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
Fig. 39
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.