How to adjust the water delivery mechanism of offs

2022-08-20
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How to adjust the water delivery mechanism of offset press

the quality of offset printing products is inseparable from whether ink and water maintain a certain balance. In the printing process, too much or too little water supply is often prone to occur, because the size of the printing plate moisture is from the dirty side of the printing plate. However, the so-called dirty is not just caused by the small amount of water. Operators often mistakenly increase the amount of water supply, causing the ink and water to lose balance, forming a vicious cycle. What are the printing consequences of excessive moisture

1. Diluting the ink makes the ink light and dull, which affects the color of the print. If we use the method of increasing the amount of ink to save the lack of ink, it will cause the ink to be large and the water to be large, making the image thick, blurred and unclear

2, causing ink roller deinking. When it is serious, there will be accumulated water on the whole ink roller, so that the text part of the printing plate cannot get the normal ink supply, resulting in the "blooming" of the text

3. Affect the drying of imprinting. If excessive water is mixed into the ink, it will inhibit the drying of the ink. In addition, more moisture is absorbed in the paper, and the drying speed of the product will be slower

4. Paper fibers absorb too much moisture, which will produce deformation and cause inaccurate overprint. It will also make the paper loose in texture, easy to lose hair, and accumulate on the blanket or printing plate, which will seriously affect the quality of integrated design products in the printing production

5. The ink emulsifies, making the ink lose its viscosity. After emulsification, the ink can not protect the pictures and texts of the printing plate, which is easy to cause "flower plate", and at the same time, it will reduce the printing resistance of the printing plate

through the above analysis, it shows that the balance of ink and water is a key link in offset printing. Besides relying on experience, it is more important for the operator to master the correct use and adjustment of the water conveyance mechanism of the offset press

in order to make the water supply of the water transmission mechanism meet the requirements of printing production, the water transmission mechanism is equipped with devices to control and adjust the water. This can be divided into three parts according to the nature of their work: first, water supply devices; Second, water homogenizing device; Third, water supply device

the water supply device is mainly composed of water tank, bucket roll and water transfer roll. The water tank is used to store water, and there is a bucket roll (also known as water outlet roll) on its upper part. The lower half of the bucket roll is immersed in the bucket solution, and they do not contact or support each other. In addition to the automatic water dispenser (which has been used by many manufacturers), you can also add water manually. Adding water manually requires the operator to add the pre prepared solution to the water tank. Finally, people in the industry say that they often add it to the water tank continuously. Since the water supply volume in the bucket roll is related to the height of the bucket solution, the bucket solution in the water tank must maintain a certain water level to make the water supply uniform. The operator should not be impatient when adding water to the bucket solution, but should slowly add the bucket solution to the water tank, and should not swing the solution in the water tank. If it swings, first, it causes the local moisture to suddenly increase during normal printing, affecting the quality of products; Second, the water bucket solution will drip to the front gauge part below the water tank, causing abnormal paper feeding and clutch pressure (this is because the solution drops to the electric tooth part of the front gauge, forming conductivity); Third, it drips on the printing products, causing water spots on the paper, and it is easy to appear double sheets when printing the next color

the water transfer roll, also known as the draft roll, is a rubber roll installed between the bucket roll and the water string roll, which swings back and forth to transfer water, and its surface is covered with water roll fleece. The adjustment requirements of the water transfer roll are that the draft should be parallel to the bucket roll and have appropriate pressure, which is adjusted by the tension springs on both sides. During adjustment, the tension of the tension spring must be consistent to ensure that the water transfer roll works parallel to the bucket roll during draft. When feeding water, it depends on the cam. When adjusting, the water transfer roller must be placed on the water string roller with appropriate pressure. There is an adjusting screw and a positioning support on both sides of the lower part of the water roller. During adjustment, it is also required that the water transfer roll and the water string roll remain parallel. The water transfer roller also has a clutch device for draught if this kind of phenomenon occurs again. When opening and closing the press, the normal draught water supply swings back and forth through 220V 0.7kg iron suction. Stop swinging back and forth when releasing pressure, that is, no longer lean against the water outlet roll. The buttons of water supply on and off on the console are used to control this iron suction, and they work according to the production situation. We sometimes find that the moisture content of the press plate increases after the press is released and then closed during normal printing. Why? This is because after the iron suction stops working, the tension of the top claw tension spring next to the iron suction is not enough, causing the drum to be still draught away from the press water transfer roll. The machine stops draught after running for oneortwo cycles. The iron suction copper head retracts slowly oneortwo beats due to the insufficient force of the top claw tension spring, which is the reason for the increase of water in the layout. It's easy to solve this problem. Just change a new tension spring or shorten the old tension spring by oneortwo sections

