Charles George Warnford Lock.

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

. (page 41 of 76)
Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 41 of 76)
Font size
QR-code for this ebook


section of the hole, the pis enters the crack and the rook is split
a straight line, simply because, under the circumstances, it cann
split in any other way. The form of hole is, therefore, almo
identical in principle with the old canister system, save that it hi
the great advantage of a shaped groove in the rock, which server as
starting-point for the break. It is also more economical than tl
canister, in that it requires less drilling, and the waste of stone is let

The mountings for drills in quarry work are tripods, bars, gaddt
frames, &c. The tripod is the most useful and general form i
mounting. Tripods are at the present time made with legs hariii
universal joints, so that they adapt themselves to all the varvii^
conditions of quarry work. It is possible to set up a rock "dx^
mounted on a tripod on rock faces of most irregular form. Holi
may be put in from a vertical position to a horizontal one.

But the tripod drill is applied less to dimension stone quarri^
nowadays than formerly. Quarry bars and gadder frames are no^
used to better advantage. In broken stone quarries where the sni
laces are irregular, and where the quarrying is done by blasting, tk
tripod is the best form of mounting. No one would think of usifl
anything else for a railroad cut, a rubble stone quarry, or for ve^
deep hole work in granite quarrying. A modified form of mounting
known as the Lewis-hole tripod, has reoentlv become very popnli
in the New England granite quarries. This is a regular tripod wi^
a slot cut in its saddle by means of which the drill may be movd
laterally and in a parallel line, thus putting in 3 holes close to eaJ
other without having to move the tripod. The partitions betw««
these holes are sometimes broken down by a broach, and the hok
charged with powder for bl isting, thus making a br^ak in a manoc
somewhat similar to that made in the Knox syhtem.

The most useful mounting for a rock drill, next to the tripod, u
quarry bar. This is a horizontal bar made either of pipe or ang'
iron some 10 ft. long, with end pieces, which rest upon 4 legs,
drill is moved along the bar bv means of a rack ; thus a numl.
holes are pnt in exactly parallel with each other, and without mov
the bar. The most popular use of the quarry bar is in sandst
quarries, where it has replaced the old system of digging a tren
with a pick for releasing by means of wedges. -Since the introdactf
" '^e quarry bar, drill holes have been put in, into which plugs t



Digitized by



Google



NON-METALLIFEROUS MINERALS. 363

feathers are inserted for breaking up. The plug and feather prooess
being done by machinery is cheaper than wedging. Another advan-
tage is, that when the splits are made the stone has not the same
tendency to " run offl" jPlug and feather holes vary in depth from
3 Id. to 10 ft. Shallow hole work is mostly confined to granite
quarrying. Granite possesses a remarkable capacity to break on a
true line, hence small holes of about the diameter and depth of one's
finger are put in on a straight line, and by means of little plugs and
feathers a furce is exerted on this line which will break a block even
to a depth of 6 ft., leaving a space as true as though it had been
channelled.

In sandstone quarries plug and feather holes are usually put in
2 or 3 ft. deep for breaks of two or three times the depth of hole, but
in almost every case the depth of a plug and feather hole must be
regulated by the breaking capacity of the stone. It is sometimes
aeoessary to run the hole entirely through the block in order to
insure a straight break. In the Tuckahoe marble quarries plug and
feather holes are put in about 10 ft in depth and only f in. diam.
[t has been found necessary to drill entirely through the blocks to
|>reyent "running ofif."

It is not necessary in every case to use plugs and feathers that
ire equal in length to the diameter of the hole, but it is sometimes
tdyisable to drill deep holes in order to weaken the block and ensure
k straight break. A system in common use in marble quarries is to
Irill plug and feather holes alternately 2 or 3 ft. in depth — that is,
irery other hole is a deep one.

