Troubleshooting Black Spots in Injection Molded Parts
Black spots are a common appearance defect found in injection molded parts. These are primarily caused by the decomposition of the plastic or additives like UV stabilizers and anti-static agents inside the barrel, which then get injected into the mold cavity along with the molten plastic. To prevent these issues, we can analyze and address them from the following four aspects:
1. Machine:
Excessive Barrel Temperature: Overheating the barrel causes the raw materials inside to decompose and turn black.
Decomposition of Residual Raw Materials: Residual raw materials in the screw and barrel decompose and char under prolonged high temperatures.
2. Mold:
Poor Mold Venting: Poor venting leads to burning, or the small size of the gating system causes excessive shearing and charring.
Presence of Inappropriate Lubricants or Release Agents: The presence of inappropriate lubricants or release agents inside the mold.
3. Plastic:
Excessive Plastic Volatiles: Excessive plastic volatiles, high humidity, excessive impurities, excessive use of regrind, or contamination of the plastic.
4. Molding:
Excessive Pressure, Speed, Backpressure, or Rotational Speed: Excessive pressure, speed, backpressure, or rotational speed can cause the material temperature to decompose, leading to black spots in the injection molded parts.
Regular Barrel Cleaning: Clean the barrel regularly to remove additives that are less heat resistant than the plastic.
