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4567 |
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Tuesday, May 10, 2016, Room 3E 2:00 PM New Processes I |
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Production rate improvement in liquid fuel HVOF spraying by modified powder injection concepts |
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Andreas Wank / GTV Verschleißschutz GmbH, Germany Thomas Schläfer* / GTV Verschleiss-Schutz GmbH, Germany |
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Coating production costs in large surface area coating jobs using liquid fuel HVOF spraying are dominated by powder, oxygen and machine costs. Powder costs are minimized by process optimization concerning deposition efficiency. Assuming high utilization oxygen and machine costs are minimized by maximizing deposition rate. Both deposition efficiency and deposition rate are system variables depending on choice of powder, torch and torch components as well as process parameters. Among liquid fuel HVOF torches GTV K2 torch is already renowned for unsurpassed process stability and deposition rates in a large number of applications. Within the last decade there has been research on expansion nozzle and combustion chamber design that resulted in novel torch components that permit setting of spraying conditions close to those of cold gas spraying. Recent research focuses on powder injection design. In particular increase of number of injection ports from 2 to 4 has been studied. Comparison of novel (4 ports) and standard (2 ports) powder injector blocks includes powder feed from 2 and 4 individual hoppers at the example of Ni20Cr powder. While increase of powder feed rate from 100 g/min to 200 g/min results in significantly reduced deposition efficiency for use of standard powder injector block, use of novel powder injector blocks permits keeping deposition efficiency constant even for powder feed rate of 300 g/min. The capability of the novel powder injector block concerning expansion of deposition rate without significant effect on deposition efficiency is also analyzed for spraying of WC and Cr3C2 based cermets. Influence of increased deposition rate on coating microstructure is analyzed by optical microscopy. |