The inking device, as an important mechanism of the printing press, together with the other three printing elements (plate, manuscript, printing material) determines the quality of the printing quality. Without a reasonable inking device as a guarantee, beautiful prints cannot be printed. The arrangement of the ink roller is an important factor that affects the performance of the inking device. Therefore, we analyze and study the ink roller arrangement of the offset press, and provide a good basis for printing the ideal printed matter by understanding and mastering the inking performance of the printing press. 1. The function and composition of the inking device The inking device quickly distributes the stripe ink output by the ink fountain roller from the circumferential direction and the axial direction, so that the ink transferred to the printing plate is uniform and appropriate. Therefore, whether the ink color of the printed matter is uniform and whether the level is clear has an important relationship with it. In general, the inking device of the offset printing press is divided into three parts: an ink supply part, a uniform ink part, and an ink injection part. The function of the ink supply part is to store ink and supply ink to the ink leveling part. The main components include the ink fountain roller (also called the ink delivery roller), the ink fountain and the ink transfer roller. The ink fountain roller rotates intermittently or continuously at a slow speed, and the ink transfer roller oscillates back and forth to transfer the strip-shaped ink layer to the high-speed rotating ink-crossing roller to quickly smooth the strip-shaped ink layer. The amount of ink supply can be adjusted according to the requirements of the printing process. Adjusting the angle or rotation speed of the ink fountain roller can change the total ink supply. Adjust the ink fountain adjustment screw to change the gap between the ink fountain blade and the ink fountain roller. It can supply ink layers of different thickness to complete the normal ink supply to the printing plate. The function of the ink leveling part is to evenly distribute the ink in a strip form, transfer it to the inking part and store part of the ink. The main components of the ink leveling part include the ink leveling roller, heavy roller and cross-ink roller. This part includes the most ink rollers. Among them, a group of ink rollers with the ink roller 2 as the core is mainly used for leveling the ink layer, and also has the function of storing ink. A group of ink rollers with the ink roller 3 as the core further distributes the ink, and finally supplies the ink to the four inking rollers. In addition, this set of ink rollers can not only distribute ink, but also store and recover excess ink. The rotation of the ink roller is driven by the shaft end gear, and there is also an axial movement driven by the swing lever mechanism; the ink leveling roller and the heavy roller are driven by surface friction. The role of the inking part is to apply ink to the graphic part of the printing plate. The inking part is composed of an inking roller (also called a form roller). There are 3-6 inking rollers, generally four. The inking part transfers the very thin ink layer (about 6-10 microns) of the ink leveling part to the printing plate. The circumferential speed of the inking roller during transfer is equal to the circumferential speed of the plate cylinder. Since the inking roller directly contacts the printing plate, compared with other inking rollers, the accuracy requirements are the highest. When printing, the ink roller should be in contact with acidic wetting fluid and ink. Therefore, the ink roller material should have corrosion resistance, oil resistance, and good lipophilicity to ensure that the surface can absorb ink evenly. In order to achieve this effect, the surface of the soft roller is generally covered with rubber, and the surface of the hard roller is chrome plated or sprayed with hard plastic or nylon. 2. Performance evaluation index of the inking device The performance evaluation indexes of the inking device include static indexes and dynamic indexes. The static indicators include: inking coefficient, uniformity coefficient, accumulation coefficient, inking coefficient, inking rate, etc. The inking coefficient Kg indicates the uniformity of inking on the printing plate. Measured by the ratio of the sum of all inking roller areas to the plate area. The inking coefficient Kg value depends on the machine type, application and process requirements, etc. It should generally be greater than 1, and the greater the Kg value in a certain range, the better the inking effect. The Kg value of a sheet-fed offset press is generally 1-1.5. The Kg value of web offset presses for books and newspapers is between 0.65-1.2. In order to increase the Kg value generally increases the number of inking rollers or the diameter of the inking roller, first consider increasing the number of inking rollers. There are 4 inking rollers for sheet-fed offset printing presses, and there are also 5 of them, while most of the inking rollers for commercial web offset printing presses are 3. The ink leveling coefficient Ky indicates the degree of ink leveling in the ink leveling part, which is expressed as the ratio of the sum of the areas of all the ink leveling rollers to the plate area. Under normal circumstances, the greater the ink leveling coefficient, the better. It depends on the performance and application of the machine. The offset coefficient of sheet-fed offset printing machine is between 4-5.5, the number of ink rollers is 15-25, and the number of ink rollers of web offset printing machine is 7-15. The accumulation coefficient Kj represents the ability to accumulate ink in the inking system. Measured by the ratio of the sum of the areas of all the ink roller and the ink roller to the plate area. The greater the accumulation coefficient Kj, the greater the amount of ink accumulation in the ink delivery system, and the ink color stability is good. However, as the Kj value increases, the ink delivery system becomes less and less sensitive to changes in the amount of ink supplied. The process of adjusting the ink color transition lengthens and the transient response becomes slower. Therefore, using a computer to control the ink color system, the Kj value should not be too large. The number of inking lines N reflects the number of times the ink is rolled, rolled and separated between the ink rollers during the process of transport and thinning, and is also called the number of contact lines. Expressed by N, the greater the value of N, the better the ink leveling effect. The inking rate of the inking roller represents the percentage of the total amount of ink on the printing plate that the inking roller supplies to the printing plate. The quality of the inking performance is ultimately determined by the uniformity of the ink applied to the printing plate, and the amount of ink applied to each inking