Introductory.
According to the best statistics available, it appears that about
eighty per cent. of the injuries received in foundries are in the
nature of burns of greater or lesser severity; the remaining twenty
per cent. being caused by defective hooks, chains, slings, flasks,
mold-boards, bottom-boards, and other equipment, and by unguarded
machinery, by falls and falling objects, and, indirectly, by inadequate
illumination, poor ventilation, and other similar general conditions.
Suitable clothing and shoes will materially reduce the severity of
foundry burns, and will entirely eliminate many of them. Approved
protection of this kind is described in the following pages, together
with safeguards for various machines, and advice is also given with
regard to precautions to be taken for the prevention of accidents in
handling the various tools and appliances that are used in foundries.
Clothing.
Suitable clothing is an important factor in protecting foundry workers
from burns. Ordinary cotton shirts and overalls afford but little
protection, because molten metal burns through them almost instantly;
and although the legs and feet are the parts of the body most often
burned in the foundry, it is advisable for the men to wear shirts (as
well as trousers) made of a thick, stout, hard-finished material,
such as khaki (twilled cotton), which will shed the molten metal to
some extent. The bottoms of the trouser-legs should never be rolled
or folded up, and there should be no other folds, nor any creases
or pockets in the clothing, in which molten metal or highly-heated
particles of any kind may lodge. Torn garments and those having holes
in them are unsafe, and should not be worn. Woolen undershirts furnish
the best protection against “shot” or molten metal, but on account of
the intense heat to which foundrymen are exposed it is hard to get the
men to wear them, particularly during the summer months.
Shoes and Leggings.
The number of burns received by foundry workers on the feet and legs
may be greatly reduced or almost entirely eliminated by the use of
proper shoes and leggings. These should be worn by every foundry worker
who has to handle molten metal, or who is exposed to it, and no one
should be permitted to work without them, where the danger of such
burns exists. Strong, substantial, well-made shoes of the “congress”
type are the most suitable for general wear in foundries, because when
they are in good condition they contain no holes through which molten
metal may enter, while in laced and buttoned shoes there are many such
openings. Moreover, congress shoes may be quickly and easily removed
when hot metal is spilled upon them. Low-cut or Oxford shoes should
never be worn by foundry workers.
Suitable leggings are almost as necessary as good, serviceable
shoes. Under some conditions safety requires that the leggings be of
asbestos or leather, but for general foundry work canvas or twilled
cotton of good quality may be used. These materials will meet with
all but the most severe requirements. The leggings, like the shoes
previously described, should be fastened in such a way that they may
be quickly and easily removed, and ordinary buckles are therefore
unsuitable. Laces and buttons are likewise unsatisfactory, and any
type of fastening that forms projections upon which molten metal may
lodge does not afford the best sort of protection. Flat spring clasps,
properly inclosed, at the top and bottom of the leggings, are the most
satisfactory type of fastening devised up to the present time. The
leggings should completely incase the legs from the knees down, and
should fit snugly, especially at the top, to prevent the entrance of
molten metal at this point.
Eye-protectors.
It is extremely important to protect the eyes of foundrymen against the
intense light and heat from molten metal and from welding flames, and
also against dust and grit, flying chips, and molten metal that may
be splashed about. Eye-protectors (also called “safety glasses” and
“goggles”) of various types are now available for all the different
hazardous operations in foundries. To insure comfort, eye-protectors
should fit well, and should be light in weight and easily adjustable
for size. They should be provided with side protectors composed of
metal screens or of perforated leather, to stop flying particles and
small objects that might otherwise enter the eyes from the sides.
The lenses should not be made of ordinary window glass, but in order
to prevent serious eye strains they should be made of clear glass
without flaws, and polished on both sides. They should also be strongly
framed, so that pieces will not enter the eyes in case the lenses are
broken. The lenses of eye-protectors that are to be used by furnacemen,
welders, and others whose eyes are exposed to unusually brilliant
light-sources should be suitably colored, to temper the intensity of
the rays and to exclude those that are specially harmful to the eyes.
Experience has shown that where eye-protectors have been provided and
worn faithfully, there has been a marked decrease in the number of eye
injuries.
Gloves.
Cupola men and others working where the heat is intense must provide
protection for their hands and arms. Gloves and sleeves of calfskin,
buckskin, canvas, and asbestos are used,--the choice of material
depending upon conditions. When gloves with gauntlets are used, the
sleeves of the shirt, coat, or jumper (whichever is worn) should be
pulled down over the gauntlets. The sleeves should then be arranged
with as few folds or creases as possible, and be secured about the
wrists by means of buttons or clasps or in some other suitable manner.
(By leaving the gauntlets _outside_ of the sleeves lodging places for
molten metal are provided, and serious burns are likely to result.)
There should be no slits or openings in the lower ends of the sleeves
(at the wrists) as in ordinary shirts, because molten metal would be
likely to find entrance through them.
Hand-leathers and gloves of various kinds must be worn by men handling
scrap, pig iron, and hot castings; and rubber gloves are important to
afford protection against acids employed in pickling processes. Thick,
clumsy gloves, which interfere with the safe handling of tools and
implements, should not be used. Care should be taken to see that no
workman wears ragged gloves, or gloves with frayed fingers, which are
specially likely to be caught by moving parts of machines or on the
sharp edges of objects being handled.
