EP0137450A1 - Method and device for moistening pourable solids - Google Patents

Abstract

For high-pressure spraying of liquid substances such as glue, it is proposed to spray the liquid substance at intervals under constant pressure, so that the sprayed quantity is controlled by changing the pulse times of the spraying without having to change the pressure under which spraying takes place. This type of spraying is particularly suitable for gluing chip material to glues that can form harmful aerosols if processed incorrectly.

Description

The invention relates to a method for moistening pourable solids, for example for gluing chips, in which a liquid substance is divided into the finest droplets and fed to the solid under high pressure. The invention also relates to a device for moistening pourable solids which is intended for carrying out this method and which has a container for holding the solids, a mixer for moving and loosening the solids in the container and at least one device for spraying the liquid substance brought up from a storage container.

Glue is sprayed onto chips under high pressure if you want to achieve an airless glue distribution, i.e. no two-substance system wishes. The airless glue division has several advantages. This avoids glue mists that occur in a two-substance system consisting of air and glue and lead to heavy soiling of the machines in which the chips are glued. Glue mist is also harmful to the operator of the machine. For this reason, for example, isocyanates should not be processed in dual-substance systems at all.

In recent times, however, it has been required that glue resins, in particular diphenylmethane diisocyanate (MDI), be added to the chip mass for the production of chipboard which can be used for living areas. Although such glues are not harmful to health when solidified, they develop toxic aerosols during processing, especially when spraying, which should not be released into the environment. Because of the high cost of the isocyanate glues, however, it is of interest to spray them in order to ensure economical consumption.

It has been shown that by means of a single-component high-pressure system, the substance to be sprayed, such as glue, can be divided up more finely than is possible with a two-component system, thereby reducing the need for glue.

Spraying liquids under high pressure is known and is used industrially. In order to ensure uniform spraying, the liquid to be sprayed is fed to the spraying device in a constant amount, as is the case, for example, with paints. It becomes problematic, however, when the amount of the substance to be sprayed has to be changed in the course of operation, for example as a consequence of another changing variable. This is the case, for example, with chip gluing if the chips to be glued are not produced in uniform quantities. The weight of the amount of chips fed to a gluing device is the key parameter for gluing, while the amount of flowable substance or glue sprayed on is a consequential quantity because the glue has to be added to the chips in a fixed ratio.

In known chip gluing systems, the weight of the amount of chips running in without interruptions cannot be kept constant. On the other hand, the outlet openings of the nozzles provided for applying the glue to the amount of chips each have an unchangeable diameter. Therefore, the amount of glue added must also be changed in the event of fluctuations in the amount or weight of the incoming chips. This is only possible with known nozzles by changing the pressure at which the glue is supplied. Pressure fluctuations of the glue supplied, however, cause changes in the spray pattern of the nozzles, whereby in extreme cases, if the pressure is too low, the glue is no longer sprayed at all, but runs in the form of a jet, while at particularly high pressure the glue is finely divided. Changes in the spray pattern of the nozzles are undesirable in operation because this does not result in uniform moistening and, in particular, no uniform gluing of the chips, even if the ratio between the incoming chip quantity and the amount of glue added or the chip weight and the glue weight is kept constant.

The invention has for its object when moistening pourable solids with the aid of liquid supplied under high pressure Substance to maintain a constant quantitative ratio between solids and sprayed liquid substance to be able to keep the pressure with which the liquid substance is essentially constant.

This object is achieved according to the invention in a method of the type mentioned in the introduction in that the liquid substance is intermittently sprayed into the mass of the solid under essentially constant pressure.

In contrast to the previously usual moistening or gluing of bulk materials such as chips, the liquid substance to be sprayed is not supplied continuously with fluctuating pressure which adjusts to the amount of chips to be sprayed, but rather in pulse form, the length of the individual pulses and / or their time interval being the amount of supplied and sprayed liquid substance determines or regulates. If a large amount of liquid substance is required, the impulses of the liquid supply are longer than the pause times or the interval between the individual impulses decreases, while with decreasing fluid requirement the impulse length decreases or the interval between successive impulses increases. In this way, the spray pattern of the nozzles can be kept constant despite fluctuating amounts of the liquid substance supplied, because the liquid substance is always supplied and sprayed at intervals under approximately constant pressure.

If a glue resin based on isocyanate is used to moisten the chips, economical consumption can be achieved because the finely divided glue which reacts with moisture, such as the moisture contained in the wood chips, does not "blow away" into the chips, but remains on their surface and thus can fully develop its adhesive effect. However, since a single-substance atomization takes place, harmful isocyanate aerosol is produced in the container, which, if working with excess air, would escape from the container and pollute the environment.

