How to do a good job of offset printing

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How to do a good job in offset printing "three leveling" is an important work in offset printing, a basic requirement for offset printing process operation, and one of the keys to achieve water ink balance. Only do a good job in the "three leveling" of offset printing, the quality of offset printing products will have a basic guarantee. Especially for the newly introduced second-hand Offset Press, this work should be done well. The author is here to talk about some experience in the work, in order to attract jade

the so-called "three leveling" of offset printing refers to the water roller leveling of offset printing machine. The ink roller is flat with the cylinder (printing plate, rubber and embossing cylinder), and the pressure is balanced and correct, so as to achieve ideal printing effect

water roll leveling

water roll leveling requires that the water roll should be straight, the surface should be flat, and the pressure of the water roll should be correct and uniform, neither too large nor too small. If the water roller is not leveled, the pressure between the water roller and the printing plate will be uneven, resulting in too much or too little water in the printing plate or uneven water coating, affecting the ink balance; As a result, the local pressure between the water roller and the printing plate and the cross water roller is too large or too small, resulting in unstable operation and accelerating the wear of the printing plate. To do a good job of leveling the water roll, pay attention to the following points:

1. check the parallelism of the water roll and whether the water roll is bent or deformed. If it is a remanufactured water roll, the rubber core of the water roll must be straight and the surface must be ground flat

2. the water roller fleece shall be well covered, sewn and firmly sewn. Pay attention to check whether the surface of the water roller fleece is flat and tight, and no relaxation is allowed. After the water roller is wrapped, it cannot be installed immediately. It should be scrubbed twice with the fountain solution, and can be installed only after it is fully wetted

3. correctly adjust the pressure of the water roll to make the left and middle. The pressure at the three points on the right is uniform. First adjust the pressure between the water roller and the water roller, then adjust the pressure between the water roller and the printing plate, and carefully measure the pressure at the left, middle and right points of the water roller repeatedly through the paper strip pulling method, so that the pressure at each point is basically balanced and consistent. Specific method: select the kraft paper strip with straight thread and cut it into 40cra. Width about 2cm, thickness 0 The paper strips between 1.5mm are placed between the water roller, the water roller or the printing plate respectively. After closing the water roller, pull the paper strip, adjust the hand wheel and the dial button to make it reach the tensile force of the paper tension. The paper

sheet can be pulled out without breaking. It is OK to confirm that it is appropriate

4. keep the bucket roll. Check whether the passive needle of the dial is clean. The water roller shall be thoroughly cleaned after work or after work. The cleaning shall start from the middle, and both ends shall be scraped and washed dry; After scraping, use your hand to flatten it anticlockwise; At work, the water roller shall be leveled first, and the two ends and the middle shall be carefully wiped

5. check the bearing of water roller. This is important, but easy to ignore. The bearing film material is a two-dimensional material composed of atoms, molecules or ions deposited on the surface of the substrate. The clearance and error are small, so the rotation can be stable and there will be no runout. If the bearing is worn and exceeds the error range, it will rotate unsteadily and affect the water transmission. At this time, the water roller can no longer meet the use requirements and should be replaced in time. During installation, attention should be paid not to exceed the error range. If possible, try not to use or use less ball bearings, but use roller bearings or needle bearings

inking roller leveling

inking roller leveling requires that the inking roller should be flat, the surface should be polished, the surface runout should not be greater than 0.05mm during operation, the inking roller pressure should be correct and uniform, and the surface performance of the inking roller should be good, with excellent inking performance, so as to ensure the uniformity of inking. stable. To do a good job of leveling the ink roller, pay attention to the following points:

1. the iron core of the ink roller shall be straight and the surface shall be flat. The surface runout shall be kept within 0.05mm as far as possible, and shall not exceed 0.1mm at most. Otherwise, excessive runout will directly affect the uniformity of ink transmission

2. the pressure adjustment method of the ink roller is similar to that of the water roller, and the same attention should be paid to the measurement and adjustment. Middle and right points to make their pressure equal and consistent. It is best to use the paper strip pull method for adjustment first, and then use the steel sheet test insertion method for adjustment. The specific operation method is similar to the strip pulling method, that is, insert and pull out the steel sheet at the corresponding position, and feel the strength is moderate according to experience. Generally, the thickness of the steel sheet is 0 2mm. Finally, the method of inking bar is used for testing. At present, most of the printed pieces are mainly printed by high-speed dot printing, so the width of inking bar is generally about 3mm

3. keep the bearing in good condition. If the wear is serious and the clearance has exceeded the error range, it should be replaced in time to ensure its smooth transmission and even ink transfer

4. the cleaning of ink rollers is also very important. At the end of work or after work, the accumulated ink and ink on all ink rollers must be thoroughly cleaned to reduce the color trace of energy consumption of 100million tons of standard coal. In addition to scraping the ink, it is also necessary to pour gasoline on the ink roller near the ink bucket to clean the waste ink on the ink roller. At the same time, the cleaned ink roller should be wiped dry with a clean, soft, lint free cloth

cylinder leveling

cylinder leveling requires that the printing plate, rubber and impression cylinder should be flat and straight, and should not be tapered. The center distance of the three cylinders should meet the standard. The cylinder should be straight and the graduation circle diameter of its transmission gear should be equal, and the liner should be flat, the rubber cloth should be smooth, the pressure between them should be uniform, and should be relatively constant in the production process. Among the three rollers, the rubber roller is most affected by the elastic deformation of the rubber blanket, so it is often the key to do a good job of roller leveling. A little careless handling will cause many problems, such as uneven pressure, point deformation, roller sliding, etc., resulting in accelerated plate wear. The following points shall be paid attention to when doing a good job of roller leveling:

1. ensure the quality of blanket and liner. In addition to the corresponding chemical or physical properties, the thickness shall be strictly measured. The thickness of the rubber blanket shall be uniform, and the flatness error shall be within 0.04mm. When measuring different parts such as its mouth and tow tip with a dry scorecard, each point shall be basically the same, and shall not exceed the allowable error range. E. there is oil leakage in the hydraulic system. The liner shall have certain hardness, finish and flatness. Manila paper is preferred as the backing paper. If other paper is selected, the paper with small thickness tolerance, uniform fiber interweaving, no holes and pulp blocks, certain tensile strength and not easy to crush shall also be selected. The wool and felt backing materials shall have certain mechanical strength, tension resistance and elasticity. The texture is dense and uniform

2. when checking the flatness of the rubber roller, the method of printing a full plate and drawing a map is usually used. Using the uniform ink layer coated on the printing plate, the surface of the blanket presents an uneven map like shape when the blanket is not fully in contact with the printing plate. Based on this, check its surface flatness, draw with a pencil, and fill the low part of the blanket with paper of different thickness to make it smooth. However, the following points shall be noted:

(1) the size of the paper pad area shall not exceed the original size of the graphics in the low recess, and there shall be no hard mouth. It is best to tear it by hand

(2) pay attention to the amount of padding, and adopt the method of gradually thickening to avoid over thickening at one time

(3) in case of multi-layer padding, the padding area shall be covered from small to large, instead of the same size of paper

3. roller leveling shall be carried out regularly, with an average of about 3 months

4. center distance between rollers. After the pressure is corrected, check whether the roller pressure is correct by the pressure bar method or the paper strip pull measurement method

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