The Mechanical Handling and Storing of Material

22 THE MECHANICAL HANDLING OF MATERIAL will be found preferable. The buckets often met with in older flour mills are of such a shape as to make a proper discharge of their contents well-nigh impossible. Figs. 17 and 18 show two elevator buckets, the former for soft and clinging material,, and the latter for more granular material. The former will be found to fill easily and discharge freely such material as flour, etc. A bucket such as is shown in Fig. 18, if used for soft material, would in many cases not fill completely, but would only allow a heap of stuff to rest on the top, leaving a hollow in the lower portion of the bucket; on ascending, the material frequently drops down to the bottom of the bucket, and when it reaches the discharge spout it will not empty in time to fall into the dis- charge shoot, consequently some of its load will miss the spout and fall down the elevator trunk. In the bucket shown in Fig. 17, the angles ab c should be 45°, 90°r and 45° respectively; whilst in Fig. 18 they should be 60°, 90°, and 30°. The buckets should be made of sheet iron or steel, and riveted or soldered together; the most modern and best buckets are, however, stamped out in one piece of mild steel. The attachment of the buckets to the elevator band is best effected by bolts with mushroom- shaped heads. Clips, which were formerly used for this purpose, lack strength and are liable to break. In selecting an elevator it is well to allow a liberal margin in its capacity, unless an automatic feeding device is used. In the following table will be found suitable sizes for flour-mill elevators, with other useful information :— Size No. Diameter of Pulley. Width. Revolu- tions per Minute. Bucket. • Pitch of Bucket. Capacity in Bushels per Hour. A. Length. B. Width. C. Depth. ’ 1 Inches. 9 Inches. 80 Inches. Inches. Inches. 2 Inches. 12 25 2 12 6 75 3 12 40 3 15 7 60 3 15 90 4 18 8 55 4 31 15 145 n 21 9 50 4> 4 18 200 6' 24 10 45 5 4| 18 400 As the different products in a flour mill vary greatly in specific gravity, a further table is appended in which is given in hundredweights the capacity of different sized elevators when working on different products. The numbers of elevators given in the top row correspond with the dimensions and particulars given in the previous table. The last four lines of the table refer to the products of the breaks of a flour mill, and the weights are based on a sample of wheat weighing 60 lb. to the bushel. Different break products are marked 1, 2, 3, 4, and refer to the break meal as it comes from the break roller mills and enters the elevators. The weights of the various materials per bushel have been carefully taken by the author, and can be accepted as reliable. In these two tables the speeds given for different elevators are good average speeds for handling most materials in a flour mill. When treating semolina and other comparatively heavy and granular materials, as well as in the handling of wheat, an increase of 10 per cent, is admissible ; while, on the other hand, with flour and very fine