Technical Service Guide: Troubleshooting 3 Common Vulcanization Defects

Defect 1: Incomplete Filling (Short Shots)

• Symptom: The finished rubber part has an incomplete appearance and voids where material did not fully fill the mold cavity.

• Root Causes:

• Material Issues: Inaccurate weighing of the compound; poor flowability; actual dosage inconsistent with process specifications.

• Mold Issues: Clogged injection gates; injection gates too small.

• Process/Machine Issues: Improper placement of the raw compound; excessive overflow/flash; insufficient injection pressure; uneven preheating of the compound in the injection machine; using inconsistent process parameters across different machines for the same product.

• Equipment Failure: Sudden power outage during the injection or transfer process.

Defect 2: Adhesion Failure (Rubber-to-Metal Bonding Failure)

• Symptom: The rubber detaches from the metal framework (insert), resulting in poor or non-existent bonding.

• Root Causes:

• Dust contamination due to inadequate dust protection.

• Contamination from mold-release agents.

• Oil contamination during equipment maintenance (inserts not moved away).

• Failure to wear clean gloves when loading the inserts.

• Inadequate Cleaning: Residual oil/grease on the metal insert before adhesive application.

• Adhesive Application Issues: Primer or topcoat not fully dried; adhesive layer is too thick or has pooling/accumulation.

• Adhesive Quality/Storage: Use of unqualified adhesive; expired adhesive storage.

• Contamination:

• Process/Mold Issues: Mold temperature too high or too low; poor mold sealing; oversized injection gates; the insert is left in the hot mold for too long; sudden power outage after mold closing but before injection; secondary processing/machining defects.

Defect 3: Ragging / Edge Tearing

• Symptom: Wrinkles, delamination, and other defects appear at the mold parting line.

• Root Causes:

• Mold temperature is excessively high.

• The distance of the tear-trim groove on the trimming mold is improperly designed/unreasonable.

• Inadequate or improper mold venting.