Method and apparatus for controlling the temperature of a press cover
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- VOITH PATENT GMBH
- Filing Date
- 2024-07-26
- Publication Date
- 2026-06-10
AI Technical Summary
The drainage ability of press coats in press arrangements deteriorates over time due to wear, leading to a reduction in void volumes and compromised drainage performance.
Implementing a temperature control method where the target temperature of the press coat is gradually lowered over its lifetime, utilizing polyurethane materials that exhibit increased strength and stability at lower temperatures, thereby maintaining optimal void volumes and drainage performance.
This approach effectively counters the reduction in void volumes caused by abrasion, maintaining the press coat's drainage ability for a longer period by ensuring the material remains stable and efficient in its temperature-controlled state.
Smart Images
Figure EP2024071284_03042025_PF_FP_ABST
Abstract
Description
[0001] Method and device for temperature control of a press jacket
[0002] The present invention relates to a method for temperature control of a press sleeve provided with depressions on the outside in a press arrangement for increasing the dry content of a fibrous web, comprising the following steps when the press sleeve is used as intended: a) determining a current actual temperature of the press sleeve; b) determining a current target temperature of the press sleeve; c) in the event of a deviation of the current actual temperature from the current target temperature, heating or cooling the press sleeve so that the current actual temperature changes towards the current target temperature.
[0003] Furthermore, the present invention also relates to a press arrangement for carrying out the method for temperature control and to a machine for producing a fibrous web, in particular a paper, cardboard or tissue web, comprising such a press arrangement.
[0004] Machines for producing a fibrous web, such as a paper, cardboard, or tissue web, typically comprise a press assembly in which the fibrous web is dewatered or dehumidified by mechanical pressure, thereby increasing the dry content of the fibrous web. The press assembly is typically located between the forming and drying sections. Such a press assembly typically comprises at least one press sleeve, although the term "press sleeve" is to be interpreted broadly in the context of the present invention. It can refer to both a roll cover rigidly connected to a roll and a flexible sleeve, as required for press assemblies with an extended press nip.The latter, in particular, is the focus of the present invention, since press arrangements with an extended press nip offer several advantages: The press nip is planar and not essentially linear as in conventional roller presses. This means that the pressure exerted on the fibrous web to be dewatered in the press nip in the running direction does not start suddenly, but can be continuously increased from a low value to a high value. This reduces the risk of the fibrous web to be dewatered being crushed in the press nip. In addition, the residence time in the press nip is increased. Thus, the fibrous web can be dewatered in an extended press nip both very efficiently and in a way that preserves its volume.For example, the fibrous web can be guided through the extended press nip together with a felt or between two felts. In a so-called shoe press, the extended press nip can be formed between a shoe press roll and a counter roll. Indentations on the outside of the press cover can temporarily absorb water, which is then forced out of the fibrous web and the felt transporting it in the press zone.
[0005] Methods for regulating the temperature of a press sleeve are already known from the prior art. For example, the document DE 37 05 241 A1 proposes to set different pressures and temperatures in sections of the press zone of an extended press nip of a shoe press, viewed in the direction of travel of the fibrous web. This is achieved by a pressure medium between the press shoe and the press sleeve, with the pressure medium being appropriately tempered to heat or cool the press sleeve. The simultaneous application of pressure and heat in the press nip can increase dewatering, but without the risk of damaging the fibrous web.
[0006] Furthermore, WO 93 / 23614 A1 proposes a shoe press assembly in which a temperature sensor is provided on both the front and rear edges of the press shoe. If a temperature difference is detected, the front and / or rear edges are specifically cooled or heated using a temperature-controlled fluid to achieve temperature equalization. This counteracts undesirable deformation of the press shoe during operation. However, the temperature of the press shoe also affects the temperature of the press sleeve, against which it presses during normal operation. A disadvantage of the press assemblies known from the prior art, however, is that - regardless of whether temperature control is present or not - the dewatering ability of the press sleeve generally deteriorates noticeably over time.A key reason for this is that the press sleeve, which is subjected to significant stress during normal operation, wears away over time. As a result, the depth of the depressions, such as drainage grooves, becomes increasingly shallow, and these can absorb less and less water. This is also referred to as a reduction in the so-called "void volume" of the press sleeve. This process can be imagined similarly to the tire tread on a car, which gradually wears down over time. When the wear becomes too severe, the worn press sleeve must be replaced with a new one.
