Charles George Warnford Lock.

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

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about 10-12 per cent, of i'
weight of matte, the
consumption over blast-f
naoe practice being due
the need of high tem{
in the matte, otherwise
long run in launder g
cold blast might dull
round the converter tuj
besides which the oom
is not always ready ixx 1
charge. The rem^t^
quires much skilL
about -25 per oent. Ume
used, to give fluidity to
well skimmings. Theme'
matte passes below
tuyers and settles in the i
to a depth of 30 in.
blast is regulated to
the matte on a level
the lip 6, from which i
occasionally drawn,
slag contains 4-5 per
copper, and is returned to the blast furnace, where it acts as a
to tne charge and gives up its metal. A fiimace 5 fL diam« ouf
requires 2 men, and will melt about 30 tons matte a day, snppl;^
3 converters. The launder ^ is of wrought iron, semioircalar
section, 12. in. diam., and supported from a swinging crane by
tackle.

The converters (Fiff. 123) are swung on trunnions a, one oommi
nicating with a wind-chest h encircling the converter, and tha
admitting the blast. The converter is in 3 sections of ^ in. rivets




Fio. 122. — Bbmelting Fubnaoe, Ooppbb.



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METALLIFEROUS MINERALS,



45 1



onghi-iron boiler plate: the upper Bection or hood has inside
merouB wronght-iron crooks e, riveted on, which afford a hold for
) lining. The wind-chest has f in. holes drilled from outsidelthrongh
outer ahell and on through the side of the converter. The outer
le 18 kept closed by an easily removable wooden plug, so that the
ler tuyer hole can be kept
ar from copper incrustation by
ustixig an iron rod through the
e into the interior of the con-
ier. The mouth of the cen-
ter is about one-quarter the
side diameter of the body, and,
BQ in position, points up into
opening in a brick gallery,
ten oommtmicates with a dust-
mber and stack. A worm-
rw operated by power takes
> a cog-wheel 20 in. diam.
kched to one trunnion of the
verter; it can be worked in
ler direction by pulleys. The
r all around tne converters
ormed of iron plates, because
he occasional spitting of matte
1 the converters, and the
ping over of slag or copper,
poxiring and wheeling. On
, the hot liquid quickly chills ;
MB not adhere to the plates,
be quickly shovelled aside.




^1 \ . .

\ri T * • r M



Fio.



123.— CopraB CovTutTEB:
Pabbot.



VHien the converter lining is eaten out, the first business is to
it : it is allowed to rest until the red heat has disappeared, and
L vrater is very cautiously introduced through a rubber hose;
r a time the whole interior is filled with water, which overflows,
I over the exterior, and escapes through a trap and drain under
iron floor. When the converter is cool enough, the water is
tied oat, and a man goes inside to remove all loose lining and
»er nuggets with a pick, or with hammer and gad ; it is then
ed month down and emptied. Frequently more man hidf the old
ig remains undisturbed, and the new lining is placed over it.
Unin^ is composed of ground quartz (98-100 per cent, silica),
L sufficient fire-clay to make it stick together ; less ^n 15 per
. best fire-day does not satisfactorily keep the lining in its place ;
ding is done in a revolving quartz-pan with stationary rollers,
mixing by a machine simili^ to an old-fiashioned clay-mixer for
vn% brick. Composition of lining in bottom and sides : crushed
^tK (^99 per cent, silica), coarse and fine, 20 parts by bulk ; best
sl^y, 3 ; for converter hood : fine crushed quartz, 6 parts by bulk ;
fixe-clay, 1 ; for remelting famace and well, and for launder,
» mm for converter bottom and sides. This lining is meant to wear
^ ; in fact, the process depends upon the union of its silica with

2 o 2

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452 ECONOMIC MINING.

