Part 2

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.