EP0109456B1 - Method of and apparatus for equalizing the density distribution in an artificial-wood panel - Google Patents

Description

The invention relates to a method for equalizing the density distribution in synthetic wood panels made from glued bulk material and a device for carrying out the method for producing synthetic wood panels with a floor conveyor bunker with discharge, the discharge width of which is the same as the spreading width for synthetic wood panels to be produced and devices downstream of the floor conveyor bunker for bringing down the discharged Bulk goods as an endless fleece on a forming belt.

In the manufacture of synthetic wood panels, there is great economic interest in the production of nonwovens that are spread as evenly as possible, because only in this way the properties of the finished synthetic wood panels, such as. ß. whose density, the bending strength or the transverse tensile strength can be the same at all points of the end product and unnecessary additions to the bulk material to be processed for glue and energy can be avoided. By the OE-C-22 14 900, which relates to a spreading device to compensate for different basis weights in the transverse direction of chip or fiber fleece or the like for the production of chipboard, fiberboard and the like, a device has become known in which a metering conveyor belt is used around from there to be able to throw off bulk material for a nonwoven to be built on a mold base. In order to compensate for different weights per unit area in the transverse direction of chip or fiber nonwovens, it is provided there that the metering conveyor belt is infinitely variable and differently adjustable in height in the transverse direction. Such additional devices are not suitable for uncovering and eliminating different basis weights in the transverse direction of chip or fiber nonwovens, that is to say of synthetic wood panels, already in the area of the formation of a bulk material veil. It is also not possible to determine the different density in the transverse direction on the metering conveyor belt.

From DE-C-25 57 352, a continuous process for the continuous scattering of a fleece from wood chips and / or fibers, which consists of several layers scattered separately from one another and whose basis weight is regulated to a predetermined desired value, is known, in which the weight of the finished scattered nonwoven is measured and displayed, and corresponding electrical measurement signals regulate the scattering of at least one layer of nonwoven to a predetermined target value of the finished scattered nonwoven. However, this also does not make it possible to even out the density distribution across the fleece. A basis weight scale (cf.wood as raw and material 40 (1982) page 385) has also become known, in which the basis weight distribution in the scattered chip fleece is determined along and across the production direction using radiometric methods and traversing devices.

Proceeding from this, the present invention is based on the object of proposing a method and a device for carrying out the method, detecting and eliminating density errors present in the bulk material as soon as it is discharged from a floor conveyor bunker and, if necessary, a density profile for a to specify the finished synthetic wood panel when the bulk material is discharged from a floor conveyor bunker. This object is achieved with the characterizing features of method claim 1.). By measuring the weight distribution over the discharge cross section and comparing it with a predetermined target density distribution of the finished synthetic wood panel, a separation command that is generally different across the cross section is generated.

An inventive embodiment of this method is protected with the characterizing features of claim 2.). To produce synthetic wood panels of the same weight, which at the same time have a predetermined target density distribution, a control command is derived from the comparison between the existing basis weight of the synthetic wood fleece and the target density distribution, which contains the target weight of the finished synthetic wood panel, with which the discharge of the bulk material can be influenced.

The characterizing features of claim 3), with which a device for the production of synthetic wood panels is placed under protection, show how, through the inventive arrangement of a measuring surface above a guide surface which is arranged between the bunker outlet and the other descending devices for the bulk material, information about the current Density distribution over the molded cross-section to be obtained, which, in combination with a density distribution specified for the finished synthetic wood panel, determine a value that, as a rule, a separating device that extends over the entire bulk width is too widely scattered over the cross-section for the decrease in density difference in individual areas Bulk material affected.

In the embodiment of the measuring surface, it is proposed in the characterizing features of claim 5) how a better approximation to the density profile over the outlet width of the bulk material is achieved by dissolving the measuring surface in individual plates provided with strain gauges, and that in an inventive manner by adapting the individual tongues the downstream separation device, this resulting density profile can be made uniform if For example, in the finished synthetic wood panel, a density profile across the width of this panel is required, which has a constant density value.

