Charles George Warnford Lock.

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

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K 'Tided with extension-boxes, to facilitate making the connections,
e ahute which distributes the load in the barge is built of light
"^arranged bo as to oonvey the coal to both sides at the same time,-
^ proportion delivered to either being regulated by the angle of
"w^tion. It is adjusted so that the coal moves in it very slowly,

I 2

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ii6 ECONOMIC MINING.

and has a minimum drop into the barge. When the eides have been
fnlly loaded, the hinged apron is folded back, and the discharge falls
in the centre of the l^ge, which is thus loaded so as to require little
or no levelling.

It is apparent that the greatest inclination of the belt should not
exceed the friction-angle of coal on iron; and that, within certain
aneles, gravity will revolve the belt, on the principle of an ordinary
indine. Though Page put a brake-wheel on the main shaft, intending
at the time to use gravity-power, he determined later to make use of
a small 6 x 8<in. engine, which was on hand to operate a capstan for
handling the barges. He connected the belt with it, and made the
greatest angle of inclination only 15°. The belt is speeded to 100 ft
per minute — the engine making 150 rev. — and makes a complete
revolution in a Httleless than 2 minutes. In actual practice, the belt
empties a 12-ton car in 2 minutes, or at the rate of 360 tons per hour.
This capacity can be increased, without additional expense, by simply
increasing the speed of the belt, or, at a very small additional cout, by
increasing its width.

As the belt has never been operated by gravity alone, it is not
possible to say exactly what the factor of friction is, but doubtless it
will revolve between the angles of 10° and 30° ; in other words, it can
be operated by gravity alone, through an arc of 20°; and with a
radius of 95 ft. this arc would approximate a difference in elevation of
34 ft, which is more than ample to cover all loading-stages in the
river. I

The little engine mentioned will run the loaded belt without
diflSculty, in a horizontal position; consequently the total friction
must be considerably less than the power of its cylinder, as it is
geared (the gravity force exerted in direction of belt, at any angle,
may be easily determined by the resolution of forces). The total oost
of all the iron in the structure was under 500i., excepting only the
engine and boiler, which cost originally about 120Z. To this must be
added 100,000 ft. of white oak timber in the crib and trestle, which
cost 400^. erected, and 1202. for stone filling, making the total cost, in
working order, under 1150^, including engine, capstan, and all
gearing. The cost in timber and stone will, of course, vary according
to conditions. It will be seen from the drawings that Page has used
timbers lavishly, both in the wings of the crib and for the protection
of the bank. The whole structure is so framed and drift-bolted I
together that no part can be moved independently of the other, in-
cluding the stone crib, which extends back to the railway grade, 60 ft,
above low water, and 10 ft. above the Chesapeake and Ohio Bail way.

The distance between bents being 24 ft., little resistance is offared
to the current (none of them is in the channel) ; and even shoold
drift or ice gain a lodging, there is as much strength to withstand
the pressure as is presented by an ordinary breakwater. The belt
can be raised clear of water, up to a 40-ft. rise, and should this fthe
highest gauge yet recorded) be exceeded, it can be lowered in safetf
beneath the surface. As the crib is fill^ so that it cannot be under-
mined, the greatest damage which could possibly result would be tlie
breaking of the bents, which are composed of 4 timbers of 12 x 12-in.



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HAULING AND HOISTING. 117

oak, each firmly bolted and braced to the stone crib and its two wing-
wills. The belt wonld of conrse remain; and even such an im-
probable catastrophe would result in small damage.

In actual worldng, only 2 men are required to run this conveyor
to its full capacity : an engineer, at 6«. per day, who also attends the
oipstan, and one man on the barge at 8«. per day, who is a carpenter
tnd caulker ; consequently the total cost per diem does not exceed 1 4«.
The trainmen dump the cars ; but if this expense be added it would
amoimt to 10«. more. The tracks are arranged so that the loads run
in, and empties out, on down grades.

In 3 months' working the cost of repairs was nothing ; and since
eTery member has a large bearing and safety fisu^r, the wear and
depreciation will be very slight. No breakwaters have been put in,
nor is there need for any.



FiQ. 66.— HuHT Coal Cqhduotob.