the oxide of iron. The linings last generally about 8 honrs. Wben
the converters are running, one is oooling while the second is diyiDir
out and being heated up, and the third is in full blast, prodncbg
metal. In each shift of 12 hours, the lining of the 3 oonvertera is pa-
formed by one liner and his helper. When the lining of one k
completed, a ladleful of hot slag is poured in, an armful of wood %
thrown on it» and on top of this 2-3 bush, coke; a gentle blast i
turned on through the tuyer holes, the lining dries out and after-
wards gets red-hot, and the converter is ready for charging. A maa
then shifts the belt, so that the converter turns on its tnumioa
through an angle of 90°, until its mouth points toward and a littk
below the tap-hole of the remelting furnace- well. The launder i
swung into place, and lowered by the chain tackle until its free ed
is thrust into the converter mouth. A helper to the lower cnpdi
man holds an iron rod, 1 in. diam. and 5 ft. long, at the t&pit^
while the cupola man drives it with a sledge. This is sometime
quite a task, as the accumulation of chilled metal around tlie t^-bd
may require the rod to be driven in 2 ft. before the liquid metal i
reached. When the rod slips in easily, on reaching the liquid meti
the helper hooks a close-fitting iron on the rod close to a knob at ii
outer end, and a reverse blow of the sledge jerks the rod out, t)
helper landing it out of the way by means of the hook iron. Ti
molten matte then spurts out with gi*eat energy, under the preasai
of about 6 lb. to the sq. inch. It is allowed to run along the laxmA
into the converter for about 10 minutes, that is, until about 2 t«
have entered. As the converter begins to fill, a light blast is tnnu
on to keep up the heat. At a signal to shut off, the cupola man plaa
a sheet-iron shield over the launder so as to cover it for a distance «
4-5 ft. from the tap-hole downward, in order to protect himself fra
the intense heat to which he is exposed while plugging the bol
The plugging is done in the usual way, by placing a pyramid of ai
clay on a disc upon the end of a rod and thrusting it into the tap-bci
The launder is then swung out of the way, the air is turned on fi
blast, and the converter is brought upright with its month pointa
into the opening in the dust-gaUery. A dense cloud of sulphmd
acid and other gases pours out of the mouth of the converter witk
noise like a heavy waterfall. The air-blast enters under an inio
pressure of 8 to 12 lb. per sq. in. (the higher pressure being lai
desirable). It is produced by a compound direct-acting pum^
blower of the Corliss type.

From this stage onward no fuel is used, the heat being supp^
by the combustion of the sulphur in the matte. It sometimes happd
however, either from the initial temperature being too low, or fa
there being too small a charge, that the combustion of the snlf^
fails to keep up the heat toward the end, and in this case a stick
wood is thrown in. The air enters the mass about 6 in. above i
bottom of the lining. Its first action is to replace the sulphur
combination with iron by oxygen, and to oxidise this sulphur to i
phurous acid gas. This double reaction is shown in the eqiuii
2PeS -h 3O2 = 2FeO -h 2SO2. The iron oxide is brought toward i
sides by the action of the currents of air, where it com^ in ccsi

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METALLIFEROUS MINERALS. 453

ih the incandesoetit quartz lining, and oombines with it to form a
dlicate of iron, which floats as a top layer. This action is shown
the equation FeO +• SiO^ = FeSiOj. The composition of the slag
OS formed varies considerably with different charges. It sometimes
[>W8 a few per cent, more SiOs than Fe, as indicated by the formula,
t it usually contains rather more iron than silica, thus showing
tt there is a small amount of the unisilicate formed. There are
K) small percentages of the silicates of lime and alumina.

This stage of the process is characterised by dense white clouds,
iged with rose and green. The rose tint first disappears and the
dte gradually diminishes, while the green becomes more constant,
oally, the close of this stage is indicated by both the white and
sen changing to a pale blue. When this change has become per-
cent, it indicates that the iron is entirely combined with the
ica.

The blast is now shut off, the slag-pots are run under, and the
Bverter is turned over. While the slag is poured off in a thin
stm the skimmer tests the stream by rasping it with a long skim-
ng-rod, which causes the fluid to spatter in all directions. When
» behaviour of the fluid exhibits the characteristic jump of white
ital, thus showing that some of this is escaping with the slag, the
immer orders the converter up a few inches, ana after lightly skim-
ng the charge, he turns on the blast, and orders the converter
light up as before. Before the converter gets up to its old position,

the white metal obtained from the slag-pots and the scraps of
pper swept up from the floor are thrown into the charge. Each of
B slag-pots wnich has just been flUed is found to contain when cold
mtton of white metal near the bottom. These buttons are easily
Mrated from the slag by a blow of the sledge, and are thrown into
nequent charges at the same stage of the process. The slag con-
118 3-5 per cent, copper, and it is sent back to the blast-furnace in
Bpany with the skimmings of the cupola-wells before described,
te converter now contains nothing but white metal, as the iron,
le, and alumina have been slagged off, and the lead, zinc, arsenic,
d antimony volatilised.

