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The water delivery mechanism is a unique mechanism in offset printing and is a very important part of offset printing. It can be said that for the offset printing machine, whether it is the design or use of the dampening device, it is very important for the final printing of high quality printed matter.
At present, in the more common printing machines in China, the more common dampening mechanisms can be divided into contact type and non-contact type. Among them, the contact type has two types: intermittent type and continuous type. Non-contact type: brush roller type, centrifugal type, roll-free version and other forms. Here are some simple introductions to these types of wetting methods:
(1) Contact dampening device: This device is a dampening form in which the dampening solution in the water bucket is conducted by various water rollers to the surface of the printing plate for wetting.
a) Intermittent: It means that the bucket roller does not use continuous rotation, but relies on the intermittent rotation of the bucket roller to intermittently transfer the dampening solution to the printing plate.
b) Continuous: Compared to the batch type, the continuous dampening mechanism removes the reciprocating oscillating water transfer roller, so that the dampening solution can be continuously supplied to the printing plate.
(2) Non-contact dampening device: This device sprays or coats directly onto the printing plate without passing through the water roller during the transfer process from the dampening solution in the water bucket to the printing plate. There is no real contact between the parts in the organization and the printed version. This type of dampening method has a small amount of water on the surface of the water roller, so it is also called a dampening method without a water storage or a continuous dampening method.
First, the contact dampening mechanism, the transfer method of dampening solution is intermittent.
The structure of this dampening device can be divided into:
1. Water supply part: consists of water bucket 1, water bucket roller 2, water supply roller 3. Its function is to supply water to the water-repellent portion quantitatively as needed for printing.
2. Water-receiving part: There is a water-feeding roller 4. Its function is to smooth the water in both the circumferential and axial directions and deliver it to the water roller.
3. Watering part: consists of two watering rollers 5, which function to uniformly coat water on the surface of the printing plate.
The water fountain roller of this dampening device is controlled intermittently by a ratchet and a pawl.
The disadvantage of this type of mechanism is that the inertia caused by the reciprocating oscillation of the water transfer roller and the water roller causes the pressure between the water rollers to be uneven, and the principle of the intermittent water transmission drive itself (such as the transmission principle of the ratchet and the pawl). , resulting in an inability to perform effective micro-control of water. In addition, due to the relatively large water storage capacity of the water roller, the control of the water quantity is relatively slow. Even with very precise water quantity control, the amount of water that the printing plate transmits to the paper surface is relatively large, which causes the final control of the quality. A great influence; moreover, the water roller used by the mechanism is often contaminated with ink or hair loss, so the water roller must be replaced frequently, which is difficult for high-quality and high-speed printing production. of.
Second, let's look at several continuous dampening mechanisms.
The continuous dampening unit can directly wet the printing plate by the water roller, or transfer the dampening liquid to the first inking roller, and transfer the dampening solution and ink to the printing plate (ie the famous Dagren mechanism) ).
(1) The outstanding advantages of the continuous dampening mode are stable water supply, easy control, wide application range, good quality of printed products and low cost, so it can be said that it is the mainstream of printing today.
The continuous dampening unit can use a common dampening solution, but now more is the use of alcohol dampening solution. At present, alcohol dampening solution is widely used at home and abroad, such as in flat offset printing machines in some countries such as Germany, the United States, and Japan. The alcohol dampening solution is essentially adding 10-20% alcohol to the ordinary dampening solution, which causes the surface tension of the dampening solution to be significantly reduced, and the contact angle of the dampening solution is also significantly reduced compared with the ordinary dampening solution. That is to say, the wetting performance has been greatly improved. Therefore, the amount of dampening solution can be greatly reduced.
(2) Dagren wetting device
The dampening device is a contact continuous dampening device that supplies water to the printing plate by the first inking roller. The dampening device was pioneered by American Harold Dagren, and the Dagren Run Edition device was named after it. It is generally believed that the Dagren dampening device has the following features: simultaneous water transfer and ink transfer from the first transfer roller to the printing plate to reduce the wear of the printing plate; before the printing, the inking device reaches the ink balance in advance, reducing The first printed waste; easy to operate, low water consumption, printing can be quickly dried.
The water fountain roller 1 is driven by a separate DC motor, and its surface linear velocity is 20% to 50% lower than the surface linear velocity of the plate cylinder. The metering roller 2 is rotated by the water fountain roller 1 to form a very thin water film therebetween. Therefore, the water fountain roller transfers the water to the printing plate by the water film having a uniform surface and then the speed difference from the first inking roller 3, and wets the printing plate. The inking roller 3 plays the dual role of the plate roller and the plate roller. It is worth mentioning that, because the ink roller 3 is constantly accumulating ink, the alcohol content in the dampening solution is generally as high as 20% to 30%, so that the easily generated paste failure can be effectively reduced.
A patented, unique ALCOLOR alcohol dampening unit schematic.
The device has five water rollers. In the figure, 1 is a water roller made of rubber material, 2 is a metering roller polished with a chrome layer, and 4 is a water roller which is not polished but is also plated with a chrome layer. 5 is a middle bar of nylon material, continuous inking device and water delivery device, playing an important pivotal role, 6 is the first inking roller.
The dampening solution required for the printing plate is mainly supplied by the water roller 3, and the dampening solution required for the ink infusion device to achieve the balance of the ink is transferred by the intermediate roller 5, the inking roller 6, the intermediate roller 5, the watering roller 3 and The surface speeds of the water-repellent roller 4 and the plate cylinder are the same.
