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Hydraulic Cylinders of Edge Strip Guidance Systems in Cold Rolling Mills

Hydraulic cylinders are used in edge strip guidance systems of cold rolling mills to maintain the position of the metal strip on the roll’s reel to prevent the telescoping of the roll and strip breakage as well as ensuring the quality of the whole strip, especially with regards to edge flatness. In addition, the guidance system decreases the need for stopping the rolling process to rewind an improperly rolled strip coil. Edge strip guidance systems are generally limited to the rolling of thin gauge strips where edge guides are not employed.

Edge Strip Guidance System

Located at the payout and take up reels of a rolling mill stand, edge strip guidance systems will ensure the position of the strip on the passline just before it traverses into the first roll bite of the mill. It will automatically adjust the horizontal (axial) plane of the roll as it is being unwound (and wound) to maintain a constant strip edge position. The edge strip guidance system is an electro-hydraulic system consisting of a hydraulic power unit, edge position regulator, motor operator (hydraulic cylinder) and edge position sensor. There are three types of edge position sensors: pneumatic, photoelectric (optical) and inductive. The photoelectric sensor is preferred over the pneumatic sensing method because it is more accurate than the pneumatic sensor and simplifies the guidance system design because the use of an idler roll becomes unnecessary. However, photoelectric sensing does have one disadvantage: increased maintenance of the photoelectric sensors due to the typically harsh environments encountered in rolling mills, such as oil, air pollution/particulates, dust and dirt.

Inductive edge position sensing systems are the most recent innovation in edge strip guidance control systems. Inductive systems possess an advantage over optical systems: they can withstand harsh environments. Inductive sensing measures the eddy currents generated in the metal strip via the measuring and sensing coils in the inductive sensor. Comparing the inductive sensor and the edge adjusting slide position, via a position encoder, an edge position signal is produced, which becomes the input of the edge position control system.

Hydraulic Cylinders

The hydraulic cylinders of the edge strip guidance system are juxtaposed to the rolled strip coils and force the reel assembly to move horizontally to maintain the edge position. The hydraulic system is powered by a dedicated hydraulic power unit (HPU). The edge position regulator receives an input from the edge sensor and causes hydraulic fluid to flow to the cylinder to pull or push the reel into position. For pneumatic sensing types, a fixed, position-sensing nozzle is mounted in a way such that it represents the desired edge position. The rolled strip passes over the nozzle. The sensing head develops the position error signal, which is the input of the position regulator. The spring-adjust position regulator uses a diaphragm jet pipe arrangement to change the regulator’s orifice dimensions; hydraulic fluid flow is then directed to the double acting cylinder to maintain the edge position. And idler roll is attached to the strip reel and moves with it to prevent strip slippage. For photoelectric types, an optical sensor is attached to the reel and moves with it. The gap between the light source and the photocell senses the edge position and provides the input to the position control loop.