Apart from the advantages already named, it has been clearly
lemonstrated that both coal and coke can be put into barges with
lalf the breakage of any other arrangement ; that there is nothing
omplicated to get out of order ; that, as the barge sinks in proportion
o the load, the belt has to be moved only for tiie different stages of
rater. Moreover, there is no danger to life or property from the
n^akage of any part, as is the case with the vertical system, in
rhiidi Irequently tiie breaking of a rope causes loss of life, barge and
ar.

With self-dumping cars, Page would feel safe in guaranteeing to
ransfer 4000 tons with this machine, within 12 hours, at a cost per
on iK>t exceeding i^^., and, with 2002. extra outlay, he would under-
ake to double this capacity, and lower the cost named.

Ab the mines of the Mt. Carbon Company are connected with the

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ii8 ECONOMIC MINING.

river by 5 miles of standard-gauge railway, and their coal is screened
at the mine-tipple, where they have 202 bee-hive ovens, no arrange-
ment has been made to separate the nut and slack at the river. The
vertical distance between the car and belt, however, could be easily
utilised for screens ; and the small coals could be conveyed to either
side of the belt, where they could be carried by a trough and scrapers,
connected to the main shafts, into separate barges, which might be
arranged inside of the lump-receiver. Under favourable conditions,
the angle of inclination to these inside barges would be sufficient
to slide the coal in fixed pipes, since breakage there need not be
considered.

In Hunt's conveyor, instead of the usual sprocket wheels for effect-
ing motion, pawls are used for pushing the chain alonff, a second pawl
taking hold before its leader lets go. As shown in Fig. 66, a pocket
is formed in each of the links of an endless chain, or the latter is
fitted with 2 pins into which a pawl drops, and 6 or 7 more of these
pawls are attached to a revolving disc, their movement to enter the
link pockets being governed by a fixed cam, which turns them toward
or allows them to drop away from the centre as may be required.
The tracks upon whicm the wheels run are supported upon timber
framing and brackets.

Wire Bopewaya, — Hardly any of the many mechanical inventions
of modem times has done more to develop the mining industry than
the simple and ingenious contrivance known as the aerial wire rope-
way ; and certainly no particular form of wire ropeway has acquired
a greater reputation or proved more successful in overcoming the
obstacles incidental to transportation in rough and rugged country
than that known as the Bleichert system. The home of this ropeway
is in the United States, where, out of nearly 500 examples erected, not
one has failed, and now it is being introduced into Europe and the
British colonies by W. F. Dennis & Co., of London. By it valleys
up to 1650 ft. in width can be spanned; rivers, buildings, roads,
railways, and other obstacles are crossed without the necessity of
erecting elaborate structures.

Gradients of 85 per cent, to 90 per cent, have been repeatedly and
successfully worked; and ropeways have been constructed with a
carding capacity up to 1000 tons per day of 10 hours.

The lines are proof against strong winds, floods, snow, ice, &Cm
and unskilled labourers can perform all the necessary operations.

The automatic connection and disconnection of the trucks oz
buckets to and from the rope ensures the greatest possible simplicitj?
of working. These trucks are designed to suit the materials that
hjave to be carried, whatever the nature of such materials may be.

The " Bleichert " system consists of two parallel stationary wir
ropes, called the '' bearing ropes," anchored at one end and straine
as required at the other end ; thus a regular and certain stress
put upon the ropes. Along the line from terminal to terminal, the
bearing ropes are supported by wood or iron standards of spe
improved construction. The ends of the two bearing ropes
connected by switches and steel shunt rails of a special shape,
that the buckets or cars are easily run off from one bearing rop



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HAULING AND HOISTING. 119

to the other at the terminals. Upon these fixed ropes the bnckets
or cars are suspended by two grooved wheels ; while a hanger and
another rope, the hauling rope, forming an endless band, working
OTer horizontal pulleys fixed at the terminals, effects the movement
of the buckets or oars along the bearing ropes. To the hauling
rope the buckets are attached by one of two patent ^p mechanisms.
It may be here pointed out that this mechanism is the vital part
of an aerial wire ropeway, and Bleicherts, after the experience of
over 20 years in the design and construction of wire ropeways, have
introduced and patented a roller friction grip for use on inoUnes up
to 1 in 4, which automatically adjusts itself to the varying gradients
of the track, thereby reducing the wear and tear on the rope to a
minimum, and at the same time being a perfectly safe attachment,
lor use in very mountainous countries, with great spans and heavy
gradients, the Bleichert patent lug grip is used ; this is absolutely
Ncore even upon gradients of 1 in 1, and on spans of 1650 ft.

