SK852002A3 - Method and device for extruding small vegetal parts - Google Patents

Abstract

The present invention relates to a method for extruding small vegetal parts, mainly wood parts mixed with binders. During the extrusion (1), the small parts are compressed by a piston (4) from a filling area (3) and through a forming vessel and through a heated curing canal (5). In order to substantially reduce the length of the curing canal (5) as well as the curing time, steam is applied from the outside onto the already compressed and cured rod at the outer area thereof, the surrounding of said rod being adequately sealed. The steam flows through the heated outer layer of the rod and entails a brisk temperature rise inside said rod due to the condensation within the latter. The rapid curing of the binder makes it possible to substantially reduce the length of the curing canal (5) as well as the curing time.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for extrusion with binders of mixed small plant particles, in particular wood, in which a mixture of particles from the filling space is pushed through the extruder piston and heating curing channel by steam extrusion. .

BACKGROUND OF THE INVENTION

In extrusion, the basic aim is to achieve faster solidification of the extrusion while reducing the length of the devices. It is known from EP 0 376 175 to provide a so-called reactor between the extruder and the curing channel which firmly retains the compressed extrudate and by which water, steam or a supplementary binder in the form of a liquid or vapor can spread to the extrudate surface.

The sole aim is to improve the surface of the extrusion. However, this known method is based on the fact that the compressed chips and particles can have only substantially less moisture than usual in order to collect water or water vapor directly.

In this known manner, however, neither the complete overheating of the extrusion nor the shortening of the setting time is taken into account.

DE 20 16 771 discloses the production of particle board in the region of a heated hardening channel by injecting superheated steam onto the overpressure and thereby into the pressurized material so that the resulting moisture is then removed again from the overpressure by blowing compressed air. In this way, on the one hand, the escape of steam along the surface of the blanket is not prevented and, on the other hand, it is not apparent that the blank is cured by steam condensation.

To accelerate the curing process, EP 0 811 471 discloses the introduction of superheated steam into the interior of the press. This inner space is formed by a perforated, rigid tube from the inside and peripheral press strips or press plate strips from the outside, between which the wood chips are pressed against the tube during extrusion. The action of the steam is therefore effected on the still non-solidified chips and is obviously intended to replace the otherwise conventional hardening duct externally heated.

SUMMARY OF THE INVENTION

The object of the present invention is to enable the steam to be superheated with a particularly rapid steam supply and thus to significantly increase the production speed of the extruder.

This object is achieved according to the invention in that the steam in the area of the curing channel spreads to a compressed external pressure already present in the curing area, where the surface of the positive pressure jacket on both sides of the steam supply is sealed against steam leakage under pressure and curing of the overpressure is carried out by condensation of steam in the overpressure.

For the professional world, it seemed misleading to direct a fully pressurized steam overpressure to the overheating of the overpressure because it was believed that the pressurized material could prevent the ingress and penetration of steam. Therefore, in the prior art, the vapor generally spreads only to a pre-compressed but not extruded yet cured.

It is therefore very surprising that the curing time of the extrudate has been substantially reduced by the method according to the invention. It is important here to protect the vapor streams directed against the surface of the casing from escaping along the surface of the casing and to achieve a targeted, complete penetration of the steam into the overpressure.

For this purpose, the invention provides various possibilities of sealing between the surface of the overpressure shell and the jaws which engage the overpressure and through which steam is introduced.

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For example, the extrudate can be radially compressed by the jaws, and by such a change in the shape of the extrudate, a natural barrier to unwanted steam leakage is created. This measure assumes that radial compression of the overpressure takes place when the overpressure is in the idle state when the plunger of the extruder is retracted. Furthermore, it must be ensured that the extrudate in the final cured state retains a uniform surface of the casing despite the pressing according to the invention.

A further possibility of sealing according to the invention is given by the provision of special sealing elements in the jaw surfaces directed against the surface of the overpressure sheath, by means of which steam is propagated. The location of these sealing elements is located in the direction of the overpressure at least on both sides of the steam supply points, which does not preclude the individual steam supply points also being sealed around.

Other methods of sealing are not in any way excluded by the invention.

The invention discloses the possibility to cover the steam supply according to the invention. of the invention, e.g. up to more than 90% of the heat input required to cure the extrusion. The steam leads to a faster reaction rate and thus a substantial increase in the extruder performance.

The method according to the invention also substantially improves the surface quality of the extrusion as well as the strength of the extrusion.

