EP0376175B1 - Method and device for controlling the compression and/or for producing a fringe with a higher density with a modified surface while extruding particles, particularly vegetable particles with binding agents - Google Patents

Abstract

The invention relates to a method for controlling the compression and/or for producing a higher-density fringe with a modified surface while extruding particles, particularly wood particles with binding agents, in which the mixture is compressed in the pressing space of an extrusion press. The invention is distinguished in that the compressed mixture exhibiting a low moisture content is transported in a reactor which adjoins the extrusion press and in which the fringe of the extrudate is brought to a higher moisture content by water, water vapour or another liquid or vaporous binding agent, as a result of which - the particles of the fringe lose their inner solidity and are laid tightly against one another with less force, - the particles of the fringe change their position in the extrudate so that the pressure on the inner walls of the reactor is reduced, - a higher-density fringe with a smooth surface is formed in the extrudate and - the compression and specific gravity can be controlled and accurately determined via the amount, temperature and depth of penetration of the reactant into the fringe. <IMAGE>

Description

The invention relates to a method and a device for controlling the compaction and / or for producing a higher-density edge zone with an improved surface when extruding small parts, in particular small plant parts with binders.
In such devices, the small parts are compressed to the desired density - usually 0.5 to 0.8 kg / dm³ - by the force of a plunger in an extrusion press. The counterforce required for compression is generated by the friction between the strand produced with the previous press strokes and the walls of a hardening duct adjoining the press chamber. To determine and adjust or change the density of the strand, an active or passive system for controlling the friction is used.

In a passive system, the static friction between the extruded part and a moving mandrel is used in extrusion molding, and one or more walls in the channel in extrusion molding.
As soon as the ram has compacted the strand to the desired extent, the mandrel or one or more walls delimiting the strand are allowed to run along to the front end position of the ram. The mandrel and / or the walls are then moved into their starting position, as is the press ram. This passive system requires its own work step to pull back said mandrel or the walls. The other walls of the curing channel can be rigid or adjustable.
One speaks of an active system when the walls of the hardening duct adjoining the extrusion press are pressed against the strand with a force that can be selected and changed during the press stroke. The compression should be regulated by the magnitude of this force, which is usually generated by clamping elements during the press stroke.
The small parts, in particular small plant parts, do not behave like a hydraulic fluid, which would pass the pressure of the press ram evenly on all sides, but only part of this force is directed against the walls of the press chamber.
The force directed against the hardening channel walls, which becomes very large immediately after the press, forces the first part of this channel to be rigid.
If the walls of this first curing duct part are placed parallel to one another, this can only be built very short, since otherwise the frictional forces would exceed the force of the press ram and the press tends to jam.
It is therefore taught to widen the first rigid part of the channel in a wedge shape in order to reduce the frictional forces to such an extent that the contact force the walls of the movable part of the curing channel, the compression can be controlled.
However, the angle of the wedge-shaped extension must be kept very small and must be adapted precisely to the type, size and in particular the moisture of the small parts.
Under no circumstances should it exceed the compression angle of the press, as the material will otherwise slide over.
If the type, size or, in particular, the moisture of the small parts changes only slightly, the compression characteristic of the small parts changes immediately - and this disproportionately.
Since the drive of the controllable friction is on the one hand relatively low due to the system, and on the other hand the angle of the extension cannot be changed, the extrusion press can only be controlled with limited accuracy to a limited extent.
Another disadvantage is the wear in the press chamber and in the first rigid part of the curing channel, which also changes the geometry of these parts.
These disadvantageous features make it possible to manufacture components of this type which are not very demanding, for example pallet blocks.
Furthermore, the constant desire of the users of these extruded products for a smooth surface and a higher density edge zone, which is, for example, water-repellent, cannot be met. Since this would require the strand to lie better against the walls of the first rigid part of the curing channel, which cannot be achieved by the described frictional forces.

DE-A-20 16 771 describes a method and a device for the extrusion of agglomerated plates and in particular chipboard, in which the heating and / or drying of the plates by means of blowing and / or discharging and / or suction, in particular steam or air he follows. This known method has the disadvantage of relatively short stroke lengths; moreover, the density can only be set to a very limited extent.

DE-A-29 32 405 describes an extrusion press for small vegetable parts mixed with binder, which essentially corresponds to the prior art in conventional bulkhead presses or simple injection molding systems.
The small vegetable parts mixed with a binder are introduced into a filling space from above, compressed with an extrusion piston and then pushed into a curing channel. With this method, too, the stroke and the stroke frequency are limited so that the effectiveness of the system is not great.

