UL Temperature Index: The maximum temperature below which a material maintains its electrical and mechanical integrity over a reasonable period.

Ultimate Elongation: In a tensile test the elongation at rupture.

Ultimate Strength: Term used to describe the maximum unit stress a material will withstand when subjected to an applied load in a compression, tension, flexural, or shear test.

Undercut: A protuberance or indentation that impedes withdrawal from a two-piece rigid mold.

Underflow: The dominant flow of two confronting flows, over the other. The lesser flow reverses direction giving poor surface appearance and structural strength. Underflow should be avoided by positioning gates so that the flow fronts meet at the end of filling.

Unidirectional Flow Pattern: Plastic flowing in one direction with a straight flow front throughout filling.

Uniform Cooling Time: Cooling time the same throughout the part to avoid warping.

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