The pneumatic system of the air-blown automatic screw feeder achieves precise control of feeding speed and flow rate through multi-stage coordinated control. Its core lies in the precise driving of pneumatic actuators, dynamic adjustment of air pressure, and mechanical linkage with the screw conveyor mechanism. The pneumatic system typically consists of an air source, pneumatic control valve assembly, actuators (such as cylinders and pneumatic motors), and sensors. These components are connected by pipelines to form a closed-loop control circuit, ensuring a stable and reliable feeding process.
The selection of pneumatic actuators directly affects the control accuracy. The pneumatic motor, as the core component driving the screw shaft rotation, has a speed proportional to the input air pressure; stepless speed regulation can be achieved by adjusting the supply air pressure. Compared to electromagnetic motors, pneumatic motors have advantages such as fast response speed and strong overload protection, making them particularly suitable for scenarios requiring frequent start-stop or load fluctuations. Furthermore, some models use double-acting cylinders to drive the axial movement of the screw shaft. By controlling the extension and retraction stroke of the cylinders, the gap between the screw blades and the feed trough is adjusted, thereby indirectly affecting the material throughput per unit time.
The air pressure regulating valve assembly is crucial for precise control. The system is typically equipped with a proportional pressure valve or an electro-proportional valve. These valves convert electrical control signals (such as 4-20mA or 0-10V) into corresponding pneumatic pressure outputs, enabling continuous pneumatic pressure regulation. For example, when a higher feeding speed is needed, the control system increases the output signal, the proportional valve opening increases, the pneumatic motor speed increases, and the screw shaft rotates faster, driving the material conveying. Conversely, decreasing the signal strength slows down the feeding speed. Some high-end models also integrate pressure sensors to provide real-time feedback of the pneumatic pressure to the controller, forming a closed-loop control to eliminate the impact of pneumatic pressure fluctuations on feeding accuracy.
The design of the screw conveyor mechanism must be matched with the pneumatic system. The screw shaft pitch, diameter, and speed together determine the theoretical conveying capacity, and actual control requires optimization based on pneumatic parameters. For example, when conveying high-viscosity materials, the screw pitch can be appropriately increased to reduce the risk of blockage, while increasing the air pressure increases the screw shaft torque to ensure smooth material delivery. For lightweight powder materials, the screw pitch and speed need to be reduced to avoid material scattering due to airflow disturbance. Furthermore, surface treatments of the spiral blades (such as polishing or applying a wear-resistant coating) reduce frictional resistance with the material, further enhancing the sensitivity of the control.
The application of sensors strengthens the system's adaptive capabilities. Level sensors monitor the material accumulation height in the trough; when the level falls below a set value, the system automatically increases the feeding speed to replenish the material; conversely, it reduces the speed to prevent overflow. Flow sensors directly measure the material throughput per unit time and feed the data back to the controller. By comparing this data with the target value, the controller dynamically adjusts the air pressure or spiral speed to achieve closed-loop flow control. Some models are also equipped with pressure switches; when the air pressure is abnormal (such as insufficient air supply or pipe blockage), an alarm is immediately triggered and the machine stops to prevent equipment damage.
The energy-saving design of the air-blown automatic screw feeder pneumatic system also affects the control effect. Optimizing the pipeline layout to reduce pressure loss, using low-friction pneumatic components to reduce energy consumption, and automatically depressurizing during shutdown to prevent prolonged cylinder pressure holding all improve the system's energy utilization efficiency. For example, using a quick-release valve can shorten the cylinder's operating cycle and reduce compressed air waste; while integrated pneumatic modules reduce leakage risk by minimizing the number of interfaces and ensuring stable air pressure.
In practical applications, control strategies need to be adjusted according to material characteristics. For materials with uneven particle size distribution, a segmented speed control method can be used: high-speed feeding to quickly fill the hopper in the initial stage, followed by switching to low speed for accurate metering in subsequent stages; for materials prone to agglomeration, a vibrator needs to be installed before the pneumatic motor to break up material clumps through high-frequency vibration, ensuring smooth conveying. Furthermore, regular maintenance of pneumatic components (such as cleaning filters and replacing seals) can prevent a decrease in control accuracy due to wear and extend equipment lifespan.
