EP0412305A2 - Apparatus for controlling the thickness of a web passing through a press nip - Google Patents

Abstract

What is provided is an apparatus for controlling the thickness of a material web passing through a nip, in which the diameter of at least one of the rollers (5) limiting the nip is variable as a function of temperature. At the same time, a flexible use of the apparatus is to be possible by a simple means. For this, there is an irradiating device (6) which irradiates the roller (5) on part of its circumference with infrared radiation. <IMAGE>

Description

The invention relates to a device for controlling the thickness of a web of material running through a nip, in which the diameter of at least one of the rolls delimiting the nip can be changed as a function of temperature.

In a known device of this type (DE-PS 35 28 365), the two rolls forming a nip are thermally influenced with the aid of air, the air in the immediate vicinity of the roll surface being selectively heated by a heating device and the energy exchange between those exiting from the nozzles , heated air and the roller surface along a directly adjoining the roller surface, gap-like and arcuate region of substantially constant thickness. The heat transfer takes place here by convection, ie the rollers to be heated are heated by the heat transfer medium warm air. The roller is heated from the outer top area, the heat being dissipated from the surface into the interior of the goods by heat conduction. A disadvantage of this method is that air must first be heated in order to be able to heat the rolls. Since a certain loss of energy occurs with each heat transfer, the known device results in a high expenditure of energy. Design measures must be taken to ensure that the device provides an essentially closed space surrounding the roll surface in a gap-like and arc-shaped manner, in which the air is kept in contact with the roll surface. A new device with a heat transfer space adapted to the roll diameter is therefore necessary for each roll diameter.

From US-PS 43 84 514 it is known to heat the surface of a roller using eddy currents. To obtain a satisfactory level of efficiency, care must be taken that the air gap, i.e. the distance between the excitation device and the roller surface remains as small as possible. The shape of the pole piece of the excitation device must therefore be adapted to the roller diameter. In addition, eddy current heating is restricted to certain roller materials that meet certain electrical and magnetic resistance requirements.

It is the object of the present invention to provide a device for controlling the thickness of a material web running through a nip, which can be used more universally.

This object is achieved in a device of the type mentioned in the introduction in that an irradiation device is provided which irradiates the roller with infrared radiation over part of its circumference.

Infrared radiation begins in the electromagnetic spectrum immediately next to visible light at around 0.78 µm and ends at around 200 µm. The technically preferred spectrum is in the range between about 0.8 and 10 µm. A distinction is made between short-wave radiation between about 0.9 and about 1.9 µm, medium-wave radiation between about 1.9 and 3.1 µm and long-wave radiation between about 3.1 and about 6.0 µm. The invention is based on the effect that two bodies which have different temperatures endeavor to compensate for this state in that the warmer body supplies heat to the colder body by means of heat radiation. The warmer body sends out infrared rays. The higher the temperature difference, the greater the heat transfer using the infrared rays. The present invention thus requires neither convection heat nor contact heat. The heat transfer takes place only by radiation.

In a preferred embodiment, the irradiation device has a multiplicity of emitters which are arranged essentially parallel to one another. The arrangement of a large number of radiators, which are arranged along the longitudinal extent of the roll, allows the roll thickness and thus the size of the roll gap to be influenced separately in a large number of zones. There are basically as many controllable zones as there are radiators.

The radiators are advantageously rod-shaped. Due to the design of the emitters as rods, the device can be used for practically any roll diameter. When changing the roller diameter, it is therefore not necessary to adapt the device to the new roller diameter. A point on the roller surface that runs past the radiator is also not suddenly exposed to a radiation field of high intensity by the device. Rather, it takes Radiation intensity gradually increases and gradually decreases again after reaching a maximum. The roller surface is therefore only exposed to gradual changes in temperature. Jumps in temperature that could lead to heavy material stress on the roller surface are largely avoided.

If the emitters are arranged essentially parallel to a perpendicular to the roller axis, the width of a zone can practically be reduced to the width of an emitter. As a result, the resolution of the roll gap thickness control in the axial direction of the roll can be increased significantly.

The irradiation device advantageously has modules, each module having at least one radiator. Each module preferably has two radiators, wherein each radiator can also be designed as a twin tube. The modular structure allows the device to be adapted to different roll lengths. In addition, it simplifies maintenance, since each module can be easily replaced in the event of a possible defect, without having to disassemble the entire device.

