Method and device for measuring the permeability of sieve belts

Abstract

A method for determining the permeability of at least one circulating screen belt (5, 5a, 5b) which, during the production of material sheets, carries a press mat (10) consisting at least partially of lignocellulosic particles wetted with binders from below and / or covers it from above, wherein a heating or cooling medium is guided through the screen belt (5, 5a, 5b) into the press mat (10) or escapes from it through the screen belt (5, 5a, 5b), and wherein the perforation of the screen belt (5, 5a, 5b) is optically inspected for blockages (25), characterized in that at least one optoelectronic system (2), consisting of at least one light source (13) and at least one light-sensitive sensor device (14) in a running area of ​​the screen belt, in which it has no contact with the press mat, determines permeability states by means of the light transmission through the perforation. of the sieve belt (5, 5a,5b) at different locations and the temporal change of the permeability states is detected, wherein the light source (13) emits its light on a light-emitting side (18) through the perforation of the screen belt (5, 5a, 5b) onto the light-sensitive sensor device (14) on an opposite light-receiving side (19) of the screen belt (5, 5a, 5b).

Description

The invention relates to a method for detecting the permeability of at least one revolving screen belt which, during the production of material slabs, carries from below and / or covers from above a pressed material mat which at least partially consists of lignocellulosic particles wetted with binders, and wherein a warming or cooling medium is conducted through the screen belt into the pressed material mat or escapes from it through the screen belt, and wherein the perforation of the screen belt is visually controlled for aggregates.The invention further relates to a device for detecting the permeability of at least one revolving screen belt according to one of the method claims, which during the production of material sheets carries a pressed material mat, which consists at least partially of lignocellulosic particles wetted with binding agents, from below and / or covers it from above, and a warming or cooling medium is conducted through the screen belt into the pressed material mat or escapes through the screen belt from the latter, wherein the perforation of the screen belt can be visually controlled for additions.In the continuous production process of material sheets, the screen belts mentioned are located, for example, in the "ContiBlue calibration presses" with a relatively low pressure level mentioned by the applicant, which are arranged in multiple upstream of the continuous presses in which a scattered mat of pressed material, which consists at least partially of lignocellulosic particles wetted with binders, is pressed between two rotating steel belts under high pressure. On the other hand, these "ContiBlue calibration presses" with a relatively low pressure level can also be used separately, however, in order to produce, for example, insulation or sound insulation panels.Such a device has been published, for example, in DE 10 2008 039 720 B4. The "ContiBlue calibration press" is frequently used as a preheating device and has at least two endlessly circulating screen belts which are guided around deflection rollers, wherein a passage gap is formed between the screen belts, through which the compressed material mat is guided. This means that the mat of pressed material is both supported by a screen belt and covered by a screen belt. Since this type of press alone is equipped with the revolving screen belts, the following presses-if present-are not taken into account in this invention.WO 2020 / 239390 A1 discloses a method and an apparatus for heating a twin-belt press with perforated revolving belts, as is also used in the invention.DE 10 2020 006 637 A1 relates to a method and a device for detecting soiling on a twin-belt press with a non-perforated revolving steel belt.The screen belts used today are, for example, capable of producing insulation panels with densities of 100-240 kg / m 2. The screen belts or screens for short serve in their operation to guide the mat of material to be pressed through the device at a desired speed by driving it at the same speed as the mat of material to be pressed. In this case, steam or a steam-air mixture can be introduced into the pressed material mat from the outside through the screen or liquid and air can be removed. As a rule, the media mentioned in the preamble should be steam, a steam-air mixture and / or hot air for heating and cold air for cooling, which pass from the outside through the screen to the mat of pressed material. However, water or moist air can also be passed through the screen from the inside to the outside, for example.In such devices, it has been found that the screens, which generally have a perforation made of plastic or wire mesh, become clogged over time by dust or glue particles. This has the result that the permeability for warming or cooling media is no longer complete and the products produced have defective sites, in particular on the surface. The term "addition" is accordingly understood to mean the increasing loss of permeability of the perforation of the screen belt, because dust or glue particles break down the open