Charles George Warnford Lock.

Economic mining: a practical handbook for the miner, the metallurgist and ... online

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driven by sea water, sewage, or small streams containing impurities
from factories higher up the stream. In such cases the formula
given would be incorrect, as it is based on 1 cub. ft. of water weigh-
ing 62 • 4 lb. Sea water, for instance, weighs 64* 1 lb. per cub. ft., and
sewage water will be found to weigh 63 lb. per cub. ft., which would,
of course, give a larger result than that mentioned in the formula.

The theoretical power cannot by any means be said to be the
power available from the mill wheel shaft, as, in the first place, there
is a leakage of water to be deducted from the efficiency, and in ad-
dition to this much power is lost by the friction caused in overcoming
the resistance of the water wheel, and in this fact will be found the
reason for the low percentage of power given by some water wheels.

From the last column of the table on p. 17, it will be seen that
there is a loss of from 25 per cent, to 75 per cent., according to the
type of water wheel. To calculate the actual power which may he
expected from a wheel, the formula given will be found sufficient, but
deduction must be made in accordance with the efficiency. For in-
stance, if the wheel is of the pitch-back type, and of good construction,
it may be expected to produce 75 per cent, of the useful effect or
efficiency, consequently, from the result obtained by the table, 25 per
cent, has to be deducted.

Turbines, in addition to generally giving a larger efficiency, may
be said to possess still another advantage over water wheels, owing
to the fact that they run at a higher speed, which can be directly
transmitted in first motion shaft, while the action of the water wheel
is so slow that it generally necessitates several pairs of geared wheels
in order to obtain the desired speed, thus causing a further outlay of
power,

OiX Engines. — The novel and important feature of the oil engine is
the use of the common petroleum of commerce (kerosene and lamp oil)
at once as fuel and working agent. From the petroleum in its crude
state are obtained several oils — liquid hydrocarbons. The heavy oil
remaining from the distillation is an excellent liquid fuel, and is used
with most satisfactoiy results for generating steam, &c. The light
or volatile products of petroleum, such as benzoline, gasoline, &c,
have been used for producing motive j>ower, but are used in a similar
way to steam, and very many and serious accidents have happened
with them. The other products from the crude petroleum are the
intermediate oils, light lubricating oils and kerosene, or ordinary
lamp or burning oils, and it is that form of hydrocarbon that is used
as the source of power in the oil engine, the method employed being



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POWER. 23

the oombostion of tbe oil within the cylinder of the engine. That
oil ifl now procnrable in all civilised countries at prices ranging in
some places from 3}€2. per gal. or even less. The engine is complete
in itself; it requires no boiler to give a supply of steam, no supply of
gas, the power in the oil engine being obtained direct from tne oil
which is in the supply cistern, the engine having to prepare its own
charge of vapour for combustion. It has been found that the most
satisfactory and only really reliable method of utilising the petroleum
as a source of power is to emplov it in the internal-combustion type
of engines in a similar way to that in which coal gas is used. The
engine, therefore, in general construction is very similar to a gas
engine, working as it does upon the same principle — that is, by the
internal combustion of a mixture of gas and air. In the oil engine
the petroleum becomes the substitute for the gas, it being vaporised
hefore entering the cylinder, and the heat generated by the combus-
tion of a mixture of oil vapour and air inside the cylinder is used
directly to expand the products of combustion and drive forward the
piston. In the horizontal type of engine the cylinder and outside
working parts rest and are fitted upon the foundation or bed-plate,
which is a casting, hollow and of box form. Inside this bed-plate,
and resting upon a sole plate which covers the entire under side of
tlw bed-plate, is the reservoir, a closed iron vessel, in which is con-
tained the oil for working the engine. The apparatus for vaporising
the oil is also fitted within the bed-plate ; and in connection with the
reservoir, upon the side of the engine, is an air pump, which supplies
air to the oU reservoir, that being necessary for forcing the oil tlurough
the spray maker into the vaporiser. The action of the engine is
briefly this : The vapour is formed by the oil being forced from the
reservoir through a pipe leading to the spray maker. There a fine
jet of oil is met at the nozzle by a supply of air, and is completely
broken up into a fine spray, which enters the chamber called the
Tiporiser ; that being warm, the spray is quickly turned into vapour,
tnd is ready for being drawn into the cylinder, together with the
necessary amount of air to make a combustible charge. An explosion
takes place in the cylinder every second revolution, the action of the
piston upon its forward stroke being to draw into the cylinder a
charge of vapour; upon its return that charge is compressed, and
upon the crank turning its centre, an electric spark in the cylinder
ignites the charge, giving the requisite impulse to the piston. The
return stroke then exhausts the spent vapour, and the next stroke
recommences the cycle. The spent vapour thus liberated, being at
this point at a high temperature, is allowed to pass around the
y&poriser, so that the heat is utilised in aiding the C(»nversion of the
inooming oil into vapour. After doing service in this way it escapes
through the exhaust pipe. The electric spark which fires the com-
prened charge is produced by allowing a current of electricity to
play between the endH of two platinum wires, which pass through the
two insulating porcelains in the igniting plug, these being connected
to an induction coil, for which a current is obtained from a simple
primary battery of the Bunsen type. The oil engine is made in
various forms, but the same method of working is carried out in all.



