Author Topic: Brazing  (Read 5479 times)

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Offline vomisaTopic starter

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Brazing
« on: August 03, 2007, 08:31:55 PM »
The tutorial on brazing has led me into a can of worms and I have come to the conclusion that the tutorial is not about brazing at all but is instead about silver soldering. After purchasing the recommended type of brazing torch (except it was $40 not $15!) I found that it would not come even close to melting a brazing rod (Nickel/Silver) and after contacting the manufacturer of the rod I was told that I would need MAPP gas to effectively use this type of rod. Research on the net indicates that the recommended method of brazing requires an oxy/acetylene torch.

Ok so I went and bought some (plumber's) silver solder. I can now barely melt the rod and despite having cleaned the surfaces, and used plenty of the right flux, all I can get is a few blobs that do not adhere to the metal surface (steel nails). I believe that this is due to the surfaces not being hot enough. The torch I am using claims a temperature of 1300C (2380F), and I am using the recommended "pure butane" gas.

Has anyone successfully used this method on steel using a small torch like this? Does anyone have any links to videos showing this being done?

Cheers.


Offline Soeren

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Re: Brazing
« Reply #1 on: August 03, 2007, 10:16:51 PM »
Hi,

First off, cleaning is the key. you need to get to bare un-oxidized metal to braze.
Second, not knowing your torch, does it (power wise)  relate to the job at hand?
Third, do you shield the heat by something able to stand the heat and isolate, to pack as much heat as possible into your work piece?
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
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Offline vomisaTopic starter

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Re: Brazing
« Reply #2 on: August 03, 2007, 10:57:12 PM »
Hi Soeren, thanks for the reply.

Hi,
First off, cleaning is the key. you need to get to bare un-oxidized metal to braze.
Yep, understood, the methods I have tried is to degrease with detergent and then cleanse with acetone, and also to grind the surface to a bright shine, neither
attempts proved successful.

Second, not knowing your torch, does it (power wise)  relate to the job at hand?

That is hard to determine. According to the brazing tutorial on this site a small hand held torch should be sufficient. The one I bought is a Model MT6000SB "Hot Devil" which claims to be suitable for brazing and to reach a temperature of 1300C. In my simple test I am using a couple of 2 1/2" nails and the torch is able to bring these to a bright red heat. Certainly the silver solder melts but does not "wet" the steel. I also tried a test on a slab of 1/8" thick steel plate, with similar unsuccessful results. I have also performed these tests with a larger butane blow torch with the same results.

Third, do you shield the heat by something able to stand the heat and isolate, to pack as much heat as possible into your work piece?

Not having access to fire bricks, I am currently using some house bricks to hold the material. I have arranged it such that the target area is in free air.

Offline Admin

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Re: Brazing
« Reply #3 on: August 04, 2007, 04:50:41 PM »
Quote
Does anyone have any links to videos showing this being done?

I was actually considering making a video yesterday . . . but I have no need to braze at the moment.

Everything I used I bought from mcmaster.com. The butane torch I got is #75195A16 for $28.87. McMaster has been raising the prices of everything lately . . .

It appears you are doing it right. You first heat up the material really hot, then apply the rod. What I suspect is that you didnt get the correct rod. The one you are using is obviously not melting, and as the manufacturer said, you need much higher heat. I think what you bought was a welding rod.

Go to mcmaster.com and do a search for 'silver brazing alloy' and a whole bunch should show up on the right.

As a reference for anyone else:
http://www.societyofrobots.com/mechanics_brazing.shtml
« Last Edit: August 04, 2007, 04:54:47 PM by Admin »

Offline vomisaTopic starter

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Re: Brazing
« Reply #4 on: August 04, 2007, 09:12:11 PM »
Thanks for the input Admin.

It appears you are doing it right. You first heat up the material really hot, then apply the rod. What I suspect is that you didnt get the correct rod. The one you are using is obviously not melting, and as the manufacturer said, you need much higher heat. I think what you bought was a welding rod.

No, it is definitely a brazing rod (the first rod I bought was a self-fluxing nickel/silver brazing rod which would be fine except you need a very high temp torch to melt it, I could get it to melt but not to an extent it would run), the second rod I bought was a brass/silver rod (the type plumbers use for brazing copper pipes) which melts and runs easily but does not 'wet' the steel target material - by 'wet' I mean adhere to the material as ordinary solder adheres to copper wire. It simply forms into globules as if the target material was not clean, although I am sure it is. The flux I am using is brazing flux for copper and steel.

Can you give me an idea of the target materials (type, dimensions) you have has success with using this method please?

Thanks again for your assistance.



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Re: Brazing
« Reply #5 on: August 04, 2007, 09:26:40 PM »
Ive done it with various 1/16" sheet steels and its worked really well.

