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Grinding Electrical Control Systems

The motor control system of the grinding mill is centralized in the controlling cabinet. Every unit shall be started sequentially in accordance with the operation procedure and rules. In the control cabinet, most of the motors are generally asynchronous motors except the motors of the main frame, classifier and feeder. As for the detailed wiring connection, please refer to the Diagram of the system principle (Fig. 5-6)

1, The starting control of the main unit and blower

In this control system, the reduced voltage start is used for the motor with the capacity over 30KW while the direct start is for that below 30KW. And the Y start is used for blower and the delta start is for the main unit.

The delta start is connected with normal operation. The control circuit is composed of contactor and time relay. In an automatic switching, the time relay is usually set with an extension of over 10 seconds. For the motor with the delta start, there are nine connectors on the stator winding. They are U1,U2,U3,V1, V2, V3, W1, W2, W3. No mistakes are allowed in the numbered terminal connections between motor and the control cabinet. In case the connector motor is damaged, it can be replaced by a common motor with six connectors at the same power and speed, but this can only perform as the Y start and control.

2, The control and automatic feeding of the vibrating feeder

The structure of electric-magnetic vibrating feeder is a tow mass-pints fixed-directional forced vibration system. It consists of a feeding channel connected with a fork armature. It hangs under the material tank and with some free moving space. It cannot be blocked and bumped by other objects to avoid noises during the operation.

(1) after installation of the electro-magnetic vibrating feeder, loose the screws (upper three and lower one) on a positioning connection fork. After loosing the screws, fix the nuts, open the rear cover of the vibration feeder, and check if the gap between iron core and armature is within 1.8-2.1mm. the tow parts should be parallel and clean. All the screws should be fastened firmly. Finally, put on the cover and fix it.
(2)no-load trial running with power on. Adjust the amplitude resistor R1 in the electrical control cabinet slowly form small to big with the amplitude ranging within 1.8-2.5 mm and the current of t1.2A. keep running for several hours to see if the amplitude current is stable. If it is normal, open the door of material tank for material feeding and check if the current of feeding materials is stable. The amplitude is allowed to fall down 0.5mm. if the amplitude current is at the rated value but cannot meet the requirements of the feeding volume, hang the vibrator at a 20 decline position to meet the feeding requirement.
(3) regulation of the automatic feeding. The antomatic feeding is realized by the current change of the main motor and blower. When the blower is running normally, and if the current of the main motor exceeds the rated value, the feeding will be stopped; if the motor current goes down, the feeding will be automaticlly started. This function is carried out by a current relay. The start and stop of the feeding can be performed by open and close of the connection between the current relay and the control voltage of a silicon-controlled device. If the blower is out of order, the feeding will also be automaticlly stopped. There are two coils in DL-12/6 over current relay. When these two coils are in series connected, the working current can be regulated from 1.5-3A. When they are parallel connected, the working current can be regulated from 3-6A. when the pulverizer is under normal working condition, the coils should be in series connection because the current on the relay caused by the current mutual inductor will not be over 3A.
(4) When the automatic feeding is started, turn the main switch on the control cabinet into an automatic position. Slowly, turn the resistor R1 knob on the control cabinet to the rated value and remain stable. Meanwhile, move the sliding arm on the current regulating relay according to the rated value to change the action current of the rally. When the curent goes higher than the rated value, the constant-closed contact will be cut off, so the contact will be closed immediately when the current declines a little. In this way, the pulverizer will be always kept in an optimal working condition. The non-load and over-load running are avoided and the efficiency of power production is guaranteed.
(5) JZT speed-adjustable motor transmission is used for the classifier. The control is carried out by the bottom of the electro-magnetic slide controller (ZLK-1) on the control cabinet. When the button is pressed, the squirrel-cage motor will be started first. Then close the slide power switch and turn the knob of rotating speed to make the classifier to reach the speed that matches the required fineness (powder particle size). The powder fineness can be controlled in this way.

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