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Installation and Debugging Techniques for Screw of Extrusion Blow Molding Machine

Key Steps for Screw Installation in Extrusion Blow Molding Machines

Pre-Installation Preparation

1. Component Inspection and Cleaning
Before installation, thoroughly inspect the screw and barrel for visible damage, such as cracks, scratches, or wear. Use a soft cloth and non-abrasive cleaning agents to remove dust, oil, or residual plastic from both components. For screws with mixing elements or special designs, check for blockages or material buildup in the grooves.

2. Alignment Tools and Lubrication
Ensure alignment tools like dial indicators or laser guides are calibrated for measuring screw-to-barrel concentricity. Apply a thin layer of high-temperature lubricant (e.g., silicone-based or food-grade grease) to the screw’s root diameter and the barrel’s inner surface. This reduces friction during initial rotation and prevents galling during startup.

3. Thermal Stabilization of Components
If the barrel has been stored in a cold environment, preheat it to room temperature (20–25°C) to avoid thermal stress during installation. For screws with hardened surfaces, ensure they are at ambient temperature to prevent dimensional changes due to thermal expansion.

Screw Installation Process

1. Barrel Mounting and Leveling
Secure the barrel to the machine frame using precision-ground shims or adjustable mounts. Use a laser level or spirit level to verify the barrel’s horizontal alignment (tolerance: ±0.05 mm/m). Tighten the barrel’s mounting bolts in a crisscross pattern to ensure even pressure distribution.

2. Screw Insertion and Alignment
Insert the screw into the barrel feed throat, ensuring the drive keyway aligns with the gearbox output shaft. For single-screw systems, rotate the screw manually (if possible) to check for binding or misalignment. For twin-screw systems, use a hydraulic puller or chain hoist to synchronize the insertion of both screws, maintaining a 0.2–0.3 mm gap between the screw tips and the barrel end cap.

3. Connection to Drive System
Attach the screw to the gearbox or motor shaft using a flexible coupling or spline joint. Verify torque specifications (typically 50–150 N·m for medium-sized machines) using a calibrated torque wrench. For direct-drive systems, ensure the motor and screw are concentric within ±0.02 mm to prevent vibration.

Post-Installation Debugging and Testing

1. No-Load Rotation Test
Start the screw at the lowest speed (10–20 RPM) and monitor for unusual noises (e.g., grinding, knocking) or vibrations. Use a stroboscope or tachometer to confirm the screw’s rotational speed matches the control panel settings. Gradually increase the speed to 50% of the rated RPM, checking for overheating at the drive coupling or bearing housings.

2. Temperature and Pressure Calibration
Set the barrel heating zones to the material’s processing temperature (e.g., 180–220°C for HDPE) and allow 1–2 hours for thermal stabilization. Install pressure transducers at the feed throat and die head to measure melt pressure (target: 10–30 MPa for most blow molding grades). Adjust the heating bands or PID controllers if temperature deviations exceed ±5°C.

3. Material Trials and Parameter Optimization
Feed a small batch of plastic pellets into the hopper and observe the screw’s conveying efficiency. For single-screw systems, ensure the flight depth and compression ratio (typically 2:1–3:1) provide uniform melting. For twin-screw systems, verify the kneading blocks achieve adequate dispersion (measured by melt flow rate consistency). Adjust the screw speed (50–150 RPM) and back pressure (5–15 MPa) to optimize output (50–200 kg/h) and energy consumption (0.15–0.3 kWh/kg).