Doug---
It has worked for many years but it's an involved process. Any cracks will propogate with heat unless stop holes are drilled. Most of the time 'T-Bones' are put in. They're acually iron keys that hold one side to the other, then the whole part is pre-heated in a furnace, THEN the torch and the brazing rod. It works great, but 99% of all brazing repairs seen are done on cold metal and that's a receipe for failure. Done right you see brass 'soak' into the iron and turn it a shiny red and you can see rivilets of molton brass running ahead of the flame and 'wetting' the iron as it goes.
When you see little brass dingle berries on a brazed piece you know they were put there plumb cold.
The problem with repairing most iron castings compensating for stress. Just for an example, take a cast iron box with no top. Five sides cast iron. If a corner is broken off and repaired while any part of the box is cold, the temperature differential will usually cause it to stress crack somewhere else, unless the whole box is nearly red hot with pre-heat. It's seldom the 'big' portion of a casting breaks. It's usually a corner or mounting ear or tab. VERY difficult to do well unless the cross section is thin enough to get plenty of heat in.
When Geneva Steel was running I watched the millwrights braze a tremendous planer mill back together. The cross section was more than a foot thick between the webs. They'd preheated two portions of it in a rolling mill pre-heat pit to 1200 F and wrapped them in insulated blankets. Air arcs were used to gouge the broken ends to a double Vee. They drilled and tapped a grid of holes in all surfaces and then set bolts in the holes as a prickly sort of re-inforcements, then started laying in the brass with monster rosebud torches and 1/4" rod and flux by the handfulls. It took days of working 24/7 with guys swapping off to cool down, but they got it back together and trammed to specs.
OH-- the planer mill had been cut in half for scrap THEN they found more work for it..