If required, an automatic counting mechanism can b >

the ropeway, registering the lyimber of loaded buckets ti ;

and further, by means of the Bleichert patent track scales, L

backets can be weighed in a few seconds.



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121



REDUCING.



IT few mineral products as they oome from the mine are in a
state for comment use, and in most instances the preliminary
tion is one intended to effect their reduction in size. Obviously
will be great differences in the size desirable in various articles,
it may be taken as a leading economic principle in every case that
*^^'; or grinding is an operation which can be best and most
performed in stages, and that it is impossible with any hard
» to reduce it to a fine state in one single treatment, either
ively or at so little cost as where the process is graduated,
nmark seems unnecessary if only on common sense grounds,
A» persistent manner in which tne principle of gradual re-
^Ti IB overlooked warrants attention being called to it here. At
^age, too, screening is essential, so as to eliminate as quickly
nbk all those particles which are sufficiently small, as not
^ those particles occupy space uselessly, but they also form
iikm for the larger particles and reduce the crushing effect of
maohine. Where power costs nothing, or next to nothing,
conditions may be to some extent neglected, especially if the
r entailed in attending to the screens, and the wear and tear
tlie screens themselves be excessive.
If the lumps of mineral are of an inconvenient size for tramming.

Bare first reduced by firing a charge of some explosive on them,
tben by large hand hammers. The next step is tlie ** crusher " or
RHkbreaker,'* of which several forms are in use.
Oae of the best known is the Blake, with its many imitations. In
• machine, at every revolution an eccentric on a shaft causes a
kbk jaw to advance about ^ in. towards a stationary jaw. Thus
of mineral dropped between the jaws are broken by each
ing bite, the fragments falling lower and getting broken again,
diey are small enough to pass out at the bottom, the distance
ai the jaws at the bottom limiting the size of the fragments,
may be regulated at wiU. This crusher is made in sizes rang-
firom a machine having a mouth 10 in. by 8 in., and giving a
ioct of 4 tons per hour, of a size suitable for fine pulverisers, up
ae measuring 30 in. by 24 in. and turning out 23 tons an hour.
Aiotiker variety of jaw crusher differs in the motion being given
l^fte crushing jaw from a crank-shaft, instead of an eccentric

Itt the Bodge crusher, the reciprocating jaw is pivoted at its lower
^•0 that the movement of the jaw is greatest at top and least at
Jtto^^ consequently the product is of more nearly uniform size and
■>Mof the product being regulated by the distance the jaws are



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122 ECONOMIC MINING.

set apart, a finer product is obtainable, though at the cost of a certain
amount of capacity.

The principal objections to jaw-crushers are {a) that the jaw does
effective work only during its forward stroke ; (6) that thin flat pieces
of rock may pass without being broken ; (c) that the product is of
varying and not uniform size.

Gyratory crushers, such as the Oates and the Comet, are a decided
improvement so far as capacity is concerned, for, the motion being
rotary, every portion of the stroke is effective. There is no grinding
action. Gyratory machines are more costly and more complicated,
besides requiring more power, but the output is disproportionately
greater and the product is uniform.

The Coles crusher is so designed that each set of jaws has a very
small amount of breaking or reduction to perform. It has two pairs
of jaws, each pair receiving its motion from one vertical moving piece,
as in ordinary machines, but the lower pair is arranged so as to make
two strokes while the upper pair makes only one, by arranging toggles
of different length. Assuming that a piece of rock entering the upper
jaws is broken in two — it would in most cases be broken into more-
then the lower jaw is supposed to be able to take the product from the
upper jaw, and, with its short length and double frequency of stroke, to
break that material and effectively give a uniform, or a more uniform,
smaller product. Such a machine is proposed as being capable of
performing something approaching twice the work of any ordinary
stone-breaker, and it is suggested as a means of obtaining gradual
reduction and enabling the machines that follow to receive material
much more likely to meet their capacity.

The Schranz crusher is of interest as forming a link between the
ordinary breaker and the crushing roll. The action of this machine
resembles rolls rather than crushers. The movable jaw has a rocking
motion, and its effective action is absolutely continuous instead of ^
being intermittent. The opening of the outlet being constant, the
product is uniform in size, and excellent work is done by this mainline
to a fineness of 8 mm. (say \ in.), at a rate of speed, figure of cost, and
degree of wear and tear far surpassing rolls.

