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Function principle of soft roll calender

Author:Jiangyin roll machinery co. LTD Publications: 23/05/2018 Click:
The nip of the calender is composed of a chilled cast iron roller that can be heated and adjusted temperature and a soft roller that can control the middle and high, and the roller shell is covered with elastic material. The deformation of the roll surface of the soft roll under the pressure causes the nip to make surface contact, and the pressure per unit area is low, and the surface of the paper web is subjected to gentle treatment, so the paper web is evenly decorated and the loss of bulk thickness is small. According to the size of the roller diameter, the hardness of the coating material on the surface of the soft roller and the pressure applied, the width of the soft roller calendering nip can reach 5 to 10 mm, which is 5 to 8 times that of the calender (hard nip) of the paper machine. The unit pressure is generally 20 ~ 40N / mm2. Even if the linear pressure of the soft calender is high, the unit pressure is only 1/3 to 1/4 of the calender of the paper machine. Due to the wide nip and the long residence time of the paper web in the nip, the increased energy consumption is transferred to the paper web in the form of heat, which softens the fibers on the surface of the paper web, making it easier to calender and increase the smoothness. To balance the effect between pressure and temperature, when the temperature of the above nip is high, the pressure in the nip can be relatively lower, which can reduce the loss of bulk and obtain a satisfactory paper finish. And because the specific pressure in the soft calendering area is low, the phenomenon of fiber crushing is greatly reduced, so that the strength of the paper can be maintained. The tensile strength of the paper in the longitudinal and transverse directions is good, which means that the operation rate of the paper machine and subsequent printing machines will be improved.

Due to the resilience of the soft roll surface material, the roll surface can adapt to any bad uniformity and quantitative changes of the paper web, so it can have more uniform smoothness and uniform tightness than the conventional hard nip calender. The thin area of the paper web is in good contact with the heating roller, and at the same time, the thickness of the thick area will not be significantly reduced, so that the fine smoothness can be increased in the thick and thin area, so the entire paper web has very uniform fine Smoothness eliminates color spots and greatly improves printing performance. Another advantage of soft calendering is that it allows the paper web to run under high moisture conditions on the premise that the paper blackening and color spot problems are basically eliminated. This not only benefits the calendering and finishing of the paper web, but also makes The moisture of the paper roll can be kept high, the moisture of the paper web is high, and the temperature is high, so that the fiber components are softened to facilitate calendering. Steam spraying has a significant impact on the calendering process. Hot steam plasticizes the paper surface, and it is also easy to calender to obtain a good smoothness. Compared with the conventional paper machine calender, the calender is mainly a hot roll with a hard roll surface and a soft roll with an elastic coating. The roll diameter and the linear pressure acting on the nip are different. The elastic coefficient of the soft-coated material should be considered. For a certain paper web, when the ratio and structure of raw materials (slurry distribution, fiber three-dimensional orientation and fiber structure formation) have been determined, its calendering effect is affected by the following conditions: the temperature of the roller, the pressure into the paper web Temperature, pressure in the nip, moisture in the paper web, residence time of the paper web in the nip, and number of nip. High temperature and low pressure are conducive to improving glossiness, the paper web's tightness is not much increased, and the roughness is small (meaning the paper surface is fine), while low temperature and high pressure, the paper web's tightness is increased, and the roughness is high (meaning the paper surface is rough ), The gloss improves less.

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