Quarry bars are used for putting in bottom holes for " lofting "
D the Indiana and Kentucky oolitic quarries. Small sizes known as
he ^ Baby " are sufficient for this work. The largest bars are used
a granite for broaching work, where holes are driUed about f in.
part and to the full depth of the bed, the partitions separating the
tolee being afterwards broken down with a broach. This work
eqnires a powerful drill, a strong bar and perfect alignment.

The size of rock drill best suited for the various conditions that
liet in quarry work is of importance. The tendency is to get a
|ower drill that is too small for the work. The quarryman wants a
ight machine. This question of lightness is frequently given more
uportance than it deserves. The early drills that were put on the
ocks in the upper part of Manhattan Island, and which were the
rst steam drills that were mounted on tripods, were light, handy
lachinee. The inventor evidently had his mind biassed by the oppo-
itiou of the drill runner to a heavy machine, and in order to get
nybody to use it, it was necessary to make it light.

It is a fact that the weights of percussive drills have been
Tadually increased during the last 15 - 20 years. That is, for the
ime kind of work a man to-day uses a heavier machine than was used
)r the same work years ago.

It is undoubtedly true that lightness is an important consideration
a a power drilL It cannot be too lieht in weight so far as handling
I concerned, but it may easily be so light that the work it does is so
itUe ki proportion to hand labour that it may hardly pay to use it



Digitized by



Google



364 ECONOMIC MINING.

The power of a percussive drill is in direct proportion to il
diameter of cylinder. The size of the piston, like the arm of a
is the gauge of strength. The steam or air pressure is
uniform, varying from 60 to 80 lb. per sq. in., so that the qu
pressure does not come in when figuring on the size of a dxil|^j
suited for the work. A rock drill of large diameter of pistoa 1 ^"
a hard blow and has strength to recover from a bad hole, while
of small piston diameter strikes a light blow and is easily
the hole.

In broken stone quarries, or even in dimension stone whean^!
drills are mounted on bars, it pays to use big drills. Where "
put in 15 to 25 ft. deep the diameter of the drill cylinder should
be less than 3^ in. In hard rock, such as that of the Pali»idea4
Hudson, it pays to use drills of about 4i in. diam. of cylinder
holes 15 ft. deep. This has been demonstrated to satisfaction.

Crimmins uses drills of 3^ in. diam. of cylinder for rodt
where holes are put in only 8 to 10 ft. deep, and he states that il
to do so. It would be an easy matter to cite numerous insta
this kind, all of which prove that experience with power drillii
work leads men to use drills of large size.

In hard rock, where the surface is irregular, it takes more
put in a hole than it does to move the machine in position for \
one. Let us assume that it takes 1 hour to drill a hole 10 fit
There are not many places where an hour is consumed in moving
machine and getting started for another hole. This being tiw^'
should evidently seek to get a machine that has as much po^
possible, or in other words, that will drill a hole as rapidly as
after once having been set up and started. We should rather
time due to moving a heavy weight than sacrifice time in <
because the drilling time is that which is longest.

There are other reasons in favour of large drills, such as po'
work through bad places, freedom from breakage, &c.

In dimension stone quarries, where the drills are provided
bars or other fi«rms of mounting by which they can be readily
it pays to use machines that are powerful enough to overcome si
and to strike a hard enough blow not only to drill the rock wbstt
hole is clean, but to penetrate the mud and muck which is in
at the bottom of a ** down " hole.

