From Bob Grammer of Grammer Vacuum Technologies a US supplier of Molybdenum and TZM alloy mill products we have the this article about Hearth Height Adjustment in vacuum furnaces. This is the second of a three part series.

“Adjustable Hearth Height for Wider or Taller Load Capability

The available width and height of the work zone in a vacuum furnace with a round hot zone is determined by the elevation placement of the top of the furnace hearth.  This distance is determined by the length of the vertical hearth support posts.  By having spare, interchangeable hearth post sets of varying lengths, one can extend the work zone width or height as needed.  The figure shows a variety of work zone dimensions that are possible with a standard 36” wide x 36” tall typical work zone as an example.  The important thing in choosing your work zone shape is to maintain an (approximately) 3” clearance between the elements and the work zone to avoid part to element contact.”

“Note:  With the symmetric shapes of modern, round hot zones there is good reason to expect good temperature uniformity anywhere within the 3” clearance ring shown in Figure 1.  If you can build a survey fixture capable of surveying all the space you want to use, you theoretically could use more than just the rectangular space shown in the examples.  Getting an auditor to accept the survey is a separate task.

Author: Robert Grammer, Grammer Vacuum Technologies, Inc.
GVT provides an extensive inventory of Molybdenum and TZM alloy mill products for vacuum heat treating. To learn more: [email protected] or visit www.gvtinc.com”