silver soldering boilers

I am working on a 3" boiler from the plans in this forum. would a MAP torch be man enough to silver solder the complete boiler :- top and bottom flanges, plus the bushings. I do have some fire brick to contain the heat.
I appreciate any advice.
Charlie

thereis no real answer at this time.What is overall size and wall thickness etc.A mapp torch is
all i have so its a question of try it and see.Any additional heat would be beneficial.I bought a
2 pack tourch in addition,with mapp and oxy but have not tried it yet Regards barry

I think you will struggle to get enough heat with a MAPP torch for a 3 inch boiler. I have used a MAPP torch for silver soldering smaller items with a firebricks set up and stuggled at times to get enough heat to flow the solder. You probably can do it but it will take a lot of time and a good setup to stop the heat loss

I agree with TonyM and guess that you will have a struggle to keep up sufficient heat. Probably you will get all sorts of nasty builds up of solder and if you do your arithmetic properly, it will cost you a fortune in 'silver' which could be better spent in more powerful heating.

You CAN still use paraffin/kerosene big blow lamps to supplement the additional heat together with screening with firebricks but you will probably 'out of your depth' of present experience at this time. I've brazed which requires a lot more heat with carbon rods arc heated from a cheap and nasty arc welder. So it CAN be done.

Good luck

Norm

The main boiler tube will try to suck up any heat applied to what you are trying to solder onto it.

I have made boilers to that size, but I used at that time, two MAP type torches, one to play onto the main tube so that it doesn't suck too much heat away and one to get up to temperature around the bits you are trying to solder onto it. It helps having three hands unless you use pallions and a good flux (Tenacity 4A or 5) spread around the joint you are trying to make

I still use the MAP type torches, but only for small stuff, nowadays I have a couple of larger torches running off tanked gas to do large jobs.

John

Charlie,
I often use an old electric hotplate to add heat to a larger silver brazing job. It works well enough to braze with propane.
Jeff

Mapp gas in 16 oz. cylinders and small torch will not work on a 3" copper boiler. I use a Victor torch set that has two tips. The smaller tip is similar to a propane or Mapp gas flame. The large tip will give you the heat needed to hard solder your boiler.
I use the Victor torch with propane gas , the hose connects to a barbecue size tank that Lowes and similar stores carry.
I bought the torch set online, do not recall from whom.
Another tip, fire brick absorbs heat, insulating refractory brick directs heat back towards the work. This is a soft brick that cracks easily. I had to buy my bricks online because none was available locally.
The broken bricks can be cemented back together with a special cement. The cement can be used to form an oven, I think I have a 2 gallon pail in the shop.

mike

I knew there were refractory bricks of different densities and the denser the brick the more heat retention but I did not know fire bricks were not refractory bricks. You learns something every day.

Steam4,
I built a small Kozo A3 switcher with a 3" copper boiler using MAPP gas that you can find in plumbing supply of your local hardware store. It requires wrapping an insulating blanket around the copper to keep it from radiating away all the heat you try to apply. The heat shield I used was also found in the plumbing supply area. It worked better than I expected it to so I bought a couple. if you don't find them in your hardware store try googling "torch shield". Mine came with brass grommets for hanging between plumbing pipes and house framing and sheet rock, but I cut them off for boiler work.

Also, the reason for using MAPP is not that it is hotter than propane, rather that it has more heat which you need for large pieces of copper. On the other hand Oxy-Acetylene is much hotter, so much so that you risk boiling the zinc and tin out of the solder which alters the composition and can ruin it, and IIUC that high temp can also spoil the flux, so for folks like me MAPP is the better choice.

if you are still reading..., I only use Harris Safety-Silv cadmium-free silver solder, 56% (1200-F MP) is super liquid and will capillary into close fitting parts but will not fill a gap, for that you will need 45% (1300-F MR) which is more "slushy" around its melting range, which unless you machine your boiler parts to a perfect fit (approx 0.005 gap) is probably what you will need to have on hand. You can probably guess why I know this !

Peter L.