During all the period of blast, the wooden plugs in the wind-
Mt are extracted one after another, and the corresponding tuyer
iee are kept clear by rods, which are hammered into the converter,
is necessary to do this continuously, on account of the rapidity with
uch noses of copper form over the tuyer holes, ^especially towards
B close. After the blast has again been turned on, and the second
1^ commenced, a rather scanty blue flame, sometimes mixed with
^te, comes away from the converter. Thijs colour changes gradu-
ly. First the blue and white lessen and a rose colour creeps in,
itQ thev disappear. The rose then deepens to red and afterwards

reddish-brown ; at the same time its size gradually contracts until

the dose only a thin, sharp tongue of flame is to be seen. The
iBcise moment when the suljmur is all gone and nothing but metallic
pper left is hard to prescriba, as it is entirely a matter of experienoe.
^ colour of the flame often varies in shade, and sometimes entirely
appears at the mouth. The changes from sulphide to copper, and



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454 ECONOMIC MINING.

X'n from oopper to oxide, are so very slight in appearance tlut tl
le charge may actually be oxidising, and give no sign until ti
oopper is too cold to pour. Snch a mishap has sometimes oocnm
and has created an enormous amount of work ; in fact, if such \
event happens when the converter is pretty well worn, it would see
most profitable to cat the rivets and take it to pieces. If^ wlusn i
flame shows the process to be nearing its close, the sparks which t
projected against the plate on the farther side of the dosi-galkr; t
carefully watched, it will be seen that some of them stick to ti
plate, glow brightly, and instantly disappear, while others, of ih
colour, rebound from the plate like red-hot shot. When those whi
stick and glow become few, and those which rebound become noiK
ous, it is time to pour.

If it be an object to get a very high per cent, of oopper, it
better to allow a small amount of oxide to form ; but care must
taken that the charge remains hot enough to pour easily. <
turning down the converter, the colour of the interior will ^low
the experienced eye whether there is sufficient heat present in i
mass. If the sulphur is not entirely gone, the surDEUse will be smool
but if any oxide nas formed, it will be seen floating on top as a bleU
mass. This cannot form so long as there is any sulphur remainii
In the pouring process the oxide is kept back by throwing a di
compost of a few pieces of scrap copper £rom the floor, acnas t
converter mouth. The copper flows out underneath this dam, and t
oxide is left inside the converter. This remaining oxide does
harm, and is not lost ; for as soon as the new chai^ is put in, %
reduced back by the sulphur in the matte.

A great deal of copper and oxide adheres to the lining, so tl
when a converter is to be lined, tbe best practice is to wash it oat
running into it as much matte as will fill a couple of slag-pots, ti
on the blast a few minutes, and then turn out the whole charge b
the pots. The clinging particles of copper and oxide are thus <£an|
back into white metal, and as this readily pours, the old lining isj
quite clean. This practice, however, is not followed when ^ i
verters are crowded with work and the blast-fumaoee are not ^
the lining has become so eaten that a clean sweep is to be made d
the entire mass is taken out and distributed among some of the b^
furnace charges. This is done because the copper, silver, and ^
work into it for 4-5 in. and would be otherwise lost.

When a converter is ready to pour, a series of removable nKffj
arranged on a wheeled car are run under it, and 4 men, with L
hooks, roll this truck forward or backward to catch the stream in
successive moulds. As the copper shrinks very greatly in coohi
3 or 4 moulds are first filled, and then the frame is run back ai»i d
are re-filled, till each may contain about 200 lb. copper. The ©«
are previously daubed with a clay mud to prevent the ]ag»
sticking to them. A charge produces about a ton of metaL
time occupied varies very greatly with tbe grade of the matte, L
temperature, and force of blast, but the average time, from fills
pouring, may be put at about 2 hours. With a low-grade matte,
slag has been formed, the converter is sometimes again filled up



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METALLIFEROUS MINERALS. 455

latte to avoid having at the close too small a mass of metal to retain
be heat. The pigs rapidly become coated with oxide as they cool,
rhich gives them the name of black copper. The fragments are
oonded off from the edges, and they are ready for shipment.

Estimate : — 1 ton 51 per cent, matte requires : coke for remelting,
20 lb. ; coke for heating converter, 10 lb. ; silica, 666 lb. ; fire-clay,
11 lb. ; lime, 5 lb. A plant of 3 converters and 1 remelting furnace

