Low pressure carburizing (LPC) in a vacuum furnace is increasingly the preferred method of case hardening for aerospace gears, and acetylene is often one of the gases used in the process. Selective case hardening is common with gears, where certain sections of a part are “stopped off” or “masked” to prevent carburization at those locations. For aerospace parts, the masking used is typically copper electroplating. The low pressures and high temperatures used in LPC lead to copper evaporation, which contaminates the vacuum furnace hot zone and components. In a worst-case scenario, deposited copper can lead to short-circuiting of power feedthroughs. This study looks at the effect of vacuum and partial pressure gases on copper evaporation and its application in production processes.

Radiation heating of materials in vacuum furnaces is critically dependent on surface characteristics, with material emissivity and absorptivity playing pivotal roles in heating dynamics. Surface properties such as color, polish, and roughness significantly influence heating rates, with bright and polished surfaces heating more slowly than dull and dark surfaces, while rough surfaces heat faster than smooth ones. When using thermocouple blocks to simulate actual load parts, precise replication of surface conditions is essential, as surface variations can cause substantial temperature disparities. Materials with different surface conditions can exhibit heating time differences of up to 100%, underscoring the importance of maintaining consistent surface smoothness and periodically reconditioning thermocouple test blocks to ensure accurate thermal simulation and process control.