Stress Cracks in Plastic Molded Parts & the Role of Molecular Orientation

Plastic Injection Molding Molecular Orientation Stress CracksWhen it comes to scientific plastic injection molding, the reliable prediction of molecular orientation behavior during the molding process stands as one of the great challenges molders continue to experience.

In scientific plastic injection molding there are 2 primary ways that molecular orientation issues causes stress cracks in plastic molded parts.

2 Types of Molecular Orientation

  • In thermoplastic polymers, molecular orientation can change properties in the resin’s flow & transverse directions. These molecules will impart strength in the flow direction, and weakness in the direction perpendicular to the flow. In an attempt to correct this imbalance the molecules try to return to their normal state by shrinking in the flow direction. This shrinking can cause stress cracks in the direction of the flow, which results in mold cavity stress cracks.
  • Disruptions in molecular orientation can also be caused by certain chemicals and/or sunlight. When this happens the resin’s structure weakens and molecular tension releases. This causes internal stress, which results in hairline cracks on the surface of the molded part. These surface cracks can occur days, months or even years after the part is molded.

If your parts have stress cracks, you should work with a plastic injection molding company that has in-house Master Molders.

These Master Molders are technically trained & certified in resolving the toughest molding challenges & creating optimized solutions that other molders can’t.

We’ll help you identify the right solution for stress cracks in your plastic molded parts.

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