Comparison of three kinds of water conveying devices

During the printing process. The source of wetting fluid is continuously transferred to the printing plate, and the water supply system of various types of offset presses is different. At present, two types of water conveying devices are commonly used in offset presses. One is the water conveying device of the swing water transfer roller, also known as the water supply for the plate format (see Figure 5-2); the other is the Dagren type water conveying device. , Also known as ink roller water supply (see Figure 5-3). The water conveying device of the oscillating water transfer roller includes a water bucket, a water bucket roller, a water string roller and one or two water contact rollers which are in contact with the printing plate cylinder, and directly coats the dampening liquid on the printing plate In the old model, the water transfer roller can swing back and forth, so it belongs to the discontinuous water supply method. The water supply is uneven, and the surface speed of the water roller is the same as the printing plate. Some models no longer have a water transfer roller, but the water bucket roller is in direct contact with the water roller. The water bucket roller is driven by the motor alone, and the water supply can be changed by changing the rotation speed. There is a surface speed difference between the water bucket roller and the water loading roller, which belongs to the continuous water supply mode. When the printing speed is increased, the thickness of the printing plate water film becomes thinner. This kind of water delivery device still belongs to the format water delivery.

Dagren water supply device (Manroland 700, KBA Rapida, CD102 machine wetting device are all of this type) is a chrome-plated water roller driven by a single motor with variable speed transmission. Apply dampening fluid to the first inking roller. One or two water transfer rollers are also arranged between the inking roller and the water bucket roller. The speed of the water bucket roller with infinitely variable speed driven by a single motor determines the amount of water supply. Adjusting the pressure between the ink roller and the water bucket roller determines the thickness of the water film transmitted to the plate. The surface speed of the inking roller is the same as the plate cylinder.

In the swing type water conveying device, there are generally four roll gap states, namely: the water roller, the ink roller and the plate image and the gap of the blank part of the printing plate, while the Dagren water conveying device is It is slightly different from the swing water delivery device. When the first inking roller is in contact with the printing plate, due to the adhesion of the wetting fluid on the blank portion of the printing plate, the printing plate is preferentially wetted by the wetting fluid, and the water film layer splits to achieve the purpose of wetting. The wetting fluid remaining on the inking roller is emulsified in the ink as it passes through the inking roller. In the graphic part of the printing plate, the emulsified ink layer of the inking roller is split to achieve the purpose of supplying ink. The advantages of this water delivery method are mainly high reaction sensitivity, small water consumption, and can quickly achieve water-ink balance, especially suitable for wetting fluids with alcohol or isopropyl alcohol.

Figure 5-2 Swing type wetting device

Figure 5-3 CD102 machine wetting device

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