FI82956C - FOERFARANDE OCH ANORDNING FOER KONTROLL AV NYPTRYCKSPROFILEN I PRESSPARTIET AV EN PAPPERSMASKIN. - Google Patents

Description

82956

Method and apparatus for controlling the nip pressure profile in the press section of a paper machine Förfarande och anordning för kontroll av nyptrycks-Profilen i presspartiet av en pappersmaskin 5

The invention relates to a method for adjusting the axial linear pressure profiles of a nip 10 or nips in a press section of a paper machine, in which method the axial direction profile of the press roll or roll outer shell is adjusted and thus line pressure distribution.

The invention further relates to a press section of a paper machine comprising at least two, preferably several, press rolls which form 20 press nip or nips with one or more press felts passed through them.

To remove water from the paper and board web, press nips are commonly used, which are formed between two opposing press rolls and press press felt or felts passing between them. In the press nip, the felt and paper are compressed so that the water they contain almost completely fills the open space. In the compression zone and possibly also to some extent thereafter, the water leaving the web escapes to the hollow surface of the press rolls, such as grooves or holes. Therefore, the moisture profile of the felt or felts entering the pu-30 cross nip has little effect on the moisture profile of the paper or board leaving the same nip. The compression nip evenly aligns the web and the moisture profile of the felt according to the transverse line pressure distribution of the nip.

The transverse line pressure profile of the paper machine in the press nip directly affects the corresponding moisture profile of the nip pressed web, so that the higher the line pressure of the nip, the higher the dry matter content of the web running at the same point.

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The line pressure of the nip must be kept below a certain limit in order for the compression process to take place without breaking the fibrous structure of the web.

It is known from the prior art to act on the transverse line pressure distribution of the press nips with deflection-compensated or adjusted rollers (tk rolls) in which there are several adjacent hydraulically loaded sliding shoes inside the roll shell. However, the line pressure distribution of the nip cannot be changed very locally and sharply with Tk rollers. Zone-adjustable rollers can also be used to adjust local errors in the line pressure distribution, which cannot be done with normal so-called with floating tk rolls.

It is already known to use internal jacket temperature profiling in press rolls and calender rolls so that the roll is axially divided into different zones into which a medium having a different temperature is introduced and thus the radius of the roll is changed based on thermal expansion. In this way, the line pressure profile of the press-nip or calendering nip can be affected quite drastically.

20 Profiling devices outside calendering rollers are also known, which are based on either hot air blowing or inductive heating. For these solutions, reference is made to U.S. Patents 3,489,344 and 3,770,578 as examples.

Referring to the prior art of the invention, reference is also made to U.S. Patent 4,738,752, which discloses prior art temperature profiling devices outside the press roll shell. In this regard, reference is made in particular to Figure 2A of the latter U.S. patent and the description thereof.

A well-known drawback in the prior art roll presses is that the temperature profile of the roll shell in the axial direction is far from uniform. The edge areas of the press roll jacket are colder or hotter (tk rolls) than the center area. The axial temperature gradient of the press roll jacket can be as large as about 20 ° C / m.

35 Temperature gradients of this order and even smaller cause such abrupt changes in the line pressure profile of the roll nip that they cannot normally be completely controlled by previously known deflection-controlled rolls or by other known means.

The temperature gradient of the roll shell is created by the restoration of the press felt, 5 by the effect of air currents, by the different properties of the rolls, such as the thermal energy generated by the end bearings of the tk roll and the thermal energy generated by the track.

Said temperature gradient of the roll jacket also occurs in connection with the refurbishment of the compression-10 felt, because the felt extractors produce an uneven felt moisture profile so that the felt is wetter in its Rauna region than in the central region. This moisture profile of the press felt is "copied" into the temperature profile of the roll, so that the wetter a certain point of the felt is, the colder the press roll in direct contact with it at the same point is cooled.

Recently, efforts have been made to develop various rolls to replace paper machine versions, such as metal rolls, in connection with which the problems of web profiling have become even more pronounced.

