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Soldering brass body of a mechanism. One joint sticks, other does not.

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cavemen

Mon Nov 23 2009, 04:09AM

Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118

I have a basic soldering iron and a benzomatic blow torch.
I am using several brands of rosin-core solder.

So far I made electronic projects.

But today I tried to make a body for a mechanism out of brass plates, cut out origami-style and solder the seams. Three parts.
Handled same way.

I soldered first two parts. Everything worked well. Parts fused and never tried to come apart. When I tried to soled those two parts to the third, the part bond broke off.
I washed it with warm water and soap, steel brushed it.

Steel brush was fairly clean. Can this be a problem?

Same result. Solder doesn't want to stick.
Then I moved to the torch. Ended up making this mechanism look ugly with solder.
Still nothing stuck together.

Then I decided to clean up the parts from solder by torch and melted everything into a puddle.

How do I make things stick?
My father was successful at using a heat gun in SMD radio component assembly.

Should I buy the heat gun?
Looks like a good tool to have.
Moves hot air slowly, making solder liquid.

Can brass oxidate and form a protective film that prevents soldering, like aluminum?

Is carbon a bad thing in soldering joint?
Rosin has carbon.

Tip of the iron got carbonized up a little bit. Is temperature important?

How to solder and have 100% guarantee that things like that won't happen?

cavemen

Mon Nov 23 2009, 04:26AM

Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118

Would the air temperature
1000 degrees F/538 degrees Celsius
do the soldering job?
Trying to pick the heat gun. Or not buy it at all.

mnr

Mon Nov 23 2009, 04:31AM

Registered Member #996 Joined: Sun Sept 09 2007, 06:17PM
Location: Canada
Posts: 16

You should apply external flux instead of relying on the rosin core in the solder.

Look up on how to solder coper pipe, like what is done in plumbing joints. The process is the same.

ConKbot of Doom

Mon Nov 23 2009, 03:37PM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329

Since you say rosin core, I'll assume its tin lead, which should work fine for brass. I dont think steel contamination from the brush should be an issue as I think you can use tin/lead for steel also.
Can you tin both parts without a problem? (lay a small piece of solder on the part near the joint, it should melt and flow and coat the part. It may bead up while the part gets up to temperature, but thats it)

And yes, a 1000F heat gun should be plenty hot to solder, as long as the part isnt too thick or large. Ive soldered pennies together (I was bored) with a heat gun.

doctor electrons

Tue Nov 24 2009, 12:06AM

Registered Member #2390 Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381

You need to clean the parts of any contamination, and yes carbon in any heat applied joint is bad. It will not melt (obviously) and will swirl around in
the solder. In the case of welding joints, it will rise to the top (usually) and destroy the surface of the bead. Or it will cause inclusions inside the bead eventually leading to breakage. Heres what i would recommend you do. 1) Use a stainless steel file to remove the solder that you have already applied.
(keep the file cleaner handy) 2) Get some liquid flux (any generic liquid flux will work) brush it on with a clean acid brush. 3) clamp the piece to a flat surface and begin to heat the edge you are trying to join (heat source blowing at the edge, not into the workpiece). 4) Attempt to "TIN" the edge (silver solder would be best for brass). If you are having trouble getting the solder to stick, its usually a heat issue. Try a hotter gas like MAPP and a more concentrated or focused flame. Also remember that different areas of the flame do different things. IE dont use the oxidizing portion of the flame! Not a good plan! Use the end of the blue cone in the flame to supply good concentrated heat (this is also the hottest part of the flame). Once all of your edges are tinned, go ahead and prop them together! The tinned surfaces will suck up the solder like a sailor in a bar on shore leave!
Hope this helps!!
Sorry, i should have double spaced that but didn't want a 2 screener.

cavemen

Tue Nov 24 2009, 04:17AM

Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118

Doctor Electronics, you seem to answer everything.
Now i bought a heat gun and some plumbing flux.
Things should get better. Thanks

ConKbot of Doom

Tue Nov 24 2009, 04:39AM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329

Or if stuff really gets hairy break out a solder pot :)

My boss had some jumper cable clamps he wanted me to put onto some relatively undersized wire he had from an old set of jumper cables that had rusted up (12-10 awg wire, but the insulation OD was at least 1/2")

Well since the wire was too slim to crimp the conenctor on I wanted to solder it on. A torch tends to oxidize the rest of the terminal (which was also half the jaw for the conenctor) so I decided to use the solder pot. I coverd up everything I didnt want solder on with kapton tape, secured the wire, dunked it for 5 seconds, pulled it out and let it cool and took the tape off.

Though you obviousley need to have a solder pot to do it. Sometimes its nice to have the thermal capacity of 5 lbs of molten lead to draw from, rather then trying to heat something up quick enough.

No pics, but for those of you with solder pots, I'd keep the method in mind, and just get a roll of kapton, which isnt too expensive from the right places.

doctor electrons

Tue Nov 24 2009, 04:44AM

Registered Member #2390 Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381

cavemen wrote ...

Doctor Electronics, you seem to answer everything.
Now i bought a heat gun and some plumbing flux.
Things should get better. Thanks

I answered this one because i have been a welder (us navy certified) for 13 years! Hope i helped seriously, i try not to post if i do not feel
it will benefit.

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