Mechanical Screwdowns & Roll Bend
Mechanical screwdowns are still used for small mill reducing and large mills for cogging and hot plate reducing where accuracy is not a precision factor, and where fire may be a concern. However, hydraulics can now be water hydraulics. By adding chemicals in the water, you have a hydraulic system that will not catch fire. However, water hydraulics require limited low pressure, and they are high in maintenance and many customers still prefer mechanical screwdowns. Mechanical screwdowns consist of a gear reducer and screw to control the roll gap and withstand the separating forces required in a rolling mill.
Roll Bend
Depending upon the amount of reduction, rolls are already crowned to take care of some deflection of the roll. Roll bend is used to adjust the roll shape and can be positive concave or negative convex to remove center buckle or stretched edges. Sometimes, roll bend is accomplished with hydraulic cylinders that are offset with the main centerline bearings, which allows the roll to bend one way or the other, usually with hydraulic cylinders located within the bearing blocks or chocks. Small hydraulic cylinders can operate at pressures up to 10,000 PSI to bend the rolls.
