For non Newtonian fluids, the volumetric flow rate Q (metering section flow rate) of the extruder is directly proportional to the screw speed. This relationship has significant guiding significance for production practice, as it indicates that increasing the rotational speed can significantly increase the output of the extruder. The development history of single screw extruders also indicates that increasing the rotational speed is one of the important ways to improve the single machine production capacity. However, in the actual extrusion process, the flow rate and screw speed are not completely linear. This is mainly because we simplified the melt viscosity, outlet pressure, melt rheological properties, etc. when deriving the above formula.
The influence of injection molding machine screws on extrusion stability
As the head resistance increases, the characteristics become "soft", which is unfavorable for the production seam location of the extruder. The 1KV system significantly improves the trapped conveying efficiency of the extruder by using slotted liners, giving the extruder a "hard" characteristic. However, from the perspective of the impact of screw speed fluctuations on flow rate, the harder the waiting time of the extruder, the greater the impact of screw speed fluctuations on flow rate fluctuations. From the above, we can conclude that the extrusion flow rate Q increases with the rotation of the screw n. Increasing or decreasing proportionally, a 1% fluctuation in screw speed will result in a 1% fluctuation in extrusion yield.
Screw speed adjustment of injection molding machine
① The output of the extruder is directly proportional to the screw speed. This indicates that increasing the screw speed can significantly increase the extrusion yield, but from the perspective of stable extrusion, this also puts higher requirements on the control of screw speed fluctuations. Conventional single screw extruders often use a transmission method of ordinary V-belt and gear variable speed. Theoretical analysis shows that the V-belt will experience elastic sliding of 1% -1.6% during operation, causing loss of rotation. Many high precision single screw extruders abroad have adopted a direct connection method of motors and reducers, eliminating belt transmission.
② The influence of motor types and control methods on the stability of the extrusion process cannot be ignored. In recent years, both domestic and foreign extruder hosts have mostly used DC motors or variable frequency motors. The working stability of these two types of motors has been greatly improved compared to previous electromagnetic speed control motors. Among them, the AC variable frequency motor controlled by FV (vector energy) represents the progress of new transmission technology. Nowadays, by using a variable frequency speed regulation electric to machine with a plastic extruder reducer, the fluctuation of screw speed can be controlled at around 0.01%.
