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Release time:

Nov 16,2023

Ordinary calender generally consists of 3 to 8 rollers), each roller is in a vertical line and installed on the same frame. The lower roller is the active roller, and the remaining rollers are driven by friction. The number of rolls of the calender is generally determined by the speed of the car and the variety of the paper. The low and medium speed paper machine is generally six rollers, the tissue paper can be three rollers, and the newsprint can reach 8 to 10 rollers. The lower roller bears all the applied pressure and the weight of each roller, so its diameter is the largest. The second roller from the lower number is directly close to the active roller, and its diameter is slightly larger due to the large tangential force during friction transmission. The diameter of each roller in the middle is the smallest, so that the rollers tend to be in line contact, thereby increasing the pressure on the paper surface to improve the calendering effect. The uppermost roller is subjected to external pressure, so the diameter is also slightly larger. In order to facilitate the introduction of paper, the top of the ordinary odd-numbered roller calender is equipped with a pressure roller, which can be made of felt. The even-numbered roller calender has no pressure roller and is suitable for compressed air to lead paper. The working part of the roller body of the ordinary calender roller is cast in the metal mold, because the heat of molten iron during casting is absorbed sharply by the metal mold, so that the working surface forms a layer of about 10~20mm, with high wear resistance. The surface of the calender roller is required to be very smooth, the conicity is not more than 0.005mm, the ovality is not more than 0.01mm, the tensile and compressive strength is large, the resistance to friction and the scratch is high, the expansion coefficient is small, not easy to rust, and can resist the corrosion of acid, alkali and salt. The contact surface between the roller and the roller must be close without slight gaps. In order to overcome the deflection deformation after compression, the upper roller and the lower roller have "medium and high" (sometimes 10-15% of the medium and high of the lower roller is allocated to the penultimate roller), so that the paper surface is flat and tightly compressed to meet the calendering requirements. General calender roll is made of nickel-chromium steel or cold cast iron, hardness of not less than 80~85 (Shore). As for the size of the roll, in addition to its position on the calender, it mainly depends on the width of the paper machine, I .e. the larger the width, the larger the diameter. After the sheet is introduced between the platen roller and the upper roller, it passes through each roller in sequence, and is peeled from the previous roller to the lower roller by means of a scraper. As the number of rolls increases from top to bottom, the line pressure increases. Generally, the two rollers at the bottom of the calender are provided with ventilation, cooling and cooling devices to eliminate the heat converted by mechanical energy during the calender process. Such ventilation and cooling devices can also be provided at the second and third rollers to adjust the calender effect in the transverse direction of the paper web. The calender has a special cooling fan. The cold air is directly blown through the center of the roller through the nozzle. Each nozzle is equipped with a valve to adjust the air volume and can move horizontally. mechanism of paper calender In the past, the mechanism of calendering was understood to be caused by the friction caused by mechanical compression and speed difference between rolls. When it was found that the speed difference between the rollers was extremely small, and the friction effect was questioned, it was also proposed that calendering was caused by the deformation of the paper sheet when the paper surface was deformed by the shearing effect between the rollers. Recently, with the help of an electron microscope, it has been clearly seen that the surface of the calender roll has a clear impression on the surface of the calender roll, thus clarifying the calender of the paper sheet, mainly in the form of transfer printing, the smoothness of the roll surface is transferred to the paper surface. Obviously, the more flexible and plastic the surface of the paper sheet, the higher the roller pressure and the longer the pressure time of the paper sheet, which is more conducive to obtaining a higher calender effect. The friction and the shear deformation of the paper surface do not play a major role.