OBSERVATIONS OF WEAR OF ABRASIVE-WATERJET NOZZLE MATERIALS

This paper addreSSes the wear characteristics of the mixing tube of an abrasive-waterjet nozzle. An effective nozzle material should possess high values of both hardness and toughness. The mixing tube, which is where the abrasives are mixed, accelerated, and focused with the high-pressure waterjet, is the component in the abrasive- waterjet nozzle that receives the greatest wear. Accelerated wear tests were conducted on relatively soft (steel) mixing tubes using a typical soft abrasive (garnet sand) and on harder (tungsten carbide) tubes using a harder abrasive material (aluminum oxide). A wide range of candidate tool materials, including several carbides and ceramics, was also tested using actual machining parameters. The tungsten carbide grades exhibited greater longevity than the harder ceramics, such as boron carbide, when garnet abrasives were used. The reverse trend was observed with aluminum oxide abrasives. Wear trends suggest that the wear mechanisms along the mixing tube change from erosion by particle impact at the upstream sections to abrasion at the downstream sections. Linear cutting tests were also conducted on several candidate nozzle materials to gain more information related to wear performance. It was found, for example, that the binder in tungsten carbide, which controls these properties, is a critical factor that also controls the lifetime of tungsten carbide mixing tubes.