porosity. This in turn means that the permeability decreases.Hitherto, the problem has been solved by continuous optical inspection by the operating personnel who caused cleaning of the screen belt when a closure to the perforation was detected. However, discoloration of the screen is often perceived as a blockage with wood, glue or other particles and the screen belt is replaced too early, i.e. when the required permeability is actually still present. It is also complicated and nonproductive if instead a compressed air pass test is carried out with standstill of the screen belt. The production is thereby interrupted in an undesired manner. On the other hand, production with soiled screen belt can be manifested in poor product quality. However, excessive and unnecessarily frequent cleaning can damage the strip and shorten the service life.It is the object of the invention to obtain automated information about possible additions of the screen belt or reduced permeability.With regard to the method, the object is achieved by the features of claim 1 and in particular by the fact that at least one optoelectronic system, consisting of at least one light source and at least one light-sensitive sensor device, detects permeability states of the screen belt at different points and the change over time of the permeability states by means of the light transmission through the perforation in a running region of the screen belt, in which region it is not in contact with the mat of material to be pressed, wherein the light source emits its light on a light emitter side through the perforation of the screen belt onto the light-sensitive sensor device on an opposite light receiver side of the screen belt.In this case, the light source uses, for example, a light source which extends over the width of the screen belt and is protected, for example, in a box with a narrow slot and can be designed in the form of a light tube or a plurality of LEDs. Or the light source is a laser light that stripes over the width of the screen belt. In addition to these two embodiments, further embodiments and light sources can be used, which are likewise intended to be covered by the invention.In the simplest case, the light-sensitive sensor unit can be a light sensor which measures the amount of light or brightness transmitted through the perforation with a photoresistor and passes it on as an analog voltage to an evaluation unit. The amount of transmitted light is an indication of the state in which the permeability of the screen is located. In order to make further measurements, the light-sensitive sensor unit can also be designed in the form of one or more cameras. If the screen belt becomes clogged over time, for example by wood or glue particles, the received signal of the light-sensitive sensor unit becomes weaker. The evaluation unit can compare the measured value with a critical limit value and give a signal if it is exceeded. Only then is it ensured that the screen belt actually has to be cleaned or replaced. If the environment is very dusty, the sensor unit, in particular a camera lens, can be kept clean by a compressed air curtain.The light source and the light-sensitive sensor unit are to be arranged in a returning region of the revolving screen belt. Only then is a preferred embodiment possible, in which the light source emits its light on the light-emitting side of the screen belt through the perforation onto the light-sensitive sensor device on the opposite light-receiving side of the screen belt.As a result, a direct measurement of the transmitted light quantity is possible and the mat of pressed material has no disturbing influence. The transmission measurement is the simplest and preferred way of checking the permeability of the screen belt. However, it should be pointed out that a characteristic value for the permeability can also be recorded using a reflection method, i.e. virtually using the determination of the amount of light not passing through the screen belt using a light source and a sensor device which is sensitive to light on the same side of the screen belt.It is preferred that the screen belt has a reference marking or a starting point defined by the drive control of the screen belt, which is / is used by the optoelectronic system as the starting point of the permeability detection.Such a starting point may be, for example, the temporal or local point at which the camera is directed when the screen belt starts. With the aid of the known speed increase and the known length of the screen belt, the instantaneous location of the point can be calculated at any time. In this way, however, the coordinates of each addition on the screen belt are also known as a function of the starting point of the permeability measurement. These coordinates are then determined, for example, during operation by calculating the time distance with the aid of the speed and the screen belt length. Thus, the exact location of the addition on the tape is unambiguously defined. The size of the addition is determined in a known manner with the light transmission measurement, in which a limit value is defined from which intervention is required.It is likewise possible for the screen band to be provided with a reference marking which is detected by the optoelectronic system as the starting point of the detector measurement.As a reference marking, for example, a