FI108072B - A method for reducing the temperature difference between the edge portions of a polymer surface disposed on the roller and its edge regions, and a device used in the process - Google Patents

Description

108072

The invention relates, for example, to a method according to the preamble of claim 1 for reducing the temperature difference between the peripheral portion of the roll surface of the polymer and the periphery of the central portion of the roll.

The invention also relates, for example, to an apparatus according to the preamble of claim 8 for reducing the temperature difference between the peripheral portion of the polymeric surface on the roll and the peripheral region of the central portion.

In paper machines, so-called soft and / or super-calendering, the paper or board web passes through at least one calendering nip, with one of the rolls forming the nip having a soft surface and a flexible one and the other being a heated metal roll. Here, the nip refers to the contact area of a pair of rollers when the longitudinal axes P1 and P2 of the rollers 15 (cf. Fig. 2) are arranged substantially parallel. In paper machines, so-called soft calendering has increasingly shifted to the use of polymer-coated rolls as flexible rolls. The coating of polymer-coated rolls does not withstand temperatures up to about 80-120 degrees without damage, and on the other hand, there is a maximum 20 temperature difference ATmax characteristic of each type of polymer that it can withstand without damage. For most commonly used polymer coatings, the ATmax is about 20-30 degrees.

The surface temperature of the heated metal roller, the so-called thermal roller, may rise to about 250 degrees during soft calendering. When soft or calendering a paper or board web roll through a nip between a polymer coated roll and a thermal roll, there is often a problem that the width of the paper or board web in the nip varies with the longitudinal axis P1 of the polymer coated roll. If the web width d is less than the nip length L (nip length equal to the length P of the cylindrical portion of the polymer-coated roll in the direction of the longitudinal axis of the roll), the thermal roll 3 and the polymer coated roll 2 can contact or too close to each other. In this case, the thermal roller heats considerably more of the peripheral portion of the surface of the polymer-coated roll than the peripheral area of the central surface of the paper or board web 5. The phenomenon is illustrated in Figures 3A and 3C. Figure 3A shows a portion of the end of a pair of rolls viewed from the side, perpendicular to the nip when the direction of transfer of the fiber web 5 faces the viewer. The pair of rolls consists of a polymer coated roll 2 108072; 2 'and a thermal roller 3. Between the rolls there is a nip 7 through which a paper or board web 5 passes. The width d of the paper or board web is smaller than the length L of the nip in the longitudinal direction of the polymer coated roll. In Figure 3C, curve K1 shows the evolution of the temperature difference ΔΤ1 on the surface 8 of the cylindrical portion 5 of the polymer roll; 8 'between the peripheral portion 8b' and the peripheral region 8a 'of the center of the same roll surface. As can be seen from the figure, there is a clear temperature difference between the peripheral portion of the surface of the polymer coated roll and the peripheral portion of the central portion. If the temperature difference ΔΤ1 becomes too high, it can result in damage to the polymer coating and thus deterioration of the roll properties and acceleration of the need for the roll or its coating 10 to be renewed.

An attempt has been made to solve the problem by driving the paper or cardboard web too wide, i.e. wider than the length P of the cylindrical portion of the polymer coated roll, and cutting off the excess fiber web width before winding. The problem with the method is the loss of paper or cardboard, which increases the cost of calendering.

Attempts have also been made to cool the peripheral portions of the polymer-coated roll with a precisely directed water jet. An example of such a cooling method is the method of cooling the edges of a polymer coated roll using a water jet described in DE-A-40 37 166. In order to accurately position the water jet, the method of the publication requires the use of a complex control system. U.S. Patent No. 5,266,167 also describes a solution in which the edges of a polymer-coated roll outside the paper and board web are cooled by a water jet applied to the edges. Even though the water jet is aimed precisely at cooling, the edges of the paper or board path get wet easily. The paper and paperboard to be calendered will be impaired if they come into excessive contact with water. Thus, after cooling the water, the method has to blow air to the edges of the paper and board web to evaporate the water, which further complicates the equipment used in the method and the water jet control method.