the homogenizing device is mainly a water roller. It is generally made of corrosion-resistant metal materials. In order to make the water on the water roller uniform, the water string roller has not only rotating motion, but also axial motion. The surface speed of the water roller is equal to the surface speed of the printing plate, so as to keep the water roller close to the plate moving at the same speed. The axial movement of the water roller is adjusted through the eccentric connecting rod, which is relatively simple, and generally does not need to be adjusted in the printing process

the water supply device can be called the plate water roller or the plate water roller. Generally, it is two, and its surface is wrapped with water roller fleece with good water absorption like simultaneous interpreting water roller. The function of the plate water roller is to transfer the aqueous solution from the water transfer roller and the water roller evenly to the printing plate. Its surface speed must be equal to the speed of the printing plate surface. Axial movement and radial runout are not allowed, which will not only turn waste into treasure, but also easily cause damage to the printing plate. The requirements for adjusting the water roller of the plate are relatively high, and the adjustment must be carried out according to the steps. First adjust the eccentricity so that the pressure between the water roller and the water roller is just right. Then adjust the cone head so that the pressure between the plate water roller and the printing plate is appropriate. The above method is to explain that when adjusting the eccentricity, it will not only change the pressure between the water roller and the water roller, but also affect the pressure between the water roller and the printing plate

when adjusting the cone head, only change the pressure between the water roller and the printing plate, while the pressure between the water roller and the water roller does not change. When adjusting the plate water roller, you should first adjust the water roller, and then adjust the water roller. The pressure of the upper water roller is better than that of the lower water roller, because in this way, the upper water roller can be used to collect the excess water. This is an experience gained from practice. When adjusting the pressure of the plate water roller, special attention should be paid to the adjustment eccentric position at both ends. If the difference is too large, it will cause the position of the plate water roller and the printing plate, the water roller is not parallel, which is easy to cause the problems of loose at both ends and tight in the middle. Therefore, when adjusting the plate water roller, we must use the method of correcting the center distance to measure the tightness between the two ends and the middle. Therefore, when adjusting the water roller against the plate, we must use the method of correcting the center distance to measure the two ends and the middle three points, so as to prevent the contact pressure between the water roller and the printing plate from being too heavy. Otherwise, the friction of the printing plate will increase and be worn, so that the printing plate graphics and texts will be "embossed", and the printing resistance will be reduced. In addition, it will also cause the water roller to jump when contacting the printing plate, so that the jumping part will be dirty, and the part that falls again will have a "water bar" (i.e. white bar). However, the contact pressure between the plate water roller and the printing plate should not be too light, which is easy to cause insufficient water supply of the plate and cause dirt. If the water supply is improperly increased, it will cause excessive moisture in the layout. So how to determine whether the contact pressure is in the best adjustment position? According to experience, it is by pressing the water roller against the printing plate, starting the machine, and then touching the support seat of the water roller against the printing plate with your hand to identify whether there is jumping during operation. Because the printing plate cylinder has the difference between the printing surface and the neutral position, the weight of the contact pressure by the plate water roller is easy to be felt. Generally, I feel a slight beating. In general, a slight beating feeling is the most appropriate. If the beating is very serious, it means that the pressure is too medium, and then it should be adjusted again

to adjust the water conveyance mechanism, the following work needs to be done: first, the liner of the printing plate should be composite standard; Second, the aqueous solution in the water tank should be free of impurities; Third, the water roller should be changed frequently; Fourth, the water outlet roll and the water string roll should be wiped frequently and must be kept clean. (end)

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