Patent GB-561968-A (GB)
Title: Improvements in or relating to electromagnetic controlling devices for mixing machines
IPC: G05D11/13
Filed: 1942-09-10
Abstract: 561,968. Electromagnet control systems for mixing machines. STURTEVANT ENGINEERING CO., Ltd., and SCOTT, J. M. Sept. 10, 1942, No. 12787. [Classes 35 and 38 (iv)] [Also in Groups XXIX and XXXVII] An electromagnetic control system for a mixing machine comprises a pair of relatively movable magnets disposed with their poles opposite to one another, one or both of the magnets being an electromagnet energized by current of a strength which is determined by the viscosity of the mixture in the mixing chamber, in combination with control means for one or more ingredients of the mixture adapted to be operated progressively in proportion to the extent of relative movement of the magnets. The relative motion may be effected by repulsion or attraction of the two magnets and may be utilized to control a valve through which liquid is supplied to the mixing chamber. Fig. 1 shows a device operating such a valve V and comprising an electro-magnet C, attached to a fixed plate E, co-operating with a similar magnet D pivoted to the plate E at G. The coils A, B of the' electro-magnets are series connected and are wound in such directions that the magnets tend to repel one another when current flows, the angle of displacement of the movable magnet D depending upon the current strength. The plate F has an arm M which actuates the stem of the valve V through links O, Q so that the setting of the valve is determined by the angular displacement of the magnet D. To increase the amount of useful movement of the magnet D the poles of the two magnets may be V-shaped as shown. The initial angle between the two magnets may be adjusted by a screw H which clamps the plate E in the desired position. To ensure complete closure of the valve a reversing switch may be provided to reverse the current through one of the coils C, D so that the magnets attract one another and give a definite closure, irrespective of gravity. The device may be provided with dashpots or other time-lag devices, and two or more devices may be coupled to produce a differential action. When the devices are to be used on A.C. the magnets may have copper shading bands," or three pairs of coils may be provided if a three-phase supply is utilised. A series of pairs of magnets may pivot about a common fulcrum. In a similar construction adapted for the operation of electric switches the arm M is arranged vertically and micro-switches N<SP>1</SP>, N<SP>2</SP>, O<SP>1</SP>, O<SP>2</SP>, Figs. 2 and 3, are disposed on either side of it, the switches being adjustably mounted on the plate E and arranged in such positions that a small force is only needed to operate each switch. The switches may be adjusted by screws P<SP>1</SP>, which control the operating pressure, as also does the point at which the arm M bears on the operating blades Q of the switch, as shown in Fig. 3. The switch may be of the leaf spring type, in which a movement of about .0001 inch on a plunger T operated by the blade Q causes the contacts to snap from one position into another and to return to the first position when pressure is released. A greater number of switches may be arranged on either side of the arm M, the arrangement being such that the switches operate in sequence as movement of the arm increases. Such an arrangement is shown in Fig. 4 for the automatic control of a valve V supplying liquid to a wet mixer, such as a superphosphate Den mixer, the control being such that the consistency of the mixture formed is substantially uniform. The mixer is driven by a three-phase A.C. motor (not' shown), the line currents of which pass through three pairs of operating coils of the control magnets A, B, so that repulsion between the magnets is proportional to the current taken by the motor and therefore to the consistency of the mixture. The valve is operated by solenoids d-g which work on a floating lever i connected by a link m to a valve-operating lever j connected to the valve stem and having an adjustable fulcrum Y, the solenoids being energised by the switches A<SP>1</SP>-A<SP>4</SP> and B<SP>1</SP>-B<SP>3</SP> of the control device. The solenoids are adjustable vertically in relation to a stop bar h so that their effect on -the lever i may be adjusted. The motor of the mixing machine is controlled by a starter U which is electrically interlocked with the starter T of a motor supplying solid material to the mixer, so that the latter motor cannot be started until the mixer is running. The starter T is interconnected with the controller Z of a contactor through which current for the solenoids is supplied, so that the contactor automatically closes when the solid feed motor is started. The switch B<SP>4</SP> of the control device is arranged to open the starter circuit of the solid feed motor in the event of the consistency of the mixture becoming too thick, the switch re-closing when the desired consistency has been re-established.