. · An attempt has also been made to solve the above mentioned problem of resistance to roll polymer coating by measuring the surface temperatures of the roll surface with an IR camera and cooling the peripheral parts of the roll surface outside the paper or board web by an air jet directed to a region outside the roll surface. remains under the fiber web in a nip. However, due to turbulence in the air, it is difficult to direct the air jet to the correct position on the polymer coated roll. Automatic air jet 35 while alignment systems are complicated and expensive due to control technology, which is why the air jet is routed manually based on the width of the paper and board web 3. The manually directed air jet, in addition to cooling the peripheral portions of the polymer coated roll surface, virtually always cools the peripheral area of the cylindrical portion of the roll which is nip below the paper or board web so that the temperature difference between the peripheral area and The phenomenon is illustrated in Figures 3A and 3C. Fig. 3A shows a dashed blasting element 6. The Pu holding element is located over the edge region 8a 'of the middle part of the surface of the polymer coated roll 2 and partly over the edge part 8b' of the surface of the roll. As a result of the cool air jet blown by the blowing element, the temperature of the surface edge portion 8b, 8b '10 decreases to the temperature TT (curve K2 in Fig. 3C), but at the same time also decreases the temperature. the temperature of the center edge of the roll surface 8a, 8a 'to T2' which is lower than T2, since part of the air flow is easily directed to the center edge of the roll surface which is nip below the paper or board web due to turbulence. In this case, the temperature difference Τ-Τ2 ′ = ΔΤ2 between the edge portion 8b ′ of the roll surface 15 and the edge region 8a ′ of the center portion is not sufficiently reduced. If the temperature difference ΔΤ2 becomes too large, the nipple must be opened and the paper or board web calendering must be interrupted.

Above, only the surface quality deterioration and degradation of polymer coated rolls due to the high temperatures used in calendering have been described. 20 However, the same problem occurs with long nip calendering. When performing long-nip quick calendering with a shoe calender, a thermal shoe is provided with a static shoe roll opposite an endless roll. While long-nip calendering is again performed on the tape calender, there is an endless tape in the nip between the thermal roller and the counter roll opposite thereof, which is tracked to rotate the counter roll by the * 25 control / clamping rollers. If the coating material of the tape used in the shoe calender or the tape calender is polymer, this will cause problems similar to those described above for the polymer coated roll if the thermal roller is allowed to overheat the polymer surface of the tape.

It is an object of the invention to overcome the drawbacks of the prior art.

Accordingly, it is a first object of the invention to provide a method of cooling the peripheral portions of the polymer surface on a roll which are outside the edges of the paper or board web in the calendering nip. The cooling is intended to reduce the temperature difference between the peripheral portions of the polymer surface and the peripheral areas of the roll surface underneath the paper-35 or board web in the nip.

4, 108072

Another object of the invention is to provide a control technology-simple method for reducing the temperature difference.

A third object of the invention is to provide a cooling process which does not wet the edges of the paper or board web.

The invention relates, for example, to a method according to claim 1 for reducing the temperature difference (Δ re) between the peripheral portion of the polymer surface on the roll and the peripheral region of the central surface of the polymer by blowing gas on the polymer surface.

The invention also relates, for example, to an apparatus according to claim 8 for reducing the temperature difference between the peripheral portion and the peripheral region of the polymer surface on the roll surface when calendering a paper or board web in a calendering nip formed by at least one pair of rolls.

The basic idea of the invention is that the peripheral portions of the polymer surface over the roll are cooled by a gas stream directed partly to the fiber surface of the polymer surface, i.e. the paper or board web, to the uncoated edge and partly to the adjacent peripheral portion of the fiber. 1A and 1B, the fiber web is usually located only in a nip on the polymer surface 8 on the roll 2 (cf. Figures 3A and 4C, showing the conventional method of feeding the fiber web to and from the nip), but in the method of the invention the fiber web is tracked to travel along the polymer surface at a distance corresponding to at least 5 degrees, preferably greater than 15 degrees, calculated from the circumferential angle of the roll underneath the polymer surface.

