Excessive injection speed—the speed and pressure of the meltas it enters the mold determine the melt’s density and consistency in packing the mold. Excessive fill speeds cause thematerial to “slip” over mold surfaces, especially at the gatearea, and the material at the slipped surface skins over beforethe balance solidifies. The slipped material does not reproducethe mold surface as does the material in other part areasbecause it has not packed as tightly in the mold. Thus, theunderpacked area has a duller finish. The injection fill speed isdecreased until proper filling occurs; barrel and mold temperatures are often adjusted as well.
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