Improvements in and relating to the control of electric motors driving metal-blank rolling mills and the like

摘要

800,109. Rolling. SVENSKA METALVERKEN AKTIEBOLAGET. Jan. 10, 1956 [Jan. 11, 1955], No. 838/56. Class 83 (4). [Also in Group XXXVII] Relates to a system for maintaining constant speed relationships between the separate sections of a rolling mill or like plant having driving motors M1 ... M4 which are mechanically coupled to tachometer generators 10 ... 40. A monitoring voltage generator LG supplies an input voltage to the first tachometer generator circuit, the said circuits being interconnected through the field regulators R1 ... R4 of the corresponding motors so as to maintain constant mutual speed relations between the sections since the regulators provide a correcting output when the currents through sensing elements 11 ... 41 deviate from zero. Means are also provided for counteracting sudden speed changes caused by variations in the load upon a section motor when the material being worked upon enters or leaves a section of the mill, for example. For this purpose, a control current impulse is supplied to the motor regulator at a predetermined period before the actual load variation on the motor takes place, the said period being adjusted in accordance with the speed of advance of the material being worked. The control impulse may be initiated when the front end of a strip being rolled arrives at a predetermined position, which is adjustable, in front of the mill section driven by the motors under control. If the driving motors are of the Schrage type, the impulses are arranged to cause displacement of the brushes. In other arrangements a device co-operating with the strip is used to control a rheostat in the field circuits of the motors or in the circuit of the monitoring generator LG. As shown, a switch 103 is actuated by the strip at a suitable time interval before the strip enters a section so that a voltage is developed across resistor 111 and the excitation of a speed control coil 113 is varied to compensate for the speed-change which otherwise would occur due to the change in load. The coil 113 is also supplied with a measure of the motor current by means of shunt 115 in the armature circuit. The control impulse may be followed by a low voltage of constant amplitude which is supplied to the regulator of the motor for compensating the drop in speed whilst the strip is passing through the section, or pulses in different directions may be provided to prevent decrease and increase of speed as the strip enters and leaves the section, respectively. One arrangement for sensing the approach of a heated wire blank before it enters a section of a rolling mill comprises a pivoted heat-sensitive device which is set manually in different angular positions by means of a scale and indicator. When the front end of the blank reaches a given position, the heat radiation therefrom reaches the sensitive device which generates a current impulse for controlling the section motor. The manual adjustment of the heat-sensitive device is made in accordance with the speed at which the blank is fed to the machine. The heat-sensitive detector may be replaced by photo-electric or other suitable devices. The current-control impulses may be supplied to the regulators of the several section motors in succession or, if the strip is fed at high speed, the control impulse may be supplied simultaneously to all the regulators.