Offset Overprinting Failure Analysis (3)

Four typical overprint fault examples

1. Constant speed, speed is not allowed.

Constant speed register refers to the printing of the same speed in a few colors, and the speed of misalignment refers to the inaccurate overprinting of different speeds. In general, different speed can register and constant speed can register, while constant speed can register and different. Speed ​​may not register.

cause of issue:

(1) The transfer tooth and the embossing (pass) roller are not at the cut point.
(2) The transfer force of the transfer paper and the transfer (paper transfer) roller are inconsistent.
(3) The handover time is too long or too short.
(4) It is too early or too late for the paper to arrive.
(5) The paper has poor stability before it reaches the gauge.
(6) Paper stretching.

2. The side of the pull gauge is accurate and the other side is not accurate. It is simply called the operating side and the transmission side is not accurate.

cause of issue:

(1) Inconsistent brake force on both sides.
(2) Eccentric asymmetry of the transfer eccentric.
(3) The gap between the front gauge and the gap on both sides of the sheet feeder is inconsistent.
(4) Paper failures include:

a Cloth belt is inconsistent.
b The pressure of the platen roller is asymmetrical.
c Brush pressure is inconsistent.
d The pressure of the paper receiving roller is inconsistent.

(5) The front gauge and the lateral gauge are not at right angles.
(6) The difference in force between the paper-feeding teeth and the roller teeth is too great.

3. All speed overprint on both sides are not allowed

This means that in the case of two speeds, the crosshair printed at a low speed and the crosshair printed at a high speed have the same error, and its manifestation: one is that the high speed is not in place. The other is over-speed, very regular, with equal distances.

cause of issue:

(1) The paper arrives before the regulatory time is late.
(2) Feeding teeth closed teeth.
(3) Inconsistent elasticity of the transfer pad.
(4) The time before the arrival of the paper is early.
(5) Feeding teeth to close teeth as early as possible.

4. Not allowed together

It is quasi-adjustable when the current gauge is overprinted separately. However, when combined with the side pull rule, that is, when the front gauge and the side gauge are used at the same time, overprinting is inaccurate, and the print operator calls such a fault to be inaccurate.

cause of issue:

(1) Bad side gauge.
(2) The gap between the side pulling plate and the iron table is too small.
(3) When the delivery paper closes its teeth, the side pulls up and raises it later.
(4) The paper arrives late.
(5) Short paper retention time.
(6) The front gauge and side gauge are not at right angles.

5. You are not allowed to sip your mouth.

cause of issue:

(1) Large print pressure.
(2) Inconsistent print lining twice.
(3) Printing plate is large.
(4) Loose cloth.
(5) Paper stretched.

6. Both sides can register, the middle set is not allowed

cause of issue:

(1) Imprinting roller dents slippery.
(2) Middle tusks.
(3) The blanket is uneven.
(4) Excessive printing pressure.
(5) There is a problem with the plate.

7. The middle can register, left and right can not be set

cause of issue:

(1) The former rule is not on the line.
(2) There are loose teeth on both sides of the impression cylinder.
(3) The water on both sides of the plate is large.
(4) There is a problem with the plate.
(5) Rejection angle.

8. Individual printed sheets cannot be overprinted

That is, more than 90% of the printed samples can be registered. Only the overprinting of individual samples is inaccurate. This phenomenon is mainly due to the problem of paper feeding, and the following are:

(1) Grooves appear in the front regulation cardboard.
(2) Horizontal and vertical filaments and paper blends.

9. Misalignment overprinting is not allowed. This kind of fault is the most difficult to solve. No matter how you debug, the regulation line always bends a line.

cause of issue:

(1) The impression roller gripper shaft bends.
(2) The delivery tooth and the impression cylinder tooth are not transferred synchronously.
(3) The roller gear clearance is too large.
(4) Opening and closing teeth cam (block) wear.
(5) The machine has been used for a long time.