WATER JET CONFERENCE - Waterjet Technology Association

SECONDARY FRAGMENTATION WITH WATER JETS
David Eddingfield, James Evers, and JoDean Morrow, Jr.
Engineering Mechanics and Materials Department
Southern Illinois University-Carbondale
Carbondale, Illinois
INTRODUCTION
In contrast to the extensive research employing high speed water jets to extract
ores and cut and clean a variety of materials, the use of water jets to perform secondary
fragmentation of rock-like material has not received much attention.
Besides applicability to conventional grinding processes, secondary fragmentation
with water jets possesses a potential for use in the "borehole" mining process. In the
borehole mining process, water jets at the end of a rotating mining "tool" extract the coal
which is then pumped up the pipe holding the mining tool. In order to be pumped to the
surface, the coal must first be reduced in size in order to pass through the inlet of the
pipe.
In order to evaluate the use of water jet secondary fragmentation, a research
program was designed and undertaken.
TEST PROCEDURE AND EQUIPMENT DESIGN
Evaluation procedures for conventional crushing and grinding devices are well
established. However, these procedures cannot be used for water jet grinding.
Consequently, a considerable amount of time and effort was devoted to devising a
method to test and evaluate the use of water jet secondary fragmentation.
The original idea was to parallel the test procedure for batch grinding so that
perhaps some comparisons could be made and some data determined for grinding
kinetics. The original apparatus shown schematically in Figure 1 consists mainly of two
concentric cylinders. Two water jet nozzles were mounted in the outer cylinder. The
water jets passed through the inner cylinder by vertical slots cut in the wall. The inner
cylinder was oscillated in an up and down fashion to expose the entire coal sample to the
action of the jets. The top and bottom of the inner cylinders had small diameter holes
drilled in order to allow the water to escape. Also the entire apparatus was submerged in
a water tank so that the coal samples would be completely submerged in water. After
several months of modification and experimentation, the approach was abandoned. The
losses of coal from the inner cylinder could not be kept to an acceptable amount. In some
runs the amount of the sample left in the container was less than 50 percent of the weight
of the original coal sample. This could not be considered a "batch" grinding procedure.
A continuous process procedure was devised by removing the inner cylinder of
the original apparatus, placing the jets closer to the lower end of the outer cylinder and
angled slightly to create a swirling flow and placing a 2 inch opening grate over the lower
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