Ah, its easy to do, furnace braising is a US institution, a product of the nuclear and space industry where dangerous isotopes can be stellite welded into special cases for safety. It is pretty simple for an engineering company with the right gear. It's best use is for torque converter reprofiling, so the fins don't bend over in extreme duty service.
Furnaces are made for many applications, smelting, casting, repair, industrial. For a laugh, look at the Chinese systems for braizing stainless and EFI fuel lines.
http://www.xaaj.com/e_show.asp?id=45
There are a vast range of types, not all have apperture windows for cyrogenic like processing. So a shop that is best to use is one that understands the cracking and cooling issues, and has a process in place to braze using a furnace.
Here Is a company that makes them for automotive repair
http://www.charlesahones.com/roll-out-f ... urner.html
Normally, repairing cast iron ceates a problem with expansion and shrinkage. In some cases, the casting must be heated entirely to a uniform, high temperature before welding. There are procedures that place a casting inside an actual furnace. The piece heats gradually to close to red hot, and the welder makes the repair , usually through a door in the furnace. Furnace welding helps prevent weld area shrinkage that causes cracks.
Braze is
much softer than mild steel welding and is much less likely to crack on cooling. Without a furnace, it still has to be done in small lengths and then allowed to cool enough to touch before welding any more. The Everdur Silicon-bronze brazing is nice and soft, and can work outside a furnace, but there are restrictions on how much you can lay down before each cooling/quencing phase.
