1266

THE COLLIERY GUARDIAN

December 29, 1916.

REFRACTORY MATERIALS.

In the course of the discussion at the meeting of the
Faraday Society last week (Colliery Guardian, Nov. 10,
p. 906), Prof. W. G. Fearnsides expressed the opinion
that while there was a lack of scientific data to help
makers of refractory materials, there was among the
foremen brickmakers and the furnacemen who handled
the material, raw and manufactured, a great deal of
information which only needed to be collected, codified,
and interpreted to make it as scientific as the best
laboratory product. One of the most pressing needs
was for scientific workers to go through the works,
both of the makers and the users, and listen while
practical men gave information in terms which were
the language of the brickyard and the foundry. A
great deal might also be accomplished if makers and
users would meet together and face each other’s diffi-
culties. At its best, the art of making refractory
materials was in advance of the science, but the prac-
tice of the art by unskilled workers left much to be
desired, and it was certain that from a scientific study
of the craftsman’s methods would come experience, in
the light of which reputative practice might be scien-
tifically controlled. He also dealt with the applica-
tion of petrographic methods to the study of refractory
materials.

Works Test for “ Green ” Material.

Dr. R. Lessing showed a series of specimens illus-
trating a method of testing he had devised for ascer-
taining the texture and rational composition of
refractory mixtures before firing. The method con-
sists of a simple process of elutriation, by which the
true clay substance of the 44 green ” clay is removed by
a gentle current of water, and separated from the water
by allowing it to settle out on standing. The rate of
flow of water is so adjusted that the 44 grog,” and also
the heavy and coarse grain residue of the 44 green ”
clay, consisting of sand, shale, or carbonaceous sub-
stances, are left behind in the elutriating vessel.
Elutriation is continued until the water becomes per-
fectly clear, with the lightest portions of the residue
floating just below the outlet. A simple form of
apparatus accurate enough for works purposes consists
of a tall glass cylinder, into which the water is passed
through a glass tube reaching nearly to the bottom.
The cylinder is placed in a bucket, into which the clay
suspension overflows, and to which the clear water is
siphoned oft after settling. For the purpose of the
test, about 500 grms. of the sample are well soaked in
water, and washed into the cylinder. The products
(clay and residue) are dried, and a grading test is then
performed on the residue, from which the texture of
the body and the ratio of 44 grog,” granular clay, shale,
and coal can be ascertained. The specimen products
obtained from retort and firebrick mixtures from the
Stourbridge and Glenboig districts, showed that before
the standard specification was adopted, mixtures for
gas retorts contained very little 44 grog,” which had,
moreover, suffered largely from excessive crushing,
yielding dust, whilst the “green” clay serving as
binder had largely remained in the form of coarse
granules, instead of being reduced to fine powder. The
change in manufacturing methods by which the “ grog ”
is crushed and graded separately, and the powdered
44 green ” clay mixed with it, were shown by specimens
taken after the adoption of the standard specification.
For comparison, a sample of a German retort mixture
was shown, which was remarkable for its large propor-
tion and size of “ grog,” viz., 66 per cent., as against
about 35 per cent, total 44 grog ” in English retorts;
21-4 per cent, out of the 66 per cent, of 44 grog ” was
larger than -J-in., and 38-4 per cent, larger than Jin.
The mixture was noticeable for the total absence of
clay residue, shale, or coal, indicating that the binding
clay had undergone some preliminary purification.

Dr. H. G. Colman gave an account of the work of the
Refractory Materials Committee of the Institution of
Gas Engineers and the Society of British Gas Indus-
tries, in drawing up standard specifications and tests
for the various classes of refractory material commonly
used in gas works, and the carrying out, as far as
means allowed, of research work on the subject. The
effects of load on refractoriness was now being investi-
gated by Dr. Mellor, using bricks whose life history was
known, which knowledge was absolutely necessary, and
could not be secured in the case of bricks obtained in
the open market. Other investigations were in pro-
gress or under consideration on the determination of
the difference in size of bricks when cold and when at a
high temperature, i.e., the combined effect of the
thermal expansion and the permanent expansion and
contraction; the cement material employed in retort
settings, and the influence of the addition thereto of
varying proportions of fine 44 grog the relative effects
of oxidising and reducing atmospheres on the refractori-
ness and permanent expansion or contraction of refrac-
tory goods; the influence of fine flue dust carried into
the settings on the refractoriness and life of the
materials employed; the effect of admixture of highly
siliceous rock (such as ganister) on the working qualities
of fireclay goods; and the effect of firing temperature on
the subsequent refractory qualities of the goods.

