Vacuum Forming: A process whereby a heated plastic sheet is drawn against a mold surface by evacuating the air between it and the mold.
Valve Gating: A type of gate where a pin is held in the gate or channel by spring tension. As the injection stroke moves forward, this gate compresses the plastic in the runner. When this pressure build-up is sufficient to overcome the spring tension, the pin is then pushed back (pulled) and the fast decompression of the melt fills the cavity at extremely high speed.
Vent: A shallow channel or opening cut in the cavity to allow air or gases to escape as the melt fills the cavity.
Vented Barrel: Special barrel unit with a vent port over the compression section of the screw to permit the escape of gases prior to injecting melt into the mold. Often used when molding moisture-sensitive resins.
Vertical Flash Ring: The clearance between the force plug and the vertical wall of the cavity in a positive or semi-positive mold. Also the ring of the excess melt which escapes from the cavity into this clearance space.
Vicat Softening Point: The temperature at which a flat-ended needle will penetrate a specimen under a specific load using a uniform rate of temperature rise.
Virgin Material: Any plastic compound or resin that has not been subjected to use or processing other than that required by its original manufacturer.
Viscoelasticity: This property, possessed by all plastics to some degree, dictates that while plastics have solid-like characteristics such as elasticity, strength, and form-stability, they also have liquid-like characteristics such as flow depending on time, temperature, rate and amount of loading.
Viscosity: Resistance to flow of a liquid.
Void: An unfilled space within a solid material.