EP1434674B1 - Device and method for vacuum impregnation - Google Patents

Abstract

A method is described for vacuum impregnation of particulate material in an impregnation installation (16, 16') which has an impregnation chamber (54, 84) that can be placed under vacuum, an inlet orifice (64, 64') for transferring the material into the impregnation chamber (54, 84) and an outlet orifice (82, 82') for transferring the material out of the impregnation installation (16, 16'), with the following method steps treatment of the material with a substance in order thus to produce a treated material, the sealing characteristics of which in a stuffing screw are improved in comparison with the untreated material, transport of the treated material by means of a stuffing screw (52) to the inlet orifice (64, 64'), transfer of the treated material by means of the stuffing screw (52) through the inlet orifice (64, 64') into the impregnation chamber (54, 84), so that the treated material seals the inlet orifice (64, 64') during inward transfer, impregnation of the material in the impregnation chamber (54, 84) with an impregnating agent under reduced pressure, transport of the impregnated material to the outlet orifice (82, 82') and outward transfer of the impregnated material from the impregnation installation (16, 16') through the outlet orifice (82, 82'), so that the material seals the outlet orifice (82, 82') during outward transfer.

Description

The invention relates to a method and a device for vacuum impregnation of small-particle material. The term small-particle material includes z. As vegetable fiber raw materials (straw chips, wood chips, natural fibers), as used for example for the production of press plates, and granular or fibrous plastic material, the z. B. can be used as filler or woven fabric use.

In particular, when impregnating chips or fibers from natural raw materials, it has proven to be advantageous to mix the material to be impregnated in a vacuum with an impregnating agent. Namely, in the pores of the raw material located gas (air) is pumped out during the impregnation (degassing), which significantly increases the absorption capacity of the raw material for impregnating agent.

Such a Vakuumimprägnier method and a corresponding device is known from DE 199 11 230 known. In this method, small-sized material is introduced through a first evacuable lock chamber in an impregnation chamber and then through a second evacuated lock chamber ejected from the impregnation chamber. The impregnation process thus takes place intermittently in this process. The lock chambers are in each case during the entry or discharge of the material - while the lock chambers are ventilated - closed by shut-off against the impregnation chamber, and are then evacuated. Thereafter, the shut-off elements are opened to the impregnation chamber and the material can be conveyed into or out of the impregnation chamber. The impregnation chamber remains evacuated during the whole process. Only the volume smaller lock chambers are alternately ventilated and evacuated.

The pumping duration and the size of the lock chambers are competing factors that, disadvantageously, can not be arbitrarily reduced at the same time. They thereby limit the throughput speed of the device. On the other hand, the device is relatively prone to failure, since the opening and closing shut-off elements are sensitive to contamination, for example, by the registered small-sized material. These contaminants can cause vacuum leaks, adding unwanted downtime to the already limited throughput rate.

The object of the present invention is therefore to provide a method and a device for vacuum impregnation, which ensures a higher process reliability and a greater efficiency.

• - Behandeln des Materials mit einer Substanz, um so ein behandeltes Material zu erzeugen, dessen Abdichtverhalten in einer Stopfschnecke im Vergleich mit dem unbehandelten Material verbessert ist,
• - Transportieren des behandelten Materials mittels einer Stopschnecke zur Eintrittsöffnung,
• - Einschleusen des behandelten Materials mittels der Stopfschnecke durch die Eintrittsöffnung in die imprägnierkammer, so dass das behandelte Material die Eintrittsöffnung während des Einschleusens abdichtet,
• - Imprägnieren des Materials in der Imprägnierkammer mit einem Imprägniermittel bei Unterdruck,
• - Transportieren des imprägnierten Materials zur Austrittsöffnung und
• - Ausschleusen des imprägnierten Materials durch die Austrittsöffnung aus der Imprägniervorrichtung , so dass das Material die Austrittsöffnung während des Ausschleusens abdichtet.

The object is achieved in terms of the method by a method for vacuum impregnation of small-scale material in an impregnator with an evacuated impregnation chamber, an inlet opening for introducing the material into the impregnation chamber and an outlet opening for discharging the material from the impregnation with the method steps

• Treating the material with a substance so as to produce a treated material whose sealing performance in a plug screw is improved in comparison with the untreated material,
• Transporting the treated material by means of a stop screw to the inlet opening,
• Introducing the treated material by means of the plug screw through the inlet opening into the impregnating chamber, so that the treated material seals the inlet opening during the injection,
• Impregnating the material in the impregnating chamber with an impregnating agent under reduced pressure,
• - Transporting the impregnated material to the outlet opening and
• - Outward discharge of the impregnated material through the outlet opening of the impregnator, so that the material seals the outlet opening during the discharge.

The object is further achieved by a device for carrying out the method.