The extruder produced according to the invention has only less than half the otherwise required heating stages compared to known extruders.

The dependent claims show embodiments and variants of the invention, the function of which is apparent from the figures and the description. Importantly, the pressing of the extrudate is preferably carried out when the extruding feeder is stationary. The steam supply is also preferably carried out during the idle state of the extrusion.

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In the connection to the pressing station according to the invention, there is a brake unit for adjusting the friction of the overpressure and the density of the raw material of the overpressure, which also serves as a hardening area. This braking unit prevents uncontrolled stretching of the overpressure in the longitudinal direction that occurs when the centric pressing jaws are opened and which can lead to cracks in the overpressure.

The length of the pressing jaws of the pressing station covers one or more strokes of the press and corresponds, for example, to the double stroke of the extruder piston. This achieves that a plurality of extrusion contact points are covered, ensuring that the entire volume of the extrusion is evenly overheated.

The invention further provides a control that allows the pressing jaws of the pressing station to be opened when the overpressure moves the piston of the extruder forward.

BRIEF DESCRIPTION OF THE DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in more detail with reference to the drawings, in which: FIG. 1 schematically shows a side view of a horizontal piston extruder with various stations, FIG. 2 is a cross-sectional view of the press station in an enlarged view along the line II-

II in FIG. 1 and FIG. 3 shows a cross-section through a variant of the embodiment according to FIG. Second

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DETAILED DESCRIPTION OF THE INVENTION

In the example of figure 1, a diagram of a normal extruder 1 is shown. The feed shaft 2 leads with the binder a mixed mixture of particles, in particular small plant particles, into the filling and pressing space 3, which can be closed upwards by means of a closing sliding part. In the axis of the extruder, the movable piston 4 of the extruder presses the mixture of particles introduced into the filling and pressing space 3 and pushes it into the curing channel 5, which can be heated in a conventional manner.

In the region of this first section of the curing channel 5, a glueing reaction begins on the outer surface of the pressed extrusion, while the inner region of the extrusion is still in the pressed but not yet reactive state.

In the region of the curing channel 5 there is a pressing station 6. which has the task of shaping the section of the extrusion located in this area radially on the axis of the extruder. For this purpose, a stable frame 10 is required which retains the reaction force of the pressurizing arrangements.

The purpose of this creep is to creep and seal the overpressure against the steam outlet on the press jaws in the radial direction, although it is already axially compressed. In this case, a deformation path in the range from 0.5 mm to 2 mm per pressing jaw is preferably achieved.

The radial compression of the extrusion and the associated shape change acts as a vapor barrier, which concentrates aids in the radial penetration of the steam into the extrusion, but prevents lateral escape of steam along the surface of the extrusion casing.

The subsequent deformation also has the advantage that the surface quality of the extrudate is improved and its mechanical strength is increased.

At the same time, the invention proposes that intensive steam supply to the overpressure occurs during or after subsequent deformation. In the example of Figure 1, the steam supply station is symbolically represented by the reference numeral 7, by means of which steam, in particular saturated steam or hot gas, is depicted.

The 31863 / T feeds through channels 14 that receive the section of the overpressure located in the pressing station 6.

In the example of Figure 2, the solid channel walls 12 and the movable channel walls 13 generally show the overpressure 16 in enlarged cross-section. In the channel walls 12, 13 there are steam supply channels 14 from which the radial injection channels 15 extend towards the overpressure. 16. Reference numerals 11 denote press plungers that slide the movable channel walls 13 against the fixed channel walls 12.

In a variant of this example, all the pressing jaws 12, 13 can also be formed movably.

Subsequently, the overprinting of the overpressure 16 takes place in the pressing station 6, while the overpressure 16 is preferably in the rest position. Once the radial pressing pressure is equalized by the press plunger 11, the steam valves are opened, thereby vapor flows into the portion of the overpressure 16 between the channel walls 12, 13. The steam condenses in the clamping matrix and causes a sudden rise in temperature, which quickly sets the curing reaction in the core of the overpressure.

Before the next stroke of the piston of the extruder 4, the pressing jaws 12, 13 are opened so that the overpressure 16 can be moved by the pressing station 6 without substantial friction.

The invention proposes a control by which the movable walls of the channel alternately open and compress. In fact, if the press 16 in the press station 6 is subjected to compression, the movable press jaws are pressed in the region of the curing channel 5. However, as soon as the piston 4 of the press presses forward in the pressing direction, the press jaws 12, 13 open. on the movable walls of the channel in the hardening channel is reduced to adjust the density of the raw material of the extrudate produced.