In the features of claim 6) a further inventive embodiment of the measuring surface is protected, in which the measuring surface itself is designed according to the invention as a narrow plate which can be moved back and forth across the entire bulk width in front of the guide surface. An embodiment of this movable narrow plate is that the arrangement for transverse movement of the plate also extends outside the dump width, so that the entire device for maintenance and adjustment work can be removed from the dump area without interrupting the pouring process.

The characterizing features of claim 4) provide a device for carrying out the method under protection, in which, in addition to compensating for the density profile, which would lead to a slightly lighter finished synthetic wood panel, this slight change in the weight of the finished synthetic wood panel compared to the predetermined synthetic wood panel by increasing the discharge of bulk material by increasing the belt speed.

The characterizing features of claim 7) protect the inventive use of a scraper belt, which simultaneously serves as a discharge element, as a separating element and as a return transport element for the proportion of incorrectly discharged bulk material. Instead of the scraper belt in which the scraper webs are arranged on circulating chains or toothed belts or belt straps, the outlet cross section of the floor belt hopper can also be provided with spiked rollers arranged one above the other, which extend over the entire width of the discharge cross section. In this case, according to the invention, the discharge spiked roller closest to the floor conveyor then takes over the function of separating the excess material that has been poured and transporting it back into the floor conveyor bunker in conjunction with a trough conveyor which is designed as a spiral vibratory conveyor or screw conveyor.

In the claims 8.) to 12.) inventive configurations for the attachment of the measuring surface as a narrow plate are protected, in which the guarantee is given that contamination of the movable parts for receiving the movable narrow plate are excluded and also Precautions are taken to ensure that the bulk material itself does not hinder the measuring surface in its measuring activity, for example by pinching the bulk material between the guiding surface and the measuring surface when moving the measuring surface across the guiding surface.

A pole-changing motor, to which control commands are applied, or a DC motor can be used according to the invention to change the speed of the belt.

In the following drawing, the subject of the invention is explained in more detail using exemplary embodiments.

• Fig. 1 zur Erläuterung des Verfahrens eine Schemaskizze der gesamten Anlage
• Fig. 2 die Anordnung einer verfahrbaren Meßfläche
• Fig. 3a eine Ausgestaltung eines Kratzerförderers
• Fig. 3b eine Ausgestaltung einer Verstellmöglichkeit einer Zunge in einer Abscheideeinrichtung
• Fig. 3c eine sich über die gesamte Austragsbreite erstreckende Meßfläche aus einzelnen Platten
• Fig. 3d Gewichtsverteilung über die Streubreite In den Figuren werden jeweils gleiche Bauteile mit denselben Bezugsziffern bezeichnet.

They show:

• Fig. 1 to explain the method, a schematic diagram of the entire system
• Fig. 2 shows the arrangement of a movable measuring surface
• 3a shows an embodiment of a scraper conveyor
• 3b shows an embodiment of an adjustment possibility of a tongue in a separating device
• Fig. 3c a measuring surface extending over the entire discharge width from individual plates
• Fig. 3d Weight distribution over the spreading width In the figures, the same components are designated with the same reference numerals.

In a plant for the production of synthetic wood panels, for example chipboard, glued chips for the production of a particle board according to the vertical arrow 3 are fed to a floor conveyor bunker 1 via a feed 2 which rotates in the direction of the arrow. Instead of the scraper belt shown, other entry processes such as plate belts can also be used. A scraper belt 4 covers the outlet cross section of the floor belt hopper. The scraper belt 4 rotates in the direction of the arrow and, in cooperation with a rotating floor belt 5 which closes the floor belt bunker downwards and whose speed can be adjusted, takes a quantity of bulk material which can be preselected for the production of chipboard from the bulk material 6 stored on the end face. This removed bulk material is fed to a scattering unit 7 and then brought down by this scattering unit 7 as a fleece 8 onto a forming belt 9. When the fleece 8 is transported further on the forming belt 9, which is preferably covered with documents 10, which close together without gaps, the respective fleece weight is determined by a scale 11, whether as the total weight including the underlay or as a pure net nonwoven weight by subtracting the weight of the underlay .

