Several printing bar solutions

Print bar: prints appear in parallel with the drum axis, ink shades of different traces of the streak, commonly known as bars, slivers, roads, heads, which is a lithographic offset printing is more common and difficult to solve the printing failure. This article analyzes the characteristics of the common phenomenon and its causes, and proposes corresponding methods for elimination.

Gear gear

(1) Failure phenomenon: The entire layout is distributed with bars, usually ink bars, shaped like a washboard. The distance between each bar is the pitch of the printing roller transmission gear (t=Ï€m).

(2) Cause of failure: The manufacturing and installation accuracy of the gear is not enough, the tooth surface is worn, the distance between the teeth is too large, or the damage of the individual teeth causes the gears to mesh and become inaccurate when the gears are driven to generate vibration, which causes sliding friction on the surfaces of the rollers that are in contact with each other. The result is that the dots of the plate layout are deformed and become elliptical or enlarged due to squeezing, and transfer marks are produced on the printed material. This type of failure will not only make the printed material appear tapers, but will also exacerbate gear wear.

If the gear has a damaged tooth or a foreign object between the teeth, there will be a bar on the print and it will be fixed in a certain position. If one of the pair of meshing gears is rotated by 90°, the position of the lever will change correspondingly, then it can be concluded that the gear is a problem; if the position of the lever is not changed, rotate the other gear by 90°. After the gears are rotated respectively, the positions of the tapers remain unchanged, and it can be concluded that the gears are not the cause.

(3) Solution: Reduce the gear center-to-center distance or gear-to-gap clearance properly, and change the drum liner to a soft liner to increase the elasticity of the liner. In severe cases, a new gear must be replaced.

2. Vibration lever

(1) Failure phenomenon: The partial position of the printed sheet has a bar, and the position is fixed, and the position where the bar appears is related to the vibration of a certain rule. Such a bar is generally an ink stick.

(2) Cause of failure: There are many unbalanced factors in the running process of the offset printing press. It is difficult to directly identify what kind of vibration is caused by the vibration. It is necessary to analyze the vibration source. The impact and vibration caused by roller emptying when it enters the rolling; the shock and vibration generated when the stamping cylinder teeth open and close; the vibration generated when the roller is pressed off; the roller itself is unbalanced and the vibration caused by the inertia during high-speed rotation The impact and vibration of the reciprocating paper feed mechanism due to the inertial force; the vibration generated when the paper receiving chain releases the paper cutting board.

(3) Solution: According to the specific situation of the tap, check the movement of the above-mentioned organization one by one or replace the unqualified parts.

3. Roller

(1) Symptoms: Wide range of bars and unfixed positions. The color of the ink before and after the print is different.

(2) The cause of the malfunction: The roller is divided into two kinds, the ink bar and the water bar. Most of them are caused by the improper design of the uniform ink system or the inappropriate adjustment of the pressure of the rubber roller, which results in insufficient supply of the uniform ink system. The diameter, support point, cylindricity of the rubber roller, the clearance between the roller head and the supporting hole, and the surface hardness of the rubber roller all affect the roller.

4. Other reasons caused by the tap

(1) Blanket. After the blanket has slackened, it will swell and slip during stamping to form a bar. This slippage is intermittent, and the greater the pressure between the plate cylinder and the blanket cylinder, the more severe the slip phenomenon. Therefore, the problem of slackening of the blanket must be solved in time, otherwise it will not only form a bar, but also cause a series of related failures. To avoid the generation of ink bars, choose a rubber blanket with small elasticity, suitable elasticity, good ink absorption, uniform thickness, and smooth surface. At present, air-cushioned blankets are the best.

(2) Pads. If rigid liners are used, although the printed dots are clear and rich in depth, they are sensitive to the precision of the machine and easily form bars, so the medium and soft liners are better. However, the pressure between the blanket cylinder and the plate cylinder is too small, and ink bars are also prone to occur.

(3) Plates. The reticulation version has a large friction and is not prone to ink bars; the field version and the thin-line version have a small frictional force, are easy to slide, and the dots are easy to appear.

(4) Paper. Whiteboard paper is more sensitive to the reaction of ink bars; coated paper is smoother than offset paper, and it is also prone to ink bars.

(5) Ink. The viscosity of large ink cohesion is not easy to appear ink, thin, transparent ink, ink sticks will be very clear. In addition, the ink and the ink bar are also related to the production, black ink is easy to show the ink bar, yellow ink and paper color is relatively close, the ink bar is not obvious.