Hard roll: hot roll, chill roll, high surface hardness, smooth and smooth like a mirror surface, heated with oil or water outside the machine and sent to the roll, also useful for induction heating, roll surface temperature from 120 degrees to 200 degrees, the highest Up to 230 degrees.
Soft roll: Controlled high roller, the surface is made of special polymer, requiring high temperature and high pressure, good elasticity, able to withstand frequent changes in load. Currently used materials are mainly epoxy, nylon, synthetic rubber, polyester urethane and so on.
The effect of soft calendering
In operation, the paper sheet is in contact with the hot roll. In a short time, the heat roller transfers heat energy to the paper and goes deeper to a certain critical depth (usually considered to be at 0.007 μm), at which time the temperature of the paper surface reaches or approaches. The softening point of the glass, when the paper surface is plastically reinforced, and the soft roll is elastically deformed when pressed, and the nip forms a surface contact. The mirror-like hard roller acts like a stamped, textured paper, smooth and shiny, and retains a good thickness.
The advantages of soft calendering
Compared with hard calendering, it has the following advantages:
1 Pressed paper tightness is consistent
A calender roll with a higher elastic modulus is generally 50 to 500 times more flexible than a steel roll. When the elastic roll is pressed against a hard roll or a hard cast roll by a certain line, the nip width becomes higher than that of steel. - Steel rollers are much wider when in contact. The peak pressure decreases with the reciprocal of the nip width, the contact surface is no longer a plane, and along the radius of curvature of the steel roll, the total radial compressive deformation of the steel roll is small (0.2% to 2%).
In the steel pressure zone, the pressure is not uniform if there are uneven patches in the sheet. When the sheets of paper that enter the nip area are too thick or with high flocculation, the pressure here will be the highest and the surrounding area will be lower. The overall result is that the high fiber density zone of the web is manifested in the low fiber density zone of the same sheet thickness, which is subjected to a lower pressure impact force. When the sheet is pressed in the calender roller of the elastic surface layer, the hard roller presses in the depth of the surface layer so that the thickness of the sheet does not change so much that the peak pressure does not change (the peak pressure is the center line of the nip The highest pressure).
2 Even if the formation of the paper is not good, the opacity can be improved and the stain can be eliminated.
Since the soft roll surface material rebounds, the roll surface can be adapted to any unfavorable formation and quantitative changes in the sheet. The thin area of ​​the paper is in contact with the heat roller, and at the same time, the thickness does not have to be greatly reduced for the thick area. Such thick and thin areas can increase the subtle smoothness and eliminate the stain.
3 Printing ink absorption is good
Due to the tightness of the sheet, the reduction in thickness is not so great, so that the pressed paper is good and uniform.
4 It is possible to make the finished product have higher moisture
Because in the soft roll nip, the paper is black and the stain is substantially eliminated, the paper sheet can enter the nip under high moisture.
5 Improves paper bulk and maintains stiffness stability.
6 The stability of soft calendering and the range of line pressure adjustment are large, which can adapt to the requirements of calendering for different paper types.
7 Due to the fact that the fibers are not strongly squeezed, the strength of the paper sheet is good, which improves the operating rate of the company.
8 Get higher smoothness and eliminate both sides.
And super calender ratio:
1 The maximum permissible temperature of super calendering cannot exceed 85 degrees, while the calender calendering temperature can reach 160 degrees to 200 degrees.
2 The soft calendering can be at the same speed as the paper machine or the coater, and it is not necessary to reduce the speed when pulling the paper.
3 The soft roller has a longer time interval and service life than the paper roller.
4 Overpressure makes paper thickness control difficult
5 The overpressure covers a large area, the plastic surface and the grinding roller are high in cost, and the investment is also high.
The main disadvantage of soft calendering
The biggest drawback 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 directly in contact with the hard (hot) roll, the soft roll surface layer is easily damaged. At the same time, the roll surface outside the paper web is in contact with the hot roll, causing a large local temperature, if the temperature difference exceeds the soft roll material. Acceptable values ​​(generally controlled within 5 degrees) are easily deformed. Therefore, in the production, it is necessary to ensure the width of the web in the press-in zone.
