Centorr Vacuum Industries, Nashua, N.H., reports that its engineers worked closely with a customer on an application involving the use of copper brazing to join stainless steel parts.
Due to the delicate balance between vaporization and safe processing of copper braze materials in vacuum, the customer placed an order for a Centorr Vacuum Industries Workhorse furnace with its proprietary G-10504B partial-pressure control system. Previous processing of the material in high vacuum resulted in the copper braze material vaporizing and condensing inside the vacuum furnace hot zone at all the cold surfaces, such as the power feedthrough locations and the front and rear hot-zone doors.
To minimize this process offgassing, Centorr provided its partial-pressure control system, which consists of a small micrometer needle valve and an on/off roughing valve. During operation, the high-vacuum pumping system is valved off, and the partial-pressure gas control system allows for a fine degree of clean, non-reactive argon gas to bleed into the chamber, spoiling the vacuum level to a controllable range between 1 and 1000 microns (i.e., 10-3 to 1 torr). This vacuum level is above the threshold where the copper would vaporize at the brazing temperatures used.
For cases where the customer must process the copper braze materials in high vacuum (due to part configuration and need for vacuum environment in the sealed brazed parts), Centorr has designed its vacuum furnace hot zones to withstand a high-degree of braze material condensation.
