The Mechanical Handling and Storing of Material

82 THE MECHANICAL HANDLING OF MATERIAL substituting a thicker layer of india-rubber to make up for the missing duck. 1 his not only makes the belt conform more readily to the troughing shape of the idlers, but the thicker layer of rubber also reduces the wear and tear which naturally comes in the middle of the belt, whilst the stiffer edges of the belt support the trough between the idlers, and give it the necessary tensile strength. . Some very interesting tests have been conducted by Mr Edwin J. Haddock, of Columbus—the results of which appear in the Proceedings of the American . Society of Mechanical Engineers—as to the behaviour of conveyor belts under tension, more particularly to ascertain the effect of initial tension on the tractive force of conveyor belts on the driving drum. . . The driving terminal used for the test consisted of a drum 42 in. diameter, with the snubbing idlers so arranged as to give a belt contact of 180 , the tail terminal being so arranged as to exercise a variable tension in a horizontal direction by means of a rope running over a pulley to receive a weight. The weights suspended were as shown in the following table, and the experiments were made in the order given :— Table showing the Effect of Different Iensions on 'ihe same Terminal of a Belt Conveyor Tension i Weight. I I nitial Belt Tension. Am peres. Effective Pull on Belt. Belt Strain. Maximum. Minimum. ; 650 325 14 0 260 455 195 800 400 16’5 330 565 235 1,300 650 24’0 550 925 375 1,500 750 •29'0 690 1,095 405 2,000 1,000 38-0 650 1,475 525 1 1,500 750 31-0 750 1,125 375 1,250 625 •25-0 575 913 337 1,000 500 22-0 490 745 255 750 375 18'0 370 560 190 3,000 1 ’ 1 1 1,500 j 5(5-0 1 - 1,450 1 ■ 2,225 775 Note. — The weights are given in lbs. Beginning with a weight of 650 lb. and gradually increasing to 1,500 lb., the belt stretched but slightly, but under the additional 500 lb. with a total of 2,000 lb. the belt elongated about 3 ft. in its total length of 158 ft. The belt then remained without further stretching whilst running under the weight. On removing the load gradually to 750 lb., the belt recovered 15 in. of the stretch; while under a load of 3,000 lb. it stretched 3 ft. 8 in., or 8 in. more than under the 2,000 lb. load. 1 he belt was then run under the 3,000 lb. load for thirty minutes without changing its length appreciably.