High Precision Thickness Control on a Rolling Mill for Flat Rolled Metal

Abstract

The high precision rolling design utilizes a high speed hydraulic roll position control along with a high accuracy roll gap measurement. The lower work roll position is fixed and the upper work roll is positioned by a hydraulic roll force cylinder using an inner and outer control loop. The inner loop is a cylinder position control that moves the upper work roll. The outer loop uses a measurement of the work roll gap to trim the inner cylinder positioning control. Both control loops coordinate together to provide a high precision and even strip thickness tolerance to + / −0.15 mils or less. Both sides of the upper work roll are controlled separately to achieve the overall tolerance goal.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]Not applicable.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]Not applicable.REFERENCE TO SEQUENCE LISTING, A TABLE, OR COMPUTER PROGRAM LISTING[0003]Not applicable.BACKGROUND OF THE INVENTION[0004](1) Field of the Invention[0005]This invention is directed to a single stand rolling mill and associated thickness control that is used to reduce the thickness of flat rolled metal stock. It is particularly directed toward methods and control that provides high tolerance thickness control when rolling metal strip that will be used in stamping out coins for common use and for specialized Numismatics coinage.[0006](2) Description of Related Art[0007]Some ancient coins were “cast,” meaning the metal was melted and poured into coin shaped molds. When the metal cooled, the mold was opened and the newly minted coin was removed. A refinement of the process was to pour fine granulated metal into the coin mold, heat the mold above ...

AI Technical Summary

Benefits of technology

The high precision rolling design uses a special hydraulic system to control the position of the rolls during the rolling process. This allows for very precise control of the metal product thickness, resulting in a flat product with a tolerance of up to 0.15 mills. The design also separates the control of the two ends of the roll to achieve the overall tolerance goal.

Problems solved by technology

In either case, the thickness control of these methods were poor by modern standards.

The in process strip thickness during rolling is dependent upon a number of factors that are difficult to control.

It is difficult to grind the work rolls to a completely uniform diameter.

This heating can be uneven and create an additional eccentricity pattern due to varying thermal expansion.

The frequent strip to roll impacts eventually cause uneven roll wear.

An additional complication is that it is very difficult to accurately measure the thickness of precious metals to the desired accuracy of 0.0038 mm in a dynamic rolling process.

Physical contact probes, x-ray based sensors, and other methods are not practical or accurate enough for control purposes.

Additionally, measuring the thickness after the strip has left the roll bite is not a satisfactory method of controlling work roll imperfections to a fine degree.

Additionally, in process techniques of measuring thickness variances, such as changes in rolling force, are not accurate and stable enough for the desired high precision control.

Further, these types of control methods are overly complicated and expensive in this field.

Such thickness determining methods are clearly unsuitable for dynamic control in a rolling mill.

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