The Ingersoll-Sergeant Drill Co. have taken a foremost
with stone quarrying machinery. A representation of their
channellerat work is shown in Fig. 98. This machine will out.
sq. ft. of channel per month, and to a depth of 10 ft, in 8|
moderate hardness. It needs no blasting, and saves all the
Completely furnished, it weighs about 3200 lb., and costs 210L

Slaie, — The slate most in demand for roofing and other pu:
a clay -rock of great compactness and very fine grain. Orij_
was a deposition from water in which it was held in suspension |V
altliooigh deposited in layers, it has, under the influence of he«l
couipression, experienced marked changes, one of the results beinj
that it will not divide along the planes of its bedding, bat spliti
readily on what are called " the planes of slaty cleavage." This fiicik



Digitized by



Google



Digitized by



Google



366 ECONOMIC MINING.

The essentials of the slate of oommerce, snob as is nsed for roofing
billiard beds, mantels, blackboards, tilings, urinals, caskets, graTi
covers, steps and risers, boxes, wainscoting, water tables, sills um
lintels, trimmings for bnildings, and many other purposes, are haid
ness and toughnesR.

When too soft, the stone will absorb moisture ; the nail hdcB o
the roofing slate become enlarged, the slates loosen, and require re
placement ; also, if too brittle, the slate breaks un<ler the weight of \
man. When a hole is punched, no tenderness in the material or ten
dency to enlargement of the opening should be seen. Struck will
the knuckles, a good slate gives out a sharp, metallic ring. Ooloor i
not a reliable guide in estimating the durability of a slate. Blad
varieties are not in favour ; the general impression is that they Iut
not the necessary durability. Dark blue, bluish black, purple, graj
and green are the common colours ; some of the purple slates carr
spots of light green, which, by the way, do not injure their dnrabOit]
but the grade is lowered by lack of uniformity in colour.

In judging of the quality of a slate by tilie eye, a great deal <
experience is required. The following tests are recommended : —

(1) Weigh the dry slate, then immerse in water for 24 houn
take out, wipe dry, and weigh again ; the increase in weight will Ij
the amount of water absorbed.

(2) Place the slate on its edge in water so that half the snrfiause i
covered ; if it be of poor quality, moisture will creep by capillar
attraction into that part of the slate above the water line, but it wij
not do so in a good slate.

(3) Breathe on the slate, and if a strongly marked argillaoeoas c
clayey odour is detected, it is safe to assume the slate will disintegral
easily under atmospheric influences.

Dark veins running through the slate are objectionable, as the;
are liable to split along the line of least resistance — nearly alwa^
found to be in the course of this vein or streak.

Crystals of iron pyrites should also be suspected (partioularl
when present as marcasite or white iron pyrite), which oxidise ver
quickly when exposed to moisture and air.

The ordinary cubiform, brassy, yellow iron pyrites have muc
greater power of resistance to meteorological influences than the mai
casite. They have been found in the atmosphere of Glasgow unaltere
after an exposure of 100 years.

The behaviour of slates towards sudden changes of teroperatnt
has also been the subject of direct experimental examination. Th
quality iii this respect may be estimated by first saturating the slat
in water, by allowing it to remain immersed for some days, and the
placing it in a mixture of salt and ice for 24 hours. Its behaviour a
heating can also be ascertained by warming a sample at about 500"" I
for 5-6 hours, and then suddenly plunging it into water. A. roug
approximation of the quality of a slate may be obtained by immersiDj
the broken fragments in hydrochloric acid, when a bad quality wil
at once be recognised by the amount of carbonic acid gas evolved fros
the limestone present. By heating some chips in a glass tube closer
at one end, a sublimate of yellow sulphur and a smell of sulphnroni
acid will be observed in most inferior kinds of roofing slate.

Digitized by LjOOQIC



NON-METALLIFEROUS MINERALS. 367

The tenacity of Blate and its power of resisting pressure is very
rreat ; on an average it takes 20,000 lb. weight to crush 1 cub. in. of
late ; hence its adaptability in thin plates for roofing purposes. The
oruposition of blue Wel^h roofing slate (Prof. Hull) is as follows : —
iilica, 60 '50; alumina, 19*70; iron protoxide, 7-83; lime, 1'12;
oajniegia, 2-20; potash, 3-18; soda, 2-20; water, 3-30.

That of purple slate (Kerwan) is: — Silicat, 48*0; argillaceous
latter, 26-0; magnesia, 8-0 ; lime, 4-0; Iron (FcaOg), 14-0.