The process design according to the invention ensures that the impregnation chamber is permanently sealed from the environment even during entry and / or removal without the upstream and downstream lock chambers having to be intermittently charged and emptied or ventilated and evacuated. Failure-prone shut-off elements between the lock chambers and the impregnation chamber are also eliminated.

Preferably, the substance with which the material is (pre-) treated to obtain a treated material having improved sealing performance is a liquid impregnating agent (in particular, an impregnating solution). This embodiment of the method according to the invention is, of course, particularly advantageous because, to improve the sealing properties of the material to be impregnated, use is made of a substance which would have to be added to the material anyway within the impregnating chamber at the latest. On the use of substances that serve only the seal, but otherwise meaningless in the impregnation process, is advantageously completely eliminated.

The treatment of the material is then preferably carried out by adding the liquid impregnating agent (the impregnating solution) during transport of the material to the inlet opening and preferably during compression of the material during transportation to the inlet opening. This causes a mixture of materials with a higher density results. Further, the impregnating solution forms a sealing film between the material and the surface of the means for transporting the material. Both effects, the increasing material density and the surface film, significantly improve the sealing behavior.

Without the (pre-) treatment of the material according to the invention with a substance improving the sealing behavior (eg an impregnating agent), it is very difficult (if at all) to achieve satisfactory impregnation results when using a screwing screw (inlet screw). It has been found that when feeding small-sized untreated material, in particular when feeding straw chips, wood chips and natural fibers, leaks frequently occur, which cause the vacuum in the impregnation chamber to collapse; in other words, the untreated material only insufficiently seals against the stuffing screw wall. Moreover, wear in a plug screw when using untreated material is particularly high when trying to produce a well-sealing plug of material. See the introduction to the description of the DE 44 19 733 A1 , in which typical problems when using a screw feeder are specified.

As a liquid impregnating agent, which also advantageously influences the sealing behavior of the material to be impregnated, a salt solution with a concentration of 25-35% and a density of 1.1 to 1.2 g / cm ³ can be used in the process according to the invention, for example. Such a salt solution has a sticky-viscous consistency. The reduced flowability (increased viscosity) of the impregnating solution on the one hand and its increased binding effect ("stickiness") on the other hand additionally reinforce the plugging of the material. As a result, both a tightness of the material plug against a pressure drop (when entering the Impregnation) as well as against a pressure increase - each viewed in the conveying direction - guaranteed. In addition, in this way an improved sliding effect between the compressed material and, for example, the inner wall of the screw plug can be produced, whereby the screw wear is reduced.

Finally, the material, by adding liquid impregnating agent (in particular an impregnating solution) to the inlet opening during transport, is already pre-impregnated before it reaches the impregnating chamber. This is done, as described above, in particular when compressing in the plug screw, so under pressure, whereby the impregnation advantageously shortened in the impregnation.

Preferably, in the method according to the invention, the material is introduced continuously through the inlet opening into the impregnating chamber and / or discharged continuously out of the impregnating device through the outlet opening.

A device for evacuating the impregnation chamber, for example a vacuum pump system, provides the required negative pressure relative to the ambient pressure. This is preferably done by permanently evacuating the impregnation chamber when carrying out the method according to the invention. Alternatively, however, the impregnation chamber can also be opened by means of a valve only when needed, e.g. be exceeded when a predetermined maximum pressure value is exceeded to a device for evacuating the impregnation chamber and otherwise separated therefrom. The valve is then preferably equipped with a corresponding regulation for pressure-dependent opening or closing of the valve.

The advantages of the preferred method according to the invention and of the preferred device according to the invention are numerous: with continuous material flow it is ensured that the important parameters for vacuum impregnation are (a) volume flow of the material fed in, (b) gas pressure and (c) moisture level in the impregnation chamber are constant. This ensures high process reliability, which on the one hand causes a saving of raw materials and energy and at the same time a uniform impregnation, a constant feed of the downstream processing stages, such as. B. the pre-dryer and fiberizing machine, and thus ultimately product sequences with consistent characteristics allows.

Furthermore, it proves to be advantageous to compress the material not only (by means of the existing stop screw) when being transported to the inlet opening, but also when being transported to the outlet opening (for example, again by means of a stuffing screw). The density of the small-particle material can then be increased not only during the input but also during the discharge, so that a plug forms, which generally improves the sealing behavior of the material. The plug is formed essentially in the area of the largest material compression (sealing area), whereby at the same time the inlet or outlet opening of the impregnating chamber or the impregnating device is defined. If, for example, conically tapered screw conveyors are used to compress the material in the conveying direction, then the sealing takes place in the region of the end of the screwing screw located in the conveying direction.

In a particularly preferred embodiment of the method and the device, the material is compressed during transport to the outlet opening in order to achieve a better seal there as well. It is advantageous to absorb excess impregnating solution that is pressed by the compression, in appropriate facilities and possibly due to reuse.

