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Comsol flux residue

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nick feast21/03/2014 19:17:21
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Does anyone have an efficient method of removing the black gunge left behind by Bridgit flux after doing a bit of Comsol soldering on a copper boiler? Strong detergent works after a fashion, meths seems to work a little, but the usual picking method is no good at all.

Any suggestions?

Neil Wyatt21/03/2014 20:13:29
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"Designed for use with lead-free solders. Works extremely well with Bridgit lead-free solder in potable water systems as equally well with other solders. Meets all requirements of the Safe Drinking Water Act. Stays active to 800oF and will not burn at soldering temperature, reducing black carbon formations that can result in voids and leaks."

There is a water-soluble version available, but the Harris website and downloads don't say what to use to remove the standard version. It seems to be a chloride based flux which pickle ought to remove, but it sounds like you may have got the 'black carbon formations' despite their hype. If it's carbon then you are probably looking at mechanical removal.

Neil

OH CHUFF!21/03/2014 21:21:41
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In central heating systems you would use a chemical cleaner ( usually known as sludge remover ) to remove fluxes and other contaminants, readily available from diy shops. The cheap stuff can be bought from places like toolstation and such like. Another way of cleaning a soldered joint is to wipe a little flux on the joint already made, heat it up ( but not to the solder's melting point ) then wipe over with a damp cloth or some fine wire wool but you would still need to chemically clean it to stop verdigris forming. I'm no expert in anything but I have sweated a few joints in my time, so hopefully this may help. Chuff.

julian atkins21/03/2014 22:33:54
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hi nick,

you shouldnt get any awkward deposit after comsoling joints. i havent used comsol for quite a few years as silver solder up firebox stays these days. did you use the correct flux from Reeves etc? i found all you had to do was brush vigorously with an old tooth brush with warm soapy water.

cheers,

julian

Keith Hale22/03/2014 09:59:26
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"Black gunge"?

Examine your heating technique. The flux is either being overheated or the time taken to get to soldering temperature is too long and the flux is exhausted.

Consider changing burner size. Assuming you are using a propane/air torch this is very simple.

Consider changing your flux.

Comsol melts at 305 deg C. Common 60/40 tin/lead melts at 185 deg.

Flux residues normally associated with comsol only require a good washing in water. More appropriate fluxes are readily available.

Regards

Keith

nick feast22/03/2014 19:04:26
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Thanks to those who answered, perhaps a little more detail is needed.

I have a silver soldered copper boiler for a 5" gauge standard class 2. not huge but big enough to require quite a lot of heat to get it up to 300 degrees. There are several stays in the top of the firebox that weep under pressure. So with the boiler inverted and Bridgit flux liberally applied(suitable for up to 427 deg C) I put small pieces of comsol solder by the relevant stay heads. Applying indirect heat i.e. around the outside of the boiler and through the regulator hole in the back head, the flux smokes and blackens before the solder melts. This is the 'black lunge'.

I had supposed that it was better not to apply direct heat as this just sets the flux alight immediately.

So really two questions, is there a better flux and how to best get rid if the black deposit? It has to be removed chemically because there may well be joints that still leak and need to be cleaned internally to have any hope of taking solder next time.

Thanks

Nick

stan pearson 122/03/2014 22:33:12
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Hi Nick

I have only done small not important soldering with Comsol and use the same flux as Silver Solder with no problem.

Regards

Stan

julian atkins22/03/2014 23:12:07
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comsol requires a special flux and nothing else should be used. with respect nick, i think you have used completely the wrong flux.

again with respect stan i dont know how you can possibly use silver solder flux for comsol!

with boiler work i dont take any short cuts and always buy the correct stuff from Cupalloys etc.

cheers,

julian

nick feast24/03/2014 09:41:05
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The flux was purchased a few years ago at the same time as the Comsol from a well known ME supplier and is labelled '86/140 flux for Comsol solder' . However their latest online catalogue doesn't show it, so perhaps it isn't that good.

I will be sourcing some different flux shortly but this doesn't actually help with removal of the black deposits on the boiler! I might give caustic soda a go as I suppose it's basically carbon and caustic shifted the black goo in my BSA bantam exhaust back in the last century.

stan pearson 124/03/2014 22:30:39
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Julian

As I said I would only use silver solder flux on non important jobs certainly not a boiler you can use any flux ! many years ago when I did my City & Guilds we were taught to solder and told most important to clean and de-grease later I worked at a Haulage firm and had to repair a leaking Diesel tank, we had no soldering fluid my boss said use grease after an argument he did the job with Lithium grease and when I left 6yrs later it was still dry.

Regards

Stan

julian atkins24/03/2014 23:00:03
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1252 forum posts
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hi nick,

im sorry to say you must have been sold some duff stuff. i have a vague recollection that the original comsol flux was discontinued as didnt comply with modern H&S rules etc. i have plenty of the old stuff. it is very active, and does the job very well though havent used it for quite a few years though when last used it was 20 years old!

pickling wont remove soft solder fluxes. caustic soda in boiling water plus a stiff brush should do the trick. Wilko's sell caustic soda as drain cleaner.

cheers,

julian

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