The shoulder iron and gap of the printing press cylinder are often important parts that are easily overlooked by printing practitioners. The work unit where the author is located has performed a cylinder replacement work, completely removing a printing tower, replacing the cylinder, shoulder iron, bearing and other components In the whole project, I have a deeper understanding of the shoulder iron and neutral of the drum.
1. Understanding the structure of shoulder iron and neutral
There are generally three large cylinders in printing presses, plate cylinders, blanket cylinders and impression cylinders.
The roller is composed of roller body, shoulder iron, journal and shaft head.
The shoulder iron is also called a rolling pillow, which refers to a circumferential surface with a certain width at both ends of the drum body.
The surface of the drum body is divided into a working surface and a blank part: the working surface is used to wrap the printing plate, blanket, pad or embossing; the blank part is used to install the plate clamp, rubber roll mechanism or paper bite row. For the COLORMAN model like 10 cylinders, the impression cylinder is hard, and there is no soft package on the outside, so there is no gap on the surface of the impression cylinder body. But like some Gaussian machines, a soft blanket is wrapped around the impression cylinder, leaving a gap, so that the paper is imprinted between the two soft cylinders, and the printing quality will be different accordingly.
Second, the role of shoulder iron
1. As a measurement standard for roller lining
The diameter of the shoulder iron and the diameter of the drum body have a certain difference, called the amount of depression. The amount of depression is for the roller to install the corresponding blanket, printing plate, and the paper is deformed properly when passing, so as to complete the embossing.
There are two factions in the design of the amount of depression of the blanket cylinder:
Shallow (American): 1.57 ～ 2.29mm
Deep system (European system): 3.25 ～ 4.15mm
The pressure adjustment during printing is achieved by changing the thickness of the blanket and the thickness of the pad. The amount of change can be measured with the shoulder iron. Whether the cushion of the blanket is soft, neutral, or hard, with the shoulder iron as a reference, accurate adjustment can be achieved. [next]
2. Improve the stability of the drum rotation
According to the use of shoulder iron, it is generally divided into two types: rolling pillow contact and rolling pillow non-contact, also known as walking iron and non-walking iron, or non-contacting.
â‘ Shoulder iron contact. The principle of the shoulder iron contact is: when the rollers are pressed together, the shoulder irons of the two rollers are in contact, and the contact pressure on the surface of the two rollers needs to be adjusted by changing the thickness of the pad. Its characteristic is that the center distance of the drum cannot be changed after the pressure is combined. Shoulder iron contact is helpful to reduce the vibration of the drum and ensure the transmission accuracy of the gear. The disadvantage is that the processing and assembly precision of the drum is high, and the shoulder iron needs special treatment.
â‘¡ Non-contact shoulder iron. The principle of non-contact of the shoulder iron is: after the roller is pressed, there is still a certain gap between the shoulder iron. When the contact pressure on the surface of the two rollers needs to be adjusted, the center distance of the roller can be adjusted. Its characteristic is that the shoulder iron does not bear the load after the pressure is combined, and the gap can be used to measure the contact pressure between the rollers, but the jitter when the roller rotates can only be guaranteed by improving the processing accuracy and performing dynamic balance.
3. As the basis for measuring the center distance of the drum
The shoulder iron also plays a very important role as a reference for adjusting the center distance of the drum. The working principle of the cylinder center distance adjustment mechanism is to adjust the printing pressure by changing the deformation amount of the cylinder pad, so as to ensure normal printing, and reduce the wear of the printing plate during the printing process, and keep the minimum amount of slip .
The machine that takes the shoulder iron should be based on ensuring that the gear dividing circle is tangent. Machines that do not use shoulder iron should be adjusted within the specified shoulder iron clearance.
Calculation of actual center distance:
â‘ Take the shoulder iron form:
â‘¡Do not take the form of shoulder iron:
After the roller is installed, the engineer will adjust the pressure of the roller, in fact, it is to adjust the pressure value between the shoulder irons or the gap between the shoulder irons. The adjustment method is: put a special professional pressure measuring aluminum foil paper between the shoulder irons, repeat the closing and separating pressure, and then check the width of the indentation; if it is not in contact, use a plug gauge to measure the two The gap between. Only when the pressure or distance between the blanket cylinder and the plate cylinder, the blanket cylinder and the impression cylinder are appropriate, can the commissioning be completed.
Generally, the form of shoulder iron can be adopted between P and B rollers, while the form of shoulder iron is not adopted between B and I rollers. The reason is that the center distance between the blanket cylinder and the impression cylinder is always adjusted accordingly with the thickness of the printing paper, so it is not suitable to use the shoulder iron form. However, the 10-roller COLORMAN model uses P and B, B and I when they leave the factory, and after a long time of use, some printing plants change it to P and B according to the actual situation. , And B and I do not take the form of shoulder iron, these can be flexibly adjusted according to the actual situation. [next]
3. Relevant knowledge of neutral
First recognize the relevant structure of the drum neutral. The neutral position refers to the non-working part of the surface of the drum, which is used to install the corresponding biting tooth structure, blanket tensioning mechanism, and plate clamping mechanism. The corresponding terms are:
Neutral angle: angle αk occupied by the neutral part
Roller utilization factor K: refers to the ratio of the arc length of the working part of the drum to the entire circumference
The relationship between the gap angle and the utilization factor of the drum is: the smaller the gap angle, the higher the utilization factor of the drum, and the smaller the diameter of the drum under the condition of the same paper width.
The utilization factor of the drum may also have some influence on the performance of the machine. For example, the improvement of the utilization factor of the drum is conducive to saving materials; the improvement of the utilization factor of the drum is to reduce the neutral position of the drum and also help reduce the power failure caused by the neutral position. The influence of balance improves the dynamic characteristics of the drum.
From the development trend of printing presses, we can also see that the gap is getting smaller and smaller. Taking the gap of the plate cylinder, from the 10mm of the COLORMAN model to the 3mm of the UNISET75 model, the reduction is as thin as a seam. There is even a tendency to have gapless rollers abroad, and the corresponding blankets and printing plates are seamless. In this case, the imbalance and vibration caused by the gap can be reduced to the most ideal state, but The corresponding supporting technology and material requirements are quite high, which can be said to be a direction we will pursue in the future.
After the roller is installed and the pressure adjustment is completed, the engineer also needs to adjust the zero position, that is, the neutral alignment, just like the calibration before the device is used, the application of a special ruler measurement to accurately locate the blanket roller and Empty plate cylinder. After the zero adjustment is completed, a trial printing is also required to check the accuracy of the corresponding zero adjustment.
From the above, we can see that there is a great relationship between the shoulder iron of the drum and the neutral. Walking the shoulder iron can compensate for the drum vibration and imbalance caused by the existence of the neutral. Of course, they have something in common. They are very important parts on the printing press. Only by grasping their characteristics can we better control the printing press and print better products.
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