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24 ECONOMIC MINING.

The reservoir in the bed-plate generally contains sufficient oil for a
day's work, bnt in case of a prolonged run being neoessary the supply
of oil may be replenished m the reservoir without stopping the
engine, either by gravitation from a larger oil supply tank, or by
forcing it in by a hand pump. Amongst the openings for oil engines,
tbeir use in collieries, mines, &c., for underground work is specially
noticeable. In deep workings of mines, the pumping of water, haul-
ing, &o., has always been a source of trouble and expense, particularly
when a considerable distance from the bottom of the shaus, so many
difficulties attending the use of steam, compressed air, <S^a, apart from
the cost of conducting such power, steam, ^c, in pipes for long dis-
tances underground.

Among the objections to steam are (1) loss of power by condensa-
tion ; (2) increase of temperature of intake or return ; (3) difficulties
in dealing with the exhaust; (4) bad effect of the exhaust, Ac, Le.
moisture and increased temperature on the roof stone ; (5) its use in
confined places attended with danger in case of leakages.

With compressed air, some of the objections are dispensed with,
but only comparatively small useful effect is obtained, more especially
at high pressures.

In some cases where the oil engine has been adopted no other
system can compare, either in first cost or actual working expenses,
with it

At one collieiy a set of pumps were originally worked from the
tail rope of the haulage system, and to dispense with this an oil
engine and a double-acting pump were put down. These were placed
at a distance of about 2400 yd. from the shaft, and at a point 165
vertical ft. in the dip. The engine was of 5-h.p., and drove the pump
by belt, this being double-acting, having a barrel 6 in. diam., with a
stroke of 18 in. ; the water was forced a distance of 1320 yd. to a
height of 72 ft. The engine house was walled in with two brick
partitions, and the temperature never exceeded 65** F. The cost of
working the oil engine plant was only 10«. Sd. per 10 hours, but here
one man was charged for as being always occupied at the engine,
whereas, in reality, after the engine was started it could be left
and the man employed elsewhere. The cost of working the pump
from the tail rope per 10 hours was 34«., or more than thrice as
much.

For rock drilling in ironstone mines, A. L. Steavenson, of Durham,
has put to work a number of drills worked by oil engines, the
apparatus being specially designed by him. The power is trans-
mitted by means of a rope band running in grooved pulleys ; the
spindle actuates the drill through bevel wheels connected to drill
spindle. There is provision made in that to allow of the drill being
released and drawn out when the hole has been bored deep enough.
The position of the drill can be altered so as to cover the face of the
rock up to 10 ft. high by 14 ft. wide. The result of working has
proved that two holes, each 5 ft. 6 in. deep by 2 in. diam., have been
drilled in 5 minutes, including the time required for changing the
drills and moving from the first hole to the second. The averages
taken over several days showed on one occasion 59 such holes per day



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POWER. 25

of 8^ hours, with one skilled attendant. The tonnage per day was
estimated at 150 tons, at a total cost of 8|<2. per ton for labour, engine
maintenance and fuel, as against 20 tons by hand labour at a cost of
If. per ton. The large cost of the necessary piping and plant for
drilling by aid of compressed air, and the horious loss of power by
leakage, were the reverse of satisfactory, but the use of the oil engine
dispensed with these difiBculties.

