Subject: How to remove rust from metal

From: [email-masked] (Roy deCarvalho)
Date: 10 Oct 1994 13:16:48 GMT

Folks,

I am working with a 4x4x1/4 foot long mild steel pipe. It will be a
bearing for my boats rudder. It is quite a complex project and it is
almost done, meaning I will take it to my favorite welder for final
composition. I have tried to sand, grind, etc., the inside of the pipe and
had to give up because I could not reach it with my tools. But I surely
need to have it shining so that I can coat it with epoxy for rust
protection. I got to do it now because after the welding is done it will
be almost impossible to reach the end part. My question is: is there an
easy way to remove rust from metal?  Some sort of spray, liquid, whatever
that will require only minimal sanding for finishing? Some one suggested
that I look into an automotive store (Prep Boys or the like) but I found
nothing like that. Am I dreaming that there is such a product? And, if I
am dreaming, how can I grind the inside of the pipe without buying any
mini, fancy and expensive tool? Thank you,

Roy

[email-masked]

--

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From: [email-masked] (21012d)
Date: Mon, 10 Oct 1994 21:06:45 GMT

>mini, fancy and expensive tool? Thank you,
 you might be able to do something with the acids sold for
cleaning concrete, but then you need to wash it out and
do some mechanical/abrasive action.  My suggestion would be
to get some loose abrasive.( SiC, silicon carbide), make
two or three wood disks about 1/8 undersize, a long bolt or
peice of threaded rod to hold them and some course fabric
to wrap the plugs in and "carry" the abrasive.  You could
probably use clean sand just as effectivly, what you want is
make sort of a paste of water and abrasive, wrap enough
cloth to make a good friction fit and work it through 
turing as well as pushing and pullng. 
Good luck.

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From: [email-masked] (Mrwizard00)
Date: 10 Oct 1994 19:33:01 -0400

In article <[email-masked]>, [email-masked] (Roy
deCarvalho) writes:

Oxalic acid will do it, I'm told; I have used dilute muriatic (impure
hydrocholoric) acid to remove rust very successfully.  It is available at
swimming pool supply places like Builders Square or Home Depot.  It
appears to remove rust but not sound steel.  It needs care in use as with
all acids, of course.  When the rust is gone, flush copiously to get rid
of the acid (I;ve used a mild bicarbonate of soda bath to be sure, but it
seems to leave some kind of reaction material behind) and dry thoroughly. 
Wire brushing the flaky rust spots first speeds things up. Half and half 
swimming-pool muriatic and water seems to work fine.

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From: [email-masked] (Tim Dockendorff)
Date: Mon, 10 Oct 94 21:15:58 PDT

> mini, fancy and expensive tool? Thank you,

 how about sand blasting??

   goodluck....

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From: [email-masked] (raymond fairfield)
Date: Wed, 12 Oct 1994 23:49:12 GMT

[email-masked] (Harry Phinney) writes:

>Norman Yarvin ([email-masked]) wrote:
>: Concentrated hydrochloric acid strips rust in seconds.
>: Take the bare metal out when it starts bubbling hydrogen -- then it's
>: attacking the steel.

>: There was one problem I noticed.  Some of the stuff I stripped started
>: rusting within an hour after I stripped it.  I did dunk it in a bucket
>: of water immediately after stripping, so it wasn't residual acid.

>That is another problem with using HCL - the resulting iron chloride
>does not adhere to the surface, leaving the surface exposed and inviting
>further corrosion.

One approach is to let that initial rust go to a fine thin layer, then hit
it with one of the rust converters. It should turn to a black adherent
layer that will last forever.

>: A more mild alternative is to use naval jelly.  This is phosphoric acid

>protection.  All of the commercially available rust removal or steel
>oriented metal prep solutions I am aware of use phosphoric acid as their
>active ingredient.  The carriers range from Naval Jelly's thick
>gelatinous substance to DuPont Quick-Prep's alcohol base.

For a really mild alternative, try molasses !  I didn't believe it either,
but dropping old rusty body panels into a mix of 50/50 (approx) water &
molasses, leave for a week or two & hose off works great. Messy & attacks
other things though. No joke, it's for real.

