| The Monthly Newsletter of VAC AERO International Inc. | If you are having trouble viewing this e-mail, click here. To log on to the VAC AERO web site, please click here. |
June 2010 |
905-827-4171 |
| Partial Pressure, Mean Free Path and Related Topics | by Dan Herring | This is the 10th in a series of articles in our Vacuum Heat-Treatment Series. This part continues a discussion begun in Part Seven (Vapor Pressure) and focuses on the use of partial pressure and related areas necessary to control vaporization and prevent damage to both the parts and the equipment.
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One of our goals in vacuum furnace processing is to minimize both alloy depletion from the part surface and subsequent hot zone contamination. Many of the materials we run are processed at temperatures and pressures at which individual elements can volatilize (leave the part surface). Partial pressure systems (Fig. 1) are designed to prevent this from happening by establishing a combination of pressure-temperature-time that minimizes the vaporization of the more volatile alloy constituents. Read more >> |
Next Time: Part 11 of this series discusses vacuum valves, penetrations, feedthrus and flanges; where they are used, how they operate and how they should be maintained.
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| Fillets in Brazing | by Dan Kay | 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.
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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. Read more >> |
| Refractory Metals in Engineered Components and Furnaces | ||
| By Mike Ferullo & Bernd Kleinpass | ||
The latest material and process developments for refractory metals are discussed. Learn how proper hot-zone design leads to improved performance and productivity.
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Metals that offer a higher melting point than platinum (3222F/1772C) are generally considered to be refractory metals (Ru, Rh, Os, Ir, Pt, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Tc, Re). For functional components in furnace construction, only molybdenum- (Mo), tungsten- (W) and tantalum- (Ta) based materials are of significant importance. For several decades these materials have been fabricated and utilized for heating elements, radiation shielding and mechanically loaded furnace fixtures. The following properties, and their synergistic effects, highlight why refractory metals are frequently chosen for such high-temperature applications: |
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