| 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. |
March 2010 |
905-827-4171 |
| Vapor Pressure | by Dan Herring | This is the seventh in a series of articles in our Vacuum Heat-Treatment Series. Here we talk about vapor pressure and how it is influenced by the various materials of construction used in a typical vacuum furnace as well as the materials we process.
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All solids and liquids have a tendency to evaporate into gaseous form, and all gases have a tendency to condense back into their liquid or solid form. In other words, all materials have a characteristic vapor pressure that varies with temperature. Formally, vapor pressure is the pressure of a vapor in (thermodynamic) equilibrium with its condensed phase(s) in a closed container or vessel. Why is Vapor Pressure Important in Vacuum Systems? In a vacuum system, we must make sure that all component parts to be heat treated, fixtures and furnace materials of construction subjected to a vacuum environment will not experience significant evaporation or volatilization Read more >> |
Next time, we will begin a discussion of the interior construction of vacuum furnaces by considering hot-zone designs.
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| Differential Metal Expansion - Part Two | by Dan Kay | In 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.
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As mentioned in last month's article, ALL metals expand when they are heated, and contract when they cooled. Fig.1 below once again shows typical thermal expansion data for some common base metals, indicating that different metals expand at different rates when heated. This month let's look at the center curve, the one for 1018 carbon steel. Please note that it contains a strange "break" in the curve, and seems to show that the 1018 steel is actually shrinking while it is being heated. Is this true? Yes, this will actually happen. Read more >> |
NEXT TIME - 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.
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| Practical Considerations for Successful Hardness Testing | ||
| By Alan Stone and Daniel H. Herring | ||
Everyone knows how to perform a hardness test, or do they? Hardness testing is made more complex by such real world factors as a hard case over a soft core, hard particles, soft inclusions, and soft layers over hard cores to name a few. Part size, shape, and weight are other test challenges. Selection of the best test method, use of proper procedures, and a keen awareness of what and where to test are needed.
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Hardness testing is one of the most common quality control checks performed. It is often used to determine the success or failure of a particular heat treatment operation or to understand the material's current condition. Hardness testing is one of the easiest tests to perform on the shop floor or in the laboratory, but it can be one of the hardest tests to do properly. |
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