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The object of the present invention is to provide a new method by which the disadvantages discussed above can be substantially avoided.

It is a further object of the present invention to provide a method and apparatus for adjusting the line pressure profile of a roll nip 25 which is simple in structure and operation and which can produce sufficiently abrupt changes in the axial temperature profile of the roll and, through thermal expansion, also in a press nip formed by the same roll.

30

In order to achieve the above and later objects, the method of the invention is mainly characterized in that the temperature profile of the outer jacket of the press roll or rolls is adjusted by directing the press felt or nip a press jet on the outer jacket of the press roll and rolls, the volume distribution and / or temperature distribution of which is adjusted to obtain the desired nip pressure profile.

The first embodiment of the device is essentially characterized in that a profiling heating device, such as a radiating device, a jet tube or a similar temperature profiling system, is arranged in the vicinity of the pressing felt before its pressing nip, extending substantially its entire width. heating effect with controlled volume and / or temperature profile.

Another embodiment of the device of the invention is mainly characterized in that a jet pipe is arranged in connection with the casing of one or more of said press rolls, through which a jet of water with a controlled volume and / or temperature profile is applied directly to said roll surface.

In the method according to the invention, when the press roll is profiled by means of a felt passing over it, other heating-cooling media such as air or radiant heating methods known per se, such as various electromagnetic radiations such as microwaves and / or infrared, can be used in addition to or instead of water jets. When using air blows, the pressing part may have difficulties in some places: 25 because large amounts of air are required that they interfere with the passage of the blankets or the web. When using water jets, the required amounts of heat can be transferred with relatively small amounts of water, which can only be in the order of 10-20 g / s / felt width m. When using water jets and air, cooling can also be used for profiling, which is not possible with radiant heating.

The invention can also be implemented using temperature profiling applied directly to the surface of the roll, but when used alone is not the most preferred embodiment of the invention. In the context of the present invention, the temperature profiling applied directly to the press roll jacket specifically uses a water jet, the volume and / or temperature profile of which is controlled.

In the following, the invention will be described in detail with reference to some application examples of the invention shown in the figures of the accompanying drawing, to the details of which the invention is not narrowly limited.

Figure 1 shows a schematic side view and partly a block diagram of a compact press in which the control method and device according to the invention have been applied.

Figure 2 shows the implementation of the control method and apparatus applied in Figure 1 in the transverse plane of the paper machine.

15

Fig. 3 shows typical surface temperature profiles of the center roll and deflection-compensated roll of the press shown in Fig. 1 without the control method according to the invention.

Figure 4 shows typical moisture profiles of the press felt before and after the nip before the implementation of the method according to the invention.

Figure 5 shows a typical temperature profile of the deflection compensated press roll 25 of Figure 6 without the control method and apparatus of the invention.

Fig. 7 shows a press roll according to Fig. 6 equipped with a temperature profiling device according to the invention, which acts directly on the cylinder shell of the roll.

The roll arrangement shown in Fig. 1 is already known. This compact press part is marketed by the applicant under the trade mark "SYM-PRESS II". The press shown in Fig. 1 comprises three successive press nips 35 N1, N2, N1, of which the first nip N, is formed between a lower roll 13 provided with a hollow surface 13 'and a snow roll 11. The first nip N, is double, 82956 Felted and passes through an upper felt 10 and a lower felt 14 guided by guide rollers 15. The upper felt 10 also acts as a pick-up felt, bringing the web W on its lower surface to the first nip N, and transferring the web W therefrom over the suction zone 11a of the suction roll 11 to the second nip N2.

5 The suction roller 11 has a perforated jacket 11 '. The second nip N2 is formed between the suction roll 11 and the center roll 16 provided with a smooth surface 16 '. A third nip N3 is formed in connection with the central roll 16 together with a press roll 17 having a hollow surface 17 '. The blanket 18 of the third nip N3 is guided by the guide rollers 19.

