Patent GB-631854-A (GB)
Title: Improvements relating to magnetic separators
IPC: B03C1/247
Filed: 1947-09-24
Abstract: 631,854. Magnetic separators. MOND NICKEL CO., Ltd. Sept. 24, 1947, No. 25973. Convention date, Sept. 24, 1946. [Class 72] In a magnetic separator of the horizontal rotary drum type in which the cylindrical surface is made up of the pole faces of electromagnets, the windings of the electromagnets are fed through a main commutator system A so that part only of their surface is energized at any instant, the supply to the brushes of the main commutator system is derived through thermionic valves having control electrodes, and the control electrodes are fed with a biassing voltage through a secondary commutator system B so arranged that the current from each valve in turn is blocked whilst the corresponding brush in the main commutator system is passing across a gap. The brushes of the main commutator system may derive their supply from a multiphase source through two or more thermionic valves with their control electrodes linked in parallel to a single brush of the secondary commutator system. Material to be separated is fed by a shoot 18 on to the counter-rotating drum, the surface of which is built up of pole faces 14 having cores 9 magnetized by current passing through the coils b<SP>1</SP>-e<SP>4</SP>, and the commutator connections are such that at any given time 180 degrees of the cylindrical magnet face is energized (i.e., the right hand side in Fig. 1) and the rest de-energized. The commutator rings a-i and the magnetizing coils b<SP>1</SP>-e<SP>4</SP> are'shown diagrammatically in Fig. 3 in a multi-phase supply circuit. The ring a is a closed ring, its circuit being common to all the magnet coils. Four groups 53-56 of three thyratrons are shown, each group connected to a lead of the transformer 45 and to its respective commutator ring b-e. The grids of the thyratrons are intermittently biassed to break the current flow in the interval of gap and brush registration (so that commutation is effected without sparking) by means of the commutator system B consisting of rings with oppositely connected contacts 59 and engaging brushes 62. The latter are included in the thyratron grid circuits, one brush being connected to the negative of a bias supply battery 64 the positive terminal of which is connected to the energizing circuit, and the other brush to the grids. The angular position of the contacts of commutators f-i correspond to the gaps of the commutators b-e respectively. As shown in Fig. 3, commutator b is opening coil circuit b<SP>1</SP>, b<SP>2</SP> and closing b<SP>3</SP>, b<SP>4</SP>; thyratrons 53 at the instant are non-conducting since the bias voltage 64 is applied to their grids through the commutator f. When valves 53 are again conducting, their output flows through coils b<SP>3</SP>, b<SP>4</SP>, and b<SP>1</SP>, b<SP>2</SP> are de-energized. At the same instant current flows from the thyratron groups 54-56 through the coils c<SP>1</SP>, c<SP>2</SP>; d<SP>1</SP>, d<SP>2</SP>; e<SP>1</SP>, e<SP>2</SP>. Approximately 45 degrees later the commutator c changes from coils c<SP>1</SP>, c<SP>2</SP>, to c<SP>3</SP>, c<SP>4</SP> and thyratrons 54 will be momentarily non-conducting; commutators d, e, follow in order, so that at any given time 180 degrees of the cylindrical magnet face is energized and the rest de-energized. A stationary yoke 36 of magnetic material embraces part of the drum and has an inwardly projecting pole-piece 39 which lies between the flanges 16 and has a non-magnetic shield 40; whilst the drum surface may be serrated as at 33, and scrapers 19, 20-counterweighted-may be provided.