Charles George Warnford Lock.

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

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oonvenienoe of handling.

The legs of the tri]^ are adjustable to any angle, being operated
<m what is equivalent to a ball joint.

PBtoB^Lar or Ivoebsoll-Sbboeant Book Dbuxs.



r of cylinder .. .. in,

Length of stroke in.

Wei^t of machine .. .. lb.
Weight of tripod without) ,k

wei^iti /**'•

Slzokes per minute at 60 lb.)>T

pnesuio /

Approximate wei|^t of blow lb.
Depth drilled without) .

<»hAngingr "bits J in.

Afoage work in 10 hours J

inchiding setting drill audi ft

changing bits |

Depth M bole each machine) #^

wiU drill easUy .. ../ "•
Bert iiie boUer to giyelnom.

steam / h.p.

Pnos of drill only .. .. £
Prke of tripod complete,)

with weights /



Letter Indicating Sin.



2

124
40

500

250

12



2*

85 10

6 5



2|

222
165

325

500

24

70

10

4
52 5
10 10



8

236
165

325

550

24

70

14

4
57 10
10 10



8*

246
208

325

650

24

75

14



P.



8J
7
310

249

300

750

24

75



62 10 67
10 10 11 10



8
620

260

250

1000

30

70

80

8
76
18 11



u.



5

8

693

260

250
1500

so

70

50

8
86 10
13 11



The ** C^timns " rook drill made by B. Sehram k Go., London, and
ninstrated in Fig. 5, works on the compound principle. The lower
end of the cylin^r is bored ont to a larger diameter than the upper
end, and, during the forward stroke of the piston, the air is exhausted
&inn the lower end of the cylinder, and the air at full pressure is
Biinultaneouslj admitted to the upper end of the cylinder, thus giving
a most powerful and rapid stroke. The air that has been used to
make the forward stroke, instead of being exhausted to the atmo-
sphere, is now taken through the valve to the under side of the lower
piston and utilised for the backward stroke ; the result of this in com-
bination with the other improvements in the construction of this
drill is that the consumption of compressed air is 40 per cent less
than that of any other drill of the same size ; and in addition to this
enormous economy, the following further advantages are claimed by
the adoption of the " Optimus " drill : —

Gonsiderablv smaller air compressors and boilers are required,
and oonsequentiy reduced first cast of plant.

Great reduction in quantity of coal burnt.

Cost of transport of plant materially lessened.

Smaller air-conducting pipes and flexible hose required.



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40 ECONOMIC MINING.

Where an air oompreeBing plant is already installed, a large
addition can be made to the number of drills without increasiiig the
plant and without any extra power.



Fio. 5.— Ophmus Rock Drill.

Tapping Wasies, — In a working approaching an old waste known
to COD tain water, bores must of necessity be kept in advance, and in
practice it has been found that, with the ordinary method of drill or
jumper, the boring of holes of over 20 ft becomes difficult, owing to
their ^tting stopped up with the dSbris made by the tool, and this
difficulty is increased when it is necessary to have a large barrier suf-
ficient to withstand the pressure of water behind, in oider to protect
the workings to the dip from being drowned. Such a difficulty pre-
sented itself at Alloa and Devon Collieries, where there are large
areas of waste with water, and to tap these wastes, and leave a suf-
ficiently strong barrier of coal, a machine was introduced by Andrew
Hunter, manager of Alloa Colliery.

The machine. Fig. 6, consists of a cylinder a, IJ^ in. diam. inside,
with packing glands. To a side opening is attached a rubber pipe 6,
I in. diam., fixed to pump chest c Two plunger pumps <2, 1 in. diam.
with 1 in. stroke, are fixed to crank spindle 6, and a second rubber
pipe leads to a cistern containing water for suction. On the one end
of the crank spindle is a handle /, 9 in. long, with which to turn the
machine, and to the other end g the rods are attached. The whole is
fixed on a bogie A, 3 ft. 6 in. long by 2 ft. 6 in. broad by 4 in. deep,
running on ordinary cast-iron rails, and set at the inclination of the
seam. In order to keep the machine moving forward while the drill
is cutting, a chain ^ in. diam. is fixed to a barrel with ratchet wheel,
and passes round two pulleys, t k, 6 in. and 10 in. respectively, fixed
to prop ly and a weight m is hung upon a hook at the other end of
chain. This hook is so made that a number of similar weights can
be placed upon it.

