Application Of VFD in Injection Molding

The application of conventional frequency converters in the plastic machinery sector leverages their precise speed regulation, high torque output, and energy-saving features to address industry challenges such as high energy consumption, unstable process control, and short equipment life. Below is an in-depth analysis of their advantages, combined with the operational characteristics of plastic machinery (e.g., injection molding machines, extruders, blow molding machines):

I. Energy-saving Optimization for High-power Systems, Significantly Reducing Production Costs

Dynamic Energy Efficiency Based on Process Stages
Plastic machinery operates in distinct stages (e.g., injection, holding, cooling) with varying load demands:

Injection stage: High torque (150%–200% of rated torque) is required for rapid material filling, and frequency converters deliver stable power via vector control;

Holding/cooling stage: Load drops by 40%–60%, and frequency converters automatically reduce speed (e.g., from 50Hz to 20Hz), with energy savings of 30%–50% compared to fixed-frequency systems.
Case: A 2000-ton injection molding machine using a frequency converter reduces power consumption per ton of product from 520kWh to 310kWh, saving ~1.2 million kWh annually.

 

Regenerative Energy Feedback for Energy Recovery
During the deceleration of extruder screws or the retraction of injection cylinders, the motor enters a generating state. Frequency converters with regenerative units convert kinetic energy into electrical energy (feedback efficiency >95%), which is fed back to the grid, replacing traditional resistive braking. This reduces energy loss by 15%–20% for blow molding machines producing PET bottles.

II. Precision Control to Enhance Product Quality and Process Stability

Multi-stage Speed and Torque Regulation

Injection molding: The frequency converter adjusts the screw speed from 0–150rpm steplessly: high speed (120–150rpm) for rapid injection, medium speed (80–100rpm) for pressure holding, and low speed (30–50rpm) for plasticizing, ensuring uniform material density (weight tolerance ≤±0.5%);

Extrusion molding: PID closed-loop control of the die temperature (accuracy ±1℃) is achieved by linking the frequency converter with a temperature sensor, preventing material degradation caused by overheating (e.g., reducing the scrap rate of PVC pipe production from 8% to <2%).

High-response Dynamic Adjustment
The frequency converter's response time (<20ms) adapts to sudden load changes (e.g., material viscosity fluctuations). For example, in the production of multi-layer co-extruded films, the speed difference between each extruder is controlled within ±0.1%, avoiding thickness deviations in the film.

III. Mechanical Protection to Prolong Equipment Service Life

Soft Start/Stop to Reduce Impact Damage

Soft start (ramp-up time 5–15s) limits the starting current to 1.5–2 times the rated value (fixed-frequency starting current is 5–7 times), reducing wear on the gearbox and screw drive system. The bearing replacement cycle of an extruder is extended from 12 months to 24–30 months;

Soft stop (deceleration time 10–20s) prevents material backflow and screw inertia impact, extending the service life of the check valve by 30%.

Comprehensive Fault Protection Functions

Overload protection (120%–150% threshold) triggers an alarm within 0.1s when the screw is stuck by metal debris, preventing motor burnout (traditional thermal relays respond in >1s);

Overvoltage protection suppresses voltage spikes caused by regenerative braking, protecting the inverter module (failure rate reduced by 60%).

IV. Adaptation to Harsh Working Environments and Special Requirements

Heat-resistant and Corrosion-resistant Design

In plasticizing workshops with high temperatures (ambient temperature ≤45℃), frequency converters use forced air cooling (cooling capacity ≥500W) to maintain stable operation at 40℃;

For PVC processing equipment exposed to acidic gases, frequency converters with anti-corrosion coatings reduce component oxidation, extending the maintenance cycle from 6 months to 12 months.

Explosion-proof Solutions for Special Scenarios
In flammable environments (e.g., ABS plastic granulation), explosion-proof frequency converters (Ex d IIC T6) are used, combined with spark-free contactors to meet safety standards (e.g., compliance with EU ATEX regulations).

V. Intelligent Integration and Production Management Upgrades

Industrial Network Communication and Process Digitization

Frequency converters connect to the PLC via Modbus/Canopen protocols, integrating with weight sensors and pressure transducers to achieve closed-loop control: automatically adjusting the screw speed when the material feeding volume fluctuates, ensuring consistent product dimensions;

Support storing 30+ groups of process parameters (e.g., speed, pressure for different plastics), enabling one-click switching between products (reducing changeover time by 50%).

 

Remote Monitoring and Predictive Maintenance

IoT modules enable real-time tracking of operating data (current, temperature, running hours) via SCADA systems, with automatic alarms for anomalies (e.g., "E017" for overheating), reducing fault diagnosis time from 2 hours to 30 minutes;

Big data analysis predicts wear of key components (e.g., estimating screw clearance based on motor current fluctuations), shifting from reactive to proactive maintenance and reducing downtime by 40%.

VI. Life Cycle Cost Advantages

Lower Initial Investment and Operating Costs

The frequency converter + permanent magnet motor solution costs 15%–25% less than traditional hydraulic systems, eliminating the need for oil cooling equipment;

Reduced grid capacity requirements (e.g., a 315kW extruder's starting current is ≤400A with a frequency converter, vs. >1200A for fixed-frequency), lowering transformer and cable investment.

Long-term Reliability and Low Maintenance

Service life of 8–10 years (based on 24/7 operation), with no mechanical parts to replace, reducing annual maintenance costs by ¥300,000+ compared to hydraulic systems;

Unplanned shutdowns are reduced by 65%, increasing annual output by ~500 tons for an injection molding production line.

Conclusion

Conventional frequency converters reconstruct the energy flow and control logic of plastic machinery by integrating "dynamic process adaptation + intelligent energy management," driving the industry's transition from "high-energy consumption" to "precision manufacturing." Whether in injection, extrusion, or blow molding, their advantages in energy efficiency, control accuracy, and equipment protection make them core technologies for smart manufacturing upgrades in the plastics industry. With the deepening of Industry 4.0, frequency converters will further collaborate with AI and cloud computing to promote the development of plastic machinery toward "predictive production" and "zero-waste manufacturing."

This equipment is composed of a frequency converter, a water pump motor, a PID controller and a pressure sensor. The built-in PID regulation function can adjust the frequency in real time to maintain a constant pressure in the pipeline network. Its energy-saving principle is based on the cube proportional relationship between the shaft power of the water pump and its rotational speed. By reducing the power supply frequency, it significantly reduces energy consumption, and the measured power-saving rate reaches 20% to 60%. It is equipped with a soft start-stop function to eliminate the water hammer effect and extend the service life of the equipment. At the same time, it supports time-segmented pressure timing control and unattended operation mode, and integrates automated management and multiple safety protection mechanisms.

 Excellent energy-saving effect: 

  

Under VFD drive, as the motor power factor improves, the operating current decreases, thereby reducing equipment power consumption and saving operating costs.