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silver solder with butane

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Eric Cox26/02/2011 10:10:12
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When silver soldering small components (copper and steel) will butane produce enough heat or will I have to use propane.
JasonB26/02/2011 11:08:19
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Depends what you term small, it will do for very small items maybe joining a nut onto a bit of 1/8" rod but much larger and you wont get enough heat into the job quickly enough.
 
J
Bill Starling26/02/2011 14:11:42
97 forum posts
I have successfully used butane for silver soldering two boilers for the Tubal Cain oscillating engine and boiler used in the SMEE training courses. They are made from approx. 1 ¾ ins x 20 swg copper tube. It was my first attempt at silver soldering. I used a Sievert 2941 nozzle and didn’t have any particular difficulty.
Bill.
mgj26/02/2011 18:14:57
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Butane and propane contain much the same enrgy. The problem with butane is its latent heat, and if one allows a large offtake one drops the caaister temperature, and one will get a very rapid pressure drop. So if you can keep that canister warm, roughly speaking, you wil get much the same energy out of butane as propane.
 
So thats why propane makes a better gas for applications which require relatively rapid evaporation within the supply canister.

(In fact butane may actually contain more energy than propane- I think it does so but wouldn't swear to it)
 
As for the answer - heat is heat. However the practicalities mean that propane is better, but one should be able to do perfectly well with butane on medium sized objects in summer or in a warm workshop. And to reduce the problems of evaporation, probably best to have a moderately well insulated hearth.
 
I ran out a butane canister through my normal propane regulator - rather than waste it. I ran it at 2 rather than 4 bar, and used the standard nozzle - whichever Calor one (for it was a Calor torch). Worked fine.
 
 

Edited By mgj on 26/02/2011 18:16:35

Tony Martyr26/02/2011 18:41:57
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My chemistry books pre-date metrication so in those ghastly old Btu:
Butane C4H10 = 3225 Btu/ft3
Propane C3H8 = 2572 Btu/ft3
a bit counter intuitive unless you take mhj's points into account
 
Nicholas Farr26/02/2011 21:33:55
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Hi, I believe I have mentioned this before in another thread, but broadly speaking both butane and propane in the compressed state turn to liquid insde the cylinder. Above the liquid level it is a gas volume at approx 7.5 bar, when the gas is drawn off the liquid begins to boil (like the water in your kettle) and while it is boiling the pressure will remain close to the same pressure. The boiling is dependent on thremal energy passing through the cylinder wall (similar to the thermal energy passing through the element in your electric kettle or the flame from your gas stove)
 
The big differance is the boiling points of butane and propane, while propane has a boiling point of -42.1 C, butane has a boiling point of 0.5 C. Therefore with a low abient temperature in the vacinaty of a butane cylinder, the less thermal energy differance there is. It would be like trying to boil a 240V electric kettle on 110V or having a gas stove on simmering level. With propane's very low boiling point, the thermal energy differance at the same abient temperature will be much higher and the same problems don't occur at the same gas rate withdrawal.
 
Like mgj says keeping the butane in a warmer ambient temperature will keep your butane gas flowing. All you have to remember is no energy in, no energy out.
 
I think if you have a flame of the same size with butane as you would with propane, I don't think you should have to much problem, providing you keep your cylinder out of the cold.
 
Regards Nick.
Chris Trice27/02/2011 01:11:29
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The hottest part of the flame is just in front of the blue inner cone. It's well above the soldering temperature of silver solder. It depends entirely on the mass of metal you're trying to heat. You can silver solder small items using one of these small self igniting butane torches sold to crispen the surface of creme brulee however you'll need a bigger torch to solder larger chunks. As long as the torch adds heat at a higher rate than the heat is lost from the subject or conducted away, it must reach soldering temperature. For many years I used a simple Taymar blowtorch available from any DIY store. For the bigger jobs, I've supplemented the heat input by standing the subject on a cooker gas ring.

Edited By Chris Trice on 27/02/2011 01:12:55

Edited By Chris Trice on 27/02/2011 01:13:22

IanT27/02/2011 14:24:00
1896 forum posts
184 photos
For small items/fabrications - you can add some heat quite simply if you have a gas hob.
 
I have a steel plate about 150mm x 100 mm by 5-6mm thick that I place on the gas hob and use to 'pre-heat' any small items I intend to solder. This heats everything up very nicely - although I don't let the plate get "red" hot (or anywhere near it).
 
For soft soldering that's all that is needed but it also helps get the general temperature up for silver soldering too. I've used both small butane and propane gas burners using this method and it definitely helps and it also keeps the cost of replacing gas cylinders down.
 
Regards,
 
Ian T
Terryd27/02/2011 22:01:45
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Hi Eric,
 
The most important piece of simple equipment for silver soldering (or brazing) is some kind of hearth on which to work. For small items this can be as simple as a few lightweight white refractory bricks, - (not hard fire bricks or the cement building blocks which some recommend for this purpose but are not very efficient as they do not create the reverberatory effect very efficiently) - which can be assembled in an 'armchair' configuration to surround and support your work. This is not simply to support the work and protect vulnerable surfaces, it has a more important function.
 
The refractory bricks will prevent heat loss by causing the flame to flow around the work and, they will get red hot and reflect heat back into the work to be soldered. It is a similar principle (but not exactly the same) as the reverberatory furnace which reflects and circulates hot gases to make efficient use of the heat.
 
If you simply direct a flame at the object to be soldered without such an arrangement, no matter what gas you use, most of your heat will be lost. By using the hearth you will not need other heat sources or preheats as long as you have a suitable size torch. I had several of those from a tiny pencil torch, a 'kitchen' torch, a plumbers one, up to a large Sieverts outfit for bigger work most using butane,.
 
Small pieces of the broken refractory can also be used to support and pack around the work to make it even more efficient and these lightweight bricks can be cut easily with a cheap hardpoint saw..
 
Best regards
 
Terry
Terryd28/02/2011 00:53:37
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Hi Eric,
 
Sorry to be a pain and butt in again, however after some research this would appear to be an excellent material to build a reasonable hearth. It is vermiculite board, non toxic, reflective, insulating, easily cut and quite a reasonable price for 2 boards, the Pack C size would make a good hearth for most purposes and could be backed by normal fire bricks, I think that I will certainly get a pack as the price includes VAT and delivery to start basic heat treatment equipment in my new workshop.
 
Some sources for other materials including casting your own are here For example you can add cheap, lightweight perlite (not to be mistake with pearlite) from Wilkinsons garden products shelves, to fire cement from builders to mix your own, refractories Here is some information about the product and it;s properties and how it can be used.
 
Best regards and don't be put off trying. Remember, some of the most beautiful sculptures ever made, the Benin Bronzes, were being produced in primitive pit fires using investment casting with wax patterns in clay moulds over in 13th Century Africa. They didn't have complex equipment I'm sure you can do just as well with your soldering.  "those that don't make mistakes, don't make anything" so don't be afraid to try and experiment.

Terry

Edited By Terryd on 28/02/2011 01:09:31

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