The rods, which are hollow, are i in. diam. outside, with ^ in.
diam. hole inside, and in 6 ft. lengths. A box is put on tbe crank
spindle, into which the first rod is screwed with f in. diam. screw.
The other rods are screwed into each other, as is done in the ordinary
method of boring. The drill n, which is also hollow, is Ij^ in. outside
diam., and of the ordinary description, as used by miners for drilling



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DRILLING. 41

holes, except that 1^ in. from the point is the hole to allow the water
to escape.

Where water enters from pumps at 6, are four small holes drilled
throngh crank spindle into the hollow — ^the hollow being continued
right out A ra)ove is also out, into which a set pin is screwed to
keep the cylinoBr in its place.

In appi3ring the macidne, the handle is turned, which works the
cranks, and water is pumped into the cylinder a, and forced into the
hollow rods to the drill point, and is discharged at the circumference
of the rods, carrying the (2^&m which has been made with it. As the
drill cuts, the machine moves forward, and is kept from going back
by the ratchet wheel. When 6 ft. has been cut, the machine is un-
Burewed from the rods, and run back, and another rod is fixed. Care
most be taken in cutting the rods not to allow them to become empty



Fio. 6. — ^Taffino Wastes.

of water, as, if this is not guarded against, they get filled with small
ooal and dSbris^ and have to be drawn. To prevent this, a small plug
is inserted at the part where the rods are cut. Should the weight m
reach the floor before the machine is up distance, it is taken up by
taming the ratchet handle.

At Devon Colliery there is a large area of waste in the lower 6 ft.
ooal, with a pressure of 135 lb. per sq. in., and waste has been tapped
at several places — the greatest distance bored for one hole l^ing
168 ft, 50 ft. of which p^sed through a hard sandstone. Up to 20 ft
or 80, two men can easily bore 1 ft. per minute, while 30 yd. on an
average can be bored in a shift of 8 hours by 2 men. At Alloa 3 holes
have been put in at dififerent angles, a total distance of 46 yd. in the
lower 5-ft coal in 8 hours by 4 men, including shifting and fixing
the machine.



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43



BLASTING.

BzpUmves. — The exploBiyes used in mining are ohiefly of two
classes: —

(a) Those which explode instantaneously Tor almost so), and
known as quick or shattering compounds. Nitro-glycerine is a
decirive type of this class.

(Jb) The weaker compounds, which explode more slowly, and per-
form their work by trajection. This class is called slow disintegra-
ting or rending compounds. Black powder is a promiuent type of
ihiB class.

Explosives of the first class are to a great extent superseding the
weaker kinds. In class (a) the initial pressure is the maximum one,
while in class (6) the explosion proceeds progressively by combustion,
and its gases gradually accumulate and reach their maximum pressure
just before the resistance gives way.

This is an important distinction, and determines the application
of one or the other of the classes, or the adoption of an explosive of
intermediate character in this respect.

The explosive principle in dynamite is primarily nitro-glyoerine,

consequently its explosive power is dependent on the percentage of
_•-» _i ? 1.

Fety and the convenience of portability
ftn absorbent is used as the carrier of
ly this absorbent was of an inert cha-
ir, an infusorial earth found in Northern
X)sed of small diatomaceous shells. The
Y by capillary absorption render it one

the absorbents was to inoorporate the
)e its liability to explosion by accidental
would be exposed in handling it. This
ipressibility, forms, as it were, a cushion
alow imparted to the cartridge contain-
iilt of this physical character of the ad-
ycerine, the eflfect of concussion of an
ad inoperative in its explosive tendency,
>low by reason of the compressibility of
le explosion.

sion, detonators are used, while powder
e the dynamite. When the d3rnamite
black powder was used as a detonator ;
y of its complete detonation, it is but
ig almost entirely replaced by com-

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44 ECONOMIC MINING.

pounds oalled falminates. Of these, the fulminate of mercury is now
the most generally used, and is the best detooating agent. The ltd'
minate of mercury is generally mixed with a small percentage of
gun-cotton and chlorate of potash (or other chemical substitutes), in
order to make it more safe to handle. When wet, it is pressed
into copper capsules, to further decrease the danger of transportation.

Many dynamite compounds employ a chemical absorbent which,
being itself of an explosive character, enhances the efficiency of the
compound.