Soft roll: Controlled high roller, the surface is made of special polymer, requiring high temperature and high pressure, good elasticity, able to withstand frequent changes in load. Currently used materials are mainly epoxy, nylon, synthetic rubber, polyester urethane and so on.
The effect of soft calendering
In operation, the paper sheet is in contact with the hot roll. In a short time, the heat roller transfers heat energy to the paper and goes deeper to a certain critical depth (usually considered to be at 0.007 μm), at which time the temperature of the paper surface reaches or approaches. The softening point of the glass, when the paper surface is plastically reinforced, and the soft roll is elastically deformed when pressed, and the nip forms a surface contact. The mirror-like hard roller acts like a stamped, textured paper, smooth and shiny, and retains a good thickness.
The advantages of soft calendering
Compared with hard calendering, it has the following advantages:
1 Pressed paper tightness is consistent
A calender roll with a higher elastic modulus is generally 50 to 500 times more flexible than a steel roll. When the elastic roll is pressed against a hard roll or a hard cast roll by a certain line, the nip width becomes higher than that of steel. - Steel rollers are much wider when in contact. The peak pressure decreases with the reciprocal of the nip width, the contact surface is no longer a plane, and along the radius of curvature of the steel roll, the total radial compressive deformation of the steel roll is small (0.2% to 2%).
In the steel pressure zone, the pressure is not uniform if there are uneven patches in the sheet. When the sheets of paper that enter the nip area are too thick or with high flocculation, the pressure here will be the highest and the surrounding area will be lower. The overall result is that the high fiber density zone of the web is manifested in the low fiber density zone of the same sheet thickness, which is subjected to a lower pressure impact force. When the sheet is pressed in the calender roller of the elastic surface layer, the hard roller presses in the depth of the surface layer so that the thickness of the sheet does not change so much that the peak pressure does not change (the peak pressure is the center line of the nip The highest pressure).
2 Even if the formation of the paper is not good, the opacity can be improved and the stain can be eliminated.
Since the soft roll surface material rebounds, the roll surface can be adapted to any unfavorable formation and quantitative changes in the sheet. The thin area of ​​the paper is in contact with the heat roller, and at the same time, the thickness does not have to be greatly reduced for the thick area. Such thick and thin areas can increase the subtle smoothness and eliminate the stain.
3 Printing ink absorption is good
Due to the tightness of the sheet, the reduction in thickness is not so great, so that the pressed paper is good and uniform.
4 It is possible to make the finished product have higher moisture
Because in the soft roll nip, the paper is black and the stain is substantially eliminated, the paper sheet can enter the nip under high moisture.
5 Improves paper bulk and maintains stiffness stability.
6 The stability of soft calendering and the range of line pressure adjustment are large, which can adapt to the requirements of calendering for different paper types.
7 Due to the fact that the fibers are not strongly squeezed, the strength of the paper sheet is good, which improves the operating rate of the company.
8 Get higher smoothness and eliminate both sides.
And super calender ratio:
1 The maximum permissible temperature of super calendering cannot exceed 85 degrees, while the calender calendering temperature can reach 160 degrees to 200 degrees.
2 The soft calendering can be at the same speed as the paper machine or the coater, and it is not necessary to reduce the speed when pulling the paper.
3 The soft roller has a longer time interval and service life than the paper roller.
4 Overpressure makes paper thickness control difficult
5 The overpressure covers a large area, the plastic surface and the grinding roller are high in cost, and the investment is also high.
The main disadvantage of soft calendering
The biggest drawback 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 directly in contact with the hard (hot) roll, the soft roll surface layer is easily damaged. At the same time, the roll surface outside the paper web is in contact with the hot roll, causing a large local temperature, if the temperature difference exceeds the soft roll material. Acceptable values ​​(generally controlled within 5 degrees) are easily deformed. Therefore, in the production, it is necessary to ensure the width of the web in the press-in zone.
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