Aprons and Rubber Boots.
In connection with pickling processes, rubber boots and rubber
aprons are often necessary to prevent acid burns and damage to
clothing. Aprons are of value in other departments of foundries also,
particularly when flasks and rough, hot castings and other objects
are being carried about, and when it is necessary for grinders to
support castings in position at the grinding wheels. For work of this
kind, and for foundrymen engaged in pouring metals, leather aprons
are recommended. In view of the high cost of good leather, however,
aprons of other suitable material may be used where the leather is not
absolutely required.
Ladles.
Several types of ladles are used in foundries, including reservoir,
crane, sulky or buggy, trolley, bull, and single-hand ladles. Many
burns are caused by defects in ladles, and by lack of care in handling
and transporting them. All ladles should be frequently, regularly, and
critically examined, and when defects are observed the ladles in which
they are found should be immediately set aside for repairs, or should
be discarded if the defects are of a serious nature.
Reservoir ladles and all other ladles operated by gearing should
receive special attention. The motors of motor-operated ladles should
be completely inclosed, not only to protect the workmen against
electric shocks and burns, but also to prevent accidents which might
be caused by metal being spilled upon the motors, resulting in short
circuits or other kinds of trouble. All the gears on geared ladles
should be completely inclosed, the covers or guards being constructed
in such a way that they may be readily removed for oiling, cleaning,
and inspecting the various parts. If guards are not provided the gears
will soon become clogged with dirt and with metal that has hardened or
set after having been spilled upon them while in a molten state; and
clogged gears are likely to be broken or stripped, and to cause serious
accidents.
[Illustration: FIG. 1. A CRANE LADLE.
(The gears should be completely inclosed, to prevent them from becoming
clogged with dirt and spattered metal.)]
Many ladles are equipped with direct-acting spur gears. This
arrangement permits rapid operation of the ladles, but it often imposes
severe strains upon the operators, making it difficult for them to hold
the ladles steady while pouring. This often results in spilling the
metal and causing it to be spattered about when it strikes the sand on
the tops of the flasks. A tilting arrangement composed of a train of
spur gears, or a combination of worm gearing and spur or bevel gears,
is to be preferred. The gears should be so designed and arranged that
at least two teeth of each wheel will be in mesh at all times. Unless
this point receives due attention a serious accident is likely to occur
if the teeth become badly worn, or if one of them should break, thus
permitting the ladle to tilt suddenly when pouring. The small pinions
and worms of geared ladles often deteriorate quite rapidly, and they
should therefore be inspected frequently and with special care, so that
they may be renewed before they become a source of danger. Every geared
ladle should be provided with a safety locking device to hold it in an
upright position while it is being carried.
The bail of each crane ladle should be examined frequently, and
particularly at the point where the crane hook engages it, because
that is where the wear is greatest. The lower parts of these ladles
should also be watched carefully for evidences of injury caused by
carelessness on the part of cranemen when transporting or depositing
them.
Sulky and buggy ladles are used only to a limited extent, but they
cause many accidents. In some foundries steel plates are laid to serve
as runways for buggy ladles, and plates are often placed between the
rails of narrow-gage industrial railway tracks also. Molten metal is
sure to splash when spilled on clean, smooth plates of this kind, and
it also forms into “shot” which roll under the feet and cause the men
to fall or to spill more metal. The danger from splashing might be
minimized by sprinkling sand on the floor, but the sand would hinder
the free movement of the wheels, and greater effort would be required
to move the buggies. This would tend to make spills more frequent, even
though in any individual case the sand might reduce the likelihood of
injury from splashing, after the metal had been spilled. Floors of
concrete and brick have been tried in other foundries, with the result
that the number of burns from spills has been materially reduced. An
excellent floor may also be constructed of metal plates with _checkered
surfaces_,--the elevations on these plates providing a surface that
is sufficiently smooth for the wheels, while the depressions (which
are filled with sand) tend to check the splashing. Overhead trolley
systems are used in some foundries for transporting ladles, and in this
way the spills and splashes that are due to poor floor conditions are
eliminated.
[Illustration: FIG. 2. A BUGGY OR SULKY LADLE.
(Observe the inclosure for the gears, and the shield to prevent the
molten metal from splashing on the operator when pouring and when
pushing the ladle along the track.)]
It is necessary to maintain a clear path for buggies that are being
moved about, because metal is likely to be spilled from them if even a
very small obstruction is encountered. Moreover, the buggies or trucks
should be inspected frequently, paying particular attention to the
wheels and bearings to make sure that they are in good condition so
that the buggies will run easily and smoothly. Each buggy should be
equipped with prong guards to hold it rigidly while pouring, and the
ladle should be properly counterbalanced so that it will automatically
return to an upright position when empty.
