Screen stretching skills of screen version in the

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The stretching skills of the Chinese version of silk screen printing

1. The stretching tension depends on the 2D vibration valve, which has two degrees of freedom of movement: the rotation in the circumferential direction and the linear movement in the axial direction. According to

in silk printing, the mesh number, diameter, spinning method and material of the silk directly affect the stretching tension. During stretching, the tension of the silk is measured according to these parameters. When measuring the tension, the tension point to be detected should be 10cm away from the inner edge of the frame, Otherwise, the measured tension is inaccurate

see the table below for the maximum allowable values of Sefen pet 1000. The maximum tension value indicated in the table is the display of specific wire strength, that is, the maximum tension value that can withstand and rebound for various mesh sizes and different wire diameters. If the tension value given in the table is exceeded, the wire will lose elasticity and become plastic deformation, which should be paid attention to in tension

unit of tension: Newton/cm (n/cm), which can be measured by Newton tensiometer. The tension can be measured in the warp and weft directions according to the relevant national standards. The so-called warp tension of silk is the tension in the winding direction of the whole reel of silk, that is, the tension in the direction of edge typing; The weft tension of silk is the tension in the direction of silk width

it can be seen from the tension table that the tension of wires with different diameters and mesh numbers made of the same material is different, that is, the tension of wires with the same mesh number is different, that is, the tension of wires with the same mesh number is different, because the tensile tension is in direct proportion to the wire diameter. For example, if a is twice the radius of wire B, the tensile strength of wire a is 4 times that of wire B. The tension values in the table are valid for high-strength frames with side length less than 1 m. when the edge length reaches 2 m, the tension value shall be reduced by 15%-20%. When the frame side length reaches about 3 m, the tension given in the table shall be reduced by%. In order to ensure that the silk will not be torn during processing and printing, it is necessary that the tension should be a little lower than that given in the table

II. Tension requirements

1. Templates for different purposes require different levels of tension

for example, for color dot printing, in order to ensure the accuracy of tone value and good reducibility, the tension n/cm is required. Fine print, dial, etc., tension n/cm. For general graphic printing, the tension is n/cm

for manual printing, rough printing products, or those without requirements for accuracy and size, the tension is 6n/cm. It is worth noting that during color block overprint, in order to make the overprint position accurate, not only the plate tension should be greater than 10n/cm, but also the tension of several overprinted templates must be consistent, which is more important for dot printing, otherwise it will cause moire and hue deviation

2. Why does dot printing require high tension templates? This is because

a, the template with higher tension can obtain a lower pitch. When the pitch is doubled, the deformation of printed graphics and text will be increased by three times. Therefore, when the template tension is low, the inking will be uneven and the point will expand the deformation, which will further increase the influence of brand popularity

b, lower distance, less pressure can be used in silk screen printing, and the template wear is reduced, which prolongs the service life of the template

c, small scraping pressure is beneficial to avoid inking and deformation around the point, improve the sharpness of the point edge and ensure the printing effect

III. factors affecting tension

1. Tension equipment

a. pneumatic tension machine is a direct tension method. Because during stretching, the air cylinder support is always against the frame edge, and at the same time, it is subject to the reaction force of the wire being pulled, which makes the frame edge bend towards the center of the frame to obtain pressure. After the tension reaches a few, it is glued and removed after drying, so that the tension is more stable and it is easier to obtain tension. Disadvantages: A. in the whole process of stretching, the silk wind always extends outward (around) close to the adhesive surface of the frame, so the frame sets resistance to the smooth extension of the silk, which is often impossible to achieve under high tension; b. The pneumatic tension is controlled by the air pressure. Therefore, if the anti air pressure is adjusted higher during the initial tension, it will be broken under the instantaneous and rapid large tension; c. The tension is controlled by the capacity of the cylinder, otherwise the high tension cannot be reached

b. mechanical or electromechanical pulling equipment can be flexible and changeable according to the needs of tension. The mechanical pulling machine is an indirect stretching method, so when the wire tension reaches the required tension, the frame will rise against the wire, so there is no l) overload protection: when the load exceeds 10% of the rated value, the machine will be shut down for protection; When stretching, the wire is affected by the friction resistance of the frame, so the tension is easy to achieve uniformity

after stretching, the gap between the collets is allowed to be 2mm-3mm. Otherwise, when the distance is far, the wire part not clamped by the collet will not get the tension directly, so that the tension of all wires on the surface is uneven, the opening size and the wire diameter are inconsistent, and defects will appear in the printing, that is, the tension of the whole plate will be uneven with the screen printing, the ink amount will be inconsistent, the depth will be caused, and the positioning will be inaccurate. In serious cases, during the screen printing, under the scraping and pressing of the scraper, Silk is easy to be broken, so we must pay attention to it

2. Frame

a. the material, section size, shape, flatness after processing, strength and aging treatment of the frame directly affect the tension of the plate and the stability of the tension in use. In most cases, the main reason is that the tension of the template decreases due to insufficient frame strength. Secondly, the degumming and stretching of the silk and the frame have exceeded the limit tension of the silk, which will also lead to the decrease of the template tension. Therefore, the frame must be deburred on the bonding surface and Chuncai edge before use. After these treatments, the frame will be evenly coated with glue, and the silk will be firmly adhered to the frame to ensure that the cloth will not loose from the frame under large scraping pressure during the silk screen printing process. Note that the adhesive must be able to penetrate into the bonding face of the silk, so that the silk can be completely bonded to the frame. If necessary, when the adhesive is not completely dry, it is beneficial to help the silk fully stick to the frame after scraping and pressing the frame by hand

b. it is worth noting that the frame must have a cross-sectional size (wall thickness) and elastic coefficient that can resist external large forces. Otherwise, it only pursues the plate tension and ignores the strength of the frame. This is an important reason for the instability and decrease of the plate tension

c. the frame is divided into aluminum alloy profile and steel frame, and the elastic coefficient of steel is 2.9 times that of aluminum. Steel frame is expected to be used for the version requiring high tension. For example, for the screen printing plate of the disc, the tension is about n/cm, and the cross-sectional area is required to be small. Therefore, the frame is made of about 3mm steel plate, so that in the process of making and printing the four-color plate, the position is consistent, the overprinting is accurate, the hue is good, and it is not easy to produce moire

d. for frames with position requirements and dot printing, the material, size, tension of several frames must be consistent with the cutting direction of the silk

e, improper ratio of frame size to printed graphic size will affect the printing accuracy and the stability of plate tension. For this reason, it is generally required that the four sides of the printed figure should be at least 15cm away from the edge of the frame for large frames, and 10cm for small and medium sizes and frames. For those with higher accuracy, the length and width of the printed figure should be 1/3 of the length and width of the frame in the frame

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