The intermittent feeding and spraying of liquid substance is preferably carried out with a predetermined pulse frequency. It is Particularly useful to regulate the amount of liquid substance to be sprayed to change the length of the spray pulses within a constant pulse frequency, which can be easily achieved with an electronic control. But you can also change the pulse frequency itself to regulate the amount of liquid substance to be sprayed. Finally, a change in both the pulse duration and the pulse frequency for the control is also conceivable if one or the other type of control is not sufficient in itself.

Furthermore, the object of the invention is achieved with a device of the type mentioned at the outset, in which the device for spraying the liquid substance is at least one spray nozzle with an unchangeable outlet opening or with a fixed cross section of the outlet opening, which contains a closing body which, in a controllable sequence, constantly closes open and close.

To spray the liquid substance and in particular the glue in controllable quantities, it is not nozzles with a changeable outlet opening that are used, but spray nozzles with an unchangeable outlet opening that is opened and closed at intervals so that the flowable substance is not sprayed continuously but in a controllable manner in an interrupted sequence. It has been shown that the pause times provided between the individual spray pulses do not cause nonuniform moistening of the solids, which is due to the fact that the length of the pause times is very small in relation to the throughput speed of the solids to be sprayed or moistened.

The spray nozzles provided according to the invention can be designed like known spray guns, i.e. contain a piston-shaped or needle-shaped closing body which cooperates with the inner end of the outlet opening of the spray nozzle.

According to a further feature of the invention, the closing body of each spray nozzle can be controlled with a for controlling the spray pulses Actuating actuating cylinder connected, which can for example be connected to a compressed air line, while a return spring is provided which presses the closing body of the spray nozzle into its closed position. To open the individual spray nozzles, the actuating cylinder is pressurized with compressed air to vent the closing body from its seat at the rear end of the nozzle opening, while the closing movements are generated by the return spring, which presses the closing body into the closed position when the actuating cylinder is relieved of pressure.

To control the compressed air supply to the actuating cylinders, a controllable opening and closing shut-off valve is provided in the compressed air line of the actuating cylinder.

The spray nozzles of the device are constantly connected to a high-pressure line for the liquid substance to be sprayed, the liquid substance under constant pressure circulating through this high-pressure line. This is a closed system from which the liquid substance can only escape in a targeted and controlled manner, namely through the spray nozzles. The spray nozzles are connected, for example, to a distributor located in the high-pressure line.

The adjustable ratio between the opening and closing times of the spray nozzles is controlled by an electronic circuit, proportional to the quantity of the bulk material to be moistened, which is supplied via a weighing system. The weighing system can contain a belt scale, a bulk flow meter or a similar device as a transmitter for the control signal. The liquid substance is accordingly added to it in relation to the amount of solids measured or weighed by the weighing system. Since experience has shown that the amount of solids is not constant even with continuous supply, the addition of the liquid substance can be controlled so that the ratio between the solid and the liquid substance is always constant. Because the liquid substance is sprayed with constant pressure, it always is uniformly divided into the finest droplets and accordingly evenly distributed over the pourable solids.

The pressure of the liquid substance in the humidification system is built up to a predetermined value by a pump such as a gear pump or a piston pump and is kept at this value. When the spray nozzles are opened, the full pressure is immediately available for spraying the liquid substance and remains unchanged until the spray nozzles close again. The spray pattern of each individual spray nozzle is therefore always the same during its opening hours, regardless of the throughput of the liquid substance to be sprayed. The spray pattern is the same from the beginning to the end of each opening interval, regardless of how long the individual opening times of the spray nozzles or pulse times of the supply are.

It is particularly expedient if the spray nozzles protrude into the container with a variable length. In this way, it is possible to let the spray nozzles open inside the material to be moistened in the container, so that the liquid substance is not sprayed onto the surface of a solid mass, but rather is sprayed into this mass. In front of the outlet openings of the spray nozzles, the solids mass is loosened up during the pulsed addition times of the liquid substance due to the spray pressure, so that there is a particularly good and uniform distribution of solid and liquid substance which results when the liquid substance is sprayed onto the surface a solid mass would not be achieved. In extreme cases, the spray nozzles open into the container directly on the wall of the container.

• Fig. 1 ein Schaltschema einer zum Durchführen des erfindungsgemäßen Verfahrens geeigneten Anlage,
• Fig. 2 einen Querschnitt des Behälters der Anlage,in dem die schüttfähigen Feststoffe mit der flüssigen Substanz befeuchtet werden,
• Fig. 3 eine schematische Darstellung einer Ausführungsform einer elektro-pneumatisch gesteuerten Sprühdüse im Längsschnitt und
• Fig. 4 ein Steuerdiagramm, das bei einer Impulsfrequenz von 5 Hz zeigt, wie die Länge der Sprüh-Impulszeiten sich gegenüber der Länge der Pausenzeiten vergrößern läßt.

