The quality of offset printing products is inseparable from whether ink and water maintain a certain balance. In the printing process, the water supply volume is too large or too small is often easy to occur, because the size of the printing plate moisture is manifested from the printing plate dirty. However, the so-called dirtying is not only caused by the small amount of water. The operator often incorrectly increases the amount of water supply, causing the ink and water to lose balance, forming a vicious circle. What are the printing consequences of excessive moisture?
1. Dilute the ink color to make the ink color lighter and dull, which affects the color of the printed product. If the method of increasing the amount of ink is used to save the ink color, it will cause large ink and large water, making the image thick, blurry, and unclear.
2. Cause the ink roller to deink. In severe cases, there will be accumulated moisture on the entire ink roller, so that the plate image and text part cannot get the normal ink supply, causing the plate image and text to "bloom".
3. Affect the drying of the blot. If excessive water is mixed into the ink, it will inhibit the drying of the ink. Coupled with the absorption of more moisture in the paper, the product will dry more slowly.
4. The paper fiber absorbs too much water, which will cause deformation, resulting in inaccurate overprinting. It will also make the paper texture loose, easy to fluff, and pile up on the blanket or printing plate, which seriously affects the quality of the printed product.
5. The emulsification of the ink causes the ink to lose its viscosity. After the ink is emulsified, it cannot play a protective role on the printing plate's graphics and text, which is easy to cause "pattern", and at the same time will reduce the printing plate's durability.
Through the above analysis, it is shown that the mastery of water-ink balance is a key link in offset printing. In addition to experience, the operator is more important to master the correct use and adjustment of the water delivery mechanism of the offset press.
In order to adapt the water supply of the water delivery mechanism to the requirements of printing production, the water delivery mechanism is provided with a device for controlling moisture and adjusting the amount of water. This can be divided into three parts according to their working nature: one is the water supply device; the other is the water leveling device; the third is the water supply device.
The water supply device is mainly composed of a water tank, a water bucket roller and a water transfer roller. The water tank is used to store water, and there is a water bucket roller (also called water outlet roller) on the upper part. The lower half of the hopper roller is immersed in the hopper solution, and they do not contact or support each other. In addition to adding water by an automatic water dispenser during operation (many manufacturers have not used it), water can also be added manually. Manual water addition requires the operator to constantly add the previously prepared solution to the water tank. Since the water supply in the bucket roller is related to the height of the bucket solution, to make the water supply even, the bucket solution in the sink must maintain a certain water level. The operator should not be anxious when adding the water bucket solution, and slowly add the water bucket solution to the water tank, and cannot stir the water tank solution. If it oscillates, one causes the local moisture to suddenly increase during normal printing, which affects the quality of the product; the other is that the bucket solution will sprinkle and drip onto the front part under the sink, causing abnormal paper feed and clutch pressure Dropped on the electric teeth of the front gauge to form a conductive); third is dropped on the printed product, causing water droplets on the paper, and it is easy to appear double sheets when printing the next color.
The water transfer roller, also known as the draft roller, is a rubber roller that is installed between the water bucket roller and the string water roller and swings back and forth to transfer moisture. Its surface is covered with water roller fleece. The adjustment requirement of the water transfer roller is that it should be parallel to the water bucket roller and have appropriate pressure when draught. It is adjusted by the tension springs on both sides. When adjusting, the tension of the tension spring must be consistent to ensure that the water transfer roller works parallel to the water bucket roller when draught. The water supply depends on the cam, and the adjustment must put the water transfer roller against the string water roller with proper pressure. There are an adjusting screw and a positioning backing on each side below the water roller. The adjustment also requires the water transfer roller and the water string roller to remain parallel. The water transfer roller also has a draught clutch device. When opening and closing the press, the normal draught feed water swings back and forth through the 0.7V iron suction of 220V. Stop swinging back and forth when the pressure is off, that is, no longer lean on the water outlet roller. The buttons for water supply opening and water supply stop on the operation table are used to control this iron suction, and they work according to the production situation. Sometimes when we print normally, we will find that the moisture on the press surface becomes larger after the pressure is removed. why? This is because after the iron suction stops working, the pulling force of the top claw tension spring beside the iron suction is not enough, which causes the drum to still be draught from the pressure water transfer roller. The strength of the tension spring is not enough, causing the suction iron to retract one or two beats, which is why the moisture on the layout becomes larger. Solving this problem is very easy to do, just change a new tension spring or shorten the old tension spring by one or two knots.
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