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Thermocouples in Furnace Brazing - Part 2

buried-tc_nlIn this month's article we will look at correct 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. By Dan Kay

Next Month: Next month let's look at a question that often comes up in furnace brazing, namely, the role of braze-fillets at the edge of brazed joints, and what purpose they actually serve.

Last Updated on Sunday, 02 February 2014 22:27

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Brazing Question Challenge - Differential Metal Expansion Part 1

Did you figure out the answer to Dan's "Brazing Challenge Question" in his article on Differential Metal Expansion - Part 1 ?  The answer is published this month on our website at:  "Brazing Question Challenge - Differential Metal Expansion - Part 1 "

Last Updated on Sunday, 02 February 2014 22:03

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Thermocouples in Furnace Brazing - Part 1

tc-circuit_mdProper temperature control within each furnace brazing cycle is essential.  It will not only insure proper brazing filler metal (BFM) flow, but can also prevent part distortion.  To accomplish this, multiple thermocouples (or "TC's" as they are often called) need to be placed in strategic positions within each furnace load. By Dan Kay

In this first of two articles on TC's and their use in brazing, I'd like to briefly look at what TC's are, and the types commonly available for use in brazing furnaces today (much more exhaustive discussions about TC's can be found on the websites of a number of thermocouple manufacturers and suppliers). In next month's article, I'll describe the actual use and placement of these TC's in different brazing furnace cycles.

Next Month we will look at correct 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 components that are being brazed together.

 

Last Updated on Sunday, 02 February 2014 22:26

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Read more: Thermocouples in Furnace Brazing - Part 1

Differential Metal Expansion - Part 2

idealized_thermal_smIn this month's article on differential expansion of metals, I will explore the effect that thermal expansion has on joint clearance, and thus, on brazed joint strength and quality of 1018 carbon-steel.  For anyone doing high-temperature brazing of carbon-steel components using a high-temperature brazing filler metal (BFM) such as pure copper, it's an important concept, and needs to be understood. By Dan Kay

Next Month: In my next article, we'll take a closer look at thermocouples -- which kind you should use, and how it should be connected to the parts in your furnace load, where they should be placed in the furnace, etc.

Last Updated on Sunday, 02 February 2014 22:10

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Read more: Differential Metal Expansion - Part 2

Differential Metal Expansion - Part 1

thermalexp_fig2_mdIn this article I will explore the effect that thermal expansion has on joint clearance, and thus, on brazed joint strength and quality. It's an important concept, and although it is well known in the brazing world, many folks today still do not take this topic seriously enough when designing brazed assemblies. This article is based on one I wrote many years ago for an in-house brazing publication at a brazing filler metal supplier, and will be written in two parts. Next month's segment will look more closely at polymorphic metals, such as carbon steels, and will attempt to explain why they exhibit their very strange thermal expansion curves. By Dan Kay

Next Month: In my next article, I'll examine the thermal expansion curve for 1018 carbon steel to see why there are strange "reversals" in the thermal expansion curve for that alloy (and for similar metals).

Last Updated on Sunday, 02 February 2014 22:10

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Read more: Differential Metal Expansion - Part 1

Voids in Brazed Joints

tube braze2-smBrazers commonly encounter voids in brazed joints and often wonder where they come from and how to avoid them in future brazements. Some common sources of voids in braze joints are: surface contamination, base metal and brazing filler-metal (BFM) constituents, brazing methods/temperatures used and poor joint fitup. The first three items listed above can often result in gas bubbles being formed in brazed joints. Such gas-bubble voids will usually try to form in spherical shape as they move through a joint. The "rounded" edges of such bubble-voids can often be clearly seen in cross-section photomicrographs of brazed joints, especially under high magnification. The inside surfaces of a bubble-void will often appear "clean" or "shiny" as well. By Dan Kay

Last Updated on Sunday, 02 February 2014 22:32

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Braze Joint Design Considerations - Part 2

joint-magnified-smFor successful brazing to occur, the joints to be brazed have to be designed properly, and then properly manufactured to attain and maintain those shapes and dimensions. This second article looks at joint clearance considerations in more detail. Joint clearances must be close together and parallel. The amount of clearance between the faying surfaces (the mating surfaces inside a joint being brazed) should ideally be kept small, on the order of about 0.000"-- 0.002" (0.000-0.050 mm) total, so that capillary action can most effectively pull the molten brazing filler metal (BFM) completely into and throughout a braze-joint. By Dan Kay

Next Month: In next month's article we'll address some additional factors in joint design, specifically the topic of "differential metal expansion". All metals expand at different rates when heated, and since braze-joint clearances are calculated based on expected clearances at brazing temperature, we need to know how to properly optimize brazing of different metals in the same assembly.

Last Updated on Sunday, 02 February 2014 21:59

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Read more: Braze Joint Design Considerations - Part 2

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