Since the early 1980s, the technology of press finishing in the soft nip has been developed, and the application of this technology has become more and more extensive. Initially, this technique was only applied to papers with low and medium finishing requirements, or hard calendered paper prior to the invention of soft calendering. Today's soft calenders have been able to achieve calendering effects that previously could only be achieved with supercalenders.
Several significant advantages of the soft nip finishing technology for super calenders provide ideas for the development of soft calenders. In order to be able to economically and effectively perform press finishing in the soft nip of the machine, various new types of equipment components must be developed, in particular controlled high rollers, heated hard rollers, and various new types of elastic roller materials.
The soft calender finish effect depends on various calendering features and device designs. The quality of calendering depends primarily on the properties of the sheet prior to calendering, the moisture content, the composition of the raw materials, the choice and treatment of the pulp, and the role of the paper machine (the entire papermaking process). If it is coated paper, the coating Formulations, coating amounts, and coating methods also play a decisive role.
Paper banner thickness control technology has made great progress in the past few years. The newly developed single-unit controlled high-roller (MULTIHV-Roll) allows the user to correct the banner thickness of wide and narrow web machines without adding equipment. The design of this roller is based on the principle of a well-established zone-controlled HV-Roll, except that each pressurizing element is individually controlled. The amount of linear full-scale adjustment is not affected by the average line pressure, and can be corrected at any desired position including roll-to-pinch pressure increase or decrease.
The soft calender can effectively and economically calender many paper grades, with uniform finishing effect, no zebra pattern or blackening phenomenon, and excellent paper printing performance.
For those paper grades with higher smoothness and gloss requirements and calendering for high-strength paper grades, multiple nips are required to achieve satisfactory results. To produce these paper grades, multi-nip calenders such as PROSOFT calenders have been successfully put into use. The typical feature of the PROSOFT calender is that the nip pressure is higher than that of a general soft calender, and each nip is perfectly controlled so as not to cause pressure roll deformation, the sheet strength properties can be maintained, and the soft roll surface is protected because the pressure is protected There is almost no shear stress in the finishing operation. The design of the PROSOFT calender enables it to be used both for internal and external calendering, and can achieve satisfactory calendering effects. PROSOFT calender is currently the most ideal internal and external calendering equipment.
2 soft nip calendering technology If the calendering technology is defined as the thermal and mechanical energy conversion of the paper web, there is no fundamental difference in the calendering mechanism between the hard nip and the soft nip. The web is pressed between two rollers, and the roller surface is pressed against the web due to the pressure on the nip. When calendering with a hard calender, the web is pressed into a uniform thickness between the press rollers that are stiff and inelastic, as shown in Figure 1. If the thicker part of the web is pressed thinner, the density is much greater. This can result in inconsistent local densities, which can lead to streaks and, in severe cases, dark spots.
In the case of a soft calender, the web is calendered with a nip consisting of a thermo-hard roller and an elastic roller. As the web passes through the nip, the full web density increases evenly because of the elasticity of the roll surface. This means that the soft roll surface distributes the nip pressure more evenly to the thicker or thinner portion of the web than the hard roll, so that even when the moisture is high, no spotting of the light is caused. Paper disease.
Therefore, the soft calendered paper not only has a good appearance but also significantly improves the printability. The thicker part is not over-calendered, so the fibers and their bonds are not damaged in the nip and the strength of the sheet is enhanced.
A given web has a certain composition and structure (material distribution, spatial orientation of the material particles, and formability), such as coated paper, as well as the effects of the coating. The calendering effect is generally also affected by the following parameters:
. Roller temperature. Web temperature. Pressure in the nip. The residence time of the web in the nip. The number of nips their effect on calendering can be summarized as follows (References 1-6):
. Due to the increase in nip temperature, pressure, residence time, and the number of nips, higher smoothness, density, and gloss can be achieved.
. High temperature calendering can achieve uniform roughness and nip pressure can be greatly reduced.
. For uncoated paper, regardless of whether high or low temperature calendering is used, it is important that the web has a certain density to achieve a certain degree of roughness.
. When the roughness is constant, the high temperature calendering has a higher gloss than the low temperature calendering.
. Paper with high temperature calendering has a higher print gloss than low temperature.
