Author Topic: First time brass brazing  (Read 6494 times)

Offline surfdabbler

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First time brass brazing
« on: March 30, 2016, 09:32:43 AM »
I am making some brass bolts for saw handles.  I will be getting some brass rod for the shaft, and flat stock for cutting out the large bolt heads.  My plan is to braze the brass rod onto the heads, but I have never done brazing before.  I've done plenty of electronics soldering, and a bit of welding, but never brazing.

I have borrowed a propane torch, and some silver brazing flux, and I have some 5% silver brazing rods.

It's probably a couple of days before I can get the brass, but I just thought I'd ask for hints in the meantime.  My plan is to clean the joints with wet-dry sandpaper, then set everything up on the concrete, cover the joints in flux, somehow hold the bits in place, and turn on the heat.  I'll keep trying the rod onto the joint and hopefully eventually it will just start melting and running in.

Also, the flux is quite liquid, probably the consistency of washing detergent.  Is this OK?  I shook a new pot in the shop, and it didn't slosh around.  Mine could be quite old - does it go off?

Offline awemawson

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Re: First time brass brazing
« Reply #1 on: March 30, 2016, 09:51:56 AM »
Most important issue is to know the melting point of your 5% silver brazing rods compared to the brass that you are using - obviously they need to be reasonably far apart to avoid disappointment.

Try and avoid doing it on concrete - it can exfoliate explosively if there is any moisture in it - a fire brick is to be preferred, or a 'Celcon' foamed cement building block.

Brush the flux on, and gently warm until the flux dries, then glazes and finally runs into the joints, then apply your silver brazing rods sparingly to the hot joint. The heat should be on the joint not the rod.

Can I suggest doing a 'test piece' first to avoid spoiling your final item.

Welcome aboard by the way. Why not tell us a bit about yourself and your projects in the Introductions section?
Andrew Mawson
East Sussex

Offline R.G.Y.

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Re: First time brass brazing
« Reply #2 on: March 30, 2016, 03:04:05 PM »
The insulation building blocks are best for making a hearth,( cut with wood saw) they reflect heat as opposed to fire bricks which absorb heat. Holding small pieces against the blast of the torch. My method is press the items in to fire cement, the torch will set the cement and hold firm. Ease cracked of when finished. Kept in its original pot and moist in will keep for months. 

Offline surfdabbler

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Re: First time brass brazing
« Reply #3 on: April 02, 2016, 08:37:34 PM »
Had a first go today, but not much success.  The metal didn't seem to bond.  The brazing rod melted to the join, but once it cooled, it was fairly easy to crack apart.  I'm not sure about the flux.  Does it go off after years of sitting on a shelf?

I did some testing with just the flux - painted some on the surface, and heated it with the torch.  It initially dried to a white residue on the surface, but as I heated it further, the residue melted and seemed to bead on the surface.  The more I cleaned the surface, the more it beaded AWAY from the cleaned surface, which is really counter productive.

I'm using a propane torch, and it takes a couple of minutes of focused heat to get up to temperature to melt the brazing rod.  The parts are very small - I'm brazing a one-inch long 4mm rod onto a one-inch square piece of brass bar.  I'm using CIG Silver brazing flux no. 2, and Weldcorp 5% silver brazing rod.  I'm using wet-dry sandpaper to clean the surfaces (don't have a SS brush).

Any suggestions?

Offline surfdabbler

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Re: First time brass brazing
« Reply #4 on: April 03, 2016, 01:30:56 AM »
Some more testing this afternoon, and the results were not good.  Am I even being realistic?  Is it possible to get a strong enough brazed bond to the end of a 4mm shaft to hold a 1 inch disc on the end as a head?  A fairly light tap will just crack the 'head' off the bolt.  I am getting disheartened as to whether this is even possible with brazing, or whether I need to sand cast a bolt, and the equipment required for that is definitely out of budget.  Anyway, I'll be off to the shops later this week to get some new brazing flux and see if that goes any better.

