Adjustment of drum pressure of the hottest J2108 o

2022-09-22
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J2108 offset press cylinder pressure adjustment

the offset press printing cylinder constitutes the heart part of the offset press. Regardless of the structure of the offset press and the matching accuracy of each part, it is for the same purpose, that is, to print good products. The roller parts of offset press are directly related to the quality of printing products. A good printing sample should have good mechanical equipment and high-precision parts, as well as good adjustment accuracy and use accuracy. Therefore, in order to achieve the complete reproduction of graphic points on a print, the change of print graphics, the printing plate's printing resistance, the length of the service life of the blanket, whether the machine itself is reasonably used, and the wear speed of the roller bearing sleeve and gear, all need to be adjusted and used properly. If the adjustment is not used properly, there may be printing and mechanical failures, such as "paper escape", "point deformation", "stencil", "paste plate", "ink bar", and so on. We should still try our best to start a series of problems from a scientific point of view. These problems are often caused by the improper adjustment of the center distance of the printing drum, that is, the improper printing pressure

printing is inseparable from pressure. Without pressure, the graphic ink on the printing plate cannot be transferred to the blanket, and the graphic ink on the blanket cannot be transferred to the paper, so there is no printing without pressure. Among the cylinders that make up the printing system, the surface of the printing plate cylinder needs to be equipped with printing plates and pads, and the rubber cylinder needs to be equipped with blanket and pads. During this period, the thickness of the paper on the embossing cylinder is not fixed, and the center distance between the cylinders is adjusted. Therefore, it involves a series of problems such as the calculation of the lining of the cylinder and the determination of the center distance. A principle should be mastered when adjusting. Under the condition of ensuring the accurate restoration of the printing sheet, the smaller the pressure, the better. At the same time, it also depends on whether the operator accurately and reasonably wraps the drum according to the specified data and the requirements of the surface linear speed of each drum as consistent as possible

if the adjustment of the center distance of the drum and the calculation of the lining are not appropriate, the drum radius may be unequal, resulting in the speed difference and sliding friction that should not exist. Pressure plays a decisive role in the printing process. When flattening the pressure, we should be very careful and know well. We should carefully analyze and study the factors affecting the pressure and measure accurately. Some factors that determine the printing pressure, such as the quality of the printing paper, the printing speed, the quality requirements of the product, the elasticity of the blanket and its liner, etc., need to be considered when adjusting the center distance of the drum and determining the liner thickness. For the paper with rough printing surface and uneven thickness, the printing pressure should be increased enough to make the impression strong, and the smaller the pressure, the better. The pressure can be judged by trial printing of samples. The pressure of white paper and offset paper is slightly higher than that of coated paper. When the printing speed increases, the printing pressure also increases. Because when the printing speed is increased, the contact time of the corresponding particles between the printing surfaces is also reduced. Different products also have different replication requirements. In addition to using different raw materials and printing plates, we can also try to adjust the printing pressure. Printing map text can make the pressure slightly higher within a certain range, so as to meet the requirements of strong imprinting. When printing line version text, we should pay great attention to the ideal pressure, so as to avoid the loss of hierarchy due to the expansion of points. In printing, attention should be paid to the ink balance of the layout. The deformation characteristics of the blanket and its backing materials are closely related to the printing pressure. The blanket that is elastic and is not easy to lose its elasticity after a large number of printing should be selected. The printing pressure can be changed by increasing or decreasing the pad. When selecting the center distance and pressure package lining, the surface linear speed of each drum in the rolling process of mutual contact transfer ink should also be considered. The ideal state should be that the surface linear speed of each drum is equal and pure rolling, so that there is no relative friction between the surfaces during rolling. But in fact, due to the change of paper thickness and the elastic deformation of blanket and liner, there is a certain pressure between the rollers, which makes the linear speed of the three roller surfaces different. This can only be made up by correctly and reasonably adjusting the center distance between the rollers and changing the lining

in order to minimize this friction and improve the service life and printing quality of the printing plate, it is necessary to make the radius of the cylinder after lining as close to the same as possible and minimize the surface speed difference. The key here is the elastic deformation of the blanket. Therefore, it is necessary to select reasonable data on the compression deformation index of blanket, and whether the printing pressure is appropriate is ultimately reflected in the print. Next, the printing pressure is calculated

known conditions:

the diameter of the embossing cylinder is φ 300mm;

diameter of rubber roller body is φ 293.5mm 

the diameter of the printing plate cylinder is φ 299mm 

the diameter of the graduation circle of the drum gear is φ 300mm。

choose neutral liner material, the thickness of printing paper is 0.1mm, and the maximum compression deformation between printing plate and rubber is f = 0.2mm, that is, the printing pressure is 0.2mm. Because the diameter of the impression cylinder is φ 300mm. When printing with 0.1mm thick paper, during printing, the paper wraps the cylinder of the embossing cylinder, so that the outer circle diameter of the cylinder in the printing state increases to about 300.2mm