Bull ladles are much safer to handle than ordinary single-hand ladles,
and should be used whenever possible. Several styles of shank-handles
are used with bull ladles, one of them consisting of a rigid fork
handle on one side and a rigid single handle on the other side. In
another style (which is preferable) both handles are forked; and in
still another form a swivel is provided at one end, which permits
the ladle to be tilted more easily and emptied with less danger of
spilling. The bowls of bull ladles should be held securely in position
in their shanks by means of clamps made of round or flat iron. The
shanks must be amply strong for the weight to be carried, and the
joints should be carefully inspected for poor welding, flaws, and other
weaknesses. Defective ladle shanks should be removed from the pouring
floor as soon as discovered, so that there will be no possibility of
using them again, either intentionally or otherwise. Ladle shanks
should not be left exposed to the weather, because such exposure causes
them to corrode and become weakened.
[Illustration: FIG. 3. A BULL LADLE IN USE.
(The handle is provided with a swivel, and one man tilts the ladle
while the other man simply sustains a part of the weight.)]
When single-hand ladles are used the shanks should be securely attached
to the bowls, because otherwise the bowls are likely to slip out when
pouring, and to cause accidents. A sheet-metal guard or shield, 6 or 8
inches high, should be firmly secured to the top of the bowl of every
hand ladle on the side next to the shank, to protect the workman’s hand
while carrying the ladle.
[Illustration: FIG. 4. POURING FROM A HAND LADLE.
(This illustration shows the correct attitude for a man to assume when
pouring. Observe also the shield on the ladle, to protect the hand
from burns caused by spattering metal. The leggings are of a good type
but, unfortunately, are not clearly shown. On general principles we
disapprove of the unbuttoned vest, although the upper part of the body
is unlikely to be burned so long as the man is engaged solely in work
of the kind here shown.)
]
When several workmen are carrying ladles from the cupola to the
molds it is better for them to pass on the side on which the bowls
are carried. This not only tends to avoid confusion and disorder,
but it is also safer, because there is less danger of burns when two
bowls are struck together by passing workmen, than there is when two
shank-handles collide.
“Horse play” and purposeless activities of other kinds should not be
permitted among the men who are waiting their turns at the cupola,
because the work is hard and dangerous, and the men must take it
seriously at all times and give their undivided attention to it, if
burns are to be avoided. The ladles should never be completely filled,
because if they are, the hot metal will surely spill while being
carried. “Cutting in” from the _back_ of a continuous stream of molten
metal at the cupola spout causes unnecessary spattering; always cut in
from the front.
New employees in foundries, and particularly the unskilled help, should
be carefully instructed with regard to the proper method of carrying
the ladles and the correct position to assume when pouring into the
molds, and they should be watched and supervised for a considerable
time after being assigned to such work, in order to make sure that
they understand how to do it properly. The men should stand at a safe
distance from the molds, so that their feet will not be burned if the
metal spills or runs out between the cope and the drag or nowel.
Ladles of all kinds, except hand ladles, are likely to cause accidents
by tilting unexpectedly, unless the bowls are properly balanced on
their shanks or trunnions, or are arranged to be locked in an upright
position. It is specially important to see that the bowls are not
top-heavy, even when full of metal. On the other hand, if the bowls
are weighted too heavily at the bottom it is difficult to tilt them,
and an unnecessary strain is imposed upon the operator and also upon
the gearing and other mechanism; furthermore, it is not easy to pour
a smooth, continuous stream from a ladle which requires considerable
exertion to hold it in the pouring position. In particular, all ladles
that are provided with bails for hoisting and transporting by cranes
should be so constructed that, when full of metal, the center of
gravity will be well below the bail, unless they are arranged with
geared devices for tilting. In addition, they should be provided with
clips or clamps to prevent unexpected or accidental overturning.
[Illustration: FIG. 5. A TROLLEY LADLE IN POSITION AT THE CUPOLA.]
When buying new ladles it is important to see that the lips are of the
correct shape to insure a smooth, narrow, undivided stream at pouring,
and to prevent the molten metal from backing up and running over the
sides at other points. Both safety and efficiency are promoted by the
use of ladles with proper lips.
“Leave-overs” (excess metal left in ladles after the molds have been
poured) are sometimes poured on the foundry floor. In this way puddles
of molten metal are left, which soon become covered over with a thin
coating of sand or dust so that they are not readily observed. The
consequence is that men are often severely burned by stepping into or
upon these puddles while the metal is still hot. Pouring leave-overs
on the floor should be prohibited, and suitable receptacles should be
provided at convenient points to receive the excess metal.
Many serious accidents have been caused by pouring molten metal
into damp ladles, the result usually being an explosion, and the
scattering of the metal in all directions. In every foundry, therefore,
special care should be taken in drying the ladles. In some plants the
core ovens or crucible furnaces may be utilized for the purpose, while
in other cases it may be necessary to provide special ovens or heaters.
Ladles should not be dried in the molding rooms by means of wood fires,
unless adequate exhaust ventilation is provided.
[Illustration: FIG. 6. A CONVENIENT LABOR-SAVING POURING DEVICE.
(By installing a monorail system a device of this kind can be used for
main-aisle and side-floor work. It can be operated by one man, with
safety. The ladle can be hoisted and lowered, thus making it possible
to pour molds at various heights. The metal shield protects the eyes
of the operator against heat and glare, and also prevents burns from
spattering metal.)]
All ladles that are not in use should be stored in a dry place, and
preferably on elevated racks, or on supports of some other kind that
will permit the air to circulate freely about the ladles.
