Ques. Mention some of the features of belt drive.
Ans. Greater flexibility in the original design of a plant is possible and new arrangements of old apparatus can be made at any time. It gives conveniently any desired speed ratio and permits the use of high speed dynamos and motors.
Ques. State some of the disadvantages of belt drive.
Ans. Considerable space is required and the action is not positive. Belts exert a side pull on the bearings which results in wear, also loss of power by friction.
Figs. 445 and 446.—Two methods of lacing a belt. In fig. 445 two rows of oval holes should be made with a punch, as indicated. The nearest hole should be ¾ inch from the side, and the first row 7/8 inch from the end, and the second row 1¾ inches from the end of the belt. In large belts these distances should be a little greater. A regular belt lacing (a strong, pliable strip of leather) should be used, beginning at hole No. 1, and passing consecutively through all the holes as numbered. In fig. 446 the holes are all made in a row. This method has the advantage of making the lacers lie parallel with the motion on the pulley side. The lacing is doubled to find its middle, and the two ends are passed through the two holes marked "1" and "1a" precisely as in lacing a shoe. The two ends are then passed successively through the two series of holes in the order in which they are numbered, 2, 3, 4, etc., and 2a, 3a, 4a, etc., finishing at 13 and 13a, which are additional holes for fastening the ends of the lacer.
Ques. Give a rule for determining the proper size of belt.
Ans. A single belt travelling 1,000 feet per minute will transmit one horse power per inch of width; a double belt will transmit twice this amount.
EXAMPLE.—What size of double belt is required to transmit 50 horse power at 4,000 ft. speed, and what diameter pulley must be used for 954 revolutions per minute at 4,000 ft. speed of belt?
