In strip processing lines, lateral migration of the strip may occur for various reasons, which may lead to damage to the product or to the equipment. Therefore, guide rollers are installed in suitable positions in the processing line which return the strip to the centre of the line or which guide the strip precisely to the next processing stage. Strip migration may be caused by the strip itself (e.g. sabre-shaped or undulated strip, staggered or biased welding of strip ends) or it is the result of incorrect treatment using support or squeeze rollers which are misaligned or acting on one side only, non-uniform heating or cooling processes and the like.

Strip guidance systems using guide rollers are constant electrohydraulic or electromechanical control circuits. Strip position sensing is in most cases carried out in the form of strip centre sensing, which makes readjustment of the sensing equipment unnecessary in the case of a change of the strip width. Deviations of the strip from the reference position are detected by the sensing equipment and transmitted to the digital strip controller. The output of the strip controller triggers adjustment of the control frame through the electrohydraulic or electromechanical actuator, so that the strip is returned to the reference position.

The use of additional rollers is avoided for strip guidance, as far as possible. It is preferable to make use of deflector rolls installed in appropriate positions. Various systems are available to suit different situations, e.g. taking account of the free strip entry distance or the characteristics of the particular installation. The essentials of the systems are a basic frame which is firmly connected to the line structure (foundation or steel structure), a control frame supporting the deflector roll(s), the required dynamic subassemblies and a suitable drive system.