July 17, 1914.

THE COLLIERY GUARDIAN.

141

car is arranged on the same shaft in the same manner.
Between the sprocket wheel B and the gear wheel C the
shaft is provided with a claw clutch D, which, when
travelling, is engaged with gear wheel, and when charg-
ing, with sprocket wheel. On the shaft A, on the opposite
side of the machine, a corresponding sprocket wheel E is
keyed, and both sprocket wheels are connected together
by means of a Renold chain, which passes between two
hoppers. Opposite each hopper the shaft A carries an
excenter G, the rod H of which reaches through a corres-
ponding slot into the lower part of each hopper. Each
excenter rod H is, just before entering the hopper, sus-
pended by a loose link I, and on its end inside the hoppers
carries a few irons generally screwed or riveted together
like a triangle K. While charging, the clutch D is dis-
engaged by reversing a lever from the travelling gear 0,
and engages with the sprocket wheel B, and drives the
shaft A by means of the chain F. The excenters G, H,
move the stirrer not only backward and forward, but,
by the suspension of the excenter rod from the link I,
the rod is also lifted up and down, so that the stirrers K
make elliptical movements. The stirring is thus very
efficient, and the hoppers are emptied without any
manual labour in a very short time. Instead of the
chain drive the excenter shaft can also be arranged to be
driven by a small separate motor.

While the stirring arrangement in the car fig. 11 is
moved by the excenter rods entering the hoppers through
slots, the stirring arrangement shown in fig. 12 made by
the Schalker Eisenhiitte, Gelsenkirchen, Germany, is
operated from the top. The arrangement is worked, as
in the previously described machine, by means of a claw
clutch, which either engages with the travelling gear or
with its other side with the stirring gear. This consists
of a strong excenter shaft A, which is fastened under-
neath the girder frame on the same side of the machine

J

4

*

ii

1

Fig. 9.

as the motor and the gear wheels. The excenter arm B
reaches to the other side of the machine between two
hoppers, and is connected to a lever C, which is keyed to
the shaft D. This shaft holds two levers E, which, by
means of two connecting rods, transmit their movement
by corresponding levers F to two shafts G in the top of
the hoppers. On each end of these shafts a horizontal
lever H is keyed, and from their ends, which are exactly
in the centre of each hopper, the vertical stirring rods I
are loosely suspended and carry on the bottom, in the
two middle hoppers, a cross K, and in the outside hoppers
two wings L so as to obtain a stirring action over the
whole area of the hopper outlets. The action of the
stirrers is understood easily from the above description,
and hardly requires any further explanation.

(To be continued.')

The North Staffordshire Institute of Mining and
Mechanical Engineers.—An excursion has been arranged to
the Stafford works of Messrs. Siemens Brothers on Monday,
July 20,

Hull Coal Exports.—The official return of the exports of
coal from Hull for the week ending Tuesday, July 7, is as
follows :—Antwerp, 262 tons; Abo, 56; Amsterdam, 517;
Algiers, 912; Alderney, 122; Assens, 2,057; Bona, 609;
Bergen, 165; Bremen, 976; Christiansund, 1,005; Cronstadt,
57,678; Copenhagen, 420; Drontheim, 272; Dunkirk, 200;
Danzig, 517: Flekkefjord, 125; Gefle, 1,620; Ghent, 732;
Hamburg, 8,239; Harlingen, 1,284; Helsingfors, 99; Heligo-
land, 184; Kristinestad, 218; Larvik, 430; Malmo, 1,737;
Newfairwater, 235; Novorossisk, 3,003; Oran, 501; Oporto,
618; Pernau, 3,971; Porsgrund, 407; Rotterdam, 5,591;
Rendsburg. 198; Reval, 4,444: Rouen, 2,290: Riga, 4,967;
Stettin, 2,831; Sark, 314; Sundswall, 1,850; St. Petersburg,
5.514; Stockholm, 1,204; Trieste, 405; Trelleborg, 1,738;
Victoria, 1,027; Wyborg, 3,859; Wasa, 204; Wyk, 129;
Ystad, 2,475—total, 126,211 tons. Corresponding period
last year, 90,901 tons.

Barriers for Arresting Coal Dust Explosions.

AMERICAN EXPERIMENTS.

In an article appearing in the Black Diamond, of
Chicago, Messrs. George S. Rice and L. M. Jones, of the
United States Bureau of Mines, give a description of
an interesting test, carried out at the Bruceton Mine,
during the recent visit of the Mine Inspectors’ Institute
of America.

The purposes of the experiment were several. The
most important was to determine the efficiency of
various forms of rock dust barriers in stopping the
propagation of a dust explosion. Another feature was
the employment of a strong ventilating current prior to
and at the time the explosion was started. The main
entry was the intake and the aircourse the return. The
loading of coal dust in the two entries was made as
nearly alike as possible, and since the igniting shot was
fired in an offset at the middle of the inmost break-
through, the conditions in the two entries were identical,
except for the air current intaking on one and returning
on the other entry.

Details of Test.