Foundry ladles must be relined from time to time (bull and hand ladles
are relined each day), and it is advisable to have all of this work
done by men selected for reliability and experience, who are interested
in making the ladles safe and willing to give them the necessary time
and attention.
All of the ladles that are in use should be examined carefully every
day, preferably by an experienced and conscientious man who has been
specially selected for this work. The bowls should be inspected for
cracks and thin, weak spots, and the shanks should be examined to
discover defective welds and erosion. Inspectors should also look out
for loose rivets and bolts, and should see that all necessary guards
are in good condition and properly secured in place, and that all
ladles are properly balanced.
Flasks and Molds.
Wooden, steel, and iron flasks are used in foundries, but those of
iron and steel are so much superior that preference should be given to
them under all possible circumstances. Iron flasks may be cast in the
foundry, and the subsequent maintenance and depreciation charges are
quite small as compared with what must be expended upon wooden flasks.
Moreover, after a wooden flask has been used for some time the faces
of the cope and the nowel become burned or broken off, with the result
that instead of fitting closely together they may be separated by a
space of an inch or more. Although this space is filled with sand, the
hot metal is likely to break through and run down the sides of the
flask. “Run-outs”, as leakages of this kind are called, often cause
severe burns on the feet and legs of the workmen. If iron or steel
flasks are used, and the cope and nowel faces are planed to insure
a close fit, there will be little likelihood of the occurrence of
run-outs.
Iron and steel flasks, as well as wooden ones, require frequent and
careful inspection to see that none of the lugs, handles, or other
parts are broken. If a flask is found with a broken or cracked lug or
handle it should be immediately removed from the shop for repairs;
otherwise, it might be used again by some person unaware of its
dangerous condition, and a serious accident might result when it was
picked up by the crane.
Congestion on the molding floor is noticeable in many foundries,
particularly in those where the work is greatly diversified; and
numerous burns are the direct result of such a condition. Sufficient
space should be left between flasks so that the molders and their
helpers will not be crowded while pouring, and so that they will be
able to get out of danger quickly and easily in case of a “run-out”.
There should always be a clear space of at least 18 inches between the
rows of flasks when pouring “side floor” by hand, and for crane work
in general; and passages 24 inches or wider are much to be preferred.
Portable horses may sometimes be used to advantage for supporting bull
ladles when pouring work of certain kinds.
Flasks, when in storage, should be piled in an orderly and systematic
manner, and the maximum height for stacking them should be such that
the workmen can handle them easily and conveniently while standing with
both feet on the floor. Unevenly piled flasks sometimes fall over and
cause serious injuries; and even though they are piled well enough to
be stable if undisturbed, they may fall in consequence of jarring due
to the motion of neighboring cranes, and sometimes they are pulled over
by chains dangling from the cranes.
Workmen often collide one with another, and are severely burned or
otherwise injured, in consequence of their view being obstructed by
foundry equipment. Obstructions likely to cause accidents of this kind
should be moved to the sides of the room. It is highly essential, also,
to keep all the aisles clear of flasks, tools, implements, and other
obstructions, particularly in plants where the illumination is not of
the best, and where, on account of insufficient ventilation, large
quantities of smoke obscure the vision.
Orderliness and adequate light and ventilation not only increase
efficiency, but also materially reduce the number of accidents; and
any reasonable expense that is involved in securing good conditions in
these respects will pay for itself by lessening the time that is lost
in consequence of the temporary demoralization to which the working
force is subject whenever an accident occurs.
Crucibles.
Crucibles are extensively employed in founding, especially in
connection with non-ferrous metals; and the importance of exercising
special care in handling them, not only to avoid accidents but also to
insure greater length of service from the crucibles themselves, has
been greatly underestimated in the past. In our larger plants, however,
foundrymen are now giving considerable attention to the systematic
instruction of their furnacemen, melters, and helpers, with a view to
keeping the number of accidents as low as possible, and obtaining as
great a number of heats as practicable from each crucible.
The clay crucibles of former days have been extensively supplanted by
better ones made largely of graphite, which is capable of resisting
exceedingly high temperatures. In fact, crucibles composed wholly of
clay have practically gone out of use for the melting of steel and
brass, because they can often be employed for only one or two heats,
and they are far more likely to break or crack unexpectedly, thereby
causing workmen to be seriously burned. Moreover, the temperatures that
occur in metal-working plants at the present time are higher than those
that prevailed when the all-clay crucible was the standard type. The
crucible that is now in general use consists mainly of the substance
that is variously known as graphite, plumbago, or black lead, and which
is a practically incombustible form of carbon. This is combined with a
small amount of a special variety of clay as a binding material, and
perhaps a little fire sand to give the mixture an open grain, so that
it can better withstand sudden changes of temperature. Some makers use,
in addition, a certain quantity of material obtained by grinding up
old, worn-out crucibles; but this practice cannot be recommended.
The graphite crucible is doubtless the most efficient yet devised, when
cost and all other elements are considered, but it is nevertheless
somewhat fragile, in view of the fact that it is expected to withstand
a heat sufficient to melt the refractory metals, and to support, at
the same time, very considerable pressures due to the weight of its
heavy fluid contents. It is exceedingly important, therefore, to
see that all employees fully understand how to handle crucibles in
order to reduce the danger of breakage to a minimum; and a great deal
can be accomplished in this direction, because graphite crucibles,
when properly made and carefully used, can be kept in a fairly safe
condition.
