We all know that in modern water-based offset printing, there are two main types of wetting, one is contact, and the other is non-contact. In production, we see many contact-type wetting devices, non-contact Relatively less, in this article, we briefly introduce several non-contact wetting devices.
1. Brush roller dampening device
As one of the non-contact dampening devices, the early models of Mitsubishi used the brush roller dampening device. The previous bucket roller was transformed into a brush-type roller made of nylon material and soaked in fountain solution. The brush roller is directly driven by the motor to rotate and can be adjusted steplessly. The main function of the brush is to carry the water out of the bucket. There is a scraper near the brush, which is mainly used to drive the water out of the brush. After being ejected, the water bounces towards the water string roller, passes through the water leveling roller, and then passes to the water roller to realize non-contact water supply. The amount of water is determined by the speed of the brush and the position of the water shield. The size adjustment is also divided into overall and fine adjustment: changing the speed of the water bucket roller drive motor can be overall adjustment; fine adjustment is to adjust the adjustment screw that controls the water shield, so that the position of the water shield is appropriate, so that it can be accurate Control the amount of water supply. If the water shield is also remotely controlled by the motor, the amount of water supply can be automatically adjusted. The biggest advantage of this mechanism is that it can adjust the local water volume.
1-water bucket roller, 2-scraper, 3-adjustment screw, 4-shielding plate, 5-leveling roller, 6-pressure roller, 7-string water roller, 8-water roller, 9-water bucket
Another structure of the brush dampening device is the brush dampening device of the United States Harris. In this structure, the brush roller is not directly immersed in the fountain solution, but is always in contact with the water bucket roller in the water bucket. The two rotate in the same direction and at the same speed. Splashed by the brush roller onto the water roller, and then passed the water roller to give the plate water. In this structure, the amount of water is only determined by the speed of the water bucket roller, and the precise control of the water output can be achieved through the stepless control of the motor.
1-water bucket roller, 2-brush, 3-string water roller, 4-water roller, 5-plate cylinder, 6-water bucket
2. Water spray dampening system
Heidelberg Speedmaster uses this device in some machine-type dampening systems. This airflow spray device has its own unique features. The smooth chrome-plated roller is immersed in fountain solution and driven by a separate DC speed regulating motor. The surface of the porous cylindrical mesh cylinder is covered with a fine mesh braided jacket and frictionally driven by chrome rollers to rotate. One side of the compressed air chamber has a row of nozzles along the axial direction, sprays the water on the woven mesh tube into a mist form and sprays it onto the water transfer roller, and then passes through the water string roller and the water roller for dampening. The control of the water supply of this system is determined by the amount of water transferred from the chrome roller to the cylindrical mesh cylinder, so when adjusting the gap between the scraper and the chrome roller, the water supply of each section of the chrome roller axis can be completed.
1-chrome plated roller, 2-water bucket, 3-scraper, 4-adjust nut, 5-mesh cylinder, 6-compressed air chamber, 7-water transfer roller, 8-string water roller, 9-water roller
Another type of water-spraying dampening device is even simpler, that is, the water bucket roller with a net continuously picks up the water, and there is a row of air nozzles inside the water bucket roller to spray the water toward the plate cylinder. The amount of water is controlled by the water outlet adjustment plate.
1-Adjustment plate, 2-water tank, 3-water bucket roller, 4-air nozzle
This water spray dampening system makes it easier to evenly apply water to the printing plate.
3. Air scraper dampening device
Also known as the Mullen dampening device, it was developed by the American Mullen. The water bucket roller of this device is a rubber roller, which is installed at a position 0.1 mm away from the surface of the printing plate, and continuously rotates to bring water to the printing plate cylinder in the form of a water film. The water supply of this device is controlled by an air scraper, which mainly blows in compressed air to blow off excess water, and then the blown water is sucked back into the sink by the suction device.
1-water bucket, 2-water bucket roller, 3-sink, 4-suction device, 5-compressed air, 6-air scraper
Although this device solves the problem of the backflow of fountain solution, its suction nozzle and blow nozzle are easily soiled and are accompanied by a certain noise during work, so it has not been widely used at present.
The most direct advantage of using a non-contact dampening device is that the emulsion on the printing plate will not flow back into the water bucket, so that the solution in the water bucket can be kept clean, and the printing plate appears dirty due to water. The possibility is effectively avoided. Of course, this kind of wetting device also has its own shortcomings. For example, the mechanism is generally more complicated, and many performances are unstable, and it is more troublesome for the operator to grasp. It â€™s not a big reason for it.
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