The Mechanical Handling and Storing of Material

BAND CONVEYORS 9r width of the belt. In both cases the speed of the belt should not be faster than is necessary to carry the load, and it is often better to carry a bigger feed on a slower belt than a thinner feed on a faster belt. As a general rule it may be taken that with belt conveyors for The Speed of the Belt may be from Minerals - 400 to 700 ft. per minute. Heavy grain and s^eds - ' - 500 „ 700 Light grain - 400 ,, 600 Coal and coke ... - 300 „ 500 Sacks and other big loads 150 ,, 300 Passengers - 100 ,, 150 Sorting and picking •20 ,, 60 The belts of conveyors generally keep clean from adherence of the materials they carry, but with some materials, such as clay, sugar, salt and other sticky substances, there is a. tendency for the belt to convey small particles past the delivery point and deposit them where they may become a nuisance. In such cases, rotary brushes (manipulated from the belt) have been used successfully. Where materials containing acids or other corrosive fluids are conveyed by belt conveyors, the whole of the metal portion of the machinery, including the finished surfaces, should be painted with graphite or white lead paint. Inclined Belt Conveyors.—Belt conveyors can be used not only in a horizontal position, but also with a slight upward or downward gradient. They can also be designed to embody all these three attributes in one and the same conveyor, provided the change from one to the other is accomplished by a gentle curve. The maximum incline at which a belt will convey depends upon the angle of repose of the material to be handled and on its formation. The presence of a large proportion of spherical pieces, for instance, will not permit of a steep gradient, as they have a tendency to roll back. It may also be noted, by observing a belt running up a comparatively steep incline, that there is a slight jar conveyed to the material wherever the belt negotiates a guide roll, which jar has a tendency to start some portion of the load to roll back. It is, therefore, recommended to place the supporting rollers closer together on all inclines, and particularly so where the maximum gradient is reached, thus keeping the belt more even and so doing away with the jar. Materials like loose gravels, pebbles, or clinkers from revolving kilns, or all-round materials, which have a tendency to run backward, must not be conveyed on an upward gradient of more than 10° to 15°. Conveyors for all other materials containing large pieces may have an upward gradient of 15° to 20°, without affecting the capacity, whilst material of a uniform and fine nature, such as sand, small coal and minerals, will negotiate an incline up to a maximum of 23°. Ridgway’s Belt Conveyor.—The latest innovation in belt conveyors appears to offer some advantages over the existing types. It was brought out by the Ridgway Belt Conveyor Co., of New York. It consists of two bands running on top of each other instead of the ordinary single band. The idler rollers are cylindrical, similar to those shown in Fig. 110, and the band is, therefore, running flat; to this inner band are fixed at intervals concave wooden blocks, on which the upper band rests and forms a trough. With this arrangement the lower band is scarcely subjected to any wear and tear, as it never comes in contact with the material; only the upper band, therefore, requires renewing at a comparatively small cost, as the two bands are each only about half the thickness of the single bands generally in use.