Analysis of the ink-discharging mechanism of sheetfed offset printing machine
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The quality of the printing press is ultimately measured by the quality of the printed product. Printed ink is uniform, no change in shade, is the minimum quality requirement. However, due to the gradual progress of people's understanding, the printing machine is also constantly improving and constantly improving. In the offset printing process, it is the key to control the ink balance. Controlling the stringing of the ink roller is an important factor to improve the quality of the printed matter. In particular, the printer operator needs to adjust it accurately, but this is often the case. It has been neglected by many people. This is also a problem that the author often ignores when operating the printing press, which affects the printing quality of fine prints.
Nowadays, the degree of automatic control of modern printing presses is getting higher and higher, and the ink-dissipating mechanism can be precisely adjusted according to different printing products: the amount of movement and the adjustment of the starting point position to better improve the product quality.
Let's talk about the structure of the ink-spinning mechanism and use it together to properly operate and operate the ink-spinning mechanism.
First, the role and composition of the ink mechanism
The ink splicing mechanism can be roughly divided into three parts: a squeezing roller, a cooling mechanism of the squeezing roller, and a power driving mechanism of the squeezing roller. The working part of the ink splicing mechanism is a squeezing roller. The squeezing roller has both a circumferential rotation and an axial movement. The effect of the circumferential rotation is the same as that of the other leveling rollers, which acts to smooth the ink in the circumferential direction. The main function of the axial movement of the tandem roller is to smooth the ink in the axial direction. Generally, the ink splicing mechanism has three squeezing rollers: the upper squeezing roller pulls out, thins and evenly distributes the uneven ink layer supplied by the ink supply device; the intermediate squeezing roller bears the ink storage, the sounding and the distribution of the ink flow. The lower ink roller is responsible for smoothing the uneven ink corresponding to the graphic and blank portions on the printing plate remaining on the roller after the ink is applied to the printing plate.
Second, the structure of the ink roller
It is not the same on different brands of printing presses. It is generally divided into two categories: integral squeezing rollers and three-segment squeezing rollers. The overall squeezing roller is simpler to manufacture than the three-section squeezing roller – geometric accuracy and radial runout are easily guaranteed, but installation and repair are inconvenient, and must be installed in a certain order. The KBA Rapida large-format offset press uses the integral squeezing roller, as shown in Figure 1.The three-section squeezing roller is composed of three parts, and the three parts are screwed together. As shown in Fig. 2, the shaft heads 1, 2 and the roller body 4 are fixed together by screws 3. Tighten the screw 3 during installation to connect the shaft head and the roller body. When removing the roller, loosen the screw 3 to remove the roller body. However, the concentricity of the shaft ends at both ends must be ensured during assembly and disassembly, and the concentricity will be destroyed by multiple assembly and disassembly. Therefore, it is generally not necessary to disassemble the ink roller without being removed.
Third, the temperature control device of the ink roller
Since the ink roller has both circumferential rotation and axial movement, the ink is rubbed by these two aspects. After the printing machine is operated, the temperature of the ink will rise to a normal working temperature of 20 ° C to 30 ° C. If there is no temperature control device, the temperature of the ink will continue to rise, and the temperature of the ink will increase to 70 ° C or above for a long time. At this time, many characteristics of the ink will change greatly, and the printing quality will definitely not be obtained. Control, so we only have to ensure the normal working temperature of the ink during the printing process, in order to print high quality prints. Modern printing presses are equipped with temperature control devices. The temperature control devices of the ink jet rollers of the printing machines manufactured in each country are not the same, but the principle is basically the same. The temperature of the ink roller to lower the temperature of the ink. Here is the cooling mechanism of the KBA Rapida press, Figure 3 is the physical map, and Figure 4 is the internal structure. In Figure 3, we can clearly see that each of the squeezing rollers has two rubber tubes at the shaft end, one of which is the coolant and the other is the outlet. Through the two rubber tubes, the circulating coolant can be circulated inside the oscillating roller. In Figure 4 you can see the mechanical sketch of the coolant.
Fourth, the adjustment of the ink mechanism
There are two aspects to the adjustment of the ink splicing mechanism: the adjustment of the movement of the squeezing roller and the adjustment of the starting point of the squeezing roller. The adjustment of these two aspects is to be adjusted according to the specific conditions of the printed products. The following is a detailed analysis based on the typical ink-separating mechanism.
1. Adjustment of the momentum of the series of ink rollers
The maximum amount of movement of the squeezing roller is different for different brands of printing machines and different types of printing machines. For example, the domestic J2108 and J2203 have a maximum amount of movement of 25mm, PW2920-1 is 40mm, and Heidelberg M-OFFSET (48×65cm). 30mm, Heidelberg CD102 is 35mm, KBA Rapida 130-162a series presses have a maximum amount of movement of 70mm, we can adjust the range from 0 to the maximum amount of movement. The above-mentioned several types of ink-spinning mechanisms are all reciprocating and reciprocating movements of the plate cylinder to the two-pass ink roller (except for the Mitsubishi printing machine, the plate cylinder is turned to the three-speed ink roller to reciprocately move once). The reversing of the squeezing roller should be carried out when the roller is in neutral position, otherwise the ink bar is prone to occur.
So what is the best amount of momentum during printing? This depends on the specific conditions of the printed matter: for most prints, the amount of movement is generally not less than the distance between the two ink zone screws, and in many cases is adjusted to half of the maximum amount of movement; for special prints, it is adjusted to a specific The amount of motion, here are two extreme examples: suppose the left side of the print in Figure 5 is a spot color solid block, and the other parts are blank. At this time, we can adjust the string motion to a small amount. If it is large, it will destroy the local adjustment of the ink (this product is often encountered in the original work unit); and if you print a print with an almost uniform amount of ink on the entire screen, then we can adjust the maximum amount of ink, to the maximum extent. The ink is evenly distributed in the axial direction, which can also compensate for the inconsistency in the adjustment of the ink zone. So how do you adjust the amount of crosstalk? The ink-driven roller drive mechanisms of different presses are not the same, which is adjusted according to the specific structure.
2. Adjustment of the starting point of the stringer
The starting point of the squeezing roller is the relative position of the squeezing roller and the plate cylinder when the squeezing roller starts to move. When this position is changed, the thickness of the ink layer in the paper feeding direction also changes accordingly. In Figure 6, the ink layer at the starting point of the printed image is the thickest. As shown by D, A is the thickest ink layer in the print. The starting point of the ink can be based on the graphic in the vertical direction of the printed matter. Adjusted to the corresponding position, B, C roughly describes the effect of different starting points of the ink on the thickness of the ink layer. For the sea bream M-OFFSET adjustment, loosen the screw, jog the printing machine, the drum rotates, the squeezing roller does not move, so the corresponding position changes, and the starting point of the ink is changed.
Figure 7 shows the adjustment of the starting point of the inking roller in the KBA105U. The starting point of the inking roller can be adjusted to any position according to the condition of the printed matter. When adjusting, you can directly adjust the setting of the lateral distribution. By changing the starting point of the inkjet roller of each color group (Value range-233～710), the corresponding starting point of the inkjet roller is also changed. . It can be adjusted according to the graphic information on each color plate.