WATER JET CONFERENCE - Waterjet Technology Association

CUTTING HARD ROCK WITH ABRASIVE-ENTRAINED WATERJET AT MODERATE
PRESSURES
Gene G. Vie
Fluidyne Corporation
Auburn, Washington 98002
ABSTRACT
It has been known that waterjet's ability in cutting hard materials can be significantly
improved if suitable abrasives could be incorporated into the jet stream. Fluidyne Corporation
has developed unique nozzles to achieve this objective without sacrificing the quality of waterjet
or creating severe wear problems. With such nozzles, waterjets of less than 20,000 psi (138 MPa)
in pressure can now be used to cut very hard rock, such as granite, quartzite and basalt, at
practical speed and minimum consumption ot water and abrasives.
INTRODUCTION
Waterjet Technology
High-pressure waterjets have been evaluated extensively for cutting and drilling concrete,
rock and minerals; numerous publications on this subject can be found among those presented at
the International Symposium on Jet butting Technology (ISJCT) and in other journals. It has
been observed that there exists a "threshold pressure" for a given rock that below which waterjet
cannot cut the rock to any depth within practical dwelling time. This "threshold pressure" was
believed to be a function of rock's compressive strength, permeability, crystalline structure and
other properties; the exact relationship, however, is not clearly understood. Some typical values
of such "threshold pressure" are 5,000 psi (35 MPa) for sandstone, 7,000 psi (48 MPa) for
limestone, 14,500 psi (100 MPa) for granite, and over 20,000 psi (138 MPa) for quartzite and
basalt. However, to obtain significant cut depth and speed requires waterjets of a pressure level
considerably higher than the "threshold pressure" of a given rock. Thus, most of the past
investigations on cutting or drilling hard rock with waterjets involved pressure in excess of
40,000 psi (276 MPa). To obtain such high pressure requires the use of special pressure
intensifiers that are known to be costly and have limited flow capacity. There are also other
constraints in applying such high-pressure waterjets in the field such that attempts to cut
concrete, rock and other hard materials at very high water pressure have not been successful to
date.
Abrasive-Entrained Waterjet
It has been known for some time that waterjet's ability in cutting hard materials can be
drastically improved if hard particles could be incorporated into the high-speed waterjet.
Unfortunately, this scheme is difficult to implement because of entrainment and wear problems.
However, efforts have been devoted to this task in recent years and Fluidyne Corp. (Fluidyne) is
one of the organizations in the world that have investigated suitable techniques. This paper
summarizes an investigative effort funded by the National Science Foundation (NSF Project
CEE8260224) to cut hard rock with Fluidyne's proprietary Abrasion-Jet technique at moderate
water pressures. Because of the interruption from an unforseen event, this project was not
completed and the data presented here are only a portion of that planned originally .
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