[0007] The object of the present invention is to solve or at least mitigate the problem described above. In particular, the deterioration of the dewatering ability of a press sleeve over its lifetime is to be counteracted.
[0008] This object is achieved by the features of the independent claims. The dependent claims relate to advantageous developments of the present invention. Thus, the object is specifically achieved by the generic method for temperature control of a press sleeve described above, which is particularly characterized in that the current target temperature is continually reduced over the service life of the press sleeve. The inventors have recognized that temperature has a significant influence on the material strength or the modulus of elasticity of the press sleeve. In this case, the material is generally noticeably stronger or more dimensionally stable at lower temperatures than at high temperatures. The inventors have further recognized that this circumstance can be specifically used to counteract the reduction in void volume that occurs due to abrasion of the press sleeve over its service life.In this way, dewatering performance can be maintained at an acceptable level over an extended period. It is important to understand that a press arrangement requires a very specific void volume of the press sleeve for optimal dewatering performance. If the void volume is too small, oversaturation in the press nip can occur, leading to undesirable water leakage in the press nip against the machine direction (also known as "backsplashing"), or to an equally undesirable high hydraulic pressure in the depressions of the press sleeve. Conversely, too large a void volume can lead to undersaturation in the press nip, which impairs dewatering there. Both too small and too large a void volume lead to a lower dry content of the fibrous web after the press arrangement and to poorer runnability of the machine.The optimal void volume depends largely on the grammage and dry content of the fibrous web before entering the press assembly. New roll covers are typically selected so that their void volume matches the aforementioned properties of the fibrous web. This already takes into account that the void volume is reduced by the pressures prevailing in the press nip. The material of the press sleeve is compressed in the press nip and partially escapes into the void volume.
[0009] If, according to the invention, the temperature of the press sleeve is continuously reduced over its lifetime, the strength and dimensional stability of the press sleeve material continually increases. This results in increasingly less deformation of the material at the same pressure in the press nip and thus a smaller reduction in the void volume. This counteracts the reduction in void volume caused by abrasion of the press sleeve, and the optimal dewatering capacity of the press sleeve can be maintained for a longer period.
[0010] As is common practice, especially for roller shells of a shoe press, the recesses can also be formed in a layer of the press shell that comprises a polyurethane, preferably made entirely of polyurethane. Polyurethane is one of those materials that is not only easy to process for this purpose, but also has the property that its strength and dimensional stability are highly dependent on temperature.
[0011] In particular, the polyurethane can be formed by reacting a prepolymer and a crosslinker component, wherein the prepolymer is a reaction product of 4,4'-diphenylmethane diisocyanate (MDI) and a polyol component containing at least one polycarbonate polyol, and wherein the crosslinker component contains a diol. In particular, the crosslinker component can comprise butanediol (BDO). Such polyurethanes have proven particularly suitable for the temperature control according to the invention, since a particularly strong influence of temperature on the dynamic compression modulus has been observed in them.
[0012] As already mentioned at the beginning, the press cover used for the present invention is preferably a shoe press cover. The press cover, especially if it is a shoe press cover, should be impermeable to prevent lubricating oil, which is conducted between the press shoe and the press cover for lubrication, from escaping and contaminating the fibrous web. Furthermore, the depressions preferably have the shape of at least one continuous or discontinuous groove, wherein the groove or grooves preferably extend(s) helically essentially in the circumferential direction of the press cover. Such a design has proven itself many times in practice and is relatively simple to manufacture.
