Black Spot

Describe

Black spots are impurities or thermal damage in plastic that cause black inclusions on the surface of the component or inside the transparent plastic component, which can affect the appearance of the product and lead to scrap. If the black spots are only distributed on a local surface, the impurities are present during the molding process of the component; If the overall distribution of black spots is irregular and scattered, with varying depths, then impurities exist before forming.

Reason: The material has been contaminated by foreign objects.

Suggestion:

Reduce the exposure time of particles.

Check the condition of the material conveying system for possible leaks, dirt deposits, or wear.

Thoroughly clean the material conveying system, drying hopper, and injection molding machine before replacing any materials.

Reason: The melt temperature is too high, causing thermal decomposition to form carbides.

Suggestion:

Check the temperature of the melt to reduce the temperature of the barrel and hot runner.

Reduce screw speed and back pressure.

Reason: The material degrades at the so-called dead points in the plasticizing device and/or hot runner.

Suggestion:

Check the design of the plasticizing device (check valve, head, nozzle) and hot runner system, and eliminate all dead corners.

Reason: Due to wear and tear, metal particles detach from the plasticizing device and/or mold.

Suggestion:

Check the condition of the plasticizing device or mold for wear or possible coating detachment; Replace the affected components.

Reason: The residence time of the melt in the barrel or hot runner is too long.

Suggestion:

Check the residence time in the plasticizing device, and replace with smaller materials or use screws with shallow thread geometry.

Reduce the residence time in the hot runner, for example, by shortening the cycle time or reducing the cross-section of the channel.

Reason: The selected heating or cooling time is too long or the machine is in a stationary state for too long.

Suggestions;

Heating or cooling the cylinder in two stages.

During interruptions, regularly purify or lower the temperature.