In a preferred embodiment, a protective pane, in particular made of quartz glass, which is permeable to the infrared radiation of the radiators is arranged between the radiator and the roller. The protective screen has several advantages. On the one hand, it prevents dirt particles adhering to the roller, which can come loose due to the centrifugal force, from reaching the infrared radiator and contaminating it. Secondly, they protect the heater from uncontrolled temperature influences, which can arise from fluctuations in the air temperature in the immediate vicinity of the roller. The air from the roller surface cannot reach the heater directly. In addition, the protection use the disc as a reflector for the back radiation emanating from the roller. As mentioned at the beginning, every body radiates radiation that is characteristic of its temperature. The temperature of the roller remains far below the temperature of the heater. The radiation emanating from the roller is therefore considerably longer-wave than the radiation from the emitter. By a suitable choice of the material of the protective pane, for example quartz glass, it can be achieved that the longer-wave radiation is better reflected by the roller on the pane than the shorter-wave radiation of the emitter, which can pass through the pane practically unhindered. The protective screen itself does not heat up. This avoids that parts of the material web, which may still adhere to the roller, can come into contact with the hot jets and ignite, which can lead to great dangers, particularly in paper processing.

Each module advantageously has a reflector on the side of the radiators facing away from the roller. The reflector enables the radiation from the radiator, which is not directed directly onto the roller, to be directed indirectly onto the roller anyway. This enables better concentration of the radiation in the direction of the roller. The reflector can also be attached, for example vapor-deposited, on the “back” of the radiator.

In a preferred embodiment, a cooling device is provided which keeps the radiation device in a predetermined temperature range. A cooling device is understood to mean any device that is able to keep the temperature of the irradiation device below the radiator temperature. The action of the cooling device largely prevents jumps in temperature. This allows the radiators to have a longer service life. Furthermore the cooling air also limits the temperature of the housing of the radiation device. When using stainless steel, the temperature of the housing should remain below 250 ° C in order to avoid tarnishing or discoloration of the stainless steel and thus impairing the appearance and the reflection properties. The temperature of the radiation device need not be constant. It is sufficient if the change in temperature over time does not exceed a predetermined level and a certain temperature range is maintained during operation.

The cooling device preferably has a blower and air guiding devices which guide cooling air through the irradiation device. The temperature control with the aid of ambient air, which generally does not exceed a predetermined temperature, can be carried out in a simple and inexpensive manner.

It is preferred that each module has its own cooling air connection. This allows the special temperature requirements of each module to be taken into account. Modules whose emitters emit more energy also have to be cooled more in order to keep the temperature of the module in a predetermined range. The supply of the cooling air to each module can be regulated centrally or locally, for example by flaps in the cooling air connection.

The reflector advantageously has openings for the entry of the cooling air into a radiator chamber formed between the reflector and the protective screen. The cooling air is therefore directed from "behind", ie from the side facing away from the roller, around the radiators. Because the openings are arranged in the reflector, cooling air flows through the reflector, as a result of which the reflector is sufficiently cooled. At the same time, an air flow is generated towards the pane.

It is particularly preferred that the openings in the reflector are arranged in an area that is cut by a plane perpendicular to the reflector in which the radiator is also located. In other words, the openings are in an area which is defined by dropping the solder from the radiator onto the reflector. Through the openings, the reflectivity of the reflector is reduced in this area. However, this disadvantage is not very significant, since the radiation that strikes the reflector perpendicularly can also only be reflected vertically and would thus hit the radiator again and not the roller. The preferred arrangement of the openings means that the cooling air can be introduced without the reflection being greatly reduced.

In a preferred embodiment, the air emerges from the heater chamber in the direction of the roller. The cooling air heats up as it flows through the heater chamber and usually becomes warmer than the temperature of the roller surface. In order to also use the energy contained in the cooling air, it is advantageous to direct it onto the roller surface. As part of the temperature difference between the cooling air and the roller surface, an additional small energy exchange takes place.

The air is advantageously discharged through at least one slot which extends parallel to the axis of the roller in the vicinity of the roller surface. The air is directed specifically onto the roller surface.

The infrared radiation is preferably short to medium-wave. The shorter the wavelength of the radiation, the greater the energy density of the radiation. The wavelength of the radiation essentially depends on the temperature of the radiator. Radiator temperatures of 1,000 to 2,000 ° C are preferred, which is a wavelength corresponds to a range from about 1.3 to about 2.3 µm. Short-wave radiators also have better control behavior. Short-wave emitters can namely be switched on or off similar to an incandescent lamp. The temperature control can therefore be done very quickly. The operator can choose between slow and fast heating, for example a temperature increase between 0.5 ° and 3 ° C per minute.

Since it is intended to cool the radiation device, but on the other hand the temperature of the radiators should not be reduced, each radiator has at least one freely suspended coil. This coil, which is the actual location of the radiation generation, is heated by the supplied electrical energy, but is not cooled by the cooling air due to the lack of heat conduction. This means that the wavelength and the frequency of the radiator are always kept in a predetermined range.

