The Mechanical Handling and Storing of Material

BAND CONVEYORS 87 the belt may not be sufficiently pliable to adhere closely to the pulley, and it is, there- fore, questionable whether the full benefit of the pressure will be obtained. Dimensions of Terminals, Guide Pulleys and Supporting Rollers Width of Belt. Number of Plies in Belt. Width of Pulleys /ind Rollers. Diameter of Driving Terminal Pulleys. Diameter of End Terminal Pulleys. Diameter of Tightening and Throw-off Pulleys. Diameter of Supporting Rollers. Inches. I riches. Inches. Inches. Inches. Inches. 10 3 12 15-18 1215 12 41 12 3 14 15-18 12-15 12 41 14 3 16 15-18 12-15 12 51 16 4 18 21-24 15-18 15 51 18 4 20 21-24 15-18 15 6 20 4 22 21-24 1.5-18 15 6 22 5 24 24-30 18-22 18 (> 24 5 •26 24-30 18-22 IS 8 26 o 28 24-30 21-24 18 8 28 5 30 24-30 21-24 18 8 30 6 33 30-36 24-30 21 S 32 6 35 30-36 24-30 21 8 34 6 37 30-36 24-30 21 8 36 6 39 30-36 24 30 21 8 38 7 41 36-42 30-36 24 10 40 7 43 36-42 30-36 24 10 42 7 45 36-42 30-36 24 10 44 s 47 42-48 36-42 27 10 46 8 49 42-48 36-42 27 10 48 8 51 42-48 36-42 27 10 Position of Drive.—At first it was a generally accepted rule that the tight side of the belt should, by preference, be used for conveying, as this is in a flatter condition than the other, particularly in cases of installations with flat belts. This practically meant that band conveyors should always be driven only at the end at which they discharge their load, but it has been demonstrated within the last few years, that conveyors work well on either the tight or slack side of the belt. This has increased the utility of the band conveyor considerably, as under these conditions it is quite immaterial from which terminal the conveyor is driven. Indeed, it might be driven at any point of its length between the terminals by employing multiple pulley drives to get sufficient contact between the driving drums and the belt. For this purpose, the belt passes over two or even more pulleys, which may be geared together, so as to revolve at the same periphery speed. Similar multiple pulleys have also been used for terminal drives in cases of extra long conveyors, and particularly in cases where the conveyor works in dusty places, or where in the cold season there is the possibility of belt and pulleys becoming slippery through dust or ice. To some extent the slip may be prevented by lagging the driving drum with india-rubber, and, according to Mr Haddock, an advantage of 7 per cent, is obtained in tractive power, so that a drum with rubber lagging will be useful not only for larger conveyors but also in cases where a slipping may be feared. With the single pulley drive at either of the terminals, the belt must always be kept taut by some tightening device, as the grip of the driving drum on the belt depends upon this, whilst with a multiple pulley drive, the grip of this group of pulleys on the belt is so great that sufficient tractive force can be exercised without relying on the tension of the belt. It has been urged that the belt will not stand being bent over pulleys in both directions when in tension, which is necessary with multiple drives, but with a first-class 1 Fast- running conveyors, at say a belt speed exceeding 500 ft. per minute, should have 6-in. diam. rollers.