Understand: The use and maintenance of blankets

In simple terms, the role of the blanket in the offset printing process is to transfer the graphic from the printing plate to the substrate (paper) through the elastic pressure generated by the compression deformation between the roller and the rubber. Most blankets consist of three layers of long-fiber cotton felt and special rubber. And it is coated with a mixed rubber layer on one side. There are subtle differences between different blankets. In order to ensure the quality, the deviation of the blanket thickness must not exceed ±O.01mm; at present, many printing companies use more advanced air-cushion blankets, which add many tiny closed air spheres to the structure and are dispersed in the adhesive layer. Therefore, it can be compressed when it comes into contact with the plate cylinder or the impression cylinder. The air-cushioned rubber sheet has stronger impact resistance, better crush resistance, and more sensitive elasticity. Its compression capacity is 0.10mm larger than ordinary blankets, elasticity, ink transfer performance, and its service life is much stronger than the latter, and is mainly used for high-speed machines, and the use of hard or neutral lining and high-end printing presses. .

Before the new blanket is on the machine, it must be in accordance with the cutting standard required by the printing machine. In theory, the four sides are all right angles. If the blanket is skewed, it will suffer from uneven force, easy to creep or twist deformation. Causes dot distortion during printing. The position of the latitude and longitude direction should be clearly distinguished when the upper folder is used. Generally, there are marks on the rubber, and the red or green line on the back surface of the back plate is the longitudinal direction of the blanket. It is also possible to use a slightly harder arm extension test, where one can feel that the apparently elongated deformation is in the weft position, that is, in the direction of the upper rubber clip, and the one that does not easily stretch is the warp position. If the wrong direction, the blanket on the machine will not pull tighter longer, the product has a ghost phenomenon, the final rubber scrapped. After confirming the direction, when the rubber clip screws should be on both sides and the longitudinal distance is the same, tighten the middle bolt first and tighten the screws in the order of the two sides. If the top is on both sides, the rubberized cloth will have wavy lines on the edges, which will affect the EN, J and blanket life. After tightening all screws, check with a ruler to ensure that the two rubber clips are parallel and the distance is the same. If the two sides of the loading plate are not parallel, the tightness of the tension rubber's axial position is not uniform, so that the blanket is loose on one side and tight on one side. The blanket will thus be twisted. When the blanket with a good rubber clip on the machine, the rubber clip must be in place, otherwise it will not be in place because of the clip, throwing damage to the machine during high-speed printing cause significant losses. The blanket and liner must be tightly wrapped around the drum to maintain sufficient tension to prevent slipping under the pressure of the print. Since the upper blanket is manually controlled, the error may be very large: Generally speaking, the tension force is controlled between 50-70kg force, the elasticity is harder when the hand presses the neutral position, and the fingerbomb has obvious “click” sound. It is appropriate. If it is too loose, the blanket will be displaced under the action of the pressing force and cannot be reset in time. This will cause ghosting failure, and the tension will be too tight, which will lead to thinning of the adhesive layer, reduced elasticity, and uneven plastic deformation.

After the new blanket is installed on the machine, it can be cleaned with pumice powder and then cleaned with a cleaning agent, which can effectively remove foreign particles on the surface due to production or transportation. The blanket stretches under tension and roller pressure, so that it must be re-tightened to a suitable degree. Therefore, the new blanket should be pressed and printed for 10 minutes, and then stretch the rubber again. Otherwise, there will be ghosting in the printed matter, and overprinting is not allowed. In particular, it should be noted that the lining must be added according to the parameters of the printing press. If the lining is unsuitable, the thickness is too soft, and the diameter of the blanket cylinder is not equal during the printing process as the squeezing of the roller affects the inconsistent linear velocity. Speed ​​difference, rubber and the printing plate and the surface of the substrate produce friction so that the printing plate graphic network points no rules to expand, reduce and appear ghosting, resulting in wide and narrow, position is not a fixed bar, can seriously feel the machine is obviously boring Sound, accelerate machine wear, damage the machine gear and so on. Of course, after the blanket is used for a period of time, the plastic deformation occurs in the thickness direction under the action of the tension force and the roller pressure, resulting in a reduction in the thickness of the blanket. As a result, the printing pressure is weakened, resulting in prints that appear imaginary, unclear characters, and ink that are not imaged; measuring with a dry-dimensioner will reveal that the thickness of the blanket is also reduced. At this time, it is necessary to consider appropriately increasing the thickness of the pad or adjusting the pressure of the machine. make up. In order to ensure the quality of normal printing products.

During the printing process, the paper wool, paper powder, and ink are accumulated on the blanket to form an indentation; the operator needs to develop the cleaning habit in time, otherwise the local printing pressure will increase, and more plastic deformation will occur locally in the rubber. Or a white smear layer of paper is deposited on the rubber and is not easy to clean. At the same time, quick-drying ink, dry oil and other use of Dl:iN will also harden the rubber layer, cause crystallization, reduce its elasticity and ink absorption, and affect the normal ink transfer of the blanket. In this case, remove the blanket, clean the blanket with gasoline or reducing agent, and then wipe it repeatedly with pumice powder and cleaning agent until the above crystallized body or paper powder is completely removed. The eraser is allowed to dry for a while on cloudy days, allowing it to slowly recover its elasticity and use. When cleaning the blanket, you should use organic solvents that volatilize faster. Slow-evaporating kerosene or other solvent cleaning blanket will swell, wash and dry the blanket, leaving no residue. In particular, when the two shifts are performed, the blanket must be thoroughly cleaned. Otherwise, due to the long accumulation of paper, paper, and ink residues on the blanket, the aging of the blanket will greatly reduce the transfer ability of the blanket. The ink on the embossing cylinder and the paper powder must also be cleaned in time. The long-term accumulation will also ruin the blanket, which will affect its service life.

In the production process, it is unavoidable that occasional sticks, screws, rotten paper, and excessively thick cardboard fall into the printing press and rub the rubber. If the surface of the blanket is relatively large, it must be replaced. If it is only partially pressed into a dent, it can be reduced with a rubber reducing agent, and then paper is placed on the back indentation to make the recess partially go up and reach the printing effect. The repaired blanket can still be used for a considerable period of time.

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