Friday, 26 July 2013

Can you braze with a propane / butane blow torch?

Can you braze with a propane or butane blow torch? - Intro

Being stingy I thought I would try and see if I could braze with a standard propane / butane plumbers blow torch. As the one pictured below. This is the type of propane / butane torch often used by plumbers or chefs for making creme catalan etc.

I have read a very good book on the subject, and for anyone thinking of attempting some brazing I would recommend it it is called "Soldering and Brazing" in the "Work Shop Practice Series". It covers all sorts of brazing methods, and yes you can use a propane, or butane torch. 

There are different gases available which you can use, MAP gas is a slightly higher temperature gas than propane, although we are talking 2100c instead of 1900c, so I am not sure how much difference that will make.   I used sievert power gas, which seems to be fine heat wise, technique is probably more important. But for more recent projects I have used sievert ultra gas.

The torch you use will likely have a greater impact on the heat output than the gas. If you intend to buy a torch look at the heat output which can range from 0.5 to 2.5 KW or more. The book doesn't really say how much you need, so I can't comment either, like I say technique seems to be most important. 

Make sure you get the right flux to work with the solder / rods you have purchased. If in doubt buy the flux and rods together to avoid confusion. The joint will need to be well fluxed to make sure the filler material runs properly. Silver solder is good at filling very small cracks. I have bicycle frame (pictures below) which I repaired using Silverflo 55, and a patch.

Can you braze with a propane or butane blow torch? - Which Filler Material

I was not expecting to be using normal brass brazing rods, because the torch would not be hot enough, instead I was hoping to use a low temperature silver solder such as JM Silverflo 55. It turns out that with the right sort of propane torch you will be able to braze with brass rods. Using a silver solder with a lower melting temperature, however will be easier.

Write up:

M Silverflo 55 is widely recognised as the best quality general purpose silver solder with a silver content of 55%. It is suitable for use on copper, copper alloys, brasses, bronze, carbon steels, tool steels, stainless steels, nickel alloys, molybdenum and tungsten alloys. It provides a high strength joint on similar and dissimilar materials with joints as small as 0.04mm feasible. Working temperatures of between 600 and 650 degrees celsius with a high fluid state. Can be used with many heat sources such as propane, butane and oxy-acetylene.

By way of comparison standard brass filler material melts at around 800c - 900c.

 Can you braze with a propane or butane blow torch? - Results

This was my first attempt at brazing for 16 years, perhaps I have forgotten how to do it. Not enough flux perhaps. The result however ugly is very strong.

Can you braze with a propane or butane blow torch? - Next Repair

For my next repair job I purchased a chromoly bike frame with a crack in it.  Picture of frame are shown below.

I used the same solder as before (Silverflo 55) and I used a "patch" across the crack made from a plate from a bicycle chain. The result was a virtually indestructible joint, which I have ridden hard on for 100's of miles, over rough terrain.

One slight question mark, it that in order to get the work piece up to temperature you have to apply heat for quite a long time, and the heat spread through the work piece is considerable and this may have effects on the properties of the metal. But as I said it worked fine, and I am still alive.

Can you braze with a propane or butane blow torch? - Conclusion

For a ugly, unsatisfactory,  but functional braze yes you can use a propane or butane torch.

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