It is also advantageous that the radiation device is thermally insulated on the side facing away from the roller. The isolation is advantageously carried out by an insulating layer on the outside of the radiation device. This prevents the irradiation device from radiating in the "wrong" direction, namely in the direction facing away from the roller. Rather, almost all of the radiation energy is emitted towards the roller, which makes it possible to work economically with the energy used.

• Fig. 1 einen Walzenstapel mit einer Vorrichtung zum Steuern der Dicke einer durch einen Walzenspalt laufenden Materialbahn in Arbeitsstellung,
• Fig. 2 einen Walzenstapel mit der Vorrichtung in War­tungsstellung,
• Fig. 3 einen Schnitt durch die Vorrichtung,
• Fig. 4 eine perspektivische Ansicht der Vorrichtung,
• Fig. 5 eine perspektivische Ansicht eines Strahlers und
• Fig. 6 eine Vorderansicht eines Strahlers.

The invention is described below with reference to a preferred embodiment in conjunction with the drawing. In it show:

• 1 shows a roll stack with a device for controlling the thickness of a material web running through a nip in the working position,
• 2 shows a roll stack with the device in the maintenance position,
• 3 shows a section through the device,
• 4 is a perspective view of the device,
• 5 is a perspective view of a radiator and
• Fig. 6 is a front view of a radiator.

A material web 1, for example a paper web, runs through several gaps 3 of a roll stack 2, for example a calender. Roll stacks 2 of this type generally serve to change the properties of the material passing through them. In particular, such roller stacks serve to adjust the thickness of such a material web 1. In general, the aim is to keep the thickness of the material web 1 constant across the direction of movement. Any unevenness that occurs can be compensated for by making the nip thinner at the point where the material web is too thick, while making it thicker at the points where the material web is too thin. It is usually sufficient to set the thickness of a single nip 4. For this purpose, a roller 5, which delimits the nip 4, is heated by a heating device 6, as a result of which it expands and reduces the nip. The size of the nip 4 can be changed accordingly over the length of the roller 5 by a targeted distribution of the heating energy over the length of the roller 5. If, for example, the heating device is operated in such a way that it only heats up the roller 5 in its axial center, the roller gap 4 also becomes thinner only in the axial center of the roller 5, but remains unchanged at its ends.

The heating device 6 is mounted on a lever linkage 10 which can be pivoted with the aid of a piston-cylinder arrangement 8 about a pivot point 9 which is fastened to a base 7. In this way it is possible to bring the heating device into a working position where it can emit the heating power by radiation to the roller 5. In a maintenance position (FIG. 2), on the other hand, it is possible to carry out maintenance and repair work without the roller stack 2 hindering access to the heating device 6.

The thickness of the material web 1 leaving the roll stack 2 is continuously determined by a measuring device 35. The measuring device reports the determined data to a control device 36, which controls the heating device 6 in such a way that the heat distribution over the axial length of the roll 5 leads to a uniformization of the thickness of the roll gap 4 and thus to a compensation of the uneven thickness distribution of the material web 1.

For this purpose, the heating device 6 has a number of identical modules 26-30. Each module has two radiators 12, which are designed as twin tube radiators. Each twin tube heater has a double piston 31, in which two coils 32, 33 are suspended in such a way that, apart from their attachment to sockets 37, 38, they have no contact with the piston 31. The radiator 12 is suspended with its sockets 37, 38 in housing sockets 13, 14, which are each connected to brackets 15, 16, which in turn extend between two side walls 17 of a module 26-30.

The side walls 17 form parts of a housing 18. A reflector is arranged in the housing 18 on the side of the radiator 12 opposite the roller. The reflector reflects the infrared rays of the radiator 12, which are emitted by the radiator in the wrong direction, ie in the direction facing away from the roller 5.

In order to also be able to reflect rays that do not strike the reflector directly, the side walls 17 of the housing 18 can also be designed as reflectors.

In principle, the width of the modules can be reduced to the width of a single radiator. This enables the roll gap thickness control to be resolved in the axial direction up to the order of magnitude of approx. 20 mm, i.e. the "roller disks" whose diameter is to be influenced are only about 20 mm wide. As a result, the material web 1 can be manufactured much more uniformly and thus with better quality.

A protective pane 20, which is formed from quartz glass, is arranged between the roller 5 and the radiator 12. Quartz glass has the property of allowing the infrared radiation of the radiator 12 to pass through without significant losses. It has a relatively high temperature resistance, a high resistance to temperature changes and a low electrical conductivity. A radiator chamber 21 is formed by the protective pane 20, the reflector 19 and the side walls 17 of the housing 18. A defined temperature environment can now be created in this radiator chamber 21. The protective disk 20 not only prevents dirt particles, which adhere to the surface of the roller 5 and possibly loosen in the area of the emitter 12, from contaminating the emitter and igniting. The protective disc 20 also prevents air vortices, which are unavoidably caused by the movement of the roller 5, from cooling the radiator 12 in an uncontrolled manner.

