Print Overprinting Failure Analysis (3)

Cause 11: The hem pendent paper is higher than the paperboard.

Solution: Correctly adjust the position. The paper pad should be level with or slightly lower than the paper feed.
The reason for overprint failure is due to the improper adjustment of the machine to prevent the accurate positioning of the paper. In addition, it should be noted that whether it is on the pendulum type or the pendulum type, the adjustment should be based on the height of the paper feeding tooth. Adjust the height of the paperboard, and then adjust the height of the front gauge based on the height of the paperboard.

Reason 12: The feeding time of the feeder is not properly matched with the drop time of the front gauge.

Solution: Before reaching the positioning position, the paper on the cardboard should be 3~5mm away from the specified front line.

Cause 13: The paper is bounced back when it is positioned at the front gauge.

Solution: The position of the brush and the brush wheel on the paper transport should be tangent to the trailing edge of the paper; the height of the tooth at the front gauge should be too low, and the already positioned paper should be topped back. It is recommended that the height of the teeth be not less than 200, and the height of the open teeth can be adjusted; when printing thick paper, especially cardboard, consider using a ball.

Reason 14: The paper is ahead of the specified bit time before the specified bit line arrives.

Solution: The paper feeder's paper feeding time and the timing of the drop of the front gauge are caused by improper cooperation. The correct matching time is when the current gauge arrives at the positioning position. The position of the paper on the paperboard is 3~5mm away from the front specified bit line.
(1) The J2205 can adjust the timing of the relative motion by adjusting the flange below the conveying surface of the transport board; the Heidelberg SM series can adjust the timing of the gear by changing the gear meshing relationship in the transmission box of the feeder.

(2) Usually, the phenomenon that the paper has reached the front prescribed bit line or has exceeded the previous prescribed bit line before the front gauge reaches the positioning position is referred to as “low paper speed”.

Cause 1: The stack is too high, even higher than the top of the front block.

Solution: The height of the stack can be adjusted by adjusting the height of the feeder or by inserting the wedge. Refer to the solution for the cause 3 in (1) for the adjustment requirements.

Cause 2: The amount of air blowing from the loose paper mouthpiece is excessive.

Solution: If the paper is unstable on the paperboard, it is easy to drift, or the paper that is being blown too high can be pulled out when a sheet is fed by the delivery nozzle.

Cause 3: The delivery nozzle is too low.

Solution: Caused by improper adjustment. What is more special is that if the orifice on the delivery nozzle of the SZ206 feeder in the domestic printing press is blocked, it will cause the delivery nozzle to fall and not lift. Adjust the position of the paper feed nozzle.

Cause 4: The roller has fallen too early.

Solution: Adjust the mating relationship as described in Reasons 6 and 8 in (1).

Cause 5: The pressure roller and brush wheel on the paper board are too tight.

Solution: Relax properly.

Cause 6: The pressure of the vacuum conveyor belt is too low.

Solution: Pneumatic paper feeder's paper feeding time and the timing of the pre-regulatory fall are not properly matched so that the paper advances before the specified time to reach the specified bit line.

For the adjustment method, see the solution to Cause 14 in (1).

Cause 7: The paper is skewed due to the fast paper on the face of the paper or the lower surface of the transmission surface or the slow paper feeding.

Solution: Generally encountered in this situation can be seen directly on the paperboard between the edge of the running paper is serrated. The most important thing to prevent paper skew is that you should pay attention to the position of each part of the paper, and adjust it symmetrically along the center line of the machine. If the suction of the left and right suction nozzles of Feida must be the same, the tension of the feeding belt must be the same, and the time of the falling of the pressure roller should be the same. From the start of paper feeding until the end of the printing, any set of symmetrical parts should be adjusted asymmetry, which may lead to overprinting.