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After the third nip N3, the web W is detached from the smooth surface 16 'of the central roll 16 and transferred to e.g. a drying wire (not shown). The central roll 16 is, for example, a roll or a coated metal-framed roll replacing it. At the suction zone 11a of the suction roll 11 there is a steam box 12, 15 with which the temperature level of the web W is raised and thus the removal of water in the second and third nips N2, N3 is intensified. The press roll structure described above is known in the art and is presented here only for understanding the background of the invention and as a basis for an application example of the invention.

20

According to Fig. 1, inside the loop of the press felt 10, a jet tube 21 is arranged to implement the present invention, which according to Fig. 2 is divided in the transverse direction into blocks 21, ... 21N, which thus have N pieces. The different blocks of the nozzle 21 have a nozzle 27 and each block is connected by its own pipe 26, ... 26N to a flow supply and control unit 20. The unit 20 can control the flow rate profile F, ... FN of each nozzle 27 and / or temperature profile T, ... T „. Before the nip N, a jet of water is applied to the inner surface of the felt 10 via a series of nozzles 21, the temperature profile T, ... TN and / or the flow rate profile F, -FN of 30 can be adjusted according to the invention. In this way, the moisture and temperature profile of the felt 10 entering the nip N can be controlled so as to obtain the axial temperature profile of the roll 11 'in direct contact with the felt 10 and thus the diameter profile such that both the nip N and the nip 35 N2 achieve the desired transverse viivapainejakautuma. In the invention, the set value is generally a uniform temperature profile of the press roll jacket, 7 82956 whereby the final adjustment of the nip pressure profile of the nip N can be carried out accurately and without interference, e.g. by using a deflection-controlled roll of the nip N, the lower roll 13.

According to Fig. 1, a jet tube 22 corresponding to the nozzle tube 21 described above is also arranged inside the loop of the first nip N, the lower felt 14, through the nozzle set 27 a water jet with adjustable quantity and / or temperature profile can be fed to the inner surface of the felt 14. 13 'to the temperature profile and thus also to the line pressure profile of the nip N, as described above.

Fig. 1 further shows a third jet tube 23 arranged inside the loop of the felt 18, which functions in a manner corresponding to the jet tubes 21 and 22 to adjust the temperature profile of the third nip N, the casing 17 'of the press roll 17 and thus also the line pressure distribution of the nip N.

It should be emphasized in this connection that although the invention is described above and below only with reference to the temperature profiling provided by the water jet, other heating / cooling media, such as air, can be used instead of water. In addition to or instead of temperature profiling of the press felt with the medium or media, various methods of radiant heating, such as microwave and / or infrared heating, can also be used, with which electrically controlled transverse temperature profiling of the felt can be easily carried out. However, water is generally the most preferred heat transfer medium, as it requires relatively little use and, when used, cooling can also be used in the control. If the invention exclusively, or as most suitably, together with the profiling of the felt, temperature profiling directly acting on the press roll jacket, a water jet is used in the latter profiling.

Figure 1 shows an alternative embodiment of the invention, or preferably only an additional feature, according to which nozzle tubes 35 24 and 25 operate, through which a nozzle array 27 can be fed a water jet F with adjustable volume and / or temperature profile directly directly to the jacket 13 of the roll 13; '; 17' and thus, alone or in combination with the nozzle tubes 21,22 and / or 23, the axial temperature profile and nip pressure distributions of the jacket of said roll 13,17 can be controlled.

The nozzles 21,22,23,24,25 shown in Fig. 1 are generally not all needed at the same time, and according to a preferred embodiment of the invention only the nozzles 21,23 spraying on the common felt 10 of the first and second nip N1, N2 and the felt 18 on the third nip are used. .

According to Fig. 1, an axial temperature profile measuring device is arranged in connection with or near the sheaths 11 ', 13', 17 'of the rollers 11, 13, 17, which according to Fig. 1 comprises a sensor set or a traversing sensor 29 which gives a measurement message to the unit 20 together or via connections 31. The unit 20 is set or programmed to implement a predetermined, preferably flat, jacket temperature profile of the rolls 11,13,17.

