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We return this month to our series on the essential criteria for brazing, to complete our current series on some fundamental issues about brazing filler metals (BFMs). As was discussed in my previous article on Essential Criteria for Brazing, if you are using BFM powder in your operations, it’s essential to not only control the mesh size of the BFM powder you are using (covered last time), but also to know and specify the ratio of BFM powder to the gel-binder in the brazing paste.   The gel-binder is cellulose-type gel-like substance added to the powder to form a creamy blend of powder and gel that can be extruded from a cartridge through a dispensing tip.  So, whether you are using BFM powder directly, or are using a pre-formed shim/ring of BFM, or BFM in paste form, you must always ask yourself this simple question: “how many times can I fill the braze joint with the BFM that I am using?” Hmmm….   The obvious answer is “one time” only! No matter how good you are, you cannot cram any more BFM into the joint after that joint has been filled by the molten filler metal ONE time! by Dan Kay

This quiz was not as easy as many of you may have thought. I chose a number of questions that I knew would “challenge” many of you to more clearly think about some of the principles of brazing, and how it works, especially as it might compare to welding. Over my 45-years of teaching brazing and working with it extensively – hands-on — in the field, I’ve seen a lot of “misconceptions” out there about brazing and how it should be correctly applied. I hope this quiz has challenged some of your own thinking on the topic, and opened your eyes and thinking to some new things about brazing you did not know before. Let us each continue to work hard to apply brazing correctly in our (and our customer’s) work, so that brazing will be more correctly applied and understood.

IMPORTANT NOTE: The Brazing Quiz published in our April column is STILL open for readers to try. Because only a few people actually sent in their replies, we encourage more of you to do so. We’ll then publish the answers in the June column (next month).

We return this month to our series on the essential criteria for brazing, and will look more closely at another aspect of brazing filler metals (BFMs). If you are using BFM powder in your operations, then it will be very important for you to understand and to control the mesh size of the BFM powder you are using, since powder mesh size can affect brazing performance.

A common way to create BFM powder is by melting the raw ingredients for the BFM in a large melting pot using induction heating, and then pouring the resulting liquid metal through a specialized atomization nozzle in which a very high-pressure gas will literally blast the molten metal stream into billions of tiny particles (inside an atomization chamber). The tiny particles will fall by gravity to the bottom of the chamber, solidifying along the way into solid powder particles.

For this month’s column we would like to challenge our readers to have some fun with a brazing quiz. If you would like to try our Brazing Quiz, please e-mail your responses to This email address is being protected from spambots. You need JavaScript enabled to view it., listing the numbers 1 through 20 and your correct “letter” response next to each number. The correct answers (with explanation) will be printed in next month’s (May) article.

We look now at the fourth of the seven important criteria that should be followed in order to insure good brazing, namely, the proper choice of a brazing filler metal (BFM) to use for your application.  You’ll find that you have a number of possible options from which to choose, but always bear in mind that the end-use application should always be the deciding factor when trying to decide on which BFM will be best for your current needs.

There are many different brazing filler metal (BFM) families, and so, for easier identification, an orderly arrangement, such as that shown in the American Welding Society’s A5.8 Specification for BFMs in Fig. 1 helps to categorize these many alloys into groups that are more meaningful.

In recent months we have been examining the essential criteria for good brazing, many of which are, unfortunately, overlooked by designers and brazing personnel, thus causing problems in production. We are currently looking at critical issues related to proper joint fit-up, and one of these issues concerns the finish (roughness) of the faying surfaces inside a braze-joint. Surface roughness can range from highly-polished to very rough, and can, in fact, have a significant effect on the ability of molten brazing filler metal (BFM) to flow into and through a braze-joint. As shown in Fig. 1, some brazing personnel have resorted to a variety of ways to roughen surfaces for brazing so that, in their opinion, the molten brazing filler metal (BFM) can “flow better”. This can be quite misleading, since good brazing depends primarily on proper joint design, proper cleanliness of the parts, and joint-gaps that are quite thin, three criteria that have been discussed in my prior articles in this series.

In honor of the one hundred anniversary of its discovery, thermal spraying looks back to its roots – early experiments in which liquids were broken up into fine particles by a stream of high-pressure gas. Efforts more directed at producing powders rather than constructing coatings. It fell to one Dr. Max Ulrick Schoop of Zurich who recognized the possibility that a stream of molten particles impinging upon themselves could create a coating.

Schoop ‘swork, and that of his collaborators, resulted in the establishment of the thermal spray process. This process has fostered a worldwide industry serving over thirty technology sectors and generating sales of over two billion dollars per year. This article traces the history and development of the principal flame and electrical thermal spray processes. and that of his collaborators, resulted in the establishment of the thermal spray process. This process has fostered a worldwide industry serving over thirty technology sectors and generating sales of over two billion dollars per year. This article traces the history and development of the principal flame and electrical thermal spray processes