The number of accidents from breakage is greater in small plants than
in large ones, in proportion to the number of crucibles in use. This
is due partly to the greater care that the crucibles receive in the
large plants, and partly to the fact that large foundries buy supplies
of crucibles considerably in excess of their immediate requirements,
storing the surplus ones and allowing them to age or “season”. It
is an old saying that crucibles improve as they grow older, and as
experience shows that this belief has some actual basis in fact, the
date of manufacture should be stamped upon every crucible, to assist
the annealing men in selecting the oldest and best seasoned of them,
when additional ones are required for use.
[Illustration: FIG. 7. A CRUCIBLE WHICH BROKE AFTER BEING RUN ONLY TWO
HEATS.]
Good crucibles are expensive, and every foundryman therefore desires to
obtain the maximum service from them. The foundryman who attempts to
increase the useful life of his crucibles by careful handling, and by
the adoption of approved methods of every other kind, is at the same
time promoting safety by preventing accidents from premature breakage.
Foundrymen, melters, pourers, and helpers, usually expect a crucible
to run a certain definite number of heats, and they are likely to be
somewhat careless when a new crucible is put in service. For this
reason it is wise to assign a number to each crucible, for recording
the number of heats taken. The record may conveniently be kept upon
a black-board, opposite the appropriate crucible number and in plain
view. Everybody then knows just how many heats each crucible has
run, and this knowledge often arouses a spirit of competition, which
tends to make the men more careful in handling the crucibles, and to
increase the service that can safely be had from them. (The dating and
numbering here recommended are now being done, quite generally.)
When crucibles are first received, it is important that they be
critically examined for cracks and flaws, not only by the eye but also
by tapping them with a light hammer; and all imperfect ones should be
rejected. If there is evidence that any of the crucibles in a given
shipment have become wet while in transit to the foundry, they should
be stored for at least four or five weeks, before being used, in a
place where they will dry out thoroughly--even though they may be
apparently dry at the time they are received.
When a new supply of crucibles has been carefully inspected and
found to be free from defects, the entire lot should be stored for a
considerable time in a warm, dry place, and provision should be made to
protect them as thoroughly as possible from contact with moisture or
with moist air. The roof of a continuously-operating core oven is an
excellent place for the storage chamber.
The proper annealing of crucibles is of far more importance than is
generally realized. It is said that crucibles, when they come from the
manufacturer’s kilns, contain less than one-quarter of one per cent.
of moisture; but after they have cooled off they absorb moisture again
from the air. To anneal a crucible properly, it should first be slowly
heated to a temperature somewhat above 250° Fahr., and it should be
maintained (or “soaked”) at this temperature for a sufficient time to
entirely remove the moisture. It may then be put into service, if it
has been thoroughly annealed by the makers. If there is any doubt on
this point, however, the crucible should next be heated for some hours
to a dull red heat, after which it should be allowed to cool again,
very slowly, to about 250°. In any case the crucible should still be at
a temperature of 250° or over, when it goes into the furnace, or the
drying-out process will not be wholly successful.
Large crucibles, with thick shells, require a higher temperature
than small-sized ones in the preliminary heat-treatment, and a
correspondingly longer “soaking” period, in order to reduce the
absorbed moisture to the allowable limit. In drying out a No. 200
crucible, for example, ten hours or more should be allowed for bringing
it up to a temperature of 250° Fahr., and fully ten hours more should
be allowed for “soaking”,--that is, for reducing the percentage of
moisture which may have been absorbed. If a crucible that has a
considerable amount of moisture in its walls is quickly subjected to a
high temperature, the moisture will be changed into steam, and this,
because it is confined within the walls of the crucible, may expand so
as to cause a rupture or crack. The same result may also follow from
the natural contraction of the drying crucible, if the moisture is
driven out rapidly or unevenly. The small “pinholes” and “skelping”
that may often be seen on crucibles are caused in this way. These
pinholes and fissures form one of the chief sources of trouble against
which users of crucibles have to guard; for although a crucible having
defects of this nature may endure for a considerable number of heats,
it is nevertheless likely to fail at a critical time (for example,
during pouring or while being pulled from the furnace), spilling the
molten metal and causing severe hand and foot burns.
After receiving heat-treatment for the removal of moisture, crucibles
are often placed on a layer of damp sand, or on the comparatively cold
furnace floor, and left there for an indefinite length of time before
charging. This should not be permitted, because when the temperature
of the crucible falls to a point materially below 250°, it will again
absorb moisture.
[Illustration: FIG. 8. THE CRACK IN THIS CRUCIBLE DEVELOPED AFTER FIVE
HEATS.]
Fine cracks (called “alligator cracks”) often cover the entire surface
of a crucible. These may be caused in a number of ways. Sometimes
they are due to heating the crucible with fuel containing too high
a percentage of sulphur; or, in oil furnaces, they may be caused by
using too little oil or too much steam. It is specially important for
the operators to thoroughly understand their work when using an oil
furnace, because an excess of air or steam, or an insufficient supply
of oil, may give rise to an oxidizing action, whereby a portion of the
carbon (or graphite) is burned out of the crucible wall, leaving the
binding clay in a somewhat porous condition; and this action, when it
occurs, greatly facilitates the formation of cracks.
