Industrial plastic molding machine is vital for manufacturing high-quality plastic products. However, operational issues such as screw slippage and failure to unload materials can disrupt production and compromise product quality. This article explores the defects caused by screw slippage, the reasons behind the problem, and actionable solutions to ensure your machine operates efficiently.
Defects Caused by Screw Slippage in Industrial Plastic Molding Machine
Screw slippage occurs when the screw continues to rotate but stops its axial movement, disrupting the material feeding process. This problem often results in:
- Material Degradation: Prolonged heating due to slippage can degrade materials before injection.
- Reduced Product Quality: Defects like incomplete filling, inconsistent weight, or material shortages can occur.
- Extended Molding Cycle Times: The slippage extends the plasticizing process, delaying the overall cycle.
When materials gather at the feed port and fail to reach the end of the barrel, the industrial plastic molding machine’s efficiency is significantly compromised.
Common Causes of Screw Slippage
Screw slippage can arise from various issues. Let’s take a closer look at the most common causes:
1. Back Pressure Too High
- Cause: Excessive back pressure prevents the screw from generating enough forward force to transport the material, leading to slippage.
- Effect: Higher melt temperatures, poor product quality, and longer molding cycles.
- Solution: Lower the back pressure to an optimal level to facilitate smoother material flow.
2. Barrel Overheating or Overcooling
- Cause: Improper temperature control in the barrel’s rear section affects the formation of the molten polymer film needed for proper material feeding.
- Effect: Pellets fail to stick to the barrel wall and move forward effectively.
- Solution: Adjust the barrel temperature to ensure adequate heating time and form the critical molten film layer.
3. Barrel or Screw Wear
- Cause: Over time, wear on the barrel and screw reduces their ability to transport materials efficiently.
- Effect: Inadequate material shearing and forward movement.
- Solution: Inspect and replace worn-out barrels or screws to restore efficiency.
4. Improper Hopper Design
- Cause: Hoppers with sudden compression zones or designed for uniform pellets may fail when processing materials with varying particle sizes (e.g., recycled materials).
- Effect: Non-uniform feeding disrupts the screw’s ability to maintain steady pressure.
- Solution: Use a hopper design suited for the material’s particle size and characteristics.
5. Processing Hygroscopic Materials
- Cause: Moisture in hygroscopic materials lowers viscosity, creating water vapor that interferes with material feeding.
- Effect: Slippage occurs as the screw struggles to move the material forward.
- Solution: Properly dry materials before processing to maintain their viscosity.
6. Check Ring Failure
- Cause: A malfunctioning check ring allows molten material to flow backward, creating resistance during screw rotation.
- Effect: Slippage and incomplete material transfer.
- Solution: Replace the check ring immediately if a problem is detected.
Troubleshooting Screw Slippage
If the industrial plastic molding machine screw slips and stops unloading, follow these steps to troubleshoot and resolve the issue:
Clean the Barrel:
- Remove residual materials to ensure the barrel and screw are free of blockages.
- Check the melt temperature to confirm it matches the set barrel temperature.
Inspect for Poor Mixing:
- Examine molded products for defects like black spots or marble patterns, which indicate poor mixing in the barrel.
Address Specific Causes:
- Adjust the barrel temperature and back pressure to optimize feeding.
- Replace worn screws, barrels, or check rings if necessary.
- Ensure proper hopper design and consistent material feeding.
Common Reasons the Screw Fails to Discharge Material
In addition to slippage, you might encounter issues where the screw rotates but doesn’t discharge material. Here are some common causes and solutions:
- Inaccurate Temperature Control
- Problem: Excessive temperature at the rear end of the barrel.
- Solution: Recalibrate the temperature settings and inspect the cooling water circuit.
- Material Buildup or Blockage
- Problem: The barrel discharge port may be blocked by molten plastic.
- Solution: Remove any blockages to restore material flow.
- Excessive Lubricant in Plastic
- Problem: Too much oil in the material causes slippage.
- Solution: Adjust the material composition to reduce excess lubricant.
- Rubber Covering the Screw
- Problem: Plastic adheres to the screw and rotates with it.
- Solution: Clean the screw thoroughly to remove any build-up.
- Worn-Out Components
- Problem: Wear on the screw, barrel, or rubber ring reduces efficiency.
- Solution: Replace worn components to prevent material leakage and improve transportation.
- Inconsistent Material Size
- Problem: Large plastic particles cause bridging in the hopper.
- Solution: Crush the material into smaller, uniform sizes before feeding.
Preventive Measures
To avoid screw slippage and unloading issues, follow these best practices:
- Regular Maintenance: Inspect and replace worn parts, such as screws, barrels, and check rings.
- Material Preparation: Properly dry and crush materials to the desired particle size.
- Optimize Machine Settings: Maintain proper back pressure, barrel temperature, and feeding rates.
- Hopper Design: Use hoppers suited to the material type and particle size for consistent feeding.
FAQ’s
Ensure proper material feed by checking hopper consistency, optimize screw speed and back pressure, and regularly clean and maintain the barrel to avoid material buildup.
Commonly broken parts include the nozzle tip, heater bands, toggle pins, hydraulic seals, and screw flights due to wear and high operational stress.
Check for obstructions in mold movement, inspect and lubricate guide rails, ensure proper hydraulic pressure, and verify the mold positioning sensors for alignment and functionality.
Screw slippage and unloading issues can significantly impact the efficiency and quality of your injection molding process. By understanding the causes—such as high back pressure, barrel wear, or improper hopper design—and implementing the right solutions, you can minimize downtime and maintain smooth production.
Always prioritize regular maintenance and material preparation to prevent these issues from recurring. With the right approach, your industrial plastic molding machine will run efficiently, delivering consistent, high-quality results.
