Suitable flux for soldering steel rail.

[Re6/6]

Having recently done some soldering of tinned copper wires to steel rail, I have obviously used the wrong flux as serious rust and corrosion of the rail has occurred. Even the rail head has become slightly pitted. What has exacerbated the problem could well be the proximity of the sea at the storage location.

It has been cleaned up twice already and still the corrosion returns. LaCo, a non-acidic flux was used an obviously the wrong assumptions were made. I have successfully used the stuff on n/s rail for years.

Firstly, what are people’s recommendations of an appropriate flux for steel rail.

Secondly, any suggestions to arrest/neutralize the corrosion .

I would assume that temporary painting could help for now.

[Philip Hall]

John,

My choice of flux for soldering steel is LaCo, and I have not suffered with corrosion problems, but I must admit that I have not used it on steel rail (yet). I keep a pot of it on my bench and plunge the soldering iron in it occasionally to help with tinning and cleaning. I think it very likely that your location and the sea air are the most likely causes of the corrosion.

Philip

[MPR]

I would suspect that there is an acidic residue- I would mechanically remove as much surface corrosion as possible, then apply neutralising solution until the fizzing stops! Any residue can then be rinsed/blotted away and the area dried.
Regards
Martin

[Tim V]

I use Copalux, but ensure I wash off after when I need to.

Was the rail clean in the first place? I use ordinary cored solder for electrical/mechanical no extra flux without problems.

Cleaning means running IPA or lighter fluid over the rail, the burnishing with a glass fibre brush, before doing any work.

[grovenor-2685]

I always use standard rosin cored solder for electronic use, I have never needed to use any additional flux and no corrosion results.
This will not help your existing joints but should resolve it for the future.
It is a 4 step process:
1. Mechanically clean the rail where the joint is required,
2. Apply iron and end of cored solder to tin the rail, observe that the tinning has taken, ie no balling up of the solder.
3. Tin the end of the wire.
4. Hold wire in position and heat with iron until the solder flows, allow to cool and give a little tug to ensure the joint is mechanically sound.
Regards
Keith

[Re6/6]

All the good advice much appreciated.

I should have mentioned that the job was fitting new droppers to maybe 20 year old+ track in situ. As much cleaning of paint and rust as possible was done.

[grovenor-2685]

I have soldered droppers in situ as you describe, I solder into the web as my layout is round the walls and only viewed from one side, hence the droppers go on the wall side and are out of sight. The problem with cleaning is the restricted space between chairs, definately easier on ply and rivet before chairing. To get in between the chairs I mostly use the end of a riffler file to get a nice shiny patch on the rail, sometimes a bit of help from a fibreglass brush is needed, then do the tinning. Rarely fails, but if it does its a bit more cleaning.
Regards
Keith

[billbedford]

It has been cleaned up twice already and still the corrosion returns. LaCo, a non-acidic flux was used an obviously the wrong assumptions were made. I have successfully used the stuff on n/s rail for years.

The msds for LaCo flux suggest the active ingredient is ammonium chloride.

The msds for ammonium chloride says that it is extremely corrosive in presence of copper. Corrosive in presence of steel, of stainless steel(304). Slightly corrosive in presence of aluminum, of stainless steel(316).

However it is soluble in cold water, hot water, and methanol.

So the best you can do is clean the joints with either water or methanol, if you have some.

[Martin Wynne]

I should have mentioned that the job was fitting new droppers to maybe 20 year old+ track in situ. As much cleaning of paint and rust as possible was done.

On old track try drilling a 20thou hole through the web of the rail, using a flexible shaft which can get down low. You will then have nice clean metal inside the hole, and to solder the wire through it just needs a smear of SMT paste, no extra flux. No other cleaning needed and no cleaning up afterwards. Insert the wire from the non-visible side and trim on the visible side afterwards. Convenient dropper wire is 1/0.5 solid wire stripped from old telephone cables.

Take care to vacuum up the drilling swarf, otherwise if steel it will end up attached to loco motor magnets, causing problems.

SMT paste ("surface mount technology") is 179degree solder cream with 2% silver, available from C&L, but it's not cheap:

http://www.finescale.org.uk/index.php?r ... ct_id=3696

It's a lot cheaper if you can buy larger quantities from electronics places.

regards,

Martin.

[John Fitton]

Another of those cases where cleanliness is next to godliness! Re recent posts somewhere about adhesives and especially cyanos....

