Elevating machines

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Elevating machines

Materials-handling machines that lift and lower a load along a fixed vertical path of travel with intermittent motion. In contrast to hoisting machines, elevating machines support their loads instead of carrying them suspended, and the path they travel is both fixed and vertical. They differ from vertical conveyors in operating with intermittent rather than continuous motion. Industrial lifts, stackers, and freight elevators are the principal classes of elevating machines.

A wide range of mechanically, hydraulically, and electrically powered machines are classified as industrial lifts (Fig. 1). They are adapted to such diverse operations as die handling and feeding sheets, bar stock, or lumber. In some locations with differences in floor level between adjacent buildings, lifts take the form of broad platforms to serve as floor levelers to obviate the need for ramps. They are also used to raise and lower loads between the ground and the beds of carriers when no loading platform exists. Lifting tail gates attached to the rear of trucks are similarly used for loading or unloading merchandise on sidewalks or roads and at points where the lack of a raised dock would make loading or unloading difficult.

Examples of industrial lifts, ( a ) Hydraulic elevating work tableenlarge picture
Examples of industrial lifts, (a) Hydraulic elevating work table

Stackers are tiering machines and portable elevators used for stacking merchandise with basically portable vertical frames that support and guide the carriage, to which is attached a platform, pair of forks, or other suitable lifting device (Fig. 2). Horizontal movement is effected by casters on the bottom of the vertical frame, and can be accomplished manually, or mechanically, by using the same power source as the lifting mechanism. These casters are usually provided with floor locks bolted in position during the elevating or lowering operation. Used in conjunction with cranes, stackers are widely applied to the handling of materials on storage racks and die racks.

Two types of electric and hydraulic stackers, ( a ) Hand type, ( b ) Hydraulic foot typeenlarge picture
Two types of electric and hydraulic stackers, (a) Hand type, (b) Hydraulic foot type

Examples of industrial elevators range from those set up temporarily on construction jobs for moving materials and personnel between floors to permanent installations for mechanized handling in factories and warehouses. Dumbwaiters are a type of industrial elevator; they carry parts, small tools, samples, and similar small objects between buildings, but are not permitted to carry people. The most common and economical elevator employs electric motors, cables, pulleys, and counterweights. See Materials-handling Equipment

McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.