In the process of the invention, the temperature difference (ΔΤ) between the peripheral portion of the polymer surface on the roll and the peripheral area of the central surface of the polymer is reduced by blowing gas onto the polymer surface while calendering the fiber path. The gas is preferably air. The fiber web is calendered by feeding the fiber web to at least: * a calender nip between one pair of rolls, the roll comprising a heated thermal roll and an opposite roll having a polymer surface thereon. Polymee-30 is sprinkled on the roll either just around the nip or across its circumference (soft and shoe calendars). In the method, the fiber web is arranged to meet the polymer surface near the nip in the first position, after which the fiber web is followed to rotate the polymer surface to the second position where the fiber web is to separate from the polymer surface. Cooling gas is blown onto the polymer surface between the first and second 108072 points, close to the nip so that the cooling gas is applied partly to the uncoated edge portion of the polymeric surface and partly to the peripheral portion of the middle portion of the fiber web.

The fiber web meets the polymer surface at the first point located before the 5 nips, near or in the nip. The second point is located in or near the nip, respectively, near the nip.

The apparatus used in the method comprises fiber path control elements and a cooling apparatus having a (gas) blowing element. The first guide element is located relative to the roll under the polymer surface such that it guides the fiber web to the polymer surface at the first point and the second guide element is located relative to the same roll so as to deflect the fiber web away from the polymer roll surface at the second position. The gas jet of the blowing element is directed near the nip, partly over the uncoated edge portion of the polymeric surface of the fiber web and partly over the peripheral region 15 of the middle portion of the web adjacent the peripheral portion.

Looking perpendicular to the calendering nip perpendicular to the direction of the cooling apparatus, the cooling elements of the cooling apparatus are partially over the uncoated edge portion of the paper or cardboard web of the polymer surface and partly over the peripheral area of the paper or board web adjacent the periphery.

By using a gas jet to cool the peripheral portions of the polymeric surface of the roll, there is an advantage over known methods of cooling the edges with a water jet to prevent water and paperboard edges from becoming wet.

In the method according to the invention, the cooling gas jet is directed partly on the uncoated edge portion of the polymer surface on the roll 25 and partly on the peripheral portion of the central surface coated on the paper or board adjacent to the polymer surface. The paper or board web prevents the polymer surface underneath from cooling. In this way, the temperature difference between the edges of the polymer surface outside the paper or board web and the portion of the polymer surface under the nip 30 under the paper and board web is reduced. By the method of the invention, the temperature difference between the different parts of the polymer surface is reduced so much that the maximum temperature difference between the different parts of the polymer surface is not exceeded. This provides the advantage over the known methods that the calendering nip need not be opened to cool the polymer surface on the roll, whereby the average calendering speed of the paper or board web can be increased.

As a further advantage of the method according to the invention, the method is very simple in control technology, since the direction of the gas jet does not have to be adjusted very precisely along the longitudinal axis of the roll under the polymer surface, since the fiber web is used to protect the polymer surface from excessive cooling. The adjustment method is also not sensitive to changes in the position of the paper or board web in the direction of the longitudinal axis of the roll under the polymer surface.

The invention will now be described in more detail with reference to the accompanying drawings.

Fig. 1A is a schematic view of a paper or board web transfer arrangement for a polymer coated roll and a roll surface polymerization cooling apparatus viewed from the end of a pair of rolls.

Fig. 1B schematically illustrates a paper or board web transfer arrangement and a polymer surface cooling apparatus for a shoe roll rotated by a polymer coated endless strip, viewed from the end of a pair of rolls. The shoe roll is shown in partial sectional pattern.

Fig. 2 shows the transfer arrangement of Fig. 1A and the cooling apparatus in the direction Π of Fig. 1A.

Figure 3A illustrates a prior art air-cooling method in which one peripheral portion of a calender nip formed by a pair of rolls is viewed perpendicular to the side of the pair of rolls.

Fig. 3B shows a gas cooling method according to the invention in which the second peripheral portion of a calender nip formed by a pair of rolls is viewed perpendicular to the side of the pair of rolls.

Figure 3C shows the evolution of the temperature difference between the peripheral portion of the surface of the polymer roll and the peripheral portion of the central portion in the nip both in the known cooling methods and in the cooling method of the invention.

