Rust sediment removal

[kernowcam]

I had a few Fluke 25 DMMeters which had water damage in the bottom 1" area. Plastic cases and circuit boards had a film of rust sediment which was very hard to remove, like a fine matt painted surface.
I struggled with acid cleaners, flux removers, paint brushes etc with some success but found the perfect answer yesterday.

I tried my small grit blaster. It totally removed the film quickly and easily in seconds. Obviously you need to take care and not overdo it but the plastic insides came up straight away, very slight matting of surface but not enough to worry about. Obviously I did not do the clear plastic window.

The board bottoms had 1" of stain / film on 4 components / fuse holders / board. Again this came off easily leaving perfectly clean everything and but not overdoing it the copper tracks and coating were undamaged. No apparant damage to anything.

[Bazz4CQJ]

I really do want a grit blaster and there is information on the internet about how to assemble a diy one, and it is working its way up my "to do list". My grit container will be an old fire extinguisher tank. Baking soda has proved to be a very effective grit which is safe to use at home.

If you still have rust stains on the windows which you don't want to blast, try a solution of citric acid (a weak acid, comparable to lemon juice). Takes a while to work, but often does the trick. Homebrewers use citric acid to clean their kit and you can get a small pack (it's a powder) in Wilkinsons or the usual online auction sites. It's also very good for getting rid of stains caused by "lawn sand" (ferrous ammonium sulphate).

[TrevorG3VLF]

Oxalic acid was used to remove rust stains on trains, it is however very toxic and goodness only knows what it will do to circuitry.

[Mike Phelan]

3:1 water and molasses will clean rust off beautifully if you leave it for a few weeks.

[Bazz4CQJ]

Originally Posted by Mike Phelan

3:1 water and molasses will clean rust off beautifully if you leave it for a few weeks.

That's a new one to me, but I see there is company in the US based on that "product". But as molasses is mostly a mixture of 'boiled up sugars', I suspect that it could well be the presence of weak organic acids present as impurities which actually do the business. Does a solution of table sugar remove rust?

[Juan Carlos]

google the molasses thing. it looks like it works pretty good. and i think it is not as corrosive as some comercial chemicals.

[GMB]

Rather than blasting with actual grit I think the gentler treatment of using a soft kind of grit like walnut shells may work well. I have been meaning to try this for ages.

At a trade show I saw another approach to blasting which is just to put the thing into a pot of "grit" which gets vibrated. It looked like a small rubber concrete mixed with the shaft connected offset. Possibly less messy than blasting with air.

[emeritus]

This sounds akin to what I understand Roman soldiers used to do with their weapons: put them in a sack packed with dry sand when on the move, and they would be bright and shiny on arrival.

[M0TGX Terry]

Originally Posted by TrevorG3VLF

Oxalic acid was used to remove rust stains on trains, it is however very toxic and goodness only knows what it will do to circuitry.

A good source of Oxalic Acid is rhubarb leaves. Boil them up in water with whatever you are cleaning, it's amazing how effective this can be. My mum used to use this method to clean her aluminium saucepans, and I remember her talking about it working wonders in removing rust-stains from clothing which has been in contact with iron or steel. In view of its effect on aluminium you might want to use a Pyrex or similar pan, and test on something unimportant before trying it on a valuable component/chassis. I have no idea what it might do to a printed circuit board, though.
Warning don't drink the water- as TrevorG3VLF says, it is very poisonous.
Cheers
Terryl

[QQVO6/40]

