1336

THE COLLIERY GUARDIAN

December 31, 1915.

Prevention of Coal Dust.

The provisions under this head are, from the point of
view of safety, amongst the most important and far-
reaching of the Act; and much more attention is given
to dealing with accumulations of coal dust. At many
mines, however, much remains to be done.

The Explosives in Mines Committee presented its
Sixth, and on the main question, its Final Report in
September 1914. They summarise the general con-
clusions of their enquiry as follow :—The experiments
which have been carried on at Eskmeals during the past
three years, and the results of which have been set out
in the six reports submitted by us, establish, so far
as experiments can, that : (1) The maintenance through-
out the roads of such a proportion of incombustible dust
in a state of fine division as would make a mixture
yielding on incineration at least 50 per cent, of ash; or
(2) the maintenance of at least 30 per cent, of water in
a state of intimate mixture with the dust throughout the
roads; or (3) a combination of the two previous methods,
i.e., the treatment of the roads first with incombustible
dust and then with water, would prove effective in very
greatly minimising, if not preventing, explosions of coal
dust.

The experimental work initiated by the Committee is
now completed, but arrangements have been made for
further work to be carried out at Eskmeals in connection
with this and other mining questions under the direction
of the Home Office. Work of an interesting and valu-
able character has been done, as to which Dr. Wheeler
has furnished the following brief account :—

The problems chosen for examination at the Experi-
mental Station have been such as could most satis-
factorily be carried out by the reduced staff which the
need for considerable curtailment of the expense of the
station, imposed by the war, has necessitated. The
further study of the conditions ’affecting the ignition of
coal dust and the propagation of flame in mixtures of
coal dust and air has for this reason been somewhat
handicapped.

Considerable progress has been made in the investiga-
tion of the manner of propagation of flame in firedamp-
air mixtures, revising the work of Mallard and Lo
Chatelier, an adequate supply of natural firedamp (con-
taining 98 per cent, methane) having been procured.
The speed of the “ uniform movement ” of flame, which
movement marks the first stage in the propagation of
flame under 'certain conditions, has been found to depend
largely upon the diameter of the tube or gallery in which
the mixture is contained, the speed for a given mixture
being more than half as great again in a 3-ft. as in a
1-ft. diameter tube. The limiting conditions under
which flame can be conveyed for a short distance
upwards or horizontally in a mixture of firedamp and
air (at rest or moving), ordinarily incapable of com-
pletely propagating flame, have also been determined.
I hope shortly to present a detailed report on these and
other investigations regarding explosions of firedamp
and air.

The study of the conditions necessary for safety and
efficiency in underground signalling has been continued.
Different forms of battery-bells have been examined, and
the use of relays and of alternating-current bells has been

mine air and dust samples have been made. The total
number of samples of mine air (which are now being
received from all Divisions) analysed up to the end of
the half-year, was 1,550.

THE “HARDIAX” COAL CUTTER.

By T. Campbell Futers, M.I.M.E.

We recently had an opportunity of seeing at work in
a 20 in. seam the new compressed-air driven coal cutter
manufactured by the Hardy Patent Pick Company
Limited, and named by them the “ Hardiax.” It is
of the percussive type, as will be seen from fig. 1, which
gives a general view of the machine mounted upon its
stand.

The new machine is built entirely of steel, the
cylinder, valve box, cradle, and gears being of a special
crucible cast steel, the outcome of some years of exhaus-
tive and costly experimenting. The valve and main
piston are hardened and ground. The standard is a solid
drawn steel tube, provided with a powerful screw-jack
and a toothed head and foot. The machine is seated in
a cone cup, forming part of the hinged clamp attached
loosely to the standard, and this clamp carries the worm
which gears with the worm wheel bolted rigidly to the

w'i'i

in. ■

Fig. 1.—Hardy Patent Pick Company’s “Hardiax” Coal-cutter.



the port B, through the diagonal port D in the collar, at
the right-hand end of the valve. As soon as the main
piston passes the port F, the air flows through this port
from the cylinder into the space between the two collars
on the left-hand end of the valve, and through the port
D1, to the end of the valve chamber, thus equalising the
air pressure at both ends of the valve. The collar Z is
larger in diameter than the other collars, hence the valve
moves over from left to right under the pressure acting
upon the larger area of the collar Z. A similar operation
takes places on the inward stroke of the piston. The
exhaust is at E, which is covered by a cap, as shown in
fig. 2, adapted to be turned round to direct the exhaust
in any required position. The valve is extremely simple
in construction, and rapid in action. Furthermore, the
valve box is bushed to receive it, and consequently the
renewal of the valve ports is particularly easy. Experi-
ence—and some of these machines, we understand, have
been at work for a period of 1| years without any repairs
being required—has shown that the wear is almost a
negligible quantity, and that “ short stroking,”
“ fluttering,” and other faults in coal cutters of this
kind are entirely eliminated by the use of this valve in
conjunction with the correct proportioning of the air
ports and passages.