It is not quite fair to compare the economy of the oil engine with
that of the steam engine, as they are used under different circum-
stances. One gallon of petroleum weighs about 8 lb., and at 4d. this
would be Jd. per lb. A ton of coal will be 10«., or y^d, per lb., against
Jii. for oiL Coal is therefore one-tenth the price of petroleum, but the
theoretical heat units of the coal are about 12,000, while those of the
petroleum are 21.000 or 22,000, or, roughly speaking, about double.
Thus, while coal is one-twentieth the price of oil it is only half as
efficient. If oil were reduced to Id. per gal. then it and coal would
be on an equality.

In regard to cost of working, oil engines can not yet compete with
the steam engine here using coal. But Uiat is not the point altogether.
Before coal can be used in the steam engine we must have a boiler
and water. A good boiler will evaporate 10 lb. of water per lb. of
coal used. In those situations where the coal and water have to be
O'uveyed to the engine, we should have 10 lb, of water and 1 lb. of
coal, altogether 11 lb., doing the work of J lb. of petroleum. It is in
BQch situations that oil endues will be very advantageous, also for
rock boring at the ends of headways in non-fiery mine^ which are a
long way from the shaft.

Electric Power. — An electrical power plant consists of four essential
parts : — (a) steam or water power to drive the dynamo ; (6) dynamo
in which the power is converted into electrical energy ; (c) conductor
by which the current is carried from the dynamo to the motor;
(i) motor which reconverts the electrical energy into mechanical
work. The motor is simply a machine capable of giving so many
hp., and may be coupled to any required work by the ordinary
methods — belting, gearing, &o. It is not necessary to understand
the principles of the motor in order to successfully work an electrical
plant.

Electric motors are being used successfully for drilling by impact
and boring with diamond drills, and are able to compete with steam
or compressed air. In rapid tunnelling, in running adit-levels, in
deep and crooked workings, or in all work requiring hasty construc-
tion, the great trouble and expense of shifting and relaying pipes,
with great losses due to leakage, &c., are avoided; the necessary
wires are simply cleated to wall or posts as work advances, thus
always being entirely out of the way. Furthermore, the room which
pipes, &C., occupy in shafts is by no means small, and is an important
item to be considered as compared with wires.

A mine ventilated by electricity, as it could be if electricity were
^teed for drilling, &a, would not require compressed air for the benefit
uf the men.

The original cost of a compressed-air plant and its maintenance is



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26 ECONOMIC MINING.

much greater than that of the electric system, and for large work, it is
not as economical to operate.

For short distances only, and in open work, steam may be more
adyantageonsly employed; beyond these conditions it cannot be
considei^ a competitor.

In placer-mining, and in mines of but a few hundred feet in depth,
also where there is uncertainty as to the location of workings, or the
permanence of the location temporarily selected, as well as in all
preliminary explorations, &c., the electric motor is so easily moved
and applied, and its scope so great, that it is cheaper and better than
any other, beyond certain limits. In very deep and large mines,
however, permanently located, probably steam, acting direct, is to be
preferred.

The best known application to mining haulage was made in 1882,
at the Zauckerode pit, near Dresden, in Saxony. They employ there
some 800 wagons, each of about 3 cub. ft. capacity. The motors are
of 6 h.p., and haul trains of from 10 to 20 wagons, maximum weight
13 tons, at a speed of about 5 miles per hour. The length of track
is \ mile. The cost of operation has been about |d. per ton. The
total cost of the plant was about 8002.

Since then ereat improvements have been made in the e£&ciencies
of motors, which to-day range from 85 to 95 per cent.

Pumping is a most impr»rtant application. For practical working,
the only methods now employed to aiiy considerable extent are those
of direct-acting steam-pumps and pumps operated from the surface
through wooden beams. Compressed air is too expensive, and there
is no practical motor for driving pumps. Wire ropes are likewise
expensive and inapplicable; and any hydraulic method is out of
the question. Steam, for any considerable distance, is entirely im-
practical.

