Some Symptoms in Letterpress Printing

In the process of letterpress printing, due to improper operation, poor mechanical debugging, wear of equipment components, and poor material quality of substrates, it often leads to various failures that not only affect normal production but also reduce product quality. Here I will analyze some common faults.

1. Paper feed skew failure

There are many reasons why the paper is skewed. First, a careful observation should be made to find out where the paper starts skewing, and then adjust the order of the paper in order. Troubleshooting can start from the following aspects.

(1) Check the flatness and tightness of the paper stack to see if the paper itself has uneven thickness, deformed depressions, and uneven unbalanced conditions caused by uneven tension. Then, according to the existing problems, appropriate Tap and fluff loose to avoid paper feed skew due to late suction and late feed on one side of the paper.

(2) Check whether the four sides of the stack of paper are stuck or not. Whether the paper press block at the tip of the paper stack slides up and down is flexible, whether there is a paper jam, and if the rear door is too tight, take measures such as fluffing the paper edge and cleaning Keep an object, adjust the pressure plate or rear block to adjust.

(3) Check if the paper feeding nozzle is up and down, whether the translation is stable, whether the level is the same, and whether there is any clogging, so that the paper feeding nozzle can be adjusted to remove paper jams and other obstructions.

(4) Check the tightness of the conveyor belt, whether the conveyor belt joint is flat, whether the pressure of the roller is appropriate, whether the steel platen of the paper-pressing tongue is too low, and there is no foreign matter on the paper-feeding board (such as loose screws). Whether the working status is normal, so as to make corresponding adjustments.

(5) Check whether the landing time and pressure of the front paper guide roller are the same, whether the paper guide roller rotates flexibly, and make corresponding adjustments according to the existing problems.

2. Paper empty sheet failure

Blank sheet is a common fault in the paper feeding process. Generally, there are two cases: continuous empty sheet phenomenon and continuous sheet feeding after empty sheet. No matter which kind of sheet sheet is faulty, it can be checked and adjusted from the following aspects.

(1) Check whether there is bow wrinkling on the paper surface. If the bow wrinkle depression is aligned with the suction nozzle, it will inevitably leak “broken”. You can tap the paper surface to change the uneven condition, or turn the paper around and print it to make it flat. The paper is aligned with the nozzle.

(2) Check whether the pile is uneven or not. If the nozzle part is too low, it will not be able to be sucked up. The paper stack or other objects can be used to properly raise and level the paper stack to meet the requirements of paper suction.

(3) Check whether the edge of the stack of paper is contaminated. If there is foreign matter or water on the edge of the paper, or if the paper is cut with a blunt paper-cutting blade, the edge of the paper is likely to be conglutinated, causing difficulty in the suction of paper and empty sheets. The paper fluffed properly.

(4) Check if the blowing volume is too small to blow up the paper edge so that the distance between the nozzle tip and the paper surface is not suitable and empty. Adjust the blowing volume accordingly.

(5) Check if the vacuum suction is insufficient or the suction nozzle is broken or the straw breaks and the air leaks. You can take care to clear the pipe and clear the clogging of the foreign material and replace the damaged rubber suction nozzle and air duct.

(6) Check whether the angle and height of the nozzle and the paper stack are appropriate. If there is any discomfort, adjust it as appropriate so that the paper surface is flush with the nozzle head and the paper stack height required by the nozzle is satisfied.

(7) Check if there is any discomfort in the position or angle of the paper brush or steel sheet. Adjust the brush and steel sheet appropriately according to the degree of paper hardness and hardness.

(8) Check if the air pump is working properly. Check if the suction force of the suction head is even. If the suction force is large or small, it means there is a problem with the air pump and it should be repaired.

3. Two or more sheets of paper failure

(1) When the vacuum suction force is too large to cause a double-sheet failure, it should be checked whether the vacuum suction force is increased due to the large diameter of the rubber suction nozzle, or whether the vacuum suction force of the air pump itself is too large. For the former, according to the thickness of the paper, choose a suitable rubber suction nozzle or no rubber suction nozzle; and for the latter, should reduce the amount of suction, to achieve the effect of printing paper does not absorb double or multiple sheets.

(2) Double sheet failure caused by insufficient air volume. The reason may be improper valve adjustment or failure of the air pump, resulting in blockage of the air path, cracking of the pipeline, reduction of blowing volume, blowing of some paper on the loose paper pile surface, and causing double or multiple failures. Should be checked one by one to exclude.

(3) Split paper brush and steel sheet do not cause double sheet failure. This may be due to excessive separation between the paper brush and the paper edge, or the length and angle of the steel sheet. The position of the brush and the length and angle of the steel sheet should be adjusted so as to maintain the function of separating paper and loose paper.

(4) The suction nozzle is adjusted too low or the paper table is raised too high to cause a double sheet failure. When the suction nozzle is too low and the distance from the paper stack is too small, double sheets of thin paper are likely to occur; if the paper tray is raised too high, some of the paper on the surface will not be blown loose, resulting in double suction. The distance between the nozzle and the paper table should be properly adjusted, and the speed of the paper table should be increased.

To sum up, as long as the operator strictly implements the production process in daily production and abides by the operating rules, according to the performance of the equipment and the characteristics of the substrate, it is necessary to carry out the necessary maintenance and debugging of the equipment, improve the equipment and The printability of paper can effectively avoid the occurrence of various failures.

Author: Kang Kai

Reprinted from: Printing Technology