The composition of green Westmoreland slate is: — Silica, 55 "8
lamina, 25*7; ferrous oxide, 9' 5; ferric oxide, 0*3; lime, 4*4
irbonio acid, 3*2; hygroscopic water, 0*2; |K)tash and soda, 0*4
^pper, traces.

Blue Westmoreland slate is composed as follows : — Silica, 59*3;
lamina, 17*5; ferrous oxide, 3*8; ferric oxide, 2*3; lime, 5*0;
irbonic acid, 2*4; sulphuric acid, 3*3; moisture, 0*3; combined
rater, 5*7 ; potash and soda, 0*2 ; magnesia, traces.

Some very practical hints on opening a slate quarry to a given
rodoctipn were -published in a paper read before the British Society
r Mining Students, from wliich the following notes are condensed.

The estimate is based on an open quarry to the extent of 6
bargains," reckoned to produce about 180 tons of slate per month,
id developed by an adit.

In front of the slate bed is a layer of hard rock (porphyry) about
) yd. thick, and as the slate rock on the surface or outcrop to the
spth of 5 or 6 yd. is unproductive, it will be necessary to commence
» level low enough to allow a depth of at least 20 yd, at the
tzB-breafit The 5 or 6 yd. bad rock on the top can be removed by
eans of an open cutting on the top, thus making considerable saving
I the distance of transit.

Having cut through the hard rock into slate, the level might be
•atinued a few yards farther, if thought necessary, to prove the rock,
though this has, to a certain extent, been done in removing the top
ck. The next step is to open communications between the end of
tnnel and top floor, by sinking down frum that floor, and by opening
} from end of tunnel simultaneously. The average dimensions of a
Ue "bargain" is about 10 yd. wide by 15 yd. high, and as it is
tended to develop the quarry to the extent of 6 bargains, we shall
qaire a clear face of 30 yd. right and left of the tunnel. First out
Bpace sufficiently wide to allow one bargain to work. This cutting
Qsoally done by miners, but after the first bargain has got to wor^
ul more space is available, another staff of men may now be set to
ork to follow set number one ; the miners are no longer required, as
« qnarrymen themselves, with a little extra price for a month or two,
ill open their own quarry. The same order is repeated until the six
o^ams are in full work.

The top floor being in full working order, and the rock turning
>t satisfactorily, thus encouraging further developnient, another
cilery may now be formed by bringing another tunnel, care being
ken to start low enough, in order to attain a good height of slate at
e fore-breast.

The width of the galleries ought to be at least 15 yd., more if



Digitized by



Google



368 ECONOMIC MINING.

possible ; if they are narrow, serious oonsequenoes may result from
falls of rock rolling over into the gallery below.

The cost of developing the quarry just described may be estimatd
as follows : —

£ <. 4.

Clearing top rock for No. 1 gallery, 60 yd. x 12 x 6 deep

= 4320 cub. yd. = 8640 tone at 9{i per ton 324

Driving level 7 ft. x 6 ft., 40 yd. long at 2i. 10«. 100

Sinking eliaft, 15 yd. deep X 8 ft. X 6 ft. at 62. lOf 97 10

Opening face on rock 30 ft. x 45 ft x 4 ft. = 66 cub. yd. at

5a. per yard 16 10



da.peryara

The necessary plant to work the quarry would
as follows : —



be



6 tons 14-lb. Bteel rails at 62. lOf. per ton 39

Sleepers, 500 at lOd. each 20 16 8

Brobs and nails 3

20 tram wagons at 72 140

2 weigh machines and sheds, one for top floor and one for No. 1

gallery, at 202. 40

Powder house 20

Smith'd shop and tools 80

Sundries 50

Management and sundry expenses, 2 years 300



£1230 16 8



837Z. 10«. of this would be spent on the quarry, and remainder
plant and materials.

