Remove rust (without using abrasives).

Little Dog

Little Dog

A2OC Donor
European-Union
I've owned a classic mini for 35 years and in that time I've learnt a thing or two about removing rust. I tend to prefer not to use abrasives as abrasives remove good metal along with the rust. The methods I will describe in this thread are:
Citric acid
Brick acid
Phosphoric acid
Molasses
Electrolytic rust removal

First I removed a few rough parts from my A2:

JQ8uEop.jpg


Then I degreased them in caustic soda:

ZxVkFaX.jpg


Leave for a few minutes, rinse in fresh water and they are ready for rust removal.
 
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Citric Acid.

I buy food grade citric acid of eBay and mix it approximately 20% citric acid to 80% warm water by volume:

QSHzUMi.jpg


Put the components in the acid without splashing and they usually start bubbling immediately:

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Wait until the bubbling has finished and any rust has turned black. Remove and rinse in tap water:

d2Dn4LQ.jpg


These components are now ready for plating.

Take necessary steps to protect yourself and others from acid splashes and spills.
 
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Have the new regulations on the sale of corrosive substances made it more difficult to buy strong acid and alkaline products

Cheers Spike
 
The regulations on the sale of chemicals - do you mean the explosive precursors laws that came out in 2016? They’ve restricted a few acids. There had been a drive to reduce availability of ‘chemicals’ for over a decade generally - public can’t be trusted
There are a few companies that will supply lab grade chemicals but usually only to companies but most corrosives are available in household products with the exception of the nasty ones like nitric and oleum. Phosphoric acid is in a lot of the ‘rust treatment’ products.


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Hi Phil

They've come up really nice and good to see it can be done with household products.
philward said:
These components are now ready for plating.
Click to expand...
I'll be interest to see how you do this. Were you aware that A2 fastening components that come into contact with aluminium are coated with Dacromet, Delta Tone or a similar coating to prevent contact corrosion. In addition these parts are coloured with a green lubricant on an alkyd resin basis to provide a clear distinction to normal fastening components.

Source: Audi A2 Body Construction and Function Self-study programme 239 http://forum.a8parts.co.uk/attachment.php?attachmentid=10544&d=1430156249 opens in external pdf reader
 
Alan_uk said:
Hi Phil

They've come up really nice and good to see it can be done with household products.

I'll be interest to see how you do this. Were you aware that A2 fastening components that come into contact with aluminium are coated with Dacromet, Delta Tone or a similar coating to prevent contact corrosion. In addition these parts are coloured with a green lubricant on an alkyd resin basis to provide a clear distinction to normal fastening components.

Source: Audi A2 Body Construction and Function Self-study programme 239 http://forum.a8parts.co.uk/attachment.php?attachmentid=10544&d=1430156249 opens in external pdf reader
Click to expand...

Thank you Allan for the reminder. Fixings that come into contact with aluminium I purchase new from Audi. Interestingly some of these are now being supplied without that green finish. I started a thread on the subject https://www.a2oc.net/community/inde...teel-nuts-bolts-screws-etc.34226/#post-306526
 
Phosphoric Acid.

Make no mistake this is industrial strength nasty stuff, the smallest of splashes soon start to sting. Use carefully, keep away from kids pets etc and store safely. I usually only use this product with a brush to prevent flash rusting of larger components that have been subject to electrolytic rust conversion or had rust removed using a molasses diluted in water. The etched surface gives a good surface for paint to adhere to.

This the first time I have used it as a dip converter:

gXXGMPE.jpg


The washer and screw are welded together by rust:

AJrI7Hm.jpg


A component in this state I would usually clean up using electrolytic rust conversion; I've set this acid quite a challenge.

Reaction is instant acid attacking both the rust and remaining plate:

zMgNRIm.jpg


A few hours later the component is free of rust and plating and ready for refinishing:

JhQNqQa.jpg


Usually paint when using this acid but this component will be plated.
 
