The Mechanical Handling and Storing of Material

WORM OR ARCHIMEDEAN SCREW CONVEYORS 55 I'he speed at which tube conveyors should run may therefore be slightly slower for a larger pitch of the screw, and vice versa. The following table gives the most suitable pitch and speed, also the capacity of cylindrical tube conveyors of different diameters Diameter of Most Suitable Most Suitable Speed. Capacity. T ube. Pitch. Revs, per Minute. Cubic Feet per Hour. (5 in. 2§ in. 80 40 8 3 ,, 75 100 10 „ 4 70 200 12 ,, 4f „ 60 r 300 14 ,, 54 „ 55 350 16 ,, 6g „ 50 550 18 ,, 7 45 700 20 ,, 8 ,, 40 900 OO 8g „ 35 1.000 21 ,, 9) „ 30 1,100 A series of experiments with this conveyor was made in 1868 by Mr Lyster, engineer of the Liverpool Docks. These were fully dealt with in a paper read by Mr Percy Westmacott before the Institution of Mechanical Engineers. 1 he results of these experiments are here given. A tubular worm, 6 in. in diameter and of 2-in. pitch, with a depth of plate of in. At 60 revs, per minute delivers at the rate of 28 cubic ft. per hour. „ 80 „ „ „ „ 36 „ 100 „ „ „ „ 30 „ „ 140 ,, ,, delivery ceased altogether, and the grain was carried round and round the tube. A second trial was then made with a 30-in. worm, calculated on the results of the preliminary experiment to discharge at the rate of 50 tons per hour. The length of this worm was 18 ft., and it had a pitch of 12 in., or two-fifths of the diameter. 1 he body of the screw was properly balanced and revolved upon finely adjusted rollers, carried in cast-iron frames. With this worm a speed of 36 revs, per minute was found to be the most effective, and at this speed the grain was carried up the side of the screw about 5 in. above the centre of the tubular casing, and the discharge was 63| cub. ft per minute, or about 80 tons of wheat per hour—a much better result than had been calculated upon. The power required was 0’40 H.P. per foot run, and the sectional area of the body of grain was 36 per cent, of the whole area of the casing. A third experiment was also made with a 12-in. worm, and a pitch of 12 in., with a view to ascertain the effect of the quicker pitch. The worm was driven at the same speed of 36 revs, per minute, the delivery being 10 tons of wheat per hour, with a sectional area of only 17 per cent. The pitch of two-fifths of the diameter proved most effective in these trials. A case in which the tubular worm conveyor is very useful is where grain has to be conveyed from one building to another on a level, but where no bridge is available to which any other kind of conveyor could be attached. The tube can be made as strong as necessary, and trussed by means of a spider in the middle, and a number of tie-rods, as shown in Fig. 59. Suess Conveyor.—A decided improvement on the tubular conveyor is the Suess conveyor. It consists of a tube of rectangular section made either of sheet steel or wood.