Cleaning Black Steel

[Tiggy_dorset]

Is there possibly a chemical method for cleaning the carbon layer from black mild steel. Without the use of sanding/grinding are there any other suggestions anybody can offer?

Thanks.

 

[Welderpaul]

I would presume it could be cleaned along the same lines as the galvanising process where it is pickled in acid first. Not sure how clean acid would get it though; its only a mild acid they use.
Also a messy dangerous and time consuming job i would imagine.

How much do you have to clean, and why keen to avoid using mechanical methods of cleaning?

 

[Tiggy_dorset]

1000x1500x12 plate both sides (2off per machine I build) and several smaller plates. All needs to be prep'd for painting. sanding hardly touches it. If using heavy grit, you really need to work hard to get through it whilst being careful not too dig in to the steel underneath. It needs to be a nice finish as any marks can easily be shown through the paint. Its bloody hard work and naturally I would like to make work easier and cut down on labour time.

 

[madkayaker]

sand blasting?

 

[TechnicAl]

Sulphuric Acid........concentrated and about 60 -70 oC

really awful stuff but it will do the job. You will need to neutralise it afterwards, limestone does it

and dont leave it in too long or you will make it look worse than it did in the first place

Alternatively buy clean, bright, oiled steel (clean of the oil just before you weld it)

 

[Hitch]

It can be pickled, you can get HRPO plate, Hot rolled, pickled and oiled.

So as mentioned, it wan be removed with an acid, that all i know about it.

 

[Fazed]

I hate black mild steel. We use it a lot at work and 36 grit linishing discs just skid off it, hateful stuff.
Luckily, the items we build out of it get shotblasted prior to paint

 

[Chipper]

Chunko mentioned this ages ago on here, citric acid, so I tried it. Takes several hours but millscale just wipes off. I've been leaving it overnight.
Of course that size would mean a decent size bath for it... and might be worth jetwashing too instead of wiping... but if it were possible, it's cheap.

I keep the mixed liquid in a big jerry can, it lasts for a long while.

After a good soak it leaves a light grey ("passivated"?) finish, a quick wipe dry in case of flash rust and it then lies around here for donks without rusting.

This pic is some little bits I did for a quick test, the dark on the angle at the top was where it poked out of the citric, the rest is free of black after a quick wipe.
(The other two bits were random crusty rusty bits, before the dunk)

 

[chunkolini]

It is good to be quoted.
What I have done on larger pieces is to soak kitchen towels with it and leave over night with some success. or do the same and cling film wrap it. A lot of fannying about at this size, but painless. Maybe get old towels/bedsheets.

Google up Bilt Hamber 'DeoxC' some kind of citric acid based stuff, this is what I was using and some wag here pointed out that it citric based. Which is cheaper.

Removing it physically is hideous on small pieces cup brushing? do you have an apprentice? acid pickles? disgusting and dangerous.

Chunko'.

 

[langy]

I have it media blasted to remove or buy bright mild to begin with, much nicer to work with.

 

[series2]

Strip & clean discs work quite well. If you get the ones for the angle grinder, and just let the weight of the grinder do the work. They barely mark the steel, a bit pricey though. Oh, and wear a dust mask!

 

[maceng]

re plate prep

The best way i find is to buy the steel plate sandblasted and primed (weldable primer)from my local stockholder.It seems expensive initially but when you factor in the preparation time saved its a fairly economical option.

 

[Parro55]

I have used brick acid, leave for a couple of hours it takes the black off, rub with a cloth and neutralise with water and bicarb, then can use flap disc etc. to finish then just protect as required.

 

[Mr shiney]

Citric acid. It drops right off.