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One More Frequently Misused Brazing Term: “Brittle”

In my last two articles, we explored the definitions of the words “brazing”, “passivation” and “defect”. Each of these words has also been mentioned and discussed in this column in years past, but I am bringing them out again to help a new generation of brazing personnel to understand them correctly. Another word that needs to be explored once again, because of its misuse by many brazing personnel today, is the word “brittle”.

Brittle: Particularly when referring to parts that have been brazed with a nickel-based brazing filler metal (BFM), I still hear some people say that those nickel-brazed joints are “brittle” joints, and thus are probably not suitable for certain applications. Be careful! This is not true! Early in my metallurgical training (I am a graduate Metallurgical Engineer from Rensselaer Polytechnic Institute) I learned that “brittle” is not a word describing “a state of being”, but instead, is used to describe a mode of failure, as in the words: “…that joint failed in a brittle manner”.

Last Updated on Friday, 06 April 2018 20:38

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Two Frequently Misused Brazing Terms: Passivation, and Defect

In last month’s column we explored the definition of the word “brazing”, so that the meaning of that important term could be more fully understood and differentiated from the terms “soldering” and “welding”. In this month’s column, I would like to take a look at some additional words that are often misused in the world of brazing, namely, the words passivation and defect. These words have been mentioned and discussed in this column in years past, but it’s time to bring them out again for a new generation of brazing personnel. I still hear people use these metallurgical terms improperly when they are describing certain criteria related to braze-prep or braze-inspection; so let’s look at them again to understand them more correctly.

Passivation vs. Pickling: In a number of brazing shops I visit there still seems to be some confusion regarding the correct use of the term “passivation” (when “pickling” is actually meant) when it comes to preparing metal surfaces for brazing. The two terms, “passivation” and “pickling”, illustrated in Fig. 1, have completely opposite meanings, and thus, these two terms need to be clarified so that brazing personnel can use these two metallurgical terms correctly.

Last Updated on Friday, 06 April 2018 20:40

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“Brazing” Definition – Clarification of the Terminology

  As we start out this new year, I think it would be good to review the definition of the word “brazing”, since it is somewhat complex, and some aspects of the definition are still being misused by a number of people in the brazing industry, not only in their speech but also in their writing. So, it’s time to take a fresh look at the word, especially for those who are somewhat new to brazing, and perhaps for some older persons who never really understood what that definition meant in the first place!

The American Welding Society (AWS), in the Fifth Edition (2007) of their AWS Brazing Handbook, defines brazing as “a group of joining processes that produces coalescence of materials by heating them to the brazing temperature in the presence of a filler metal having a liquidus above 840F (450C) and below the solidus of the base metal. The filler metal is distributed between the closely fitted faying surfaces of the joint by capillary action.” The handbook goes on to state in its Preface that brazing needs to meet the following three criteria: “(1) The parts must be joined without melting the base metals. (2) The filler metal must have a liquidus temperature above 840F (450C). (3) The filler metal must wet the base metal surfaces and be drawn into or held in the joint by capillary action.”

Last Updated on Friday, 06 April 2018 20:28

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Essential Criteria for Brazing: Item 7 – Knowledgeable Inspection of Finished Brazed Assemblies.

Essential Criteria for Brazing: Item 7 – Knowledgeable Inspection of Finished Brazed Assemblies.Sherlock Holmes was a famous detective in some British spy stories written in the late 1800’s by British author Sir Arthur Conan Doyle. Sherlock was a great detective primarily because he was an expert observer. When he inspected a crime scene he saw things that others often overlooked. From these keen observations, and from his extensive experience, he was able to solve problems others seemingly could not.

In this month’s article, we wrap up our discussion of the seven (7) essential criteria for good brazing (see Table 1), by looking at what constitutes “knowledgeable inspection” of finished brazed assemblies. I often encourage people to “become a Sherlock Holmes” in their work when trying to solve brazing problems, and during final-inspection of brazed assemblies. Our goal should be to produce parts that have “zero-defects” (see Fig. 2), and to do this, each “inspector” needs to understand what a defect actually is, how to accurately find it, and what to do with the brazed assembly when an actual defect is found.

Essential Criteria for Brazing: Item 5 – Fixturing: Use of Thermocouples in Furnace Brazing (Part 2)

Essential Criteria for Brazing: Item 5 – Fixturing: Use of Thermocouples in Furnace Brazing (Part 2)In this month's article, we will look further at the placement of TC's in furnace brazing loads, and how, together with correct furnace heating/cooling rates, they can help to maximize uniformity of temperature throughout each brazing load and minimize any distortion of the components being brazed.

To have good control of any furnace-brazing process-run, you will need to know the temperature of the parts being brazed inside the furnace, and in batch-type furnaces this can only be done via well-placed thermocouples (TC's) throughout the furnace and in the load of parts being brazed.

 

Essential Criteria for Brazing: Item 5 – Fixturing: Use of Thermocouples in Furnace Brazing (Part 1)

In this month’s article, we continue to look at methods you can use to keep fixturing-weight down to a minimum, especially in furnace brazing, remembering once again that fixtures (baskets, frames, grates, dead weights, etc.) represent a large mass of metal (the material most often used in fixturing) that absorbs a lot of heat and can thus significantly increase the brazing time needed to complete a braze. Make it your job to significantly reduce the amount of fixturing-weight put into your brazing furnace.

In last month’s article, I mentioned that someone increased the productivity of their brazing operations by over 75% when they implemented the fixturing recommendations  I made to them during the brazing-seminar they attended (the same recommendations I’m making in this article).

 

Essential Criteria for Brazing: Item 5 – Fixturing: Keeping weight to a minimum (Part B)

In this month’s article, we continue to look at methods you can use to keep fixturing-weight down to a minimum, especially in furnace brazing, remembering once again that fixtures (baskets, frames, grates, dead weights, etc.) represent a large mass of metal (the material most often used in fixturing) that absorbs a lot of heat and can thus significantly increase the brazing time needed to complete a braze. Make it your job to significantly reduce the amount of fixturing-weight put into your brazing furnace.

In last month’s article, I mentioned that someone increased the productivity of their brazing operations by over 75% when they implemented the fixturing recommendations  I made to them during the brazing-seminar they attended (the same recommendations I’m making in this article).

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