992

THE COLLIERY GUARDIAN

May 26, 1916.

STONE OUSTING BY MACHINERY.*

The Federal Bureau of Mines has made a large number
of explosion tests at the experimental mine at Experi-
ment, Pennsylvania, to determine the efficiency of stone
dust in preventing the initiation of mine explosions, as
well as in checking their propagation. The proportion
of shale dust to coal dust required to prevent or check
explosions has been determined for coal dust from many-
seams.

The stone dust method seemed to have such advan-
tages over watering methods when water is applied
infrequently, in that more constant protection is afforded,
that arrangements were made with a coal company in
the Pittsburg district to stone dust a part of one of its
mines, and keep accurate account of the costs. Bureau
engineers inspected the stone dusted zones from time to
time, and took samples to ensure that the zones were in
safe condition.

This work was continued for a year, the entries being
re-dusted from time to time as the occasion required.
The test has been so satisfactory that the dusting has
been extended to three other mines, and conferences
have been held with officials of other companies for the
purpose of explaining results with the view to adopting
the method. Considerable interest has also been shown

Fig. 1.—Stone-dusting

Machine in Operation.

in other parts of the country, particularly in Colorado,
where stone dusting has been carried on in the Delagua
Mine of the Victor-American Fuel Company for more
than four years. The probable wide adoption of this
method of rendering coal dust inert, therefore, makes
desirable the development of suitable machinery, both
for preparing the dust, and for its application.

Size of Material.

The first stone dust that was used in the Pittsburg
district was pulverised limestone of such fineness that
about 75 per cent, would pass through a 100-mesh sieve.
This dust was satisfactory, but a coarser material would
be easier and cheaper to prepare; therefore, explosion
tests were made in the experimental mine to determine
the relative efficiency of fine and coarse dust. It was

...l4^Diam

Zn Nipple

Z" Elbow-

fhsif we Slower
Z83cu.in.Vol.

1000R.pm.

Pressure V

Zlb.persqin'

3"Short Nipple
3*Tee



Stirring arrangement
necessary if slope is less

.-Nipple tapers to There and
upon the proper adjustment
cm • of this nipple's position de-
| ’ pends the proper operation
• • of dust feed and blower.

I —.vX	* Rubber Hose with Z*

Hose Couplingfordirect-
i\ZxT'hipple;. In3 Stream many direct-
? 1 <rr

Tx 3"Bushing-

Dust

Hose may be connected through entry stopping into return air course to make a rock-dust
mantle over accumulation of fine coal dust

When such entries have no track, frequently no attempt is made to treat coal dust.

Fig. 2.—Diagram of Stone Duster.

found that material prepared by grinding in a hammer
crusher, equipped with aTLin. slotted screen, was only
a little less efficient than the pulverised dust. It is
believed that suitable equipment to secure such pulveri-
sation can be obtained at a low cost.

Method of Dusting.

In stone dusting a mine entry, the best way to apply
the first coating is, under most conditions, to throw the
dust on by hand, because a thicker and better distributed
coat is thus obtained. In time, coal dust settles on the
stone dust, and re-dusting is desirable. This is best
done by a stone dusting machine, which blows into the
air current a cloud of stone dust that settles in a mantle
over the coal dust. The use of a machine decreases the
cost, and greatly increases the convenience of re-dusting.
Such a machine as used at the experimental mine, and
similar to one in use at Delagua, Colorado, is shown in
operation in fig. 1.

In order to stimulate interest in the development of
suitable machinery for use in connection with the stone
•dust method of rendering coal dust inert, the Director
of the Bureau of Mines has addressed the crusher and
blower manufacturers on the subject.

* Coal Age.

To Manufacturers of Crusher Apparatus. — As the
result of mine explosion experiments at the experimental
mine and explosion prevention investigations in the field,
the Bureau is strongly recommending the use of finely
crushed or pulverised stone dust, having no, or a very
small percentage of, combustible matter, as a preven-
tive for coal mine explosions.