The preferably designed as stuffing screws means for transporting the material to the inlet opening and the outlet opening (hereinafter referred to as entry or discharge screw) usually have in the conveying direction a tapering of its outer periphery. In the impregnation of chopped or chopped straw, the ratio of the entrance-side cross-section to the exit-side cross-section of the feed screw is typically 1.05: 1-1.3: 1 in an input side Cross section of, for example, 600 mm. The discharge screw typically has a taper of 1.1: 1-1.4: 1 with an input-side cross-section of, for example, 400 mm. The conicity and cross-sectional data are given by way of example for chopped or chopped straw to which impregnating agent is added during compression in the feed screw. However, depending on the compressibility and grain size of the material to be impregnated, you can deviate considerably from this.

As an alternative to a conically tapered plug screw, a compression of the material can also be achieved by a decreasing pitch of the screw with a constant cross section or by a combination of both variants. However, a conical design of the plug screws is always more advantageous, since the output-side cross section, at which the plug formation essentially takes place, is smaller for the same delivery quantity than for a screw with a constant cross section and thus a smaller cross sectional area is to be sealed.

Preferably, the device of the entry screw and / or the discharge screw downstream means, with which the material is loosened after the introduction or the discharge.

It is advantageous if, in the method according to the invention, the amount of impregnating agent additionally used prior to entry into the impregnating chamber and / or during impregnation is regulated as a function of the quantity of untreated material transported to the inlet opening in order to control the sealing behavior of the material and / or to influence its impregnation.

1. 1. natürliche nachwachsende Faser-Rohstoffe, beispielsweise:
   • alle Holzarten, das heißt sowohl Hart- als auch Weichhölzer;
   • Bagasse (Zuckerrohr), Bambus, Baumwollstauden (Baumwolle), Jute, Sisal, Hanf, Ramie, Getreidestroh aller Art, Reisstroh, Reisschalen, Chinaschilf, Elefantengras, Riesengras (Miscanthus), Flachs (Fasem und Schäben), Kokos, Kenaf, Alfagras, Agavenfasem etc.
2. 2. Kunststoffe, beispielsweise:
   • Viskose, Polystyrol, Vinyl-Polymerisate, Acrylnitril, Polyamide, Polyurethane, Polyester, Perlon, Nylon, Kevlar, Polyterephthalat etc.

The inventive device can be used for impregnating a variety of materials. As examples of materials may be mentioned:

1. 1. natural renewable fiber raw materials, for example:
   • all types of wood, that is both hardwood and softwood;
   • Bagasse (cane), bamboo, cotton perennials (cotton), jute, sisal, hemp, ramie, cereal straw of all kinds, rice straw, rice husk, Miscanthus, elephant grass, giant grass (miscanthus), flax (fibers and shives), coconut, kenaf, alfagrass, agave fiber, etc.
2. 2. plastics, for example:
   • Viscose, polystyrene, vinyl polymers, acrylonitrile, polyamides, polyurethanes, polyesters, perlon, nylon, kevlar, polyterephthalate etc.

1. 1. OSB (Oriented Strand Board)-Späne:
   • Länge bis 150 mm, Breite bis 30 mmm, Dicke bis 1 mm.
2. 2. Hackschnitzel:
   • Länge bis 40 mm, Breite bis 15 mm, Dicke bis 6 mm; Schüttgewicht im Bereich 180-220 kg/m³.
3. 3. Späne:
   • Abmessungen innerhalb eines weiten Bereichs variierbar; Schüttgewichte von 20-250 kg/m³.
4. 4. Strohhäcksel:
   • Länge bis 60 mm, Breite bis 6 mm, Dicke entsprechend der Halmdicke.
5. 5. Vereinzelte Fasern und Faserbündel beliebiger-Länge.

In the field of naturally renewable raw materials in particular particles fall under the term "small parts":

1. 1. OSB (Oriented Strand Board) chips:
   • Length up to 150 mm, width up to 30 mm, thickness up to 1 mm.
2. 2. wood chips:
   • Length up to 40 mm, width up to 15 mm, thickness up to 6 mm; Bulk density in the range 180-220 kg / m ³ .
3. 3. chips:
   • Dimensions variable within a wide range; Bulk densities of 20 -250 kg / m ^3.
4. 4. Straw chop:
   • Length up to 60 mm, width up to 6 mm, thickness according to the thickness of the stalk.
5. 5. Isolated fibers and fiber bundles of any length.

The specified dimensions are to be understood as examples.

As a liquid impregnating agent or component of a liquid impregnating agent, in particular the following materials can be used:

Fire retardants; Fungicides, biocides, germicides, insect repellents, termite protectants such as polyborus / disodium octaborate tetrahydrate or cashew nut shell oil / alkenyl phenol; organic and inorganic silicates; Substances for increasing or decreasing the electrical conductivity; antistatic agents; metallizing agents; antioxidants; water repellents; stability increasing means; paints; resins; finishes; latexes; hardening oils, waxes, paraffins, bitumen; Hardening, buffering and absorbing substances; odor-improving substances; Surfactants.

