Soda Crystal Electrolysis Vs Phosphoric Acid

[ale36]

hello basically i have a set of car calipers that i need de-rusting prior to powder coating, the question is which process would be more efficient but safe to use with the brake calipers as i have the pistons removed and i don't want the internal bore to change size as this is not rusted

Thank you

 

[steveo3002]

think the acid will pit the piston bore or remove any plating

 

[ale36]

think the acid will pit the piston bore or remove any plating

what about Electrolysis?

 

[brightspark]

mask it up with gaffer tape and sandblast them

 

[Shox Dr]

that or use some rubber bungs, or wood dowels to protect the barrels

 

[ale36]

mask it up with gaffer tape and sandblast them

i thought about it but i haven't got a big enough compressor to handle the air consumption

 

[steveo3002]

i think the electroylosis would be ok , most of the sits claim it doesnt touch good plating , seems to have been ok on what ive used it on

 

[awemawson]

Citric acid would be best and should not affect the bores if they are sound

 

[ale36]

Citric acid would be best and should not affect the bores if they are sound

where could i get this from with out having to get if from the internet and what proportions would you dilute?

 

[Shox Dr]

Chemist. Not the nationals, they won't know what your are on about

 

[Qwertyco]

chip off any big loose stuff, pickle it in warm cheap vinegar for a few days then scrub it,
Rinse, and repeat,
then electrolysys if it still needs work.
I've done loads of calipers this way.
Vinegar is 14p a pint at tesco.

 

[awemawson]

I buy citric acid by the 5Kg load on ebay and it arrives next day - very cheap and readily available in smaller quantities. I'd use perhaps a cup full in a large bucket - if you use too much it fails to dissolve and settles on the bottom as a crust, but dilution is not critical, if it is weak it still works just slower. Advantage of citric acid is not only is it effective, but it is also safe to handle, you can put your hands in and come to no harm (it'll sting if you have a cut), also you can legally pour it down the drain unlike phosphoric.

 

[pedrobedro]

How much do you need ?£7.79 for 2kg.

 

[Chipper]

Citric leaves less of a coating on steel than phosphoric, works v.fast in hot solution, should be done in an hour or two.

 

[MattF]

Electrolysis would also do fine, as long as there's no ally in there.

 

[awemawson]

Citric leaves less of a coating on steel than phosphoric

As I understand it that's because iron citrate is water soluble, but iron phosphate isn't.

 

[vdubz]

Molasses and water works great and does not damage the metal as it only removes the rust.

 

[Fergus]

Molasses and water works great and does not damage the metal as it only removes the rust.

Got some here that came from a local bloke who restores old tractors, he recommends a 1:4 mix of molasses to water and a 3-4 day immersion for heavy corrosion. Paint and good metal left untouched.

 

[outofthefire]

Molasses is a new one to me i'll have to give it a go. You can buy citric acid from home brew shops if you dont want to use the net.