These compounds are likewise so made as to reduce the quantity
and deleterious character of the fumes which are generated by the
explosion of the nitro-glycerine. These fumes are very deleterious
in confined or badly ventilated places. Nitro-glycerine powders,
however, when fairly detonated, produce innocuous gases. The dele-
terious gases above referred to result from the incomplete detonation
and the slower combustion of the powder, frequently due to the use
of detonators too weak to effect complete detonation.

Dynamite cartridges properly made may be burned in an open
space without exploding, but when burned in a confined space are
liable to be explosive, because the gases generated cannot freely
escape; consequently, the best method for the transportation of
dynamite is not in iron or other strong boxes, which prevent the
escape of the gases when the powder is ignited, but packed in
sawdust in wooden boxes.

Carefully made cartridges, dried internally sa well as externally,
can be transported on very rough roads, and be exposed to consider-
able jars and shocks without danger.

Leaky cartridges, on the other hand, wet from the percolation of
the nitro-glycerine, are very dangerous, and should be condemned as
unsafe for handling. In view of the possibilities of imperfect prepara-
tion of the dynamite, and the terrible effects attending its explosion,
great prudence should always be observed in its use.

At any temperature below 30*^ F. (dynamite freezes at 40° F.)
nitro-glycerine will not explode from any ordinary cause. It is
more sensitive at high than at low temperatures. When heated to
360*^ F. it either bums or explodes. An increase of temperature
likewise increases the liability of the dynamite to leak, whence
explosions may result.

Many accidents result from endeavouring to thaw frozen dynamite
cartridges. The method frequently employed of roasting, toasting,
or baking the powder when frozen is almost suicidal in its character.
Numerous accidents from these methods are annually recorded.

This practice of thawing is not only attended with great danger,
but destroys to a great degree the efficiency of the powder thus
treated. The original Eieselguhr dynamite was more affected by low
temperature than the modern compounds using chemical absorbents.
With strong detonators, the latter class of explosives will do fairly
good work even when frozen.

In thawing frozen cartridges, they should be put into a vessel
contained in another vessel of water. The interior vessel holding
the cartridges should be made of one sheet of iron, so as to preclude



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BLASTING. 45

the poesibilitj of the escape of nitro-glycerine into the lower vessel,
through defective soldering of the joints, when the vessel is made of
more them one piece.

The grade of dynamite with respect to the nitro-glycerine it holds
is designated as follows :



No. 1 = 70 I


per cent.


nitro-glyceriue.


No. 1» = 60


»


)t


No. I** = 50


»9


99


No. 2 =40


»)


99


No. 2* = 35


99


99


No. 2»» = 30


99


99


No. 3 =20





99



Ammonite is a mixture of ammonium nitrate and mono-nitro-
luiphthalene in the proportion of 81*5 to 8*5, according to Colonel
Cimdill, and is appaiently similar to Favier's explosive. The
cartridges are enclosed in a thin casing of a lead alloy, closely resem-
bling the tubes in which artists' pigments are sold. They are
hermetically closed, and have a small tubular projection at one end
which makes the attachment of the fuse very simple. They are, of
course, quite watertight.

For experiment, a weight of 59 lb. was allowed to fall from a height
of 5 ft on to an iron block, upon which the explosive under test was
placed. Tonite, gelignite, blasting gelatine, dynamite, stonite, and
gun-cotton all exploded at the first shock. The sample of carbonite
did not explode until the shock had been repeated. The gunpowder
tried did not explode. The quantities used were approximately equal
in all cases.

An ammonite cartridge was then out in two, and one-half tried
with the same weight and block, but with a fall of 23 ft. instead of
5 ft; no explosion resulted. When a detonator was inserted, and
the operation repeated, a violent explosion ensued. Gunpowder was
then again tried, also with a fall of 23 ft., instead of 5 ft. as in the first
trial, and exploded. Cartridges were then exhibited immersed in a
freezing mixture, where they had been for 3 hours — according to
Butterfield, the company's chemist, under whofe direction all the
^cperiments were carried out— at a temperature below anything
likely to occur, at any rate in England. The cartridges were stiU
quite plastic, and on one being exploded in the usual manner, it was
seen that their properties had not apparently been in any way altered
hy this attempt at freezing them. Another of them was then thrown
on to a bright coke fire, and burnt away fairly rapidly but quietly,
giving off rather dense black fumes. Several cartridges arranged in
a light frame were fired at and pierced by a bullet from a rifle, but
no explosion occurred. One of the pierced cartridges was exploded
hy means of a detonator. A small parcel of dynamite cartridges
exploded at the first shot from the same rifle.

