970

THE COLLIERY GUARDIAN.

November 6, 1914.

The most convenient size of firehole is an oval shape,
Ilin, by 14 in. or 15 in., and the ring should stand
I in. or | in. proud of the inner and outer plates in order
to protect the joints from the firing tools. Doubly to
protect the inner plate some engineers have a protection
casting fitted, which practice is to be commended.

(To be continued.)

USES OF THE HYDRAULIC MINING
CARTRIDGE.*

By James Tonge, M.I.M.E., F.G.S.

The difficulty of removing rock and other material in
places where the shock attendant upon blasting opera-
tions would be damaging and dangerous to surrounding
strata or foundations is one which has not hitherto been
thoroughly overcome. The objection to the use of explo-
sives, however, in many circumstances, is that the effect
of blasting can seldom be harnessed or controlled so as
to prevent the disintegration of the material beyond the
area which it is desired to dislodge. Further, pulverisa-
tion by explosives involves enormous waste of power, as
it usually represents great excess of explosive charge;
in other words, the use of explosives must involve either
the risk of accident through an insufficient charge, or
the production of misapplied energy.

The simplest form of mechanical means for breaking
ground is, of course, the wedge, and this is used in vary-
ing lengths and shapes, in metalliferous and in coal
mining, in all parts of the world. Various improve-
ments on the simple wedge have been used at various
times, viz., the stub and feather, and the multiple
wedge. The former consists of a steel “ stub ” or wedge
driven in between two tapered liners of steel called
“ feathers,” which have their thin end near the front
of the hole. The multiple wedge is placed in a hole
previously drilled, and has liners also, but a pair of
” feathers ” may be inserted between them, driven up
as far as possible, and then a second or a third ‘‘feather”
may be used until the rock or coal is broken down. In
coal mines special efforts have been made to devise
mechanical wedges capable of breaking down coal,
notably those invented by Bidder, Burnett, Shreeve, and
Hall, and these have been used to' a greater or less
extent in a few mines. In some of these the wedge was
driven in by means of a screw and handle, like a hand-
drilling machine, and in one case by hydraulic power.

These machines are not now in use, and it may be
taken that they have proved to be impracticable. This
is no doubt due to the great pressure put upon them,
even under favourable conditions, and the difficulty of
devising and supplying a hydraulic pump capable of
working at high pressure for a considerable time. It
must also be remembered that a mechanical wedge must
perform more work than that required to wrest the rock
or coal from its position, as a certain amount of power
is consumed in overcoming the friction of the sides of
the wedge as it is driven up. Again, it is a disadvantage
to have the material at the front of the hole breaking
away as the wedge enters—the full weight of the falling
material should if possible be utilised ‘ to assist the
operation. With this object in view machines have
been designed to operate at the back of the hole first,
the wedge being drawn towards and not driven from the
front. Except in the case of the simpler forms, it may
be said that no mechanical wedges are now being used
with success for excavating purposes of any kind.

The hydraulic mining cartridge differs from all other
mechanical substitutes for blasting. It is not worked
on the principle of the wedge, and consequently the
power expended in forcing a wedge into the hole is
saved. Instead of employing a wedge, the disrupting
effect is obtained by means of a number of small rams
or presses working at right angles from a strong cylinder
of steel (fig. 1). In order to make these rams more
effective in their operation, by obtaining a greater travel
from their original position, they are made of a duplex
or telescopic form, one part sliding and fitting upon the
other (fig. 2). In some cartridges these pistons operate
from each side of the cylinder alternately, thus greatly
increasing the travel. To retain the rams in position,
a sliding plate is used fitting in grooves in the barrel
(b, fig. 1); this is so formed and secured that it is per-
fectly rigid and firm when the machine is in operation,
but is readily removable if it is desired to detach or
replace any of the rams. By a suitable arrangement of
passages (c, fig. 1) a communication is made between
each of the rams, whereby simultaneous action is
obtained. Machines are made of various diameters,
viz., 2|in., 3|in., and 4 in., and of various lengths, say
with eight, six, or five rams, the smaller diameters
having the larger number of rams. Pressures of three,
four, or five tons per sq. in. are usual, so that machines
are made to withstand great stresses.