Instead of the spreader unit 7 shown, a further spreader unit may be present in mirror image to the one shown while maintaining a floor conveyor bunker, or there may be two floor conveyor bunkers which feed the spreader units arranged in mirror image arrangement. Instead of the scattering units shown, which operate by means of the throwing principle, it is also possible to use scattering units which, by means of a blower, bring about a spreading good for the production of a nonwoven. Here, too, mirror images can be arranged Blower outlet openings with a high throughput of fleece to be scattered, as known, can be used, and combinations between scattering units based on the throwing principle and scattering units based on the wind scattering principle, as known, can also be used.

A measuring surface 12 is arranged between the floor belt bunker and the spreading unit 7, which is explained in more detail in connection with FIGS. 2 and 3c. This measuring surface indicates the weight distribution of the pouring stream 13 in accordance with the bulk flow 13 conducted over it across the width of the spread s (cf. FIG. 3d). These values are fed to a controller 14, to which a setpoint 15, which contains the total weight of the finished chipboard with a uniform density distribution, is simultaneously fed. From the different weight information of the bulk flow 13, which is a measure of the different density distribution in the particle board, compared to the constant information from the target value 15, a control variable that changes over the scattering range is obtained and is fed to an actuator 16. This actuator now acts on tongues 17 of a separating device 18 in such a way that the individual tongues 17 protrude more or less far into the bulk flow 13 according to the distribution (cf. FIG. 3d). As a result, chips accumulate on the individual tongues, which are stripped from the tongues 17 with the aid of the scraper belt 4 and are returned to the feeder 2 of the floor belt bunker 1 via the returning run of the scraper belt 4. It has proven to be advantageous if a guide plate 19 is provided over the total spreading width in the region of the deflection of the scratch 4.

If the actual weight of the fleece 8 having the same density distribution is now also fed to the controller 14 via the scale 11 and there is now a difference between this actual weight and the target weight 15, a control gear 21 with a control command becomes via a further output 20 of the controller 14 acted on, so that a larger bulk flow 13 is discharged from the floor conveyor bunker 1 by changing the speed of the floor conveyor 5.

If, instead of the scraper belt 4, a row of scraper rollers arranged one above the other is used, the last scraper roller also has a guide plate 19 as a partial sheathing, to which a trough conveyor (not shown) is connected for returning the material to be returned to the belt bunker 1. The trough conveyor can be provided with a screw or can be designed as a vibratory conveyor. The arrangement of a guide plate 19 thus prevents return material from falling back into the bulk flow 13.

The measuring surface shown in Fig. 2 has a narrow plate 22 which is arranged on a lever 23. The lever 23 is supported on the one hand on a cross spring joint 24 and on the other hand is supported on a support rod 26 via a force measuring device 25. The support rod 26 is mounted in a transverse guide 27 which extends over the entire spread.

A threaded nut 28 is also fixedly arranged on the support rod 26, as a result of which the narrow plate 22 can be moved transversely to the bulk width in cooperation with a threaded rod 29.

A housing 30, which contains the narrow plate 22 and the suspension parts of the narrow plate 22, carries a guide surface 31 in front of which the narrow plate 22 is moved at a distance a. The distance a is selected according to the invention such that when the narrow plate 22 is moved, no part of the bulk flow can get stuck between the guide surface 31 and the narrow plate 22, so that there is no fear of failure of the narrow plate. The narrow plate still ends within the guide surface 31, so that the scattering unit 7 cannot be influenced by a non-uniform inflow of the bulk flow 13. Since the area b, in which the narrow plate 22 is currently located, ends so far above the end of the guide surface that this partial bulk flow 13 can unite again with the remaining bulk flow 13 and evenly from the end edge 32 of the guide surface 31 to Spreading unit 7 flows off.