If necessary, an arrangement for measuring the moisture profile of the web W coming from the press can also be arranged in connection with the control system according to the invention. This arrangement is shown schematically in Figures 1 and 2 by a block and an associated humidity profile measuring sensor set 33 or a traversing humidity sensor. The humidity profile measuring system 30, which is not always necessary, can be helpful in establishing the setpoints of the control system so that a pre-set generally uniform moisture profile is achieved for the web W coming from the press.

Figure 3 shows typical surface temperature profiles of press rolls without the control method according to the invention. The profile P, shows a typical temperature profile 30 of the outer surface 16 'of the central roll 16 as shown in Fig. 1 along the entire length L of the roll shell. The roll 11 has a rather steep temperature gradient on both the treatment side length 1 and the drive side length 12. The profile P2 is a typical temperature profile of the sheath 13 'of the deflection compensated lower roll 13 of a press as shown in Fig. 1. Profile P2 shows that the roll jacket temperature is approx. 10 ° 35 higher on the operating side than on the treatment side. The present invention generally i; , 82956 is achieved with a uniform roll shell temperature profile, which is shown in Fig. 3 by a broken line as a profile Pe.

Figure 4 illustrates additional moisture profiles of a press-S as shown in Figure 1 without the effect of the method of the invention. In Fig. 4, the profile P4 shows the moisture profile H of the press felt 10 before the nip N, and the profile P3 shows the moisture profile of the felt 10 after the nip N. It is found that the nipple N, the incoming felt 10 is wetter in its edge areas than in the middle and that in the edge areas of the roll 11 the moisture profile drops in the nip N 10, considerably more in the middle area. This drop in moisture profile is denoted in Figure 4 by AH.

If necessary, the invention may use, instead of or preferably in addition to profiling by means of felt or felts, a water jet applied directly to the casing of the press roll, the distribution of which is adjusted in temperature and / or amount in the axial direction of the roll. This embodiment is illustrated in Figures 5, 6 and 7. Figure 5 shows the temperature profile T 'of the jacket 13' of the tk roll 13A of Figure 6 along the length L. According to Figure 5, the deflection compensated roll 13A has significant temperature gradients in the region 1 and 12 near its ends. , that in the immediate vicinity of the roll ends the temperature is higher than in the central region of the roll 13A. Because the edge regions of the tk roll 13A tend to heat up due to heating of the jacket bearings (not shown). According to the invention, this anomaly of the temperature profile T? The mode of action of the control can be, for example, such that colder water is sprayed on the edge areas 1 and 12 of the roll 13, whereby the water 30 penetrating the hollow surface 13 of the jacket effectively cools the edge areas and the temperature profile T0 of Fig. 5 is substantially horizontal.

In particular, water jets are used in the temperature profiling 35 applied directly to the press roll casing, because water provides an efficient heat exchange, especially on the hollow surface of the roll, relatively little water is required, and cooling can also be used in profiling.

The following claims set forth within the scope of the inventive idea, the various details of the invention may vary and differ only from those set forth above by way of example only.

Claims (11)