The cartridge is operated by means of a .pump (fig. 1),
to which it is directly connected by a pipe d. The pump
is of special design. At the commencement of the
supply of water it is desirable that the latter should be
supplied in such quantities as to fill up quickly all the
spaces within the rams and passages, while at the same
time allowing the operator, when the rams begin to
move and the pressure to increase, to supply a less
quantity of water, but at a greater pressure, to complete
the final operations of the rams. This is done by
having the piston e operated by the piston rod /, which
passes through a supplementary or hollow rod g, and
has an appropriate handle for operating the piston
within the pump cylinder. By these means the piston
may be quickly reciprocated by the user moving the
small handle until the desired quantity of water has
been supplied, or until the pressure to be exerted over

* From a paper read before the Society of Engineers.

the rod / is beyond the power of the user, when the
supplementary rod g may be brought into use to finish
the operation, this advancing by screw motion, and
great pressure being obtainable in this way.

After the rock or coal has been prepared with one or
more loose sides, and the drill hole of 3 in., 3|in., or
4| in., has been drilled to a suitable depth (say three or
more feet), the cartridge is pushed in with liners if
necessary. The water tank is filled and hung on the
pipe, the rubber suction pipe coupled, and the taps
turned. The small handle and then the large one are
operated as already described. The pressure being fully
on, the enormous power of the apparatus is soon appa-
rent, for the rock or coal is heard to be rumbling and
cracking. This is allowed to continue until the breaks
are of such a size that the mass can be pushed or pulled
over, and usually is in such condition as to be easily
and safely handled.

It is easy to understand that when a shot is fired in
rock or concrete, the direction of the breakage will be
chiefly in the line of the weakest part. If the material
is of uniform strength this direction would be a straight
line from the explosive to the nearest unsupported edge.
But stratified beds, seams of coal, and walls of stone or

Fig. 2.—Section of Piston and Plate.

jSSxXXXXXXXXXXXX	;

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Fig I.—Sectional Elevation of the Hydraulic Mining Caririige.

brick are not usually of uniform strength; rock and coal
beds contain breaks, cleats, and faces, while concrete
beds are invariably irregular in constitution or -struc-
ture. It follows, therefore, that the line of least resist-
ance is not necessarily the shortest line from the charge
to the surface. The difficulty and danger of explosive
firing is that whatever this line may be, it is not often
possible to make use of it; the pressure generated,
though not equally effective, is equally applied in all
directions owing to the instantaneous character of the
decomposition. This involves high temperature in the
explosive gases, a large portion of the heat being
absorbed and wasted in the portions which are not
capable of being blown down. When mechanical means
are employed the time involved in the operation allows
the whole of the power to be exerted and applied in the
desired direction without waste of heat energy. Not
only is power lost in heat energy in the case of explo-
sive compounds, but the result often proves that there
has been counter action whereby the rock displacement
is reduced through one line of force operating against
another, closing in or reducing the area of broken
ground.

In practice it is found possible so to arrange the
hydraulic cartridge holes as to enable much greater areas
of material to be moved than could be done with a safe
quantity of explosive, while in some cases the displace-
ment has been greatly extended by the use of small-sized
boreholes towards which the slowly developing line of
least resistance can assert itself. In other words, the
power exerted by the rams can be controlled, after a
little experience, so that the full pressure can be use-
fully applied.

Use in Miies.

The appliance was originally introduced into mines
in order to supply the acknowledged need of a different
method for bringing down coal in mines in the best pos-
sible condition after it had been undercut by hand or
machine. The use of high explosives for this purpose,
apart from the element of danger, has always been
considered undesirable by mining experts, because in
using them coal is shattered and wasted and dust made.
Now that coal has to be won from greater depths than
formerly, and the distances and areas underground
increase, the dangers and extent of explosion have pro-
portionately increased, as many recent colliery disasters
bave shown. The mines in which the cartridge has
been chiefly adopted may be divided into two classes :—■

(a)	Where the coal is so friable as to render the use
of explosives impossible for commercial reasons.

