GB712093A - Screening and classifying apparatus - Google Patents

Abstract

712,093. Sifting apparatus. MAHRENHOLZ, A., [trading as KALKER TRIEURFABRIK UND FABRIK GELOCHTER BLECHE MAYER & CIE.]. July 13, 1950 [July 29, 1949; Oct. 25, 1949; March 13, 1950], No. 17584/50. Class 117 In an apparatus for screening, classifying and aspirating granular material, in cooperation with an exhauster in which the material to be cleaned is fed to the front part of a set of superposed screens, arranged within a box provided with front air inlet openings, and passes therefrom to the rear part of the set of superposed screens to be classified and discharged, the screens are mounted on the side walls of the box, the box, screens, and the exhauster which is mounted within the box being mounted for oscillatory motion. As shown in Fig. 1, a grain cleaning apparatus comprises a box 1 suspended within a stationary supporting frame 22 and enclosing a roughage screen 2, a kernal screen 3, and a sand screen 4, which are rigidly connected to the walls of the box 1. A hopper 5, mounted on the top of the box 1, feeds the grain to be treated to the screen 2, which is inclined towards the front wall and is shorter than the screens 3 and 4, to provide space for the casing 6 of a fan 56, which has a discharge trunk 57 and intake openings 17. Between the screens 2 and 3, a baffle 14 guides the material dropping through the screen 2 forwardly to a point where it is subjected to the aspirating effect of the air current which enters through an inlet 8 in the front wall of the box 1, and a baffle 15 intercepts particles dropping from the air current and guides them towards the centre of the screen 3. The baffles 14 and 15 also guide the aspirator air current. Substantially the whole of the air current produced by the fan enters the box 1 through the openings 8 and 9 which extend across the width of the box, the outlet for the roughage retained by the screen 2 being closed by a leather apron 16 which prevents the entry of air but permits the roughage to be discharged. The different grades of the classified and cleaned material and the waste leave the box through discharge chutes from the openings 7, 59, 20 and 21 respectively, which may be provided with leather aprons and respectively co-operate with the screens 2, 3, 4, and the bottom 53. A vibrator shaft 11 journalled within the side walls of the box 1 is belt driven at a speed of about 2,000 r.p.m. by an electric motor 10, mounted in the supporting frame 22, which also drives the fan shaft 55. The discharge trunk 57 of the fan is connected by a resilient hose 12 with the inlet of a cyclone separator 13, wherein the dust is separated from the air current. The screen box 1, Fig. 4, is mounted in the supporting frame 22 by means of a pair of leaf springs 23 attached to journals 24, which are mounted on the side walls of the box and accommodate the vibrator shaft 11. Alternatively, Fig. 5 (not shown) a pair of leaf springs may be attached to the side walls by means of brackets. The shaft 11 is asymmetrically shaped so as to have its centre of gravity off-set from its axis of rotation. It is stated that by increasing the frequency of the screen oscillation far above the critical limit for the particular material being classified, and at the same time substantially reducing the amplitude of oscillation, the efficiency of operation is considerably improved and the screens are kept clean without the provision of special cleaning means such as knocking hammers or the like. The critical frequency is defined as the frequency at which the grains no longer pass through the screens, but pass across them in the form of a loose mass. In modifications, Figs. 7 and 8 (not shown), the shafts 11 and 55 are replaced by a single shaft functioning as both the fan shaft and vibrator, shaft.