The machine we saw at work was cutting in a seam
20 in. thick, and was operated by two youths of 18 and

Figs. 2 and 3.—“Hardiax” Coal-cutter (Section and Plan).

B
L D

Fig. 4.—“Hardiax” Coal-cutter (Section through Valve).

investigated. In this work I have had the advantage of
the co-operation of Prof. W. M. Thornton, D.Sc., of
Armstrong College, Newcastle-on-Tyne. A report on
the subject is in course of preparation.

Laboratory experiments regarding the spontaneous
combustion of coal have been carried out with a view
to determine the nature of the reactions that take place
when coal “ self heats.” The results will be laid before
the Spontaneous Combustion Committee.

A useful experiment has been the enlistment as
voluntary workers at the Experimental Station during
their summer vacation, of a party of six post-graduate
students of Prof. W. A. Bone, D.Sc., F.R.S., of the
Imperial College of Science. Each was of considerable
assistance in carrying out special investigations. In
particular I may mention Mr. S. G. Sastry, M.A., who
studied the electrical ignition of gaseous mixtures, and
Mr. L. H. Howlett, B.Sc., who, with Mr. W. E. King,
B.Sc., studied the mechanical efficiency of trembler
signalling bells. Mr. T. Otagawa, of Tohoku Imperial
University, Japan, also spent two months at the
Experimental Station, and conducted a useful series of
experiments on the propagation of flame in gaseous
mixtures.

In addition to the research work of the station, some
of which has been outlined above, routine analyses of

standard or column. Hence, by turning the worm
handle, the coal cutter moves easily round the column,
whilst the forward movement of the cylinder supported
in the cradle is obtained by the feed screw and handle
shown at the back of the cradle. The machine may be
fixed on the column so as to cut at any height between
the floor and roof. It cuts an arc-shaped channel or
undercut, increasing in depth and width as longer cutter
bars are fitted to the machine, until the requisite depth
of undercut is reached, after which the operator com-
mences to square out the corners by using different
lengths of cutter bars and short sweeps of the machine.
By this means cuts up to, say, 20 ft. wide and 4 ft. or
4 ft. 6 in. in depth may be obtained at one setting of
the machine. The height of the cut varies from 3| in.
to 4| in.

Figs. 2 and 3 show the machine in plan and section,
from which an idea of its construction will be obtained.
The chief feature, however, is the patented valve work-
ing in the valve box, which is secured to the cylinder by
the four bolts shown in the plan. This valve is shown
in the enlarged section, fig. 4, from which its mode of
working will be better understood. Air is admitted from
the side of the valve box to the ports B and B‘, and
the valve is held in the position shown, which is for the
forward stroke of the main piston, by air flowing from

16 years of age. In 23 minutes from starting to cut
they had undercut, to a depth of 3 ft., an arc of a circle,
the chord of which was 13 ft. in length. This time
included changing the picks. The working air pressure
at the machine was approximately 45 lb. The
elder youth, however, who was driving the machine, was
not satisfied with the result, and said that, when the air
pressure was good, they could make the first cut in
much quicker time than they had done on the morning
of our inspection. In the hands of expert drivers, with
an air pressure of 45 to 50 lb. per sq. in., an average
cutting speed of 133| sq. ft. per hour has been attained
on a longwall face. In a seam 3 ft. thick, and a total
length of face of 47 yds., with a 5 ft. undercut, a total of
705 sq. ft. was cut in 7 hours 53 minutes. On another
occasion six bords were cut, 18 ft. wide by 4 ft. deep, in
6 hours 18 minutes, including all stoppages for changing
cutters, cleaning cuts, meal times, etc. In the latter
case the air pressure was 55 to 60 lb. per sq. in.

These machines are made in three sizes :—(1) Type
“ X ” is a light, specially designed machine for both
undercutting and shearing, that is to say, both for hori-
zontal undercutting and vertical shearing or “ nicking,”
and is very suitable for heading work where explosives
are not permissible. (2) Medium type “ Y,” weighing
about 2351b., is designed for bord and pillar workings