capable of treating continuously 25 tons 51 per cent, matte a day,
id may be crowded up to 30 tons. There are 2 shifts of 12 hours
«b ; day and night shifts change men twice a month ; labour
quired per shift : 1 foreman at 20«., 2 cupola men at 15«., 1 liner at
t«., 1 skimmer at 148., 7 labourers at 12^. — ^total, 82. 2«. This gives
e coet per day of two .shifts, 162. 4«. If 6 converters are run
gether with 2 remelting famaces, the total cost of labour is some-
bat diminished, as follows : 2 foremen at 20«., 6 cupola men at 158.,
liners at 148., 4 skimmers at 148., 28 labourers at 128.— cost per day,
1 4#« If the capacity of 6 converters be crciwded up to 60 tons per
7, the force must be increased for both shifts, thus: 2 foremen,
Mipola men, 4 liners, 4 skimmers, 36 labourers — cost per day, 352. 48.
le seoond case gives the lowest price for labour per ton, but is only
ssible where the two remelting furnaces are so situated as to allow
one cupola man above attending to both. Labourers act as helpers
aU skilled workmen, and shift about as needed, except a few who
» aasigned to definite duties.

Cost of treatment per ton of matte at Butte: labour, 2*93 dol.
U. 2d.); fuel, 0*98 doL (48. 1(2.); silica and fire-clay, 1*84 dol.
, SA); blast, 0-90 dol. (38. 9(2.); total, 6-65 doL (278. 8(2.). To
s must be added interest on investment and on the expense account

30 days, between shipment and marketing; at 10 per cent, per
inm this will amount to an additional 13 cents (6^.) per ton;
aire and renewals will add another 13 cents per ton, giving a total
6-91 doL (298. 10(2.) per ton of matte, or 13-55 doL (568. 6(2.) per

of copper. The price of fuel is based on ooke laid down at
O doL (348.) per ton.

Tlie cupola shaft at the Parrot works, Butte, has been water-
ceted: this is a very decided and obvious improvement, readily
geeted by blast-furnace practice. The metal-well has also been
;er-jacketed ; this is not so evident an improvement, because the
^te, when sometimes kept a long time in the well, owing to some
\y in the converters, gets chilled to a great depth about the tap-
^ and bottom. The lining of the well, as before practised, would
n to be the better plan.

Converters have been made of f-in. cast-iron, in 3 sections, sepa-
Le Trhen bolts around the edges are removed. These converters are
crvable from their trunnions, and are handled by a car and crane.
en the lining is to be repaired, the converter is removed by run-
^ a car under it. The car is provided with 4 adjustable platform-
wn^ which are screwed up until they impinge upon 4 projections

upon the side of the converter. The trunnion screws are then
eoed and removed, and the converter is run out on a track, where
9«am-crane picks it up and sets it on the floor. The 3 sections are



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456 ECONOMIC MINING.

then separated by unscrewing the bolts around the circumferaice,
and the interior, thus exposed to the air, soon cools sufficiently for
relining. Meanwhile another extra converter, which has been pre-
viously relined, is put up in the place of the one just removed, lliis
arrangement requires a double set of converters, one being worked
while the other is being cooled, relined, and heated up again. The
cooling is sometimes effected by a blast of cold air passed in thrcmg^
the trunnion, and the same blast heats it up again when a fiie is
kindled inside. By means of the steam-crane the parts are easilj
picked up and put together after relining. The arrangement for
turning the converters consists of a rack-and-pinion wheel, the latter
being attached to the trunnion, and the rack being moved by a pistoc
in a water-cylinder. The water-pressure is furnished by a doabk
plunger-pump and a hydi-aulic accumulator.

The use of a double set of converters, the preparation of one while
its mate is running, the opening of the converter for relining, vA
the handling of it by a crane are great advantages, but th^y aR
partially offset by several disadvantages in the practical method ol
carrying out the idea. The use of cast-iron is of no advantage; as
the contrary, it makes the converter heavy and unwieldy, and tk
mass of metal absorbs much heat, thus prolonging both the cooling
and reheating operations. Again, the cast-iron cracks very soon ii
every conceivable direction, and frequently 2 weeks' service will find
several bolt-holes cracked out. Occasionally, however, one will be
found to stand the wear very well. The work of separating the paitBi
seemingly so simple, is sometimes very arduous, for the reason ^
the lining bakes together at the junction, becomes continuous, and ^
a stone hardness. When the bolts are removed, the parts refuse ta
budge, and much time and hard work are consumed in prying ^
sections apart, to the frequent injury of the converter. The metW
of cooling by an air-blast is not so expeditious as that describd
below. By making the converter in 3 sections instead of 2, moH
time and strength are expended in separating the lower sections tki
are compensated for by any advantage gained; henoe it is zai^
done. The two lower sections had better be in one, and of a difiena^
shape, to facilitate the extraction of the old hard-baked lining— <fc(
most serious work encountered in handling the process.

