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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!.

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wide variety of larger sizes, up to and including large metal paste containers from which the BFM-paste can be steadily withdrawn either automatically or semi-automatically.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.

As 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.

What 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

Don’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

A number of companies I’ve visited who conduct vacuum brazing operations have asked for assistance in understanding how to properly use a torch-brazing (flame braze) process to repair some of the assemblies that did not fully braze during their vacuum brazing operations.

The components were such that they did not want to send the entire assembly back through the vacuum brazing furnace, but merely needed to fix a small portion of the assembly where it did not fully braze. So let’s take a brief look at torch-brazing to see what it is, and how it can be used by brazing shops today to meet some of their production-repair needs. by Dan Kay

People sometimes ask me to help them determine if it is better for them to purchase a vacuum furnace or a continuous-belt furnace for their particular brazing needs. This important decision (for any brazing company) should not be a difficult question for them to answer for themselves, and involves understanding primarily three (3) key factors about their production: what is the quantity of brazed components that they need to produce, what is the sensitivity to oxygen of any of those base metals that they are planning to braze, and thirdly, do any of those base metals contain elements that will easily and readily outgas when heated. by Dan Kay