Figure 4A illustrates one embodiment of the cooling method 30 of the invention when viewed with a nip perpendicular to the end of a calendering nip formed by a pair of rollers.

7th 108072

Figure 4B shows another embodiment of the cooling method according to the invention. The designations of the figure and the presentation are the same as in Fig. 4A.

Figure 4C shows a prior art cooling method. The designations of the figure and the presentation are the same as in Figures 4A and 4B.

In the polymer-coated roll surface cooling quench system shown in Fig. 1A, the fiber web 5 is calendered by a polymer-coated roll 2 formed by a rotating pair of rolls; In a calendering nip 7 between the 2 'and the opposite thermal roll 3; 7 '. The rolls rotate in different directions: the polymer-coated roll rotates counterclockwise and the thermal roller rotates clockwise. The fiber web 5 meets the surface of the polymer coated roll 10; 8 'at A; A 'and may detach from the surface of the polymer coated roll at position B; B \

Figure 1B shows a shoe calender with a static shoe roll 2 opposite the thermal roller 3; 2 "surrounded by an endless polymer coated strip 8; 8". The fiber web 5 is imaged to meet at the A "A" A "A" A "A" circumferentially circulating shoe roll circumferential surface of the shoe roll, and is detached from the surface of the polymer coated ribbon at B; B ". The fiber web is pressed against the thermal roller at nip 7; 7" due to the pressure exerted by the shoe roll shoe 9 on the polymer coated web. In a shoe calender, the length of the nip parallel to the longitudinal axis of the shoe roll is equal to the width of the endless belt in the longitudinal direction of the shoe roll.

Figure 2 is a side view of the cooling system of Figure IA. Polymer coated roll surface 8; 8 'is applied to the peripheral parts 8b' and to the peripheral areas 8a 'of the central surface of the surface by means of a cooling device 1. As shown in the figure, · the longitudinal axes P1 and P2 of the polymer coated roll and the thermal roller are substantially parallel. The blowing element 6 of the cooling apparatus 1 is located partly on the peripheral portion 8 ', 8b' of the surface of the polymer coated roll 25 and partly on the peripheral region 8 'of the central portion; 8a 'on.

Figures 3A-3B show a second edge portion of a calendering nip formed by a pair of rolls, viewed perpendicular to the side of the pair of rolls. Fig. 3A illustrates a prior art air-cooling process wherein the width of the fibrous web, i.e., paper and cardboard web, is d less than the length P of the cylindrical portion of the polymer coated roll in the direction of the longitudinal axis of the roll; 7 'a polymer coated roll 2; 2 'is the length L. parallel to the longitudinal axis P1. The fiber web is cooled by the blowing element 6. Figure 3B shows, as in Figure 3A, the second peripheral portion of this calender nip. The width of the fiber web is d, the length P of the coated part of the polymer coated roll and the length of the nip L. The fiber web 5 is on the surface 8 of the polymer roll; 8 'also after the nip. The fiber web is cooled by the blowing element 6. The blowing element 6 is in each case partly over the edge portion 8b 'of the polymer-coated roll and partly over the edge region 8a1 of the central portion.

Figure 3C shows the calendering nip 7; 7 'taking place on the surface edge portions 8' of the polymer coated roll 2; 8b 'and a peripheral region 8' of the central portion; Development of the temperature difference ΔΤ in the nip between 8a '. Curve K1 illustrates the evolution of the temperature difference T1-T2 = ΔΤ1 io if the peripheral parts of the roll surface are not cooled. The curves K2 and K3 illustrate the evolution of the temperature difference as the peripheral parts of the roll surface are cooled by various methods. Curve K2 illustrates the evolution of the temperature difference ΤΓ-Τ2 '= ΔΤ2 by the prior art cooling method and curve K3 the evolution of the temperature difference T1 "-T2" = ΔΤ3 in the method of the invention. T2, T2 'and T2 "denote the temperature 8'; 8a 'of the center of the cylindrical region of the polymer-coated roll (T2 is about 60 degrees) and T1, ΤΓ and T1" represent the peripheral portion 8' of the same roll; 8b '(Tl is about 80 degrees).

