Step-by-Step Guide to Replacing the Screw in a HD Injection Molding Machine

### **1. Pre-Replacement Preparation**  

1. **Tools & Materials**  

   - New screw (compatible with the machine model)  

   - Torque wrench, screw puller, brass rod, heat gun  

   - High-temperature lubricant grease, cleaning cloths, hex key set  

   - Safety gloves, goggles, heat-resistant clothing  

2. **Safety Precautions**  

   - **Disconnect the main power supply** and hang a warning tag. Ensure the barrel temperature cools below 50°C (122°F).  

   - Release residual hydraulic pressure and shut off cooling water valves.  

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### **2. Removing the Old Screw**  

1. **Disassemble the Nozzle and Barrel Front**  

   - Use a hex key to remove the nozzle bolts and detach the nozzle.  

   - Remove the barrel front flange (mark alignment positions for reassembly).  

2. **Extract the Screw**  

   - Enter **manual injection mode** and push the screw to the forward position.  

   - Secure the screw’s rear end with a puller. Slowly rotate and pull the screw outward to avoid scratching the barrel’s inner surface.  

   - If the screw is stuck, apply localized heating to the barrel (≤150°C/302°F) using a heat gun to loosen it.  

3. **Clean the Barrel**  

   - Remove residual plastic from the barrel using a brass brush or soft cloth (avoid metal scrapers).  

   - Inspect the barrel for wear or scratches; replace the barrel if necessary.  

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### **3. Installing the New Screw**  

1. **Prepare the New Screw**  

   - Apply a thin layer of high-temperature lubricant to the screw surface.  

   - Check the screw threads and check ring (non-return valve) for damage; remove any anti-rust oil.  

2. **Insert the Screw**  

   - Align the screw with the barrel entrance and manually rotate it into place (ensure proper engagement with the drive shaft).  

   - Gently tap the screw’s rear with a brass rod for alignment (avoid forceful impacts).  

3. **Reassemble and Tighten**  

   - Reinstall the barrel front flange and nozzle, aligning the marked positions. Tighten bolts to the specified torque (typically **80–120 N·m**).  

   - Verify the screw-barrel clearance (≤0.1mm) and manually rotate the screw to confirm smooth movement.  

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### **4. Post-Installation Testing**  

1. **No-Load Test**  

   - Restore power and heat the barrel to the material’s processing temperature (e.g., ABS: 200–240°C/392–464°F). Soak for 20 minutes.  

   - Rotate the screw at low speed (≤30 RPM) in manual mode; monitor motor current for abnormalities.  

2. **Load Test**  

   - Purge the barrel with cleaning material (e.g., PP or HDPE) to remove debris.  

   - Verify injection stability and measure product weight tolerance (±1% is acceptable).  

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### **5. Key Warnings & Troubleshooting**  

- **Critical Safety Rules**:  

  - Never disassemble the screw before cooling (risk of burns).  

  - Avoid using mismatched tools (risk of thread damage).  

- **Common Issues**:  

  - **Screw Misalignment**: Confirm barrel/screw dimensions and OEM compatibility.  

  - **Injection Inconsistency**: Recalibrate backpressure settings or check the check ring’s seal.  

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### **Maintenance Tips**  

- Record the screw’s service life and inspect wear every 3–6 months (measure outer diameter degradation).  

- Frequent screw replacements may indicate issues with material contamination, temperature settings, or backpressure.  

*(Note: Procedures may vary by machine model. Always prioritize Haida’s official technical guidelines.)*