. Especially for high-quantity paper and coated paper, the use of high temperature calendering is less than the loss of looseness of low-temperature calendering, but the composition of the web, the coating formulation, and the measurement system also play an important role in the calendering effect. The relationship between bulk and gloss and Parker Printsurf print gloss is easier to change than the relationship between bulk and Bekk smoothness and Bendtsen roughness.
. When the web has a high moisture content and is calendered at high temperatures, the fibers are softened and easily calendered. Therefore, steam injection has a significant effect on the calendering process.
Different types of soft calenders, the number of nips depends on the different uses. The single pressure zone structure is a feature of soft calendering. Compared with overpressure light, the distribution of line pressure in each pressure zone is greatly improved, and at the same time, since the roller surface of the soft roller is only subjected to one-time extrusion when it is rotated once, the roller surface has enough time to restore the original shape, so even if it is very At high vehicle speeds, the pressurization efficiency is also high and the service life is long. A major feature of soft calendering in single nip zones is the ease of threading, which is more important for high speed paper machines. The temperature in the nip and the line pressure can be controlled individually to a large extent, so the calendering effect can be varied, and the difference in the two sides of the web is reduced to a minimum.
Heat Roller - The PERITHERM Roller has a series of holes in the circumferential direction, which can be heated by hot water, steam or hot oil depending on the requirements of the roll surface temperature. Hot rolls generally use chilled cast iron rolls or steel rolls. For paper grades with high requirements for smoothness and gloss, a carbon layer can be added to the roll surface. For high speed paper machines, the maximum temperature of the roll surface can reach 200°C.
The controllable high-rolling roller (SwimmingRoll), the controllable medium-high roller (HYDROVARIO Roll) and the unit-controlled high roller (MULTIHVRoll) manufactured by Kuesters BELOIT can control the deflection of the roller (References 7-9). According to the requirements of calendering, the hardness of the elastic roller surface ranges from 72-93°SHD. The roller cycle can vary from 6 weeks to several months, depending on the operating conditions and the type of paper.
In general, all soft calender rolls are equipped with a doctor blade. The use of special equipment can be used for quick roll change, even during operation.
4 Application of soft calender Since the soft calender was put into the market in the early 1980s, its scope of use has been very extensive. In particular, paper grades with high requirements for smoothness can only be processed with super calender in the past and are now available. Instead of a soft calender, the heat roller surface temperature is only controlled at 130-220°C.
FIG. 7 shows a common calendering method for different publication papers, and FIG. 8 shows the development trend of a calendering method in the future.
5 Banner Thickness Control Since unit-controlled high roller (MULTIHV Roll) was put on the market in 1994, banner thickness control can be precisely implemented without additional fine-tuning equipment (Reference 8,10), as shown in Fig.9.
The roller is characterized by the elimination of the defects of the common thermal correction system, such as: long reaction time after the breakage, low efficiency when the roller surface temperature is high, and high energy consumption. The deflection of the MULTIHV roll can be corrected in seconds. The control efficiency of the thickness of the paper banner is adjusted up and down simultaneously with the nip linear load. Through computer calculations, the paper web thickness can be adjusted at the coater or paper machine control system. This banner thickness control has been successfully used to calender general newsprint, advanced newsprint, rotary newsprint, LWC offset, all kinds of cardboard and coated paper.
Soft calender is a versatile, efficient and economical calendering device. Each press nip has a large line pressure and temperature adjustment range, and the temperature and line pressure are independent of each other. After pressing, the paper is printable and has no calender spots. For the processing of cardboard and high-grade paper grades, high temperature calendering can be used to make it have good bulk. In addition, due to the soft calendering in the machine, the high temperature of the paper sheet itself helps to improve the calendering effect and reduce energy consumption. The number of nips in the calender depends on the calender quality requirements and can be determined on a pilot calender.
The MULTIHV roller provides an effective tool for controlling the thickness of the paper sheet banner. The adjustment of the thickness can be done instantaneously without increasing the energy consumption.
The PROSOFT calender is suitable for high quality calendering of paper webs inside or outside the machine. This multi-nip calender has much greater compressive stress than a typical soft calender. At the same time, due to the use of a nip energy control system, the nip pressure distribution is well controlled and no shear stress is generated. The roll surface has a long service life, the possibility of cracking of the coating is minimal, and the strength of the sheet is guaranteed.
Both research trials and actual production operations have proved that the use of MULTIHV Roller Single Pressure Zone and Multi-Zone Soft Calender can achieve the purpose of controlling the thickness without auxiliary correction equipment, and the thickness control precision and efficiency can be compared with the traditional ones. The method is comparable.