The invention is further explained with reference to the drawing and an exemplary embodiment for the gluing of wood chips, and that shows

• 1 is a circuit diagram of a system suitable for carrying out the method according to the invention,
• 2 shows a cross section of the container of the plant in which the pourable solids are moistened with the liquid substance,
• Fig. 3 is a schematic representation of an embodiment of an electro-pneumatically controlled spray nozzle in longitudinal section and
• Fig. 4 is a control diagram showing at a pulse frequency of 5 Hz how the length of the spray pulse times can be increased compared to the length of the pause times.

The system shown in Fig. 1 is used for gluing chip material, for example with glue resin based on isocyanate. The chip material is continuously fed into a closed cylindrical container 31 of a gluing machine 1 via a belt scale 2. The container 31 contains a rotatably mounted agitator 32 which circulates the input chip material and also transports it from an inlet 3 at one end of the container 31 to an outlet 4 at the opposite end of the container.

The container 31 of the gluing machine 1 is provided with spray nozzles 5, which are attached to the cylindrical wall 33 of the container of the gluing machine 1 and open into the container 31. To each spray nozzle 5 a feed line 6 is connected for liquid glue which sees under high pressure. 1 shows three spray nozzles 5, but the gluing machine 1 is generally equipped with more spray nozzles, for example with a total of twelve spray nozzles.

Each feed line 6 contains, for example, a manually operated gate valve 7 and is connected to a common distributor 8 provided for all spray nozzles 5.

The distributor 8 is located in a line 9, for example a hose line, through which liquid glue under high pressure is brought in and is circulated in the process.

The glue is removed from a storage container by a high-pressure pump 10 and conveyed to the distributor 8 at the desired pressure through a double filter 12 arranged in the line 9. The one from there Glue not directed to the spray nozzles 5 flows in the line 9, further and back through a control valve 13 to the storage container 11, so that no glue can solidify and settle in the line system. A maintenance unit 14 is connected to the high-pressure pump 10 if a piston pump is used.

The belt scale 2 consists of an endless conveyor belt 35 which can be driven in the direction of an arrow 34 and which runs over terminal deflection rollers 36 and 37. The deflection roller 36 is supported on a fixed bearing 38, shown. The deflection roller 37 is also supported, but its bearing is omitted to simplify the drawing in Fig. 1. Pourable material transported via the conveyor belt 35 is poured into the inlet 3 of the container 31.

The belt scale 2 uses a measuring section 39 and a transmitter 40 to supply control signals to an electronic control unit 41 which is used to control the spray nozzles 5 and is connected to the latter via an electronic line 42 or individual lines 42a, 42b or 42c. The transmitter 40 is connected to the control unit 41 via an electrical line 43.

In Fig. 2 it can be seen that the container 31 of the gluing machine 1 is cylindrical and stands on feet 44. In the center of the container 31, a shaft 45 of the agitator 32 is rotatably mounted, on the circumferential and length of which helically distributed agitator tools 46 are attached, which extend up to the cylindrical wall 33 of the container 31. When the shaft 45 is driven by a motor 47 (FIG. 1) in the direction of an arrow 48 at a sufficiently high speed, the pourable material in the container 31 forms a material ring 49 which runs along the wall 33 of the container 31 on a helical path from Inlet 3 migrates to outlet 4.

From Fig. 2 it can also be seen that the spray nozzles 5 project eccentrically into the container 31 and open into the material ring 49, so that the glue supplied through the individual spray nozzles 5 is sprayed into the material ring 49. In front of the mouth 50 of each spray nozzle 5, a loosened zone 51 forms in the material ring 49 during the spray pulse times, in which the solid particles of the material ring with the fine droplets of glue, into which the glue brought in by the spray nozzles 5 has been divided, are intensively formed and be mixed uniformly. The zone 51 can be identified by a bulge 52 on the inside 53 of the material ring 49. The direction of rotation of the shaft 45 is selected so that stirring tools 46 do not counteract the direction of spray of the spray nozzles 5 and accordingly do not compress the loosened zones 51.

The spray nozzles 5 are displaceable and adjustable in their axial direction in the wall 33 of the container 31, as indicated by a double arrow 54. The mouth 50 can thus project to different degrees into the container 31 and thus to different depths into the material ring 49. In an extreme case, the mouth 50 can also lie on the wall 33 of the container 31.

From Fig. 3 it can be seen that each spray nozzle 5 has a housing 14 with an axially displaceably mounted piston rod 15, the tapered outer end 16 of which cooperates with the inner edge of a nozzle opening 17. On the piston rod 15, a coil spring 20 is arranged between a shoulder 18 and the rear wall 19 of the housing 14, which presses the piston rod 15 towards the nozzle opening 17, so that the pointed front end 16 of the piston rod 15 normally seals against the inner end of the Nozzle opening 17 sets.