• Echte Lösungen aus flüssigen oder festen Stoffen in einem Lösungsmittel (z.B. Wasser);
• Emulsionen, Dispersionen;
• anorganische und organische Flüssigkeiten, z. B. Öle.

It is possible to use liquid or aqueous impregnating agents, in particular in the following forms of use:

• Real solutions of liquid or solid substances in a solvent (eg water);
• Emulsions, dispersions;
• inorganic and organic liquids, e.g. For example, oils.

Preferred fire-retardant impregnating agent solutions that can be used in the device according to the invention are disclosed in US 5,348,337 WO 97/46635 described; they include ammonium sulfate, borax and trisodium phosphate, which are preferably dissolved in water. All in the WO 97/46635 defined impregnating solutions are by way of reference a part of this application.

If a liquid impregnating agent, as is preferred in the context of the present invention, serves as a means for improving the sealing behavior of the material to be impregnated in the screwing screw, then the skilled person can always take into account the primary task of the impregnating agent (eg fire or insect protection or the like). the chemical design of the impregnating vary according to the particular application in order to increase the sealing behavior of the material to be impregnated in the desired manner.

With regard to the physico-chemical principles, the skilled person will take into account that (a) by a suitable combination of low and high molecular weight substances (short-chain and long-chain organic compounds), (b) by use of mixtures of easily and hardly soluble additives (salts or the like) , (c) by adjusting the concentration of eg impregnation agent present in aqueous solution and / or the density and / or viscosity of the corresponding impregnating agent solution and / or (d) the sealing behavior can be influenced by adding water-softening additives.

An impregnating agent used for influencing the sealing behavior can be, for example, (a) an aqueous solution which is only a single one Or (b) a mixture of at least two products such as a combination of a low viscosity and a highly viscous agent or (c) viscosity regulatives such as silicates (especially sodium metasilicate), phosphates, polybor, acrylates, glycols (polyethylene glycols) , Glycerol, starches, fatty acids, fatty acid esters, fatty alcohols or the like.

If impregnating agent is used as a means for influencing the sealing behavior, a dosing of the impregnating agent from a single storage container is possible according to a preferred embodiment. From the storage container, the impregnating agent preparation (a) can then be fed to the stuffing screw (feed screw) via separate lines, which transports the treated material to the inlet opening, and / or (b) is introduced into the impregnating chamber. If both a supply line to the feed screw and the impregnation provided, the entire amount of impregnating used before the impregnation (preferably in the plug screw) can be added to the material to be impregnated (100% of the impregnating agent to be used before entering the impregnation to the impregnating material added) or it can, for example 50% or 60% of the impregnating agent preparation is added to the material to be impregnated in order to improve its sealing behavior in the stuffing screw and the remaining 50% or 40% of the impregnating agent preparation is added to the impregnating chamber. In this context, it should be noted that even with complete (100%) addition of the impregnating agent to be impregnated before entering the impregnation chamber (preferably within the plug screw) via the vacuum in the downstream impregnation chamber and the associated removal of air from the Pores of the material to be impregnated a very good penetration of the impregnating agent in the material to be impregnated (especially chips or fibers) takes place.

According to a further preferred embodiment, it is not a uniform impregnating agent that is used, but two different additives, which have separate supply lines to the impregnating chamber or to the entry screw (or one of the entry screw upstream region, which must pass through the material to be impregnated) are assigned. It is advantageous, for example, to add a first additive to the material to be impregnated before entering the impregnation chamber, which has a high viscosity and can be evenly distributed on the surface of the material to be impregnated to form a durable sliding film, thus enhancing the sliding properties of the material to be impregnated To improve material in the entry auger.

A second additive having lower viscosity compared to the first additive, to which preferably penetration aids such as surfactants, metasilicates and the like are added, is then preferably metered into the impregnation chamber. The additives may each contain impregnants themselves, but this need not be the case.

Overall, a whole range of different combination options are available to the person skilled in the art, by means of which he can improve the sealing behavior of the material to be impregnated in the feed screw, without causing any relevant additional costs. Preferred are always those process designs in which a liquid impregnating agent is also used to set a sufficient sealing behavior of the material to be impregnated in the feed screw. The process according to the invention can be used in particular for impregnating small-sized materials from renewable raw materials (in particular straw). It therefore makes possible the use of stuffing screws, which have hitherto not seemed suitable for relatively dry, limitedly compactable and transportable materials (such as straw).

Further advantageous embodiments of the inventive method and the device will become apparent from the claims and will be explained with reference to the following examples with reference to the figures.

