The measuring of the the thickness of metal strips in cold-rolling mills requires an accuracy of ±1 µm.
Until now this has not been practice-oriented possible by laser measurement technology due to the rough conditions in a rolling mill. Today VOLAS sensors are used for this application, and they have proved.
The laser measurement technology with VOLAS sensors will increasingly gain market shares due to the contact-free and alloy-independent measurement.
The following illustration opposes the measurement of a contact gauge (bright curve) to the measurement with a laser gauge (green curve). The measured strip thickness across the length of the strip is shown. The measuring curves are shifted mutually as both gauges have been installed one after another in direction of transport.
Both measurements show nearly identical measurement results in the range of 1 µm.
VOLAS sensors with a measurement range of 12 mm (sensor for reading the bottom face of the strip) and 16 mm (sensor for reading the top face of the strip) are used in these strip thickness gauges. With a measurement frequency up to 50 kHz, the thickness measuring values will be recorded at rolling speeds of several 100 m/min, filtered, and provided to the mill control in real time by an analog interface.
Special protective devices ensure that the optical windows of the sensors will remain clean despite adverse conditions (mist due to rolling oil or roller oil emulsion, splashes).
The high temperature stability of VOLAS sensors has proven useful in this application. Despite considerable changes in ambient temperature at the operation site of the gauge, a reliable measurement with an accuracy of ±1 µm is ensured.