Part 6

=38.= Timber frames are usually built by the mining company from its own designs. Steel frames are generally built by the structural steel companies from detailed plans and designs furnished by the mining company, or from a skeleton diagram furnished by the mining company, giving the loads on the rope and the general conditions about the shaft to which the frame must conform, the frame being then designed and erected in detail by the steel company.

=39. Enclosing Head-Frames.=--Head-frames are sometimes wholly or partially enclosed to protect them and the men from the weather. A covering of boards is warmest. All woodwork should be painted with fireproof paint and ample means for extinguishing fire should be provided. A covering of corrugated sheet iron well painted on both sides to prevent rusting is often used instead of wood and lessens the danger of fire, but is not as warm a covering as wood.

=40.= In many states, it is required by law that the top of the shaft be protected by a fence or by gates to prevent persons falling down the shaft. This protection is secured at the sides of head-frames by extra timbers or beams forming part of the frame, or by means of a fence placed near the sides of the frame. The ends of the shaft are protected by a bar placed across uprights, by gates that swing like an ordinary door, or more generally by vertical sliding gates that are raised by the cage when it comes to the surface and drop into place when the cage descends. Similar gates, doors, or bars should be used at all landings below the surface.

HEAD-FRAME SPECIFICATIONS

=41.= The following is a sample set of specifications for a steel head-frame to be built from detailed plans furnished by the mining company.

This head-frame to be made from drawings to be furnished by the---- Coal Company, and placed on foundations furnished by said company.

=Material.=--Structure to be built throughout of soft structural steel, net strength 55,000 to 62,000 pounds per square inch; elastic limit not less than 30,000 pounds per square inch; elongation, 25 per cent.; bending test, bend flat on itself without fracture.

Builder agrees to guarantee structure to withstand strains specified on drawings with factor of safety of 10, to provide for possible overwinding or sticking in shaft.

No steel shall be used less than ¼ inch thick except for lining or filling vacant places.

=Workmanship.=--The tower to be built in a neat and workman-like manner. The pitch of the rivets (distance between centers) shall not exceed 6 inches or sixteen times the thinnest plate, nor be less than three diameters of the rivets.

The rivets used shall generally be ½ inch, ¾ inch, and ⅞ inch in diameter.

The distance between edges of any piece and the center of rivet hole shall not be less than 1¼ inches, except for bars less than 2½ inches wide; when practicable it shall be at least two diameters of the rivet. All rivet holes shall be spaced and punched, so that when the several parts are assembled together a rivet of ¹/₁₆ inch less diameter than the hole can be entered hot into any hole, without reaming or drifting. The rivets when driven should fill the holes. The heads must be rounded; they must be full and neatly made, and be concentric to the rivet hole, and thoroughly pinch the connecting pieces together. Field riveting must be reduced to a minimum. All joints and connections shall be neatly made, the several parts to be brought together without twists, bends, or open joints.

=Inspection.=--All facilities for inspecting the material and workmanship shall be given by the builders during the erection of the head-frame. The company reserves the right to reject any or all parts not built in accordance with the plans or these specifications. Final inspection of work 1 month after being in actual service.

=Painting.=--All work, before leaving the shops, shall be thoroughly cleaned from all loose rust and scale, and be given one good coat of paint well worked into all joints and open spaces. In riveted ironwork, the surfaces coming in contact shall each be painted before being riveted together. Bottoms of bearing plates and any parts that are not accessible for painting after erection shall have two coats of paint. After the structure is erected in place, it shall be given one coat of paint. All recesses that will retain water, or through which water can enter, must be filled with thick paint or some waterproof cement before receiving the final painting. The paint shall be a lampblack paint, mixed with pure linseed oil, or of red lead mixed with raw linseed oil containing Japan dryer.

=General Clauses.=--The specifications and drawings are intended to cooperate and to indicate the principal dimensions and requirements necessary to the complete structure. It being understood that while some work may be shown in the plans and not described in the specifications, or vice versa, and some minor details and fastenings are omitted from both plans and specifications, the work is to be executed without extra charge therefor, the same as if the minutest details were set forth in full in both drawings and specifications. The contractor is to make good any defects of material or workmanship developing within 1 year after final acceptance.

The contractor shall furnish a location plan and also two copies of the detail shop drawings for convenience in making future alterations and repairs.

=Erection.=--The head-frame is to be erected complete, secured to foundations provided by the---- Company.

Contractor shall furnish all foundation bolts and washers. Iron stairway with hand rails beside main back bracers and platform with wooden floor under sheaves, also iron stairs from platform under sheaves to back sheave pedestal for oiling. Wood furnished by the---- Company.

Price includes all material for completion of work delivered, erected, and riveted in place and painted.

The---- Company will furnish and place in position the sheaves, with the shafts and boxes belonging to the same, also the wooden guides.

=Delivery.=--The head-frame to be erected, complete, and secured to foundations in---- weeks from date of order.