(b)	Where the condition of the mines in regard to
gas, etc., render shot-firing an exceedingly dangerous
proceeding.

Of course the question of cost enters very largely into
the matter. As is usually the ease when a new appli-
ance is introduced, its qualities are quickly estimated
from the effects upon the working expenses. At a later
stage it will be seen that its effect upon the working
cost is slight, whilst its general advantageous effect
upon the selling price of the coal is quite striking. Dur-
ing the past 10, years the appliance has been employed
in mines in Great Britain, the United States, Russia,
Japan, Germany, and Austria.

In removing coal a series of holes is drilled in the top
of the seam, adjoining and running parallel with the
roof. These holes are at intervals determined by work-
ing conditions, usually from 6 ft. to 10 ft. apart, and

from 3 ft. to 5 ft. deep. The operator begins at the first
hole, and pumps off each in succession, usually leaving
the supporting sprags to be removed by the collier., who
fills .the coal thus broken, and prepares the coal behind
for a repetition of this process. One operator can
pump from 30 to 40 shots per working shift of eight
hours, using only one machine, which lasts with repairs
from three to four years. This procedure is adopted
where a large wall of coal has been opened out, and
where the coal is got in pillars and headings the process
is somewhat modified. The coal across the face of the
heading is undercut (almost universally now by a per-
cussive machine operating from a fixed standard) and a
vertical slot or “ shearing ” is cut up the centre of the
coal, thus providing a loose end. One hole on each side
of the 11 shear ” is then sufficient to bring down the coal.
The holes are placed as near as practicable to the fast
side in order to bring the coal down as near the “ fast
corner ” as possible. (Fig. 3 shows the cartridge in use
in mines).

Among the mines in ■which these machines are at
present in use are the following :—

Colliery No. 1.—At this colliery an average of over
1,000 explosive shots per week -were formerly fired in

coal in the various mines. By the introduction of the
hydraulic cartridge the whole of the explosive shots
have been discarded, and there is not now a single shot
in coal in any seam. In one seam alone a total of
28,500 hydraulic cartridge thrusts were made in one
year, by which it is estimated that 92,626 tons of coal
were produced, or about 3} tons per thrust. The seam
was 3 ft. thick, and four cartridges were in daily use.

Colliery No. 2.—In a seam using five hydraulic cart-
ridges 450 .tons of coal are produced per day, of which
75 per cent, is large coal, and 25 per cent, small.
When the coal in this seam was brought down by explo-
sives the percentage of large coal was 65 per cent., and
the percentage of small was 35 per cent. The average
price of large coal was 13s., and of small coal 7s. per
ton. The profit obtained by the use of the cartridges
on this seam on 450 tons is therefore 4114 5s. per day.
Fifteen machines are employed at this colliery, making
a total advantage over explosives of £42 15s. per day.

Fig. 3.—Hydraulic Cartridge in use in Coal.



Moreover, an extra 6d. per ton is obtained for the coal
brought down with hydraulic cartridges, on account of
its greater hardness and freedom from dust.

Use in Reservoirs, Docks, Harbours, and Canals.

The operations in these places have all certain features
in Common which allow of their being classed together,
and they may be divided into three classes :—

(a)	In Open Trenches. — The introduction of the
hydraulic cartridge into this class of work will, it is
hoped, help to solve this question. During the past
few years it has been thoroughly tested under most
varied conditions and in all classes of deposits. Work
of this character has been done by the cartridge in con-
nection with the Derwent Valley Waterworks and the
Cwm Taff Reservoir, Liverpool Corporation, and tests
are now being made for the Abertillery water scheme.

(b)	Under Water.—The appliance has been used in
many cases under water, chiefly to remove rock, either
from the sides of canals, or from the sides of harbours
and docks, where it was obviously impossible to use
explosives, the machine being operated from the bank or
from pontoons. In the Alexandra Docks at Newport,
and in the new dock at Swansea, the appliance has been
used to break up ledges of rock occurring in the vicinity
of walls which would have been damaged by the use of
explosives. The holes were put in and the cartridges
inserted under water by divers, and pressure was applied
from the pump placed on a raft on the water.