Offline SwarfnStuff

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Re: First time brass brazing
« Reply #5 on: April 03, 2016, 01:46:52 AM »
Hi Surf,
         Are you getting both bits cherry red? Interested to see if fresh flux helps, also interesting that the flux seems to run away from the cleaned part.
    You don't say how thick the 1" disk is and this may be critical as brass sure conducts the heat away from the joint area.

Good luck with it anyway,

John B
Converting good metal into swarf sometimes ending up with something useful. ;-)

Offline Joules

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Re: First time brass brazing
« Reply #6 on: April 03, 2016, 02:00:43 AM »
How tight is your thread, you might want to chamfer the hole so your solder has more metal to key onto, or even use a needle file to add some grooves for the solder to wick into.  Dip your solder when warm into the flux so it also gets a coat at the tip.

See if you can buy/borrow some fresh flux.
Just get doing and make swarf, you can decide what its going to be later.   :thumbup:

Offline awemawson

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Re: First time brass brazing
« Reply #7 on: April 03, 2016, 03:27:58 AM »
Perhaps a few photographs of the components, and the result might help us visualise the issue  :scratch:

Silver soldered joints only need a few thou for 'wicking in'

Have you tried heating a sample of your brass to cherry red to check it survives the temperature?
« Last Edit: April 03, 2016, 05:10:28 AM by awemawson »
Andrew Mawson
East Sussex

Offline DMIOM

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Re: First time brass brazing
« Reply #8 on: April 03, 2016, 04:22:18 AM »
If the flux is beading / 'running away', I wonder if the surface might not be clean enough - have you tried de-greasing?

Dave

Online Fergus OMore

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Re: First time brass brazing
« Reply #9 on: April 03, 2016, 04:49:29 AM »
I haven't seen the job but my thoughts are two fold.

The first is that there is too much heat and the second is that the wrong brazing/silver solder  is being used. I'd use a higher silver content and not blast the hell out of getting brazing rod to run.

My thoughts :doh:

Regards

Norman


Offline awemawson

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Re: First time brass brazing
« Reply #10 on: April 03, 2016, 06:18:00 AM »
The 'Heating and Ventilating' chaps when installing air conditioning use a phosphorous copper alloy that needs no flux. I got some years ago when I was making up fittings for my 100 kW induction furnace that needed water cooling pipes plumbing in.

I was sure that I still had some, so as I had a break between lambs arriving this morning I thought I'd do an experiment with it before I recommended it to you - so here are the results.

The stuff I have is 'Harris Phoson', but there are many brands of the same thing:

http://eu.harrisproductsgroup.com/en/Products/Alloys/Brazing/Phos-Copper/Phoson.aspx

Not having 1" brass stock nor 4 mm bar I sliced a bit off a 20mm hexagonal bar, and also turned a 1/4" hex brass bar down to 1/4" round and cut an inch off the end. Then I drilled a small recess in the 20mm hex for the 1/4" round to sit in to give it a location.
Andrew Mawson
East Sussex

Offline wgw

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Re: First time brass brazing
« Reply #11 on: April 03, 2016, 06:21:27 AM »
Have you drilled a hole in the flat, or you trying to butt the rod to the flat. I don't think a butt will be strong enough. At these sizes a propane torch should be ample with the correct solder and flux.

Offline awemawson

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Re: First time brass brazing
« Reply #12 on: April 03, 2016, 06:22:57 AM »
Then with it sitting on a fire brick, with a carbon rod balanced on top to stop it blowing away, I heated it with my Rothenburger propane torch and applied the Phoson strip to the joint on the far side away from the flame. It flowed nicely but I put far too much on!

Then I cleaned it up, and to prove that it was a sound joint, mounted it in the lathe, skimmed the rod down to 6 mm and ran an M6 die down it.
Andrew Mawson
East Sussex

Offline awemawson

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Re: First time brass brazing
« Reply #13 on: April 03, 2016, 06:27:12 AM »
Now the point of the exercise was to show if only a slight location dimple was going to give enough surface area for a sound joint. And it was. The forces on the 6 mm bar when turning would have broken off an unsound joint, and then running a die down it would have been the last straw.

