The important material properties to be considered for the construction of flat belts are high coefficient of friction between the belt and the rim of the pulleys, flexibility, durability and strength of the belt.
surfaces as in the case of the V-belt drive, owing to the system design, the wear on the belt and pulleys is
In contrast to flat belts which are characterized by a uniform distribution of tension over the entire belt width,
V-belts have the disadvantage that the tensions in the individual belts are unevenly distributed due to different
effective diameters which are brought about by unequal wear on the belt and pulleys as well as manufacturing
tolerances. Such belt tensions lead to vibrations and fluttering, uneven and noisy running.
made from 1.2 metres to 1.5 metres long strips cut from either side of the back bone of the top grade steer hides. The hair side of the leather is smoother and harder than the flesh side, but the flesh side is stronger. The fibres on the hair side are perpendicular to the surface, while those on the flesh side are interwoven and parallel to the surface. Therefore for these reasons the hair side of a belt should be in contact with the pulley surface as shown in Fig. 18.2. This gives a more intimate contact between belt and pulley and places the greatest tensile strength of the belt section on the outside, where the tension is maximum as the belt passes over the pulley.
Most of the fabric belts are made by folding convass or cotton duck to three or more layers (depending upon the thickness desired) and stitching together. These belts are woven also into a strip of the desired width and thickness. They are impregnated with some filler like linseed oil in order to make the belt water-proof and to prevent injury to the fibres. The cotton belts are cheaper and suitable in warm climates, in damp atmospheres and in exposed positions. Since the cotton belts require little attention, therefore these belts are mostly used in farm machinery.