In the housing 14 leads an inlet port 21 which is connected to the branch line 6 of the spray nozzle in question and thus the distributor 8 of the line 9, so that glue under high pressure is introduced into the housing 14 through the inlet port 21, which comes out of the nozzle opening 17 is sprayed out when the pointed end 16 of the piston rod 15 is released from the nozzle opening 17. The glue is then split into the finest droplets in the form of a spray cone 22 and sprayed out of the spray nozzle 5, provided that the material ring 49, not shown in FIG. 3, does not influence the shape of the spray cone.

At the rear end of the piston rod 15, a piston 23 is attached, which is slidably seated in an actuating cylinder 24. A compressed air line 25, which contains a shut-off valve 26, opens into the front end of the actuating cylinder 24. This shut-off valve 26 is connected to the control unit 41, which opens the shut-off valve 26 as soon as the spray nozzle 5 is to spray glue into the container 31.

The piston 23 is then displaced by the compressed air introduced into the pressure chamber 28, as seen to the left in FIG. 3, as a result of which the pointed end 16 of the piston rod 15 is lifted from the nozzle opening 17 and, accordingly, the high-pressure glue from the nozzle opening 17 can leak.

If the shut-off valve 26 closes, the pressure chamber 28 is ventilated via the closed shut-off valve, so that the return spring 20 pushes the piston rod 15 back to the nozzle opening 17, whereby this is closed and no more glue can escape.

The control unit 41 operates electronically at a predetermined frequency, but the pulse lengths of the opening times of the shut-off valve 26 can be changed within the predetermined frequency according to control signals supplied by the belt scale 2, as shown in FIG. 3.

4 that the length of the pulse times 29, during which glue is sprayed, and the length of the pause times 30, during which the spray nozzles 5 are closed, are variable at a constant frequency. In each case, a pause time 30 is provided between the pulse times 29. The pressure available for spraying the glue is practically the same during all pulse times 29, regardless of how long the individual pulse times are.

If a piston pump is used to generate pressure, the delivery pressure of the glue can be kept practically constant. However, other pumps can be used that deliver a substantially equal working pressure.

Claims (11)

1. A method for moistening pourable solids, for example for gluing chips, in which a liquid substance is broken down into fine droplets and fed to the solid under high pressure,
characterized,
that the liquid substance is intermittently sprayed into a mass of the solid under essentially constant pressure. 2. The method according to claim 1, characterized in that the liquid substance is sprayed intermittently into the mass of the solid with a predetermined pulse frequency. 3. The method according to claim 1 or 2, characterized in that for regulating the amount of liquid substance to be sprayed, the length of the pulses is changed within a constant pulse frequency. 4. The method according to claim 1 or 2, characterized in that the pulse frequency is changed to regulate the amount of liquid substance to be sprayed. 5. Apparatus for moistening pourable solids for performing the method according to one of claims 1 to 4, with a container (31) for receiving the solids, a mixer (32) for moving and loosening the solids in the container (31), at least one device (5) for spraying the liquid substance brought from a storage container (11) into the container and a device (2) for continuously feeding solids into the container (31)
characterized,
that the device for spraying the liquid substance has at least one spray nozzle (5) with an unchangeable outlet opening (17) and a closing body (15, 16) which can be opened (ventilated) and closed continuously in a controllable sequence, is connected to a feed line (9) under approximately uniform pressure and by means of the device (2) for feeding of the control signals supplied, for example electro-pneumatic, can be opened intermittently. 6. The device according to claim 5, characterized in that the spray nozzles (5) are designed like known spray guns and the closing body (15, 16) of each spray nozzle (5) is connected to a controllable actuating cylinder (24). 7. The device according to claim 6, characterized in that the actuating cylinder (24) is connected to a compressed air line (25) containing a controllably openable and closable shut-off valve (26), and that a return spring (20) is provided, which presses the closing body (15, 16) into its closed position. 8. Device according to one of claims 5 to 7, characterized in that the spray nozzles (5) are constantly connected to a high-pressure line (9) through which the liquid substance, which is at substantially constant pressure, circulates. 9. The device according to claim 8, characterized in that the spray nozzles (5) to a in the high pressure line (9) located distributor (8) can be connected. 10. Device according to one of claims 5 to 9, characterized in that the spray nozzles (5) protrude through openings in the container wall with an adjustable length in the container (31). 11. Device according to one of claims 1 to 10, characterized in that the spray nozzles (5) by means of differential pressure monitoring in their feed lines (6) are controllable.

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