The so-called ink bar is the phenomenon that the dots in the axial strip area appear on the printed matter both increase or decrease.
In the daily work of offset printing, the problem of ink bars in prints is often annoying. Because the causes of ink sticks are manifold, they need to be comprehensively analyzed and judged before they can be effectively solved. We will analyze the phenomenon and causes of the more common phenomenon of the ink bars in production.
Generally speaking, the ink bars that we can encounter in our work can be roughly divided into four types: vibratory ink bars; gear-like ink bars; roller ink bars; and other causes of ink bars.
Below we classified for discussion:
I. Vibrational ink bars
Vibrating flash means that the contact pressure between the plate, blanket, paper, and impression cylinder changes instantaneously (may increase instantaneously or may become smaller instantaneously after the machine vibrates abnormally during the printing process). ), resulting in distortion of outlets.
Blanket: The role of the blanket in the printing process is not only to increase the transfer rate of the ink to the paper, but also to absorb the vibration of the machine caused by the imprint. When the blanket is hardened, it is impossible to effectively absorb the vibration generated during the operation of the machine during imprinting. When the vibration is manifested on the printed matter, the problem of the ink stick may occur. Many home-made printing presses in China use soft liners due to their low manufacturing precision and large vibrations during the printing process.
Poor oil supply: When the machine's moving mechanism fails to supply oil, it will have a certain impact on the smooth running of the machine. When this effect is large enough, it will cause the machine to vibrate. At the same time, it will vibrate. The transfer of outlets has been affected to a certain extent, resulting in the deformation of local outlets and the appearance of ink bars.
Bad embossing force: When the pressure of the roller is too large, the vibration of the machine can also occur at the time of imprinting, resulting in the generation of ink bars. Especially when the printing plate cylinder and the blanket cylinder have just entered the embossing area (mouth), if the pressure is too high, the contact between the blanket cylinder and the impression cylinder will be affected by the vibration. When the blanket cylinder and the impression cylinder have just entered the embossing area from the mouth, if the pressure is too high, the same effect occurs. A vibration bar appears in the contact area between the plate cylinder and the blanket cylinder, and then it is transferred to the blanket cylinder. On paper.
Bearing wear or pressure instability: When the drum head oil running or long-term use of the machine to produce natural wear, so that the roller head and the bearing gap increases, with poor, due to tremor at the time of pressure caused by ink marks. In this regard, it is advisable to make trapezoidal traps in the inner liner of the rubber in order to reduce the impact during the imprinting state and reduce the degree of ink bar marks. In addition, the serious wear of the drum shaft head or bearing should be considered to take repair or replace the new bearing replacement to eliminate the traces of ink marks.
Loosen screws loose: The angle screws are the foundation of the entire press. If the foundation is unstable, then the machine will not be able to run smoothly. During the installation and commissioning of the machine and during the annual maintenance of the machine, it is necessary to specifically check the anchor bolts and tighten the loose screws in time to ensure that the machine can run smoothly.
The other reasons that can cause vibrating ink in printing are:
The vibration of the ink transfer roller; The vibration caused when each roller is pressed; The vibration caused by the opening and closing of each gripper; The motor is not suitable for rectification; The rotation is not uniform; The chain is loose; The bolts on the main part of the machine are loosened; Heart; roller imbalance; gear eccentricity and other reasons.
Second, the gear stick
Causes of ink sticks: Wear of the roller gear, excessive gear clearance, or accumulation of foreign matter between gear teeth.
When the roller gear wears, gaps or adhesion of foreign matter in the teeth, during the operation of the machine, the roller gears can not be meshed with each other accurately, so that the line speed between the rollers is not consistent enough. In addition, the backlash is too large, the drum is also prone to tremor jitter, the formation of print marks, so that the printed layout of the track and the gear pitch similar to the ink marks. There is a foreign body obstacle in the backlash, and it is easy to cause the drum to tremble due to the “top gear†phenomenon, so that the horizontal layout of the print product forms a strip-like ink stick. In this regard, the center distance between the rollers should be adjusted to reduce the tooth gap. For gears with severe wear, new gears should be replaced. Adhesion between foreign bodies in the teeth should be cleaned before the effect of eliminating the ink bars can be achieved.
