Part 3
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._
FIG. 11. SAFEGUARDS ON A LARGE LADLE CRANE.
(This crane is larger than is used in the average foundry but it has some safety features that should be universally adopted. At A is the landing platform leading to the foot-walk on the crane bridge; B is a stairway which extends from the safety platform, C, just outside the operator’s cage, to the landing platform. The railing and toe-board on the crane bridge and on the trolley are also essential for safety.)]
All electrical wiring should be installed in conduits; and it is particularly important that hoist-limit stops be provided, in all cases, both for the main and for the auxiliary hoists. In the best crane practice the hoist-limit stops employ dynamic braking to check overtravel and to assist in lowering loads. To prevent the crane from being operated by unauthorized persons, or while repairs are being made, there should be a safety switch in the main line, mounted above the cab where it can be conveniently reached from the foot-walk. This switch should be fitted with a lock so that it can be secured in the open position, and the key should be only in the possession of the crane operator or the head repairman.
Woodwork should not be used about a crane, because it is likely to become oil-soaked, and it is then exceedingly combustible. If it should take fire and the craneman, in order to make his escape, should run the crane to a stairway, the time required for this purpose might increase his danger quite materially, and the motion of the crane would also tend to increase the fire. If, on the other hand, he tries to leave the crane in any other way than by the regular stairway, he will be exposed to hazards of other kinds, and these will be accentuated by his haste.
[Illustration:
_Courtesy of the Shepard Electric Crane & Hoist Company._
FIG. 12. SOME SAFETY FEATURES OF A TRAVELING CRANE.
(This illustration shows a part of a crane on the erecting floor of the manufacturer. There are no exposed revolving parts throughout the entire length of the crane bridge. Some of the safety features are as follows: A--inclosed gearing; B--inclosed drive-shaft coupling; C--pipe inclosure for drive shaft; D--device for sanding rails when crane is used out-of-doors. See also Fig. 13.)]
Keep all tools, oil-cans, and waste in a closed metal box securely fastened to the crane or to the runway at some convenient point.
Careful, watchful, intelligent, and trustworthy crane operators, floormen, and repairmen, can do a great deal toward preventing accidents, and only such men should be employed about cranes. The following suggestions relate to the work of these men, and if faithfully followed will be the means of promoting safety in a marked degree.
[Illustration:
_Courtesy of the Shepard Electric Crane & Hoist Company._
FIG. 13. SOME SAFETY FEATURES OF A TRAVELING CRANE.
(This is a nearer view of some of the safeguards shown in Fig. 12. A is the track sander which is operated by a rope or cable attached to the lever and extended to the craneman’s cage; B shows more clearly the drive-shaft coupling. The shaft inclosure also appears more plainly.)]
During the ordinary operation of an electric crane the craneman should never leave his cage without making sure that all the controllers are in the off position, and that the main switch is open. Before he leaves the crane the safety switch should also be locked open. If the electric current should be shut off at any time, the same precautions should be observed; and before closing the main switch, when about to resume work after an interruption due to any cause whatsoever, the craneman should again make certain that all the controllers are in the off position.
When about to lift a load, the motor should be run at low speed until the slack in the chain or cable has been taken up, after which the controller handle may be advanced slowly from point to point to increase the speed. Before a motor is reversed it should be brought to a full stop, except when an accident can be averted only by disregarding this advice.
When handling a heavy load the craneman should hoist it a few inches above the floor, and then, before proceeding further, he should assure himself that it is properly balanced and that the slings are secure, and should also test the brakes to make sure that they will hold the load safely. If there is any doubt whatsoever about the safety of the operation, the load should be lowered and the slings or brakes adjusted, or other necessary measures taken to avoid danger. It is also desirable, at the beginning of each shift, to test the foot brakes and limit switches thoroughly.
It is extremely important, at all times, and particularly when handling molten metal, to “spot” the trolley directly above the load to be hoisted. Failure to do this will cause the load to swing sidewise as soon as it is clear of the floor, and usually the metal will be spilled, or men or objects near by may be struck by the load.
