WATER JET CONFERENCE - Waterjet Technology Association

3.3 Abrasive Feed Systems
For abrasive-waterjet cutting, precise control of the abrasive flow rate is an essential
requirement, a feature that is not offered by commercial systems. Therefore, Flow Industries
developed an abrasive feed system that provides both steadiness and precision of abrasive flow
rate. Dry abrasives are fed into a collector just after the waterjet is formed. An orifice is used to
control the abrasive flow rate. The waterjet and abrasive-jet nozzle act as an injector pump to
accelerate the abrasives. For feeding abrasives in underwater applications, a pressurized, sealed
tank may be required. Feeding dry abrasives over long distances needs further development.
The slurrying of abrasives shows promise for better control of their flow characteristics
but introduces the need for a separate slurrying circuit. Because slurries result in less efficient
mixing of the abrasives with the waterjet in the mixing chamber due to the additional mass of the
carrier fluid, higher pumping flow rates for waterjets, along with increases in power, will be
required. More development of slurried abrasives is necessary before this approach can match
performances obtained with dry abrasive feed systems.
3.4 Abrasive-Jet Nozzles
The abrasive-waterjet cutting nozzle should provide (1) an efficient mixing of the
abrasives with the water, (2) a coherent, focused abrasive stream at the nozzle exit, and (3) a
reasonable service life cycle. Two basic concepts have been tested that show great promise for
commercialization.
The first concept, which has been tested extensively, is shown in Figure la. High-pressure
water enters the center of a mixing chamber into which abrasive particles are fed from side ports.
The water entrains the particles and accelerates them to high velocities. The shape and material
of this mixing chamber are critical in determining both its wear rate and the jet's performance.
Typical commercial nozzle materials are tungsten carbide and boron carbide. For optimum
performance, the configuration of the mixing chamber may be different for different
applications.
Another nozzle design, which has been tested with encouraging results, utilizes multiple
waterjets that converge to form a single stream. The abrasives are fed into the core of that
stream, Figure lb. The prime advantage of this design is the increased service life of the mixing
chamber or, possibly, the complete elimination of that chamber.
The angle of convergence and the mixing chamber shape are critical parameters.
Investigations with multiple jet nozzles for limited water flow rates of up to 2 gpm showed that
nozzle performance greatly depends upon machining accuracy to produce perfectly symmetric
jets. Extensive research will be required before an optimum nozzle of this type is fully developed
for commercial use.
3.5 Abrasive and Water Catcher Systems
The development of catching systems to collect the abrasives and water is of prime
operational importance. The catcher design depends on whether the cutting system is for a (1)
factory application with stationary nozzles, (2) factory application with moving nozzles, (3) field
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