The reasons that can lead to gear bars are summarized as follows:
Gear wear; bearing preload is too large or too small; accuracy is not high; tooth surface and gear end chamfer is not proper; circumferential joint error; tooth error tooth surface finish is not high; gear skew; improper tooth gap; excessive tension of the drive belt Or insufficient; there is a foreign body on the tooth surface; foreign matter accumulates at the root of the tooth.
Third, roller roller
There are generally two kinds of ink bars produced by rollers. One is a white bar (also called a water bar), and the other is an ink bar (for convenience, we call them both ink bars here). The former is generally due to water. The problem with the roller is caused by the problem of the ink roller. However, whether it is the water roller or the roller caused by the ink roller, the reason is basically the same.
The most common reason for the appearance of ink bars in daily production is that the roller pressure is too strong.
When the contact pressure between the rubber roller and the printing plate is too large, during the operation of the machine, the ink roller and the printing plate are in contact with each other to roll, and it is easy to generate shock and cause tremor, so that the increase of the frictional force causes a streaking bar. If the pressure of a few printing rollers is too large, the density of the bar marks will be greater. In this regard, by adjusting the contact pressure between the rubber roller and the printing plate to maintain uniform and moderate contact conditions, eliminating the excess resistance, the ink bar can be better eliminated. In addition, when the pressure between the ink roller and the iron roller is too large, the iron roller will produce a squeeze on the rubber roller and the glue roller will temporarily deform due to its elasticity, which will cause sliding friction to the printing plate and cause ink bars. Moreover, due to the different pressures of the collector roller and the serigraph roller and the printing plate, it is easier to cause the surface line speed of their surface to be out of synchronization to cause ink bars. Therefore, the pressure between the rubber roller and the chain iron roller should be adjusted properly to avoid the roller being squeezed, and the resistance and the friction force are increased and the ink bar easily occurs. There is also a situation where the cohesiveness of the rubber roller is not good and not straight, and the ink bar is also prone to happen. This is because during the rolling process of the machine, the contact pressure between the rubber roller and the plate is inconsistent, and when the machine rolls, local friction increases to cause stripe marks. In this regard, high-precision ink rollers should be replaced for printing full-field and textured versions.
Similar to the ink roller caused by excessive roller pressure, there are some reasons in the printing that can cause the roller roller, and the principle is basically similar to the ink roller caused by excessive roller pressure. Such as: roller bending; roller expansion, cracking; poor cleaning; ink roller, water roller aging; ink roller shaft wall hole do not care; bearings, gears and other wear and tear; roller arrangement problem; roller bearing fulcrum problem.
Fourth, other ink bars
In addition to the three situations mentioned above, the reason why ink bars sometimes appear in printing production is really hard to imagine. Here we will introduce some of the reasons that may lead to ink bars for reference.
Material: wrinkles of plate-making table paper; wrinkles on the underside of blanket; uneven thickness of plate; uneven thickness of blanket; remaining residual coating oil; wear of rollers and bearings on machine; excessive clearance of bearing support , The preload is too large; the bearings are skewed;
The plate cylinder or the blanket cylinder is too large: If these two conditions exist, the strip marks will be caused due to the inconsistence of the linear velocity of the surface, and the impact of the cylinder will be caused by the vibration of the cylinder. The contact between the two cylinders is easy. Friction triggers ink marks. In addition, sometimes the ink sticks are easily caused due to the inconspicuous imprinting of the mouthpiece (lower pressure) and excessive number of paper strips.
In this regard, the thickness of the lining should be accurately adjusted, and the ink layer should be uniformly transferred with the minimum printing pressure so as to maintain the consistency of the line speed between the rollers as a precondition. When adding padding to the mouth part of the mouth, gradual padding should be adopted, and no padding should be added at once to avoid the appearance of ink marks.
The blanket is loose. If the blanket has just been changed soon, the stretching during the printing process becomes loose, and it is not tightened in time, so that sliding friction easily occurs during rolling, and thus a stripe-like ink stick trace appears. Therefore, when the blanket has a loose condition, measures should be taken to tighten it in time to prevent the production of printing ink bars.