased. They have survived without being cleaned and still look the same silvery grey they started. If I can find the time I will experiment some more, using a warmer solution to enable better dyeing - but right now I have some more important issues to deal with - electrical gremlins !
Steve
