Hydrochloric acid to disintegrate rust to remove pin in bearing

[ryanmech]

Hello

I have a series of pins which have seized in a bearing.

Has anyone had experience with using Hydrochloric acid to break the corrosion between a pin and the inside of the inner race of a bearing? This has been suggested to me but i have had no experience with this practice.

We need to remove the pin to replace the bearing, but due to the location of the pin and bearing we are having trouble extracting the pin....

Thanks
Ryan

 

[Skogsgurra]

Some say that Coca-Cola also works. It will not disintegrate your machinery like the HCl will ;-)

CRC 5-56 usually works well if we shall be more serious.

 

[ryanmech]

Thanks Skogsgurra

But we are passed the stage of simply using a liquid penetrant. We have put 40 tonnes onto this pin and it only moved slightly then bound up.

I am looking for someone who has used HCl to disintegrate rust between two mated surfaces.

ie.
hydrochloric acid + rust --> ferritic chloride + water
6HCl + Fe2O3 --> 2FeCl3 + 3H2O

Has anyone used this theory in a practical manner?

Thanks
Ryan

 

[israelkk]

What are the material that the bearing and the pin are made off?
Are you sure it is corrosion? If the pin and bearing are from stainless steels then it might be a cold welding between the pin and the bearing inner race.

 

[ryanmech]

Thanks Israelkk

Yeah, i had considered cold welding as a possibility, early on but because the pin actually moved i ruled that out?

Unfortunately we have not been able to remove a pin or bearing as yet, so we cannot confirm what the exact cause of the problem is. Also the machinery is still in service so we have limited time when we can attack each unit.

The machinery is situated on a wharf, so is exposed to salt water spray conditions.

The materials are: Pin - stainless steel 316, bearing - some type of carbon chromium steel.

We are looking at putting in a plain spherical stainless steel bearing, after we have removed the current ones. Both the current and the intended replacement bearings are supposedly maintenance free bearings, which have a fabric liner which the inner ring runs on. These bearings have no lubrication and have seals on the inner ring to keep out contaminants only.

I am sure that it is corrosion because several of the pins have rust coloured dust on them, from rust stained water running down them - which seems to be coming from the inside of the bearing!

Does the Aerospace field use only Ceramic bearings for avoiding colding welding?

Thanks
Ryan

 

[ryanmech]

I know that the pickling paste that i had used during my apprenticeship was based on HCl. We used it for mainly for cleaning welds after tig welding, but had occassionaly used it to clean rust off steel items.

Thanks
Ryan

 

[israelkk]

I have never used ceramic bearing we use stainless all the time but not in the same environment as yours. Is the pin is press fitted to the inner race? if so it may the cause for cold welding. The fact that the pin moved a little "and then stopped" can be an idication for cold welding. If it was just rust it should not have been stopped. The nature of cold welding is that it builds up. It starts moving and then more and more area become welded until the area large enough to resist the puling force.

 

[ryanmech]

Thanks Isrealkk

Sounds interesting! The pin is not press fit into the inner ring of the bearing.
What special precautions do the aerospace industry use to avoid cold welding? What type of bearings do you use?

But as i said, i don't think it is cold welding because it moved a little when we put a high load onto it (I think that this is the rust on the inside of the inner ring binding up the pin). And because there was rust dust on the stainless pin which came from somewhere inside the bearing!

Thanks
Ryan

 

[diamondjim]

Are you certain that it is not
a tapered pin rather than a spring
pin? Sometimes spring pin holes
are not drilled all the way thru
and may have to be extracted from
the far side. If the pin moved
initially, you have broken any
microwelding or rusting, so the pin
should move easily. I have seen
easy outs used to remove some pins.

 

[rnd2]

Is it possible to heat the material? Rust is Fe2O3.+XH2O The bound up H2O takes up space. Heat drives off the bound up H2O and this may assist with the movement.

 

[Tmoose]

(1)"We have put 40 tonnes onto this pin and it only moved slightly then bound up."

(2)"The fact that the pin moved a little "and then stopped" can be an indication for cold welding."

I don't have a good mental picture of the pin and bearing arrangement, but I would base the next repair attempts on statement (2). I'd say either the pin galled/cold-welded and is now seized hard, or it hit the a shoulder or the bottom of the hole.

I might be thinking about using a carefully guided carbide drill first, to put a hole thru the pin to allow using oil or grease to hydraulically remove the pin in reverse. Then, if necessary, enlarging the hole to reduce the pin to a thin shell that can be collpased inward, broken and picked out.

 

[ryanmech]

Thanks
DiamondJim - The pin i am talking about is a stainless pin which passes through a spherical bearing, it is not tapered nor a spring pin.

rnd2 - I had a maintenance crew apply heat to try to break the corrosion, but it did not seem to help. They seemed to have gone overboard with the heat and now the stainless steel is very hard.

Tmoose- I would not attempt to drill through the pin now due to the heat that has been applied- ie hard stainless. I will have to wait till i finally get the bloody thing removed before i can find out whether it is corrosion or cold welding. Although all indications are that it is corrsion rather than cold welding due to the fact that there is rust staining on the stainless pin...

That brings me back to my original question, incase it has been forgotten---Has anyone had experience using Hydrochloric Acid to disolve rust?

Thanks
Ryan

http://www.mooring.co.nz

 

[diamondjim]

Another possiblility is that these
are dowel holes used to keep two
separate rings aligned. Which
means that they could be seated
in one ring i.e. blind holes and
the mating part have thru holes
with a slightly larger hole.
Is it a double spherical bearing?
Do you have the serial number and
manufacturer model number.
They might use these for machining
purposed to keep the parts alinged
to grind or clean up the od or id.
as a unit. Are they angularly
arranged using equal spacing?

 

[ryanmech]

sorry Jim

You are barking up the wrong tree.

There is no split pin, roll pin, spring pin nor dowell pin, the pin inserted into the bearing is a plain machined stainless pin.

Apparantly posting email addesses on this website is not allowed, so if you look at our website and find my address, i will return email you the drawing.

Regards
Ryan

http://www.mooring.co.nz

 

[aviat]

I have used mureatic acid for a similar purpose and it works great. It is sold in a hardware store to adjust the PH of pools, and has a concentration of 20 - 45%. You have to dilute it a lot from that. Do not let the acid spill on concrete, because it will eat it, or leave container without lid on it. After you get it apart you should wash everything in baking soda and water, then oil it with WD 40 or something similar.
Sometime you need more than a 40 ton press to free corroded parts.
Cheers!

 

[ryanmech]

thanks Aviat

will give it a try!!

Cheers
Ryan

 

[rnd2]

Mureatic acid is I think hydrochloric, so you may have your answer.
Good Luck.

 

[Skogsgurra]

Right! And if you look for "muriatic" you will find that the old name for HCl used to be muriatic acid.

http://www.thefreedictionary.com/Muriatic

 

[ryanmech]

Hello Aviat

How long did you leave the HCl on for approximately?

Thanks
Ryan

 

[diamondjim]

Ryan,
Tried the URL that you listed and
keep getting a blank page.
Would like to see the drawing.