SK4912003A3 - Extruder for vegetal particles mixed with a binding agent - Google Patents

Abstract

The invention seeks to significantly reduce investment in expensive drying systems for vegetal particles, especially wood, during pre- preparation of the extruder when such vegetal particles exhibiting a high degree of moisture, for example, 8-14 % atro are intended to be pressed. In order to solve the above-mentioned problem, a conventional extruder is used, wherein the mixture of particles is pushed through a receptacle (4) and a hardening channel (6) by means of an extruder piston. The invention is characterized in that the walls (8) of the first section of the hardening channel (6) downstream from the receptacle (4) are arranged in such a way that they can yield (8,9) and thereby reduce friction as the extruder piston (3) advances. This prevents the strand of extruded material from becoming blocked in the pre-heating section of the hardening channel.

Description

PUSH-PRESS FOR VEGETABLE PARTS MIXED WITH BINDERS

Technical field

The invention relates to an extruder for plant particles mixed with binders, in particular for the production of pallet blocks from wood waste, with the features mentioned in the preamble of claim 1.

BACKGROUND OF THE INVENTION

These are known from DE-A-32 15 693, in which it is disclosed to support at least one wall of a curing channel which is capable of buckling against the spring action in order to prevent jamming of the pressed particles. However, the known embodiment does not have an overpressure calibration container and does not include the theory of how wet chips can be extruded without the risk of jamming.

WO 99/48659 describes a typical construction of a conventional extruder according to which a fixed part of the curing channel, which is referred to in the technical terminology as a preheating passage, is first fed to the pressing space. This fixed part should make it more difficult or prevent the axial deflection of the still unheated extrusion during the return stroke of the extruder piston. In principle, however, the overpressure is calibrated in this fixed part.

As far as the extrusion of wood particles is concerned, in practice, dried wood material from 2% to 3% and at least the residual moisture has been used in practice. In order to achieve this state of drying, substantial investments are needed in the basic means, which, for reasons of economy, assume that a correspondingly large consumption of dried chip material for extrusion is available.

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However, the residual moisture is raised considerably by the addition of a water-containing adhesive, resulting in a final product with about 7% to 9% moisture.

If wood particles are to be made of pallet blocks, this low wood moisture is not required. In conjunction with pallets, the wood has a moisture content of about 18% after production, while naturally the pallet stack, which has less moisture, retains water. In later use of pallets, moisture contents are set between 14% and 30%, depending on the conditions under which the pallets are stored.

Therefore, it is questionable to press the pallet blocks with very low wood moisture, which is actually not necessary at all, since the moisture content is significantly higher in the pallet assembly and later use.

Thus, it would be possible to compress wood particles of higher humidity to produce pallet blocks, which, however, could not be successfully accomplished with known devices.

In fact, the higher humidity chips cause a rapid increase in the feed resistance in the extrusion press, which leads to a failure of the press during the low strokes of the extruder piston. The blasting material exhibits different elastoplastic behavior with higher humidity. While the dry chip is virtually incapable of flow (the so-called non-rising mixture) and thus only transfers a slight fraction of the pressure of the main piston to the channel wall, the material reacts increasingly plastic with increasing moisture. With the same feed resistance, the material is compacted higher and the pressure on the side walls of the container increases. This means that more stroke force is required in the next stroke to overcome the higher friction against the walls and this overpressure is more compacted than the previous, which again increases the wall pressure and friction. This process is intensified and leads to jamming of the press during few strokes.

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SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide an extruder with which plant particles, in particular wood waste, can be extruded with higher moisture contents, so that investment in expensive chip-drying equipment becomes unnecessary. The aim is to process wood material with about 8% to 14% wood moisture. This wood moisture is common in the production of glued wood products and wood waste from gluing plants is available in sufficient quantities.

The invention solves this problem by the features set forth in the characterizing part of claim 1. By this embodiment of the invention the blocking of the overpressure is prevented and the calibration of the overpressure is achieved.

It is known from DE-A-25 35 989 and from DE-A-32 05 866 to support the walls of the hardening channel on the motors of the lifting mechanism. In the case of DE-A-25 35 989, this is carried out in order to vary the friction force acting on the extrusion without changing the path of the hardening wall. In the case of DE A 32 05 866, the motors of the lifting mechanism cause a change in the path of the movable walls of the curing channel so that different dimensions of the product can be produced on the same device.

