Charles George Warnford Lock.

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drills are used, these perform a valuable service in this respect. The
exhausted air from the drills keeps the atmosphere fresh and pure
during drilling, and after a blast, the stopcock of the pipe conveying
the air to the drill is turned on, and the compressed air rushes into
the £m» of the drift, or whatever place worked, and soon restores good
air. This is a very expensive system of ventilation, and is not em-
ployed where artificial air is necessary on a large scale.

Blowers of various designs are used for ventilation. Amons the
most popular of these blowers are the Baker, the Sturtevant, and the
Hoot The smaller mines use blowers of sizes corresponding to
Xos. 1, 2, and 3 of the Baker Botary Pressure Blower, while blowers
in on at the larger mines correspond to Nos. 4, 4]^, and 5. No. 2 has
ft ci^MMdty of 5 cub. ft. per minute. No. 5 has a capacity of 24 cub. ft.
per minute.

The temperature of the mines is more dependent upon the system



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6o ECONOMIC MINING.

of Tentilation employed than upon the increase of temperature due to
depth. In testing the temperature of many mines in California, it
was ascertained that no significant increase of temperature, due to the
increase in depth, was evident, the temperature being so much de-
pendent upon the circulation of the air as to obliterate any influence
that would otherwise exist because of the difference in depth of the
points of observation.

The following notes* show the great differences in the coefficient
of resistance to air-currents in mines under various conditions ; e. g.
presence of timber either across the shafts or as supports in the
roadways, the repeated enlargements and contractions of the airway,
sudden bends in the ways, or the abrupt junction of two air-passages,
are all important factors in the increase of resistance. Shortly, the
alternate increase and decrease in the velocity of the current, the
degree of smoothness of the sides, &c., and the change of direction
of the air current, are the most important fstotors in the loss of
pressure.

The following table shows the amount of variation. In this and
the other tables the coefficient in all cases represents the total pressure
which must be distributed over the transverse section of the airway
for every square foot of rubbing surface, in order \o maintain a velocity
of 1000 ft. per minute in the airway. It will be observed that this
is a constant quantity for the same kind of surface, and independent
of the dimensions of the airway.

Goeffldenta in lb. per

sq. ft. (rf* rubbtng

surfiMe, Telod^

1000 ft. per minute.

Straight airwayp, very even in eection, without timber, driven I .0027^9

in the coal seam I

Straight airways, irregular section, without timber, driven inl .003594

theooalseam /

Straight airways, regular section, withont timber, very jagged^ . aa4qqa

sides j "*^*^

Straight airways, regular section, timber plentiful, driven in^ '004792

the coal seam .. .. .. /

Shafts timbered (buntars or brattioe) -003686

Straight airways, very irregular aectioQ, without timber,^ * 005510

driven in the ooal seam f

Straight airways, driven in the coal seam, irregular section,! .005595

plenty of timber /

Aurways, round bord and pillar, face of workings '0136S5

The increase shown between the first condition and the last is
nearly 400 per oent.

Having in view the general condition of the several parts of the
mine, the following coefficients might be adopted for use in calcula-
tion : —

Coeffldents
as before.

Shafts (timbered) -0037

Intakes 0042

Workings 'OlS?

Returns '0056



• T. L. Elwen.

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VENTILATION. 6i

The above resnlts are similar to those derived from experiments
made in Belgium, viz. : —

OoefBdents
as before.

ATeragMofallthegalleriesof acoal mine *009S6

At the faoe of the workings *01419

Galleries and pita of unifonn section, and without obstruotions * 00208

The praotioal concliisions that may be drawn are that, next to
having we airways large in section, the most important thing is
to keep them as straight, as regular in section, and as &ee fiom
ohstruction as possible.