John Fitton

[Re6/6]

Further to the corrosion problem with the steel rail, a couple of weeks ago some ‘flux neutralizer’ (from C & L) was given to us in the hope of arresting it. It was applied to the rusted areas and left for two weeks with disastrous results. The corrosion has increased badly. Reading on this thread this morning that the LaCo flux is alkaline and we must assume that the inhibitor was also alkaline which has made matters even worse. Strangely the same LaCo flux was used on brand new steel rail with no corrosion whatsoever. One might assume that there are differences in the steel used 20+ years ago to the stuff now available.

On reflection, a schoolboy chemistry mistake, but it is what it is now and a solution to prevent it progressing further is sought.

Would applying mild phosphoric acid (Jenolite) or anything else be helpful in arresting it?

Thanks.

[Albert Hall]

The neutralising rinse referred to is indeed an alkali as the main ingredient is caustic soda aka sodium hydroxide.

AH

[steve howe]

I had this problem with steel rail and LaCo flux and I also live near the sea. Two things seemed to help: I discovered by accident that a vigorous scrub with meths and a hog bristle brush seemed to neutralise the flux, and, a mate of mine in the car trade suggested a product called KuRust which I used on some a quite badly corroded rail after mechanical cleaning with glass fibre brush, and the rusting has not re-appeared. I now scrub the work with meths after each session and so far no more rusting

Steve

[Re6/6]

Excellent Steve. Many thanks for that.

[grovenor-2685]

I now scrub the work with meths after each session and so far no more rusting

Why not just stop using corrosive flux and save yourself the extra work?
Regards

[Guy Rixon]

I would be wary of adding acids to your alkaline problem in situ. The neutralisation reaction will generate heat: possibly a lot of heat. It may spray corrosives around the place. As they say with the cleaning-product ads "test on an inconspicuous area first". "Inconspicuous" suggests not on the layout, and preferably outside away from anything that can be hurt or set on fire.

[billbedford]

The active ingredient of LaCo flux is Hydrochloric acid. The MSDS is here.

What may be causing problems is the ammonium chloride, which will act very much like common table salt and will need to be flushed away with plenty of water. Not a good idea for trackwork.

[steve howe]

I now scrub the work with meths after each session and so far no more rusting

Why not just stop using corrosive flux and save yourself the extra work?
Regards

I did try using Carrs non-corrosive flux, but found it totally ineffective. The problem with resin cored solder, at least for me, is I don't have enough hands to hold the work, the iron, and the solder all in place at the same time

[Re6/6]

Many thanks all.

Warnings noted.

[Terry Bendall]

The problem with resin cored solder, at least for me, is I don't have enough hands to hold the work, the iron, and the solder all in place at the same time

Melt some solder onto the end of the soldering bit and then apply to the joint. Alternatively, or even as well, tin the parts to be joined ( i.e coat with a thin layer of solder), bring the parts together and apply heat from the iron and apply pressure, e.g a small piece of wood or tweezers.

Another solution would be to talk to Roger Sawer at Scaleforum at his soldering helpdesk.

Terry Bendall

[grovenor-2685]

I now scrub the work with meths after each session and so far no more rusting

Why not just stop using corrosive flux and save yourself the extra work?
Regards

I did try using Carrs non-corrosive flux, but found it totally ineffective. The problem with resin cored solder, at least for me, is I don't have enough hands to hold the work, the iron, and the solder all in place at the same time

This is tinned copper wire to rail, yes?
First is to clean the patch of rail you want to solder onto, I solder mine into the web on the non-viewing side. Use a fibregrass brush or the end of a riffler file, whatever you need to get into the right spot. I find the riffler will get between chairs. When you have the clean patch tin that spot, one hand holds the solder, the other hand holds the iron. Prepare the dropper wire by pushing it through the hole in the baseboard leaving about 6 inches sticking out, bare the end and turn the last 2mm through 90 degrees. The wire will be held well enough to be tinned as for the rail (even pre-tinned wire benefits from a bit more). Now pull the wire down from below and arrange it so the tinned end sits nicely against the tinned patch on the rail.
Now use the iron to fuse the two tinned surfaces together. Let it cool then give the wire a tug from underneath to confirm it is attached.
Regards

[Terry Bendall]

Keith's description is exactly the same as the method I use. Works every time.

Terry Bendall

[Re6/6]

Thanks again Steve. Success!
This was trackwork built by Norman Soloman 20+ years ago.
The Kurust certainly did the trick with banishing the oxide. Careful working with a fine file, a fine slip stone and finished with a polishing wheel with Shiny Sinks in the Dremel.
There are still small amounts of pitting on the railhead, but it is what it is...better than before though...a lesson learned!!

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