Vacuum Calibration for Rigid Profiles

Vacuum calibration is used to size complex, rigid shapes requiring a high dimensional precision and accuracy, such as window profiles. One or more calibrators or sizing fixtures are used with a secondary spray cooling tank. Enough heat is dissipated in the calibrator to hold the profile dimensions after exiting the calibrator, even though additional profile shrinkage occurs as the profile cools to room temperature. Calibrators can be made of aluminum, steel, or stainless steel. Cast aluminum calibrators may have steel inserts machined to the desired profile shape to extend the wear life of the calibrator. Aluminum is inexpensive and easy to machine, but the wear surface has to be hardened to extend its life. If a calibrator is going to be used in high-volume production, stainless steel is the material of choice. The calibrator surfaces can be highly polished or chrome or nickel plated to improve the profile surface. One of the most important factors is the calibrator length. It has to be sufficiently long to provide enough cooling to hold the dimensions while running at high throughput rates. Once the profile exits the calibrator, it is cooled further with water spray. For cooling, the calibrator body has water channels to circulate water through the calibrator and a heat exchanger to remove the heat from the circulating water. The calibrator may also contain vacuum connections where a vacuum source can be connected to the calibrator to expand hollow profiles.

The calibrator can be mounted on a calibration table where the water and vacuum lines are connected to the calibrator. After exiting the calibrator, the profile may pass through an additional cooling tank. Alternatively, the calibrator may be placed on a table that is in the first calibration tank section. The hoses and vacuum lines are connected to the calibrator with the lines going to a manifold that can be quickly connected and disconnected through individual couplings. Manifold systems with individual flow control valves and vacuum gauges with quick disconnect couplings allow calibrator tooling to be changed quickly. Most calibration tables have their own self-contained vacuum system and water recirculation system with heat exchanger to provide both uniform vacuum and constant water temperature and flow. The first part of the unit is where the dry calibrator is located, with water and vacuum lines going from the manifold on the calibrator table to the tooling. In the second part of the tank, a water spray or additional calibrators are used to fix the part geometry as the profile is being cooled to room temperature.