DETACHING HOOKS

=42.= In hoisting, there is more or less danger of overwinding or lifting the cage too far, and dashing it against the top of the head-frame, or if the top is open the cage may be pulled entirely over the top. =Detaching hooks= are intended to prevent this. Several varieties of such hooks are made, which differ from each other only in their smaller details. In all of them, detachment is effected by passing the rope through a circular hole in an iron plate or through an iron cylinder, the diameter of which is sufficient to allow the upper portion of the hooks to pass through when passing upwards, but the lower portion is made larger and so arranged that when this larger part strikes the plate the upper portion is forced open and the hoisting rope released. After the upper part has been thus opened, it is too large to pass back through the opening and the plate and the cage is therefore held suspended. Fig. 39 shows such a hook. It consists of two outside fixed plates slightly narrower at the top than the diameter of the hole in the disengaging plate _h_. Between the frame plates _a_ are two inner plates _b_ that move about a strong pin _c_ passing through both plates _a_ and _b_, but near the bottoms there are two projections _d_ to prevent the hook from passing entirely through the hole. The winding rope is attached to the top shackle _e_ and the cage to the lower shackle _f_. When the two movable plates _b_ are closed as tightly as possible at the top about the pin of the shackle _e_, they are secured by a copper pin _g_. In case of overwinding, when the hook passes into the hole of the disengaging plate _h_, the two projections _k_ on plates _b_ are pressed inwards, shearing off the copper pin _g_ and allowing the plates _b_ to turn about the central bolt _c_, thus releasing the shackle _e_. The plates _b_ are then in such a position that the projections _l_ on them cannot pass down through the hole. The cage then hangs by the hooks from the disengaging plate, and the rope passes on. An objection raised against this hook is that, being constructed of plates, there is considerable surface in contact between the moving parts, and unless they are regularly taken apart and oiled, there is danger of their rusting firmly together.

In England, detaching hooks are used quite commonly, and also in certain parts of the Central Basin in the United States, but they have not yet been generally adopted throughout the United States.

=43.= It is claimed by many that such devices inspire the engineer with a misleading feeling of security; that they are more or less complicated in construction and so need care, and destroy the simplicity of the plant; that they may be the direct cause of accident by introducing new elements of danger; that they add to the cost; and that they are not thoroughly reliable. Again, it is held that the surest prevention of overwinding is obtained by the employment of a sober, reliable, and competent engineer, who is held personally responsible for overwinding accidents; by having a good brake and an engine thoroughly under the control of the engineer; by a reliable method of indicating the position of the cage; by sufficient height to head-sheaves to allow of considerable hoisting over and above that necessary for landing.

SIGNALING

=44.= Some method must be provided for communicating between the bottom or any level of a shaft and the top landing or the engine room, also between the top landing and the engine room, so that the hoisting engineer may be notified when both the head-man and foot-man are ready for him to hoist. A common method of signaling is by means of a gong, bell, or triangle placed in the engine room and connected by a wire or small wire-rope with the point from which it is desired to signal. Attempts have been made in different localities and by different associations to adopt a standard code of hoisting signals, and while it would be advantageous if this could be done, none of the attempts made have been entirely successful. Although there is no uniform system of signals, one bell generally means stop, two bells lower, three bells hoist, and four bells hoist men.

=45. Hammer-and-Plate Signal.=--Fig. 40 shows a hammer-and-plate signal, the plate being a piece of boiler iron or steel. The hammer is often located beneath the plate instead of above, as shown. Another style of hammer-and-plate is shown in Fig. 41. The hammer is made of 2-inch square iron and heavy enough to balance the weight of wire hanging in the shaft and to take the sag out of the horizontal wire connecting the top of the shaft with the lever _a_. A simple dial turned by a ratchet motion attached to the lever _a_ is sometimes used to show the number of strokes, and thus check the number counted by the engineer. The dial is reset by the engineer as soon as he understands the signal.

=46. Electric Bells.=--Electric bells operated by push buttons are rapidly coming into use for mine signaling on account of the ease and completeness with which such a system can be installed. Electric flash lights are also extensively used for signaling purposes. The principle of action and details of the wiring for electric signals and flash lights have been described in _Transmission, Signaling, and Lighting_.

=47. Speaking Tubes.=--The laws of certain states require speaking tubes, in addition to the ordinary means of signaling. These speaking tubes are generally made of 2-inch iron pipe and are from 300 to 1,500 feet long, and are often provided with whistles at the end of the pipe and at each level of the mine, by which the attention of persons at any level can be attracted or the whistle may be omitted and the attention of persons attracted merely by rapping on the pipe with a piece of iron.

=48. Pneumatic Gong Signal.=--Fig. 42 shows an attachment that can be connected to a speaking tube and that is widely used for signaling. It consists of a brass cylinder _a_ fitted with a piston _b_ containing valves _c_. The gong _d_ is attached to the cylinder _e_ inside of which the clapper _f_ fits loosely. When the piston is pushed inwards, as shown by the arrow, by means of the handle, the air in the cylinder and in the pipe _h_ is compressed and forces the clapper _f_ upwards against the gong _d_. The arrangement of these gongs in the mine is shown in Fig. 43. A cylinder and whistle are usually placed at each landing and a gong and whistle in the engine room, though, if desired, a cylinder, whistle, and gong may be placed at each landing and in the engine room.

=49. Telephones.=--Telephones connecting the different levels with the top and the engine room are now frequently used in connection with other signal systems, but they are not as well adapted as bells or gongs for rapid-hoisting signaling.