GB587473A - Improvements in or relating to process of and apparatus for separating or grading comminuted material, such as abrasive grains and the like - Google Patents

Abstract

587,473. Coating fabrics successively with adhesive and powdered material. STEVENS, A. H. (Behr-Manning Corporation). Aug. 17, 1943, No. 13361. [Class 140] [Also in Groups II and XXIII] Comminuted material, e.g., abrasive grains or fibre flocks, is passed through an electrostatic field of alternating polarity and the frequency of the field is controlled to separate the finer sized particles and apply them to an adhesive coated backing, such as paper or cloth or a combination of paper and cloth. The coarser particles may be separately removed and collected, or may be applied to the same backing on top of the finer grains. There are simultaneously passed through an electrostatic field of alternating polarity produced between electrodes or banks of electrodes 3 and 6 an endless travelling belt 10 carrying a layer of abrasive grains from a hopper 9, and a backing 1 of adhesive-coated paper. The applied voltage is generally sufficient to lift all the grains from the belt 10 and the frequency is adjusted so that only the smaller grains reach and stick to the adhesive coated backing while the larger grains drop back. Some or all of the larger grains may be subsequently applied over the smaller grains in a second field of lower frequency or of constant polarity produced between electrodes 4 and 7. Any rejected grains fall off the belt 10 while passing around roller 13 and may be used for making coarser sandpaper. The spacing of the electrodes may be uniform or may decrease as shown towards the exit end. The specification indicates the voltages and frequencies suitable for use with specified grades of abrasive grains. Alternatively the smaller sized particles removed by the alternating field may be secured by a temporary adhesive such as water, which may contain a wetting agent or starch, to an endless belt, from which they are later removed by means of a vibrator and/or a rotating brush while passing through a heated chamber.