WATER JET CONFERENCE - Waterjet Technology Association

INTRODUCTION
Developing an unique technology for coal cutting and rock fracturing to suppress
dust; eliminate sparks; reduce the load acting on support systems, and to protect
surrounding work from damage has been a most important problem for mining, all over
the world.
For the last two or three decades, a wide variety of experimental studies into
fracturing and cutting rock have been carried out in many countries. Of these, the cutting
and fracturing of coal and rocks using high pressure water jets has been found to be one
of the more effective and promising of the novel coal mining technologies examined to
date. However, little is known of the best ways to raise the efficiency of coal cutting and
rock fracturing, or to lower the energy consumption of coal cutting, in order to make a
practical means available for productive application.
In 1970, an experimental study of high pressure water jet cutting technology was
begun, based on the practice of hydraulic coal mining. In order to raise the technical level
in coal mines more rapidly and to improve working conditions for miners, great attention
has been paid to the new technology of coal cutting with high pressure water jets in China
(3).
In an experimental study, aimed at the rapid application of high pressure water
jets into production, three principles were followed:
1. The high pressure water system used, should be very reliable in underground
operation to guarantee a long-term and continuous operation.
2. In order to make full use of the energy, an appropriate process of coal cutting with a
water jet must be carefully designed.
3. Because drivage mechanization lags behind that of coal mining in general, at the
present time, the technology of entry drivage using water jets
Starting in early 1979, the technology has been developed through theoretical
design, evaluation of reliability, experimental studies and underground trials, based on
the above ideas, and has been found to be basically effective and popular with mines.
BASIC THEORY OF COAL CUTTING WITH A SWING OSCILLATION WATER
JET
To meet the requirements of coal drivage, it is necessary that any high pressure
water jet should be capable of cutting and deep kerfing. In general, a jet should have three
functions, which are as follows:
1. Maximizing the area cut per unit time.
2. Attaining the maximum depth of kerf.
3. Minimizing the energy consumption during coal cutting.
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