Stickney suggests * that this process may be made more prodnctiTS
at less expense, by certain changes in the machinery and the meiia'
of handling it. The most obvious drawbacks at present are : (1) 1^
waste of heat io cooling the matte and again remelting it; (2) til
short life of the lining, with the attendant neoossity of cooling 4
converter and heating it up again ; (3) the length of time reqiii*^
to cool the converter ; (4) the difficulty of separating the parts wba
held together by the hard-baked lining ; and (5) the great amcmot^
hard labour required to extract the old lining.

By arranging the blast-furnace on an elevation above the readi
ing furnace, the necessity of much handling of the matte willll
avoided. In such a case the matte may be run into small mouldiAi
♦ * Mineral Industry,' 1893,



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METALLIFEROUS MINERALS.



457



ow. The hopper may



size of hricks, arranged in gangs on one babe, and, as soon as they
cool enongh to set, they may be shot down an incline to a small iron
bin, which has a small opening opposite and quite near to the feed-
door of the remelting furnace. From this bin the cupola man will
feed. The mass of matte will therefore enter this furnace at a little
lefis than melting heat. If the blast is at any time producing more
matte than is needed at the remelter, the overplus may be allowed to
cool, and, being dumped into another bin, it may be used whenever
the blast is producing less than the remelter requires. In this way a
large amount of fuel, probably one-third of that now used, may be
taved. It must not, however, be forgotten that the temperature of
the matte as it enters the converter must be considerably higher than
irhen it leaves the blast-furnace, and hence the remelting furnace
:amiot be done away with.

The duration of the lining may be greatly prolonged by placing
m iron hopper with an air-tight cover above the trunnion of the
inverter, forming a communication between the hopper and the
'last-pipe by a vertical pipe entering the latter at a point near its
utrance to the converter. The vertical pipe should have a gate
tadly closed and opened by the workmen
» filled with perfectly dry
nd powdered quartz, or
rith any powdeied quartz
re which contains no metals
xoept gold and silver. A
ery small percentage of
opper might not be detri-
lental. By a judicious regu-
ition of the supply turned
ito the blast-pipe, so that
be quantity shall be slightly
elow the needs of the oxid-
ing iron in the matte, the
ning will bo called upon
>r but little silica, and its
fe will thus be very greatly
rolonged.

The converters may be
>oled much more quickly by
ttroducing a cold spray,
roduced by inserting a small
r blast-pipe into a water
tpply pipe near its end.

J3ut a more important sug-
»tion is to modify the con-
raotion of the converter, as
town in Fig. 124. It is made of A-^* ^teel boiler plate, riveted,
LO body in one piece and the hood in another, the two being
parable by driving out wedges from dogs on the outer rim. The
aiii body tapors downward about 1 in. in 1 ft. False bottom and




[iWiii* i || t ■ ftt Til I ,

1 ©II I



. #*' ~.



....♦,



FiQ. 124.— Ck)ppiB Contebteb: Stioknet.



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4S8 ECONOMIC MINING.

sides are made in pieoes of ^in. sheet iron. The hood ia of tiu
same material, and has no falsia lining, but pins near the lower edg<e
and at intervals over the inside (kept in plaoe by a small shonldei
inside and a wedge outside fitting into a slot in the part of the pii
that projeots through the converter shell) take the place of the catdio
and hold the overhanging roof of the converter in place. When it i:
desired to remove the lining, the outside wedges can be quickl.^
driven out, and the pins driven inward through the lining.

The lining is put in place in the following manner: The fids
bottom and sides are fii^t polished with graphite and placed ii

Sosition. The bottom is pounded hard with lining composition to :
epth of 18 in. A kettle, which has been made of |-in. boiler-iron
2j^ ft. diam. on the bottom, 4 ft. high, expanding at a 8omewh&
greater rate than the converter shell, and perfectly smooth on th
outside, with handles at the top, is set on the pounded quartz bottoo
exactly in the centre of the converter, and the uning is then shovellei
in and pounded hard around it. Afterward the kettle is lifted on
by a crane, and a cavity is left in the centre of a strong wall linin;
about 15 in. thick at bottom and 12 in. at top. This wall extends u]
flush with the top edge of the main body. The top of the wall al
around is then sanded with fine dry sand. The hood, having its pin
in place, is turned hollow side up and is plastered with lining com
position to a depth of 12 in. at the edge, gradually diminiahing U
3 in. around the mouth. The hood is then picked up by the csrane
turned upright, and placed on the body. The flanged edges ai<
secured together by dogs and wedges, and, after being heated, tlu
converter is picked up by the crane, landed pn the carriage, and rolled



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 51 of 76)