3.2 Water delivery mechanism The requirements for the water delivery mechanism are uniform, stable, and continuous water supply to the printing plate. This is an important condition to ensure the balance of water and ink. Because the viscosity of water is small, it is easy to evenly mix, so the clutch and pressure regulating mechanism of water path roller, water string roller, water transfer roller, water roller. The role of each part is detailed below. 1. Water bucket and water bucket ink The function of the water bucket is mainly used for holding water. The function of the water bucket roller is to pass the water in the water bucket to the string water roller. The relationship between the water bucket roller and the water bucket is not as strict as that required between the ink fountain and the ink roller. Normally, the thickness of water on the bucket roller is fixed (by affinity adsorption). Changing the amount of water can only be achieved by changing the angle of the bucket roller. There are two types of rotation of the bucket roller: intermittent and continuous: With intermittent water transfer, water easily flows on the bucket roller, that is, the water is in a different state on the bucket roller during rotation and stop, and it is greatly affected by temperature. If the speed is low and the temperature is high, the water is easy to volatilize, causing unevenness in the water supply, so this structure has now tended to be eliminated. Continuous water supply, as long as the speed is constant, the state of the water on the bucket is the same, and because the air near the bucket roller is always in a flowing state, the temperature is relatively lower, which is conducive to the formation of water on the bucket roller. Ensure stable water supply. When the water supply quantity needs to be adjusted, it can be changed to the rotation speed of the bucket roller. Since the impact caused by the speed change is eliminated, the operation is smooth and the structure is more reasonable. At present, almost all multi-color offset printing machines use a continuous water supply device, and the rotation speed of the water bucket roller is driven by a DC speed regulating motor and a set of speed reduction mechanisms. Because the pH value of fountain solution is generally between 4-6, it is slightly acidic, and it easily reacts chemically with the surface of the water bucket, causing corrosion of the water bucket. Therefore, when not working, it is best to remove the water in the bucket. 2. Water transfer roller The function of the water transfer roller is to transfer the water of the water bucket roller to the water string roller. The requirement of the water transfer roller is that it must be in a parallel state when contacting the water string roller and the water bucket roller to prevent uneven water transfer. The pressure of the water transfer roller in contact with the two sides must be moderate, that is, it can play the role of water transfer without causing a large impact. Because the water transfer roller is oscillating back and forth, there is always more or less some inertial impact. In order to solve this problem, some devices currently use metering rollers to supply water, and the swing type water transfer roller is eliminated. This water supply method uses the speed difference between the bucket roller and the metering roller to control the amount of water. 3. String water roller The function of the water roller is to distribute the water in the circumferential direction and the axial direction to ensure that the water on the water roller is always evenly distributed. It is much easier to evenly distribute water and evenly distribute the ink, so the requirements for the water roller are not as strict as the ink roller. The requirements on the surface of the water roller are hydrophilic and ink repellent to prevent the ink from returning to the water bucket. Otherwise, if the ink sticks to the water roller or the water bucket roller, because the ink repels, the water cannot be applied to the ink, and the uniformity of the water supply is destroyed. The movement of the water roller is driven by the ink roller. 4. Water roller There are four functions of the water roller: (1) Water supply to the surface of the printing plate is its main function. The water on the printing plate is consumed in the following forms: a. Ink emulsification: Ink emulsification is an important destination for water loss. From the perspective of ink transfer, ink emulsification is necessary. When the water roller is in contact with the graphic part with ink or the ink roller is in contact with the water in the non-graphic part, it is possible for water to be squeezed into the ink to form a water-in-oil ink emulsification. In color printing, one color printing is finished. When printing two colors, the two-color ink may be printed on the paper where there is water. If the ink is not emulsified, the ink cannot be transferred to the paper. b. Paper absorption: The water on the printing plate is transferred to the printed sheet through the blanket. Due to the good hydrophilicity of the paper, most of the water on the blanket is absorbed by the paper. The paper swells after absorbing water, bringing a series of difficult. c. Evaporation: Because the water roller and the ink roller are driven by the friction of the printing plate and the cross-ink roller. Friction generates heat. One of the generated heat is transmitted through the air, and the other is absorbed by the water, causing the water to evaporate. When the room is relatively dry, the water on the plate will also be lost to the surrounding air. d. Loss: During printing, due to vibration and impact, the water on the water roller is sometimes thrown away, and a special water receiving device is generally installed under the water bucket of the printing machine. If the water in the water hopper is not replenished in time, the water-ink balance will be destroyed and printing will not proceed normally. (2) Make up for the errors on the surface of the printing plate and the water roller. The outer layer of the water roller is made of water rubber fleece. The water rubber fleece is easily deformed, so its ability to make up for the error is very strong. (3) Cushioning and absorbing vibration The water roller forms an impact on the surface of the printing plate every week. If the surface is easily deformed, it can absorb the energy of the impact, thereby achieving the purpose of absorbing vibration. (4) Safety effect When a foreign object enters between the water roller and the printing plate, due to the deformation of the surface of the water roller, the printing plate suffers little damage. 5. Adjustment of water roller The adjustment of the water roller is basically the same as the adjustment of the ink roller, but it should be noted that the interaction between the upper and lower water rollers is shown in Figure 3.16. When the pressure between the upper inking roller and the water-supplying roller is too large, the water may not squeeze on it, and the amount of water on the lower water roller will be reduced. The water filling amount of each water roller can be calculated to be 50% by analysis. When the water is loaded on the water roller, it can also play the role of uniform water at the same time, and does not need to be as complicated as the ink path. When two water rollers apply water, they can complement each other, which makes it easier to keep the water even. For general quality prints, two water rollers are needed. For a print with low quality requirements, one water roller is also acceptable. The upper water roller is sometimes shared with the first ink roller, which saves one water roller, which is generally used for alcohol wetting. The landing mechanism of the water roller is basically the same as that of the ink roller, and will not be described in detail here. 6. Water glue line The function of water rubber fleece is to absorb water, store water and add water, and use the phenomenon of hair suction to attract water to its surface. Water velvet has no selectivity for water and ink, whichever is first, it will be adsorbed, so water should be applied first when printing, so that there is enough water on the surface of the water roller, because the ink repels, the ink is difficult to transfer to The water roller went up. If the surface of the water roller is sticky and dirty with ink, the water transfer is difficult, and the water glue fleece is dirty and must be cleaned in time. The water rubber fleece cannot be reversed, otherwise the water supply will be uneven and the printing plate will be worn. Sports bag Mianyang Crossing Cross-Border E-Commerce Co., Ltd. , https://www.wycybag.com
(Figure 3.16)
Offset collar machine must read: water transfer mechanism of offset press