point-wise or linear color marking that is high in contrast to the screen band can be defined or a color point on the screen band that is easily recognizable for an optoelectronic system can be used in a particularly simple manner. Alternatively, however, inductive signals are also conceivable, for example, if the screen belt is provided with a magnet or magnetic strip. Thus, during each revolution of the screen belt, the reference marking is redetected by the optoelectronic system in a trigger-like manner and the time or distance distance value for a clogging is determined accurately continuously in only one belt revolution. This eliminates slip-dependent displacements which can occur. The starting point of the permeability measurement is thus reset by the reference mark for each revolution. This means that changes in the degree of additions can be detected particularly easily.The described detection has the advantage that increments of perforation detected on the screen belt after the beginning of the permeability detection can be passed on to an evaluation unit with an absolute or relative time or distance value to one another.In the evaluation unit, a type of "map" can then be generated which precisely shows the locations with a particularly high degree of occupancy.It is preferred that a time indication is also stored for each pass of a clogging through the optoelectronic system. The amount of addition resulting from the permeability measurement by detecting the amount of transmitted light of the screen at each location can also be displayed in shades of color in a display on a monitor.It is also advantageous if, in the case of at least one further pass of a supplement through the optoelectronic system, the image size of the supplement and the permeability detection are compared with one of the preceding passes.In this way, the size development of the addition over time can be understood. If a predefined limit value is exceeded or approached, a warning signal can also be generated automatically. The real-time data are provided with a time indication and stored in a database. Thus, the local change of the screen belt over time can also be understood. If the screen belt experiences increased additions within a short time, for example, this circumstance can be matched to process parameters in order to detect possible causes. Also, the general condition and quality of the screen belt can be easily monitored.It should be noted that the evaluation unit can also be programmed in a self-learning manner, so that after a learning phase it can automatically and automatically emit a warning signal during a specific development of the additions.In a particularly preferred manner, a preferably two-dimensional developed image of the screen belt is generated by the evaluation unit with the permeability measurements and the addition representations are generated on a monitor in the poor state of the screen belt.In this rectangular representation of the (cut open) screen belt, the coordinates of any inadequate permeability or addition can be entered by the known position. By means of an envisaged possibility of time scrolling, the development of each addition is quickly recognizable. By detecting the time at which a condition arises, a determination of the cause is clearly simplified.It is particularly advantageously provided that an addition of the perforation using the stored time or distance distance value is moved in the evaluation unit to a suitable cleaning position with respect to the starting point of the permeability detection and is removed there at least partially manually or with a cleaning device.It can also be expressed in reverse that with the aid of the knowledge where there is an unacceptably high addition in the screen belt, a cleaning device can be activated when this added point of the screen belt passes by the latter.In this case, such an activation of a cleaning device can be effected, for example, by placing a cleaning brush on it or by switching on a strong jet of air or water which is directed onto the screen belt.With regard to the apparatus, the object of the invention is achieved by the features of claim 8 and in particular in that at least one optoelectronic system, consisting of at least one light source and at least one light-sensitive sensor device, detects permeability states of the screen belt at various points by means of the light transmission through the perforation and the change over time thereof in a running region of the screen belt in which it is not in contact with the mat of material to be pressed, wherein the light source emits its light on a light emitter side through the perforation of the screen belt onto the light-sensitive sensor device on an opposite light receiver side of the screen belt. The apparatus is suitable for carrying out the method according to one of the method claims.The detection of the sensor device with a light-sensitive sensor device can, as already described in the method, take place in the simplest case with a photoresistor; however, a camera system is more advantageous for a targeted evaluation, which can in particular view and detect the entire screen bandwidth.The light measurement of the sensor device can be passed on to an evaluation unit which compares the transmitted measured quantity of light or the measured brightness by the cameras with stored