The apnlication of the electric motor is simple, since most pumps
are adapted for belts or gears. The only thing to provide for is a
belt or a pinion for the armature-shaft. The intervening distance
between the power-station, on the surface, and the point where the
pump is needed, is of small consideration as regards construction, for
copper wires can be easily run irrespective of distance or oonditions.

A number of applications have already been made, notably at
St. John's colliery, Normanton, and at the Thallem colliery, on the
Danube. Another application is a small plant at the Trafalgar colliery,
where the duty of the motor is to pump 114 gal. per minute through
3900 ft. of 7-in. pipe, with a lift of 300 ft.

One of the most interesting installations for electrical transmission
of power for coal mining purposes in Europe is in operation at the
Decize Collieries, France. This installation is remarkable firom the
fact that diphase alternating currents are employed for transmission,
and diphase alternating current motors are used for reconverting the
electrical energy into mechanical power at the dififerent pits. In
designing this plant the problem to be solved was to erect a central
generating station for the distribution of electrical energy at the
different pits where it could be utilised in electromotors for operating



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POWER.



27



ventilating faDB, hauling machinery, pumps and for lighting purposes.
A general idea of what had to be aocomplished is shown in me annexed
table:—







Distance




Site.




from


Etedrical Machtnery or Lamps recdviiig the






GeDenting
Sutloo.




l.-Wert.




Tsrdi




PoiUdes ChAgnats


,,


5090


80 h.p. eleotrio motor.*


FendnedeeLaoets..


,,


8466


,,


Poits des Coupes ..


^,


2058


*

19 )y


PdtB des Zagots ..


,,


1084


Electric hanling machioe of 15 h.p.t


t-6eoentiDg station.








Yarioos installations


,,





6 aro and 100 iooandesoent lamp8.t


a-Esst








Fendne de Marizj ..


..


1800


80 h.p. electric motor and 24 arc ]amps.§


Sorthig and washing shopsl
ofthePrtChsrpin ../


2490


500 incandescent lamps of 16 cp.t


ChampTcrt .. ..


••


8250


12 h.p. electric motor.)



* Used for ventiUtiiig fian. f Inclined plane. % Lighting.

^ VcDtilaiing llui tad lighting. B Pomplng.

The generating station is situated respectively at 3*1 miles and
1*86 miles from the extreme points which have to be supplied with
current. It contains a battery of 6 boilers and 2 units (steam engines
and dynamoe\ each of a capacity of 100 kilowatts ; a farther unit will
Bhortly be laid down. The two units may be worked singly or in
panlleL The engines are horizontal non-condensing, running at
^ rey. per minute, and driving the diphase alternators by belting.
Each electrical unit comprises a twin alternator, or in reality two
machines, placed one at each end of the shaft, the driving pulley
carrying the engine belt being arranged in the middle of the shaft.
Where current is employed boSi for lighting and for power purposes,
one of the circuits may become more loaded than another, and in this
event the equilibrium mnst be established by varying the ratio of the
electromotlTe forces. The arrangement adopted in the Decize instal-
lati^ allows of this being accomplished, as each of the two circuits
hanng a distinct field, it is only necessary to vary the exciting cur-
rent by means of rheostats to get the desired effect. The generators
introduced are Zipemowsky 10-pole alternators, with revolving field
loagDets. The 10 field magnets are connected together in series, and the
exciting current is led to them by means of two metallic rings carried
on an extension of the driving shaft on the opposite side to that of
the driving pulley — ^that is to say, on an outer extensiou of the shaft.
Two ordinary brass brashes press upon these rings, to which the
^ting current is furnished by a direct current dynamo. This latter
iDadiine is operated by a belt from the shaft of the alternator. At
^ rev. a minute this direct current dynamo supplies the exciting
^^'^rrentfbr the twin alternator, being between 26 and 30 amperes
^t 110 volts. The fixed armature of the alternators is formed of



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28 ECONOMIC MINING.



10 coils, any one of which can be withdrawn and replaced with little
trouble.

