Why does the surface of the molded part produce silver?

Mold

• Due to defects in the design of the mold (for example, poor gate position, too small gate, asymmetrical gate layout, small flow path, and unreasonable mold cooling system), the mold temperature difference is too large to make the melt The flow in the cavity is discontinuous, and the passage that blocks the air causes the piece to appear silver.

• The corner position of the mold is too sharp, and the cut is too large to cause the silver grain when the flow passes.

• The mold parting surface lacks the necessary venting holes or insufficient venting holes, the position is not good, and there is no machining gap such as inserts or thimbles, so that the air in the cavity cannot be removed, resulting in silver streaks in the parts.

• The surface of the mold is too rough and the frictional resistance is large, causing the local temperature of the mold to be too high, so that the passing plastic is decomposed. Lead to the appearance of silver on the surface of the part

• The mold leaks oil, leaks, and leaks, causing silver streaks on the surface of the part.

equipment

• The nozzle hole is too small, the material flows or draws at the nozzle, the barrel or the nozzle has an obstacle, and the high-speed material passes through the friction heat to decompose the material.

• The barrel, the screw wears or the rubber head and the apron have a dead angle of the material, which is decomposed by heat for a long time.

• The heating system is out of control, causing the temperature to be too high to decompose the plastic

• Improper screw design, easy to bring in air

Process

• The material temperature is too high, causing decomposition

• If the barrel temperature is too high or the heating is out of adjustment, the barrel temperature should be reduced step by step.

• The temperature of the feed section is too high, so that a part of the plastic melts prematurely and fills the groove, and the air cannot be discharged from the feed port.

• The injection speed is too fast, so that the molten plastic is decomposed by large shearing action to generate decomposition gas.

• The injection speed is too slow to fill the cavity in time, resulting in insufficient surface density of the product to produce silver streaks.

• Insufficient material, too large feed cushion, too low material temperature or too low mold temperature will affect the flow and molding pressure of the melt, resulting in bubbles.

• The screw pre-plastic back pressure is too low and the rotation speed is too high, so that the screw is retracted too fast, and the air is easily pushed along with the material to the front end of the barrel.