Ray Fairfield
Toowoomba, Australia

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From: [email-masked] (Russ Kepler)
Date: Thu, 13 Oct 1994 03:49:31 GMT

In article <[email-masked]>,
Norman Yarvin <[email-masked]> wrote:
>[email-masked] (Mrwizard00) writes:
>>hydrocholoric) acid to remove rust very successfully.
>
>Why dilute it?  It works even better straight.  :-)
>
>No, really.  Concentrated hydrochloric acid strips rust in seconds.
>Take the bare metal out when it starts bubbling hydrogen -- then it's
>attacking the steel.  The original questioner wanted to strip a large
>metal pipe, so he probably doesn't mind losing a gram or two of steel.

Don't ever use hydrochloric acid to strip rust from a gun barrel, or
anything that'll be used to contain pressure as the acid will donate
hydrogen to the metal, resulting in hydrogen embrittlement.  (Removing
significant rust from a gunbarrel is something pretty dangerous anyway
if you're planning on firing afterwards.  Be sure to push a greased
lead bullet through the bore to see what the resulting bore diameter
is as rust can seriously constrict the bore.)

If you do use HCl  to strip rust you can bake out the H2 in a 400 degF
oven.  Leave the metal a couple hours after the temp is through.

-- 
Russ Kepler posting from home  [email-masked]

                      Please don't feed the Engineers

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From: [email-masked] (David Jenkins)
Date: 12 Oct 1994 07:26:50 GMT

In article <[email-masked]>, [email-masked] (Roy
deCarvalho) writes:
|> Folks,
|> 
< stuff on rust removal deleted>

|> 
|> Roy
|> 
|> [email-masked]
|> 
|> --

An old method for removing rust from steel gun parts was a solution of
boric acid.  This eats iron oxide far faster than the steel, leaving
the base metal with a slightly etched surface - probably very good for
coating/painting!  There's very little loss of base material.  (Note:
I'm no chemist - there may be process of conversion here, rather than
dissolving - all I know is that it works)

It also has the advantage of being relatively safe (within reasonable
limits) when compared with other rust removers.

It does take some time - maybe 24 hours.

It's probably worth getting a small quantity from somewhere, making up
a reasonably strong solution and trying it on an offcut of pipe, to
see for yourself.  Note that my book on gun finishes doesn't bother to
quote the strength of solution - it just says don't make it too weak! 
When you consider that other formulae are quoted in exact quantities
then this casual approach is significant.

-- 
David Jenkins

"This looks like a job for... somebody else!"
	- Plucky Duck

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From: [email-masked] (Harry Phinney)
Date: Wed, 12 Oct 1994 22:25:03 GMT

Yes, that is one problem with using HCL - it attacks the iron at the
same rate it attacks the iron oxide.

: A more mild alternative is to use naval jelly.  This is phosphoric acid
: in some kind of spray gel.  The bottle I have even claims that it
: contains something to prevent any further rust within 24 hours.

Phosphoric acid reacts with iron oxide at a higher rate than it reacts
with bare iron.  Some of the iron phosphate which is produced will also
adhere to the surface and provide substantial protection from further
corrosion.  No additional "something" is required to provide this
protection.  All of the commercially available rust removal or steel
oriented metal prep solutions I am aware of use phosphoric acid as their
active ingredient.  The carriers range from Naval Jelly's thick
gelatinous substance to DuPont Quick-Prep's alcohol base.

: Coca-Cola contains phosphoric acid too.

Yes, but only in very small quantities.

Harry Phinney   [email-masked]

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From: [email-masked] (Norman Yarvin)
Date: 12 Oct 1994 17:00:11 -0400

You do have to watch out a bit with this stuff.  The acid I used was
emitting white fumes.  These are not good to breathe, and they attack
all sorts of things.

There was one problem I noticed.  Some of the stuff I stripped started
rusting within an hour after I stripped it.  I did dunk it in a bucket
of water immediately after stripping, so it wasn't residual acid.
Whether this is just a property of wet and completely bare steel in a
hot summer, or whether some acid byproducts got left on the steel, I
don't know.  In any case, next time I'll plan to put some sort of
protective coating on them immediately.

A more mild alternative is to use naval jelly.  This is phosphoric acid
in some kind of spray gel.  The bottle I have even claims that it
contains something to prevent any further rust within 24 hours.  Naval
jelly takes several minutes to work, rather than the seconds for
hydrochloric acid.

Coca-Cola contains phosphoric acid too.

--
Norman Yarvin						[email-masked]
 "So convenient a thing it is to be a reasonable creature, since it
  enables one to find or make a reason for every thing one has a mind to
  do." -- Benjamin Franklin