Preferably, the pressing stations 6 and the steam supply stations 7 are combined in one building unit 8, as also shown in Figure 2.

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A braking unit 9 is provided in connection with the pressing station 6. This is heated and has adjustable channel walls, by means of which the friction of the channel walls on the overpressure 16 can be adjusted. Thus, the brake unit 9 acts as a hardening area.

The length of the channel walls 12, 13 according to FIG. 2 preferably corresponds to the double stroke of the extruder piston 4, whereby a plurality of contact points of the pressed sections of the extrusion are covered.

It is an object of the invention to substantially increase the performance of known extruders and their curing devices. The steam supplied at the steam supply station 7 transports most of the thermal energy needed to cure overall, in particular in the range up to 90%.

The object of the invention is therefore a feasible new. a method in which the extrusion, which is only peripherally partially cured, is pressurized in the extrusion direction, under pressure, by spraying with steam, which is supplied in such a quantity that a sudden increase in temperature occurs over the entire cross-section of the extrusion. At the same time, the overpressure in the region of the steam supply is creeping and thus experiences a radial constriction of about 0.5 mm to 2 mm.

The advantage of this measure lies o.i. in that a higher reaction rate and thus a higher extruder performance is allowed, while the surface quality of the extrusion is improved and the strength of the extrusion increases. This also implies a substantial reduction in the design length of the extruder with curing channel, since only less than half of the heating stages measured in the prior art are required.

In the example of Figure 3, an alternative embodiment of the invention is shown in which radial deformation of a peripherally already cured extrusion 16 as a means for sealing the extrusion housing surface 17 against the inverted inner surfaces 18 of the jaws 12, 13 is omitted. 13 are provided with sealing elements which are spaced from the injection channels 15.

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As shown in Figure 3 in cross-section, the sealing elements 19 extend from both sides of the injection ducts 15 parallel to the extrusion direction and thus prevent steam escape transversely to the axis of the extruder. However, the sealing elements may also be approximately circular on the end faces of the jaws 12, 13 in order to prevent the escape of vapor in the extrusion direction or vice versa.

Suitable sealing elements 19 are strips of plastic, rubber, foam material or those which are rigidly connected to the jaws 12, 13 and can optionally be anchored in suitable recesses 20 of the inner surfaces 18 of the jaws.

Essentially, all the state of the art dealing with the sealing of adjacent surfaces is applicable to this exemplary embodiment. Therefore, some shaping options for the sealing elements 19 are shown symbolically in Figure 3, it being noted that it is up to the skilled person to choose which of the molds to be used.

Claims (6)

PATENT CLAIMS 1. Method of extrusion with binders of mixed small plant particles, in particular wood, in which the mixture of particles from the filling space (3) is pushed by the extruder piston (4) and the heated curing channel (5) by steam extrusion, wherein the steam extends in the region of the curing channel (5) to the compressed external pressure already existing in the curing region and already in the external region, characterized in that the surface of the positive pressure jacket (17) is sealed from both sides of the steam supply under pressure steam leakage and curing of the overpressure is accomplished by condensation of the steam in the overpressure, leading to a sudden rise in temperature. Method according to claim 1, characterized in that the sealing of the vapor escaping surface (17) is effected by radially compressing the extrusion section in the area of the steam supply. Method according to claim 1, characterized in that the sealing of the overpressure casing surface (17) against the escape of steam is effected by sealing elements which in the direction of the overpressure are pressed against both sides of the steam supply points (7) against the overpressure casing surface. The method according to claim 1 or any other, characterized in that the steam supply is carried out in tact during the momentary state of the extrusion during the extrusion. 31863nsll / T Device for carrying out the method according to claims 1, 2 or 3, characterized in that in the region of the heated curing channel (5) of the extruder (1) there is a pressing device with an integrated steam supply arrangement acting radially around the already cured extrudate. 3. The method of claim 1, wherein the radial change in the shape of the overpressure is a vapor-tight sealing means directed towards the overpressure housing. Device for carrying out the method according to claims 1, 2 and 4, characterized in that in the region of the heated curing channel (5) of the extruder (1) there is a steam supply arrangement acting radially around the peripherally already cured extrusion within a multi-part in the shape of the surrounding extrusion so that sealing elements (19) are applied in the direction of the extrusion on both sides next to the steam supply points, which act on the extrusion housing and make it more difficult or prevent vapor escape along the extrusion housing.