Analysis of the shoulder and iron of the printing machine drum
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The shoulder iron and neutral of the printing machine drum are often important parts that are easily overlooked by the printing practitioners. The working unit of the author has carried out a drum replacement work, completely removing a printing tower and replacing the drum, shoulder iron, bearing and other components. In the whole project, I have a deeper understanding of the shoulder iron and the neutral of the drum.
First, Understanding the structure of the shoulder iron and the neutral
There are generally three rollers in the printing press, a plate cylinder, a blanket cylinder and an impression cylinder. The structure of the drum is shown in Figure 1:
It can be seen that the rollers are composed of a drum body, a shoulder iron, a journal and a shaft head.
Working surface, neutral, shoulder iron, roller body, journal and shaft head
Figure 1 Structure of the drum
The shoulder iron is also called a roller pillow, and refers to a circumferential surface having a certain width at both ends of the drum body.
The surface of the drum body is divided into a working surface and a neutral portion: the working surface is used to wrap the printing plate, the blanket, the pad or the embossing; the neutral portion is used to mount the plate, the rubber band or the bite row. For a COLORMAN model like a 10-roller, the impression cylinder is rigid and does not wrap any softness on the outside, so there is no neutral on the surface of the impression cylinder. But like some Gaussian machines, wrapping a soft blanket on the outside of the impression cylinder leaves a gap, so that the paper is embossed between two soft rollers, and the print quality will be different.
Second, the role of the shoulder iron
1. As a measurement basis for the drum liner
There is a certain difference between the diameter of the shoulder iron and the diameter of the drum body, which is called the amount of depression. The amount of undercut is used to mount the corresponding blanket, the printing plate, and the paper is properly deformed as it passes, thereby completing the imprinting. As shown in Figure 2.
The design of the undercut of the blanket cylinder has two factions:
Shallow (US): 1.57~2.29mm
Deep (European): 3.25~4.15mm
Figure 2: The amount of depression of the plate cylinder, blanket cylinder, and impression cylinder
The pressure adjustment during printing is achieved by the thickness of the blanket and the thickness of the liner. The amount of change can be used as a measurement basis for the shoulder iron. Whether the pad of the blanket is made of soft, neutral or hard pad, the shoulder iron can be used as a reference for accurate adjustment.
2. Improve the smoothness of the drum rotation
According to the way the shoulder iron is used, it is usually divided into two types: the contact of the roller and the contact of the roller. It is also called the shoulder iron and the shoulder iron, or the shoulder iron contact and the shoulder iron are not in contact.
2.1 shoulder iron contact. The principle of the shoulder iron contact is: when the drum is pressed, the shoulder irons of the two rollers of the roller are in contact with each other, and when the contact pressure of the surfaces of the two rollers needs to be adjusted, the thickness of the gasket can be changed. It is characterized in that the center distance of the drum cannot be changed after the pressing. The shoulder iron contact is beneficial to reduce the vibration of the drum and ensure the transmission precision of the gear. The disadvantage is that the processing and assembly precision of the drum is high, and the shoulder iron is specially treated.
2.2 shoulder iron non-contact. The principle of non-contact of the shoulder iron is: after the drum is pressed, there is a certain gap between the shoulder irons. When the contact pressure of the surface of the two rollers needs to be adjusted, the center distance of the drum can be adjusted. The characteristic is that the shoulder iron does not bear the load after the pressure is combined, and the gap between the rollers can be measured by the gap, but the jumping of the drum can only be ensured by improving the machining precision and balancing.
Figure 3 Shoulder iron contact and non-contact diagram
3. As the basis for the measurement of the center distance of the drum
The shoulder iron also plays a very important role as the basis for the adjustment of the center distance of the drum. The principle of the roller center distance adjusting mechanism is to adjust the printing pressure by changing the deformation amount of the roller pad, thereby ensuring normal printing, and reducing the amount of plate wear during printing, and maintaining the minimum slip amount. .
The machine that walks the shoulder iron should be based on the tangent of the gear indexing circle. Machines that do not carry the shoulder iron should be adjusted within the specified shoulder clearance.
Actual center distance calculation:
1 walking shoulder iron form:
2 does not take the shoulder iron form:
After the drum is installed, the engineer adjusts the pressure of the drum, which is actually adjusting the pressure 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 pressure and pressure, and then check the width of the indentation; if it is not in contact, measure the two with a plug gauge. The gap between them. It must be ensured that the pressure or distance between the blanket cylinder and the plate cylinder, the blanket cylinder and the impression cylinder are both correct.
Usually, the shoulder iron form can be used between the P and B rollers, and the shoulder iron form is not used between the B and I rollers. The reason is that since the center distance of the blanket cylinder and the impression cylinder is always adjusted correspondingly to the thickness of the printing paper, it is not appropriate to use the shoulder iron form. However, the 10 roller COLORMAN models are used at the time of delivery. P and B, B and I are both shoulder-shoulder irons. After a long period of use, some printers change them to P and B shoulders according to actual conditions. And B and I do not take the form of shoulders, these can be flexibly adjusted according to the actual situation.
Third, the relevant knowledge of the neutral
First understand the relevant structure of the roller neutral. Neutral refers to the non-working part of the surface of the drum for mounting the corresponding bite structure, the blanket tensioning mechanism, and the plate clamping mechanism. The corresponding terms are also:
Neutral angle: the angle αk occupied by the neutral part
The utilization factor K of the drum refers to the ratio of the arc length of the working part of the drum to the entire circumference length.
It can be seen from the formula that the relationship between the neutral angle and the utilization factor of the drum is that the smaller the neutral angle, the higher the utilization factor of the drum, and the smaller the diameter of the drum under the same paper web condition.
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 beneficial to save material; the utilization factor of the drum is increased to reduce the neutral of the drum, and it is also beneficial to reduce the power caused by the neutral. The effect of balance increases the dynamics of the drum.
From the development trend of the printing press, we can also see that the gap is getting smaller and smaller. Take the gap of the plate cylinder, from about 10mm of COLORMAN model to about 3mm of UNISET75 model, it is reduced as a seam. There is even a trend in foreign countries where there are no free rollers, and the corresponding blankets and plates are seamless, so that 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 perform the zero adjustment, that is, the alignment of the neutral is performed, just like the calibration before the device is used. The special ruler measurement is applied to accurately position the blanket cylinder and The neutral of the plate cylinder. After the zero adjustment is completed, the test printing is also carried out to check the accuracy of the corresponding zero position debugging.
From the above, we can see that there is a great correlation between the shoulder iron and the neutral of the drum, and the shoulder iron can compensate for the vibration and imbalance of the drum caused by the presence of the neutral. Of course, there is something in common. They are all very important parts on the printing machine. Only by mastering their characteristics can they better control the printing press and print better products.