Work of the Geological Survey.

Mr. J. Allen Howe spoke of the recent work of the
Geological Survey on refractory materials. He said that
when war broke out, Dr. Strahan organised a survey to
locate the sources of the raw refractory materials in this
country. Arrangements were being made for testing
the physical properties of refractory materials, and these
would be incorporated in the report. For the first time
in this country, there would be a publication dealing at
first hand with all its refractory materials. The pre-
paring, blending, and firing of the materials were out-
side the sc^pe of the enquiry, but others would know

how this work should be organised and placed upon its
feet.

Mr. T. Crook, assistant superintendent in the scien-
tific and technical department of the Imperial
Institute, gave the assurance that the British Empire
contained within its boundaries an abundance of all the
minerals we required. The Empire was well provided
with refractories, and in this connection he mentioned
that should a demand for zirconia arise, it could be
provided in large quantities as a by-product from the
working of the Travancore monazite sands.

Mr. Cosmo Johns, speaking of silica as a refractory
material, said that in the manipulation of this material
competent workmen were very necessary. Dinas bricks,
which came from his native Welsh valley, had set a
standard to the world in this material. If the manu-
facturers of firebricks and the makers of steel could be
persuaded to work harmoniously, much might be
achieved.

Mr. W. J. Jones and Mr. McDougall Duckham, of
the Ministry of Munitions, urged closer co-operation
between brick makers and users. Mr. Jones, speaking
of coke oven bricks, said there was a wide field for
science to co-operate with practice, because the coke
oven brickmakers did not possess the necessary know-
ledge to enable them to vary the composition of their
quartzite bricks so as to meet the varying conditions
they had to comply with in regard to the different
qualities and chemical composition of the coals used.
Mr. Duckham said they had the materials in this
country and the brains to say how the materials should
be treated, and all that was wanted was co-ordination.

Dr. P. G. H. Boswell said the ultimate test of
refractories must be in the works themselves. Silica
had previously been imported, but there were abundant
supplies in this country. The number of men working
on refractory materials was enormous, and there was
no means of linking them up. It would be a great
advantage if, as a result of that meeting, there was a
general union of the workers in this line of research. A
great deal of overlapping would be saved.

Dr. W. C. Hancock said that he was engaged at the
Imperial College of Science, under the direction of Prof.
Bone, in an investigation on the behaviour of bricks in
coke oven practice. He was in close touch with the
builders of coke ovens, and also with many of the lead-
ing manufacturers of oven materials, as it was only in
that way that results could be achieved.

The President, in closing the discussion, said this
subject was of vital importance to the nation, and the
question was how it was to be pushed home in a
practical way. He suggested, as one means, that the
papers read should be repeated locally, in the districts
most interested.

SPRINKLING CAR FOR MINE USE.*

By F. F. Jorgensen.

The ordinary type of sprinkling car used in mines is
a wooden tank mounted on trucks, the tank having a
large hole in one end at the bottom. Before filling the
tank, a wooden plug is driven into this hole; and when
the car reaches the piece of road to be sprinkled, the
plug is removed. None of the dust except that between
the rails is reached by the water, and that part is
thoroughly soaked. This dust is usually not very
harmful, for it is pretty well mixed with shale dust.

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SIDE AND REAR ELEVATION OF SPRINKLER

The dangerous dust, of course, is on the ribs and
timbers; and to reach this the sprinkler described in the
following paragraphs was devised.

The device consists of a two-compartment steel tank
mounted on trucks to run on track of any gauge. The
tank, as shown in the accompanying drawing, is
equipped with two valves H and G, and two short
lengths of hose, each having a quick connection coupling
numbered 1 and 2. The tank is also equipped with a
valve I at the rear, to which is attached the pipe con-
nections 3. These connections are drilled in such a
manner as to make a spray when water is forced
through them.

Where the valves H and I are connected to the tank,
a pipe connection on the inside runs close to the bottom
of the tank. Two pressure gauges C and D are con-
nected to the tank, one in each compartment. The tank
is also equipped with a pressure reducing valve E and a
check valve F, which are connected to the tank by
means of pipe and pipe connections 4 and 5. These con-
nections are located on opposite sides of the partition
that divides the tank into the two air- and watertight
compartments A and B. Compartment B is equipped
with a manhead to make it accessible for cleaning out
and repair purposes.