The effectnal cooling of mines is a subject which has long occupied
the minds of engineers. An invention of some moment has been
introdnced to the managers of the Cornish mines by Captain Williams,
and is one very likely to become adopted by coluery managers also.
The machine is simple, and the moving parts are enclosed in a large
upright box, and may be made in different sizes to suit the require-
ments of particular mines. Within the box is a cup-shaped cylinder
which swims in water, whilst the motion of the piston-rod, actuated
by steam power, produces a strong current of air at both its upward
and downward strokes. It can be placed at any required depth in the
mine or colliery, and receives its full supply of air from the surface.
No grease or oil being used, the air is, of course, preserved in the
same condition as snppued. The under portion of the machine always
contains about 6 ft. of water, and the up-stroke of the cup piston
going to the top of the machine, with the water running down the
sides, keeps the inner part of the machine deluged with water, by which
means the air is cooled before it is delivered into the mine^-even to
a temperate heat in the hottest summer. The inventor claims that
the machine will force some 5,598,720 cub. in. of cool air into the
interior of the mine, each minute, or that it will only require an
engine of some 2 h.p. to deliver 7000 to 8000 cub. ft. of air into any
part of the mine or colliery per minute. At the Planitz Colliery, in
Saxony, the air used for ventilation is caused to turn a wooden lap-
wheel working in water. The flaps or blades are thus being con-
tinually moistened, and a portion of the n^oisture is given up to the
incoming air.

The winning of coal is exceedingly dangerous during all periods
of low or diminished atmospheric pressure. At those times falls of
roo's and of other parts, and also escapes of gas, frequently occur.
The main diftculty is, of course, to get rid of the gas. The system
of ventilation used tends to evil whenever the air is rapidly drawn
through the w6rkings of the mine during such low or decreased
atmospheric pressure, as the direct or forward motion and force of
the air destroy its power of propping the roofs and sides and likewise
lacilitate explosions owing to the gases being drawn out of the solid
coaL The present system of ventilation in coal mines only deals
with the danger of sas, that is to say, the gas escapes under the force
of gravitation, whicn remains practically the same while the atmo-
spl^ric pressure is seriously less; hence the great increase of gas
which must be discharged.

To overcome these defects in ordinary methods of ventilation.



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62 ECONOMIC MINING.

Jabez Stanley proposes accomplisliing by mechanical means what
nature does when the atmospheric pressure is favourable, and when,
therefore, there is a minimum of danger. To attain this object he
forces air, as may be required, into the mine down the ordioaiy
down-cast shaft, such air passing through the workings in the mine
as at present, and from thence out through the o> dinary up-cast shaft.
When both are drawing shafts, the usual doors to prevent ingrea
and egress of the air are required for both up-cast and down-cast
shafts ; the air enters the latter below the doors. The up-cast shaft
is provided in an offshoot from the top of the shaft with a regulating
valve or valves consisting of a swivel door made to partially open or
close by its own weight, so that a favourable or maximum pressure of
air is maintained during all weathers, through all parts of the mine,
at any time and in all seasons.

To ensure more perfect ventilation of large coal mines, Stanley also
employs an additional supply of compret^sed air. A metal reservoir
or receiver is provided in which the air is received from the blast
engine or blower through an opening in the reservoir, which can
be closed or opened when necessary. This reservoir is placed in
the most convenient part of the mine, that is to say, either inside
the workings or outside the mine. One or more iron or steel mains
or conduits are fixed and laid inside the mine and workings, so as to
proceed from the air-reservoir or receiver as permanent outlets thereof
from which branches in the form of pipes or tubes are attached.
Wherever the ordinary current or currents of air fail to displace and
discharge the gas or foul air from the mine, or to supply thoroughly
any part of the workings with pure air, the air-mams and branches
are used as accessories.

In order to obtain satisfactory results in ventilation, it is not
enough to force a great quantity of fresh air into the mine, but this
air must be brought into as cIono proximity as possible to the face of
the workings. The solution of this problem is all the more difficult
because it varies with the circumhtances, and also for the reason that
it depends on the attention, goodwill, and intelligence, not only of
those who have the supervision of affairs, but also of the men them-
selves.

Special arrangements for ventilating the working fieioes consist of
air-pipes, partitions, compartments, parallel roads and borings. The
use of air-pipes supposes the mouth of the pipe which reaches the
working face to be received by the air-door, wnich can either be set
up in the gallery which first receives the air-current, or in the return
airway. But, as a general rule, the use of air-pipes is only advisable
in large-sized galleries and for short distances.