Nearly all mine explosions in bituminous coal mines,
once initiated, are extended by the fine coal dust that is
found on the surface of most mine entries. This dust,
when blown into a cloud, is explosive. If stone dust is
thrown on the surfaces it covers the coal dust, or
becomes mixed with it, and if a sufficient amount is
used, the cloud of dust blown from such surfaces in the
event of an explosion is non-explosive, and quenches the
flame. The more finely divided the dust is, the better it
is for stone dusting. Tests have indicated, however,
that a dust, all of which will pass through a T’s in.
slotted screen, and having about 40 per cent, through a
100-mesh and 25 to 30 per cent, through a 200-mesh
screen, is satisfactory for the purpose. Further detailed
information concerning the use of stone dust in mines
can be obtained from Bureau of Mines Technical Paper
84.

To Blower Manufacturers.—It is desired to call atten-
tion to the demand, which has arisen in connection with

the work of prevention of coal dust explosions in mines,
for a machine designed to blow a cloud of stone dust.

One of the methods now strongly recommended by the
Bureau of Mines for the prevention of coal dust explo-
sions is to coat the mine entry surfaces with stone dust,
so that in the event of an explosion a thick stone dust
cloud will be formed and quench the flame. The first
coating of stone dust is thrown on the mine entry sur-
faces by hand. After a time some coal dust settles on
the stone dust, and it becomes desirable to apply another
coating of stone dust. This is probably most conveni-
ently done by the use of the stone dusting machine. It
blows a thick cloud of dust into the air current, which
carries it for long distances, the dust gradually settling
out and forming a mantle over the coal dust deposits.

The apparatus, as used at the experimental mine of
the Bureau of Mines, consists of a small positive blower,
the air from which passes through a 2 in. pipe to the
injector chamber into which the stone dust is fed from
a hopper; the air and dust, becoming mixed in this
chamber, is blown through a hose into the atmosphere.

The attached diagram (fig. 2) shows an outline
arrangement of the apparatus. The blower used has a
volume of about 288 cu. in., and is run at about 1,000
revolutions per minute. The pressure in the outlet
pipe, when the machine is operating, is about 21b.
per square inch.

The injector chamber should be carefully constructed.
The 2 in. air inlet is reduced to a nozzle of 1 in. open-
ing, and the nozzle should extend far enough into the
chamber of the 3 in. tee so that the nozzle opening is
below the outer edge of the dust hopper opening. The
dust then falls, or is drawn forward into the air stream,
and is blown through the hose. A flexible hose is
desirable for an outlet, so that the air stream can be
pointed in any direction; also this permits its connec-
tion to pipes through stoppings to direct the dust stream
into air courses or entries having no track, and which
ordinarily receive no treatment to render the coal dust
present inert.

Coal Shipment Licences.—It is announced that with regard
to licences for the shipment of coal, when an extension of
time is required, it is now no longer necessary to forward
the licence itself to the War Trade Department for endorse-
ment. If an extension is required, application may now be
made by letter giving the grounds which necessitate the
application, and if it is approved a letter will be issued by
the Department, the production of which will satisfy the
Customs requirements.

Hull Coal Exports.—The official return of the exports of
coal from Hull to foreign countries for the week ended
May 16 is as follows :—Alexandria, 4,812 tons; Amsterdam,
89; Calais, 850; Dunkirk, 1,123; Dakar, 5,845; Guernsey,
346; Gibraltar, 4,502; Gothenburg, 3,250; Harlingen, 368;
Rotterdam, 203; Rouen, 2,212; Treport, 357—total, 23,962
tons. Corresponding period May 1915—total, 38,038 tons.
These figures do not include bunker coal, shipments for the
British Admiralty, nor the Allies’ Governments.

COLLIERY MACHINERY LUBRICATION *

By George R. Rowland.

The lubrication of colliery machinery does not require
any special lubricant to be manufactured for this particu-
lar purpose, but can be efficiently and economically taken
care of with the same grades of lubricants as are used in
connection with other operating conditions where the
machinery is of similar construction.

The most important features to be considered in
colliery and mine lubrication are the following: Steam
cylinders, air cylinders, pneumatic tools, electric gene-
rators and motors, mine cars, external lubrication of
power-house equipment, and wire ropes.

Steam Engine Lubrication.

