The Mechanical Handling and Storing of Material

46 THE MECHANICAL HANDLING OF MATERIAL introduction of the Suess conveyor (page 55) there was not a suitable conveyor for really heavy work of this class, and worms were used because there was nothing better. Close-bladed or continuous worms are also made with a larger pitch for lighter material, generally with a pitch of about two-thirds their diameter. These answer their purpose well, as the capacity of these continuous conveyors is nearer the theoretical capacity than is the case with open spirals or with paddle worms. The reason why closed spiral worms are not often made with a pitch more than two-thirds to three- quarters of their diameter is that it is difficult to bend or roll the blades to a large pitch, but their greater efficiency brings their capacity up to nearly that of paddle and open spirals of a larger pitch. The following tables give the capacity of continuous, paddle, and spiral worm conveyors of different diameters with their respective pitch and speed. It is obvious that the capacity of a continuous worm is greater than that of a paddle or open spiral conveyor, these two latter being about equal in capacity if other conditions are equal. Conveyors of double pitch have twice the capacity, and should be driven, if more than 9 in. in diameter, by means of gearing and countershaft, unless they are very short. Capacity of Small Pitch Worm Conveyors of the Con- tinuous or Close-Bladed Type for Heavy Materials Diameter. Pitch. Diameter of Hollow Spindle. Revolutions per Minute. Capacity. Inner. Outer. Cubic Feet Inches. Inches. Inches. Inches. per Hour. 4 2 1 130 30 G 3 u 1 r j 120 60 8 4 H ih 100 180 9 If 2f¥ 100 250 10 5 2 90 300 12 6 2 2Ä 90 600 14 7 2i 2H 80 900 16 8 2H 70 1,000 18 9 60 1,300 Table giving Diameter, Pitch, and Capacity of the Continuous or Close- Bladed Worm oe the more usual Construction for Light Materials Diameter of Worm. Pitch of Worm. Outer Diameter of Hollow Spindle. Diameter of In- ternal Bearings and End Gudgeons. Revolutions per Minute. Capacity in Cubic Feet per Hour. Length between Bearings. Inches. Inches. Inches. Inches. 4 4 1T% 1 130 70 5 5 Ü 1-20 100 - 8 feet. 6 6 1Ä u 120 175 - 7 6 U 110 250 J 8 (> u u 100 300 9 8 2g 2 100 400 ■ 10 feet. 10 8 24 •2 90 500 11 10 2| 2 90 650 12 10 2 ■90 850 13 10 2H 80 1,000 14 10 80 1,200 12 feet. 15 12 2i4 70 1,350 16 12 2H, 70 1,550 ]8 12 2JL 60 1,800 1J