Calibration of Profile Extrusion

Calibration and Cooling Tank

Cooling and sizing or calibration is used to set the part dimensions while preventing the part from warping and twisting. Part fixtures or sizing depends on the part complexity. The simplest setup has adjustable metal fingers shaping the soft polymer as it exits the die, with fans blowing air on the profile to cool it. The profile may be supported by wood forms or by a metal rack. Although this is the simplest way to cool a profile, it is also the most inaccurate, producing profiles with very low dimensional tolerances. For thermoplastics generally, more intricate sizing fixtures or calibrators are used with complex shapes in calibration tanks. The sizing unit may be a long metal fixture containing the desired profile shape where the molten polymer is pulled through and allowed to solidify, possibly in a water environment. As the part exits the die, it passes through a small air space and into the sizing unit or calibrator where it is cooled with air or water spray, flooded with water, or goes through a metal calibrator with circulating water and a heat exchanger to freeze or solidify the part to its final dimensions.

Water cooling begins when the profile enters a bath below the water level and enters a fixture to size and hold the profile during cooling. The profile may pass through a ring spraying water on all sides simultaneously or water nozzles prior to entering the water tank. Water cooling is very efficient, is good for short runs, and may suffer in repeatability between short runs, depending on the fixture quality, its location, and the operator skill. Options available are the tank length; the number of chambers in the tank; whether the water is applied in the form of a mist or spray, flood, or a combination of both in different parts of the chamber; temperature of the water (hot or cold); self-contained recirculation systems.