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Design and application of hydroabrasive jet cutting heads

The conventional waterjet cutting head system, using lateral abrasive feeding has been optimized by creating a self centred head and designing a natural shape nozzle. For extension of wear life in industrial application a nozzle length of approximately 75 mm was found to be optimal. By incorporation of a natural shape bore design (featuring an elongated entry cone) the break in time of such nozzles could be drastically reduced (from 15 to 1 minute).

Field testing of ceramic nozzles in comparison with conventional tungsten carbide cobalt nozzles has shown that selfbonded boron carbide exhibits best wear life irrespectively of used abrasive slurry (olivine garnet alumina). However, for general applications (ie handling the convenient abrasives olivine and garnet) commercial tungsten carbide based nozzles show a better cost effectiveness.

Rather unexpectedly, the new boron carbide titanium boride nozzles have not been qualified as replacements for monolithic boron carbide nozzles. Obviously the major toughening mechanism in boron carbide titanium boride composites is not effective for improvement of wear resistance against abrasive waterjets in the nozzle bore.

However, for the alumina abrasive slurry, the new boron carbide nozzles have greater than 18 times the wear life of hard metal nozzles. The latter were completely used up after only 5 minutes cutting with alumina slurry (ie they are not economically viable for such applications). It is believed that the development of boron carbide nozzles for the use of alumina abrasive is a major breakthrough in the abrasive waterjet technology.

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K SCHWETZ
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