Ventilating partitions offer much greater security, for by their
means two independent currents of air of almost equal i$ection, and
reaching the working face, can be obtained. They are made of brick-
work or of boarding ; and of sailcloth, either stretched on frames or
hung loosely. Brickwork partitions are specially suited for long
cross-cuts, and the sailcloth arrangements tor the working properly
so called. The partition should naturally be kept airtight, and
approach as closely as possible to the working face.



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VENTILATION, 63

In deep levels and broad roads, the embankment, if sufficient, may
serve for partition purposes, but an airway must be maintained in
the lower part, to permit of the passage of fresh air, and the gallery
proper must be intercepted by a door which will expel the foul air
issuing from the working face, in the direction of the nearest heading.
Bot in this case it is absolutely necessary that the embankments
should be carefully made, and especially that a facing as smooth and
impermeable as possible be made the length of the airway and also of
the gallery. But in the event of a violent explosion this arrangement
presents the great inconvenience of its being easily destroyed, which
might result in the entire suspension of the ventUation of a portion
of the mine.

When winning in fiery beds, where there is an abundance of gas,
it is better to proceed with the deep levels, self-acting planes, and
other main galleries, and at the same time also to drive a secondary
parallel gallery in the seam or rock, which should connect with the
principal gallery by means of shafts which ought not to approach
each other too closely. In this case it is best to forward the working
£m» of the parallel gallery (upper) with respect to that of the main
gallery (lower), but the air-current ought to arrive there in the
last place, in order that the gases which are liberated from it may
be carried away immediately. Under some circumstances it would
be necessary not to drive the two galleries simultaneously, but one
after the other, and in portions. In fiery seams it is also strictly
necessary to set up a ventilating partition in each of the two galleries
from the last rubble to the face of the working. Lately, particularly
in the coal mines of Westphalia, ventilating rubbles have been replaced
by bored air-holes, which have this great advantage — that they do
away with the always dangerous necessity of driving ascending
galleries. But, on account of their small size, it is not usually
possible to circulate the air-current through them, which, in the
event of an explosion, might be the cause of serious danger. Never-
theleas, if by boring holes of greater diameter this defect were
remedied, they would answer all requirements.

Of the various means of ventilation enumerated above, preference
is usually given to parallel roads for such operations as shafts, cross-
cnt8> and isolated galleries; but even for these, partitions, embankments,
or air-pipes, provided the latter were of adequate size, might suffice.
In fiery mines the works cannot be executed without the help of one
of these means of ventilation. All airways which have become useless
should be stopped up as completely and in as durable a manner as
possible.

It is not always possible to efficiently circulate either tho main
or partial current through all the working places, without its becom-
v^% either dangerously enfeebled or receiving a downward direction.
Therefore, in narrow mines especially, it becomes necessary to supply
badly ventilated and isolated parts of the mine with independent
means of ventilation. The most simple means of effecting this is
the method which is adopted in fiery parts of Prussian mines — namely,
that of setting up fans combined with pipes.

Fans may be exhausting or blowing. As a general rule, the latter



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64 ECONOMIC MINING.

are preferable, because the meohanioal effect of the air-current is
better able to keep the workings free from gas, and to continually
convey fresh air to the miner ; whilst with an exhausting fan, the
air, before its arrival at the working face, has already absorbed the
gases which have been liberated from previous portions of the
gallery. On the other hand, it is true tnat the ^edlery itself is
better ventilated by an exhausting fan. In all cases it is strictly
necessary that fans shall only be placed in currents of pure air.
When they exhaust there must also be an air return pipe which
will lead the foul air as directly as possible into the issuing
current.

The most prominently successful colliery fan now in use is that
made by Bumsted & Chajidler, Hednesford, Staffordshire, and known
as the '* silent " pattern.