The question of the internal lubrication of steam
engines is of great importance, and nothing is more
capable of destroying the good effects of a high grade
cylinder oil than applying it in the wrong manner. Prac-
tical experience has taught us that steam itself is the best
medium for carrying oil to the places where it is needed.
This can best be done by introducing the oil into the
steam line as far away from the valves and cylinders as is
consistent with the construction of the steam line, as well
as the inserting of a spoon-shaped connection or atomiser
at about the centre of the steam line, at which point the
velocity of the steam is the greatest. This has the effect
of causing the oil to be broken up into small particles, and
the steam on its way to the valves and cylinders will
carry along these particles of oil, which will come into
contact with all surfaces needing lubrication. The same
method can be made to apply to the low pressure
side of compound engines by placing the feed pipe from
the lubricator in the steam line at a point as close as
possible to the receiver. Much greater efficiency and
economy can be accomplished by this method in the
lubrication of high pressure cylinders, and the amount of
oil necessary for the lubrication of low-pressure cylinders
operating under normal conditions is considerably less
than that required for high pressure cylinders, from the
fact that a certain amount of properly atomised oil will
carry over from the high-pressure cylinders and be
utilised in the lubrication of the low-pressure cylinders.
Many theories have been advanced in regard to the lubri-
cation of cylinders where superheated steam is used. A
number of practical tests have proved conclusively that
there is no necessity of using any special grade of cylin-
der oil for superheated steam conditions, and that where
a suitable grade of oil is used for saturated steam,
the same oil can be used for superheated steam.
This may appear somewhat contradictory, but the secret
is that the flash point of cylinder oil is determined in the
laboratory under atmospheric pressure, and if the
cylinder oil were to be tested under the high pressure
existing in the steam pipe, the flash point undoubtedly
would be found to be considerably higher, just as the
boiling point of water which at atmospheric pressure is
212 degs. Fahr., increases with any pressure above that
of the atmosphere. Furthermore, there is no air in the
steam to affect the oil. The important feature essential
for bringing about the lubrication of any class of steam
cylinders are the furnishing of a high-grade mineral
cylinder oil, to which should be added the proper propor-
tion of animal oil, a good type of mechanical lubricator,
and the introducing of the oil at a point in the steam line
where atomisation can be properly accomplished.

Air Cylinders.

The oil used for the lubrication of air cylinders should
be a high-grade straight mineral oil of as light body as the
operating conditions will possibly permit; and it should
be fed very sparingly under all Circumstances, as very
little oil is required for this class of work if the proper
grade of air compressor oil is used. Excessive feeding
of oil into an air compressor can only do harm, as it leads
to carbonisation and the accumulation of deposits; and
to bring about the best results the oil should be fed either
into the inlet valve or into the air-intake pipe. Troubles
in this class of work, from a lubricating standpoint, may
arise from any of the following causes :

Use of an unsuitable, slow-acting oil, which means an
increase in power consumed by friction, and probably
excessive carbon; use of an oil containing animal or
vegetable oils, which causes the gathering of gummy
deposit and excessive friction; excessive or irregular feed,
which will give the dust, if any, the best chance of
accumulating and choking, or producing an irregular
working of the valves; dust entering the air cylinders and
accumulating; inefficient water cooling; carelessness on
the part of the operating men in failing to keep the com-
pressor discharge pipe and receiver clean; improper
laying out of air lines, which.often permits the forming
of pockets where oil deposits are likely to accumulate to
the degree where trouble results.

Motors and Generators.

The lubrication of electric generators and motors can
be efficiently taken care of with the use of any high-
grade, light-bodied mineral oil, whether these units are
operated by the ring-oiler, chain-oiler, or circulating
feed system. High-grade oils used in connection with
this class of work will run for a long period of time, as the
bearings and oil wells are usually of such construction as
to prohibit foreign matter coming into contact with the
oil. However, it is desirable to empty the oil wells
occasionally and put the oil through a suitable filter. The
oil will then be as good as new, and can be used over and
over again with the addition of a little fresh oil used to
make up for the losses from evaporation and other causes.
Satisfactory lubrication in this class of work is very im-
portant, from the fact that if wear takes place it means
that the rotor is lowered and the magnet will then exert
a pull on the rotor in a downward direction, which further
increases the pressure and wear, accordingly, on the
bearings.

* Lehigh Employes’ Magazine.