Just looking around and noticed this thread.
I have used the 30% molasses and 70%water mix for rust removal for years and I find it very successful.
Make sure that the mix is put into a non metallic container as it will eat through a steel one and make quite a mess. I use a large plastic barrel for my jobs.
Far safer than any of the proprietary compounds which usually contain acids that are injurious to human health. In this part of the world we use it as a supplement to cattle feed. They love it and if you open a bucket of it they will chase you around the yard to get at it.
If you do not have access to molasses you can use rotting fruit to do the same job. Toss the fruit in a plastic container and let it go all mushy and submerge your pieces of rusty steel in the tub. Keep a regular eye on the proceedings and remove when clean. The fruit one is a bit faster than the molasses mix but like anything, there is a price. If you are going to use fruit then you had better have a very long back yard and put the barrel as far away from the house as you can. The rotting fruit version can get very stinky and I mean very smelly.
The molasses version has very little smell to it.
Both methods are reasonably environmentally safe to dispose of after use. Just be aware of the smell with option 2.
I prefer the molasses and have used it for cleaning rusty old tools bought or given at farm clearing sales. I have ended up with some really good blacksmiths tools, some of which looked like lumps of rusty dirt after being buried on farm shed floors for a long time.
Just a little extra. I wash the parts in a good engine de-greaser to remove as much oil and grease as possible as I find this speeds up the cleaning process.

Cheers, Robert.

[kalee20]

I'd go for the oxalic acid treatment (yes it is rather poisonous but it does slowly dissolve rust). However I've also heard things about Coke which might be interesting to try - this contains phosphoric acid.

Watered down molasses is a new one! Yes, as QQV06 observes, it is a good feed supplement, especially for encouraging sick animals. However, for rust removal I'd suggest going to a health food shop for a small tin rather than feed merchants for a 25 litre drum...

[QQVO6/40]

I think the last time I bought molasses in a 20 litre bucket it cost me I think about $6AU. I think that is about £3.60.
It is quite slow and gentle compared to the usual chemical options but horses for courses I guess.
The rotting fruit one is good for tormenting the neighbours. Hihi.
The majority of vintage and veteran car restorers in this area use the molasses option for cleaning up car parts. I would guess because of it's low cost and large quantities used. Cleaning the rust from a car front mudguard would use quite a bit of the mix.
Biggest advantage is is not toxic. If you spill it then the place gets a bit sticky and the ants love it but that is about all. I will leave it at that.

Cheers, Robert.

[kernowcam]

I have a small ultrasonic washer unit - I wonder if item was poly bagged up with grit and water added as normal if that would work.

The grit blast did work well though.

[Bazz4CQJ]

I've used ultra-sonic cleaners for decades and that is not a method I have ever heard of. I think the critical process in ultrasonic cleaning is bubble cavitation at the surface. Whether or not using a dilute suspension of micron-sized abrasive (e.g. silica) particles might offer any benefit is an interesting idea, but I suspect that if it worked, it would already be on the market. Heading in to water-jet cutting territory I guess.

[AC/HL]

One post split off to a new thread

[FrankB]

The item GMB is describing is very much like what we use here as a shell casing cleaner for reloading of rifle and pistol ammo.

It can be used with most media, walnut shells, sand, soda, etc.
A company here in the states, Harbor Freight Tools, sells the Chinese made versions of the unit, fairly cheaply.

[vidjoman]

Originally Posted by kalee20

However I've also heard things about Coke which might be interesting to try - this contains phosphoric acid.

I had an interesting conversation with a woman who ran a plating company who mentioned Coke. It's simple, cheap and easy to do at home.
Use for small parts, screws, washers etc - put parts and coke in a bottle (she used a glass bottle) place on a window ledge in bright light, give it a daily shake and the rust comes off without any effort.

[Boater Sam]

JENOLITE is phosphoric acid based, diluted it strips rust and turns the ferrous oxide into ferrous phosphate which is a good rust preventer.

BAR KEEPERS FRIEND cleaner is oxalic acid, very fast at removing rust and rust stains on fabric.
Both are commercially available.

Sam.

[Bazz4CQJ]

Yes, but the two are very different animals. Phosphoric acid reacts with both with rust and metal, but oxalic acid is a much weaker acid and is good at complexing rust, but far less reactive with metal. In the context of removing staining, I think that oxalic is certainly the place to start. Oxalic can be bought on the high street; it is the friend of homebrewers too! (I am not a homebrewer!)