Loads should be raised high enough to give proper clearance above men and objects on the floor, but they should not be carried for any considerable distance at an unnecessary elevation. So far as possible, the craneman should avoid transporting loads directly over workmen. Special care should be exercised to keep loads under control when lowering them, and the speed should always be restricted to a reasonable and safe limit.
Some definite person must be held responsible for the selection of the chains and slings that are used for hoisting, and for making suitable hitches about the loads. If the foundry is large enough to employ a special floorman, these matters may well be left to him, because he is necessarily familiar with the constantly-changing conditions, and he should therefore be able to select the proper sling quickly and intelligently. Moreover, experience will have taught him the best method for attaching the sling, or for hooking on to the load. If no special floorman is employed, this part of the work should be supervised by a specially assigned foreman, or by a skilled hooker-on. When applying the hook to the load, and when holding the hook in place while the slack is being taken up, the hooker-on should be careful to avoid having his hands caught and crushed between the sling and the load. Hooks with safety handles may be had, and these add greatly to the safety of the men when hooking up. If safety handles are not provided, pieces of wood notched at the end may be used with advantage for holding the hooks in place,--the notch being pressed against the hook to prevent it from moving before the tension comes on it.
When the hooks or slings are in place and the slack has been taken up, the workmen should immediately move back several feet from the load. When a load is being deposited, all persons should keep at a safe distance while the slings are being withdrawn from under it, because the slings may snap out suddenly, or may catch on the load and tip it over. When slackening-off the hoisting cables the hooker-on should avoid pulling down on the _inrunning_ side of the block, because his fingers may be caught between the sheave and the cable and be cut off or badly crushed. It is far safer to grasp the outrunning side, and pull up and away from the sheave. Greater safety in this work is insured by inclosing the block to which the hook is secured. Blocks guarded in this manner are available and should be generally adopted.
The crane operator should never allow chains, slings, cables, or hooks to drag along the floor, and he should never start the crane carriage or trolley until all such appendages are entirely clear. Even in the short distance that the crane might travel before they leave the floor, the slings or hooks might become caught on some obstruction and cause an accident.
No one should be permitted to ride on a load or on the crane hook; and if the craneman observes a violation of this rule he should stop the crane and refuse to move it until the person who is riding is in a safe place on the floor.
In a busy foundry the craneman must be specially alert, and his attention must be given, unremittingly, to following the various operations on the floor, taking the signals from the floorman, and controlling the movements of the crane.
Before an inexperienced man is permitted to take charge of a crane, he should be thoroughly trained in the work by a careful, well-qualified craneman, who should see that he becomes familiar with the operating mechanism, and skilled in the manipulation of the various levers and controls.
A signal gong, operated by hand or foot, or electrically, should be part of the equipment of every crane, and should be rung when the crane is started, and as frequently thereafter as may be necessary. Occasionally the gong is actuated by the mechanism that moves the crane, so that the warning signal is sounded automatically and continuously so long as the crane is moving. The objection to this method is that the sound of the gong is likely to become so familiar that its value as a warning of danger will be lost and the men will give little heed to it. Furthermore, the gong should always be treated as an _extra safeguard_, and no other safety precaution should be omitted or allowed to fall into disuse merely because the gong is used, nor should vigilance and caution be relaxed in any respect whatever.
Some person should be specially designated to transmit to the craneman the signals for moving the loads, and the craneman should disregard signals given by other men. The signalman should stand in plain view of the craneman and should take care to give all his signals clearly. A definite and unmistakable code of signals, consisting of motions of the hands and arms, should be arranged. Signals given orally are unsatisfactory and unsafe, not only because it is often difficult to distinguish them with certainty unless the foundry is quiet, but also because the sound of loud voices will always distract the attention of other men from their work. When a load is being transported some person designated for this purpose should always walk in front of it to warn workmen who are in danger of being struck, and he should also see that the load is carried high enough to clear all obstacles in its path, because the craneman, on account of his location, sometimes finds it hard to judge the height of the load correctly.
A crane that is to be repaired should be moved to one end of the runway or to some other point where it will cause the least interference with the movements of other cranes. The controllers and the main and emergency switches should be placed in the off position before starting any repair work on cranes, and the safety switches should be locked, or the fuses removed, to prevent any movement of the crane, and to avoid accidental short circuits that might result in injury to the repairmen.