Shape Control
Looking at the photo, you can see there is a shape coming out of the exit side of the mill Shape may include stretched edges or center buckle. The operator can see this when operating the mill. Many shape controls are adjusted by the operator at speeds up to 7,000 FPM. Instead of having gauges across the width of the strip, say every 2”, to measure the difference in thickness, you really want to measure the tension across the width of the strip. If you have an elongated edge, you will see a wave. If you see an elongated center, you will see center buckle. The operator needs to make adjustments accordingly. He first may adjust for roll bend. When you run very light gauges, roll bend is not satisfactory because you need to get a finer measurement than roll bend. Instead, the shape is controlled with coolant.
Coolant nozzles with valves are placed approximately every 2” across the width of the work roll or back up roll or both. If there is a wavy center, it means that the center is expanding and more coolant is applied in the center. This allows the roll to change its shape by thermal expansion. The roll can actually change its shape anywhere along the surface of the roll with coolant. Instead of observation of the outgoing shape by the operator, it can be done with a shape roll. Shape rolls are usually a series of rollers that measure the deflection across the width of the strip. These rollers are air actuated and each shape roll can be every 2”. If the shape roll detects center buckle or stretched edges, it deflects the strip under tension and is measured accordingly. This gives a reading on the screen as shown above. Some shape rolls use a common shaft with rolls every 2” using air bearings. As the roll is under pressure, air is measured under each air bearing and gives a reading every 2” across the width of the strip. All shape rolling can be done by observation or automatically. An automatic shape roll system is very expensive because it needs to operate the nozzles to change the shape of the rolls at any speed. The air for the air bearings must be highly filtered for this purpose.
