Removing Anodizing.
Sodium Hydroxide (Caustic Soda)
Safety gear should be worn for all these methods, goggles, gloves, apron etc. when using acid I always use a face mask as well, and good ventilation.
You can use Sodium Hydroxide (Caustic Soda), try starting off with one tablespoon to 2 litres of water and mixing. Always add the powder to the water. I normally use a stronger solution as it removes it faster and seems to give a more even finish.
This method will damage / disolve aluminium if used for too long / too strong / too hot. It can even damage aluminium before all the anodizing is removed. It is a lot more effective when used with warm / hot water, but is very dangerous, at close to boiling point it will explode when the powder is added.
Other methods.
The following methods cause far less damage to aluminium, but are far more dangerous. You have to consider whether a melted face is worth the risk for saving 20 year old bike parts that aren't manufactured anymore. Exactly, read on.
You should read all safety data sheets for these chemicals first as some of the are very dangerous and can kill.
These recipes are from Ministry of Denfence guidelines, they should be used with very good ventilation and full safety wear. You should have a quantity of something like baking power solution to neutralise any spills / for first aid.
Phosphoric acid 3.5% v/v
Chromic acid 2.0% m/v
Used at close to boiling point.
The following cause slightly greater attack of metal:
Sulphuric acid 15% v/v
Chromic acid 5% m/v
Used at 50 celcius.
----------------------------
Sulphuric acid 10% v/v
Potassium fluoride 4% m/v
Used at room temperature.
----------------------------
Personally I use:
Sulphuric acid 15% v/v
at around 30-40 celsius.
It takes a few minutes to work, then there's a lot of fizzing and the anodizing is gone in seconds.
To tell if something is anodized or not use a multimeter set to resistance, anodized aluminium doesn't conduct electricity (titanium does!), but bare aluminium will have a low resistance.
Sodium Hydroxide (Caustic Soda)
Safety gear should be worn for all these methods, goggles, gloves, apron etc. when using acid I always use a face mask as well, and good ventilation.
You can use Sodium Hydroxide (Caustic Soda), try starting off with one tablespoon to 2 litres of water and mixing. Always add the powder to the water. I normally use a stronger solution as it removes it faster and seems to give a more even finish.
This method will damage / disolve aluminium if used for too long / too strong / too hot. It can even damage aluminium before all the anodizing is removed. It is a lot more effective when used with warm / hot water, but is very dangerous, at close to boiling point it will explode when the powder is added.
Other methods.
The following methods cause far less damage to aluminium, but are far more dangerous. You have to consider whether a melted face is worth the risk for saving 20 year old bike parts that aren't manufactured anymore. Exactly, read on.
You should read all safety data sheets for these chemicals first as some of the are very dangerous and can kill.
These recipes are from Ministry of Denfence guidelines, they should be used with very good ventilation and full safety wear. You should have a quantity of something like baking power solution to neutralise any spills / for first aid.
Phosphoric acid 3.5% v/v
Chromic acid 2.0% m/v
Used at close to boiling point.
The following cause slightly greater attack of metal:
Sulphuric acid 15% v/v
Chromic acid 5% m/v
Used at 50 celcius.
----------------------------
Sulphuric acid 10% v/v
Potassium fluoride 4% m/v
Used at room temperature.
----------------------------
Personally I use:
Sulphuric acid 15% v/v
at around 30-40 celsius.
It takes a few minutes to work, then there's a lot of fizzing and the anodizing is gone in seconds.
To tell if something is anodized or not use a multimeter set to resistance, anodized aluminium doesn't conduct electricity (titanium does!), but bare aluminium will have a low resistance.
