This paper investigates the need and requirements for developing an improved sensing scheme for plasma spray, which would aid in compensating for the large variations in deposition rate. Experimental evaluation of a variety of current sensors reveals poor correlation with deposition rate. Important issues that explain these results include reconsidering what particle state characteristics should be measured and determining what sensing characteristics are required to achieve better correlation with deposited mass. A new particle flux sensor is proposed that meets these challenges is evaluated.

Real-time control offers the potential to reduce plasma spray variations that affect yield and coating quality. Important factors for designing such controllers are discussed including dominant nonlinearities, cross-coupling interactions, and sensor issues. The performance of several alternative strategies to achieve better coating thickness control are evaluated.

This study evaluates the performance characteristics of three different torches. A variety of different sensor systems were used to determine how each system resolves the differences in torch spray conditions. Torch performance characteristics include the long term drift behavior in terms of spray pattern and coating profile, the ability to control the particle state, and each torches nonlinear characteristics such as bifurcation (sudden jumps) and on/off repeatability. Sensors include commercially available particle sensors (Tecnar’s DPV 2000, Oseir’s Spraywatch, and Inflight’s IPM), as well as monitoring of plume intensity, acoustic emission, and high frequency voltage/current. Torches include Praxair’s SG 100 (internal injection), Sulzer Metco’s 9MB, and Progressive Technologies 100 HE. The study focused on spraying YSZ under each torches typical operating conditions. Abstract only; no full-text paper available.

This paper investigates the advantages that an advanced control system can provide for plasma spray deposition in terms of variation reduction and greater ability to engineer coating structure. We report our work on implementing a feedback control system that automatically adjusts system inputs to maintain the desired particle states in spite of process variations. The limitations and performance capabilities of both feed forward and real-time control are evaluated. Important system characteristics needed to develop such controllers are discussed including dominant nonlinearalities, dynamics, cross-coupling, distributions, and sensor issues. Performance is evaluated in terms of engineering coating structure and production objectives.