values. The measured values correlate with a state of the permeability of the screen belt. If the value is too low, an alarm can be triggered, for example.It is good if the screen belts have their own drive.This enables a constant speed of the screen belts and a continuous measuring operation.In addition, this advantageously makes it possible that, if the screen belt has a starting point of the permeability detection, all further detected additions can be forwarded with a time or distance distance value from this starting point of the permeability detection to the evaluation unit and stored there.This means that it is possible to create a map of the screen belt surface on which the degree of permeability (for example colored) is represented and thus aggregates can be immediately recognized. Preferably, the map can be transmitted to a monitor.As a further advantageous embodiment, it can be provided that the control of the drive and the evaluation unit correspond to one another. It is then possible for the drive of the screen belt to be suitable, with the aid of a controller for regulating the screen belt speed, for driving this addition, in particular insofar as it is classified as critical by the evaluation unit, to a cleaning position on the basis of recorded distances between the starting point of the permeability detection and an addition and for activating the cleaning device there.Further features of the device claims correspond analogously to the method claims and exploit the advantages mentioned there.The invention is explained in more detail below with reference to drawings illustrating exemplary embodiments. They show FIG. 1 is a schematic side view of the apparatus according to the invention for producing material sheets according to the invention FIG. 2 shows a schematic illustration of an optoelectronic system of the invention, FIGS. 3 ato 3 c show a passage of a supplement through the optoelectronic system, FIG. 4 shows the screen belt on a monitor.FIG. 1 shows a schematic side view of the device according to the invention for producing material slabs, in particular insulation slabs in the form of a continuous screen belt press 1. a pressed material mat 10, which at least partially consists of lignocellulosic particles wetted with binders, is treated between an upper revolving screen belt 5a in an upper press part 1a and a lower revolving screen belt 5b in a lower press part 1b.The mat 10 of pressed material is heated within the one upper and lower sieve circulation with steam or a steam-air mixture, for example, via steam blow boxes 20 and finally cured by heat and optionally pressure application via calibration plates 7 a, 7 b. The discharged steam of the steam blow boxes 20 penetrates through the perforation of the revolving screens 5a and 5b into the mat 10 of pressed material and condenses. Emerging residual steam and residual air can be discharged via the suction device 22.A further device for steam application 20 can be arranged, for example, in the inlet, even in the region of the inlet mouth 6 which is going in. The generated moist surface reduces the friction on the screen belts 5 aand 5 b, which leads to additional drive energy savings.In the further forward run of the pressed material mat 10, effective calibration plates 7 a, 7 bare arranged, which can be heated by different systems. Here, for example, channels provided with heating liquid, inductive heaters, electric heaters or steam heaters are possible, the latter also being able to deliver the steam directly to the mat of pressed material.In the calibration region, the mat 10 of pressed material is guided between the two pressure plates 7 a, 7 b, which are adjustable relative to one another by pressure transmitters 8.In this exemplary embodiment of a continuous screen belt press 1, the mat of material to be pressed is cooled and fixed at the outlet of the device by means of a suction device 22, which brings about air cooling 21.The screen belts 5a, 5b are guided over belt deflection drums 9, 9a, 9b, wherein a belt deflection drum 9a, 9b is driven for each screen belt. The drives of the screen belts can of course vary in different continuous screen belt presses. These shapes are also intended to be encompassed by the invention.If the screen belt is equipped with a marking that can detect a sensor, for example also by the optoelectronic system 2 required for the invention, a starting point for the permeability detection can be established therewith.This is then effected with the optoelectronic system 2, which comprises a light source 13 located on the light emitter side 18 and, on the other side of the screen belt, the light receiver side 19, a sensor device 14 for detecting the amount of light transmitted through the perforation of the screen 5 a, 5 b. The measured light intensity by the sensor device 14 can be considered and evaluated as a measure of the degree of permeability.FIG. 2 shows the preferred construction of the optoelectronic system 2, which is also provided in variable embodiments for the invention. Purely schematically, a light source extending over the width of the screen belt is indicated at the bottom, which light source emits, for example, a linear light pattern. The light beams 32 (indicated as arrows) pass through the perforation of the screen 5. A sensor device 14 arranged above the screen belt 5 in the exemplary embodiment