Soldering Flux Paste Solvent

After finishing soldering my Very First model airplane fuel tank, I went
to do the last step of any soldering project -- cleaning off the flux.
Unfortunately, while I know that the flux I use yields to scrubbing with
hot soapy water, I don't know what -- if anything -- will just take it
off. I'm experimenting.
I've got some in each of four cups, with lacquer thinner, mineral
spirits, isopropyl alcohol, and plain drinking water. None of them seem
to be having any effect except the mineral spirits, which appears to be
separating it into two components.
In the mean time, I'm checking here to see if anyone has any pointers.
It's "Top Line Quality Soldering Paste Flux". Bought over thirty years
ago (I don't go through flux very fast). It looks like bearing grease,
& it sizzles when the iron touches it. Works great, but leaves a
residue which I don't want inside my engines!
So -- anyone happen to know if there's a common soldering flux that
contains calcium chloride and has this consistency, and if so how to
clean out the inside of an itty bitty fuel tank made with it? If all
else fails I'll run really hot water through it along with dishwashing
detergent -- but that doesn't leave me 100% confident.
Reply to
Tim Wescott
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I am not sure exactly, but I might try two different things.
The first would be methylene chloride (Jasco paint remover.)
The second would be either lye or automatic dishwasher soap (cascade).
The latter might be the best choice as it should rinse clean.
I would test this on a couple of older copper pennies. Heat them and slather some flux on till it sizzles and them let them cool then dunk them in hot water and the alkaline solution of either the lye or the dishwashing powder.
You might also do a test on some scrap copper pipe and fittings. This then can be cut open after cleaning so you can judge how it will work on the inside of your fuel tank
I use the dishwashing powder to soak nasty cleaning jobs like Pyrex roasting pans that have that burned on grease that seems to defy all other ordinary dishwashing attempts, and it works wonders, with no scrubbing needed.
I suspect that your flux residue is a lot like the burned on crud on the baking dish
Reply to
Roger Shoaf
I usually have good results with Berryman B-12 Chemtool for defluxing.
Reply to
Jon Danniken
Jeweler's pickle?
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Reply to
Ned Simmons
Won't the acid be a problem? While not stated, I had assumed that the fuel tank was made of copper or brass. If you look at the last part of the cited article it indicated that the acid pickle eats copper.
Reply to
Roger Shoaf
That paragraph is talking about the pickle plus peroxide. I've never used that mix so I don't know how agressive it is, but copper or brass can stay in the regular mix for hours with no apparent damage. This is effective on brazing flux and I assume would work on soft solder flux, though I've never tried it myself.
Reply to
Ned Simmons
Acid flux uses zinc chloride and should be washable with water. Rosin flux can be taken off with alcohol or some really active dishwasher detergent. Ammonium chloride flux comes off with hot water. Have never seen any flux with calcium chloride in it, sounds like it would turn into rock when heated. Try some vinegar. I would have used some electrical soldering paste, myself.
Reply to
I think I have a couple of cans of that stuff. Grease mixed with zinc chloride. Dad used to make the flux by dissolving zinc in hydrochloric acid (muratic acid). The grease is supposed to burn off with the soldering heat, but usually never does. I have never used the stuff on something that I could not get into to wipe out, so can't help there.
Reply to
The paste flux used for plumbing is ZnCl2 in a vehicle of petroleum jelly. If that's what you have, any waterless hand cleaner will loosen it, and you can flush with water. It's inconvenient to do this inside a finished tank, so consider tinning the seam bits, cleaning the flux off, then pressing together and heating without any extra flux.
Boiling water rinse is a good starting step. When most of the petroleum jelly is dissolved, the ZnCl2 will dissolve in water.
Reply to
Actually the tank is made out of poor-man's tinplate -- it's a Dole chunk pineapple can, cut up and bent on a Harbor Fright brake.
So, if I use any pickling solution that'll eat steel, I want to not leave things in there for long.
Reply to
Tim Wescott
Dangit, it is zinc chloride. I let half a minute pass between reading what's in it and writing it in a post, and look what happens.
But it's in some sort of greasy carrier that resists water.
If I can't find a good cheap process to wash this stuff off I'll probably get some liquid flux that I know will rinse off easier.
Reply to
Tim Wescott
That sounds exactly like what I have, except that it's brown instead of the clear you'd expect from petroleum jelly.
I think I'll try hot, then boiling water with hand dishwashing detergent, then hot and boiling water with Cascade if the hand stuff doesn't do the job.
Reply to
Tim Wescott
Petroleum jelly, like heavy grease, doesn't (in my experience) emulsify well with normal detergents; it's easy to get loose with whatever is in waterless hand cleaner, though. I've also used the waterless hand cleaner mixed with water (it turns milky) in an ultrasonic cleaner, it's a good degrease solution. The water is key to getting rid of that ZnCl2, or you could just use mineral spirits.
Reply to
30 years ago we used to use 1,1,1 TCE which dissolved & removed the flux in short order. It's outlawed now but if you have any in a dusty corner ... Art
Reply to
2K paint thinners (not pure acetone) will dissolve both petroleum jelly and tallow (which is a decent flux).
I was using some last weekend for the job and found it better than the other solvents I had to hand.
Mark Rand RTFM
Reply to
Mark Rand
The question about copper or brass probably is moot because in later posts, Tim said the tank is made of tin-plate steel sheet. (From a "Dole chunk pineapple can" he said, but it seems to me other brands or cuts of pineapple might work too.)
Anyway, HCl + H2O2 (which might be but probably isn't what the ganoksin link refers to) is so aggressive that it's commonly used to etch copper printed circuit boards. As noted in many web pages, eg , by itself HCl doesn't attack copper, but CuO + 2HCl --> CuCl2 + H2O. Ie, when copper is immersed in the mix, H2O2 keeps oxidizing Cu to CuO and HCl keeps on forming copper chloride.
Reply to
James Waldby
Grease - acid - need a strong base. Base will take off the oil/grease. It will nuke the acid.
Strong stuff in the house - sodium hydroxide IIRC.
Strong soap and the like would work.
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Reply to
Martin H. Eastburn
You are removing zinc chloride and vaseline. Try brake cleaner to cut the vaseline. If it's real heavy, use gasoline or perhaps napththa for gross cleaning, then brake cleaner for the solvent stage. Then I'd use a good proprietary alkalai metal cleaner as from Birchwood Casey or Caswell, or make your own with TSP and sodium carbonate or sodium hydroxide. Some add some sodium silicate but I don't think it's necessary. These steps should result in metal that is chemically and waterbreak clean, suitable for plating.
Since it's itty bitty, I'd at least try a run in my HF ultrasonic cleaner with their pretty good cleaning stuff heated to 160F or so. That doesn't always work but it gets 'er done surprisingly often.
Reply to
Don Foreman
That works????
Thanks! I try that!
Reply to
Gunner Asch
If you used a pineapple can, your problem might not be the flux residue.
Modern food cans have the interiors coated with a resin. It is difficult to remove in the best case and it is impossible to remove after it gets roasted.
If your problem is a crusty residue near the joint that thins out to a transparent brown, then that is what you have. When I need tinplate I scrounge it from gallon lacquer thinner cans. The interior isn't usually coated and you can remove the paint on the exterior with paint remover before you start working.
Paul K. Dickman
Reply to
Paul K. Dickman

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