| 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. |
May 2010 |
905-827-4171 |
| Heating Elements | by Dan Herring | This is the ninth in a series of articles in our Vacuum Heat-Treatment Series. This part talks about heating elements used in vacuum furnaces, the materials and temperatures of operation, forms and maintenance practices. The design and location of the heating elements is critical to achieve proper heating and uniformity of temperature.
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Almost all high-temperature vacuum furnaces are electrically heated. Resistance heating elements are constructed from metal or graphite in a variety of styles. In general, one of the following materials is used: - Stainless steel alloys, 300 series alloys (e.g., 304L, 316L) can be used for heating elements up to approximately 760C (1400F). - Nickel/chromium and iron-aluminum based alloys. These typically operate up to temperatures of 1150C (2100F) and exhibit good-to-excellent oxidation resistance, making them useful for a number of applications including hot wall-type furnaces. - Inconel and other nickel alloys. Depending on material and vacuum level, they can be used up to 1150C (2100F). Above 800C (1475F), there is a risk of evaporation of chromium from these materials. Read more >> |
| Thermocouples in Furnace Brazing - Part Two | by Dan Kay | In 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.
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First of all, remember that good furnace control means you need to know the temperature of the parts inside a brazing furnace, and this can only be done in batch-type furnaces via well-placed thermocouples (TC's). I recommend that brazing shops use a minimum of at least three (3) Type-K (or perhaps Type-N) load-TC's in each furnace brazing run, and even more TC's than that, if possible, if their furnace will allow. The more TC's used, the better will be the overall control of the cycle variables. Read more >> |
NEXT TIME - 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.
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| Materials Characterization & Testing: The Challenge of Holding Tight Rockwell Test Result Tolerances | ||
| By Ed Tobolski | ||
Manufacturers sometimes impose tight Rockwell hardness specifications on themselves in an attempt to improve quality. Other times heat treaters are asked by customers to meet tightly controlled limits such as +/-1.0 Rockwell point. Are these tight limits realistic, and do they have any real product benefit?
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As manufacturers strive to increase the quality of the products they produce, there is a corresponding need to improve the accuracy of the measurements used to control or monitor the product's quality. Rockwell hardness testing is one of those measurements. In an effort to reduce the variations in the performance of their products, some users are attempting to hold the Rockwell results on critical parts to +/-1.0 Rockwell point. This article will discuss the realities of trying to hold such a tight tolerance and will provide some insight on how to do it. |
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