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Essential Criteria for Brazing: Item 1 — Proper Cleaning (Part A)

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.

Last Updated on Thursday, 01 September 2016 21:52

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Essential Criteria for Brazing: Item 1 - Proper Design for Brazing

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.

Last Updated on Saturday, 01 August 2015 21:42

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Electroless Nickel Plating as a Brazing Filler Metal

A number of questions have come up in recent months about the use of electroless nickel plating as a brazing filler metal (BFM). To begin with, yes, electroless nickel (EN) plating can be an effective BFM, when properly applied. The eutectic nickel-phosphorus alloy composition (89Ni-11P) is already available commercially as a separately purchased BFM in powder or paste form from different manufacturers, and is listed in the American Welding Society (AWS) Specification A5.8 with a “BNi-6” designation.

Please note that the process of “electroless” nickel plating is quite different from “electrolytic” nickel plating, and their end-products are also very different. Electroless nickel will deposit a nickel-alloy (either nickel-phosphorus, or in some rare cases, nickel-boron) onto a surface by chemical means (no electricity being used), which (because it is an alloy) can start to melt at temps as low as 1616°F (880°C), whereas electrolytic nickel plating uses electricity in a chemical bath to deposit a layer of pure nickel onto a substrate, which will not start to melt until 2651°F (1455°C). It is VERY important that end-users of nickel-plating thoroughly understand this difference, or brazing problems can (and have) resulted!.

Last Updated on Wednesday, 06 July 2016 20:46

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Brazing-Paste – Part 3: What happens when the BFM-paste “separates”?

Brazing-Paste – Part 3: What happens when the BFM-paste “separates”?

This is the third in a series of articles dealing with brazing filler metal (BFM) in paste form, i.e., when the BFM powder is mixed with a suitable gel-binder to form an extrudable paste. As we’ve seen in the previous two articles, such BFM-paste can be supplied in small hand-held cartridges, or in a wide variety of larger sizes, up to and including large metal paste containers from which the BFM-paste can be steadily withdrawn either automatically or semi-automatically.

An example of a semi-automatic system is shown in Fig. 1, in which paste is contained in a large container, attached to the bottom of which is a dispensing gun and hose. The small black hose in the top of the unit is an air-pressure line that supplies pressurized air to push a close-fitting piston that sits inside the container on top of the BFM paste, in much the same manner as the plastic piston in a caulk-cartridge helps to move the caulking paste through the tip of the caulking gun when pressure is applied to that piston. The blue unit in that photo is used to manually adjust the pressure going into the container as well as into the positive-displacement dispenser’s (PDD) dispensing tip.

Last Updated on Sunday, 25 September 2016 01:53

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Dispensing Brazing Paste – Part 2

Figure 1 200x200As mentioned in last month’s article, there are many suppliers of brazing paste out there, many of whom will put their brazing-paste into small tubular cartridges from which the paste can be easily and quickly dispensed onto components that are to be brazed. As shown in Figure 1, proper dispensing of paste from a cartridge begins with an electronically-controlled source of pressurized air (which can be adjusted over a wide range), and may also contain optional timing mechanisms. All of this can be contained in a simple table-top unit, such as the one shown, but which also comes in different shapes and sizes, and with other options.

The air hose coming from the dispensing unit should have a connector that is able to attach to, and lock onto, the back end of the paste-cartridge in a leak-tight fashion, thus allowing the high-pressure air to push the piston in the paste-cartridge forward. The dispensing unit may also have digital or analog meters on their face to show what the air pressure is in the hose, and it may also contain controls to allow the operator to vary dispensing time (which could vary from a small fraction of a second all the way to continuous-flow) if it is desirable to automate, or semi-automate the paste dispensing process.

Last Updated on Wednesday, 21 September 2016 01:31

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Brazing Paste-Cartridge Tips

Figure 1 smWhat kind of dispensing-tip should be used for brazing-paste cartridges?.

There are many suppliers of brazing paste out there, and many of them will put that paste into small tubular cartridges for you, from which that paste can be easily and quickly dispensed onto components that are about to be brazed. BUT, the choice of the actual type of cartridge-tip that you will use to extrude that brazing-paste from the cartridge is YOUR decision, NOT the decision of the paste-supplier, your customer, or some industry “tradition” you may be heard about, or perhaps observed being used at some brazing shop. by Dan Kay

Last Updated on Friday, 11 March 2016 14:12

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Stress Concentration

Fig1 wsDon’t Blame the Braze because Joint was Poorly Designed, and NO, larger fillets won’t compensate for that!.

Have you ever heard someone tell you something like this: “Well, brazing may be okay, but if you really want a strong joint, you should weld it!” Such comments are often made when someone sees what appears to be a cracked brazed-joint, such as that shown in Figure 1, and they then assume that (1) the crack they are looking at probably extends all the way through the brazed-joint, and that (2) if the joint had been welded it would not have cracked. by Dan Kay

Last Updated on Friday, 11 March 2016 14:12

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