The Mechanical Handling and Storing of Material

BAND CONVEYORS 85 smallest diameter idlers, which is obviously wrong, as a glance at the following table illustrates. With a belt speed of from 200 to 600 ft. per minute a 4-in. roller will make from 190 to 570 revs, per minute. A 5-in. roller at the same speed will make 150 to 460 revs. A 6 /,, „ „ 125,, 375 „ A 7 ,, ,, 110,, 330 ,, A 8 „ ,, „ 100 ,, 300 ,, A 9 ,, ,, ,, 85 ,, 255 ,, A 10 „ ,, ,, 75 „225 ,, Fig. 115. Five-Roller Troughing Idler of The Link Belt Co. Fig. 116. The “Conweigh” Ball-bearing Troughing Idler. From this table it will also be seen that the speed of the idler pulleys, except those of 4 in. and 5 in., at the high speed, is not too high to ensure satisfactory running, and, if properly lubricated, the weight of the belt alone should be sufficient to turn them easily. Should any of them become stuck it will be due to grit or insufficient lubrication. The greater the number of rollers in each idler frame, and, therefore, the shorter each individual roller, the smaller the chance of damage by attrition to the belt in case of any one roller becoming fast. The slope of the idler pulleys for troughing, as first introduced, stood at an angle of 40° to the horizontal, but was subsequently changed to anything between 30° and 25°, so as to avoid too sharp a bend in the belt. Later designs for wide belts use idlers with five and six rollers, to form a trough resembling a section of a circle. This gives sufficient