Sheetfed offset printing machine is not allowed to be faulty--longitudinal overprinting is not allowed (one)
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Overprinting is not a complicated technical problem in printing. It has four phenomena and three factors. Four kinds of phenomena, namely, the printing overprinting is inaccurate, the partial printing of the printed sheet is not allowed, the overprinting is not allowed, and the back printing is not allowed. The three factors are the original printing caused by plate making, filming, imposition, and overprinting caused by paper stretching. Inaccurate overprinting caused by malfunction of the offset printing machine or improper operation and adjustment. Overprinting is not allowed to be specifically divided into two types: vertical overprinting and horizontal overprinting. The following is a summary of dozens of overprinting failures in combination with production practices, and proposes solutions.
Vertical overprinting is not allowed
1. Imprinting caused by the unilateral failure of the paper
Insufficient unilateral overprinting means that the vertical unilateral crosshairs are not overprinted, and the overprinted crosshairs are in the direction of the standard line. There are 7 types of fault analysis and solutions.
(1) The time when the side gauge falls is too early
When the paper that has been normally transported has not yet reached the front gauge, the side gauge pulls the paper ball too early to drop and press the paper, so that the paper is not in place, resulting in inaccurate overprinting.
Solution: The normal time of the side gauge should be after the paper is normally transported to the front gauge; the pick-up time should be when the paper is swayed by the swaying paper, that is, the swinging and closing the tooth roller leaves the cam. The two positioning screws on the side gauge cam can be loosened to reverse the cam until the time of the above falling and lifting is met.
(2) The front gauge tongue is too low
When the current paper flap is less than 3 times the thickness of the printed paper, the paper will be blocked and will not go out.
Solution: Loosen the adjusting screw of the front gauge, lift the front gauge, insert 3 sheets of paper under the paper stopper, and tighten the adjusting screw. The idling machine stops at the position where the front gauge falls for several weeks, and then three sheets are inserted under the paper stopper for retesting, so that three sheets of paper can enter and exit freely, and four sheets of paper can not be inserted.
(3) Paper positioning time is too late
Sometimes the paper arrives too slowly before the paper arrives. Especially when the side gauges are pressed by the side gauges, they cannot be advanced. The other side continues to advance to the front gauge, which will also cause a single-sided failure.
Solution: Loosen the fine adjustment screw that adjusts the paper feed time, turn the paper feeder handwheel in the direction of fast paper feed, and then tighten the screw to retest. After the front gauge is in place, the front edge of the paper should be 6-8 mm away from the paper stop.
(4) The side gauge pulls the paper ball up too slowly
The reason is: when the paper is swaying and the paper starts to move forward, the paper is still pressed against the paper, and the paper is pulled out from the swaying paper, and the overprint of the printed product and the single side is not allowed. The phenomenon is the same.
Solution: The side gauge pulls the ball and lifts it too slowly, indicating that the cam working point is not adjusted. At this time, the two positioning screws of the side gauge cam can be loosened, then the cam is dialed some more, and the screw is tightened and then re-tested until Meet the requirements.
(5) The gripper is too light
The embossing roller crepe paper and the swaying crepe paper are too light, the crepe paper is too small, or the squeezing force is uneven. It is also easy to cause the overprinting to be inaccurate, which is reflected in the same phenomenon that the printing is not inaccurate.
Solution: If it is a fatigue problem of the spring or tension spring, it should be replaced; if the tooth of the swaying paper is too low and uneven, it should be replaced. After the installation, the printing machine can be jogged to the intersection of the impression cylinder and the oscillating gripper with the total adjustment method, and the swinging pad is 0.3 mm from the plane of the impression cylinder. When adjusting the whole, you can loosen the overall iron plate of the tooth pad, adjust the nut on the swinging shaft, turn the tooth pad up clockwise, and turn the tooth pad counterclockwise until it reaches 0. 3mm. As for too little paper, it is necessary to ensure that the paper is swayed and embossed, and the crepe paper is between 5 and 6 mm.
(6) The tip of the tractor is lost.
The slight positioning of the brush is mainly to prevent the paper from entering the front gauge and then popping up. It may have the following reasons: 1 When the paper feed is stopped due to skewing of the paper feed, in order to take out the paper on the paperboard, the frame is turned upside down and the action is too heavy, causing the brush to be lifted or flipped. 2 The brush is fixed in one position for a long time. If it is used for a long time, the part where the brush rubs against the edge of the paper is damaged and loses its effect. 3 The position where the brush is pressed against the paper is incorrect. The paper is on the tip of the brush or at the root.
Solution: The first and third problems need to be re-adjusted; the second problem is to remove the brush and burn it on the fire. The method is as follows: firstly, a small piece of flat iron plate is burned red in the fire, and then flattened on the ground after being thrown out, and then the brush is gently drawn on the red iron plate according to the original inclination. It is convenient to be flattened. If it is worn out, it can be burned several times until it is flat (please note that this brush should not be cut).
(7) The brush wheel is too light or the two platen rollers at the tip of the tip do not bear against the back edge of the paper. The brush wheel and the 2 platen rollers at the tip of the tractor ensure the stability and accuracy of the paper when it enters the front gauge. Their pressure on the paper should not be too heavy or too light, too heavy to cause the back to be dirty; too light on the paper to lose its proper function, easy to make the paper out of place. Sometimes 2 of the brush wheel or 2 platen wheels, one pressure is appropriate, the other pressure is light, and the light one will cause the one side to go out of place.
Solution: The two brush rollers that play an important role in overprinting and the two paper balls at the tip are kept in the same pressure, and they must be in place, that is, the brush wheel must be pressed against the paper on the paper feeding belt; The two paper balls at the tip of the tractor should be tight against the back edge of the paper.