therefore, I cover an area of 8000 square feet. When considering the lining of the printing plate and the rubber drum, we should also make the diameter of the drum after the lining of these two drums close to the diameter of the embossing drum in the printing state, that is, 300.2mm

the diameter of the rubber drum is 293.5mm, and the total thickness of the package on it is about:

h rubber = (300..5)/2=3.35mm

if the thickness of rubber blanket is 1.85mm, the lining thickness is:

h 'rubber =3 85=1.5mm。

the diameter of the printing plate cylinder is 299mm, and the total thickness of the package on it is about:

h seal = (300.)/2=0.6mm。

if the printing plate used is a standard PS plate with a thickness of 0.3mm, the thickness of the printing plate pad lining is:

H 'print =0 3=0.3mm。

after calculating the total thickness of the wrap on the surface of the rubber cylinder and the printing plate cylinder, we can calculate the gap between the rubber cylinder and the printing plate cylinder and the embossing cylinder back, that is, the gap value of each cylinder to be adjusted. If the used printing pressure f = 0.2mm, the drum body gap between the rubber drum and the embossing drum should be:

ca=3.35+0 2=3.25mm

similarly, the gap between the rubber cylinder and the plate cylinder body is:

cb=0.6+3 2 = 3.75mm

in the actual printing process, the pressure between the printing plate and the rubber cylinder can be slightly smaller. If we take the printing pressure between the printing plate cylinder and the rubber cylinder as 0.15mm, the gap between them can be adjusted as:

C 'b=0.6+3 15=3.8mm

in the process of normal pressure, due to the gap between the roller bearings, the gap size varies with the machine, and is generally controlled within the range of 0.05mm, which is what we usually call the drum clearance value. Under the action of printing pressure, the center distance of the drum will increase by about 0.05mm, which should also be taken into account when accurately calculating the center distance of the drum

the thickness of the rubber drum should be 0.05 ~ 0.10mm greater than the calculated thickness h before it is loaded into the drum, because according to the actual test, the thickness of the blanket will be reduced by about 0.05 ~ 0.10mm after it is loaded into the drum, and the paper thickness a is about 0.1mm for common paper, which can be regarded as the lining of the embossing drum. The center distance between the front rubber drum and the embossing drum is calculated based on the paper thickness a = 0.1mm. When the paper thickness is greater than 0.2mm, the center distance between the rubber cylinder and the plate cylinder should be adjusted

there are two methods to adjust the pressure, that is, changing the center distance of the drum through the adjustment mechanism and changing the drum diameter by increasing or decreasing the drum lining to change the printing pressure. No matter which method is used to adjust the pressure, we should first consider the nature of the printed paper, thickness, type of printing plate and its requirements for products, and then determine the printing pressure. The printing pressure of the drum should be higher if the soft lining is used, and lower if the hard lining is used. The size of the pressure is actually determined by the deformation degree of the two contact areas. The softer the material, the greater the deformation degree, and the greater the pressure used. On the contrary, the pressure is smaller. In general, the pressure can be changed by changing the gasket. When the thickness of the paper changes greatly, the printing pressure should be changed by adjusting the center distance between the rollers through the pressure regulating mechanism. However, it should be noted that improper lining is easy to cause printing elongation or shortening failure. The center distance between two sides of the drum must be adjusted at the same time when the pressure regulating mechanism is used to adjust the drum center distance, so that both ends of the drum translate parallel, which can be ensured by adjusting the equal shoulder iron gap on both sides of the two drums. The specific steps are as follows:

1. Remove the printing plate, blanket and gasket on the drum, and clean the tested part of the drum with gasoline

2. Manually close the pressure until the drum is fully closed, and measure the pressure in the closed state. Based on the impression cylinder, first measure the center distance between the impression cylinder and the rubber cylinder, synchronously press both ends of the soft fuse with appropriate diameter into the gap between the shoulder iron of the cylinder for turning (turning), take it out after rolling, measure its thickness, and adjust the corresponding pressure regulating mechanism to make the indentation thickness of the fuse on both sides meet the requirements and equal, or directly measure the cylinder body, Take three representative points on the drum body (the three points should be on the same straight line) for measurement

3. Adjust the center distance between the rubber cylinder and the printing plate cylinder in the same way. Because the impression cylinder is a reference cylinder, the adjustment of the impression cylinder and the rubber cylinder is achieved by adjusting the eccentric sleeve of the rubber cylinder. When adjusting the center distance between the rubber cylinder and the printing plate cylinder, it is achieved by adjusting the eccentric sleeve of the printing plate cylinder

in 4. The intelligent judgment function of the experimental results should pay attention to the adjustment range of the center distance when adjusting the center distance of the drum. If the center distance is too small or too large, it is not allowed, and it should be adjusted strictly in accordance with the instructions of the machine

(author/Wei Xin)

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