The explosion was caused by a blown-out shot of 4 lb.
of FFF black powder, tamped with 3 lb. of clay stem-
ming, discharged from a cannon at the face of a 20 ft.
offset, on the north side of the 1250 cut-through, equi-
distant from entry and aircourse. The offset and 1250
cut-through were loaded with pure coal dust; that is,
coal dust not mixed with other dust. The distance from
the cannon through the cut-through to the centre of
either entry was about 50 ft. From opposite the 1250



cut-through, the entry and aircourse was each loaded
on sides and cross shelves with a mixture of 60 per cent,
coal dust and 40 per cent, shale dust, at a rate of 3-J- lb.
per ft. The amount of coal dust per foot of entry way
was 2 lb., which is equivalent to about loz. per cu. ft.
of entry space. This loading extended for 550 ft. out
by the cut-through. The mixture had an ash percentage
of about 38 to 40 per cent.

At the end of this zone on the entry there was
installed a Rice concentrated barrier loaded with 2| tons
of rock dust. The principal features of the barrier are
as follows :—It has two hinged platforms, 7 ft. by 7 ft.
by 1 ft. deep, near the roof of the entry. The floor
plank of the platforms are not attached to the side
boards, which are fastened to timber cross bars, but are
hinged at one end of the cross bar of a timber set
between the platforms. The other ends of the planks
of each platform are supported by an angle iron, which
in turn is held up by one of a system of levers. There
are vanes hung from the roof 100 ft. distant inbye and
outbye the barrier, so arranged that when an explosion
wave causes one to swing, the movement is reversed by
a pulley and chain and a pull transmitted by wire to a
trigger which trips a system of levers causing the drop-
ping of the angle irons supporting one end of each
platform. Alternate planks then fall about 9 or 18 in.
depending on the length of chains fastened to them
and an overhead timber or to the roof, the side frame
of each platform, however, being still held up in
position. On release, the dust, which had been placed
on the platforms, falls from the planks in a shower in
the entry, blanketing the flame of the explosion when
it reaches the barrier. Should the advance vane
operating arrangement fail, another vane near the
barrier, by means of a hinged bumping block attached
to it, pushes the trigger, causing the operation of the
barriers.

At the end of the mixed dust zone on the aireourse
were installed a set of six Rice box barriers, spaced 10 ft.
centre to centre, each containing about 600 to 700 lb.
of crushed shale dust. These boxes are 7 ft. long, 21 in.
wide inside and 9 in. deep. The boxes are built so that
two bottom boards rest upon narrow bottom strips
fastened to the box frame. The box frame is supported
by four eye bars, the eyes resting on hooks projecting
from the roof. When the explosion wave reaches the
box, it causes the latter to swing in the direction the
explosion wave is travelling until the side of the box
knocks two hanging bars off the hooks, whereupon the
frame falls, pivoting*about the supporting hooks on the
other side of the box, to which the other two eye bars
are still attached. The bottom boards do not fall with

Taffan*! barrier

Pur* coal dust

Flame

3J

j ~Taffanel barrier

» £250

J £450

3 £350

£50

E 150

£1050

E850

E1150

E950

E650

E550

lock dust stopping

■ier

Mixed dust
40%shale & 60% cool

U

Rice box^-
barrier

E75O

.Rice concentrated

n 1303

11 .

Fig. 1.—Plan of Experimental Mine,
showing Details of Experiments.

The course of the flame is depicted by the jagged line.

the box frame, but drop a few inches when they are
caught by supporting chains. More or less of the dust
on these shelves either falls off as they swing or is blown
off by the explosion wave. With a light preliminary
wave, considerable dust may remain on the shelves,
which is a measure of protection against a following
explosion wave.

Outbye both the concentrated barrier and the box
barriers were placed 200 ft. zones of pure or unmixed
coal dust to furnish fuel for continued propagation of
the explosion, should it get through the stopping
devices; in other words to determine if the latter were
efficient. At the end of these coal dust zones were
'placed Taffanel barriers to check the explosion should
the coal dust become ignited.

Across the mouth of the first right butt was built a
rock dust stopping, which consisted of board sides with
a compartment between them, 18 in. wide, filled with
2| tons of shale dust. The sides were braced just
sufficiently to withstand the pressure of the dust filling,
but not enough to give much additional strength. Coal
dust was placed for 10 ft. inbye the stopping to test its
efficiency. In the first and second left butts, 15 ft. in
from the aircourse, were built rock dust protected
ventilating doors. These doors had compartments at
each side and above them containing rock dust. The
door frame held the boards of the compartments in
place. When an explosion wave struck the door, the
frame not being strongly braced, would tend to become
displaced and the rock dust would be launched into the
entry. The door in No. 2 butt opened outward, while
that one in No. 1 butt opened inward. Unmixed coal
dust was distributed in both butts to determine the
efficiency of the stopping devices. To obtain symmetri-
cal conditions in the aircourse and entry, no door or
curtain was placed across the aireourse between the
butts.

An air current with a velocity of about 850 ft. per
minute was intaking on the main entry and returning on
the aircourse. It was thought that the symmetrical
loading on entry and aircourse would permit a good
comparison of the effect of the high velocity of air
current travelling with and against the explosion. This
velocity gave a volume of 46,000 cu. ft. per minute.

The mine was very wet throughout. The bottom was
muddy in places, while the packed clay floor throughout
was slightly sticky. The roof had beads of moisture
on it.

Recording pressure manometers were placed in
stations E-1150, 750, 550, A-1150, 750, and 550. Flame
circuit breakers were placed at all stations in the mixed
dust zone and others at intervals outbye. Wires were
connected to the stopping devices, terminating the