Many of today’s vacuum furnaces are equipped with a partial pressure control system, which can be designed to operate with a single gas or multiple gases of various types – for example, nitrogen, argon, hydrogen, helium. Partial pressure is typically programmed into the furnace temperature controller, activated as one of the programmed events.
The primary purpose of a partial pressure system is to avoid vaporization (i.e., boiling away) of elemental constituents, chromium as an example, from the component parts being run. Partial pressure also minimizes diffusion bonding (i.e. sticking or fusing of part surfaces together) that can take place on adjacent metal surfaces. In the case of brazing, it also serves to minimize or prevent vaporization of the constituents in the braze alloy. A secondary purpose of partial pressure control is to dilute and help sweep away unwanted vapors that may be present when outgassing occurs during heating. In most cases, however, a properly designed and robust pumping system will remove any outgassed vapors before the partial pressure setpoint is reached.