Efficient ventilation should aim at rendering the mine atmosphere
free from mechanical impurity, as well as from poisonous gases, and
this is especially the case where friable lead ores are being worked,
or other minerals producing an injurious dust. At the well-known
Broken Hill mines, water-mains have been laid underground, and
the faces and workings are sprinkled at intervals, thus keeping the
atmosphere in a fairly satisfactory state, even in the worst portions
of the mine.



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65



LIGHTING.

It has been justly observed by a writer in the *Iroii and Coal
Trades Review/ that no invention connected with mining woi% has
be«i looked forward to with greater interest than that of the electric
i^np, which is to displace the old Davy and Clanny. It is perhaps as
well to remember that the old miners' lamp fulfils two distinct duties ;
h gives light for the miner to work by, and it shows him where gas
i* present. The first duty, that of giving light, it performs in such
ft erode fashion, that every new idea which promises a better light is
eagerly welcomed. So there have been numerous improvements on
the old original I^^i all tending either to increase the light given,
or to increase the safety of the lamp in the presence of the strong
currents of air now used in the ventilation of mines. This brings us
to another point. Even the most improved form of oil or spirit-burning
lamp, while giving infEillible and easily understood warning of the
presence of inflammable or explosive gas, is itself not safe if the gas
be driven through its meshes at a given velocity.

Now, it will be obvious that the electric lamp can fulfil two of
the above requirements. It can give a better light than is the
mle with oil or spirit-burning lamps, and it can give that light
in such a form that no matter what the velocity of the gas-laden air
dUToit may be, no particle of gas can penetrate to the glowing
filament. But, up to the present, no electric miners' safety lamp
Baa been provided with a simple, safe, and reliable apparatus that
will warn the user of the lamp that he is working in a gaseous
atmosphere. Nearly every inventor has tried to solve the problem
bj attaching a platinum wire to his lamp, which is allowed to
glow at a dull red heat behind a metallic gauze screen, except when
gas is present, when the platinum wire assumes a yellow heat. Apart
from the electrical difficulties of ensuring that you have always such
ft corrent-strengih passing through the wire as will raise it to the
proper dull red temperature, it is evident that the adoption of this
plan surrenders the most valuable property of the electric lamp under
the conditions, viz. the absolute impossibHity of contact between the
^•8 and the source of light.

Swan and Pitkin & Niblett have tried other plans, each, however,
depending upon the presence of heat in some form in a body exposed
to the gaa, and therefore not fulfilling the primary condition that any
f^as-teeter attached to an electric miners' lamp must conform to.
A.pparently for this purpose a new discovery is necessary, and the
liiaooTery if made will probably be in the domain of the chemist. A
careful and exhaustive examination of the properties of the explosive
jrases which are found in coal mines will probably reveal something,

F
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66 ECONOMIC MINING.

suoh as that some snbstanoe ohanges its colour, or its form, or its
pbysical condition when these gases are present, in suoh a manner as
to be readily observed, even in the comparative obscurity of the mine,
and by the eyes of uneducated men, after a little training. It is
possible that electricity may aid the process. An electric current may
set up a certain state in a certain body or class of bodies, such that
the presence of gas is readily detected by its influence on the same
bodies. But, until some such discovery has been made of some
substance that, without heating, vriU give indications of the presence
of gas, as surely and as easily read as those given at present by
the old Davy lamp, the miners* electric safety lamp vnll not be
complete.

Meanwhile, pending the above discovery, it may be interesting
to discuss in' what position the electric safety lamp stands at present,
with reference to its fulfilling the other duties named. Though it
will be inconvenient to be without a gas indicator on each lamp, the
advantages of additional light, and absolute freedom &om the
possibility of ignition of gas, are so great, that means can be taken
to provide for the presence of gas being indicated by means of a
certain number of the old form of lamps specially provided for the
purpose. It vriU be remembered, of course, that the miner can
have no temptation to open an electric lamp. He cannot light his
pipe at it, nor can he warm his ** tommy." And if he should succeed
in opening the lamp, he can do no furtner harm than leaving himself
in darkness.

