Several non-contact dampening devices
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In modern water offset printing, there are two main types of wetting, one is contact type and the other is non-contact type. We see a lot of contact type wetting device in production, and the non-contact type is relatively less. In this article, we briefly introduce several non-contact wetting devices.
1. Brush roller dampening device
As one of the non-contact type dampening devices, Mitsubishi used a brush roll dampening device in the early models. The previous bucket roller was converted into a brush-type roller made of nylon material and immersed in the fountain solution. The brush roller is directly rotated by the motor and can be steplessly regulated. The main function of the brush is to bring the water out of the bucket. A squeegee is placed near the brush, mainly to drive the water from the brush. After the water is shot, it is bounced to the water roller, and then passed through the water roller to the water roller to realize the non-contact water supply. The amount of water is determined by the rotational speed of the brush and the position of the water shield. The adjustment of the size is also divided into the whole and the fine adjustment: the overall adjustment can be made by changing the rotation speed of the water roller drive motor; the fine adjustment is to adjust the adjustment screw for controlling the water shield, so that the position of the water shield is appropriate, so that it can be accurately The amount of water that is controlled by the amount of water. If the water shield is also remotely controlled by the motor, the 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-shield, 5-water roller, 6-press roller, 7-string water roller, 8-water roller, 9-water bucket
Another structure of the brush dampening device is the hair brush dampening device of Harris, USA. In this structure, the brush roller is not directly immersed in the dampening solution, but is always in contact with the water fountain roller in the water bucket, and both rotate at the same speed in the same direction, and the water sucked up in the water fountain roller The coat roller is sprinkled onto the water roller, and the water is applied to the plate through the water roller. In this structure, the amount of water is determined only by the speed of the water fountain roller, and the precise control of the water output can be achieved by 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
The Heidelberg Speedmaster uses this device in some machine-type dampening systems, and this airflow spray device has its own unique features. The smooth chrome roll is immersed in the fountain solution and driven by a separate DC speed motor. The porous cylindrical mesh tube is covered with a fine mesh woven outer cover and is rotated by a chrome roll. One side of the compressed air chamber is opened in the axial direction with a row of nozzles, and the water on the woven mesh cylinder is sprayed into the water transfer roller, and then subjected to dampening through the water roller and the water roller. The control of the water supply of the system is determined by the amount of water transferred from the chrome roll to the cylindrical cylinder, so that the water supply amount of each section of the chrome roll axial direction can be completed when the gap between the scraper and the chrome roll is adjusted.
1-chrome roll, 2-water bucket, 3-blade, 4-regulating nut, 5-wire cylinder, 6-compressed air chamber, 7-water transfer roller, 8-string water roller, 9-water roller
Another type of water spray dampening device is simpler, that is, the water bucket roller with the net is continuously selected to turn the water up, and there is an air nozzle in the water fountain roller to spray water to the plate cylinder. The amount of water is controlled by the outlet adjustment plate.
1-Adjustment plate, 2-water tank, 3-water bucket roller, 4-air nozzle
This water jet dampening system makes it easier to evenly feed the plate.
3. Air scraper dampening device
Also known as the Murren Run version, it was developed by American Mullen. The water fountain roller of this device is a rubber roller which is mounted at a position of 0.1 mm from the surface of the printing plate and is continuously rotated to bring water to the plate cylinder in the form of a water film. The water supply of such a device is controlled by an air scraper, mainly by blowing in compressed air to blow off excess water, and then sucking off the blown water back to 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 backflow of dampening solution, its nozzle and mouthpiece are easily soiled and have a certain noise in operation, so it has not been widely used.
The most direct benefit of using a non-contact dampening device is that the emulsion on the plate does not flow back into the water bucket, so that the solution in the water bucket is kept clean and the plate is dirty due to water. The possibility is effectively avoided. Of course, the dampening device also has its own shortcomings. For example, the mechanism is generally complicated, and many performances are unstable, and the operator is troublesome to master. This may also be the scope of use of the non-contact dampening mechanism. Not a big reason for it.