Patent GB-693206-A (GB)
Title: Blast cleaning
IPC: B24C3/18
Filed: 1951-08-29
Abstract: 693,206. Control of several motors. PANGBORN CORPORATION. Aug. 29, 1951 [Nov. 7, 1950], No. 20370/51. Class 38 (iii) [Also in Group XXIII] A control system for electric motors controlling an abrasive-throwing machine (see Group XXIII) is operated by switches 610, 608, 668, 690, 688, 630, 628 on a control panel 666. Power is supplied to the control circuit through conductors 600, 602 of which the latter is earthed at 604. A motor 131 for rotating an impeller for the abrasive is controlled by a relay 612 energized by a temporary depression of the switch 610, a holding contact 618 maintaining the circuit through the relay and a circuit overload breaker 614 after the switch 610 has been released. The overload breaker 614 has contacts connected in series to two of the three-phase conductors in the motor 131. A further motor 129 for operating a conveyer for the abrasive is also controlled by a relay 632, an overload breaker 634 and a holding contact from the switch 630. A chamber in which workpieces to be cleaned are rotated about their own axis on a rotatable table has a blast shield to prevent abrasive entering the chamber when the door thereof is open. A green lamp 654 is connected between the conductors 600, 602 and controlled by a switch 652 operated by the blast shield and contacts 648, 649 operated by a main relay 720. The switches 690, 688 controlling the starting and stopping of the motor for rotating the work-table are connected to a lead 631 from the switch 630 through switches 687, 689 operated by the access door to the blast chamber and by the angular position in its cycle of operations of the table respectively. A red warning lamp 754 is connected to the conductor 602 and to the switch 690 by a conductor 700. A secondary relay 712 and a further table cycle limit switch 789 are connected between the conductors 700, 602. The secondary relay is connected to the main relay 720 and a relay 733 controlling time delay in the rotation of the table motor through contacts 710, 711 respectively, the relay 733 being connected to the conductor 602 and through a switch 730 to the conductor 700. The motor for rotating the table remains inoperative until energized through a main relay contact 848 by the closing of a contact 827 which is effected by an arm 825 driven through an electrical clutch 795 by a timer motor 823. The table rotating motor may be controlled by a relay 812 and a contact breaker in the same way as the motor 131. A further motor controlled by a relay 832 rotates rolls supporting the workpieces on the table. The relay 832 is connected to the switch 688 through a conductor 800 and a contact 849 controlled by the main relay 720. Air cylinders controlling the supply of abrasive to the impeller and the operation of the blast shield are operated, respectively, by controls 862, 860 connected to contacts 831 on the relay 832, a limit switch 864 for the blast shield being provided in the circuit to the control 862. The abrasive cleaning cycle, which normally occupies one complete rotation of the work-table, is started by depressing switches 610, 630 to start the abrasive impeller motor 131 and conveyer motor 129, the lamp 654 being energized if the blast shield limit switch 652 is closed with the blast shield preventing abrasive particles entering the chamber. With the workpieces in position in the chamber, the doors thereof are closed to close the door limit switches 687 and energize conductor 800 through switch 688. At the start of its cycle, the table holds the switch 689 closed so that operation of the switch 690 energizes the conductor 700, the lamp 754 and the main relay 720 through lead 726, relay contacts 730 and lead 736. Consequently, all the main relay contacts are operated resulting in deenergization of the lamp 654, isolation of the switch 668, energization of the roller motor control 832, raising of the blast shield and opening of the abrasive supply gate by its control 862. The clutch 795 is energized through the main relay contact 748 and closes a contact 818 to energize the motor 823 and start the arm 825 in motion. After the adjustable time delay, the contact 827 is closed by the arm 825 and the table rotation motor energized. If the roller motor is stopped by its breaker 834, the blast shield will be released to prevent abrasive from entering the chamber, thus opening the switch 864 to stop the supply of abrasive. The automatic cycle of operations cannot be started by operating the switch 690 if the table is not in the correct starting position, since the switch 689 would be open. The table can be "inched" into the correct position for starting the automatic cycle by a switch 668 connected through the main relay contacts 648, 649 to the conductor 600 and by a conductor 670 to the table motor control 812. A lamp (not shown) may be illuminated by the switch 689 to indicate when the switch has been closed. After the automatic cycle has started, table cycle switch 689 opens and switch 789 closes energizing the secondary relay 712 which closes the contacts 710, 711. Contact 710 provides a second energizing circuit for the main relay 720, the first circuit being broken by the influence of contact 711 on the time delay relay 733. At this point the relays 712, 733 may be connected to deenergize the clutch 795 or the timer motor 823 or both. The automatic cycle ends, after one revolution of the table, when the switch 789 opens and deenergizes the main relay 720 which allows the controls 862, 860 to stop the supply of abrasive and drop the blast shield. Opening of the switch 789 also deenergizes the time delay relay 733 which, after a time delay sufficient to stop the blasting operation, restores the circuit through the contacts 730 and lead 726 to the main relay 720. The table motor may be stopped and the main relay 720 de-energized by opening the switch 688. In various modifications (not shown), instead of re-starting the table cycle from its initial position following an interruption in the cycle, it may be re-started at the point of interruption. The conveyer motor 129 may be arranged to operate only when the impeller motor 131 is running. Also, the switches 608, 610 may be of the permanently shifting type.