HIGH SPEED STRIP THICKNESS CONTROL

Screwdown Control

Principles and components
Requirements for a high speed strip thickness control are a quick and well-designed servo hydraulic mill screw down and highly accurate strip thickness gauges with sufficiently fast response times. 

The variations of the control scheme are many: Position control, direct roll gap control, roll force control, mass flow control, feedback control, feedforward control and more that combine these modes. Depending on the type of mill, the strip material and other factors, we will create a control scheme for the specific mill.

Adaptation of control concept to the requirements
The performance data, design and application of the different mills vary widely from each other. In order to achieve the required finished strip tolerances, the requirements for medium strip steel with a speed of 1000 m/min, for example, are significantly higher than for stainless steel with 300 m/min. Vollmer control systems are adapted to the requirements of the mill, so that the customers´ requirements will be satisfied by an optimal solution.

Speed measurement
In addition to the strip thickness, the strip speed is an important factor in many control schemes. We apply non-contact laser speed meters where necessary. On many mills, the use of rotary sensors on the deflector rolls is sufficient. Which type of speed meter applied, depends on the strip acceleration, the wrap angle on the deflector rolls and other factors.

Gap sensor

Gap control
A specific feature in the diversity of Vollmer control systems is the direct gap control where gap sensors measure the roll gap directly on the work rolls. There is no faster control. The advantages are particularly evident with wedge strip and on tandem mill trains, when beginning and end of the strip are rolled out and with automatic threading.

Display of information
The visualization of the control gives the operators an important insight into the mill sequences. The multilingual design and the neat display of the strip condition, the control success, the interface situation and many other parameters including diagnosis tools (such as crash records), have been well-proven for many years. Constantly new important additions by users at our customers´ plants have made the visualization a sophisticated control tool.