Extrusion Minimum Runs Measured in Tonnes Rather than Pieces
Extrusion runs are quoted in tonnes because start-up scrap, thermal equilibration, and bulk resin compounding operate as continuous mass processes.
Vacuum Calibration Tank
Meaning
Downstream extrusion component that uses a combination of negative pressure and cooling water to set the final dimensions of a profile. As the hot plastic leaves the die, it enters a series of calibrators inside the tank where a vacuum pulls the molten walls against a metal mold. This vacuum calibration tank ensures that hollow profiles do not collapse and that external dimensions are held to tight tolerances.
Dimensional Stability
Internal pressure must be lower than the pressure inside the hollow sections of the profile to force the plastic outward. If the vacuum level in the vacuum calibration tank is inconsistent, the profile wall will pull away from the calibrator, leading to size variations. Careful adjustment of the vacuum valves is required to balance the cooling rate with the pulling force.
Cooling Efficiency
Water temperature and flow rate within the tank determine how quickly the part solidifies. If the profile is still too soft when it leaves the vacuum calibration tank, it will warp or shrink unevenly. Efficient heat transfer is achieved through a combination of spray nozzles and submerged sections that surround the profile on all sides.
Surface Quality
Friction between the moving profile and the stationary calibrator can cause scratches or chatter marks. Lubrication with water is essential to allow the plastic to slide smoothly through the vacuum calibration tank. Properly maintained calibrators are the key to achieving the high-gloss or textured finishes required by many architectural applications.