The housing 30 also carries a baffle plate 33 which, together with the guide surface 31, forms a slot along which the narrow plate 22 can be moved.

As already shown in FIG. 1, according to the control commands of the controller 14, tongues 17 protrude into the stray current 13 in order to remove excess material as described in FIG. 1 and to feed it back to the bottom belt bunker 1 together with the scratcher 4 or with a scraper roller.

3a shows tongues 17 standing in the bulk stream 13 and a baffle 19 within the angled scraper 34, which absorb the material picked up by the tongues 17 by moving along the inside of the baffle 19 and, due to their angular design, without returning, transport them back into the floor conveyor bunker.

The configuration of the adjustment of a tongue 17 shown in FIG. 3b shows the tongue 17 in a roller bearing 35. The tongue 17 has at its rear end 36 a threaded bore 37 which interacts with a threaded pin 38. The set screw 38 is mounted in a guide 39 and is adjusted by an adjusting drive 40, in the simplest case as a drill chuck, on its threaded head 41 by turning the adjusting drive 40 to the right or left for its region of the pouring stream 13 into or out of the pouring stream .

Corresponding to the resolution of the entire bulk width in a multitude of such tongues 17, which are all arranged next to one another, the guide 39 can be supported as a cross-member extending to the left and right of the bulk width across the entire bulk width. In this case, the adjustment drive 40 moves from tongue 17 to tongue 17 transversely to the stray current 13 and adjusts each individual tongue according to the information received from the controller.

The measuring surface 12 shown in Fig. 3c consists of a plurality of plates 42, the individual widths b, to b _n are selected according to the requirements. If, for example, measurements in the finished particle board have determined that the greatest density fluctuations occur at the edge of this plate, it will be advisable to provide small widths b there. The individual plates 42 are provided with strain gauges 43 and thus enable the measurement of the respective weight distribution over a certain partial width of the entire bulk width. This results in the weight distribution image shown in FIG. 3d over the scattering width s without a narrow plate having to be moved over the guide surface 31.

In the simplest form, the tongues 17 are formed in their width corresponding to the plates 42, so that there is a direct connection between the measured instantaneous distribution and the quantity to be taken off.

Claims (12)

1. Method for equalizing the density distribution in artificial wood boards produced from loose material (6) covered with glue, characterised in that as a function of the weight distribution, measured over a discharge cross- section, of the loose material (6) which is discharged out of a store (1), a separation command is formed for separating out the weight quantities of the loose material (6) present in corresponding partial cross-sections and deviating from a predetermined desired density distribution.

2. Method according to Claim 1, characterized in that the discharge (4) of the loose material (6) is influenced as a function of a comparison between the actual weight per unit area of the artificial wood layer and the desired density distribution in the artificial wood board and its desired weight.

3. Apparatus for carrying out the method according to Claim 1 for the production of artificial wood boards with a silo with a bottom belt conveyor (1) with discharge (4), the discharge width of which is equal to the width of scatter for the artificial wood boards which are to be produced, and devices arranged after the silo with the bottom belt conveyor for depositing the discharged loose marerial (6) as a continuous layer (8) onto a forming belt (9), characterized in that the stream of loose material (13) emerging out of the silo with the bottom belt conveyor (1) is passed to a guide surface (31) covering the entire width of scatter, that a measuring surface (12 resp. 22 resp. 42) is spaced parallel to and in front of the guide surface (31), that the weight information emerging from the measuring surface (12 resp. 22 resp. 42), taking into account momentary partial cross-sections, is passed to a regulator (14) after conversion into electrical signals, to which regulator in addition a desired value (15) for the weight of the finished artificial wood board with equal density distribution is passed, that the resulting regulating signal is passed to an adjustment drive (16) arranged at the output of the regulator (14), and that individual tongues (17) of a separation device are adjusted, which device consists of a plurality of tongues (17) able to be adjusted with respect to each other, and which covers the entire width of scatter (s).

