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Solutions to air streaks and incomplete filling (lack of glue) in molds

• 2025-08-09

Solutions to air streaks and incomplete filling (lack of glue) in molds

The air streaks of the mold

Phenomenon: During the production process of transparent protective covers, thin layers of air streaks often appear near the water outlet.

Analysis: The raw material melt is prone to decomposition at high temperatures during shearing, generating gas. The high brightness of the mold surface is not conducive to the discharge of gas. The gas is drawn in through the water inlet due to the pressure drop.

(1)Characteristics of injection molding machines

Grade: HT-DEMAG, clamping force: 100t, plasticizing capacity: 150g.

(2) Mold characteristics

Mold ejection number: 1×2, glue injection method: point gate, top block ejection: Mold temperature: 100°C (constant temperature machine).

(3) Product characteristics

Material: PC, Color: Transparent, Product weight (single piece) : 1.5g, nozzle weight: 13g.

(4) Analysis of causes of defects

The main channel of the mold is quite large. The method of injecting glue is submersible. The molten material flows near the glue inlet. Due to the excessive speed and the high gloss of the mold surface, the high shear causes the molten material to heat up rapidly in an instant, resulting in the decomposition of the raw material and the generation of gas and pressure drop. The gas is drawn in through the water inlet, forming gas streaks.

(5) Countermeasures

1. Utilize multi-level injection and position switching

2. In the first section, fill the flow channel's glue inlet at a relatively fast speed and find the corresponding switching position. Then, in the second section, fill the area near the glue inlet at a slow speed and a very small position. In the third section, quickly fill 90% of the mold cavity to prevent the high-temperature molten rubber compound from cooling down. Finally, switch to the pressure-holding switch position and appropriately extend the pressure-holding time.

Injection molding process table

Auto Mould_Taizhou Jiefeng Mould Co.,Ltd. (jfmoulds.com)

The mold is not fully filled (lacking glue)

Phenomenon: During the production process of electrical product bases, there is often a phenomenon of insufficient filling (lack of glue) at the bone position, right-angle position or fusion connection 

point.

Analysis: Insufficient filling caused by trapped air in the bone position (lack of glue); The connection point of the glue flow fusion is not fully filled (insufficient glue).

(1)Characteristics of injection molding machines

Grade: HT120T, Clamping force: 120t, plasticizing capacity: 150g.

(2) Mold characteristics

Mold ejection number: 1×1, injection method: point gate, ejection method: Ejection by ejector pin, mold temperature: 100°C (constant temperature machine).

(3) Product characteristics

Material: ABS UT10B, Color: black, Product weight (single piece) : 6.3g, nozzle weight: 5.2g.

(4) Analysis of causes of defects

The mold's glue feeding method is two-point submersible glue feeding. If the material flow rate is too fast, it is easy to cause air entrapment at the right Angle of the bone position, resulting in incomplete filling (glue shortage). If the material flow speed is too slow, it is easy to cause incomplete filling (lack of glue) at the end of the material flow fusion line.

(5) Countermeasures

1. Utilize multi-level injection and position switching.

2. In the first section, fill the flow channel at a moderate speed through the glue inlet and the corresponding switching position. Then, in the second section, fill it quickly to the vicinity of the bone position and find the corresponding switching position. In the third section, fill the bone position at a slow and short speed to facilitate gas discharge. Finally, fill it quickly and switch to the pressure holding switching position, and appropriately extend the pressure holding time.

Injection molding process table

Commodity Mould_Taizhou Jiefeng Mould Co.,Ltd. (jfmoulds.com)