Taking 30 tons as the monthly production of each slate
the quarry with six bargains would be equal to a monthly piodi
of 180 tons.

When the slate bed crops up to the surface, and promisee to be
good quality, the following method of opening out might be ad
tageously adopted, providing the hill slopes rapidly.

It will require a cutting 60 yd, wide. Of this, at first, a third naj
be taken, allowing two of the bargains to be working while tt
remaining two-thirds is being cut. Each bargain being 10 yd. wuh
and the distance from the face of one gallery to the faoe of the sci
behind being, say, 15 yd., a space of 60 yd. x 15 yd. must be cleai«
for each gallery, and allowing for the slope of the hill, the rock to I
removed would at leafit average a depth of 9 yd. Each subeeqiui
gallery could be opened in the same manner, care being taken not!
cover any good slate rock below with the debris from the gaUer
above. To avoid this an incline is sometimes made the full length I
the quarry, by the aid of which all the good as well as the bad nd
is conveyed to the bottom, and the bad rook deposited on unproducdi
ground. Care should be taken not to fix the incline so as to interfti
with the extension of the quany.

The cost may be estimated as follows : —

£ «. ^

Clearing top rock 15 yd. x 60 yd. x 9 yd. = 8100 cub. yd.

= 16,200 tons at Sd. per ton 607 10

Incline, with drum and Duiidings 200 •

Cost of plant, &c., as per particulars in estimate for preyiuus

quarry, say 400

£1207 10

Digitized by V



y Google i



NON-METALLIFEROUS MINERALS. 369

The produce of this quarry would be equal to the other, viz. 180
»08 per month.

Slate quarries are usually deep open cuttings, with sides as rude
} imagination can paint. Those situated on hillsides are worked
J means of tunnels ; but there are quarries worked similar to a coal
ine underground.

In the first place it is necessary to blast the rock down from the
iff side. The " docker-up " views the huge blocks, which by means
^ a hammer and chisel are reduced to more convenient sizes, loaded
ito trucks, and by means of a water balance or some other convenient
Tangement, are hoisted out of the pit and delivered in front of the
tlitting sheds. The blocks have now reached their final destination
revious to being made into slates.

Suppose a block 6 ft. long by 2 ft. wide. This is much too long
r the largest slates that are required. To cut it into the most
arketable size, making it into two blocks 3 ft. by 2 ft., a small
>erture is cut in one side, and by means of a series of heavy blows
L the other side, immediately above the apei*ture, with a large
XKien mallet, the block is cut in two; it is now taken into the
ilitting sheds and there awaits further development at the hands of
e splitter. In quarries where machinery is in use for sawing the
cckiB the mallet is not used.

Two methods of splitting are used in England, but only one in
ales, viz. the mallet and chisel, whereas in England they use both
d ** chisel " and '* hammer."

The *^ chisel" man arranges his blocks along his left side, and
ter adjusting himRelf on a low seat, takes a block which be rests
»on his left knee ; by placing his chisel on the end of his block and
-ikiiig it with his mallet, he is able to reduce a thick block into thin
ites. The '' hammer " man, unlike his colleague, does his work
mding ; he takes a block of slate and places it on a raised platform
^nt of him, erected for the purpose ; he holds the block with one
nd and the hammer in the other, the splitting of the block being
somplished by a series of gentle blows along the end.

The speed of splitting is regulated by the cleavage ; when the
lavage is bad, the work of the splitter becomes very slow and
lions, the slates are heavy, rough, and of inferior quality. When
3 cleavage is good, the work is much more expeditiously done, the
tes are more uniform in thickness, finer, and better.
The manner in which the Colly weston slates are made is some*
lat novel. Large blocks are dug in the autumn, and being placed in
lifferent position from that which they had in the quarry, the rain
annates itself between the layers of the stone, and in frosty weather
» water, swelling as it becomes ice> splits the block of stone into
ites of a proper thickness. The dresser now takes the tiiin slabs in
nd, and with his dressing knife and travers-e cuts the slates to
>per shape and sizes. To give an idea of the fineness to which
xl blocks can be split, it may be stat^ that a block 2\ in. thick can
split into 40 slates measuring 20 in. x 10 in.
borne queer technical terms are used in connection with slating,
inet are used to indicate the sizes of slates. One 10 in. by 13 in.

