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Braze Joint Design Considerations

butt_lap_joints_xsmThere are basically two types of joint designs used in brazing:  butt-joints and lap-joints.  All other joint designs are modifications of these two.  There are a number of important considerations when designing such joints in order to insure proper service life.  This article looks at just a few of those considerations. By Dan Kay

Next Month: Next month I'll discuss the issue of braze gap clearance for some different base-metal and brazing filler metal (BFM) combinations, and how that affects joint strength and hermeticity.  In succeeding months we'll address issues such as dissimilar metal brazing and how that affects joint design.

Last Updated on Sunday, 02 February 2014 21:57

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How to Determine Braze Gap-Clearances for Your Furnace

vcts-after_xsmGood brazing depends on the ability of capillary action to draw the molten brazing filler metal (BFM) in all directions throughout the joint being brazed, either vertically or horizontally.  A unique Vertical Capillary Test Specimen (VCTS) was developed to help brazers find out the maximum gap-thicknesses that capillary action can fill in their particular brazing furnaces. By Dan Kay

Next Month: Next month I'll discuss some important design issues regarding braze gap clearances and configurations, and in succeeding months we'll address issues of dissimilar metal brazing, and joint strength and its optimization in more detail.

Last Updated on Sunday, 02 February 2014 22:18

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Are the use of dead-weights for fixturing a recommended practice?

fixture_fig_2_smmThe effective use of "metallurgical fixturing", instead of a lot of dead-weights, to effectively "load" parts with enough pressure to keep braze joints close together for effective brazing is described in detail.

The use of heavy weights on top of parts being brazed is a common practice. Its purpose is to load the top of the assembly with enough weight so as to insure that the components of the assembly will be pressed together sufficiently to keep the joints from opening up during furnace brazing. This should then insure that good capillary action of the brazing filler metal (BFM) into those joints will occur during the furnace cycle.  But in real-life brazing, such use of dead-weights can lead to extended cycle times, and fail to so what it was supposed to do.  This article explains why. By Dan Kay

Last Updated on Sunday, 02 February 2014 21:58

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Partial Pressure Brazing

mass-furnace-door-openAs mentioned in previous articles, more and more brazing shops are using vacuum furnaces.  These furnaces are quite complex, offering more options for heating, cooling, partial pressure, or multi-bar pressure (pressure capabilities above one atmosphere) for high-speed cooling.

The overall effectiveness of the equipment, however, still lies with the people who program and run the furnaces. Figure 1 (below) shows a series of vapor pressure curves for a number of common metallic elements.  Each curve shows the melting point of the element (indicated by a small circle along the curve) and, where the curve crosses the dotted line across the top of the chart, its approximate boiling point (where it wants to turn to a gas) at one standard atmosphere. By Dan Kay

Last Updated on Sunday, 02 February 2014 22:20

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Selecting Brazing Fixture Materials

select_brz_fix_mat_smWhich base-metal should I use for braze fixturing so that it will last the longest?

This question is not an uncommon one. Although I have never personally seen any kind of chart showing an "expected life" for fixture materials, it is important that people understand that there are a number of factors that will control the "life expectancy" of any fixturing material used in brazing, and all of these factors relate to the service conditions that the fixtures will encounter during the brazing process. By Dan Kay.

In August's article, I'll address the commonly used method of adding a lot of "dead weight" onto parts in an attempt to keep them flat during brazing!

Last Updated on Sunday, 02 February 2014 22:23

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VAC AERO is launching a New Monthly Vacuum Brazing Column with Dan Kay!

dankay-logo-2We are pleased to announce the launch of a New Vacuum Brazing column in the April 2009 issue of VAC AERO’s What’s HOT! NEWSLETTER

The new column, written by brazing expert Dan Kay will be published monthly and will offer helpful vacuum brazing applications, tips and techniques to commercial and captive heat treaters alike. Dan Kay is an independent brazing consultant, who has consented to write articles on brazing for VAC AERO since many of our vacuum furnaces are used for brazing. However, his willingness to provide this service to VAC AERO readers does not imply his specific endorsement of our furnaces, but rather his desire to help VAC AERO furnace users to understand brazing better. Read Dan Kay's Biography 

 

Last Updated on Sunday, 02 February 2014 22:29

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Brazing - A Great joining Process for this 21st Century!

woodwardsc2-2-2Brazing has proven to be a highly versatile joining process for permanently joining many different kinds of metals and ceramic materials together in a variety of industries as diverse as aerospace and automotive.

Brazing has a long history of use, dating back to the time of the ancient Egyptians, and truly came into its own as a high-volume production technique during the twentieth-century, not only via torch-brazing, but especially with the development of well-controlled continuous and batch-type brazing furnaces.  In the last few decades, the steady increase in vacuum furnace technology made vacuum brazing a preferred method by the end of the twentieth century for many companies doing brazing. By Dan Kay

In my next article, I'll talk about vacuum atmospheres in brazing. Yes, vacuum is still an "atmosphere" in the technical sense of the word, since the gas inside the vacuum chamber has actually not been completely removed from the chamber, and those remaining molecules of gas must not be able to interact in a negative way with the faying surfaces of the brazement.

Last Updated on Sunday, 02 February 2014 21:59

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