The water fountain roller 1 is directly driven by the motor and is adjusted by the speed compensation of the electronic control circuit, and then transmitted to the shaft end gear transmission metering roller 2, so that the metering roller always rotates at the same speed as the water fountain roller, in both A very thin wetting film is formed (the thickness of the wetting film can be controlled by a motor with stepless speed regulation). The water roller 4 and the water roller 3 are rotated by the plate cylinder. The speed of the water roller is faster than that of the metering roller 2, and when the two are in contact, the wetting film is elongated and thinned, and can penetrate into the ink of the water roller, and then wet the printing plate.
The working procedure of the device is:
1. Non-working position: the metering roller 2 and the water-feeding roller 3 are disengaged, and both the water-feeding roller 3 and the inking roller 6 are disengaged from the printing plate. The ink is transferred from the inking roller 6 to the water roller 3 and the water resering roller 4 via the intermediate roller 5, while the water fountain roller 1 and the metering roller 2 are also operated to prepare the liquid supply. In this position, the dampening unit can be cleaned by the inking unit.
2. Pre-wetting position: the metering roller 2 is in contact with the water-feeding roller 3, the intermediate roller 5 is also in contact with the inking roller 6, and the fountain solution is transferred to the rollers 3, 4, 5, and 6 with ink to make the inking device The ink roller in the middle absorbs a certain amount of water to achieve the ink balance. The water-feeding roller 3 is in contact with the printing plate, and after the pre-wetting of the printing plate for 6 times, the printing process can be carried out.
3. Official printing position: Both the watering roller 3 and the inking roller 6 enter the working state, that is, water and ink are simultaneously delivered to the printing plate. The inking roller 6 is in contact with the printing plate and enters normal printing. Due to the pre-wetting position, the water and ink quickly reach equilibrium on the plate, and prints that meet the quality requirements can be obtained from the beginning of printing.
In addition, the device is also provided with a blowing rod on the ink roller, which will cause a local excess of the dampening liquid to volatilize, thereby realizing the control of the size of the local dampening solution.
Third, non-contact dampening device
Water bucket roller
Scraper
3. Adjustment screw
4. Water shield
5. Water roller
6. Heavy roller
7. Water roller
8. Water roller
9. Water bucket
10. Plate cylinder
1. Brush roller water supply device. The brush roller dampening device was developed in the 1960s. The basic principle is that the water roller 1 is made into a brush roller, and the tributary motor directly drives the rotation to bring up the water in the water bucket, and the water is bounced to the water roller 7 by the scraper 2, and the water roller 5 is passed through the water roller 5 . It is passed to the water roller 8, and then directly passed to the printing plate by the two watering rollers 8 for wetting.
The device is convenient for adjusting the water supply amount. When the overall adjustment, the rotation speed of the water roller driving motor is changed, and the position of the water shielding plate can be adjusted during partial adjustment, so that the amount of water supply can be controlled more accurately.
Brush dampening device. The brush roller 2 and the water fountain roller 1 are always in contact with each other and rotate at the same speed. Therefore, the water adsorbed on the surface of the water fountain roller is sprinkled by the brush roller onto the water roller 3, and is transmitted to the printing plate via the water roller 4. 5. The speed of the water bucket 1 determines the amount of water.
The brush roller water supply dampening device adopts a separate transmission, and the dampening liquid, paper wool, dusting powder, emulsion ink and the like on the printing plate are not easily returned to the water bucket, thereby keeping the dampening liquid clean. Sex. But its uniformity is not particularly ideal.
2. Centrifugal spray dampening device
Spray dampening unit. The basic principle of the device is that the smooth chrome roll 1 is driven by a separate DC speed motor and immersed in water for rotation. The perforated cylindrical mesh cylinder 5 has a fine mesh woven outer casing and is rotated by the chrome-plated roller 1 by friction. One side of the compressed air chamber 6 (air supply by the air pump) has a row of nozzles in the axial direction, and the chrome roller 1 is transmitted to the braided outer casing 5, and the water is sprayed into a mist and is sprayed onto the roller 7, and then the water roller 8 is The printing plate is wetted by a water roller 9.
Since the angle of the jet can be adjusted, a row of adjusting screws 4 along the axial direction of the chrome roller 1 is used to adjust the gap between the squeegee and the chrome roller, so that the water supply amount of each section along the axial direction of the chrome roller can be adjusted more accurately. In the device, a water tank is additionally provided, and the water pump circulates water supply by the water pump.
Rotor
2. Water
3. Return water
4. Water supply
5. Water transfer baffle
6. Plate cylinder
Another centrifugal spray dampening device: a turbo dampening device.
The characteristics of the above two centrifugal spray devices are basically similar to those of the brush dampening device. The water supply part and the water supply part are not in direct contact, and the dampening solution does not reverse flow, and the water supply amount can be controlled by adjusting the rotation speed of the water fountain roller. The uniformity of the water spray on the printing plate is better than the brush roller wetting, but because of its high cost, the wetting effect is not very significant, so it has not been promoted.
3. No roller wetting device
Rollless wetting devices typically operate using an air squeegee or nozzle system using the principles of spray, ultrasonic, static, and condensation.
The well-known non-roller wetting device includes the Murun Run version device and the Luotai Xun system dampening device.
These two devices are used sparingly compared to other types of dampening devices. In fact, the use of non-contact dampening devices is not a lot. So there is not much to introduce here.