In either of these cases, the overprint for calibration purposes does not compress a radially varying shape.

However, this does not take into account the extrusion of wood particles with higher humidity, nor is it possible to calibrate the extrusion properly.

In contrast, with the embodiment according to the invention, the pressing of the wood particles at the same time achieves higher humidity without the risk of blocking the extruder as well as proper calibration of the extrusion.

The movable side walls of the radial press station are suspended on hydraulic cylinders, which can again be connected to the pressure reservoir. In the inlet stroke, the pressure is reduced to a certain level and maintained by pressure

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32113upr / T t cartridges. In this way, the walls of the radial pressing station rest with constant force on the extrudate produced. The higher pressure on the wall of the product is reduced to a predetermined level by deflecting the wall. The pressure reservoir acts as a pneumatic spring and the return force remains approximately the same. When the main piston is lifted back, the overpressure is in a quiet state. Now, the container is retracted and the hydraulic pressure is increased to such an extent that the portion of the extrusion located in the radial pressing station is pressed to a predetermined dimension that is smaller than the nominal dimension. Before the next stroke, the pressure level decreases again and the tank is connected.

It now cushions the material overpressure to the nominal size. In this way, the elastic tendency of the extrusion material is absorbed. The pressing force of the side walls can be measured such that the elastic cushioning of the extrudate material leads to the desired friction and there is no dimensional change in the following movable heating corridors.

In another aspect of the invention, there is provided a station for supplying saturated steam to the outer surface of the molded extrusion housing in which a sealing means, in particular a pressing jaw, is provided to prevent steam escape along the surface of the extrusion. Such a workstation was proposed by earlier PCT / EP00 / 06872. However, its use is not intended for pressing chips of higher humidity. By the present invention, on the other hand, the introduction of saturated steam onto an overpressure, which is also advantageously carried out in such a process, causes intense overheating of the overpressure, with the result that the binder solidification takes place by impact and curing of the overpressure proceeds faster than hitherto.

In one variation of the invention, it is provided that the saturated steam feed station is integrated into a radial press station. In both stations, for the same reason, the same functional elements are present which exert a pressure radially on the outside of the still untreated or only the edge-cured extrusion and thus cause slight formation. It is therefore expedient to use the device necessary for controlling the friction ratios according to the invention also for supplying steam. Said radial pressing station is suitable

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However, the heat and surface pressure required to produce the final outer contour is sufficient to ensure that the press jaws are sealed against leakage of process steam.

The extruder constructed in this way is particularly short and requires only a shortened length of the heating passage for the combined radial pressing / steam supply station, which keeps the material clamped until the adhesive reaction is so complete that the inherent stresses of the compressed product material no longer shape changes. It is common to all the described embodiments that, in the area of energy supply and temperature increase, the side walls either ventilate in such areas or have sufficient interspaces to prevent the nominal vapor pressure from being generated in the structure. In conjunction with a heating corridor, which is shortened compared to conventional extruders, the friction ratios of the walls are exactly controllable.

Alternatively, however, the saturated steam feed station may also be provided in the region of the heating passage of the curing channel, in which the temperature in the peripheral region of the extrusion is increased in a conventional manner.

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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 is a vertical cross-sectional view of an extruder with flexible walls of a first section of a curing channel downstream of the container and a subsequent radial press station; FIG. 2 shows a vertical section through the variant according to FIG. 1 with a radial pressing station integrated in the first section, FIG. 3 is a vertical cross-sectional view of the extruder of FIG. 2 with an additional saturated steam feed station; and FIG. 4 is a vertical sectional view of the extruder of FIG. 2 with an integrated saturated steam feed station in a radial press station.

DETAILED DESCRIPTION OF THE INVENTION

In the example of figure 1 there is shown schematically an extruder (1) in which the plunger (3) of the extruder is movable in a horizontal direction back and forth. This extruder piston (3) forms an extrusion (2) which is compressed by the container (4) and the curing channel (6). The container (4) consists of solid walls with an opening angle (7) extending in the direction of extrusion. This opening angle (7) may be greater than that of conventional devices when it comes to extruding overpressures from plant particles, especially wood, with high humidity.

