As early as the first Vertical roller mill was developed in Germany in the 1920s, it overcomes many of the shortcomings of the ball mill grinding mechanism with its unique grinding principle. However, due to the late start of industrialization in China, the performance research of the Vertical roller mill is also later than that of the western countries. Some domestic Vertical roller mills still have shortcomings!
The grinding of the Vertical roller mill is mainly caused by the following reasons: 1 the feeding amount is too large; 2 the exhaust air volume is too small; 3 the powder selecting machine is faulty. Once the mill is saturated, the motor will be in an overloaded state, so a protective device must be provided to avoid burning the motor. Some domestic Vertical roller mills do not have a full-fresh protection device. This problem can be taken by SBM heavy machine. The following protective measures can be taken: a pressure measuring hole is opened on the side of the grinding chamber, and the negative pressure in the grinding machine is measured. According to the principle that the negative pressure in the grinding chamber is proportional to the material, this is The negative pressure is converted into a millivolt signal by a YSH-1 Hall micro pressure transmitter, and this signal is input into an XCT-123 type display regulator. When the negative pressure in the mill reaches the upper limit set value (this When the value is measured by actual measurement and the mill model is different, the relay contact in the regulator is displayed and an alarm signal is sent to remind the operator to reduce the feed amount. If the negative pressure continues to exceed the set value for 60 seconds, the feeder is controlled to stop feeding. When the negative pressure in the grinding is lower than the set value, the feeder restarts normal feeding.
When the Vertical roller mill is started, sometimes an overload start occurs, which is caused by the residual material in the mill. Some domestic Vertical roller mills generally use the XJ01 series of auto-decompression starters, and the power line switches generally use HZ series knife switches. Therefore, once the motor is overloaded, the protection device appears to be imperfect and easily causes a step-by-step trip. In order to solve this problem, the SBM heavy machine will change the switch to the DZ10 type automatic air switch. The rated current of the electromagnetic release is set according to the rated current Ie of the motor, the operating current of the trip unit is set according to 4Ie, and the instantaneous release is 8Ie. Tuning. The automatic air switch operates once an overload occurs during the starting process. Secondly, when the mill started by the autotransformer is started in the automatic mode, the intermediate relay ZJ2 may not operate due to various reasons, so that the starting process cannot be switched to the full-pressure operation mode, which tends to burn the autotransformer easily. We have made some improvements to the original line for this phenomenon. The improved circuit is shown in Figure 2. The circuit works as follows:
Put the combination switch in the automatic mode position, press QA, QC suction and self-locking, SJ is powered, and ZJ1 is self-locking. After the set time, the normally open delay contact of SJ1 is closed, and ZJ2 is energized. When the XLC is energized, the entire starting process is completed. ZJ1, ZJ2, and SJ are all powered off, and only XLC and SJ1 are powered. This not only prevents the possibility of direct starting of the motor, but also prolongs the life of the intermediate relay, and the ZJ1, ZJ2, and SJ no longer consume energy when operating at full pressure. Especially during starting, if ZJ2 does not work for various reasons, then SJ1 is energized, and the normally closed delay contact of SJ1 string in the current transformer protection loop is disconnected after a certain delay (this time is greater than the setting time of SJ). The thermal relay RJ acts as an overcurrent protection. This forms a dual protection against the incoming current switch with the incoming air switch.
In the automatic control of some domestic mills, there is still a lack of alarms such as feeding device blockage and delayed shutdown. Sometimes the vibration is too large due to too large feed particles or metal inclusions in the material. If the tank gear oil temperature is too high or the oil level is too low, it cannot be alarmed. Therefore, certain measures must be taken to make the mill run safer and more reliable.
It can be seen that some domestic Vertical roller mills need to strengthen research and improvement in technology and performance, and soon push China's Vertical roller mills to the world to create a world-renowned Chinese Vertical roller mill brand.