Brick acid.

A building product for removing cement splashes from brick work. My existing acid was bought from Wickes but is no longer in its original container so I can't post a meaningful picture. I need an acid dip prior to yellow passivisation of zinc plate so have this product on order:

https://www.everbuild.co.uk/product/407-mortar-stain-remover/ .

There some useful data sheets to read. If it doesn't work for rust conversion I will advise.

My existing brick acid has been set quite a challenge:

4aVolNy.jpg


Again I would usually clean up a component in this state using electrolytic rust conversion.

Reaction in the acid is instant and quite lively, I must have stored this acid quite warm:

DNbzjM4.jpg


Several hours later:

i5cC1nb.jpg


The component is ready for plating.
 
Pinkythelabrat said:
The regulations on the sale of chemicals - do you mean the explosive precursors laws that came out in 2016?


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Click to expand...

Not exactly.
Following on from the recent horrendous 'acid' attacks in London I thought the Government was going to make it more difficult to buy high strength corrosive chemicals. Wondered if the brick acid came into that category

Cheers Spike
 
I'm enjoying these comparison tests by philw.
Being a fan of Bilt Hamber products I'd be interested to see if their rust killer produces better results than the 'no frills' chemicals already tried.


Cheers Spike
 
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Electrolytic rust conversion.

First you need a battery charger or other power source:

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Get yourself an iron sacrificial anode, this is a brake cylinder from a classic mini:

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Get yourself some cheap washing stain remover:

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A scanky tub:

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Put in a couple of scoops of stain remover:

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Fill with water and dissolve soap:

2g7XjEJ.jpg


Clamp sacrificial anode in place and connect to +ve of charger output:

dPCzzsM.jpg


Wire components to be treated:

GDviOl5.jpg


Clamp components with -ve of battery charger:

xW4QXsR.jpg


Switch on charger:

https://imgur.com/uYvDvrV

Be impressed if you like bubbles and admire electrochemistry in action.

o4kpUGr.jpg


To be continued.

PS apparently it can explode and I set one on fire so if you tempted to just go for it, be careful.
 
Electrolytic Rust Conversion (Cont).

One the good things about electrolytic rust conversion is that you can't over do it. When the rust has gone it stops reacting. As a result I've never timed how long I leave components in there. These parts have been in approximately 16 hours and the worst clip was very bad.

Edit 240208, electrolytic rust conversion can be over done. It takes a while but the sacrificial becomes covered in slime and stops conducting. The work pieces the sacrifice their lower edges to convert the top edges.
Best to keep an eye on things, a limit I now set myself is 24 hours on the tank. P

I find it useful to check the items part way through the conversion. If it is working correctly the fine rust will have turned black and the thick rust will be chipping off in flakes. At this stage a quick rub with wire wool reduces the overall conversion time:

vevjiBH.jpg


On this occasion the conversion was too slow:

V32B3bN.jpg


Slow conversion usually results for scale and other deposits on the anode but it had been cleaned before I setup the tank. The problem is then most likely to be a poor connection between the anode and the +ve lead clip. Make a better connection and get the components back in.

Got a much better reaction and here is the final result:

Xanb7SC.jpg


I'm pleased with this result and now I can get on with plating. You can see a disadvantage of electrolytic conversion; flash rusting. I usually avoid this by wiping or brushing with phosphoric acid but it does not matter as these will be platted this morning. Also an advantage, it leaves plating in place which is useful if you intend to paint your components.

Risks with this process are, the gas given off is flammable so use in a well ventilated area. Also if the anode and components touch there is a risk of fire, fit an inline fuse or clamp anode and larger components to prevent movement.
 
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I think it’ll be hydrogen gas off of the anode and oxygen off of the cathode so pretty flammable! Good ventilation is important. Safety first.

You can also use steel wool for a sacrificial substrate - high surface area too.

I’m enjoying this I have to say.


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