Vacaero

Manufacturers of heat treating and brazing vacuum furnaces and controls, complete hot zone and vacuum furnace retrofits, thermal spray coatings, plasma, HVOF and paint coating services.

VAC AERO Service Experience Trust
Canada FrançaisAccessibility |

Archives for May 2013

Mechanical Booster Pumps for Vacuum Systems

by

In many vacuum systems, especially those where the chamber is large, has a large internal surface area and the chamber load adds extra surface area, the pump down can be slowed substantially when the chamber pressure drops to the range where the water vapor molecules on the surface desorb and have to be pumped away.

Pressure and temperature determine when this vapor desorbs, but at ambient temperature around seventy two degrees Fahrenheit or twenty degrees Centigrade the vapor desorbs from about 50 Torr down to about 0.1 Torr. The vapor pressure of water at ambient temperature is about 18 Torr, so that is where maximum desorption may occur.

Dimensional Changes After Heat Treatment

by

One of the questions all Heat Treaters are asked is, “How much, if at all, will my part change (i.e. shrink or grow) during heat treatment?” While the heat treater would love to be able to give a precise answer to this question, in most situations volumetric size change during heat treatment cannot be accurately predicted, at least not accurately enough to allow for final machining and/or grinding to close tolerances prior to heat treatment.

Experimental work has been done on many materials to show the effects of heat treatment on size change. As one might expect, the effects are different for every material grade. For example, an 80 mm (3.15”) cube of D-2 tool steel (Fig. 2) reveals growth (0.08%) in one dimension and shrinkage in the other two dimensions as a result of vacuum hardening. This graph demonstrates how knowing the part orientation from the mill-supplied bar is important when trying to plan for size change during heat treatment. By Dan Herring, THE HERRING GROUP Inc., and Patrick McKenna, Nevada Heat Treating, Inc.