Technical note: Automated powder mass flow monitoring and control system

Abstract

Increasingly difficult coating quality requirements and the subsequent need for improved process control and consistency has necessitated the need for more accurate real-time information about key plasma-spray coating process parameters. A recent Garrett Turbine Engine Company (GTEC) project in association with Resonant Systems Technology, Inc. has resulted in the development of a powder mass flow monitor and control system. This equipment employs the principle of mass resonance to achieve real-time determination of powder mass flow rate. The monitor is adapted to standard powder feeders, which dispense material through a hose in conjunction with a carrier gas. Automated set-up and closed-loop control capabilities have been added to the basic monitor to provide enhanced powder feed systems. Much of the industry's effort has been directed toward regulatory systems based on the weight loss of the powder feeder. The technology described in this paper presents the alternative of measuring powder mass flow independent of the powder feeder. This paper presents both means of powder mass flow measurement with an emphasis on the latter system's operating principles and characteristics, and the results of benchmark tests using various types of powder feeders and powders. The results are summarized and supported with data and graphs depicting accuracy and precision of the powder mass flow monitors as well as illustrations of the powder feeder closed-loop control enhancements.