In order to maintain a temperature in a defined temperature range in the radiator chamber 21, a cooling air supply line 11 is provided, which is supplied with cooling air by a pipe system (not shown) and a blower (also not shown). By Air entering the air inlet 11 into the housing 18 is passed through openings 23 in the reflector into the radiator chamber 21. Each module 26-30 has its own air inlet 11, so that the temperature in the heater chamber 21 of each module 26-30 can be set independently of the temperature in the heater chambers of other modules. The air that enters the housing 18 through the air inlet 11 can escape again through slot-shaped openings 24, 25. The slot-shaped openings 24, 25 extend parallel to the axis of the roller 5 and direct the escaping air against the surface of the roller 5. This makes part of the energy that the air receives as it travels through the heater chamber 21 useful for heating the roller 5 used.

Each radiator 12 is connected to the control unit 36 via an electrical feed line 22. The control unit supplies each radiator 12 with so much electrical power that the filaments 32, 33 of the radiator heat up to a temperature between approximately 1,000 and 2,000 ° C. The radiators 12 then emit infrared radiation with a wavelength between approximately 1.3 and approximately 2.3 μm. This leads to a relatively high energy density on the roller surface, which heats up the roller relatively quickly and thus also changes the diameter of the roller 5 relatively quickly. If the electrical energy that is supplied via the electrical supply line 22 is switched off, the radiator 12 stops heating relatively quickly. The roller is cooled, inter alia by the material web 1, and contracts, as a result of which the roller gap 4 is enlarged at the point at which the radiator 12 is switched off. This makes it possible to change the thickness of the nip relatively quickly.

The housing 18 is surrounded by an insulating layer 34 (only shown in FIG. 3). The insulating layer 34 provides thermal insulation of the housing. Radiates on the side of the housing 18 facing away from the roller 5 therefore only relatively little heat. This prevents the environment on the side of the housing 18 facing away from the roller 5 from overheating and enables almost all of the energy of the infrared radiators 12 to be directed onto the roller 5.

Claims (17)

1. Device for controlling the thickness of a web of material running through a nip, in which the diameter of at least one of the rollers delimiting the nip is temperature-dependent, characterized in that an irradiation device (6) is provided, which the roller (5) on a part irradiated with infrared radiation. 2. Device according to claim 1, characterized in that the irradiation device (6) has a plurality of radiators (12) which are arranged substantially parallel to one another. 3. Apparatus according to claim 1 or 2, characterized in that the radiators (12) are rod-shaped. 4. Device according to one of claims 1 to 3, characterized in that the emitters (12) are arranged substantially parallel to a perpendicular to the roller axis. 5. Device according to one of claims 1 to 4, characterized in that the irradiation device (6) has modules, each module (26-30) having at least one radiator (12). 6. Device according to one of claims 1 to 5, characterized in that between the emitters (12) and the roller (5) is arranged for the infrared radiation of the emitters (12) transparent protective pane (20). 7. The device according to claim 5 or 6, characterized in that each module (26-30) on the roller (5) facing away from the radiator (12) has a reflector (19). 8. Device according to one of claims 1 to 7, characterized in that a cooling device (11) is provided which keeps the irradiation device (6) in a predetermined temperature range. 9. The device according to claim 8, characterized in that the cooling device has a blower and air guiding devices (11), the cooling air through the irradiation device (6). 10. The device according to claim 9, characterized in that each module (26-30) has its own cooling air connection (11). 11. Device according to one of claims 8 to 10, characterized in that the reflector (19) has openings (23) for the entry of the cooling air into a radiator chamber (21) formed between the reflector (19) and the protective screen (20). 12. The apparatus according to claim 11, characterized in that the openings (23) in the reflector (19) are arranged in an area which is cut from a plane perpendicular to the reflector, in which the radiator (12) is also located. 13. The apparatus of claim 11 or 12, characterized in that the air outlet (24, 25) from the lamp chamber (21) in the direction of the roller (5). 14. The apparatus according to claim 13, characterized in that the air outlet takes place through at least one slot (24, 25) which extends parallel to the axis of the roller (5) in the vicinity of the roller surface. 15. The device according to one of claims 1 to 14, characterized in that the infrared radiation is short to medium-wave. 16. The device according to one of claims 1 to 15, characterized in that each radiator (12) has at least one freely suspended coil (32, 33). 17. The device according to one of claims 1 to 16, characterized in that the irradiation device (6) is thermally insulated on the side facing away from the roller.

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