[0013] A simple and therefore preferred variant for determining the current actual temperature in step a) provides for it to be measured, preferably without contact, directly on the outside of the press sleeve. For this purpose, thermometers that operate without contact via infrared or visible laser light can be used. The use of thermal imaging cameras is also possible. An alternative variant for determining the current actual temperature in step a) provides for the use of temperature sensors integrated into the press sleeve. A typical shoe press sleeve usually contains a reinforcement structure made of a thread lay or woven fabric embedded in a matrix structure, in particular made of polyurethane. The clothing industry has recently developed specially developed sensors, particularly for functional underwear, which have a thread-like structure and can therefore be integrated into the fabric of a textile.At the same time, the data captured by the sensor can be read using RFID technology and transmitted, for example, to a nearby mobile device. These thread-like sensors with RFID technology, developed for the textile industry, can also be perfectly integrated into the reinforcement structure of the press sleeve without causing problems as an obstruction.
[0014] Even though runtime-related abrasion and the associated reduction in void volume have the greatest influence on the deterioration of the press sleeve's dewatering ability over time, there are also other influencing parameters that can change to a limited extent over time (with otherwise identical machine settings). Therefore, in an advantageous development of the present invention, it is proposed that at least one, preferably several, of the following influencing parameters be taken into account when determining the current target temperature in step b).are: i) dry content of the fibrous web before the press arrangement; ii) grammage of the fibrous web; iii) running time of the press sleeve; iv) abrasion condition of the press sleeve; v) machine speed; vi) pressure profile and / or peak pressure in a press zone formed by the press sleeve during normal operation for the fibrous web; vii) running time and / or volume of a felt which is arranged between the press sleeve and the fibrous web during normal operation of the press sleeve. Since the relationships can be very complex and are not fully known, it is further proposed to use a self-learning control algorithm in step b) when determining the current target temperature. Using artificial intelligence, an optimal target value for a control system can now be determined relatively quickly and easily, even in very complex situations.
[0015] For the targeted adjustment of the current actual temperature to the current target temperature in step c), there are several options that can be used alternatively or cumulatively. One of these options proposes applying, in particular spraying, a coolant, preferably cooling water, to the outside of the press sleeve. Another option proposes embedding temperature control elements in the material of the press sleeve itself. These can, for example, either heat or cool using electrical current. The current can be introduced inductively. Furthermore, another option provides for the temperature and / or flow rate of a circulating fluid, in particular a cooling oil, to be adjusted inside the press sleeve.This essentially corresponds to the solution from the prior art described at the beginning, namely DE 37 05241 A1 and WO 93 / 23614 A1, to whose disclosure content reference is made in this regard.
[0016] According to a further aspect of the present invention, the above-described object is also achieved by a press arrangement for increasing the dry content of a fibrous web, comprising a press sleeve provided with depressions on the outside and means for temperature control of the press sleeve, preferably according to the method according to the invention described above, wherein the means for temperature control comprise: a) means for determining a current actual temperature of the press sleeve; b) means for determining a current target temperature of the press sleeve; c) means for heating or cooling the press sleeve, so that in the event of a deviation of the current actual temperature from the current target temperature, the current actual temperature changes towards the current target temperature; wherein the means for determining the current target temperature are designed to continuously lower the current target temperature over the service life of the press sleeve.
[0017] The advantages and technical effects described above in connection with the method according to the invention also apply mutatis mutandis to the press arrangement according to the invention and vice versa.
[0018] The press arrangement may further comprise a counter roll to form a press nip for the fibrous web together with the press cover.
[0019] Furthermore, the invention relates to a machine for producing a fibrous web, in particular a paper, cardboard or tissue web, comprising the press arrangement according to the invention described above.
[0020] The invention will be explained in more detail below using an exemplary embodiment described with the aid of schematic figures. In the following:
[0021] Figure 1 : a schematic representation of a press arrangement 1 with a
[0022] Press sleeve 6;
[0023] Figure 2: a schematic cross-sectional view of a section of the
[0024] Press jacket 6 from Figure 1;
[0025] Figure 3: a schematic representation of an active temperature control of the
[0026] Press jacket 6;
[0027] Figure 4: a schematic diagram illustrating the influence of temperature on the dynamic compression modulus of the material of the press sleeve 6 over the load rate; and
[0028] Figure 5: a schematic diagram illustrating the influence of temperature on the reduction of the void volume of the press sleeve 6 over the pressure. Figure 1 shows a schematic representation of a press arrangement 1, wherein the press arrangement in this exemplary embodiment is designed as a press arrangement with an extended press nip 7. Such a press arrangement 1 is also referred to as a shoe press. The extended press nip 7 is provided by two press elements, namely a shoe press roll 2 and a counter roll 3. The shoe press roll 2 comprises a press shoe 5, which is supported on a stationary yoke 4, and a flexible press sleeve 6, which is arranged so as to be rotatable around the press shoe 5. During normal operation of the press arrangement 1, a fibrous web 8 to be dewatered is guided through the extended press nip 7, preferably sandwiched between two press felts 9.The press shoe 5 has a substantially concavely shaped surface over which the press sleeve 6 runs, while the press shoe 5 presses it with a high pressure force F in the direction of the counter roll 3.