Figure 4A shows one embodiment of a cooling method in which a cooling gas, such as a cooling line, is blown in a nip 7; 7 'in proximity when the fiber web 5 is arranged 20 to travel a certain distance to the outer surface 8 of the polymer coated roll; 8 '. The fiber web passes from left to right and meets the surface of the polymer roll at position C. The fiber web is separated from the surface of the roll immediately after the calendering nip at position D. The fiber web is guided to the surface of the polymer roll 8; 8 'and away from the guide rollers 4a and 4b. The cooling gas is blown by a blowing element 6 which, viewed from the nip, is located on the supply side of the fiber web. The angle between C and A is calculated from the circumferential angle of a roll 2 '.

Fig. 4B shows another embodiment of a cooling method in which a cooling gas such as cooling air is blown in a nip 7; 7 '. The fiber web 5 is ··· in the nip of the surface of the polymer coated roll, i.e. at point A; A 'and the fiber web detaches from the roll surface at position B; B '. The fiber web is guided to pass onto the surface of the polymer coated roll 8; 8 'and away from the guide rollers 4c and 4d. The cooling gas is blown by a blowing element 6 located relative to the nip at the outlet side of the web.

Figure 4C illustrates, for comparison, rolls 2 currently coated with polymer; 2 'air cooling method used. The air is blown by the blowing element 6, 35 which is located relative to the nip at the outlet side of the web, the fiber web 5 passing from the left. 108072 9 to right nip 7; 7 'and meets the surface 8 of the polymer coated roll; 8 'only in the nip.

As stated earlier, the temperature of the heated thermo roll in many paper and board grades will need to be raised so high that the thermo roll tends to heat the peripheral portion 8b of the polymer surface substantially more than its fibrous web, particularly in the 5 nips where the surface of the thermo roll is area 8a. Thus, the temperature of the polymer surface edge portion tends to rise to T1 without cooling the polymer surface edge portions, while the temperature of the center surface edge region io remains below T2 with the temperature difference of the portions Δ 1 (cf. Fig. 3C curve Kl).

In the method according to the invention, the fibrous web, i.e. the paper or board web, is guided close to the nip 7 by the guide rollers 4 to the polymer surface 8. The fiber web 5 can be tracked to travel along the polymer surface 15 on the roll either before or after the nip, the latter being technically easier to track. The fiber web 5 is introduced into the guide roll 4; 4a; 4e, 4c to a calender nip 7 between a pair of rotating rolls; 7 ', 7 ". The fiber web meets the polymer surface 8 on the roll 2; 2', 2"; 8 ', 8 "near the nip, i.e. at C or A; A', A" depending on whether the fiber web 5 meets the surface of the roll 2 before 20 nips (C) or in the nip (A). At each end of the polymer surface, an edge portion 8b is formed which does not have a fiber web on its surface if the paper web width d is less than the nip length L. The fiber web is then guided by a guide roll 4; 4b, 4d, 4f separated from the polymer surface. The fiber web thus rotates the polymer surface 8 such that the angle between the entry point C or A on the fiber web and the exit point D or B therefrom is a calculated from the circumferential angle of the roll 2. Depending on whether the fiber web 5 passes along the polymer surface before or after the calendering nip 7, a cooling gas, such as cooling air, is blown in the vicinity of the nip, looking in the direction of supply or exit of the web. The cooling air is blown by a pu blast element 6 near the calendering nip 7, partly to the peripheral portion 8b of the polymer surface 8b and partly to the peripheral region 8a of the center surface between C and D or A and B depending on whether . Since there is a continuous fiber web 5 between C and D and A and B over the peripheral region 8a of the center of the polymer surface, the air jet cannot now significantly cool the peripheral region of the center of the polymer. 35 In this case, the temperature difference between the periphery of the polymer surface and the peripheral region of the central portion 10108072 ΤΓ'-Τ2 "= ΔΤ3 decreases and the surface quality of the polymer coating does not suffer from too great a temperature difference.

