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Wednesday, May 16, 2007 - 8:20 AM

DELTA Gun - An Improved Multiple Electrode Plasma System

A. Schwenk, GTV GmbH & Co. KG, Luckenbach, Germany

A.     Schwenk1, T. Grund2, B. Wielage2, J. Zierhut3, M. Dzulko4 and K. D. Landes4

 

1 GTV GmbH & Co. KG

2 Technische Universität Chemnitz

3 Zierhut Messtechnik GmbH

4 Universität der Bundeswehr Neubiberg

 

 

The claim of industrial applications is to improve the efficiency of thermal spray processes most notably in regard to deposition efficiency and spray time as well as coating quality. Conventional techniques, as for example the common F4/F6 one cathode - one anode plasma technique, are limited due to the process instabilities and the power input. Since almost one decade, new innovative developments have been introduced by multiple arc systems in order to stabilize the process. The process efficiency is advanced by increasing the power input and therefore the powder feed rates up to 150 g/min using the common oxide ceramics Al2O3, Cr2O3 and YPSZ.

 

The new innovative “Delta” gun is characterized by a single cathode and three electrically isolated anode segments. At the exit of the torch the cascaded arc is separated into three anodic arc roots located on one anode segment each. Therefore, both an axial and a radial stabilisation of the electrical arc roots can be achieved, which leads to an improved powder treatment due to the localisation of the arc anode attachment points. The stability of the process as well as the length of the arc result in an optimisation of the heat  load and acceleration of the injected powder particles.

 

To analyse the plasma process of the “Delta” gun and to verify the advantages of this new technique, oxide ceramic coatings are sprayed (Al2O3, Cr2O3 and YPSZ) and investigated by common abrasive wear tests as the ASTM G65 Rubber Wheel, ASTM G75 Miller and ASTM F1978 Taber Abraser. The chemical composition is investigated by XRD analysis. To quantify the process in regard to the thermodynamics of the plasma jet and the influence on the “in-flight” behaviour of the injected powder particles, both 2D simulations by using FluentÒ as well as measurements of the average particle temperatures and velocities using the diagnostic tool SprayWatchÒ are presented.


Summary: The new innovative “Delta” gun is characterized by a single cathode and three electrically isolated anode segments. At the exit of the torch the cascaded arc is separated into three anodic arc roots located on one anode segment each. Therefore, both an axial and a radial stabilisation of the electrical arc roots can be achieved, which leads to an improved powder treatment due to the localisation of the arc anode attachment points. The stability of the process as well as the length of the arc result in an optimisation of the heat load and acceleration of the injected powder particles.