[0029] The compressive force F with which the press shoe 5 presses against the press cover 6 is preferably selected to be large enough that the peak pressure acting on the fibrous web 8 in the extended press nip 7 is at least 8 MPa, preferably at least 10 MPa. The length of the extended press nip of the main press 1 is preferably at least 150 mm, more preferably at least 190 mm.
[0030] It has proven particularly advantageous at such peak pressures if the shoe press jacket 6 consists at least partially of polyurethane which is formed by reacting a prepolymer and a crosslinking component, wherein the prepolymer is a reaction product of 4,4'-diphenylmethane diisocyanate (MDI) and a polyol component containing at least one polycarbonate polyol, and wherein the crosslinking component contains a diol, in particular butanediol (BDO).
[0031] As schematically illustrated in the enlarged cross-sectional view of the press sleeve 6 in Figure 2, a reinforcing structure 11 in the form of a thread mesh or thread fabric can be embedded in the polyurethane. Furthermore, the press sleeve 6 has depressions 10 on its outer side, which can be designed, for example, in the form of several grooves extending helically in the circumferential direction of the press sleeve 6. These depressions serve to provide a so-called void volume for the liquid which is absorbed in the extended press nip from the fibrous web 8 or from the press felt 9 arranged between the fibrous web 8 and the press sleeve 6. In the present exemplary embodiment, according to the view in Figure 2, the depressions are essentially rectangular and have a defined width and a defined height, at least when the press sleeve 6 is still in a new condition and is not subject to load.If the press sleeve 6 is subjected to the compressive force F in the extended press nip 7, the polyurethane of the press sleeve 6 is elastically partially pressed into the void volume, thereby reducing the void volume, particularly with regard to its width. In addition, over the service life of the press sleeve 7, more and more polyurethane is abraded, thereby further reducing the void volume, particularly with regard to its height.
[0032] While the first effect, i.e., the reduction of the void volume due to the compressive force F in the extended press gap 7, is generally already taken into account in the design of the press sleeve 6 during its installation, so that it can initially be operated in an optimally saturated range, it has not yet been possible to specifically counteract the second effect, i.e., the reduction of the void volume due to abrasion of the press sleeve 6 over its lifetime. This is precisely where the present invention comes in.
[0033] Although the present invention cannot prevent the abrasion of the press sleeve 7 over its service life, the inventors have found another way to counteract the resulting reduction in void volume. The inventors have determined that the void volume loss due to the compression of the material in the press nip is directly related to the dynamic compression stiffness of the press sleeve material. Closer investigations have shown that, depending on the material, there is a very large change in stiffness depending on the temperature of the press sleeve 7. The invention utilizes this effect by integrating active temperature control of the press sleeve 7 into the control system of the press assembly 1.
