Practical Comparison of Cylindrical Nozzle and De Laval Nozzle for Wire Arc Spraying
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JTTEE5 23:1470–1477 DOI: 10.1007/s11666-014-0156-4 1059-9630/$19.00 Ó ASM International
Practical Comparison of Cylindrical Nozzle and De Laval Nozzle for Wire Arc Spraying Marc-Manuel Matz and Markus Aumiller (Submitted March 19, 2014; in revised form September 3, 2014) In this article, two different nozzle designs (cylindrical nozzle and de Laval nozzle) are compared for use in wire arc spraying. The choice of nozzle is of particular importance because its geometry has a significant influence on the spraying result. The materials used for spraying are steel and copper. By using the de Laval atomizing gas nozzle, the aim is to improve adhesion on the one hand while reducing cost on the other. These objectives have been achieved for the most part, indicating that continued research and development in this area would be useful. Significant potential exists to optimize the efficiency of both the free gas jet and nozzle which have considerable impact on the gas velocity and thus, ultimately, on the spraying result. The measurements carried out have shown that there is a close correlation between the velocity of the gas flow and atomization of the droplets. An explanatory model for varying spraying results with different wire materials using open nozzle systems with de Laval orifice is given and confirmed. For new burner head constructions, an interaction of the atomizing gas nozzle, the contact tips, and wire materials must be considered to achieve all benefits of a de Laval nozzle.
Keywords
nozzle design, particle size, particle velocity, supersonic stream, wire arc spray
1. Introduction Components for technically sophisticated applications such as internal combustion engines are constantly exposed to increasing loads and pressures. In order to withstand these demands, the quality of the components must be continually improved. At the same time, high quality alone is no longer enough to remain globally competitive. Costs are now also a significant product property. The characteristic of a wire arc sprayed coating can be controlled by the wire feed rate, atomization gas pressure, voltage, current, stand-off distance, etc. Many scientific contributions that describe these correlations exist (Ref 1-5). The quality of wire arc sprayed coatings is mainly influenced by the surrounding environment during flight and in particular by the particle formation process. This process has been investigated intensively (Ref 6-10). Also, dynamic and numerical models of the wire dispersion have been continuously improved (Ref 11-14). The nozzle design and the gas kinetics were identified as key elements (Ref 15-17). Thus improved coating quality can be achieved through the use of a de Laval nozzle instead of a cylindrical atomizing gas nozzle, while maintaining and, ideally, optimizing the economic advantages of this very inexpensive method.
Marc-Manuel Matz, Engelschalkstr. 1, Friedberg, Germany; and Markus Aumiller, Friedberg, Germany. Contact e-mail: [email protected].
1470—Volume 23(8) December 2014
Cylindric
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