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Why does Brazing require temperatures above 450C (840F)?

Brazing, when performed correctly, is a joining process that produces a permanent bond between two or more materials by heating them to a temperature above 450C (840F), but lower than the melting-temperature of any of the materials being joined, and a permanent, metallurgical bond between these materials is produced when capillary action draws a molten brazing filler metal (BFM) through the clean, closely fitted faying surfaces of the joint. The filler metal is not supposed to become fully liquid (i.e., have a "liquidus") until the brazing temperature reaches at least 450C (840F). If the liquidus of the filler metal is below 450C (840F) then that filler metal would commonly be called a "soldering alloy".

Last Updated on Sunday, 02 February 2014 22:33

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Can I Use Standard Aerospace Vacuum Furnaces to Braze Aluminum?

horiz-hot-zones_smAs aluminum brazing continues to grow, some folks are asking: "Can I use available furnace time in my aerospace vacuum furnace to perhaps do some aluminum brazing?" There are a number of reasons why that is a VERY bad idea, but I will briefly review just two of the more obvious ones below.

Temperature control - Shown below is a photograph of a typical hi-temp aerospace vacuum furnace metal hot zone. Notice that there are six (6) heating elements connected around the OD of the hot-zone, as well as heating elements on the back wall of the furnace. By Dan Kay

Last Updated on Sunday, 02 February 2014 22:06

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Using a "Stop-Off" in Brazing

zyp_braze_stop_25_wsAs the name of this product-type indicates, a brazing "stop-off" is supposed to be something that "stops" molten brazing filler metal (BFM) from flowing into areas where it is not supposed to be, thus keeping it "off" surfaces that are supposed to remain clean and free from the presence of any BFM.

First of all, brazing filler metals (BFMs) do not like to bond to (or flow over) dirts, greases, or oxides.  The presence of any of these contaminants on the surface of parts to be brazed can literally prevent the BFM from flowing over surfaces on which any of these contaminants are located. By Dan Kay

Next month:  As aluminum-brazing continues to grow, some folks are asking: "Can I use available furnace time in my aerospace vacuum furnace to perhaps do some aluminum brazing?"  Let's look at why that is a VERY bad idea!

Last Updated on Sunday, 02 February 2014 22:30

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Making Your Own Brazing Paste

paint-shakerwsThis is Part 2 of the article Shelf-Life and Expiration-Dates for Brazing Paste

Brazing paste is not difficult to make yourself. All you need is some brazing filler metal powder, a gel-binder, and a paint-shaker. Sound easy enough? Let’s see...

First, procure the desired brazing filler metal (BFM) in powder form from one of the BFM manufacturers.· I show a listing of such manufacturers on my website at http://www.kaybrazing.com/sources.htm, and each company’s name is a “hotlink” to that company’s webpage. By Dan Kay

Next Month: In next month's article, we'll consider brazing stop-offs, and how they are correctly and incorrectly used in many brazing shops today!

Last Updated on Sunday, 02 February 2014 22:20

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Shelf-Life and Expiration-Dates for Brazing Paste

brazing-paste_wsPeople in the industry have asked me if I know of an industry standard dealing with the topic of brazing-paste shelf-life, or whether or not there is a particular rule of thumb that I could suggest to them about handling the issue of brazing-paste shelf-life and expiration-dates.  Their primary concern in asking such a question centers around the usability of brazing paste that may be older than the recommended shelf-life given by the paste manufacturer.  In vacuum brazing this question may carry additional implications of potential furnace contamination by the gel-binders used in the so-called "expired" paste.

Answer: There is no "industry standard" that I am aware of to which someone could go for any guidelines about shelf-life or expiration-dates of brazing-pastes. Each manufacturer uses different criteria for setting their own shelf-life or expiration dates for their brazing filler metal (BFM) pastes, with a number of manufacturers having stopped showing an expiration date on their paste containers altogether, but instead, merely show a "date-of-manufacture". It used to be common to find an expected shelf-life printed on the containers, but because of rejections of good BFM paste, merely because of a printed date on the container, some manufacturers have stopped doing that. By Dan Kay

Next Month: In next month's article, we'll consider brazing stop-offs, and how they are correctly and incorrectly used in many brazing shops today!

Last Updated on Sunday, 02 February 2014 22:23

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Brazing Base Metals Containing Small Amounts of Titanium, Aluminum

tspec13_wsWhen nickel brazing Inconel 718 base metals in a vacuum furnace some of the difficulties experienced with the brazing include base metals that come out of the furnace dark and discolored, and the brazing filler metal doesn't wet the surfaces well. In this article we will explain why this is happening, and what can be done about it?

This is not an uncommon problem with a variety of base metals containing small amounts of titanium and/or aluminum. Both titanium and aluminum will easily oxidize, and once those oxides are formed they cannot be easily removed in a standard vacuum-furnace atmosphere. Yes, vacuum is an "atmosphere" in normal production environments since the level of vacuum in the furnace during typical brazing is such that there is, relatively speaking, a goodly number of air molecules still in the furnace, including moisture in that air. Of course, moisture represents the presence of oxygen, which can indeed react with either titanium or aluminum to form very tenacious titanium oxides and aluminum oxides on the surface of the base metal, which will inhibit or prevent brazing filler metal (BFM) flow. By Dan Kay

Last Updated on Sunday, 02 February 2014 22:00

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Vertical Test Specimen for Furnace Brazing

may14-wsFurnace brazing is a common brazing process around the world, and I have witnessed many brazing furnaces in action in many countries – from here to mainland China. Furnaces are convenient for brazing since the parts to be brazed can be easily loaded into a batch furnace or onto the belt of a continuous-belt furnace. The operator depends on the various furnace parameters (temperature, time, ramp rates, atmosphere controls, etc.) to ensure that the job of brazing each component will be done reliably, correctly and identically for each part that is subjected to those brazing cycles in that furnace.

An interesting question I have often encountered over the years with furnace brazers is this: "How do I know if a particular gap-clearance will work in my brazing furnace?" Please understand that each brazing furnace is unique and behaves in its own unique way. By this, I mean that even two furnaces of the same model number are not actually identical. Each one has its own personality, and the furnace operator needs to try to understand and work with each "personality." By Dan Kay

Last Updated on Sunday, 02 February 2014 22:31

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