There are two methods of arranging a miners* portable electrio
lam^. The lamp may receive its current from the ordinary lighting
service of the colliery, by means of a pair of flexible wires connected
to the electric light mains, or it may receive the current from some
form of battery which is carried about with the lamp. The first
ilan, though it has been tried on one or two occasions, is too
iangerous for adoption until the working collier has been educated
up to it. Falls of roof are so frequent where these lamps would be
used, that except with great care and supervision, there would be
constant danger of wires breaking, sparks passing across the break,
and gas being fired if present. There are also two methods of oarrj-
ing out the second arrangement, namely the attachment of a* port-
able battery to the lamp. The battery, in this case, corresponds to
the reservoir of oil in l^e old form of lamp, which allows the wick
to bum its allotted time. The two methods are, by means of what
are termed primary and secondary batteries.

In the primary battery, a metal, usually zinc, is consumed in some
form of acid, and in consuming or burning, furnishes an electrio j
current which can be used to give light by means of an incandescent
or glow lamp. To complete the primary cell, as each vessel in
which zinc is consumed is termed, another plate, usually of carbon,
sometimes of copper, is required ; and with some batteries it is sdso
necessary that this second plate shall be immersed in a second liquid,
in order that certain products of combustion, the smoke and ashes
of Uie galvanic cell, may be got rid of It is further necessary with
the present glow lamps, at any rate, to have two or more of these






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LIGHTING. 67

cells, in order that a sufficient E.M.F. may be generated to famish
the required light with a small expenditure of current. The cells,
whether one, two, four or more, must be held together in some form of
cise, to which iJso must be attached the lamp and a handle for
cuTjing the whole apparatus by. The sdno and carbon plates also,
if inunersed in separate liquids, must be separated by a porous
partition, and the plates of the <ii£ferent cells must be connected
together, and to the lamp terminals in a certain order. If the
light given also is to be much better than that of the old Davy,
and the battery furnishing the current is to occupy a small space,
the acids used must be very ^werful, such as will quickly eat
wires in two, destroy connections to terminals, make holes in
many forms of containing vessels, and produce other troubles.

in the secondary battery, we have the same condition of things, viz«
two different metals, or two pieces of the same metal in different phy-
sical states, immersed in acid ; but in this case the conditions are pro-
duoed by the action of an electric current, which is passed through the
cells for several hours before the battery is required for use. The metal
plat«s used in the secondary batteiy are lead, one sometimes being
coated with a layer of oxide of leaa. On the electric current being
applied, one lead plate becomes oxidised, or if already covered with
ox^e, tiie latter is raised to a higher oxide, while a deposit of what
is called spongy lead appears on the other plate. Spongy lead and
lead oxide, in the presence of sulphuric acid, form a powerral galvanio
cell, and so it happens that after the plates of a secondary cell have
been prepared in this way by means of an electric current, they will
famish a current — in the opposite direction to that which created
their electromotive force^if required to do so.

It will be seen that here are no highly corrosive adds, only weak
sulphuric acid being used, and no porous divisions ; but the same
necessity for a number of cells exists, and for connecting their plates
in a certain order among themselves and to the terminals of the lamp.
With the secondary battery, however, as refilling or recharging is
effefTted by merely passing a current through the cells, the connec-
tions between the plates and to the lamp should be able to be made
permanent. And in fact, at first sight it would appear as if the
secondary battery lamp fulfilled all the conditions required, except
that of being able to test for gas. In practice, however, things are
not quite so rosy. Though only weak sulphuric acid is used, and the
metal employed is lead, one not so easily attacked, the sulphuric acid
does combine with the lead not only within the cell, where it does
useful work in the process, but outside the cell, at the points of con-
nection between cell and cell, and between the cells and the lamp,
forming there a hard white substance which offers enormous resist-
ance to the passage of the current, in proportion to the E.M.F.
present, with the result that the light goes down and is finally
extinguished. The presence of this troublesome lead salt beine un-^
yuspected, the connections being concealed, adds to the inconvenience,
aa the lamps may go out for no apparent reason. The sulphuric acid
also attacks any copper connections that are present, and in the same
manner may be doing its work unseen and unsuspected, till some



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 8 of 76)