| 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. |
October 2009 |
905-827-4171 |
| The Theory of Gases | by Dan Herring | This is the second of a series of articles in our Vacuum Heat-Treatment Series. This part is intended to teach us all about how gases behave in a vacuum environment, look at the equations needed to explain their behavior and explore what happens when we pump down a vacuum vessel.
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It is important to understand something about the Theory of Gases since a vacuum environment is hardly a space containing nothing at all. What remains inside the vacuum vessel will definitely affect the component parts we process.
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In vacuum heat, we are always dealing with the movement of gases. So, everyone needs to understand something about the nature (theory) of gases and how they behave, especially in vacuum. The main difficulty, however, is that too much theory tends to become a distraction. Our mission is to learn how these equations help us understand what goes on inside a vacuum vessel. Read more >> |
NEXT TIME - Part three of this series begins to explain how mechanical pumps and blowers help us achieve a controlled environment needed for processing in vacuum. We will also explore the functionality of these pumps and some of the features that make them well suited for the task.
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| How to Determine Braze Gap-Clearances for Your Furnace | by Dan Kay | Good brazing depends on the ability of capillary action to draw the molten brazing filler metal (BFM) in all directions throughout the joint being brazed, either vertically or horizontally. In many brazed joints there is often the need for the BFM to flow upwards against gravity, and if the gap clearance is properly made, this should not be a problem.
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However, if the gap-clearance between the faying surfaces in a joint to be brazed is too wide, then gravity will dominate the situation, and capillary action may not occur. Therefore, it is very important for all brazing shops to know the "capillary-capability" of each of their furnaces they use for brazing. This is not hard to do. |
Optimal gap clearance varies according to the combination of base metal and BFM used; e.g., copper BFMs prefer tighter joint clearances than for aluminum BFMs. Also, depending on the reactivity of the BFM with the base metal being joined, you may find that a given BFM will prefer either a tight gap or a wide gap. NOTE: By reactivity I mean the ability of the BFM to alloy with, and diffuse into, the base metal. You will also see that this reactivity will affect the distance that a BFM is able to flow into a joint being brazed. Read more >> |
NEXT TIME - Next month I'll discuss some important design issues regarding braze gap clearances and configurations, and in succeeding months we'll address issues of dissimilar metal brazing, and joint strength and its optimization in more detail.
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