Show it

FIG. 1

a schematic representation of an impregnation plant with an impregnating device according to the invention;

FIG. 2

a schematic representation of a first embodiment of the impregnating device according to the invention;

FIG. 3

a cross section through an impregnation chamber of the embodiment FIG. 2 ;

FIG. 4

a schematic representation of a second embodiment of the impregnating device according to the invention.

In the FIG. 1 impregnation system 10 shown comprises a dosing bunker 12, a subsequent in the process direction belt weigher 14, which in turn is followed by a vacuum impregnation device 16 according to the invention. Next in the process direction, a dewatering screw 18 is arranged, to which a dryer 20 and behind a reversing screw 22 connects.

To be impregnated small-particle material, spielsweise dry straw with a humidity of 20-25% and a bulk density of about 45 kg / m ³ , is abandoned by a storage container, not shown, or directly from a shredder or hacker, not shown on the Dosierbunker 12 (symbolizes by an arrow 24). The metering bunker 12 transfers the material by means of a conveyor belt 26 to the belt scale 14, from which the material of the Vakuumimprägniervorrichtung 16 is supplied. On the belt scale 14, the weight of the discontinued material is measured. Based on the determined weight, the conveying speed of the conveyor belt 26 and / or the belt weigher 14 can be changed by means of a control 28, so that the volume flow transferred from the belt scale to the vacuum impregnating device 16 substantially maintains a constant predetermined value. It should be noted at this point that instead of weighing a volume measurement is possible.

On the functioning of the impregnating device and in particular on the aspect of improving the sealing behavior by (pre) treatment of the to be impregnated material with reference to the FIGS. 2 to 4 commented separately.

The vacuum impregnator 16 is connected to an impregnating agent adding device. This essentially consists of an impregnation solution reservoir 32, a measuring and control unit 33 for measuring and dosing the impregnation solution concentration, a controllable metering pump 34 and a flow meter 36. The metering pump 34 and the flow meter 36 are connected to the controller 28 (PLC control) and can be adjusted to a predetermined flow rate of, for example, 35 wt .-% or 35 vol .-% depending on the thus also regulated volume or mass flow of the transferred from the belt scale 14 (dry) material (Atro material). The flow rate may vary with respect to the volume or weight of the impregnant solution, i. depending on the density and thus the concentration of the solution. In this way, it is ensured that the amount of impregnating solution or impregnating agent that is just required is always ready for impregnation, whereby the saturant consumption of the system can be reduced.

The impregnation device 16 is further connected to a vacuum system 40. The vacuum system 40 has a control valve 42 and one or more vacuum pumps 44 connected in series. As vacuum pumps 44, for example, rotary vane pumps, roots pumps, liquid ring pumps or combinations of such pumps and optionally also combinations with a backing tank come into consideration. The vacuum generated in the impregnating device can be set automatically or manually to a preselected pressure range of, for example, 10-50 mbar and preferably 25 mbar by means of the control valve 42. For this purpose, (a) an unillustrated pressure gauge, which receives the pressure in the impregnation chamber, and (b) a control also not shown required, which operates depending on the recorded and the preselected pressure / range, the control valve and in this way the impregnation optionally with the vacuum pumps connects or separate them from these. The design of the vacuum pump (s) depends on the expected leakage losses of the impregnator.

The impregnated in the impregnating device 16 material is passed to the dewatering screw 18 after impregnation. This is presently designed as a conically tapered conveyor screw in the conveying direction. It has openings for dewatering (not shown) along its circumference, substantially in the region of the plug formation, through which the excess impregnating agent adhering to the impregnated material can flow out during compression. The impregnating agent is collected after dewatering and passed through a return line. 46 with a control valve 48 and a filter 50 in the reservoir 32. Immediate dewatering, collection and the continuous recycling of excess impregnating agent further reduce the consumption of impregnating agent.

Depending on the amount and concentration of the recirculating impregnating solution, the concentration of the impregnating solution in the reservoir 32 also changes. The desired concentration (for example, 25% aqueous solution) is automatically adjusted by means of the measuring and control unit 33 for metering the impregnating solution concentration regulated addition of water or solvent and / or the impregnating substance (s) to be dissolved restored. Overall, it is thus ensured that a certain amount of impregnating material is added to a predetermined amount of impregnating agent.

The impregnated and dewatered material, ie straw in the example mentioned above, is passed on to the dryer 20 by the dewatering screw 18 - now with a moisture content of 120-160% and a bulk density of about 200 kg / m ³ . In it it is freed by heating to a desired residual moisture content of the remaining water from the impregnating agent. This is, for example, a drum dryer, in which the material is set in motion by a rotation of a drum and in this way well ventilated and at the same time transported in the direction of an outlet opening of the drum dryer becomes. From the dryer 20, the material is transferred to a (reversible) screw conveyor 22. From this, the impregnated and dried material to the subsequent processing processes such. B. forwarded to defibration.