A method for adjusting the axial linear pressure profiles of a nip or nips (N, Nj, Nj) in a press section of a paper machine, wherein the method in turn, which in turn affects the transverse line pressure distribution of the machine 10 of the press nip or nips (N ,, N2, N}) formed by the press roll or rolls (11,13,16,17), characterized in that the press roll or rolls (11,13 , 17) the temperature profile of the outer jacket (11 ', 13', 17 ') is adjusted by applying a roller to the press felt or felts (10, 14, 18) passing through the pressing nip or nips (N 1, N 2, N 3) formed by the roll in question. axially profile adjustment-15 ty heating / cooling effect and / or a water jet (F) directly on the outer jacket of the press roll and rolls, with a number distribution (F, ... FN) and / or the temperature distribution (T, ... TN) is adjusted to obtain the desired nip pressure profile. A method according to claim 1, characterized in that the temperature profiling of the press felt is performed before the profiled press nip using a water jet (F) and its quantitative and / or temperature profiling, thereby providing a certain temperature profile for the felt going to the profiled press nip, which "copies" to the temperature profile of the press roll casing in contact with the profiled press felt, and that the temperature profiling directly applied to the roll jacket used in the method uses volume and / or temperature-profiled water jets (F). Method according to Claim 1 or 2, characterized in that the water jet (F), which has a temperature profile (T, ... TN) and / or a quantity profile (F, ... Fn), is applied to the press felt (10) or felts. (10,14,18) on the outer and / or inner surface of the loop before the nip whose line pressure profile is adjusted. 35 ---- I2 82956 A method according to claim 1, 2 or 3, applied in a press section comprising a compact press roll assembly (11, 13, 16, 17) in which at least two, preferably three, nips (N 1, N 2, Nj) are formed. between the press rolls between the nips 5 (N1, N2, N3) of the web (W) supported by the roll surface or the press felt, characterized in that the method is applied in connection with the first upper felt (10) of the press section by spraying on its inner surface before the first nip (N 1) - and / or a water jet with a controlled profile (F) and / or that in the method a water jet (F) with a controlled temperature and / or volume profile is sprayed on the inner surface of the lower felt (14) of the first nip (N,) before the first nip (N,) and / or a jet of water (F) with a controlled volume and / or temperature profile is sprayed on the inner surface of the felt (18) of the third nip (N3). Method according to Claim 4, characterized in that a water jet (F) with a fixed and / or temperature profile is sprayed directly onto the outer jacket (13 ') of the lower roll (13) of the first nip (N,) of the press, preferably a deflection-controlled roll. that a jet of water (F) with a controlled quantity and / or temperature profile is sprayed directly on the outer surface (17 ') of the upper roll (17) of the third nip (N3) in order to control the compression pressure profile of the third nip (N3). Method according to one of Claims 1 to 5, characterized in that the method measures the temperature profile of the outer jacket of a press roll with a temperature profile with a sensor set or a traversing temperature sensor (29) and that the temperature message thus obtained is fed to a system (20). the volume and / or temperature profile of the water jet (F) (F, ... FN, T, ... TN). 30 Method according to one of Claims 1 to 6, characterized in that the method measures the transverse moisture profile of the web (W) coming from the press and uses the measurement signal thus obtained as a feedback signal or an auxiliary signal in generating the setpoint signal set of the control system 35. i3 82956 A press section of a paper machine comprising at least two, preferably more, press rolls (11,13,16,17) which together form a press nip or nips (N | (N2, N,) through which one or more press felts ( 10,14,18), characterized in that a profiling heating device, such as a radiating device, a jet tube (21,22,23,24,25) or a similar temperature profiling device extending substantially the entire width of the press felt is arranged before its pressing nip. a system comprising a series of spray nozzles (27) through which a heating effect with a controlled temperature and / or temperature profile (F, ... FN, T, ... TN) can be applied to the adjacent felt (10, 14, 18). A press section of a paper machine comprising at least two, preferably more, press rolls (11,13,16,17) forming together a press nip or press nips (N ,, N ,, N,) through which one or more press felts are passed. (10,14,18), characterized in that a jet tube (24,25) is arranged in connection with the casing (11 ', 13', 17 ') of one or more of said press rolls (11, 13, 17), through which said a water jet (F) with a fixed and / or temperature profile on the roll surface (13 ', 17'). 20 Press section according to Claim 8 or 9, characterized in that the press section uses both temperature profiling devices (21, 22, 23) acting on the press felt and water jet devices which apply temperature profiling directly to the outer jacket (13 ', 17) of the press roll or rolls (13, 17). '). Press part according to Claim 8, 9 or 10, characterized in that the press part comprises a transverse measuring sensor (29) or a corresponding sensor set and connections (31) for traversing the transverse temperature profile of the surface of the temperature-profiled press roll or rolls. ) or the measurement message from the sensor set can be routed to the temperature profiling control system (20) and / or that the apparatus comprises a transverse measurement sensor or sensor set (33) and a connection 35 (32) or connections 35 (32) or connections for pressing said measurement message from the press. to the roll shell temperature profiling control system (20). i4 82956