The next experiment consisted in exploding a 1 lb. canister of
gunpowder in the midst of a case of ammonite cartridges. Is one of
the ammonite cartridges exploded under this treatment, but some of
the scattered fragments that were subsequently collected responded
promptly to the action of a detonator.



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46 ECONOMIC MINING.

Ammonite seems to have many good qualities, particularly that of
safety, both in transport and in handling. Its manufacture is also
simple and apparently very free from risk of accident. That it can
compete successfully with dynamite, or the gelatine explosives, in
anything like hard rock is not as jret evident, but in soft ground,
coal, &c., it should be a useful blasting agent, providing it is com-
paratively free from liability to ignite the gaseous mixtures occurring
in coal mines, and does not give o£f fumes either in large volumes or
of a very noxious nature. To ensure successful explosion, detonators
containing 1*25 grm. of fulminate are required.

According to James Ash worth, the use of high explosives in coal-
getting has resulted in their being applied without any attention to
the question of leverage. That is to say, where a 2-in. diam. hole
has been used for blasting powder, a 2-in. diam. hole has been con-
tinued for high explosives. Hence, instead of occupying, say, 8 in.
or more, of the length of the hole, the high explosive occupies, say,
1 or 2 in., and the pressure exerted is as great or greater on the
tamping than on the side of the hole, where the rending should take
place.

The worst disasters from blasting have always occurred with shots
which faced ventilating currents of high velocity. Detonating
vibration appears to be created under such conditions, whereas, if the
force of the shot goes with the current, it is not created ; and he
urges that no explosive is sufficiently safe for use in a dusty or gaseous
mine, if its detonating vibration is Hke that of a mixture of coal-dust,
firedamp, and air.

Becent experiments* with a new explosive called Westphalite seem
to indicate that it is up to the present the safest of all for blasting
in coal mines, as it has been fired without tamping in mixtures of
gas and suspended coal-dust without resulting in ignition, explosion,
or flame.

Tainptn^. — The packing which holds the blasting cartridge in

Slace is called " tamping." The success of a shot very greatly
epends on the tampine being efficiently performed, and to careless-
ness in this operation a large proportion of the accidents due to blown-
out shots are traceable. There is therefore a double advantage in
having perfect tamping, firstly that the effectiveness of the sbot is
utilised to a maximum, and secondly that the risk of accident is
reduced.

There has recently been introduced a tamping plug for which it
is claimed that it automatically increases the chamber, both of gun-
powder and dynamite, at the time of explosion, while it greatly in-
creases the safety by causing sufficient resistance to entirely prevent
blown-out shots, ^his is shown in Fig. 7. a is an octagonal piece
of pinewood, out of which a wedge 6 has been sawn ; c is a piece of
gummed paper which is stuck down over the sides of the block when
the wedge is in place.

Fig. 8 shows a section of a blast-hole with the wedge in position :
a represents the charge of powder ; 6, the tamping plug ; c, a quantity
of loose tamping thrown in above it ; d, the fuse. When the diafge
• J. Higson, « Mining JonmaV Not. 17, 1894.



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BLASTING.



47




18 fired, the exploeion, it is stated, drives the wedge upwards into the
body of the block, jamming it tightly against the sides of the hole.
The driving in of the wedge increases the size of the chamber in
which the powder is placed by about a lineal inch, thus allowing the
powder a Httle extra time and space in which to ignite before the
explosion takes place. The
result is claimed to be that
8-10 per cent, lees powder
needs to be used with this
block to produce the same
efiect as when ordinary
tamping is employed.

Henry Johnson main-
tains that inefficient blast-
u^g* together with the atten-
dant disastrous e£fects, is
to be principally attributed
to the following causes: —
(1) Incomplete cleansing,
and consequent amalgama-
tion of explosive and ooal-
dnst or borings, left in the
borehole. (2) The use of
ooal-dust,- or underolay
mixed with coal-dust and
fragments of coal, or under-
day mixed vdth fragments
of hard olunch or rock for
stemming. (3) Too. much
explosive with too little
tamping. (4) Unequal
strength of tamping, compact at bottom and loose
at top and sides, in consequence of rammer head
bong excessively smaller in area than borehole, and
by its own weight always seeking the bottom of
the borehole, rather than the bottom, top, and sides. _
(6) Irregularity of borehole. ^^^- %";;J^^"^^

With the view of overcoming these difficulties
Johnson has designed an apparatus consisting of an improved punch,
a cleanser and rammer, and some compressed cartridge tamping.