Several significant advantages of the soft nip finishing technology for super calenders provide ideas for the development of soft calenders. In order to be able to economically and effectively perform press finishing in the soft nip of the machine, various new types of equipment components must be developed, in particular controlled high rollers, heated hard rollers, and various new types of elastic roller materials.
The soft calender finish effect depends on various calendering features and device designs. The quality of calendering depends primarily on the properties of the sheet prior to calendering, the moisture content, the composition of the raw materials, the choice and treatment of the pulp, and the role of the paper machine (the entire papermaking process). If it is coated paper, the coating Formulations, coating amounts, and coating methods also play a decisive role.
Paper banner thickness control technology has made great progress in the past few years. The newly developed single-unit controlled high-roller (MULTIHV-Roll) allows the user to correct the banner thickness of wide and narrow web machines without adding equipment. The design of this roller is based on the principle of a well-established zone-controlled HV-Roll, except that each pressurizing element is individually controlled. The amount of linear full-scale adjustment is not affected by the average line pressure, and can be corrected at any desired position including roll-to-pinch pressure increase or decrease.
The soft calender can effectively and economically calender many paper grades, with uniform finishing effect, no zebra pattern or blackening phenomenon, and excellent paper printing performance.
For those paper grades with higher smoothness and gloss requirements and calendering for high-strength paper grades, multiple nips are required to achieve satisfactory results. To produce these paper grades, multi-nip calenders such as PROSOFT calenders have been successfully put into use. The typical feature of the PROSOFT calender is that the nip pressure is higher than that of a general soft calender, and each nip is perfectly controlled so as not to cause pressure roll deformation, the sheet strength properties can be maintained, and the soft roll surface is protected because the pressure is protected There is almost no shear stress in the finishing operation. The design of the PROSOFT calender enables it to be used both for internal and external calendering, and can achieve satisfactory calendering effects. PROSOFT calender is currently the most ideal internal and external calendering equipment.
2 soft nip calendering technology If the calendering technology is defined as the thermal and mechanical energy conversion of the paper web, there is no fundamental difference in the calendering mechanism between the hard nip and the soft nip. The web is pressed between two rollers, and the roller surface is pressed against the web due to the pressure on the nip. When calendering with a hard calender, the web is pressed into a uniform thickness between the press rollers that are stiff and inelastic, as shown in Figure 1. If the thicker part of the web is pressed thinner, the density is much greater. This can result in inconsistent local densities, which can lead to streaks and, in severe cases, dark spots.
In the case of a soft calender, the web is calendered with a nip consisting of a thermo-hard roller and an elastic roller. As the web passes through the nip, the full web density increases evenly because of the elasticity of the roll surface. This means that the soft roll surface distributes the nip pressure more evenly to the thicker or thinner portion of the web than the hard roll, so that even when the moisture is high, no spotting of the light is caused. Paper disease.
Therefore, the soft calendered paper not only has a good appearance but also significantly improves the printability. The thicker part is not over-calendered, so the fibers and their bonds are not damaged in the nip and the strength of the sheet is enhanced.
A given web has a certain composition and structure (material distribution, spatial orientation of the material particles, and formability), such as coated paper, as well as the effects of the coating. The calendering effect is generally also affected by the following parameters:
. Roller temperature. Web temperature. Pressure in the nip. The residence time of the web in the nip. The number of nips their effect on calendering can be summarized as follows (References 1-6):
. Due to the increase in nip temperature, pressure, residence time, and the number of nips, higher smoothness, density, and gloss can be achieved.
. High temperature calendering can achieve uniform roughness and nip pressure can be greatly reduced.
. For uncoated paper, regardless of whether high or low temperature calendering is used, it is important that the web has a certain density to achieve a certain degree of roughness.
. When the roughness is constant, the high temperature calendering has a higher gloss than the low temperature calendering.
. Paper with high temperature calendering has a higher print gloss than low temperature.
. Especially for high-quantity paper and coated paper, the use of high temperature calendering is less than the loss of looseness of low-temperature calendering, but the composition of the web, the coating formulation, and the measurement system also play an important role in the calendering effect. The relationship between bulk and gloss and Parker Printsurf print gloss is easier to change than the relationship between bulk and Bekk smoothness and Bendtsen roughness.