[0034] Such active temperature control can be provided, for example, as schematically shown in Figure 3. The current actual temperature of the press sleeve 6 is measured by a temperature sensor 12. The measurement can, for example, be carried out contactlessly from the outside on the outer surface of the press sleeve 7, or the temperature sensor 12 can be embedded in the polyurethane of the press sleeve 6. The measured current actual temperature is transmitted from the temperature sensor 12 via a wired or wireless signal line to a temperature control unit 13. The temperature control unit 13 compares the current actual temperature with a current target temperature and heats or cools the press sleeve 6 if the current actual temperature deviates from the current target temperature, so that the current actual temperature changes towards the current target temperature.The temperature control unit 13 can achieve this, for example, by controlling an internal temperature control element 14, in particular a temperature control element 14 embedded in the polyurethane of the press sleeve 6. Alternatively or additionally, the temperature control unit 13 can also control a press sleeve cooling pump 15 and / or a cooling oil pump 16. The press sleeve cooling pump 15 can apply a cooling fluid, in particular water, to the outside of the press sleeve 6 via an external temperature control element 17, such as spray nozzles, in order to cool it in a targeted manner. The cooling oil pump 16, on the other hand, can pump a cooling oil 18 into the interior of the shoe press roll 2, where it can, for example, specifically cool the press sleeve 6 from the inside in the area of the extended press nip 7.
[0035] It should be noted that - as is usual for such press arrangements - in addition to the cooling oil 18, other oil flows can also be pumped into the interior of the shoe press roll 2, such as, in particular, oil 20 for lubricating and / or cooling the press shoe 5 and / or oil 21 for controlling the contact pressure of the press shoe 5 by means of a pressure oil pump 19. The oils 18, 20, 21 introduced into the interior of the shoe press roll 2 can be returned via a return line to the cooling oil pump 16 and / or the pressure oil pump 19, wherein a heat exchanger 22 is preferably provided in the return line in order to cool the oil, for example by means of cooling water.
[0036] Through the active temperature control of the temperature control unit 13, the dynamic compression modulus and thus the void volume can be influenced via the temperature of the press sleeve 6. Figure 4 shows how, depending on the temperature, the dynamic compression modulus plotted on the Y-axis, measured in MPa, changes across the load rate, measured in MPa / s, plotted on the X-axis, for a specific polyurethane, referred to here as PU-A. Although the dynamic compression modulus increases with increasing load rate at both 25°C and 60°C, the curve at 25°C generally runs above the curve corresponding to 60°C. In other words, the polyurethane has a higher dynamic compression modulus at lower temperatures and is therefore more dimensionally stable.
[0037] If, according to the invention, the current target temperature is continually reduced over the service life of the press sleeve 6, the material of the press sleeve 6 becomes increasingly more dimensionally stable. In this way, the reduction in the void volume due to the elastic deformation of the press sleeve 6 in the extended press nip 7 continues to decrease. This counteracts the reduction in the void volume due to abrasion of the press sleeve 6 over its service life. The void volume thus remains in a range optimal for the dewatering capacity of the press sleeve for a longer period, or is removed from this range noticeably more slowly. This is schematically illustrated in Figure 5, where the reduction in the void volume in % is plotted against the pressure in MPa on the Y-axis. It is clearly visible that the curve at a temperature of only 20°C is noticeably flatter than the curve at 60°C.
[0038] Finally, it should be noted that in practice, the void volume is not only reduced over time by the abrasion of the press sleeve 6, but that the material of the press sleeve 6, particularly if it is predominantly made of polyurethane, also loses strength over time due to hydrolysis and can therefore no longer withstand the compressive forces in the extended press nip 7 as well, which leads to an elastic deformation of the material into the recess 10 and thus also to a reduction of the void volume in the extended press nip 7. This effect can also be counteracted according to the invention by the active temperature control of the press sleeve 6.
[0039] List of reference symbols
[0040] 1 press arrangement
[0041] 2 shoe press rollers
[0042] 3 Counter roller
[0043] 4 standing yoke
[0044] 5 press shoe
[0045] 6 Press jacket
[0046] 7 extended press nip
[0047] 8 Fibrous web
[0048] 9 press felts
[0049] 10 recesses
[0050] 11 Reinforcement structure
[0051] 12 Temperature sensor
[0052] 13 Temperature control unit
[0053] 14 internal temperature control element
[0054] 15 Press jacket cooling pump
[0055] 16 Cooling oil pump
[0056] 17 external temperature control element
[0057] 18 Cooling oil
[0058] 19 Pressure oil pump
[0059] 20 Oil for lubricating and / or cooling the press shoe 5
[0060] 21 Oil to control the contact force of the press shoe 5
[0061] 22 heat exchangers
[0062] F compressive force
Claims
Patent claims 1. A method for temperature control of a press sleeve (6) provided with depressions (10) on the outside in a press arrangement (1) for increasing the dry content of a fibrous web (8), comprising the following steps when the press sleeve (6) is used as intended: a) determining a current actual temperature of the press sleeve (6); b) determining a current target temperature of the press sleeve (6); c) if the current actual temperature deviates from the current target temperature, heating or cooling the press sleeve (6) so that the current actual temperature changes towards the current target temperature; characterized in that the current target temperature is continuously reduced over the service life of the press sleeve (6).