But the fact is it is a very sound joint - so yes I recommend this Phoson stuff as very easy to use. However I do vaguely remember a caveat from years ago not to use it in steam boilers  - can't remember why.

« Last Edit: April 03, 2016, 09:14:20 AM by awemawson »
Andrew Mawson
East Sussex

Offline awemawson

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Re: First time brass brazing
« Reply #14 on: April 03, 2016, 06:35:31 AM »
Probably worth noting that I deliberately did NO cleaning of the brass before brazing - it was straight off the lathe. So although it was fairly clean it would have had some oil on the surface
Andrew Mawson
East Sussex

Offline JHovel

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Re: First time brass brazing
« Reply #15 on: April 03, 2016, 10:46:28 AM »
Hi Surfdabbler,
I think its been well covered already. But to emphasize a couple of points: the 5% siver solder is for plumbing fittings which have a large surface area in their sockets on corresponding pipes. For small surface areas like yours, I would not try it. 45% silver or the Phoson (I have no idea where to get that in Australia though, try BOC for either.) is the stuff to use. By the way, they are the fillers used to braze tungsten carbide onto tools.
Your flux should be OK. In fact clean brass and copper will siver solder/braze without flux. Steel won't. If your flux is runny, then the borax has settle out. Scrape the bottom of the container and mix it back into the liquid.
Lastly, I have a suspicion your not getting the joint hot enough. THe flux will 'run everywhere' when up to brazing temperature - and the silver will run towards the heat. Beading of your flux is a sign on not quite enough heat. Incidentally, the silver solder you used should run 'like water' not make fillets or leave lumps at the right temperature. Did it?
Cheers,
Joe

Offline mattinker

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Re: First time brass brazing
« Reply #16 on: April 03, 2016, 12:36:19 PM »
45% silver or the Phoson (I have no idea where to get that in Australia though, try BOC for either.) is the stuff to use. By the way, they are the fillers used to braze tungsten carbide onto tools.

Just a tiny hi-jack!

Hovel,
That's interesting, I didn't know that Phoson was used for brazing carbide tooling, I've got lots of it from plumbing, cheaper than silver solder!

Thanks again, regards, Matthew

Offline DavidA

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Re: First time brass brazing
« Reply #17 on: April 03, 2016, 12:43:08 PM »
Surfdabbler,

Probably a silly question, but are you sure that it is brass ?  And not something like ally-bronze.

I was caught out by this years ago.

Dave.

Offline surfdabbler

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Re: First time brass brazing
« Reply #18 on: April 04, 2016, 07:02:49 AM »
Wow, thanks for all the replies.  Awemawson, you have pretty much done what I am trying to do.  The head of your bolt is slightly thicker - I think mine is 1/8", or about 3mm thick.  I think I have to track down a couple of firebricks to work on too, or make up a sand/kitty litter tray.  Your balancing trick looked clever - I have something like this that I can set up to help balance during brazing.

To answer various other points raised...

- Yes, I'm sure it's brass - bought new from a reputable brass supplier the other day.
- I was wondering about the silver content.  The high silver content rods are pretty expensive, but I might have to shell out for some if this doesn't work.
- My brass is not getting glowing hot at all.  I was taking it just far enough to melt the brazing rod, but perhaps I should take it further.  It's an old torch, so I might need to insulate around the workpiece to get it hot enough.
- I had assumed that a butt joint would be fine, but I can try a dimple
Will try some more soon, and take some pics...

Offline awemawson

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Re: First time brass brazing
« Reply #19 on: April 04, 2016, 08:14:02 AM »
Happy to post you a Phoson rod if you like. It'll cut up into envelope lengthed bits so shouldn't be too pricey.
Andrew Mawson
East Sussex

Offline chipenter

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Re: First time brass brazing
« Reply #20 on: April 04, 2016, 12:06:17 PM »
Wilkinsons sell refletive fire bricks for the back and sides of an open fire .
Jeff

Offline vtsteam

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Re: First time brass brazing
« Reply #21 on: April 06, 2016, 08:36:43 PM »
5% silver is not what you want for this.
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline grg12

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Re: First time brass brazing
« Reply #22 on: April 07, 2016, 04:14:11 AM »


- My brass is not getting glowing hot at all.  I was taking it just far enough to melt the brazing rod,

That sounds a bit suspicious. Are you really sure you got brazing rod and not some tin/silver "eco" soldering alloy?