A first section (5) of the curing channel (6) is provided in connection with the container (4), which generally consists of solid walls in conventional extrusion presses and is referred to as a preheating corridor. When the plant particles are pressed

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32113upr7T t higher humidity, such a solid preheating corridor would lead to blocking of the press. Therefore, the invention proposes to make the walls (8) of this first section (5) of the curing channel (6) capable of buckling, which can be carried out, for example, by elastically supported walls (8). A radial pressing station (5 ') is provided in connection with the section (5) with the walls capable of yawing, the walls of which are pushed against an overpressure by means of the lift mechanism motors (11) during the return stroke of the extruder piston to calibrate the overpressure. In the embodiment of figure 2, the radial pressing station (5 ') is integrated in the first section of the curing channel (6).

In this case, a radial pressing station (5 ') is provided with yaw-able walls (8') that replace the preheating passage available with known devices.

This lateral movement of the walls (8 ') does not yet cause a clear contour of the outer surfaces of the extrusion (2) to be formed. For this reason, the walls (8 ') are pushable by the motors (11) of the lift mechanism onto the overpressure during the return stroke of the extruder piston (3). The walls (8 ') of the radial pressing station (5') thus exert pressure on the area of the overpressure (2) located between the walls (8 '). This pressure adjustment of the side walls (8 ') takes place in such during the return stroke of the extruder piston (3). In this way, the outer contour of the extrusion is precisely determined.

In connection with the radial pressing station (5 '), a curing channel (6) is provided, which is conventionally equipped with heating pipes (15) to cause the extrusion (2) to cure and dry. The formation of such a curing channel is known and therefore does not need closer illustration.

The example of figure 3 shows how the overprint (2) can overheat by feeding saturated steam and can therefore solidify more quickly. Starting from the embodiment according to figure 2, a work station (10) for supplying saturated steam is provided in connection with a plurality of heating passages of the curing channel (6) by means of steam supply bores (14). In order to prevent saturated steam from escaping along the surface of the extrusion (2), it has a working

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32113upr / T t station (10) press jaws (13) that are pressed against the overpressure (2) by the motors (11) of the lift mechanism. A braking and cooling zone (16) is provided in connection with the steam supply station to prevent uncontrolled expansion of the still uncured extrudate.

However, as shown in Figure 4, the functions of the radial pressing station (5 ') and the steam supply station (10) can also be combined. This embodiment complements the radial pressing station (5 ') with the steam dispensing and supply units. The pressing of the pressing jaws (13) leads to the contracting of the extrusion in order to produce the final outer dimensions of the extrusion (2). It is essential that this molding is used to prevent the supplied steam from escaping along the extrusion (2).

Claims (5)

PATENT CLAIMS 1. An extruder for plant particles mixed with a binder, in particular for the manufacture of pallet blocks of wood particles, in which the extrusion (2) of the extruder piston (3) is moved in such a container (4) and a curing channel (6), 8) are provided in the first section (5) during displacement of the extruder piston (3) so that they are capable of skewing (8, 9), thereby reducing friction, characterized in that for extruding higher moisture particles, for example 8% to 14 The% atro is in this first section (5) or in the following section (5 ') a radial pressing station equipped with stroke actuators (11) movable walls controllable in such, in order to calibrate the overpressure. Extrusion press according to claim 1, characterized in that the pressing pressure of the walls (8 ') in the radial pressing station (5') is measured such that the final dimension of the extrusion (2) is determined by calibration. The extruder according to claim 1 or 2, characterized in that a working station (10) is provided in which the sealing means, in particular the pressing jaws (13), are provided for supplying saturated steam to the outer shell surface of the extruded press (2). to prevent steam escape along the surface of the extrusion. The extruder according to claim 3, characterized in that the saturated steam feed station (10) is integrated into the radial press station (5 '). PP 0491-2003 32113upr / T I The extruder according to claim 3, characterized in that the saturated steam supply station (10) is provided in the region of the heating passages of the cured channel (6), in which the temperature increase in the peripheral region of the extrusion (2) is carried out in a conventional manner.