In the Lancaster crusher, the jaw is hung on a toggle or vibrating
link above, and attached to the reciprocating arm below, producing a
compound motion, with beneficial results as to quantity and uni-
formity of output. A simple mechanical arrangement of the driving
gear permits double the number of reciprocations at a given speed as
compared with eccentrics or cranks, and a lever gives control over the
stroke of the jaw duiing operation.

The most remarkable development of the crusher principle is the
Blake multiple-jaw machine which, in combination with an ordinary
breaker, can be used in the reduction of any hard ore or mineral to
almost any degree of fineness, and certainly so fine that aU particles
will pass a 30-meeh wire screen, though the economical limit of such
a system of crushing will probably be found between 14- and 20-
mesh.

In the construction of the multiple-jaw crusher, the main ft1 i<^ing
or toggle jaw is replaced by main swinging, thus doing away with



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REDUCING,



"3



the npwmrd tlunst on the tension rods and consequent wear. Experi-
ence has alBO shown that in machines of not oyer \ in. width of
opening it is better to nse several small machines with a series of jaw
openings say 15 in. x \ in., than a single large machine with a series
of openijigB 24 in. x ^ in. or 36 in. X ^ in.

It is a necessary condition fur most economic working that the
material to be operated npon be sufficiently dry to screen readily, so
as to take ont the fines as rapidly as made, or it must be fed with
inch an exoess of water as will ensure successful screening. Accumu-
lations will mean diminished output or even actual stoppage.

The first mill built on this system was for the Chateaugay Com-
pany in 1882, and it crushed many thousand tons of tough magnetic




"S a

Fio. 67.— Blake Multipli-jaw Grcsheb.

iron ore to pass a ^ in. round screen. Another large installation was
for tike Haile gold mine, dealing with a tough, coarse quartzite. As
at first arranged, the system consisted of one 20 in. X 10 in. breaker,
the prodnct of that going to a 30 x 5, product again being split and
pssBcd to parallel sets of 60 x 2 multiples, each with three jaws,
leaving at approximately |-in. gauge, and going thence to rolls for
reduction to 40 mesh. Fig. 67 illustrates a section of the 60 x 2
midtiple-jaw.

A second installation for the Chateaugay Company was erected in
1886, with a daily capacity of 600 tons from 15 in. down to ^ in. A
iectional elevation of this mill is shown in Fig. 68. The ore is
bionght to the mill by rail, in side-dumping cars, carrying on the
average 7i^ to 8 tons each. The mill consists of two groups or
■Jttems of crushers, with elevating and screening appliances, each



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124 ECONOMIC MINING.

group being an exact duplicate of the other, a "jack-pulley" on
main-line sifting being placed centrally between them. Each group
confiists of the following crushers : — one 20 x 15, crushing fix)m 15 in.



t
>
m



a



e



to 2 or 2 J in. Product of each 20 x 15 is divided, going to two
30 X 58. Product of 30 X 58 is elevated and screened ; that paadng
\ in. round hole is finished product, as far as crushing is concerned,
and is carried to the jigs. The "coarse," li ix) ^ in., goes to three



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REDUCING. 125

60 X 2 mnltiple-cniBhers, each with 3 jaw openings 20 x 2 in.
Product of these is elevated and screened, formerly through holes
\ in. diam., now through -j^ in. holes. That passing through the
xV screen-holes goes to jigs ; that going through 4^ in. holes goes to
two 15 X 7 fine-cmshers. Each of the 15 x ^ crushers has 7 jaw
openings, each 15 x j^ in. Material not passing \^ in. holes, but
going out the end of screen, goes back to the 60 x 2 multiple crushers.
Product of 15 X ^ fine-crushers is elevated and screened, material
not passing ^ in. holes returning to them. Each group of crushers
has 3 jigs.

The actual quantity crushed from Sept. 1886 to January 1888
WIS 122,814 tons of 2240 lb., at a cost for crushing and concentration
of 34*36 cents (1». 5d.) per ton, distributed as follows : —

Fuel for power 7 cents or 3M*

Labour 17 „ „ SJd.

Oil, waete, &0. 2 „ „ Id.

Benewala and repairs 8 „ „ 4(i.

Total 34 „ „ U 5(2.

