The slow-speed mode for closing the die of the Koenig & Bauer extrusion granulator is not working
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The Krones extrusion granulation unit used in our factory has recently developed the following problem: In a normal granulator, the dies move forward rapidly at first and then switch to a slower speed before coming into contact with the template. However, now the slow speed setting is no longer available; the dies move directly at full speed toward the template, which causes significant damage to the equipment. The forward and backward movement of the pelletizer is controlled by hydraulic oil. There is a proportional valve in the hydraulic circuit, as well as a 3/4-way solenoid valve for control. The proportional valve is operated via the WANDFLUH SD6 controller (parameters can be modified using PASO software). Through the SD6 controller and the proportional valve on site, the flow rate of the hydraulic oil can be adjusted, thereby controlling the speed of forward movement. I took a look at the SD6 manual; it seems that the control of the valve isn’t based on a simple 24V signal, but rather some kind of high-frequency wave (PWM). The question now is: how is the overall speed control achieved? What signal is used to control the valve? How to set up the PASO software? The documents provided include the SD6 instructions in both Chinese and English, photos, screenshots of the parameter settings from the original PASO software, screenshots of the pelletizer’s interface, circuit diagrams of the valves on site, as well as the instructions. I hope experts who are knowledgeable can give some guidance; thank you!
Attached is the oil circuit diagram of the pelletizing machine trolley for your reference; the proportional valve has been marked with a red box, along with the three-way and four-way dual solenoid valves.
Dear friends from Sichuan, I downloaded an online brief introduction to proportional valves. In the oil circuit diagram, it is not a simple solenoid valve, but rather an adjustable proportional valve. By adjusting the magnitude of the current flowing through the coil, the position of the sliding rod inside the valve can be changed, thereby regulating the flow rate of the hydraulic oil. But one thing I don’t understand is (refer to the screenshot): current alone is sufficient, so why is a high-frequency pulsating signal (a dither signal, also known as a PWM signal) needed? What is the purpose of this high-frequency pulsating signal?
Contact after-sales support, explain the problem to them, and have the relevant technical staff try to resolve it. If they can’t fix it, you’ll still need to pay to have someone come and deal with it; this is also an opportunity to learn something new. I’ve never worked with the instruments of this type of equipment, so it’s difficult for me to help.
PWM is also a control signal; for this system, you’d better turn to Kollmorgen to handle it.