Back in 1991, I remember that the C3-Committee of the American Welding Society (AWS) rightly decided to incorporate an entirely new chapter on “Braze Welding” into the 4th edition of their AWS Brazing Handbook so that people might come to understand better what this process was really all about. That same chapter was then carried over (and slightly updated) into the 5th edition of the AWS Brazing Handbook in 2007 in chapter 19 (pp. 359-368).
Although those chapters describe what the process is, what various types of equipment are used (torches, spot-welders, etc.), what kind of filler metals might be appropriate, etc., they weren’t written with the intent of showing someone how, with the same identical torch, they might use it for braze welding. By adjusting the torch settings and hand positions, the torch can be used for effective torch brazing of a different kind of assembly. By then modifying the torch settings and hand-positioning techniques once again, a proper torch-welding process can be conducted, all with the same torch.
The reader of those chapters on braze welding is left to their own imagination and experimentation to figure it all out. Yes, the same torch can be used for each process (brazing, braze welding and welding), but the torch-handling techniques involved – and the training – are VERY different.
Problem: Nowhere in any of the literature I’ve studied on the subject of braze welding (and I’ve read a lot) is there any thorough description of precisely how to physically hold and manipulate a torch relative to the filler-metal rod when trying to braze weld a large tube-in-fitting joint. Nor is there any explanation of why braze welding might be preferred over torch brazing for that same joint depending on the end-use situation into which the joined assembly is to operate. The differences between the two processes are huge, and they must be understood by any brazer who thinks that they are able to do both brazing and braze welding or when trying to decide whether one process would be preferred to the other.
Torch-handling example: Over the last several decades I’ve watched many self-proclaimed torch “experts” show me their alleged torch-brazing skills to join some large tubular assemblies, when, in reality, they were actually demonstrating their braze-welding skills to me instead without even realizing it.
The “brazer” heated up a 2-inch-diameter copper (or bronze or brass) tubular fitting using a single-holed torch tip with an intense flame (sometimes not properly adjusted to a non-oxidizing flame). The flame was moved around the top of the joint to preheat it (i.e., while keeping the flame right against the top of the joint) so that the inner cone of the torch flame was often touching the base metals. (He told me that this helped him to heat up the joint faster.) Then, while heating the joint area in that manner, he fed the BFM rod through the flame, allowing the flame to melt the BFM, which was then deposited at the top of the joint where the large-diameter tube went into the fitting.
He then slowly worked his way around the top of the joint feeding more and more BFM around the top of the joint, as needed, until a nice fillet was neatly deposited around the entire top of the joint. He told me that his customer wanted him to build up a fairly good-sized fillet around the joint. I complimented him on his good braze-welding technique. Yes, he did indeed know how to braze-weld, but he obviously did not know how to properly braze.
Important side note: Does the “splash heat” of the torch flame during the braze-welding process actually cause some of the molten BFM to flow down a little into the fitting of the joint so that, unlike pure welding, the BFM is not strictly a fillet sitting only on the top of the joint? Yes, some of the molten BFM may actually be pulled into the joint by capillary action, but such action is minor and is not the intent of braze welding.