the effect of Electrolytic de-rusting on Soldered joints

Hi All

I'm a newbie here and I have what may appear to be a simple question but I haven't managed to find any kind of answer so far so here's my issue......so I'm restoring a 1927 Sunbeam model 9 motorcycle not a scale model but the real thing.....the combined petrol / oil tank of Flat tank design is of original of soft Soldered Tinplate construction unfortunately it is very rusty inside so I'm hoping I can de-rust it using Electrolysis.....but before I start doing this I really need to know if this will dissolve / erode the Soldered joints can anyone he me out

There are LOTS of unknowns here, so hard to say. Who knows what grade of solder Sunbeam used, or if the tin plate is just steel and tin plating or some combination of plating and galvanizing. I have seen many combinations. I have done some electrolysis on old engine parts (iron and steel only) using a washing soda / water solution and never damaged anything but I would recommend a test with a scrap holed or rusted out Sunbeam tank if you can find one. You could test some ordinary tinplate or galvanised steel and a make a soldered joint to test. One recommendation - you would be wise to watch it like a hawk initially, so if anything goes wrong you can stop it as soon as possible.

I have noticed that on hollow castings the internal passages and cavities take the longest to get clean of rust, and constant re-positioning and renewal of the sacrificial iron plate, bar or strip inside the cavities is often needed to keep the reaction going. Star shaped plastic plates fitted onto bar are a good way to keep the bar from making short circuits to the cavities.

Electrolysis or JENOLITE (Phosphoric acid based)? I use Jenolite as the flux for stainless steel soft soldering and it does the solder no harm in that application and it certainly kills rust.

Cant't say wether Electrolysis would damage solder. Perhaps we need a chemist's view on the subject ?

Bob

I would use a de rusting agent such as Evaporust. Once the rust has been removed, then use one of the epoxy treatments which are intended for petrol tanks.

Andrew.

Edited By Andrew Tinsley on 24/11/2022 14:29:53

thanks for the replies chaps......the elctrolyte solution I would use is basically washing soda (Sodium Carbonate) mixed with hot water that's all nothing corrosive as far as I understand I'm just wondering as the solution attracts and lifts the rust would it do the same to any lead in the soft solder.....agh......such an easy thing to do but is it on a soldered tank.....using a proprietary de-rustng solution might be worse

I don't think there will be an adverse effect on the soldering, as the reactivity of lead and tin are low, compared with steel. That is why steel parts are coated with lead (eg battery terminals) or brass with tin (eg crimped connectors). In use, both types of component involve electricity, and a range of other metals.

It would be useful, I suggest, to ask advice from the makers of rust-removing products. But I recognise that with the general trends to get products made a long way from home, and to refer all questions to a computer, you may not get an answer.

Cheers, Tim

thanks Tim.....I'll keep asking around on the interweb someone somewhere has restored one of these tanks somewhere......cheers

This is something I'd experiment with. It depends partly on the electrolyte, which I assume would be Washing Soda. In theory, I'd expect Tim's answer to be correct - the action would mainly effect the rust rather than a Lead/Tin mix. But electrolysis is a powerful way of ripping molecules apart, so I'd want to double check by trying it on a victim.

Why not solder some tin-plate together (old cans), rust them up by scratching and wetting with salt water, and then electrolytically clean them. I'm 80% confident electrolysis won't damage the soldered joints, but I wouldn't risk doing it to a treasured tank unless I'd gone the extra mile and made certain!

Dave

Lead, which will be the main constituent of the solder willl be pretty unreactive. Electrolytic cleaning will be fine.

Forgive me for poking my nose in when I know little about the subject... My limited understanding of electrolytic rust removal suggests that the rust has to be able to "see" the electrode, rather like electroplating, where shrouded surfaces tend to build up a much thinner plating than those near to the electrode. So, if this is correct, I'd think that getting the electrode into the tank(s) might be more trouble than it's worth. Phosphoric acid should be safe. You can help it along by adding gravel to the tank and shaking.

The way it is commonly done (and it is very commonly done,) is to put a piece of rebar through the filler cap hole. A handful of gravel is a common addition but I wouldn't with a soldered tank.