After passing through the switchboard, the current i« transmitted
mainly by means of overhead wires to the points of utilisation, the
only portion laid underground being towards the end of the principal
line leading to the Chagnats Pit. The wires forming the overhead
line are of silicon-bronze, and are carried on porcelain insulators
attached to poles 24 ft. high. The diameter of the wires constituting
the principal line to the western part of the district is 6 mm., and
4 mm. in the case of the remainder of the line. The same poles
carrying the transmission wires also support telephone wires, the
latter being arranged 12 ft. from the ground. In order to counteract
the effects of induction in the telephone wires, the line conductors are
crossed at distances averaging 640 yd., and by this means the difficulty
of understanding conversation along the telephone wires which use
the earth as return, has been overcome. The small portion of under-
ground line forms a lead-covered cable, laid in a wooden conduit, as
also does the telephone line for the same distance. Suitable lightning
conductors are provided at the generating and distributing sub-
stations and at intervals along the line. The electromotors at the
sub-stations, where the current is utilised for the diflferent purposes
mentioned in the table given above, are of the same type as the
generators. These diphase motors are easily set in operation, and
are to all intents and purposes left to themselves for several hours
together. The only attention they receive is a visit eveiy 6 or 8
hours to ascertain whether the motors are working properly. The
sub-stations are situated in the forest, and the facility of working on
this system as compared with the erection in each place of a boiler,
engine and ventilating fan, is remarkable, apart from the question of
the cost of transporting fuel.

From the published statements of leading electrical firms, it is
possible to deduce approximate costs for transmission plants based on
100 h.p. unita. The primary power (engine or turbine) is estimated
at 8^. per h.p., the dynamos at 6^. per h.p., and the motors at
8Z. per h.p., using 1000 volts. For distances of a mile or less, 80
per cent, efficiency can be counted on, and the cost of the electric
plant will be 16Z. to 17/. per h.p., and of the total plant (including
engine or turbine) 24Z. to 26/. per h!p. For distances up to 5 miles,
70 per cent, efficiency, and 27/. and 36/, per h.p. cost respectively.
For 10 miles, 50-55 per cent, efficiency, and 40/.-42/. and 66/.-58[.
per h.p. cost respectively.

Up to the present time a danger has been felt to exist in the use
of electric motors in fiery mines, from the fact that bad setting or
wearing of the brushes might result in sparking, and ignition of any
gas that might be present ; in fact, the use of electric motors in any
mine where safety lamps were necessary has hitherto been considered
unsafe. All previous attempts at the construction of a safe motor
have taken the direction of encasing either the whole machiixe, the
armature, or the commutator and brushes. These arrangements not
only introduced difficulties in the ventilation of the armature, but



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POWER. 29

also Beoessarilj included a considerable air space, so that when this
space became filled with gas it would be possible for an explosion to
take place inside the case, of such yiolence as to entirely destroy the
cover or case, and communicate with the outside atmosphere, thus
causing an explosion. The safety commutator designed by Davis and
Stokes, and naade by John Davis and Sons, Derby, overcomes these
difficulties, and is so arranged that the commutator itself is practically
equivalent to a locked safety lamp enclosing the brushes, since it can-
not be worked unless closed, and cannot be opened while running ;
the junction between the fixed and the revolving portions of tne
machine being made by a flame-tight joint which requires no packing
and causes no friction.

The most marked deviation from the ordinary commutator is, that
instead of the brush contact being on the outside of the cylinder
formed by the commutator segments, this cylinder is hollow, and the
brushes bear on the inside face of the segments. The method of con-
struction is as follows : — The commutator segments are clamped
between a ring and a disc, the latter being keyed on the shaft. This
disc forms a permanently closed end to the commutator cylinder at
the side nearest the armature. The brass bearing of the shaft is ex-
tended nearly up to the disc, leaving room for a slight end play (the
shaft of course only bearing in the usual portion of the brass), and
means are provided to prevent the oil from the bearing working along
the extended portion of the brass and entering the commutator. The
open end of the commutator cylinder is closed by a disc sliding on the
extended brass bearing and carrying the brush holders and brushes ;
and a clamping handle provides for setting the disc and brushes in
their proper position. This disc, as stated, closes the end of the
hollow cylinder, the latter revolving with a clearance of ^^ in. from
the disc; and in order to avoid the chance of the disc with its
brushes being withdrawn while the machine is running, or started
before properly closed, a locking ring is provided. Small windows
are fitted in the disc, so that any sparking at the brushes can be seen
and corrected; and the brushholders are furnished with springs
working on the outside of the disc, for adjusting their pressure while



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 4 of 76)