2. Method according to claim 1, characterized in that the depressions (10) are formed in a layer of the press jacket (6) which comprises a polyurethane, preferably consists entirely of a polyurethane.
3. The method according to claim 2, characterized in that the polyurethane is formed by reacting a prepolymer and a crosslinking component, wherein the prepolymer is a reaction product of 4,4'-diphenylmethane diisocyanate (MDI) and a polyol component containing at least one polycarbonate polyol, and wherein the crosslinking component contains a diol.
4. Process according to claim 3, characterized in that the crosslinking component comprises butanediol (BDO).
5. Method according to one of the preceding claims, characterized in that at least one of the following statements applies: i) the press cover (6) is a shoe press cover; ii) the press cover (6) is impermeable; iii) the depressions (10) have the shape of at least one continuous or discontinuous groove, wherein the groove or grooves preferably extend helically substantially in the circumferential direction of the press cover (6).
6. Method according to one of the preceding claims, characterized in that in step a) the current actual temperature is measured, preferably without contact, directly on the outside of the press jacket.
7. Method according to one of the preceding claims, characterized in that in step a) the current actual temperature is measured by means of temperature sensors integrated in the press jacket.
8. Method according to one of the preceding claims, characterized in that in step b) when determining the current target temperature at least one, preferably several, of the following influencing parameters is or are taken into account: i) dry content of the fibrous web (8) before the press arrangement (1); ii) grammage of the fibrous web (8); iii) running time of the press sleeve (6); iv) abrasion state of the press sleeve (6); v) machine speed; vi) pressure profile and / or peak pressure in a press zone (7) formed by the press sleeve (6) in normal operation for the fibrous web (8); vii) Running time and / or volume of a felt (9) which is arranged between the press cover (6) and the fibrous web (8) during normal operation of the press cover (6).
9. Method according to one of the preceding claims, characterized in that in step b) a self-learning control algorithm is used to determine the current target temperature.
10. Method according to one of the preceding claims, characterized in that in step c) a coolant, preferably cooling water, is applied, in particular sprayed, to the outside of the press jacket (6) in order to adjust the current actual temperature to the current target temperature.
11. Method according to one of the preceding claims, characterized in that in step c) for adjusting the current actual temperature to the current target temperature, tempering elements are embedded in the material of the press jacket itself.
12. Method according to one of the preceding claims, characterized in that in step c) the temperature and / or the flow rate of a circulating fluid, in particular a cooling oil (18), is adjusted in order to adjust the current actual temperature to the current target temperature inside the press jacket.
13. Press arrangement (1) for increasing the dry content of a fibrous web (8), comprising a press cover (6) provided with depressions (8) on the outside and means for temperature control of the press cover (6), preferably according to a method according to at least one of the preceding claims, wherein the means for temperature control comprise: a) means (12) for determining a current actual temperature of the press sleeve (6); b) means for determining a current target temperature of the press sleeve (6); c) means (14, 15, 16, 17) for heating or cooling the press sleeve (16) such that, in the event of a deviation between the current actual temperature and the current target temperature, the current actual temperature changes in the direction of the current target temperature; characterized in that the means for determining the current target temperature are designed to continuously lower the current target temperature over the service life of the press sleeve (6).
14. Press arrangement (1) according to claim 13, characterized in that the press arrangement (1) further comprises a counter roll (3) in order to form, together with the press cover (6), a press nip (7) for the fibrous web (8).
15. Machine for producing a fibrous web (8), in particular a paper, cardboard or tissue web, comprising a press arrangement (1) according to claim 13 or 14.