GB795079A - Improvements in the grinding and classification of solid material - Google Patents

Abstract

795,079. Husking and reducing grain. MICROCYCLOMAT CO. March 12, 1956 [March 28, 1955 ; May 2, 1955 ; Aug. 8, 1955], No. 7612/56. Class 58. [Also in Group II] A flour milling operation is carried out in a mill comprising a rotor which is journalled for rotation in a cylindrical casing 11, Figs. 1 and 2, and fitted with radial grinding blades so that upon rotation it serves as a fan unit for drawing grain into the mill through a tangentiallydisposed inlet 28 in a gaseous stream and discharging the flour into an expansion chamber 27 disposed over one quadrant of the casing. The rotor comprises a tube 17 mounted on and surrounding a driven shaft 15 and provided with a series of spaced discs 21, 24 of which the alternate ones 21 are of smaller diameter than the others and carry a number of radiallydisposed blades 22. The inlet 28, which is arranged tangentially and lengthwise of the cylindrical casing, is fed with grain through a metering gate 31 from a hopper 30 and with the gaseous carrier through an inlet 32 fitted with a regulating gate 34 ; suitable gaseous carriers are air, carbon dioxide, helium, nitrogen, chlorine, oxygen and hydrogen. The expansion chamber 27 extends adjacent the hopper 30 and, as shown in Figs. 1 and 2, is fitted with an inclined screen 39 which permits only the finer particles to pass to the outlet 42 under the action, if necessary, of a fan or other exhaust means and is mounted so as to leave a narrow throat 40 at one side ; the larger particles drop back into the mill for further grinding. The milling action occurs principally by the action of the particles against each other as they are whirled around the mill and pass into vortices set up between the adjacent rotating blades 22. The inside of the casing is fitted with a lining 11A which may be smooth, corrugated or provided with cutting edges and the upper end of the casing or lining may be extended as shown in Fig. 7 to project between the casing and the expansion chamber. Pieces of stone and other undesired material are withdrawn through one or more openings 35 in the bottom of the casing to either a valvecontrolled duct or an endless conveyer disposed transversely of the casing. In the modification shown in Fig. 3, the radial blades on the rotor are replaced by longitudinal rods 45 supported by discs 24A fixed in spaced relation on the tube 17 ; in this arrangement, the flour is withdrawn from the expansion chamber 27A by an external fan through a duct 47 which is formed with a Venturi-throat 49 and subdivided by vertical vanes 50. In the arrangement shown in Figs. 7 and 8, the particles discharged in a gaseous stream from the mill pass upwardly through a passage formed between the walls 68, 88 to a classifier mounted on a driven shaft 74 in a casing 67 ; the classifier comprises a number of spaced annular discs 82 fixed in surrounding relation on the shaft 75 on which are also mounted fan blades 84 in a housing 72 and a sleeve member 75 shaped to provide a passage of gradually increasing cross-section from one end to the other of the classifier. The finer particles are therefore drawn inwardly of the classifier through the spaces between the discs 82 and then discharged through an outlet 87. The larger particles, which are thrown against the inner surface of the casing 67, are skimmed off by an adjustably-mounted bar 89 positioned at the top of a passage formed between the wall 88 and a rear wall 69 so as to be returned to the mill for further grinding. Preferably, an additional exhaust fan is provided in series with the fan 84 to ensure an adequate flow through the mill and classifier. In the modification shown in Fig. 9, the mill is fitted with a classifier 103 consisting of a fixed transverse tube 104, with one or more openings which are controlled by suitably rotating a similarly-apertured inner tube 105. An exhaust fan induces a draught through the mill and classifier resulting in the particlecontaining discharge from the expansion chamber 27 passing upwardly through a duct 114 of gradually-decreasing cross-section and then through a curved duct 97 to the classifier. The fine particles are withdrawn through the inner tube 105 of the classifier and the over-size particles, which are thrown outwardly in the curved duct, pass downwardly through a return duct 115 to the mill ; the degree of fineness of the particles withdrawn is determined by the setting of the inner tube 105 and a damper 116 at the lower end of the return duct. The machine shown in Fig. 3 is stated to be suitable for the initial separation of the fibre or bran from the endosperm in a flour-milling operation, the material being passed several times through the mill and the separated bran germ and endosperm being removed during each stage for segregation in the usual manner ; the fibre-free endosperm so produced is subject to complete milling in a mill of the kind shown in Figs. 1, 7 or 9 having its casing fitted with a corrugated liner. Specification 759,997 [Group II] and Canadian Specifications 531,857 and 542,235 are referred to.