When crucibles are stored on the top of a furnace, the melters or
furnacemen should make sure that the covers over the furnace openings
fit properly. If the furnaceman is careless in this respect the moist
gases that are given off when fresh fuel is placed on the fire will
escape through the openings to some extent, and they are likely to come
in contact with the crucibles, causing alligator cracks to form.
Cracks and fissures are also likely to form if the metal to be melted
is not carefully placed in the crucibles. The men usually work rapidly
when introducing the ingots, so that the furnaces will not be left open
any longer than necessary; and the ingots are often thrown in with a
force sufficient to indent the bottoms of the crucibles, or otherwise
damage them. An indentation in a crucible, whether caused in this way
or in any other way, is quite likely to develop, shortly, into a crack
or fracture. The ingots should be introduced carefully and loosely,
sufficient time being taken to insure that this is properly done. When
a crucible is first filled it is desirable to place as many ingots
in it, for the first melting, as practicable; but it is exceedingly
important to see that they are not wedged or jammed, because when they
are heated they will expand more than the crucible itself, and the
walls of the crucible are likely to be cracked in consequence.
When a new crucible is put in service for melting, it should be heated
quite slowly for a few runs, and this is _specially important the first
time it is used_. After one or two runs it will become vitrified, and
the danger from too sudden a heating is then materially reduced. It is
a good plan to keep on hand a few extra crucibles that have been used
before, to avoid loss of time in case an extra crucible is needed on
short notice.
[Illustration: FIG. 9. A CARRYING POT, WITH SHANK.]
A great deal of harm is done by carelessness in handling the tongs and
shanks, and the life of a crucible may be seriously shortened in this
way. When a tilting furnace is used, as many as fifty heats can often
be obtained from a crucible; but if the heating is in furnaces from
which the crucibles must be removed by means of tongs, they can be used
for only about fifteen heats, on an average.
A crucible is soft and plastic at a white heat, and may easily be
squeezed out of shape by the pressure exerted upon it when the handles
of the tongs are forced together. The walls of the crucible gradually
become weakened by treatment of this kind, and eventually, if the
crucible is not discarded, a complete rupture will probably occur, with
its attendant toll of injuries and burns.
[Illustration: FIG. 10. TONGS PROPERLY APPLIED TO A CRUCIBLE, FOR
REMOVING IT FROM A STATIONARY FURNACE.]
Three styles of tongs are in general use in foundries--one-pronged,
two-pronged, and spade tongs. The different styles are designed for
various special purposes and operations, but they are sometimes
improperly used interchangeably. It is essential to see that the tongs
that are used are of the proper shape, and that they fit perfectly
from the widest part of the crucible (usually called the “bilge” or
“belly”), down to within a few inches of the bottom. They should not
extend to the _extreme_ bottom, however, because this would make it
hard to place the crucible in the shank. On the other hand, if they do
not extend down far enough the crucible will be badly squeezed. The
proper use of the tongs consists in taking hold of the crucible below
the bilge and lifting it in such a way that the least possible pressure
is exerted against the crucible walls.
One-pronged tongs should be used only for lifting the smaller-sized
crucibles,--say up to size No. 40. For larger sizes two-pronged tongs
should be used. It is not uncommon to see large crucibles, ranging
from No. 200 to No. 300, lifted by one-pronged tongs. This practice
should be condemned, because when one-pronged tongs are used for
lifting a crucible, pressure is exerted against only a single point of
contact,--namely, at the bottom,--and the crucible, when hot and soft,
is likely to be cut or ruptured, if it is large and heavy, because the
pressure at the point of support is severe. Serious burns, from the
spilling of the molten metal, often result when the lower prong of a
two-pronged pair of tongs is cut off, on account of a lack of space
between the crucible and the furnace wall; because the crucible is then
lifted from above the bilge, and tilted. Melters should be cautioned
against the practice of driving down the ring of the tongs with a
skimmer or other implement, because this is almost sure to cause cracks
and fissures in the crucibles.
Molten metal is often spilled from crucibles in consequence of using
tongs that have become bent or otherwise misshapen. It is important to
see that the tongs fit the crucibles properly, and that they are also
in good condition in every other way. For restoring bent tongs to
their proper shape, it is advisable to procure a set of cast-iron forms
similar in size and general shape to the crucibles that are used in the
plant, but slightly larger from the bilge upward. To restore the tongs
to their original form it is only necessary to put them in the furnace,
raise them to a red heat, clamp them to the proper iron form, and bring
them back into shape by means of a heavy hammer. Tongs may be fitted
easily and cheaply in this way, and a great saving of time results. If
cast-iron forms are not provided, the blacksmith cannot be expected to
restore the tongs to their correct shape with accuracy; but if iron
crucible-forms of the proper sizes and shapes are used, and the tongs
are fitted to them as here recommended, the likelihood of squeezing and
distorting the crucibles will be reduced to a minimum.
Two pairs of tongs, at least, should be provided for each size of
crucible, so that if one pair becomes badly bent or worn, the other
pair may be placed in service without loss of time.