of FIG. 2 measures the amount of transmitted light and passed on the measured value to an evaluation unit 3. In the exemplary embodiment, 4 cameras are used for this purpose over the screen width. The number of sensors is not relevant to the invention, however. For the sake of completeness only, the direction of passage of the wire 5 is indicated by the arrow 31.As stated, the optoelectronic system can also be used to identify a starting point of the permeability measurement. If each measured value is supplied to the evaluation unit 3 at a spatial or temporal distance from the starting point, a type of map of the aggregates can be recorded over a complete sieve circulation and compared with the preceding one for each circulation. Thus, increasing opacity may be provided by enlarging an additive 25.If the measure of opacity is exceeded with respect to a predetermined maximum value, the permeability of the screen is no longer sufficient. In this case, a warning signal can be generated or displayed on a monitor, for example.In a particular manner, however, the evaluation unit 3 can also be adjusted with the control 4 of the screen belt speed, as is indicated in FIG. 1. Thus, a cleaning position 11 can be provided for the screen belt 5 a, 5 bto which the location of the screen belt 5 a, 5 bis moved in order to be freed of the aggregates there. In the embodiment according to FIG. 1, the cleaning position 11 is provided with a cleaning brush 12 which can be placed on the screen belt. However, various other cleaning devices are also conceivable here, which are likewise intended to be covered by the invention. This is in a particularly effective form even a nozzle which acts with a water or air jet on the corresponding admixture 25.For a better understanding of the permeability measurement, FIGS. 3 ato 3 c show how an addition can be detected and estimated as a temporal sequence, that is to say virtually as individual images of a movie. In FIG. 3 a, a possible camera section 23 with a line can be seen as a light pattern on an undamaged screen belt section 5. The arrow indicates the direction of the sieve belt circulation. Above the line, i.e. approaching the light pattern 16 captured by the cameras 15, at the later point in time of FIG. 3 b, there is a geometric addition in the screen belt surface, which is tangent to the light pattern by its edge region as a result of the belt circulation. This makes it possible to detect an interruption of the measurement of the quantity of light from the light line 16. FIG. 3 cshows how the addition leaves the light pattern 16 detected by the sensor 14.Of course, the light pattern 16 does not necessarily have to be a line. The present resolutions of cameras also allow large-area considerations. For this purpose, it is advantageous if the light source likewise illuminates an area which is reviewed by a camera. For evaluation, the image can be divided again into a plurality of elements on which we measure the quantity of light in each case. The measured light transmission of these elements, for example squares, can be colored on a monitor, i.e. for example green squares in the case of an uncontaminated screen belt location and red squares in the case of added screen belt locations. Color gradations in between would be expedient.When detecting a condition, the position and size are stored in a database of the evaluation unit 3. Thereafter, if desired, a message can be made to the plant guide according to predefined rules. Via an optional monitor 17, the plant operator can manually assess the condition of the screen belt and determine the need for cleaning processes up to the replacement of the screen belt.FIG. 4 shows schematically the representation of the screen belt 5 in the unwound state 24 with its additions on a monitor 17. The presentation software can output the exact coordinates 29 by clicking on a corresponding addition 25 (see indicated cursor 26), with respect to the beginning point 27 of the permeability measurement. Furthermore, the screen belt 5 can thereby be moved via an interface to the controller 4 to a previously defined cleaning position 11 and can be treated there automatically by cleaning devices 12. Thus, the manual search of the addition location is saved.For the clicked addition, not only the exact coordinates 29 are displayed on the development 24, but also, for example, a time indication is assigned on the right side of the monitor, in which the addition 25 had the displayed size, wherein the development of the size can be followed back via time selection buttons 28.In a further developed illustration, as already mentioned, the surfaces of the same light transmission can also be displayed stepwise in different colors.List of reference characters1 Continuous screen belt press 1 a Oberer press part 1 b Unterer press part 2 Optoelectronic system 3 Evaluation unit 4 Control for the screen belt speed 5 Screen belt 5 a Oberes screen belt 5 b Unteres screen belt 6 Inlet mouth 7 a Obere pressure plate 7 b Untere pressure plate 8 Pressure transmitter 9 Belt deflection drum 9 a Obere belt deflection drum (driven) 9 b Untere belt deflection drum (driven) 10 Press material mat 11 Cleaning position 12 Cleaning device, for example, mountable cleaning brush 13 Light source 14 Sensor device 15 Camera 16 Light pattern, Line 17 Monitor 18 Light-emitting side of the screen belt 19 Light-receiving side of the screen belt 20 Steam blower box 21 Cooling air supply 22 Suction 23 Camera section 24 Developed representation of the screen belt 5 25 Addition 26 Cursor 27 Starting point of the permeability detection 28 Time selection key 29 Coordinates 30 Time indication 31 Direction of travel 32 Light beams transmitted through the perforation of the screen

