Method of slitting or edge trimming strip material

An edge trimming device for slitting or trimming the edge of strip material on a process line, comprising:

• a sub-base arranged for movement transversely to the process line and strip material;
• means for moving the sub-base;
• a base pivotally mounted on the sub-base;
• means for pivotally moving the base;
• one or more pairs of trimmer knives arranged on the base for edge trimming the strip;
• means for determining the lateral position of the strip relative to the lateral position of the trimming device;
• means responsive to the determined, relative lateral position of the strip for controlling the sub-base moving means so that lateral movement of the trimmer varies with lateral movement of the centre line of the strip, to keep the trimmer and strip in constant relationship;
• means for determining the longitudinal speed V of the strip;
• means for determining the lateral speed V.sub.T of the or each pair of trimmer knives;
• and means for controlling the base pivoting means so as to vary the angle .alpha. the or each pair of knives make with the centre line of the process line such the angle .alpha. tends to equal a required angle of tan .sup.-1 (V.sub.T/V) or any approximation thereto, and thereby that the or each pair of knives remains substantially parallel to the line of cut made in the strip.