roller directly affects the uniformity of the ink layer on the printing plate. According to the direction of rotation of the plate cylinder, the inking rate of the first two inking rollers is generally around 80%, and the inking rate of the last two inking rollers is around 20%. Dynamic indicators include system response time, system stability time, and ink layer thickness consistency. The system response time refers to the time elapsed from the change of the input ink volume of the input system of the ink transfer system to the change of the thickness of the ink layer on the substrate at the output end of the system. Generally speaking, the response time of the inking system of the long ink path is long, and the response time of the inking system of the short ink path is short. During the printing process, I hope that the shorter the stabilization time, the better, because the shorter the transition time, the more time, resources, and waste of overprinted paper. The consistency of the thickness of the ink layer refers to how close the thickness of the ink layer on the substrate is to the thickness of the target ink layer, and is expressed by the standard deviation of the two. The smaller the standard deviation, the smaller the deviation between the thickness of the ink layer and the target ink layer, and the better the consistency. [next] 3. Arrangement of ink roller According to the arrangement of the ink rollers before the next ink roller, there are single-channel, double-channel and multi-channel ink transfer. Figure 2 shows the arrangement of the ink roller of the German Kenich Bauer offset press. It adopts the single-pass ink transfer method, and the ink is transferred to the lower ink transfer roller through the middle ink transfer roller and the uniform ink transfer roller. The two-way ink transfer is that the ink is divided into left and right to pass to the lower ink roll after reaching the middle ink roll. According to the arrangement position of the ink roller, there are symmetrical type and asymmetrical type. The ink rollers of a lithographic printing machine belong to a symmetrical arrangement. As shown in Figure 5, the ink is divided into two paths symmetrically by the inking roller, and then the ink is supplied to the ink roller via the ink leveling roller. According to the characteristics of ink transfer and ink distribution, it is divided into multi-roller type and ink storage roller type. The characteristic of the multi-roller type inking device is that the ink passes through a series of soft and hard rollers of different diameters to distribute the ink before reaching the ink roller. The ink storage roller type inking device uses a large metal roller in the middle of the inking system and is surrounded by a series of soft ink rollers to store, transfer, and distribute ink. In order to better transfer and distribute ink, the ink roller of the inking device should be used in combination with a soft ink distribution roller and a hard string ink roller, so that the ink rollers contact each other well under a certain pressure. The arrangement of the ink roller should be conducive to the reasonable distribution of the inking volume of the inking roller. Most printing presses are supplied with printing plate ink by the first group of inking rollers, and the second group mainly plays the role of ink distribution except for a small amount of printing plate ink. That is to say, when arranging the arrangement of the ink rollers, it is necessary to satisfy the principle that the amount of ink supply should be prioritized and then lighter. Most modern printers use symmetrical ink roller arrangements. In some printers with symmetrically arranged ink rollers, in order to improve the ink supply distribution of the inking rollers, heavy rollers are added after the intermediate ink rollers, that is, during the splitting, to increase the pressure between the ink rollers, so as to add ink to the heavy rollers The roller increases the amount of shunted ink. At the same time, when the contact pressure between the inking roller and the printing plate is adjusted, the contact pressure between the inking roller and the printing plate with the weighted roller is higher than the pressure between the inking roller and the printing plate without the weighted roller, so Increased the inking rate of the inking roller with heavy rollers. The arrangement of ink rollers should also consider the overall layout of the printing press and the number of ink rollers. A good overall layout can make reasonable use of space, make the machine compact, and facilitate the installation and disassembly of ink rollers. The greater the number of ink rollers, the better the ink leveling performance, but at the same time the system response time becomes longer and the dynamic performance becomes worse. Therefore, the static performance and dynamic performance should be considered comprehensively to determine the number of ink rollers required. 4. The influence of the arrangement of ink rollers on the performance of inking In the inking system, the arrangement of the ink rollers is slightly changed, the transmission path of the ink between the ink rollers will change, and the amount of ink on each ink roller will change, resulting in a change in the inking rate of each ink roller to the printing plate . The arrangement of the ink rollers also affects the ink delivery performance by affecting the length of the ink path. In the case of ensuring the performance indexes of the inking device, a certain number of ink rollers adopt different arrangements, which directly affects the ink path and the inking rate of the ink, and is related to the uniformity of the ink applied to the printing plate and the quality of the printing. In the printing process, the ink path is too long, the thickness difference of the ink layer on the ink roller from the ink transfer roller to the ink roller is large, and the ink discharge is slow, and the excessive amount of ink is accumulated on the upper ink roller. When the paper feeding fails or other reasons require the cylinder to be depressurized, the inking roller is separated from the plate idling, the ink layer thickness difference of the inking roller is reduced and tends to be uniform, the inking roller ink layer thickness is increased compared to normal printing; when the pressure is printed again , Too much ink has been applied to the graphic parts of the printing plate, which may cause the phenomenon of pasting or dark ink. The ink path is too short, and the speed of ink discharge is fast. The ink roller can not evenly align the ink axis in time, which will inevitably make the ink color transferred to the graphic uneven. However, the speed of ink discharge is fast, which can reduce the bad phenomenon caused by the long residence time of ink. Therefore, the arrangement of the ink roller will affect the length of the ink path and further affect the performance of the ink delivery. 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