The Vakuumimprägniervorrichtung 16 is in FIG. 2 shown in the form of a first embodiment. It has an entry screw 52, a vacuum impregnation chamber 54 flanged thereto and a discharge screw 56 flanged thereto again. Both the entry screw 52 and the discharge screw 56 are designed as conically tapered in the conveying direction Stopfschnecken. The Vakuumimprägnierkammer 54 has a mixer, with reference to FIG. 3 will be explained in more detail. The transferred from the belt scale 14 straw (see. Fig. 1 ) first passes, for example, under the influence of gravity (arrow 58) on the input side into the feed screw 52. This feeds it with a previously set speed in the direction of its axial end tapered on the output side. The conveying speed is adjusted via the speed of the screw conveyor by means of a control 60 so that, taking into account the amount of material applied by the belt scale, it is always ensured that the material forms a plug in the region of the tapered output end of the screw.

Impregnating agent solution is already added to the material in the feed screw 52 via a first feed line 62 in order to improve the sealing behavior of the material in the region of the outlet end of the feed screw 52 and to simultaneously preimpregnate the material under the pressure exerted by the feed screw 52. Additionally or alternatively, the material may have a separate in FIG. 2 not shown, a liquid is added, which does not comprise impregnating agent, but improves the sealing behavior of the material within the feed screw 52.

The output end of the feed screw 52 also forms an inlet opening 64, through which the material is introduced into the impregnation chamber 54. The impregnation chamber designed as a continuous mixer 54 has two shafts 66, 68 provided with a multiplicity of (adjustable) mixing tools 70, cf. FIG. 3 , which loosen the material in a counter-rotating manner, mix together with the impregnating agent and at the same time transport it in the direction of the discharge screw 56.

The impregnation chamber 54 is connected to the vacuum system 40 (see also Fig. 1 ) and is evacuated by means of the control valve 42 as a function of the pumping capacity of the vacuum pumps 44 to a desired pressure of, for example, 25 mbar. Due to the negative pressure, the registered material is sufficiently degassed to ensure better absorption capacity for the subsequent or simultaneously added impregnating agent. The design of the vacuum pump (s) depends on the expected leakage losses of the impregnating device. The leakage losses are in turn determined by (a) the cross sections of the inlet and outlet openings of the impregnating device and (b) the sealing behavior of the material.

Impregnating agent is introduced into the impregnating chamber 54 in the form of the impregnating solution via a second supply line 72 during the impregnation. This is done by spraying the solution into the impregnation chamber 54 by means of a nozzle 74 above the flow mixer and the material mixed therein. The amount of the total impregnation solution added, which is injected in part into the feed screw 52 and partly into the impregnation chamber 54, is metered by the metering pump 34 and the flow meter 36 (not shown here, cf. Fig. 1 ) limited to the required depending on the volume flow of the registered material to be impregnated measure. In the Fig. 2 shown embodiment of a horizontally arranged impregnation chamber is preferably used for low impregnation levels.

The mixing time and mixing intensity in the impregnation chamber 54 can be controlled by means of a further control 76 (converter), which controls the speed of the shafts 66, 68 in conjunction with exit flaps arranged at the exit end of the impregnation chamber 54. It is possible in this way to increase the mixing intensity by the speed of the Shafts 66, 68 are set higher without shortening the mixing time by keeping the exit flaps 78 closed as long as desired and / or closing as much as desired. Thus, on the one hand, the material is conveyed faster to the exit-side end of the impregnation chamber 54, but lingers there for a correspondingly longer time in order, for example, to undergo prolonged degassing after impregnation. The control of the exit flaps can also be carried out in dependence on the current consumption of a (not shown) drive motor of the shafts 66, 68, for example, to prevent a jam. If a lower shaft speed is selected, the residence time of the material in the impregnation chamber as a whole and in particular below the injection nozzle 74 can be extended due to a lower transport speed.

The injection nozzle is preferably arranged in the initial region near the inlet opening of the impregnation chamber. Depending on the impregnation process, however, it may also be arranged closer to the center of the impregnation chamber in order, for example, to extend the period of time for degassing the material prior to impregnation.

The distribution of the impregnating agent solution onto the part injected into the feed screw 52 and into the impregnating chamber 54 can be adjustable, for example, by means of flow meters and / or valves (not shown).

The impregnated material is transported by opening the outlet flaps 78 into the inlet area of the discharge screw 56, which is also tapered towards its outlet opening. The material is in the discharge screw again in the region of the tapered output-side end, which also forms an outlet opening 82 for discharging the impregnated material from the impregnation device 16, compressed so that it forms a plug which seals the outlet opening 82. That this is ensured, ensures a control 80, which controls the speed of the discharge screw 56 in response to the - discontinuous in alternately open and closed or partially closed discharge flaps 78 - volume flow of the impregnated material. The snail fulfills a dual function: namely, during the grafting excess impregnating agent is pressed in the manner described above and fed via the return line 46 into the reservoir 32. By pressing off excess impregnating agent, the total amount of impregnating agent required is kept substantially constant as a function of the volume flow of the material.