2 B



Digitized by



Google



370 ECONOMIC MINING.

is known as a " double." Smaller slates are called ** small doaUes,**
The next larger size are known as '* plantations *' ; the next sis ii
called " viscountess." Sizes ranging from 8 in. by 12 in. to 10 in. bj
16 in. are called "ladies"; from 10 in. by 20 in. are called " coun^
tesses," up to 14 in. by 24 in., which are known as '' princesses."

In American practice slates run simply by inches, from 7 in. Iqi
14 in. up to 17 in. by 24 in. The thickness of slates ranges froq
* 125 to *3215 in., and their weight varies from 2 lb. to 4J^ lb. persq. fi
A square of slating is rated as any other roofing equal to ICK) sq. fu,
the gauge is the distance between the courses, while lap is counted ai
the distance which each slate overlaps the slate lengthwise not
below but one.

Lap varies from 2 in. to 4 in , and a standard lap is about 3 is.
As above stated, a good slate roof should have about square pitdi, bq
slates should never be put upon a roof which pitches less than 1 fi ii
4 ft. When it is desired to compute the surfeice of a slate when laij
and the number of squares of slating, subtract the lap from the lengdj
of a slate which is taken as distance frum nail-hole to tail, and osq
half the remainder will give length of surface exposed ; this wb^
multiplied by width of slate will give the surface required. |

To ascertain the number of slates required for a square, di *
14,400, which is the area of one square in inches, by the
obtained above, and the quotient will give the number of sUi
required fur one square. For an example, take a slate 12 in. by 24 i
taking a standard lap 3 in., the number required for a square will
found, by subtracting 3 from 24=21, and 21 divided by 2 = 10|i
which, multiplied by 12 = 126 in. ; 14,400 the total area to be coven
divided by 126, which equals the area of one slate, gives 114 29-i
slates required for the square.

Slate weighs 165 lb. to 180 lb. per cub. ft., and, in consequence <
lap, it requires an average of 2^ sq. ft of slate to make 1 ft. of slatief
When slate *125 in. thick is laid on laths, it weighs 4*75 lb. pi
cub. ft. ; when the same is laid on 1-in. boards, it weighs 6-75 lb. pi
cub. ft Slate *1875 in. thick on laths and boards weighs 7 lb. ai
9 lb. respectively. A •25-in. slate weighs 9*15 lb. and 11-25 U
respectively. The thickest kind, gauging * 321 5 in., weighs 1 1 * 15 1|
and 14*10 lb. on laths and boards.

A slate roof composed of 6-in. by 13-in. slate weighs 1680 lb.
square, and rci^uires 480 slates. A 10-in. by 20-in. slating wei
6720 lb, and requires 171 slates per square. A 12-in. by 24-J
slating requires 125 slates, and weighs 4480 lb.

The output of slate in the United Kingdom reaches nearly hilf
million tons a year, with a value of about 50«. a ton. i

Jtff2/«(ofie8. - Stones adapted for the making of mills for gxindia
grain, seeds, cements, phosphates, pigments, and similar subetanoesl
a fine powder are of several kinds, embracing " grits " and ^^ buhq
which are sandstones of frcHh-water origin, as w^ as certain qi
ites (metamorphic), and lavas (volcanic). The qualities desuvd
such stones are hardness combined with toughness or cohesion,
sufficient porosity to give the grinding surface a good hold. As i
in mills, the stones are built up from numerous pieces about 1



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 41 of 76)