Mining and Metallurgy Volume 109-114 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1916 Excerpt: ...mechanically to the hoist drums. This cam mechanism thus serves two purposes: (1) in automatic operation it provides the automatic slowdown and stop; and (2) in hand operation, if the operator does not begin retardation at the proper point, this mechanism will retard the hoist in practically the same manner as when hoisting automatically, thus providing protection against overwinding when operating by hand. Protective Devices The protective system resembles those of a considerable number of large direct-current mine hoists, of the same general type (except the automatic operation) as the Inspiration hoists. In the latter, as has just been noted, the automatic control system provides against overwinding in hand operation. An additional set of emergency-limit switches is used, which gives similar protection in case of failure of the automatic control. During hand operation there are effective, therefore, two complete sets of protective devices against overwinding. For each hoist a hand-operated emergency switch is provided on the operating platform, and a similar emergency switch is located at the foot of the corresponding shaft, by means of which either or both hoists may be stopped quickly from the operating platform, or the foot. Without appreciable complication, additional emergency switches may be installed at other points, if desired. The operation of any one or more of these emergency devices cuts off power from the hoist and makes an emergency application of the brakes. An emergency, which affects one hoist only, acts on the power and brakes of that hoist only. The failure of excitation or alternating-current power, which affects both hoists, cuts off power and makes an emergency application of the brakes simultaneously on both hoists. Adjustments in ...