The gripper rollers of the printing machine are installed on the cylinders. Each cylinder has two gripper rollers. Its function is to drive the rotation of the cylinder and control the tightness of the gripper on the cylinder. The gripper roller has a great role in ensuring the smooth progress of the printing process. It is particularly worth noting that if there is a problem with the gripper roller, it may also lead to ghosting failures, but few operators will The fault is connected to the gripper roller. The author has a deep understanding of this, and now sums up some of the experiences as follows, hoping to discuss with industry insiders.
Ghost failure caused by two gripper rollers not rotating
The paper has to be handed over many times during the printing process, and the function of gripping teeth is very important. If there is a problem with the gripper, it is easy to cause wrinkles, ghosting, inaccurate overprinting, and color cast. The problem of gripping teeth is generally caused by factors such as wear of dental pads and dental discs, unevenness, and fatigue failure of the dental seat spring. However, if the printed product has continuous ghosting and is accompanied by color cast, it is necessary to consider whether the gripper roller is malfunctioning. Most of the current multi-color printing presses use double-diameter impression cylinders and paper transfer cylinders. The above-mentioned situations are mostly caused by the inconsistent gripping force of two pairs of grippers on the same drum, and the two gripper rollers do not rotate, which causes the degree of wear. Different. If the two gripper rollers do not rotate, the degree of wear will inevitably be different, so it is impossible to maintain a consistent gripping force on the gripper, and it is difficult to maintain stability in the process of handing over the paper. When the cylinder is handed over, the paper has already been bent and deformed, and even wrinkles have appeared, so that when the following colors are printed, when these deformations (or wrinkles) are partially crushed, the first color mark (especially the tail) will be in The axial direction is larger than the latter colors. As a result, the printed dots at the tail of the first color paper are seriously deformed, the writing is unclear, the lines appear double-lined, and the color areas appear discolored.
The solution is to find the unrotable gripper roller according to the ghost image and color cast of the printed product, take loose, oiled and other measures to make the gripper roller rotate again, and then try to print a few sheets, if the ghost disappears, then The problem is solved. If the problem persists, the gripper roller has been completely worn and needs to be replaced.
Two gripper rollers have a ghosting failure caused by non-rotation
One of the two gripper rollers does not rotate, which often causes some unbelievable failure problems. The problem I encountered was that the printed matter "bounced", that is, good and bad prints appeared alternately and regularly indefinite. This situation will cause many operators to be at a loss: the blanket is wiped over and over again, the printing plate has been disassembled and assembled several times, and the equipment is constantly corrected, but it is still difficult to find the cause of the problem.
This situation generally occurs on four-color printing machines, which have four units, and the chance of such problems is relatively large. According to experience, if one of the two gripper rollers does not rotate, it will not only cause ghosting failure, but also affect the color reproduction of the four-color printing machine and appear color cast. Among them, the manifestation form of ghosting is that the printed matter with ghosting and the printing without ghosting appear alternately; the manifestation form of color cast is also that the prints with colors that meet the requirements of the original appear alternately with the color cast. The root cause of this problem is that the non-rotating gripper roller causes insufficient gripping force at the gripper, which causes ghosting of the printed product at the gripper; when the roller turns to the normal gripper roller, then The print is normal. In the same way, the reason for the repeated color cast is due to the first few colors, and the color shift will occur when the unit has a problem with the gripper roller.
If such problems occur, the gripper rollers that cannot be rotated should be oiled and loosened. If the gripping roller can be loosened, the two axes should be corrected to ensure that the gripping force of the gripping teeth is even; if it is not loose, it should be removed and replaced.
There are many reasons for ghosting failure, and it is only one possibility that the gripper roller does not rotate. Moreover, the probability that the gripper roller does not rotate is low, unless the operator does not pay attention to the daily maintenance of the printing press, such as not washing the car in time after the printing operation is completed, or not oiling the printing press, etc. Blocking the normal rotation of the gripper roller will also cause this to happen. Therefore, we should pay attention to the maintenance work of the gripper roller.
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