In addition, in the production operation should pay attention to the order of the adjustment of the machine: the first impression cylinder or the first transfer cylinder, a paper feed tray, a paper feed table, a time before the arrival of a paper, reach the paper feed time, the first The impression cylinder has a first transfer cylinder and a second impression cylinder. It can be seen that the first impression cylinder or transfer cylinder is the adjustment reference of the whole machine, and adjustment according to this order can ensure the relative relationship between the various parts of the whole machine is accurate.

In the adjustment need to pay attention to the following points:

1 The drive cam of the pendulum axis of the paper press wheel on the transfer table is a quiet path at the low point. At this time, the gap between the roller and the cam on the pendulum is about 0.15mm, so as to ensure the smooth motion when the paper is fed. .

2 The front gauge is also static during positioning. There must also be a corresponding method when adjusting (many machines adjust the limit nut) to ensure stable positioning.

3 When adjusting the feeder, it is recommended to adjust the feeder height and other parts under the premise of ensuring the formation of the paper stack (by inserting the wedge and the paper strip). This can ensure the smooth distribution and delivery of the paper.

4 In the case of loose paper, each time you can stack less paper on the feed table, to avoid paper pile under the pressure of the presser foot under the amount of depression is too large, resulting in paper failure, resulting in overprinting is not allowed.

2. Inaccurate positioning due to misregistration of front gauge and side gauge

The delivery of paper teeth is also the key to ensure accurate printing. The following discusses some of the more common causes of failure in production.

Cause 1: The upper swing-type front gauge is too high or the cover gauge on the hem-type front gauge is too high, causing the paper to tilt at the front when positioning.

Solution: The correct position can refer to the solution of Cause 10 in 1(1).

Cause 2: The time before the rules was incorrect was not properly located.

Solution: This situation is rare and sometimes occurs after the machine has just been overhauled. The conventional adjustment method is to pull out the positioning pin on the front gauge cam, and adjust the angular position of the cam by adjusting the position of the long hole. After the adjustment is completed, the positioning pin hole must be re-aligned to insert the positioning pin to prevent the operation in the future. There is a change in position. Adjust the drop time by changing the position of the cam.

Cause 3: When the front swing-type front gauge is used to check for empty sheets, the reed is too hard to block the positioning of the paper.

Solution: The reeds generally used in domestic printers are not standard parts, and they tend to have uneven thickness. In such cases, sandpaper can be used to thin the reeds.

Cause 4: Foreign matter such as paper and ink residue on the wheel or the baffle plate may cause the paper to not reach the positioning position.

Solution: Clear the paper on the wheel or bezel. Ink residue and other foreign matter.

Cause 5: The side cover gauge is too high to cause the paper to pull over, or too low to pull it in place.

Solution: The correct height should be 3 sheets of paper thickness or thick paper plus 0.2mm.

Cause 6: The spring is too tight, causing the paper to pull over, or too loose to pull it in place.

Solution: Make adjustments based on the thickness of the paper.

Reasons 3, 4 and 5 mentioned above all refer to mechanical misalignment caused by mechanical side gauges, and pneumatic side gauges are easily blocked by paper, etc. Therefore, they must be cleaned frequently.

Cause 7: The flanks fell too early, causing the paper to be held in place by the side profile before the specified position was completed.

Solution: In accordance with the angular position of the machine, adjust the side gauge to the exact time of fall, wait until the paper is correctly positioned by the front gauge, then drop the paper (or the vacuum side gauge starts to draw paper). When adjusting the side gauges, it should be noted that the side gauges should only be lifted when the paper feeds the paper, so as not to cause the paper to be free on the paper conveying board. The phenomenon of "three nos." drifts.

Cause 8: Lateral rules were lifted too late.

Solution: When the paper-handling tooth has started to hold the paper and leave the paper-feeding board, if the side-rule is not lifted, there will be disputes. Sometimes it will cause the paper to slip backwards, resulting in overprinting failure. The lifting time of the side gauge should be before the paper exits the paper feed tray.