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Controlling Suppliers and Customers: Key to Successful In-House Brazing?

115828_wsTrying to braze materials from outside suppliers that are not compatible with your brazing process and trying to meet customer's unrealistic specifications can create headaches in the braze shop that are not necessary, and can be alleviated by working closely with suppliers and customers to make effective brazing a shared goal.

Over the years, many brazing shops have experienced brazing problems (leakers and nonwetting surfaces, for example) due to "unknown" variables that crept into their brazing operations, resulting in the failure or rejection of many brazed assemblies. An evaluation of these situations often shows that some of the subcomponents of the brazements (such as brackets, fittings, etc.) come from outside suppliers, and the brazing shop is not aware of details of the manufacturing processes used by the suppliers to make the components that subsequently will be brazed. As a result, many shops are caught up in trying to fix the problem by trying to determine what is wrong with their own in-house brazing operations, often leading to frustration because no cause can be identified. In many such cases, this is due to incorrect assumptions about the sources of the problem. By Dan Kay

Last Updated on Sunday, 02 February 2014 22:09

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Reducing Metal-Oxides in Brazing - Part 2

mmo_curves_wsLet me make two important statements right at the start: 1.  Surface-oxidation of metals will prevent effective brazing. 2.  Brazing filler metals (BFMs) do not like to bond to, or flow over, oils, dirt, greases, or oxides on metal surfaces.

Thus, if any of the surface contaminants just mentioned are present on the metal surfaces to be brazed, effective brazing will not occur.  Surface-oxidation is a common source of problems in commercial brazing.  Parts to be brazed must be cleaned BEFORE assembling the parts for brazing, and then must be kept clean during the brazing process. One very effective tool that brazing engineers and shop personnel must understand and learn to use is the famous "Metal / Metal-Oxide Equilibrium Curves" published in 1970 in the AWS Welding Journal. By Dan Kay

Last Updated on Sunday, 02 February 2014 22:21

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Reducing Metal-Oxides in Brazing - Part 1

metal_metal-oxidecurves_wsLet me make two important statements right at the start: 1.  Surface-oxidation of metals will prevent effective brazing. 2.  Brazing filler metals (BFMs) do not like to bond to, or flow over, oils, dirt, greases, or oxides on metal surfaces.

Thus, if any of the surface contaminants just mentioned are present on the metal surfaces to be brazed, effective brazing will not occur.  Effective brazing requires the BFM to be able to alloy with (i.e., diffuse into) the base-metal being joined in order to form a strong, leak-tight metallurgical bond.  The amount of alloying required is not large, e.g., copper BFM on steel actually alloys/diffuses much less than 5% and yet forms very strong, leak-tight brazed joints on steel. By Dan Kay

Next Month: In next month's Part-2 article, we will look further into the interpretation and use of the metal/metal-oxide equilibrium-curves shown in Fig. 1, and describe a bit more about the oxidation/reduction reactions that may be occurring inside the brazing furnace throughout the brazing cycle.

Last Updated on Sunday, 02 February 2014 22:21

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Honeycomb-Brazing Essentials for Successful Use As Turbine Seals

93036_wsA honeycomb structure serves as an excellent gas flow seal and a sacrificial wear-surface to rotating turbine blades in high-temperature turbines. Achieving the ideal honeycomb construction requires careful attention to the amount and placement of brazing filler metal and brazing time and temperature.

Honeycomb structures, one of nature’s unique designs, are widely used in such diverse applications as automotive, packaging, high-pressure containers, lightweight aerospace wing panels and engine nacelles, and high-temperature turbine seals for ground power and aircraft jet engines, taking advantage of honeycomb’s high structural strength with minimum weight. In the gas-turbine industry, honeycomb is used primarily in shaft-type labyrinth seals and rotating (rotor) blade shroud seals. This article focuses on the latter, and more specifically, on the use of open-face metallic honeycomb structures in high-temperature gas-turbine seal applications in aircraft jet engines and in industrial ground-power gas/steam applications. By Dan Kay

Last Updated on Sunday, 02 February 2014 22:17

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Liquation of Brazing Filler Metals – Good or Bad?

ih1109-mfj-fig2-nlWhen a brazing filler metal (BFM) is melted during a brazing process, it is not uncommon for “liquation” to occur.

Liquation in brazing is defined as the tendency of the lower-melting constituents of a BFM to separate out and flow away (by capillary action) from the higher-melting constituents of the BFM during heating. Sometimes a non-melted “skull” of alloy remains at the point where the BFM was applied. Liquation is usually apparent in BFMs having a wide melting range, i.e. having a large difference between the solidus and liquidus (Note 1) temperatures. It occurs when the BFM is heated slowly through that melting range (such as when furnace brazing). Liquation is not typically encountered when rapid brazing techniques – flame brazing or induction brazing – are used. By Dan Kay

Last Updated on Sunday, 02 February 2014 22:19

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Repair Brazing - Fixing faulty jobs and worn-out components.

repair_brazing_nlBrazing is a versatile process used in many industries to join materials permanently. Repair brazing is an essential part of the industry and usually is done for one of two reasons - to braze repair parts in-house before they are released to customers and to perform repairs on brazed components that have worn out in service.

The former involves in-house quality assurance programs designed to detect braze defects before they get out the door. The latter involves brazed components worn out from corrosion, erosion, or fatigue (thermal and/or mechanical) in cyclic service, resulting in surfaces that are cracked, pitted, or eroded. By Dan Kay

Next Month: In my next article we will be discussing that when a brazing filler metal (BFM) is melted during a brazing process, it is not uncommon for “liquation” to occur.

Last Updated on Sunday, 02 February 2014 22:22

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Fillets in Brazing

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Brazing fillets can be a greatly misunderstood phenomenon in brazing. Some people insist that big fillets are needed, whereas others say that they are not. Let’s take a closer look at fillets in brazing, what they are, what they do and what characteristics about them are desirable.

A braze fillet is actually a casting along the outside of a braze joint that shows that the brazing filler metal (BFM) has melted and flowed along the edge of a braze joint. It doesn’t tell you if the BFM has adequately penetrated the joint, and caution is therefore strongly recommended to anyone attempting to use the many characteristics of a fillet as inspection criteria for judging the overall quality of a braze joint. Fillets are not a significant factor in determining joint strength. What does a fillet do? Fillets, first of all, are a natural outcome of the brazing process and merely give evidence that the BFM has melted and flowed. Fillets can also show whether or not there is good compatibility between the BFM and the base metal, and they may also be able to tell you about base-metal cleanliness. However, strong caution is advised against depending on fillets to be a distributor of stresses. By Dan Kay

Last Updated on Sunday, 02 February 2014 22:16

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