. When the web has a high moisture content and is calendered at high temperatures, the fibers are softened and easily calendered. Therefore, steam injection has a significant effect on the calendering process.
Different types of soft calenders, the number of nips depends on the different uses. The single pressure zone structure is a feature of soft calendering. Compared with overpressure light, the distribution of line pressure in each pressure zone is greatly improved, and at the same time, since the roller surface of the soft roller is only subjected to one-time extrusion when it is rotated once, the roller surface has enough time to restore the original shape, so even if it is very At high vehicle speeds, the pressurization efficiency is also high and the service life is long. A major feature of soft calendering in single nip zones is the ease of threading, which is more important for high speed paper machines. The temperature in the nip and the line pressure can be controlled individually to a large extent, so the calendering effect can be varied, and the difference in the two sides of the web is reduced to a minimum.
Heat Roller - The PERITHERM Roller has a series of holes in the circumferential direction, which can be heated by hot water, steam or hot oil depending on the requirements of the roll surface temperature. Hot rolls generally use chilled cast iron rolls or steel rolls. For paper grades with high requirements for smoothness and gloss, a carbon layer can be added to the roll surface. For high speed paper machines, the maximum temperature of the roll surface can reach 200°C.
The controllable high-rolling roller (SwimmingRoll), the controllable medium-high roller (HYDROVARIO Roll) and the unit-controlled high roller (MULTIHVRoll) manufactured by Kuesters BELOIT can control the deflection of the roller (References 7-9). According to the requirements of calendering, the hardness of the elastic roller surface ranges from 72-93°SHD. The roller cycle can vary from 6 weeks to several months, depending on the operating conditions and the type of paper.
In general, all soft calender rolls are equipped with a doctor blade. The use of special equipment can be used for quick roll change, even during operation.
4 Application of soft calender Since the soft calender was put into the market in the early 1980s, its scope of use has been very extensive. In particular, paper grades with high requirements for smoothness can only be processed with super calender in the past and are now available. Instead of a soft calender, the heat roller surface temperature is only controlled at 130-220°C.
FIG. 7 shows a common calendering method for different publication papers, and FIG. 8 shows the development trend of a calendering method in the future.
5 Banner Thickness Control Since unit-controlled high roller (MULTIHV Roll) was put on the market in 1994, banner thickness control can be precisely implemented without additional fine-tuning equipment (Reference 8,10), as shown in Fig.9.
The roller is characterized by the elimination of the defects of the common thermal correction system, such as: long reaction time after the breakage, low efficiency when the roller surface temperature is high, and high energy consumption. The deflection of the MULTIHV roll can be corrected in seconds. The control efficiency of the thickness of the paper banner is adjusted up and down simultaneously with the nip linear load. Through computer calculations, the paper web thickness can be adjusted at the coater or paper machine control system. This banner thickness control has been successfully used to calender general newsprint, advanced newsprint, rotary newsprint, LWC offset, all kinds of cardboard and coated paper.
Soft calender is a versatile, efficient and economical calendering device. Each press nip has a large line pressure and temperature adjustment range, and the temperature and line pressure are independent of each other. After pressing, the paper is printable and has no calender spots. For the processing of cardboard and high-grade paper grades, high temperature calendering can be used to make it have good bulk. In addition, due to the soft calendering in the machine, the high temperature of the paper sheet itself helps to improve the calendering effect and reduce energy consumption. The number of nips in the calender depends on the calender quality requirements and can be determined on a pilot calender.
The MULTIHV roller provides an effective tool for controlling the thickness of the paper sheet banner. The adjustment of the thickness can be done instantaneously without increasing the energy consumption.
The PROSOFT calender is suitable for high quality calendering of paper webs inside or outside the machine. This multi-nip calender has much greater compressive stress than a typical soft calender. At the same time, due to the use of a nip energy control system, the nip pressure distribution is well controlled and no shear stress is generated. The roll surface has a long service life, the possibility of cracking of the coating is minimal, and the strength of the sheet is guaranteed.
Both research trials and actual production operations have proved that the use of MULTIHV Roller Single Pressure Zone and Multi-Zone Soft Calender can achieve the purpose of controlling the thickness without auxiliary correction equipment, and the thickness control precision and efficiency can be compared with the traditional ones. The method is comparable.
Full Cassette Motorized Retractable Awning
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