High Speed Strip Thickness Control

Principles and components
Requirements for a high speed strip thickness control are a quick and well-designed servohydraulic mill screwdown 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 that will achieve the required close strip thickness tolerances.

Adaptation of processor concept to the requirements
The performance data of the different mills vary widely from each other. To achieve equally good finished strip tolerances, the requirements for the control are significantly higher for strip speeds of 1000 m/min, for example, than for strip speeds of 100 m/min. Vollmer control systems are also adapted to the requirements of the mill with regard to the processor hardware (from the high-speed VME-Bus processor to the less expensive PLC assembly), 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 speedmeters where necessary. On many mills, the use of rotary sensors on the deflector rolls is sufficient. Which type of speedmeter applied, depends on the strip acceleration, the wrap angle on the deflector rolls and other factors.

Display of information
The graphic user interface provides the human interface to the mill sequences for the operator. Depending on the customers´ requirements, we offer alternatives. Among others, Intouch or WIN CC visualisation systems have often been applied. The multilingual design and the neat display of the strip condition, the control success, the interface situation and many other parameters have been well-proven for many years. Most sophisticated control solutions include diagnosis tools such as crash records, multi-channel strip recorders and other features that have proven to be useful in finding and solving operational problems.