I seem to remember trying it with copper, but not sure. Its worked on all my attempts.

If you ever figure it out Im curious to know . . .

Offline Soeren

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Re: Brazing
« Reply #6 on: August 04, 2007, 10:04:00 PM »
Hi,

[...] but does not 'wet' the steel target material [...] It simply forms into globules as if the target material was not clean, although I am sure it is.
It sounds weird and the only explanation I can think off is, that perhaps you're not flux'ing correctly or you may be heating it too much before you apply the rod - most flux'es should be heated until transparent like water, then the rod is applied.

You might try another way: File the rod into "powder" and mix that with the flux. Clean the surface totally (i.e. fine emory paper for the last run). Apply the flux/metal paste immediately and heat it up with a soft flame, making sure the joint and surroundings heat evenly. Apply a pointed flame when you can see the brazing metal beginning to shine.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline vomisaTopic starter

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Re: Brazing
« Reply #7 on: August 05, 2007, 01:16:20 AM »
Hi,

It sounds weird and the only explanation I can think off is, that perhaps you're not flux'ing correctly or you may be heating it too much before you apply the rod - most flux'es should be heated until transparent like water, then the rod is applied.

You might try another way: File the rod into "powder" and mix that with the flux. Clean the surface totally (i.e. fine emory paper for the last run). Apply the flux/metal paste immediately and heat it up with a soft flame, making sure the joint and surroundings heat evenly. Apply a pointed flame when you can see the brazing metal beginning to shine.


I suspect you are right about the flux, however when I tried your suggestion I could not get the flux to pass through the transparent phase, it simple goes from powder to black (it appears to burn). I have tried a soft flame gradually increasing until the flux changes, and also by indirectly heating the material so that the heat "runs" up to the fluxed area, to no avail.

The flux is specified for brazing copper OR steel so it should work.

Can someone tell me what the constituents of the flux they are using is please?

Mine comprises Boric Acid and Sodium Metaborate.

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Re: Brazing
« Reply #8 on: August 06, 2007, 01:10:58 PM »
Ok I looked up the mcmaster part numbers . . .

White Silver Brazing Plaste Flux 1 Pound Jar
7693A2

High-Fill 35% Silver Brazing Alloy
7676A4

Hope that helps . . .

And my flux paste definitely turned translucent/parent

Offline vomisaTopic starter

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Re: Brazing
« Reply #9 on: August 06, 2007, 07:08:40 PM »
Ok I looked up the mcmaster part numbers . . .

White Silver Brazing Plaste Flux 1 Pound Jar
7693A2

High-Fill 35% Silver Brazing Alloy
7676A4

Hope that helps . . .

And my flux paste definitely turned translucent/parent

Indeed it does. It does confirm that what is being described in the tutorial is what is commonly referred to as "silver soldering", or, more correctly, as silver brazing. The lower melting temperature, due to the silver content, makes it possible to use the cheaper, lower temperature, gas torch, whereas the lower or no silver content require MAPP or oxy/acetylene.

In my case, it would appear that the second brazing rod I obtained, is what is known as phosphor-copper brazing rod that is used for fluxless brazing of copper pipes, fluxed brazing of brass, but apparently, cannot be used for steel. I don't think that this is the reason for the braze not wetting the steel however, and can only assume that it is the wrong flux that I am using, or too low heat.

Unfortunately I don't have access to McMaster or similar and none of the suppliers I have used know diddly-squat about brazing, so more research for a supplier is needed.

Thanks for your help.

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Re: Brazing
« Reply #10 on: August 06, 2007, 07:10:43 PM »
Try Grainger

Offline vomisaTopic starter

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Re: Brazing
« Reply #11 on: August 07, 2007, 11:44:48 PM »
Success at last!

I finally found a supplier for 45% silver brazing alloy (boy was it expensive), and the correct flux.

The small gas torch I bought (similar to that shown on the tutorial) started to play up and so I have had to send it back, none-the-less I found that my old blow torch was sufficient to use with this alloy.

Ultimately I am not sure that this is the best way to go, as there are much cheaper brazing fillers available (for instance the first Nickel/Silver blue flux coated one I bought) however these require much higher temperatures and so needs more expensive equipment, this, however, is a one-time expense (unless you go for oxy-acetylene), and so would work out cheaper in the longer term. I may follow this up in the near future and report back.

Cheers.

Offline dunk

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Re: Brazing
« Reply #12 on: August 08, 2007, 03:52:57 AM »
did you try lead based plumber's solder?
plumbers use it for brazing copper pipes.
it's relatively cheap and melts easily.
it definitely works for copper but i'm not sure if it will be strong enough for your application. (i've only ever used it for plumbing.)

dunk.

 


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