The two plugs in the region of the inlet opening 64 of the impregnation chamber 54 and the outlet opening 82 of the discharge screw 56 cause the material in the entire area therebetween to be exposed to the vacuum generated by means of the vacuum system 40. It passes through within the vacuum both a section (below the injection nozzle) in which the impregnating agent is applied, as well as a section in which no further impregnating agent is applied, but in which it is only mixed and / or transported to degas and to achieve a total of the best possible penetration of the impregnating agent in the material.

The discharged through the outlet opening 82 of the discharge screw 56, impregnated material is fed to the downstream dewatering screw 18, see. FIG. 1 , With adequate dewatering in the discharge screw 56, however, can also be dispensed with a downstream, additional dewatering screw 18, so that the material can be entered directly from the impregnation 16 in a downstream dryer 20.

This in FIG. 4 shown embodiment of the vacuum impregnation device 16 'according to the invention also has an entry screw 52' and a discharge screw 56 ', which are designed as conically tapered plug screws. Unlike in the embodiment previously shown, however, the impregnation chamber 84 arranged between the two plug screws is embodied here as a large-volume mixing screw. The impregnation chamber 84 is tilted out of the horizontal in the process direction rising. Furthermore, the impregnating device 16 'differs from the impregnating device 16 according to FIG Fig. 1 in that the total impregnating agent is introduced by means of the line 62 'in the feed screw 52' and no further line for direct injection of impregnating agent is provided in the impregnation chamber 84.

The mixing screw used for vacuum impregnation is equipped with two control mechanisms to achieve the desired mixing time and mixing intensity. On the one hand an adjusting device (indicated by arrow 86) is provided, by means of which the inclination of the impregnating chamber relative to the horizontal is adjustable, and on the other hand, a speed control 88 is provided for adjusting the conveying speed of the mixing screw.

The impregnating agent injected via the feed screw 52 ', together with the now already pre-impregnated material, is introduced through the inlet opening 64' into the impregnating chamber and collects there in a lower section 98. Depending on the inclination of the impregnating chamber 84, the speed of the mixing screw and the amount of impregnating agent introduced, the material comes into contact with the impregnating agent over a longer mixing time. This type of immersion impregnation is particularly suitable for higher impregnation levels.

In the conveying direction at the end of the mixing screw of the impregnation chamber 84, the impregnated material is transferred to the outlet screw 56 ', which compresses the material as in the aforementioned embodiment on the one hand and thereby excess impregnating agent presses the other hand at the same time a Materialpfropfen in the region of the outlet opening 82' for discharging of the material from the impregnation device 16 'forms. The material plug in the inlet opening 64 'and the material plug in the outlet opening 82' also limit the volume evacuated by means of the vacuum system 40 '.

The impregnated material is transferred from the discharge screw 56 'to a dissolution unit 90, which essentially comprises two needle rollers 92, 94, with which the impregnated, partially lumped material is loosened after discharge, before, for example - if no downstream dewatering screw is provided - to a dryer (see. Fig. 1 ). A similar dissolution unit can also be provided behind the inlet opening within the impregnation chamber 84 for loosening up the material after the introduction.

The speeds of the entry, the discharge screw 52 ', 56' and the mixing screw and the inclination of the impregnation chamber 84 are controlled by means of controls 60 ', 80', 86 and 88.

All arrangements of the embodiments shown can be connected to one another via an arithmetic unit and, in particular, also with the other arrangements of the impregnation system 10 (cf. Fig. 1 ), so that the impregnation process is fully automatic. It also proves to be advantageous to provide further measuring and control circuits with which, for example, monitors the pressure or the pressure change in impregnating 54 and 84 and the respective measured value is used, the speed of the entry and discharge screw in dependence on the discontinued material - And impregnating agent to change so that the greatest possible vacuum seal is guaranteed.
In addition to the exemplary embodiments shown, further embodiments of the impregnation chamber are possible. For example, this may comprise a rotatable drum with adjustable or fixed blades for mixing the material and the impregnating agent. It may also include a chain conveyor or a bucket conveyor (Redler system).

