ABS resin injection molding processing points

1. Material Drying

• Importance: ABS resin is hygroscopic. Moisture can cause bubbles in products during injection molding, reducing mechanical properties and causing surface defects like flow lines and silver streaks. It may also lead to material hydrolysis.

• Conditions: The recommended drying temperature is 80 - 90 °C, which removes moisture without altering material properties. Drying time is usually 2 - 4 hours, but it should be adjusted based on initial moisture content, drying equipment efficiency, and environmental humidity, aiming for a moisture content below 0.1%.

2. Injection Temperature

• Range Basis: The melting temperature of ABS is 220 - 260 °C, determined by its molecular structure and physical properties. In this range, the material can flow smoothly during injection.

• Control Points

• Barrel Temperature: It should increase from the rear to the front of the barrel. The rear end is 200 - 220 °C to prevent premature melting, and the front end near the nozzle is about 240 - 260 °C for complete melting. Stable temperature is crucial.

• Nozzle Temperature: Usually 230 - 250 °C, matching the barrel front - end temperature. Too high a temperature may cause degradation, while too low may lead to nozzle clogging.

  
  

3. Injection Pressure

• Selection Basis: ABS has higher melt viscosity than some other plastics due to its molecular structure. Higher injection pressure is usually needed, but for small, simple, and thick parts, lower pressure can be used.

• Impact on Quality: Pressure at gate closure affects surface quality and silver - filament defects. Low pressure can cause atomization, while high pressure may lead to scratches, strains, and mold sticking.

4. Injection Speed

• Selection Principle: Medium injection speed is generally best for ABS, ensuring smooth mold - cavity filling and reducing quality issues.

• Impact on Quality

• Too Fast: Can generate friction heat, causing plastic burning, decomposition, and defects like melting joints and poor luster. It may also suck air into the melt.

• Too Slow: Unsuitable for thin - wall and complex parts, as it may result in short shots and insufficient filling due to rapid cooling of the melt.

5. Pressure and Time

• Holding Pressure Setting: Increasing holding pressure can improve product shrinkage and internal quality, but too high pressure causes high internal stress. A lower holding pressure should be chosen, e.g., 50% - 70% of the initial injection pressure for high - requirement products.

• Holding Time Setting: Based on the time when the gate cools and solidifies and the screw stops applying pressure. Too long time leads to excessive filling and high internal stress, while too short time causes shrinkage and size instability. The optimal time is when the product weight is unchanged.

6. Mold Temperature

• Range and Function: The general mold temperature is 75 - 85 °C. For large - projection - area parts, the fixed mold temperature is 70 - 80 °C and the moving mold temperature is 50 - 60 °C. Higher mold temperature improves part flow, welding strength, and reduces internal stress but prolongs the cooling time.

• Impact on Quality: Too low a mold temperature can cause high internal stress, reduced product performance, brittleness, and surface quality problems.

7. Material Control

• Influence of Quantity: When injecting ABS plastic, the injection volume is usually 75% of the standard volume to improve melt fluidity and distribution. To enhance part quality, a 50% calibration injection volume can be used, which also facilitates mold cleaning and maintenance.

• Selection Basis: A smaller injection volume ensures smoother melt flow and filling, reducing quality issues.

8. Mold Design

• Wall Thickness Uniformity: Product wall thickness should be uniform, with the wall - thickness difference of ABS products controlled within 25% to prevent stress concentration caused by uneven cooling and shrinkage.

• Reinforcement Design: Add rounded corners or reinforcing bars to weak post roots to prevent breakage. Fastener roots should also be rounded, with the r - angle to wall - thickness ratio above 0.3, considering surface shrinkage.

• Cooling Water Design: The mold cooling waterway should ensure uniform cooling to avoid internal stress and uneven shrinkage, especially for complex - shaped products.