When the KBA Rapida 104 four-color machine was printing on coated paper with a basis weight of 105g/m², severe wrinkling occurred at the tail end of the paper.
From the fault symptoms, it was preliminarily determined that the wrinkles were generated after the first color impression. After analysis, it was found that before the paper entered the first color unit and reached the register, the bite force of the grippers was uneven, preventing them from securely holding the paper. This caused the paper to slip inside the grippers, resulting in an uneven surface, which in turn led to the formation of wrinkles during the first color impression. Further analysis focused on identifying the specific part where the problem originated. Starting with the delivery grippers as the reference point, the KBA Rapida 104 four-color machine uses an intermittent double-row gripper cylinder for paper delivery, followed by a single-row gripper transfer cylinder before the paper enters the printing unit. By manually operating the machine and feeding a few sheets into the grippers, it was discovered that several grippers on the transfer cylinder were unable to hold the paper properly. The bite force of these grippers was increased and adjusted to ensure uniformity. After restarting the machine, the fault was resolved.