Just in the same way that the compressed powder cartridge or
bobbin has so conveniently and safely superseded loose powder, so it
is expected will the machine-made clay pellets supersede the rough
looie stemming. In these patents the fuse or battery vnre is kept
central throughout, obviating abrasion against the VTall of the hole,
through the use of the rammer.

The price of the tools is not extravagant.

EUdrie Firing. — The most striking advantage of this overall other
BjBtems of firing is that the moment of firing can be determined, and
any number of shots can be fired simultaneously ; besides which it is
the only reliable subaqueous method.



FiQ. 7.— TAMPiNa
Plug.



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48 ECONOMIC MINING.

An eleotric fuse is an explosive substance placed in the oirciiit of an
electric current, which is passed in either of two ways— n^a) by " high
tension," (6) by " low tension " or " quantity " machines. The former
have some advantages, especially in simplicity of handling by non-
electricians, but with them it is necessary, yet difficult, to ensure
perfect insulsition. Quantity fuses do not demand complete insulation.
The exploder may employ a frictional or a magneto-electric current.
Frictional electrical machines are very effective when in good
working order, but as soon as they become damp their power decreases
considerably. In consequence of the greater outlay for wires of high
insulation, and the care and time expended in keeping the apparatus
dry, frictional machines are not so suitable for blasting purposes as
ma^eto or dynamo-exploders.

It is of primary importance that an exploder should possess great
power. The mistake of using weak machines has done more than
anything else to hinder the adoption of electrical firing.

In cases where only short lengths of conducting wires are em-
ployed, and these frequently shifted or subjected to such rough usage
as would endanger the insulation of the cable, the use of electricity of
small electromotive force is advisable, for this will pass without loss
through a cable with faults in the insulation, whereas currents of
greater force would readily escape. In such cases, therefore, the
quantity exploder should be selected. On the other hand, when the
conducting wires remain for the greater part of their length undis-
turbed, hiffh tension electricity is preferred, because its greater power
of overcoming resistance enables it to fire a larger number of fuses
through longer distances. On this account the tension exploder is
better suited where the firing of a large number of fuses simultaneously
through long circuits is required.

For blasting, the tension exploder is also usually preferred, in
consequence of tension fuses being cheaper than platinum wire fuses.
When, however, a system of mines has to remain a long time in*
operative, and yet in a condition to be fired at a moment's notice,
daily electrical tests must be taken, and this can only be done when
platinum wire fuses are used. In such cases quantity exploders are
employed.

In Siemens Brothers' dynamo-electric mine exploders, electro-
magnets are substituted for the permanent magnets of the magneto
machines, and a Siemens armature is caused to revolve between the
poles of the electro-magnets. The coils of the latter are in circuit
with the wire of the revolving armature, and during rotation the
residual magnetism of the soft iron electro-mas^iiet cores at first
excites weak currents, which pass into the coils and increase the
magnetism of the core, thus inducing still stronger currents in the
armature wire. This accumulation by mutual su3tion goes on until
the limit of magnetic saturation of the iron cores is reached.

The choice of the most suitable leading wires and cables depends
upon the nature of the blasting operations that have to be undertaken,
and the distance of the exploder from the shot-holes. As a general
• rule, wires insulated with gutta-percha should be employed for sub-
aqueous work, and rubber-covered wires for surface blasting on land,



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BLASTING. 49

and sabterranean work. In oases where there is no likelihood of
damage being eansed to the wires leading from the machine, un-
armoored cables can be used, theee requiring two separate lengths of
wire from the exploder to the shot-holes ; or concentric or twin cables
can be adopted. These latter types have the main and return wires
together in one cable, so that only one length is needed
for connecting the machine with the fuses.

In electrical blasting it is of the first importance
that each joint in the fuse wires, and the joints be-
tween the wire of each end fuse and the leading wires
or cables from the machine, should be so well pro-
tected as to avoid any chance of earth contact, or short
circuit. The bared conducting wires after having been
craped clean are twisted together, and then (in the
case of gutta-percha wires) slightly smeared with
Cliatterton compound and coverod helically with a



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 6 of 76)