Acid-flux soldering trick.

Problem with using acid-flux solder is that you have to carefully scrub the soldered parts off with soap and hot water after soldering so as to be *certain* that you've removed the last of the acid. Failure to do so will cause the acid-exposed parts to darken and corrode at the very least, and will also eat any paint off from underneath after it's been applied!

So while charging my motorcycle battery this morning it struck me: we use common baking soda to neutralize spilled battery acid, so why not use it after doing an acid-fluxed solder joint?

Tried it this afternoon after doing some long-put-off repairs on a brass loco, and can report that it works *just fine*!

I simply put a small amount of baking soda into an old 35mm film can, dipped a Q-Tip into some water, rolled the wet Q-Tip around in the soda for a second or two, and then spread the resulting thin paste liberally over the still-cooling solder joint.

Although invisible to the eye, the acid bubbled like mad for a few seconds when the soda hit it, and then subsided.

You still have to wash the soda-paste off of the joint in question after the bubbling stops, but there's no longer any doubt about whether or not the left-over acid has been completely neutralized!

The little film can of baking soda has now earned a place on the shelf beside all of my other soldering equipment.

~Pete

(Snippity)

Odd. I only posted it once.

Can computers develop the hiccups?

~Pete

Amazing the things that were "Well known, to the 'old Timers'" that just aren't common knowledge anymore.

But you DO still need the water wash, to get rid of the 'salts' created when the acid was neutralized. It can cause it's own problems.

Story from many years ago: Slip Gauge Guild, Pasadena Calif. Original layout. HOn3, 35' X 30' approx. (memory is a bit dim, it was 38 +/- years ago.)

We were using a 'spline' roadbed construction, a 'spline trough' filled with 'Acoustic Plaster', top surface planed/ sanded to desired contour, individual wood ties glued down, final light sanding to remove any minor humps. Hand spiked Code 70 Nickel Silver rail, butt soldered to eliminate 'joint problems' (acid core solder, neutralized with Baking Soda to eliminate possible corrosion problems.) Sounds good, right? --- all the club members were happy that all possible problems were being taken care of.

Pasadena, is located in the L.A. area of Southern California. You wouldn't guess from looking, but it's basically a 'Desert Climate', I.E. minimal rain. low humidity.

Comes the next Spring Rainy Season, And we started noticing troubles operating locomotives. Seemed to be 'Shorts', but they couldn't be found.

To finish a long story. The Elusive shorts were traced to, the salts created soldering the rail joints, and using baking soda to 'clean up the acid. The 'salts' were soaking into the acoustical plaster roadbed, during most of the year, this created no problem, but when the humidity rose during the 'rainy season' (to all of 30% maybe) the plaster absorbed enough moisture that the 'salt solution' created a 'short' between the spikes of the opposing rails.

That one took us a few weeks of thought to figure out!!!!! Most annoying!!

Chuck D.

yes, sometimes very bad cases of them. (don't ask.)

(Snippity)

Odd. I only posted it once.

Can computers develop the hiccups?

~Pete

True. But I *AM* an old-timer, and I'd never heard tell of it! (Seemed like *way* too obvious an idea to have been original though...)

Thanx for the tip and the story as well, Charles. I've been washing the soda off anyway, but it's good to know why I should continue doing so.

I wasn't a chemistry major. }:-P

~Pete

Okay, I won't. I likely wouldn't understand an explanation anyway.

(Crosses fingers serrupticiously.) X X

~Pete

Sounds OK, but all the mixing of baking soda with wet Q-tip is just too much work for me. I've used plain old household ammonia to neutralize the acid. Works well and rinses off very easily.

Then there's the nasty paste fluxes that seem to resist washing. From rec.crafts.metalworking some time ago was the tip to use 2-butoxy ethanol/acetate. That's white board cleaner for us chemically challenged.

Then there is Alcohol from the drug store. But if you do, get the 'good stuff' 91% . Slightly more costly than 'Rubbing Alcohol' [you probably already have some of this in the house.] BUT "Rubbing Alcohol" usually has 'additives' to soothe the skin (oils, perfumes, and other possibilities).

Chuck D.

On 1/5/2009 9:47 AM Charles Davis spake thus:

But that won't neutralize the acid. Seems like the baking soda would be better, maybe followed by alcohol to remove whatever sticky parts of the flux remain.

And they're not 'additives', they're just additives. Besides, most rubbing alcohols I've seen are just cut with plain water, nothing else.

The alcohol is to 'cut' the "Nasty Paste Fluxes". Doesn't do a thing for/ against 'acid' problems. Chuck D.

You are doing the fourth way: a bad job, that is not even quick.

Using paste fluxes should be avoided absolutely. At least where the remainders cannot be washed away, without traces in the environment, as in track building. Hear CHarles Davis's tale. The only allowed flux is resin. Yes, you'll have to clean the metal thorougly..

That depends upon what you're soldering.

Resin fluxes are fine for soldering electrical connections, but don't work worth a *darn* when you're repairing -or building- a brass locomotive, car, structure, or what-have-you.

For that you need a water-thin mild acid flux that will be sucked into the solder joint by capillary action and will allow the molten solder to flow in after it as the heat evaporates the flux. (Note: don't inhale the fumes!)

An acid flux also makes for a structurally stronger solder joint than does a resin flux, which is intended to provide good electrical continuity and little else.

~Pete

Re-read what I said. Resin flux is the only way if the remainings of acid flux cannot be washed away. When you are building repairing whatever metal structures generally you can wash away the remainings. That is how you and I do it, and that is ok. Building track is different: you cannot wash away the remnants without soaking the roadbed with it. That is why you should not use acid flux, but resin instead. A flux that provides a good and reliable electrical conductivity should also provide mechanical strength. Both rely on metal-to-metal bond.

I understood it fine the first time.

Not the same thing.

You get a *stronger* metal-to-metal bond by using an acid flux, and this is because it not only allows the solder to flow freely -as does resin- but by etching the metal a bit it also provides the cleanest possible metal for the solder to get a grip on.

You also use an entirely different solder for brass work than you do for electrical work, and *that* provides a much stronger solder joint as well.

Horses for courses.

~Pete

That's what happened to that railroad! It was a nice layout.

-- Bob May

rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net

The carrier for the past fluxes is a grease. That means that you need detergent to ge tthem off. I just stay away from acid fluxes because of all the problems mentioned. The electronic type fluxes are all inactive when cold and are designed to be removed easily from PC booards with simple procedures and can stay on track and so forth without any problems of salts generated from neutralizing the acid and so forth.

-- Bob May

rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net

On 1/5/2009 11:39 AM Charles Davis spake thus:

Didn't you read my reply? That's exactly what I was saying.

You are referring to 'The Slim Gauge Guild"? They moved to another location 3+/- miles west. and as far as I know are still there. (Basement location, Sn3 and HOn3 layouts).

It's been several years since I've been there to see how they are doing.

Chuck D.