Furnacemen should make sure that no clinkers or pieces of unburned coal
or coke are stuck to the walls of the crucibles when about to grasp
them with the tongs, because if the tongs are applied over a clinker
the clinker will probably be forced into the crucible and a rupture
may then occur at any moment. It is also important to see that the
bottom of the crucible (on the outer surface) is free from clinkers or
other adherent substances, so that when the crucible is in the furnace
its weight will be evenly distributed, and not concentrated at a few
projecting spots or regions. It is best to support the crucible by
means of a foundation or pedestal, of graphite, fire-brick, or other
infusible substance, though the fire-bed may be made to give a fairly
satisfactory support if it is carefully prepared and smoothed.
When a heat has been poured it is important to see that no metal is
left in the bottom of the crucible, because when a residual mass (or
“button”) of such metal cools, it contracts at a different rate from
the crucible, and serious strains and cracks are likely to result.
Ramming the fuel bed is bad practice, in general, because it is likely
to damage the crucibles seriously. If ramming appears to be necessary
at special times, the utmost care should be exercised in doing it.
(We are indebted to the General Electric Company for the photographs
that are used in this section.)
Cupolas.
Tapping-out is the most hazardous part of cupola work. This is
specially true if the melter is inexperienced or careless, for it is
almost entirely within his power to prevent excessive spattering of
the hot metal if he properly controls the flow from the cupola. If
dangerous spattering of the molten metal, with its attendant burns,
is to be eliminated, it is important that the melter be taught the
correct and only safe method of stopping up the tap hole. Under no
circumstances should the stopping bot be thrust directly into the
stream of flowing metal in order to “bot-up” the hole. Instead of this,
it should be brought immediately _over_ the stream, and, when near the
hole, should be carried down obliquely so that it will make a sharp
angle with the stream, and thus effectively and instantly close up the
hole without any undue spattering. In drawing molten metal from the
cupola into buggy or trolley ladles, it is necessary to stop the flow
of metal when a ladle has been filled and while another is being moved
into position. This is done by the melter, who inserts the stopping
bot into the hole and holds it there temporarily. After doing this
several times the fire clay on the end of the stopping bot becomes
burned off, and consequently the hole may not be closed properly. One
or more extra stopping bots, already prepared with fire clay, should
be conveniently at hand, which may be substituted for the burned-off
one when necessary. The melter and all other workmen engaged about the
cupola should wear well-designed goggles having side shields, because
statistics show that a high percentage of eye injuries occur about the
cupola.
Accidents occur about cupolas not only when drawing off the metal, but
also during charging time, and when repair work is being done. As a
general thing workmen engaged in charging a cupola must bring the coke
and the iron (both scrap and pig) from the storage bins or yard, up to
the charging platform. These workmen should be instructed to pile the
iron evenly on the barrows, and to exercise great care in taking the
scrap from the pile, in case the latter is in such a condition that
it is likely to collapse or slide. Many workmen have been severely
injured, while filling their barrows, by the sudden collapse of piles
of scrap iron.
In many foundries elevators are used for conveying the charges to the
charging floors. In every such case it is essential that a gong or
other signal be sounded before the elevator is taken from the charging
floor by a workman below; and the elevator should not be moved, after
the signal has been given, until sufficient time has elapsed for any
person who may be in danger to respond and to move into a place of
safety. Many serious accidents have been caused by elevators suddenly
descending while the workmen were loading or unloading them. To further
guard against such accidents there should be a door or gate at each
entrance to the hoistway, provided with an interlocking device so
arranged that the elevator cannot be started until the door or gate has
been closed. The unused sides of the car platform should be completely
inclosed to a height of 6-1/2 feet (or to the top of the crosshead),
and a substantial iron grating should be placed on the top of the car,
to stop falling tools and other objects.[1]
[1] Further information with regard to the care and operation of
elevators in general is given in a booklet published by the Engineering
and Inspection Division of THE TRAVELERS INSURANCE COMPANY. Copies
of this booklet may be procured by applying to the Home Office at
Hartford, Connecticut.
The charging opening in a cupola should be fitted with a door or
gate, which should always be closed except when charging is going on,
and workmen engaged in charging should be specially careful to avoid
tripping or losing their balance when in the vicinity of the opening,
and especially when throwing heavy pieces of scrap or pig metal into
the cupola.
When the interior of a cupola is being relined it is recommended that a
watchman be stationed near the opening, or that a conspicuous warning
sign be posted beside it, stating that men are working inside. We
have known of cases where metal thrown into the cupola has struck and
seriously injured workmen who were engaged in making repairs to the
shell or lining. An effective guard against accidents of this kind
consists in a circular screen of a diameter slightly smaller than the
inside of the cupola, and made of heavy wire netting or of stout
expanded metal, substantially framed. The screen should be divided in
the center, and the two sections hinged together. In using this device
it is suspended above the point where the men are at work, from a piece
of scantling laid diametrically across the cupola so that it rests upon
the walls where they are offset for the single brick lining, or upon
the ledge formed by the charging doors,--the screen being supported
by chains at several points around its circumference, and having its
hinges on the under sides. When arranged in this way it tends to remain
open and flat, although it can easily be folded by raising it at the
middle. A screen of this kind will intercept falling pieces of slag and
brick, and other objects, and will thus protect the workmen below.