Claims

Method for detecting the permeability of at least one revolving screen belt (5, 5a, 5b) which, during the production of material sheets, carries from below and / or covers from above a pressed material mat (10) which consists at least partially of lignocellulosic particles wetted with binders, and wherein a warming or cooling medium is conducted through the screen belt (5, 5a, 5b) into the pressed material mat (10) or escapes from the latter through the screen belt (5, 5a, 5b), and wherein the perforation of the screen belt (5, 5a, 5b) is optically controlled for additions (25), characterized in that at least one optoelectronic system (2) consisting of at least one light source (13) and at least one light-sensitive sensor device (14) in a running region of the screen belt, In which it is not in contact with the mat of pressed material, permeability states of the screen belt (5, 5a, 5b) at different points and the change over time of the permeability states are detected by means of the light transmission through the perforation, wherein the light source (13) emits its light on one light-emitting side (18) through the perforation of the screen belt (5, 5a, 5b) onto the light-sensitive sensor device (14) on an opposite light-receiving side (19) of the screen belt (5, 5a, 5b).Method according to claim 1, characterised in that the screen belt has a reference marking or a starting point defined by the drive control of the screen belt, which is / is used by the optoelectronic system as the starting point of the permeability detection (27).Method according to claim 2, characterised in that increments (25) of perforation detected on the screen belt (5, 5a, 5b) after the beginning of the permeability detection are passed on to an evaluation unit (3) with an absolute or relative time or distance value to one another.Method according to one of Claims 1 to 3, characterized in that a time indication (30) is also stored for each pass of a deposit (25) through the optoelectronic system (2).Method according to one of Claims 2 to 4, characterized in that, in the case of at least one further pass of a supplement (25) through the optoelectronic system (2), the permeability detection is compared with one of the preceding passes.Method according to one of Claims 3 to 5, characterized in that the evaluation unit (3) generates a preferably two-dimensional developed representation (24) of the screen belt (5, 5a, 5b) with the permeability measurements on a monitor (17).Method according to one of Claims 3 to 6, characterized in that a continuation (25) of the perforation is moved to a suitable cleaning position (11) using the stored time or distance distance value with respect to the starting point of the permeability detection in the evaluation unit (3) and is removed there at least partially manually or with a cleaning device (12).Device for detecting the permeability of at least one revolving screen belt which, during the production of material sheets, carries from below and / or covers a pressed material mat (10) which at least partially consists of lignocellulosic particles wetted with binders, and a warming or cooling medium is conducted through the screen belt (5, 5a, 5b) into the pressed material mat or escapes from the latter through the screen belt (5, 5a, 5b), it being possible to visually control the perforation of the screen belt (5, 5a, 5b) for additions, characterized in that at least one optoelectronic system (2) consisting of at least one light source (13) and at least one light-sensitive sensor device (14) in a running region of the screen belt in which it is not in contact with the pressed material mat (10), The permeability of the screen strip to light at various points and its change over time is used to detect permeability states of the screen strip at various points by means of the light permeability through the perforation, wherein the light source (13) emits its light on one light-emitting side (18) through the perforation of the screen strip (5, 5a, 5b) onto the light-sensitive sensor device (14) on an opposite light-receiving side (19) of the screen strip (5, 5a, 5b).Device according to claim 8, characterised in that the at least one screen belt (5, 5a, 5b) has its own drive.Device according to claim 8 or 9, characterised in that the screen belt (5, 5a, 5b) has a starting point of the permeability detection and that all further detected additions can be forwarded with a time or distance distance value from this starting point of the permeability detection to an evaluation unit (3) and stored there.Device according to claim 10, characterised in that the drive of the screen belt (5a, 5b) with the aid of a controller (4) is suitable for regulating the screen belt speed, on the basis of recorded distances between the starting point of the permeability detection and a clog, to move this clog, in particular insofar as it is classified as critical by the evaluation unit, to a cleaning position (11) and to activate the cleaning device (12) there.

Images