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Offline vtsteam

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Re: First time brass brazing
« Reply #23 on: April 07, 2016, 11:44:15 AM »
5% silver IS mostly tin.

It used to be here in the U.S. at least, that "silver solder" was actually silver braze with a very high percentage of silver (65%-95%). With the advent of lead reduction, yes, now sellers seem to advertise tin solder with any percentage silver in it as "silver solder".

It isn't silver solder. It's tin solder, with a tiny amount of silver in it. It has little more strength than ordinary plumbing solder, melts at near their temps (roughly 475-500 F). True silver solder (braze) melts at much higher temps (800F+) and has far better mechanical properties -- it is used commercially to braze carbide tips on saws, join bandsaw blades, etc.
I love it when a Plan B comes together!
Steve
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Offline surfdabbler

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Re: First time brass brazing
« Reply #24 on: April 10, 2016, 11:08:34 PM »
Had some time to try again on the weekend, and it worked much better this time.  I used the original flux (with a good stir to make sure nothing important was settled out.  Drilled a location hole in the 'head' of the bolt, and also ground the end of the rod to roughly match the shape of the hole.  I brushed in a drop of flux to the hole and to the end of the brass rod, and cut off a small piece of brazing rod and threw it into the hole from the start (you can see it in the first photo).  I also managed to find some 15% silver rod at bunnings, so I used that instead of the 5% silver.  From there, I heated the whole think in a small crucible.

Last time it was taking several minutes to heat up, but this time it was much quicker.  I think using the crucible really helped to reduce heat loss, and cutting off a piece of the flux was a huge improvement, compared with trying to bring the rod in with my third hand.  It meant that I could hold the brass rod in place with one hand, and hold the torch with the other hand.  After about 15-20 seconds, it was up to temp, the rod melted, and pow, beautiful joint! I made a few crooked bolts on the first try, but a quick reheat allowed me to move them straight again.

Thanks for all the help and recommendations, and a special big thanks to awemawson for the photos of the whole procedure and great tips!  You guys rock!
 :nrocks:

Offline awemawson

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Re: First time brass brazing
« Reply #25 on: April 11, 2016, 02:21:17 AM »
Excellent to see that you've got a good result  :thumbup:
Andrew Mawson
East Sussex

Offline Pete W.

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Re: First time brass brazing
« Reply #26 on: April 11, 2016, 04:40:18 AM »
I like the idea of using the crucible as a micro-hearth.   :mmr:   :nrocks:   :mmr:   :nrocks: 
Best regards,

Pete W.

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Offline surfdabbler

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Re: First time brass brazing
« Reply #27 on: April 17, 2016, 02:37:57 AM »
Just out of curiosity, I tried the original brazing rod again, just to see, and I managed to get another very nice result with the original rod.  So, the 5% silver rod was fine.  I still haven't had a lot of experience to compare the two, but I did feel that the 15% silver was a little nicer to use, but they certainly both worked.  So the original problems just came down to technique.
« Last Edit: April 17, 2016, 06:08:16 PM by surfdabbler »

Offline mattinker

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Re: First time brass brazing
« Reply #28 on: April 17, 2016, 11:27:09 AM »
Just out of curiosity, I tried the original welding rod again, just to see, and I managed to get another very nice result with the original rod.

Some people think I'm pedantic, but I think it's important to call a brazing rod just that and not a welding rod. I know that there are a lot of people who refer to brazing as welding, but there is a fundamental difference in the two processes.

I'm glad you got it sorted! Regards, Matthew

Offline surfdabbler

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Re: First time brass brazing
« Reply #29 on: April 17, 2016, 06:14:46 PM »
Some people think I'm pedantic, but I think it's important to call a brazing rod just that and not a welding rod.

Absolutely right!  I fully agree and have edited my post to fix my mistake.  Thanks for pointing out my error.