4. Apparatus for carrying out the method according to Claims 1 and 2 for the production of artificial wood boards, with a silo with a bottom belt conveyor (1) with discharge (4), the discharge width of which is equal to the width of scatter for the artificial wood boards which are to be produced, and devices arranged after the silo with the bottom belt conveyor for depositing the discharged loose material (6) as a continuous layer (8) onto a forming belt (9), characterized in that the stream of loose material (13) emerging out of the silo with the bottom belt conveyor (1) is passed to a guide surface (31) covering the entire width of scatter, that a measuring surface (12 resp. 22 resp. 42) is provided, spaced parallel to and in front of the guide surface (31) that the weight information emerging from the measuring surface (12 resp. 22 resp. 42), taking into account momentary partial cross-sections, is passed to a regulator (14) after conversion into electrical signals, to which regulator in addition a desired value (15) for the weight of the finished artificial wood board with equal density distribution is passed, that the resulting regulating signal is passed to an adjustment drive (16) arranged at the output of the regulator (14), that individual tongues (17) of a separation device are adjusted, which device consists of a plurality of tongues (17) able to be adjusted with respect to each other, and which covers the entire width of scatter (s), and that from a balance (11) arranged in the forming belt (9) information regarding the momentary weight of the artificial wood layer is passed to the regulator (14), that in the regulator (14) a comparison is carried out between a predetermined weight (15) of the artificial wood board at the desired density distribution and the artificial wood layer possessing the desired density distribution, that this regulation signal is passed to a variable gearing (21) to alter the speed of the bottom belt (5) in the silo with the bottom belt conveyor (1).

5. Apparatus according to Claims 3 or 4, characterized in that the measuring surface (12) consists of a plurality of plates (42) arranged adjacent to each other, each plate being provided with a strain gauge strip arrangement (43).

6. Apparatus according to Claim 3 or 4, characterized in that a narrow plate (22) can be driven over the entire width of scatter (s).

7. Apparatus according to one of the preceding apparatus claims, characterized in that the outlet cross section of the silo with the bottom belt conveyor is covered over by a scraper belt (4), the fore-running end of which is arranged so as to be drivable in the discharge direction, that the length of the individual scraper bars (34) covers the entire discharge width (s) of the silo with the bottom belt conveyor (1), and that the scraper bars (34) in the return end of the scraper belt take up as carriers the glue-covered loose material which has been separated from the stream of loose material (13) by the separation means, and return it into the silo with the bottom belt conveyor (1).

8. Apparatus according to one of the preceding apparatus claims, characterized in that the narrow plate (22) is arranged on a lever (23) which is mounted at one end via a cross spring joint (24), that the other end of the lever (23) is supported via a load cell (25) onto a supporting rod (26) mounted in a tranverse guide (27) and secured against rotation.

9. Apparatus according to Claim 8, characterized in that a threaded nut (28) is fixedly arranged on the supporting rod (26), and that a rotatable threaded rod (29) is provided which cooperates therewith and extends over the entire width of scatter (s).

10. Apparatus according to Claim 9, characterized in that a housing (30), carrying the transverse guide and support brackets for the threaded rod, has a baffle plate (33) extending over the entire width of scatter (s), that the housing (30) carries the guide surface (31) and that the baffle plate (33) and guide surface (31) are arranged parallel to each other, overlapping each other at a distance from each other.

11. Apparatus according to one of the preceding apparatus claims, characterized in that the measuring surface (12 resp. 22 resp. 42) arranged at a predetermined distance (a) in front of the guide surface (31) terminates in the direction of the stream of loose material at a predetermined distance (b) in front of the end edge (32) of the guide surface (31).

12. Apparatus according to one of the preceding apparatus claims, characterized in that each tongue (17) in the separation device is adjusted via an adjustment drive (40), which can be driven over the distribution width (s), in accordance with the corresponding regulating signal.

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