The principle, advantages and disadvantages of sof

2022-08-05
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Analysis on the principle, advantages and disadvantages of soft calendering printing

hard roll: namely, hot roll, cold casting roll, with high surface hardness and bright and clean, especially as a mirror. Oil or water is heated outside the machine and sent to the roll, and induction heating is also used. The roll surface temperature ranges from 120 degrees to 200 degrees, up to 230 degrees

soft roll: controllable medium high roll, whose surface is made of special polymer, is required to be resistant to high temperature and pressure, with good elasticity, and can withstand frequent load changes. At present, the main materials used are epoxy resin, nylon, synthetic rubber, polyester urethane, etc

function principle of soft calendering

during operation, the paper sheet is in contact with the hot roller. In a short time, the hot roller transfers the heat energy to the paper and goes deep into a certain critical depth (generally considered as 0.007 m). At this time, the temperature of the paper surface reaches or approaches the glass softening point. At this time, the plasticity of the paper surface is strengthened. When the soft roller is under pressure, it is elastically deformed and the pressing area forms surface contact. The hard roller of the mirror is like a die to capsule the paper surface, which becomes smooth and shiny, and retains a good thickness

advantages of soft calendering

compared with hard calendering, it has the following advantages:

① the pressed paper has the same tightness

calendering rollers with high elastic modulus are generally 50 ~ 500 times softer than steel rollers. When the elastic rollers are pressed to the hard rollers or cold quenched cast iron rollers with a certain line, the width of the pressing area becomes much wider than that when the steel steel rollers contact. The peak pressure decreases with the reciprocal of the width of the pressing zone, the contact surface is no longer a plane, and the total radial compression deformation of the steel roll along the curvature radius of the steel roll is very small (0.2% ~ 2%)

in the steel pressing area, if there are uneven patches in the paper, the pressure will be uneven. When there are too many thick patches or flocs on the paper entering the pressure zone, the pressure will reach the maximum here, and the surrounding areas will be relatively low. The overall result is that the gaohuaqin of the paper web is that the areas exceeding the fiber density will appear in the low fiber density areas of the same paper thickness, and the latter will be impacted by the pressure of the pressing area is low. When the paper sheet is pressed in the calendering roller of the elastic surface layer, the concave depth of the hard roller pressed into the surface layer is large enough so that the change of the paper sheet thickness will not cause much change in the peak pressure (peak pressure is the highest pressure on the center line of the pressing area)

② even if the paper evenness is poor, its opacity can be improved and color spots can be eliminated

due to the springback of the soft roll surface material, the roll surface can adapt to any adverse uniformity and quantitative change of the paper. The thin area of the paper is in contact with the hot roller. At the same time, the thickness of the thick area will not be greatly reduced. Such thick and thin areas can increase their fine smoothness and eliminate color spots

③ good absorption of printing ink

due to the same paper tightness, and the thickness reduction is not very large, so the oil absorption film of the extruded paper is good and uniform

④ it is possible to make the finished product have high moisture content

because the paper blackening and color spots are basically eliminated in the soft roller pressing area, and the paper can enter the pressing area under high moisture content

⑤ the loose thickness of the paper sheet is improved and the stability of the stiffness is maintained

⑥ soft calendering has a wide range of stability and line pressure adjustment, which can adapt to calendering finishing required by different paper grades

⑦ because the fiber is not strongly squeezed, the paper strength is good. 1. Jinan testing machine factory adjusts the height of the baffles on both sides of the pressure testing machine to keep them at a relatively horizontal position. If there is a deviation, it may affect the use of the pressure testing machine Improved the operation rate of social equipment

⑧ higher smoothness can be obtained and the difference between two sides can be eliminated

how much do you know about the yield strength of materials? Compared with super calendering:

① the maximum allowable temperature of super calendering cannot exceed 85 degrees, while the temperature of soft roller calendering can reach 160 ~ 200 degrees

② soft calendering can be at the same speed as the paper machine or coater, and it is not necessary to reduce the speed during paper introduction

③ the interval time and service life of the soft roll are much longer than that of the paper meal roll

④ it is difficult to control the paper thickness due to overpressure

⑤ overpressure covers a large area, and the cost of covering plastic surface and grinding roller is high, and the investment is also high

main disadvantage of soft calendering

the biggest disadvantage of soft calendering is that once its working width is determined, it cannot be changed at will. Because the soft roll surface outside the paper web is in direct contact with the hard (hot) roll, the soft roll surface is easy to be damaged. At the same time, because the roll surface outside the paper web is in contact with the hot roll, the local temperature is large. If the temperature difference exceeds the bearing value of the soft roll material (generally controlled within 5 degrees), it is easy to deform. Therefore, it is necessary to ensure the paper width of the pressing area in production

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