The Mechanical Handling and Storing of Material

86 THE MECHANICAL HANDLING OF MATERIAL troughing to carry a large capacity, and ensures the centring of the load, thereby- increasing the tendency for the belt to run straight. Ball bearings for idlers have of late been introduced with great success. 1 he advantages of this construction are obvious, as these idlers run so easily that it is quite impossible for them to get stuck, to the detriment of the belt or the expenditure of driving power. The makers of the idlers are The Conveying Weigher Co., of New York. Fig. 116 shows one of these sets of idlers, from which it will be seen that the whole of the bearing is enclosed in a dust-tight chamber in the interior of the rollers. I he space is filled with sufficient lubricant to last from six to twelve months, according to whether the conveyor runs long or short hours. The distance apart of the supports depends upon the weight of the material to be carried, and also upon the rigidity of the belt, a troughed belt being naturally more rigid than a flat one. rhe following table gives this information undei average con- ditions and for troughed belts :— Width of Belt. N umber of Plies in Belt. Pitch of Idlers. For Minerals. For Grain and Seed. Inches. 10 to 16 18 „ 22 24 ,, 30 32 ,, 36 38 ,, 48 3 to 4 4 ,, 5 5 ,, 6 6 ,, 7 7 „ 8 Ft. In. Ft. In. 4 6 to 5 0 4 0 ,, 4 6 3 6 ,, 4 0 3 0 ,, 3 6 2 6 ,, 3 0 Ft. In. Ft. In. 5 6 to 6 0 5 0 ,, 5 6 4 6 ,, 5 0 4 0 ,, 4 6 3 6 ,, 4 0 Support of Return Strand.—The idlers supporting the return strand should be about twice as far apart, or say from 6 ft. to 12 ft. Provided the return idlers are not too small in diameter, there is no detriment in spacing them a little further apart than stated, as the sagging of the return belt caused by this has a tendency to keep the working strand taut. The distance between these idlers has been known to be as much as 20 to 25 ft. Lubrication of Idlers.—This is of great importance. Oil, of course, is the best lubricant; but as this is likely to spill on the belt, it is better to use a viscous lubricant, particularly when rubber belts are used, as the oil may injure the rubber. Grease- lubricated conveyors take slightly more power, but grease is a more suitable lubricant, as, when forced into the bearings in the usual way, it forms an effective dust protector for the journal. Driving Terminals.—The driving mechanism of a belt conveyor is the simplest possible. It consists, in its original form, of a terminal or driving drum, or pulley, supported by a substantial spindle and pedestals, to which the driving power is applied. The terminal at the other end is similar, but is usually fitted with an adjustment for keeping the belt taut. These terminals are so simple and so well known that there is no call for going into further details, except to say that the drums should be stronger than ordinary pulleys, with a good rim and sufficient arms, particularly for wide con- veyors, and they should be well rounded on the face. It is also advisable to secure the driving drum to the spindle with two keys 90° apart. The following table gives the diameters and widths of terminal drums and guide and idler rollers, which are recommended for ordinary conditions. If the pulley or drum is less in diameter than the dimensions given in the table,