With the sharp flute four dispositions of the acting edges are per missible, as shown in Fig. 3, thus providing for different qualities and condition of the grain—as, sharp to sharp for tough wheat, and dull to dull for hard wheat ; with the other arrangements for intermediate qualities.
In December, 1881, Mr. William D. Gray, of Milwaukee, Wis., took out letters-patent for a form of corrugation in which the ribs were abrupt on one side and rounded on the other, thus obtaining the cutting and non-cutting according to the dispositions of the acting sides of the flutes. With sharp-cut rolls the edges left by the corrugating tool are soon lost, a day or two, it is stated, being sufficient to make them feel smooth. They can be used from one and a half to two years before requiring to be recut. A twist or spiral direction along the roll is given the grooves to prevent those of one roll catching in the grooves of its mate. This also tends toward a more severe shearing action.
The direction of the twist may be the same on each roll of a pair, or disposed in opposite directions, In the former case the grooves cross at line of contact of rolls, while in the latter they are parallel at that line. On May 25, 1880, Mr. John Stevens, of Neenah, Wis., received letters-patent for a roll having a dress formed of grooves with rounded divided ridges, as shown in Fig. 2.
For this forte of corrugation is claimed less cutting of the bran and breaking of the germ. The number of grooves employed for the several stages of reduction increase as the products become finer. For the five successive break rolls usually employed they may be 10, 12,14, 16, and 20 grooves per in. of circumference of roll. The bran-rolls may have 24, and the mid dlings reduction-rolls 32 grooves per in. With sharp corrugations there are more grooves than with the round, and practice varies in regard to the numbers given above, some preferring finer grooved rolls. The differential usually employed for breaks is 24 to 1, while the same, or 3 to 1, is used with scratch-rolls rolls with dress fortned of shal low-waved grooves, 32 per in. The diameters of rolls generally used arc 9 and 6 in. ; the lengths. 12 to 30 in. Nine-in, rolls are usually run at 300 to 400 revo lutions per min., and the 6-in. rolls GOO revolutions, the periph eral speed being 706 to 942 ft. Per min. First-break rolls run at these speeds will pass from 90 to 112 lbs. of wheat per in. of length of roll per hour. Where six breaks are employed, an increase of about 1 to 14 times the grinding length of first - break roll is made, this taking place at the third or fourth and following breaks.
Variation in practice makes it difficult to state proportions of grinding surface for middling rolls. A given size of roll grinding middlings will handle about three fourths the weight of material that the first-break roll of same size will pass. The pressure on roll-bearings is the controlling factor in the calculation for power required, the actual work of granulation being comparatively insignificant. Pressures up to 3,500 lbs, per bearing are used, the work of fric tion thus being for a 2-pair mill 15 horse-power. About 1,000 or 1.500 lbs. per bearing are perhaps average pressures for 9-in, rolls, having spindles 24 in. diameter. Six-in, rolls are used with 600 to 1,000 lbs. per bearing.
Fig. 4 is shown the well-known Stevens roller-mill. The frame is of the
"skeleton" construction, composed of the two side-frames or legs, which are bolted to a rectangular bed or top. The rolls are mounted in boxes as shown, the two inside boxes being rigidly fastened to the bed, the two outer ones sliding on finished surfaces. A V-shaped gib, bolted to the bed, preserves the linear motion of the sliding-box. Relative position of the rolls is attained by the adjust ments, as shown in Fig. 5. At each corner of the bed of the machine *re cast lugs which sustain the backward thrust of the movable rolls. Into these lugs are fitted threaded sleeves, through which the hand-wheel stem is passed. A hexagon head on the outer end of this sleeve provides for turning it, and it is screwed firmly into the lug, so as to act as a stud for the spring-nut shown to work upon. The hand-wheel stem is threaded at its inner end, and passing through a hexagon nut seated in the sliding-box, abuts against the fixed box as shown. Turning the hand-wheel moves the sliding-box away from or toward the fixed box, and the proper grinding tension or pressure is secured by setting up the spring-nut. Vertical adjustment of the fixed roll is secured by the parts as shown in Fig. G. The adjusting screw and dowel in which the box rests raise or lower it, while the binding screws secure the box firmly to the brackets after the necessary adjustment has been made. The dowel aids to preserve the fixed lateral position of the roll-bearing. The boxes project beyond end of the short roll-necks and have enlarged recesses to retain the oil and prevent its running down into the frame. The tightened pulley. mounted in its spindle, runs in a frame vertically adjustable by means of a rack and pinion operated by the cross shaft shown, which latter is held from rotating by pawl and ratchet-whecl, and is readily turned when deiired ft-inn either end of the machine. The pulleys shown drive the first rolls of each pair, their mates being driven either by belts or gears, arranged to provide the differential of t he latter varying generally bet %vein' 3 to 1 and 1 to 1. The spreading device shown he front of t he machine provides for the simultaneous movement, of t he ends of the movable roll wit bout disturbing the working adjustment as made by the hand-wheels at each end of the roll. Projecting from the bed is a threaded stud, on which turns the curved arm shown, the hub of this arm being threaded to tit the thread on the stud. In front of this arm is a dog with hub threaded the same as the arm, and having its outer end bent so as to form a stop for the curved arm to rest against. At the outer end of the stud is a small hand-wheel haw iug a left-hand thread. Extending front the stud to each hand-wheel are levers, one end of each pressing against the hub of the curved arm, the other ends bearing against the inner end of the hand-wheel hubs. Near the hand-wheel stem and attached to the threaded sleeve through which it passes, is placed a fulcrum, the latter be ing thus between extremities of the levers—the operation of the whole being such that by rota ting the curved arm, say from left to right, it advances along the stud, pushing the inner lev er-ends toward the frame, and forcing the hand-wheels in the opposite direction, and there fore the roll away from its mate.