Improved anti-wrap device for a web press

摘要

A system and method for preventing a broken printing web (30) from wrapping about or otherwise fouling the blanket cylinders of printing press units. The system and method includes a web tensioning device located downstream of the printing press units (10A-10D) for maintaining tension upon a broken web (30) and pulling the web from the printing press units. The device includes a plurality of web disturbance detectors (15) for detecting a wave, ripple or other disturbance indicative of a web break. A pair of anti-wrap rollers (50) located above and below the web are engaged upon detection of a web break to engage the web between them to exert tension onto the web and pull it from the printing units. The anti-wrap rollers are rotated at a surface speed nominally greater than the surface speed of the printing rolls (5). The anti-wrap rollers (50) include a plurality of opposed peak and valley portions which enable them to interlock and grip the web along a line of contact. The system and method also includes a flow bar system to reduce false detections of a web break . A blow-down bar is also used to force air, or some other fluid, downward on a broken web so as to harmlessly force the broken web to the ground as it exits the web tensioning device. A series of sensors (340) which projects two beams in the form of a crossing pattern are utilized to more rapidly and accurately detect a web break.