Claims (20)

1. The invention relates to a method for the vacuum impregnation of small-particle material in an impregnating device (16, 16') comprising a dischargeable impregnating chamber (54, 84), an inlet (64, 64') for introducing the material into the impregnating chamber (54, 84), and an outlet (82, 82') for removing the material from the impregnating device (16, 16').The inventive method comprises the following steps:

   - the material is treated with a substance, in order to produce a treated material having improved sealing behaviour in a stuffing screw compared to the untreated material,

   - the treated material is transported to the inlet (64, 64') by means of a stuffing screw (52),

   - the treated material is introduced into the impregnating chamber (54, 84) through the inlet (64, 64') by means of the stuffing screw (52) in such a way that the treated material seals the inlet (64, 64'), as it is introduced,

   - the material is impregnated in the impregnating chamber (54, 84) at low pressure using an impregnating agent,

   - the impregnated material is transported to the outlet (82, 82'), and

   - the impregnated material is removed from the impregnating device (16, 16') via the outlet (82, 82') in such a way that the material seals the outlet (82, 82'), as it is removed.
2. Impregnation method according to Claim 1, characterized in that the substance the material is treated with in order to produce a treated material having improved sealing behaviour in a stuffing screw compared to the untreated material, is a liquid impregnating agent.
3. Impregnation method according to any of the preceding Claims, characterized in that the treated material is continuously introduced into the impregnating chamber (54, 84) through the inlet (64, 64') and/or that it is continuously removed from the impregnating device (16, 16') via the outlet (82, 82').
4. Impregnation method according to any of the preceding Claims, characterized in that the material is compressed, as it is transported to the outlet (82, 82').
5. Impregnation method according to Claim 4, characterized in that the material is compressed as it is transported to the outlet (82, 82') and that excess impregnating agent is absorbed.
6. Impregnation method according to any of the preceding Claims, characterized in that the material is loosened after the introduction and/or the removal.
7. Impregnation method according to any of the preceding Claims, characterized in that the quantity of the material transported to the inlet (64, 64') and to the outlet (82, 82') is controlled, in order to influence the sealing behaviour of the material.
8. Impregnation method according to any of the preceding Claims, characterized in that additional impregnating agent is introduced into the impregnating chamber (54, 84) whilst the material is being impregnated.
9. Impregnation method according to any of Claims 2 through 8, characterized in that the quantity of the impregnating agent additionally used before the material is introduced into and/or as the material which is impregnated is controlled, depending on the quantity of the untreated material transported to the inlet (64, 64'), in order to influence the sealing behaviour of the material and/or its impregnation.
10. Impregnation method according to any of the preceding Claims, characterized in that the impregnating chamber (54, 84) is permanently discharged.
11. A device for the vacuum impregnation of small-particle material comprising a dischargeable impregnating chamber (54, 84), an inlet (64, 64') for introducing the material into the impregnating chamber (54, 84), and an outlet (82, 82') for removing the material from the impregnating device (16, 16'), a stuffing screw (52, 52') for transporting the material to the inlet (64, 64'), a device (62, 62') allocated to or upstream the stuffing screw for treating the small-particle material with a substance in order to produce a treated material having an improved sealing behaviour in the stuffing screw (52, 52') compared to the untreated material, means for transporting impregnated material to the outlet (82, 82') and a device (40, 40) for discharging the impregnating chamber (54, 84).
12. A device according to Claim 11, wherein the stuffing screw (52, 52') and the means for transporting the impregnated material to the outlet (82, 82') are designed in such a way that the material seals the inlet (64, 64'), as it is introduced into the impregnating chamber (54, 84) and seals the outlet (82, 82'), as it is removed from the impregnating device (16, 16') at least, in general, in a pressure sealed way.
13. A device according to Claim 12, characterized in that the means for transporting the impregnated material to the outlet (82, 82') are designed in such a way that the material is compressed.
14. A device according to Claim 13, characterized in that the means for transporting the impregnated material to the outlet (82, 82') include a stuffing screw (56).
15. A device according to any of the Claims 11 through 14, characterized in that the device features a control unit (60, 60', 80, 80') for controlling the speed of one or several of the stuffing screws (52, 52', 56, 56') available.
16. A device according to any of the Claims 11 through 15, characterized in that the device (62, 62') allocated to or upstream the stuffing screw for treating the small-particle material is installed for the purpose of adding a liquid impregnating agent and/or a liquid agent, increasing the sealing behaviour of the small-particle material, to the material.
17. A device according to any of the Claims 14 through 16, characterized in that the device features an appliance (46, 46') for the collection and recirculation of the excess impregnating agent in the area of the stuffing screw (56, 56') for transporting the material to the outlet (discharge screw).
18. A device according to any of the Claims 14 through 17, characterized in that the device of the inlet screw (52, 52') and/or of the outlet screw (56, 56') features downstream means (90) for loosening the material after its introduction and/or its removal.
19. A device according to any of the Claims 11 through 18, characterized in that the device features means (62, 62', 72) for the adding of impregnating agent to the impregnating chamber (54, 84).
20. A device according to Claim 19, characterized in that the device features a control unit (28, 34, 36) to control the adding of impregnating agent, depending, in particular, on the speed of the stuffing screws (52, 52', 56, 56').

Images