The operation of the sprinkling tank car is as follows :
Hose 1 is connected to a compressed air supply line, and
the valve on the supply line and the valve G are opened,
admitting compressed air into compartment A. When

* Coal Age.

the pressure in compartment A rises above the limit set
by the reducing valve E, compressed air begins to flow
through pipe connection 4, reducing valve E and pipe
connection 5 into compartment B. When the pressure
in compartment B reaches the limit set by the pressure
reducing valve E, the valve in the supply line and the
valve C are closed, and the quick connection 1 is
uncoupled. The limit set by the pressure reducing
valve may be anything desired, from zero up to the
maximum pressure available in the supply line.

Connection is then made at 2 with the water supply
line. The valve in the water supply line and the valve
H are opened, and water is admitted to compartment B.
This water must be under great enough pressure to flow
against the pressure in the tank. As the water flows
into compartment B, the air in this compartment is
compressed and the pressure rises. When this pressure
exceeds the pressure in compartment A, the air starts to
flow from compartment B, through connection 4, check
valve F, and pipe connection 5, into compartment A.
When compartment B has filled with water, the valve
in the supply line and valve H are closed, and connec-
tion 2 is uncoupled. The order of filling with air and
water may be reversed; that is, compartment B may be
filled with water first, and then compartment A filled
with compressed air; but in this case the pressure of
the compressed air supply must be higher than in the
first order of filling.

The tank is now ready to begin sprinkling. Both
compartments A and B have the same pressure, but as
soon as valve I is opened the pressure in compartment
B drops to the pressure at which the pressure reducing
valve E is set. The air continues to pass from com-
partment A, through the pressure reducing valve E, into
compartment B, maintaining a constant pressure over
the water in compartment B until the water in that
compartment is forced out through sprinkler connection
3. The sprinkler 3 is so made and connected that the
spray of water may be directed against the roof and
sides of an entry, or in any other direction.

Any water getting over into the air compartment A
when filling compartment B with water may be blown
out through connection 1 by opening valve G.

The sprinkler may also be used for fire fighting pur-
poses, or any other purpose where water may be needed,
by connecting the desired length of hose to connection 2
and opening the valve H.

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MECHANICAL COAL CUTTING.

With every year the question of coal cutting by
machinery obtains a greater amount of attention, and
mining engineers are more and more disposed to examine
the now generally accepted economic advantages result-
ing from the employment of coal cutters. It has been
established that, when the coal seams and other con-
ditions are favourable, the output per man may be
greatly increased by the use of these machines, and the
cost of production is appreciably reduced: also that an
increased value of output per ton may be obtained. The
proportion of round coal, which increases the coal value,
has also been raised, whilst greater safety is ensured to
the miners. In one colliery, the proportion of serious
accidents declined from one per 77,000 tons of coal got
when the coal was hand worked to one for every 450,000
tons of output after the introduction of machines.

It is admitted that in some
seams the machines have not
given good results, and in other
cases it has been regarded as use-
less to take them down the shafts.
This is notoriously the case in
the South Wales colliery districts,
including the Cardiff and Swansea
areas. The aggregate coal output
of these districts is a very large
one, but the quantity obtained by
machinery is only about 1 per
cent. Two of the probable reasons
for coal cutters not being suitable
for the local conditions in South
Wales are : the comparatively
little holing required, and the
fact that the roofs are of such a nature as to
necessitate very close propping for safety. Many
of the seams worked for many years are thick, whilst
the 44 slips,” or lines of cleavage, occur with such regu-
larity that there is not much labour required in work-
ing the coal. The number of coal-cutting machines
increases as thin seams are more extensively opened out,
especially in those districts where the production of the
highest percentage of large coal is of importance.

Fifteen years ago, only one ton of coal out of every
50 was machine mined: in 1906, it rose to one ton out
of every 25; whilst now, it approximates to 10 per cent,
of the whole output of Great Britain. In the United
States it is about 50 per cent, of the total production.
As coal-cutting machinery was introduced into this
country about 50 years ago, the progress made has there-
fore not been rapid. The adoption of this class of
machinery was probably retarded by the inferior design
and capabilities of the earlier machines, and also by the
prejudice of the miners. The thicker and better seams
were being worked, and it is in these that coal-cutting
machines give less favourable results. Moreover,
manual labour was cheaper than it is now. An expert
once asserted that the introduction of coal-cutting
machines into a coal mine was a big innovation, requir-
ing for its success careful thought, hard work, and
strong determination on the part of the management,
combined with a reasonable and willing disposition on
the part of the men.

The following table gives particulars of the growth in