Document rLKOQoBLbJ2O43X1mXE4baGv

HOISTING APPARATUS AND CONVEYORS 3 A second telephone circuit, which may be grounded if desired Suitable bghtug should be provided at critical. points for night operation and re pairs Portable conveyors Belt, flight, apron, and fixed bucket con veyors are made also as inclined portable units on a pair of large wheels, for loading railroad cars and trucks with bulk materials (Fig. 18-33). The various types of portable conveyors should be provided with guards as specified for the corresponding types of fixed conveyors Weatherproof electrical equipment should be used With three-phase power, the flexi ble cord that is connected to the power outlet should be a four-conduct or, the fourth wire being grounded m all plugs and re ceptacles The ca ble should be so arranged that it cannot be run over by trucks or other machines If the cable must cross a driveway, it should be hung on poles Fig. 18-33. Portable conveyor. at a minimum height of 14 ft If two or more sec Courtesy Conveyor Equipment Menutecturers Associetion tions of cable are required, the connectors should be kept above the ground, since these machines are used most m the worst weather Portable conveyors should have skirtboards or sideboards not less than 10 in high to keep heavy material from falling over the sides and light or loose material from blowing off This safety feature ap plies to belt conveyors as well as to the other types because troughing of the belt gives insufficient protection against such spillage The conveyor should be stable and should be fitted with a locking device to hold the conveying unit at various fixed elevations The mechanism for raising and lowering the boom on all types of portable conveyors should be closely checked periodically, it constitutes one of the greatest sources of hazard in the use of such machinery Any positive type may be used, but the self walking worm or jack-screw type is prefer able Gear drives should be completely housed and run in oil All chains within easy reach of workmen should be thorough ly guarded, and a system should be pro vided for convenient oiling of chains In warehouses, the boom of portable conveyors usually consists of two sections to permit their use in a small space These conveyors should be so designed that material will not roll bade from one section to the other at the transfer point When portable conveyors are used for loading or unloading railroad cars, a suit able safety device should be provided to prevent the car from being shifted during the operation The device should not be re moved until the crew is sure that no one is in the car A red banner or a standard blue warning sign at each end of the car is rec ommended as a warning to switchmen (See the section "Plant Railways'* m the next chapter ) Gravity conveyors The fact that gravity conveyors (Fig 18-34) depend wholly upon die natural force of gravity for their operation often leads to disregard of some necessary safe practices Even though it is not powerdriven, this equipment can be the source of senous accidents There is real danger if an employee climbs upon a conveyor to release a block ade He may either slip on the rollers or be knocked down should the jam suddenly be Fig. 18-34. Types of gravity conveyors. Left: roller conveyor. Right: spiral chute. Courtety Conveyor Equipment Manufacturer! Anociation 18-38