When furnaces are to be entirely relined, only trustworthy and
experienced men should be allowed to perform the work. Moreover, the
fire-bricks that are used should be of the best quality obtainable, in
order to insure long life of the cupola. Between the bricks and the
shell a space of about 3/4 of an inch should be left, which should
be filled with dry sand to act as a cushion, so that severe stresses
will not be thrown on the shell when the bricks expand. The rivets and
the shells of all cupolas should be inspected periodically, to see if
any of the rivets have sheared off or worked loose, or if the shell
has become weakened in any way. After making repairs of any kind,
care should be taken to see that the cupola is thoroughly dried out,
and that all tools, and all materials used for scaffolding or other
purposes, are removed.
Explosions occur in cupolas from time to time, and if the shell of a
cupola is weak, a serious catastrophe is likely to result. Carbon
monoxide, when combined with air in certain proportions, forms a highly
inflammable and explosive mixture, and the explosions are mainly due
to this gas, which collects in the wind box and blast pipe during
interruptions in operation. In an incredibly short time enough carbon
monoxide gas may collect in this way to cause a violent explosion
when the blast is turned on again. If the iron comes too fast a
temporary shut-down may be unavoidable; but interruptions from other
causes,--such, for example, as the slipping of the blower belt,--should
be prevented, so far as possible, by frequent inspections of the
equipment and by making all necessary adjustments and repairs when the
cupola is not in operation.
A gate or damper should be placed in the blast pipe, close to the
cupola, to prevent the explosive gas from entering the pipe. This gate
should be closed _immediately_, whenever the blast is shut off, and it
should be opened cautiously and slowly when starting up again. At the
time that the blower is shut down one of the tuyeres should be opened
also, to maintain a slight draft of air.
Explosion doors provide another means for preventing damage from gas
explosions. Some authorities recommend that these doors be placed in
front of the tuyeres, so that when the blast is turned off the doors
may be opened to admit the outside air. When this arrangement is
adopted the doors should not be closed until the blast has entered the
wind box, so that any gas remaining therein may escape through the
doors.
With a positive-pressure blower, which is probably the best type for
cupola work, a safety-valve should be provided for the protection
of the blast pipe or blower. This will prevent the bursting of the
blast pipe in case the blast gate is closed suddenly, or if the cupola
becomes clogged with slag in such a manner as to obstruct the passage
of the air to a dangerous extent. The weights on the safety-valve
should be sufficient to prevent blowing-off unless the obstruction
is quite serious, because a constant blast-volume is required in
modern cupola operation, and if the volume is decreased an undesirable
lowering of the temperature occurs.
Charging and lighting-up should be done carefully and by experienced
workmen, and the charges should be laid as nearly level as possible.
When the charging has been completed, and after lighting-up, sufficient
time should be allowed for the cupola to become thoroughly warmed up
before starting the blower.
Traveling Cranes.
Cranes of various types are used in the foundry, but most of the heavy
work is done by electrically-operated traveling cranes. The suggestions
that follow therefore relate mainly to that type, although many of them
are applicable to all cranes, and to hoisting devices of other kinds.
A substantial stairway or ladder should be installed at one end of the
crane runway, to provide access to the crane cab or cage; and when two
cranes are operated on the same runway, stairways or ladders should
be installed at both ends of the runway. Cranemen should always use
this means of entering and leaving the cages. Every crane cab should
be inclosed to a height of at least 42 inches on all sides, except
where entrance is actually effected. The inclosure should preferably
be of sheet metal or expanded metal, or of heavy, woven-wire mesh. If
railings are used there should be an intermediate rail midway between
the top rail and the floor of the cab, and a six-inch toe-board should
also be installed. A stairway or a ladder should always be provided for
passing from the cab to the top of the crane bridge. This should be
substantially built, and properly protected so that the crane operator
or repairman will be in no danger of falling when he uses it.
A foot-walk should be constructed along the bridge of the crane, or
on both sides where the width of the bridge demands. This will give
easy and safe access to the trolley in any position, and to any part
of the bridge. The construction should be substantial, and the width
must be sufficient to provide ample room for passage. Double railguards
42 inches high should be erected along each foot-walk, and six-inch
toe-boards should also be provided.
Whenever possible, a substantial walk should be installed beside the
crane runway, and this should be protected by strong railings and
toe-boards along its entire length. All traveling cranes should be
equipped with spring bumpers or oil bumpers, and suitable stops should
be installed at each end of each rail of the runway.
All gears on the trolley and other parts of the crane should be
completely incased, and no one should be allowed on top of the crane
while it is in motion. A stout sheet-metal pan, or a substantial floor,
should be provided under the trolley, to catch any parts that may work
loose, and to prevent them from falling upon employees below. This
pan or floor should be solid except for the cable openings. Guards,
fenders, or brushes should be attached in front of the bridge and
trolley wheels, to remove any obstructions that may be upon the tracks,
and to prevent injury to persons who may be working in such positions
that their hands or feet might be crushed by the wheels.
[Illustration:
_Courtesy of The Alliance Machine Company._