Heat Treat Industry News

April 08, 2010

Hot Zone Construction

Typical all-fiber-lined hot zone

This is the eighth in a series of articles in our Vacuum Heat-Treatment Series. This part talks about vacuum hot zones, their history, construction and maintenance. The type of hot zone construction is often important both to the material and to the process.

The first commercial vacuum furnace was sold to industry in 1929. In these early years vacuum furnaces were hot-wall retort designs; that is, alloy retorts placed inside atmosphere furnaces in which a vacuum was pulled on the retort interior. By the late 1950s, vacuum furnaces were gaining wider acceptance, particularly within the commercial heat-treatment industry. Larger sizes were especially in demand, prompting furnace manufacturers to consider alternative designs. The early 1960s saw the introduction of the first all-graphite-felt hot zone with graphite (cloth) heating elements. This was followed a few years later by a hot zone construction consisting of a molybdenum hot face backed with Kaowool insulation and graphite (tubular) heating elements. These early designs suffered from a combination of ills (leaky vacuum vessels, poor element life, workload contamination and contact carburization concerns) as the industry struggled to understand how vacuum furnaces needed to be built.

Construction Methods ....

by Daniel H. Herring - April 1, 2010 (photo courtesy of Surface Combustion)

Read More:

http://www.industrialheating.com/Articles/Online_Exclusives/BNP_GUID_9-5-2006_A_10000000000000793044

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