This economy is the more remarkable when it is considered that
the ore instead of being reasonably dry for screening was often wet
or frozen. With really dry ore, or with the adoption of efficient wet
•creening, the cost could doubtless be much reduced, in favourable
instances perhaps to as low a figure as 1«. or 24 cents a ton. Acci-
dental intmsion of foreign bodies such as gads and picks does not
result in injury to the machine. Packing of all the jaws with damp
fine stuff mixed with the coarse is a much more serious matter, which
ttust be avoided by proper screening.

Ordinary Cornish rolls are a simple form of machine for crushing
mineral after it has passed through a breaker and reducing it to
perhaps 20 mesh. In their range of applicability and general qualities
they compare with fine jaw-breakers, and there is not much to choose
between these two classes under ordinary conditions. The substitu-
tioo of steel eprings or rubber buffers is a great improvement on the
old weighted lever principle.

Where rolls are to be used at all, Erom's system is much to be
preferred to the old Cornish pattern, the principal advantages being : —
(a) That the crushing tyres are made of forged steel, and are firmly
»nd simply secured to the shafts by cone-shaped heads ; (6) that belt-
piilleyB are substituted for tooth gearing, enabling the rolls to be run
»t any desired speed, thereby increasing their capacity; (c) the
adoption of swinging pillow-blocks ; (<i) that the crushing strain is
taken up by bolts, mounting powerful springs ; (e) that a special form
of hopper spreads the ore evenly across the face of the rolls.

The chief point determining the value of rolls is whether the faces
of the tyres wear evenly, and do not become grooved. The life of
Krom's rolls is prolonged by their being, in general, arranged in
double sets, one pair receiving bean-sized ore from the breakers, the
other** finishing" or finely pulverising the screened coarser produce
of the first pair. At the Bertrand Mill, Nevada, Erom's rolls are
stated to crash 50 tons of hard quartzose ore in 12 hours, to pass



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126 ECONOMIC MINING.

through a 16-me6h screen; while in the Mount Corry Mill, Nevada,
50 tons are reduced to SO-mesh in the same time ; and the pulverising
is so done as not to cause the production of an excessive quantity of
" slimes." The very fine dust produced, in greater or smaller quantity,
according to the character of the rock, may be separated by erhaustion
with a fan.

The average speed of the rolls is 80 to 100 rev. per minute. Two
sets of 26-in. rolls with faces 15 in. long give rather more effective
crushing surface than 50 gravitation stamps, each 8 in. diam.« falling
at the rate of 90 drops a minute, the average diameter of the rolli
being taken as only 24 in., so as to allow for their gradual wearing,
while their speed is taken at 100 rev. a minute.

Krom's rolls were designed as dry-crushers. On the other hand,
a small percentage of moisture will not prove a serious disadvantage,
unless such slightly moist ore be argillaceous. An accident to any
part of the machine causes a stoppage of the whole ; but this defect
is of less importance, because the whole operation is so graduated and
regular that there is little room for accidents.

Krom rolls as made by Bowes Scott & Western, London, are much
superior to the original pattern.

Though designed for dry crushing, and occupying the foremost
position of any machine in the market for dry crushing to a fine
mesh, these rolls are being largely used as wet crushers. In one
instance, with copper ores not needing to be crushed very fine, six
sets of rolls, each consisting of three pairs, are turning out 1000 tons
a day, and working very satisfactorily ; but any attempt to increase
the fineness influenced the output largely. The rollers are removed
immediately they show signs of wear from the last mill to the first
of the series.

At a dressing-floor belonging to the Mosel-Labn Company, at
Trier, rolls are used to crush per hour 3 to 3^ tons of wet ore, fh>m
bean-size to pass 2 mm. (say ^^ in.) circular holes, without incon-
venience so long as the rolls are kept clean by a jet of water. A way
of reducing the drawbacks attendant on the uneven wear of the rolls,
which must happen to a certain extent in every case, is to cast the
rolls extra heavy in the first place and to fix a slide-rest to the frame,
so that the face of the rolls can be turned whenever desirable without
removing them at all.

A system of convex and concave rolls has been introduced by
Bowers, for which it is claimed that there is a grinding action inci-
dental to their form, and that they have no tendency to end thrust or
wear against the collars.

Stamps consist of a series of heavy pestles, shod with iron or steel,
arranged in *' batteries " of 5 stamps each. These pestles are lifted by
cams keyed on a horizontally revolving shaft, resting in bearings
secured to the framework of the battery, and dropped in a certain
order, e. g. 1, 4, 2, 5, 3, upon ore fed into a mortar box or coffer, and



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 14 of 76)