Only one embodiment of the idea according to the invention is described above. It will be apparent to one skilled in the art that the invention may be embodied in many other ways within the scope of the invention set forth in the claims. Thus, it is possible to replace the cooling apparatus 1 shown in Figures 1 and 2 with another cooling apparatus to which, for example, edge sensors are connected. The polymer-coated roll may also be a roll entirely of polymer.

««, »

Claims (11)

A method of reducing the temperature difference (ΔΤ) between the edge portion (8; 8b) of a polymer surface of a roller and the edge region (8; 8a) of the middle portion of the polymer surface by blowing gas against the polymer surface of the roller upon calendering a fiber web (5). ) By inserting the fiber web into the calendering nip (7) between at least one pair of rolls, wherein the pair of rolls comprises a heated thermo roll (3) and an opposing roller (2) coated with a polymer surface, characterized in that - the fiber web is arranged to hit the polymer surface (8) in the vicinity of the nip at a first point, after which the fiber web is arranged to circulate down the polymer surface to a second point, where the fiber web is deflected from the polymer surface, and - towards the polymer surface, cooling gas is blown between the first and second points, near the nip , so that the cooling gas is directed partly towards the non-fibrous edge portion (8; 8b) of the polymer surface (8) and partly to the edge region (8; 8a) of the middle fiber-coated portion adjacent the edge portion. 15 Process according to claim 1, characterized in that air is blown to the polymer surface and that the cooling gas is cooled. Method according to any of claims 1-2, characterized in that the angular distance between the first and second points is more than 5 degrees, preferably more than about 15 degrees, calculated on the peripheral angle of the cross-sectional circle of the roller. 20 Method according to claim 3, characterized in that the first point is located near the nip (7) before or during the nip and the second point is located in the nip or its proximity after the nip. Process according to any of claims 1-4, characterized in that the fiber web is a paper web or cardboard web. 25 Method according to any of claims 1-5, characterized in that the polymer surface (8; 8 ') is firmly connected to the rotating roller (2; 2'). Method according to any one of claims 1-5, characterized in that the polymer surface (8; 8 ") rotates around a stationary vane roll (2; 2"). An apparatus for reducing the temperature difference between the edge portion (8; 8b) of a polymer surface (8) on a roller (2) and the edge region (8; 8a) of the middle portion of the polymer surface upon calendering a fiber web (5) in the calendering nip (7). ) between at least one roller pair, the roller pair comprising a heated thermo roller (3) and an opposing roller (2) lined with a polymer surface, the plant comprising control elements (4) for the fiber web as well as a cooling system (1) with a blower element (6), characterized in that - the first guide element is positioned in relation to the polymer-coated roller so that it guides the fiber web (5) on the polymer surface (8) at a first point, and a second guide element is positioned relative to said same roll said to guide the fiber web away from the roll-coating polymer surface at a second point, and - the gas jet of the blowing element is directed in the vicinity of the nip (7), partially towards the polyhedron-coated edge portion (8; 8b) of poly the outer surface and partly towards the edge region of the two middle web (8; 8a) adjacent to the edge portion. Installation according to claim 8, characterized in that the guide elements (4) are placed in relation to the roll (2) below the polymer surface such that the fiber web (5) rotates along the circumference of the roll, which is lined with a polymer surface, for the calender nip (7). or after the nip at least about 15 degrees calculated on the circumferential angle of the cross sectional circle of the roller. Installation according to Claim 8 or 9, characterized in that when the calendering type is viewed perpendicular from the cooling system, the blowing element (6) of the cooling system (1) is partly on the non-coated edge part (8; 8b) of the polymer surface (8) and partly on the fiber web lined center portion (8; 8a) of the edge region adjacent the edge portion. Plant according to any of claims 8-10, characterized in that the control elements (4) are placed in relation to the roll (2) below the polymer surface such that - they control the fiber web to hit the polymer surface at a first point (A) or (C) and - they control the fiber web to be deflected from the polymer surface at a second point (B) or (D), the angular distance between said second point and first point being more than about - 15 degrees calculated on the circumferential angle of the cross section of the roller ( 2) below the surface. r