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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

As shown in my last four articles, there are a number of very important steps that must be followed in order to insure good brazing, as shown here once again in Table 1. We’ve looked at some proper design criteria for brazing, and the last three articles have covered some important aspects of cleanliness in brazing. In this current article we will explore tumble-deburring as an excellent method to use to prepare surfaces prior to their being assembled for subsequent brazing, but with some strong precautions.

Tumble-deburring surfaces involves placing a number of parts in a special container and then causing those parts to literally “tumble” many times onto each other, or within a special media (for gentler tumbling) so that any burrs on the edges of each part can be removed prior to those parts being subsequently assembled for brazing. Tumble-deburring equipment usually is of two types, either a container that can be closed and then tumbled over and over on a rack such as shown in Fig. 1, or the deburring can be done in an open container (with rounded inner walls) which is then vibrated (agitated) causing the parts to move up the rounded walls of the container and then fall back into the tumbler.

As shown in my last three articles, there are a number of very important steps that must be followed in order to insure good brazing, as shown here once again in Table 1. We’ve looked at some proper design criteria for brazing, and the last two articles have covered some important aspects of cleanliness in brazing. In this current article we will explore grit blasting and tumble-deburring as common methods many companies use to prepare surfaces prior to their being assembled for subsequent brazing.

Grit blasting surfaces involves placing parts in a special chamber, as shown in Fig. 1, and then using a high-pressure stream of hard particles being blasted at the surface of the part in order to remove certain surface contaminants, such as surface oxides, that would otherwise interfere with good brazing, i.e., would prevent the molten brazing filler metal (BFM) from being able to effectively alloy with, and bond to, the base metals onto which it is being applied.

As shown in my last two articles, there are a number of very important steps that must be followed in order to insure good brazing, as shown here once again in Table 1. We’ve looked at some proper design criteria for brazing, and last month we began looking at the very important topic of cleanliness in brazing..

As we saw, parts must be clean BEFORE they are brazed, and part of that cleanness-issue, as we will examine in this month’s column, involves the handling of parts during assembly and the application of brazing filler metal (BFM) to those parts. It’s at this point that many shops fail in their understanding of what it takes to keep parts clean prior to brazing. Namely, bare hands are too often used to assemble parts, resulting in contamination of surfaces that are to be brazed. Let’s take a closer look at the role of the cleanliness of the brazer’s hands and how to prevent contamination of the parts by the brazing personnel themselves.

As shown in my article last month, there are a number of very important steps that must be followed in order to insure good brazing, as shown in Table 1 of this article. Last month we looked at Criterion#1: Proper Design for Brazing. Let’s now investigate the second item in that list, Criterion# 2: Proper Cleaning before brazing. This topic itself will be divided into two articles over the next two months, the first dealing with the cleanliness of the parts themselves coming into your braze shop and how to clean them, and the second article will deal with the cleanliness of the brazer’s hands and how to prevent contamination of the parts by the brazing personnel themselves.

Proper cleaning of parts before brazing. This is number two on our hit-parade of the most important things to consider for proper brazing. Too many brazing shops, unfortunately, overlook this important second criterion in my list, depending instead on the brazing furnace to “burn off” any lubricants or to dissociate any oxides present on the parts, thus “saving time” in their opinion, their reasoning being: “Oh, don’t worry about that. The furnace will clean the parts up….” or: “don’t worry about that, just put more flux on the parts” (if they are torch-brazing or induction brazing out in air). Both such statements are incorrect, and can result in poorly brazed assemblies that either leak in service or do not have sufficient braze-strength to handle the service conditions to which they are subjected.

Over the almost 45-years of my brazing career I have discovered that there are a number of fundamental principles that must be understood and followed if successful brazing is to occur. Over the next few months we will look at each of these principles in more detail, but I will merely introduce them to the reader here.

Brazing is a wonderful joining process, and also a forgiving process. By this I mean that even when you do not follow all the brazing principles exactly, brazing can work pretty well for you, but within limits. Gross disregard for some of these principles will, in fact, lead to failure of parts in the field (or in your brazing shop before parts are to be shipped to your customers) and are responsible for most of the problems people face with poor-quality brazed joints. By comparison, when people understand these principles, practice them well in their shops, they usually find that there are very few, if any, problems with their brazing operations and, as a result, their customers are quite satisfied with the brazed products shipped to them.