Blistering/bubbles

Bubbles appear inside or on the surface of the product. Bubbles can be classified by shape: spherical bubbles with smooth and glossy inner walls (moisture or decomposition gas), irregular cavities with rough inner walls (vacuum shrinkage cavities), slender stringy gas marks (entrapped air). The distribution position of bubbles can provide important diagnostic clues——near the gate it is mostly screw air entrapment, at the end of the product it is mostly poor venting, and at the center of thick walls it is mostly vacuum shrinkage cavities. The mechanical strength at the bubble decreases by more than 50%, and it becomes a fatigue crack source under alternating loads.

1. Process parameter factors: volatiles or moisture in the material, poor mold venting, transfer speed too fast entrapping air, gas released from the curing reaction. 2. Runner and gate design factor: In transfer molding, the material needs to enter the cavity through runners and gates; the runner length, cross-sectional shape and gate size directly affect pressure loss, fiber breakage and filling balance, and unreasonable design is the root of many quality problems. 3. Feeding factor: The volume of the feeding chamber, the feeding amount and the preheating state of the material directly determine the transfer pressure and filling effect, and are key variables unique to transfer molding.

1. Process parameter optimization and adjustment: fully dry and preheat the material, improve mold venting, lower the transfer speed, add degassing operations. 2. Systematic troubleshooting method: Troubleshooting of transfer molding problems follows the order of 'runner -> feeding -> parameters -> mold'. First check whether the runners and gates are blocked or worn, then verify the feeding amount and material preheating, then adjust the transfer pressure and speed, and finally check the mold venting and temperature uniformity. 3. Preventive management: Establish standardized process parameter cards and quality control limits for each set of mold/product, and regularly conduct process capability index (CPK) evaluations. For recurring problems, use fishbone diagrams or 5Why analysis to trace the root cause, and solidify the countermeasures as PFMEA control points.

The three major causes of bubbles (moisture, air entrapment, vacuum shrinkage cavities) need to be treated differently: moisture type——sufficient drying; air entrapment type——optimize plasticization and injection parameters; vacuum shrinkage cavity type——strengthen holding pressure feeding. Accurate cause diagnosis is the prerequisite for effective solution.