The invention is based on the object of specifying a method for controlling the compression and / or for producing a more highly compressed edge zone with an improved surface when extruding small parts, in which adjustment of the compression is possible in a simple manner.

The invention is based on the knowledge that small plant parts, and in particular small wooden parts, do not oppose any appreciable resistance to the compaction that has taken place for a certain period of time after they have been compressed to a desired level.

However, further knowledge is required to solve the task:
The time after which this resistance breaks down can be shortened and precisely determined by temperature and humidity, i.e. by the introduction of hot steam. The force introduced by the ram into the small parts is projected to the outside depending on the moisture of the small parts.
Here, the projected force changes non-linearly to change the moisture.
Smaller drier wood parts, for example those below 10% moisture, are too rigid for extrusion, they project a large part of the compression force introduced into them outwards, transversely to the direction of extrusion.
Moist chips, for example those with more than 15% moisture, are relatively plastic and lie flat against the boundary walls of the press room or the curing channel and also cause too much friction for extrusion.
The known extrusion processes for small plant parts, in particular small wooden parts, can therefore only be carried out if the small parts, for example wood shavings, have a moisture content that corresponds to their size and type, for example 14% Atr. have what must correspond to an exact opening angle of the rigid first part of the curing channel.
The invention takes advantage of the disadvantageous properties of the small parts to solve their task.
Drier small parts, for example of 10% moisture, are used to carry out the method according to the invention.
These are filled in a manner known per se Press space of an extrusion press introduced, compressed therein by the extrusion die and transported in this state into a reactor connected to it.
Its inner profile largely corresponds to that of the extruded profile. The reactor is heated and has suitable inlet openings for water or steam. Its temperature is above the pressure of the boiling point associated with the water of reaction or corresponds to the curing temperature of the curing channel.
Under pressure, steam or water is introduced into the strand at one or more points through the inlet openings of the inner profile of the reactor in the pressing direction.
The amount of steam or water introduced is such that only the outer zone of the strand is brought to a higher density, for example 20%, to a desired density, for example to a depth of 2 mm.
The distance to the first inlet opening lying transverse to the extruded profile should be greater than the length of a press stroke. It is particularly expedient if the introduction of the steam or water into the outer zone of the strand takes place intermittently while the strand is being pressed.
The moisture in the edge zone of the strand is increased particularly uniformly when the water or steam takes place in several planes lying one behind the other across the strand in the reactor. The more inlet openings in the pressing direction that the reactant introduces into the strand, the better and more uniform the result. Conversely, since the total quantity to be supplied is very small, the requirements for quantity and time control are becoming ever greater.
It has proven to be inexpensive and easy to carry out, for example, to arrange 5 entry levels in a row with a strand of about 100 mm ⌀, the distance from the first to the last level being four times the length of the Press stroke of the strand corresponds. This can of course be changed depending on the application.
The distance from the first level of the inlet openings for the reactant in the reactor to the end of the strand depends on the cycle speed of the extruder.
In principle, the distance should be greater than the length of a press stroke. This prevents water vapor from entering the filling and pressing room.

In particular, the planes in the reactor can have a different spacing from one another than the length of the strand part formed with each press stroke.

According to the invention, the mixture of small parts that is too dry according to the method reacts as follows:
The dry small parts are very rigid and project a relatively large part of the force of the ram against the inner walls of the reactor. However, this force is reduced immediately if these rigid small parts can only deflect to the outside by a very small amount. Exactly this alternative is made possible by introducing the reactant into the outer zone. The small parts located in this zone immediately lose their rigidity as a result of the wetting agent, and lie close together without great pressure. You therefore need a smaller space, with which the rigid small parts not wetted by the reagent can yield to the desired extent.
The more or the deeper the reactant penetrates the strand, the lower the friction of the strand in the reactor.
The control for introducing the reactant is possible both very precisely and very quickly and easily via pressure (pressure valves), quantity (pressure flow valves) and time (check valves).
This allows the reactor to be designed to be relatively long, and in particular so long that the binder in the strand, when leaving the reactor, has set by heating it to such an extent that the internal dimensional stability is sufficiently large is. In the adjoining curing channel, the strand is only guided to finally cure.
The cross section of the reactor can now be designed according to the specific requirements.

A particular advantage of the invention lies in the fact that the geometry of the entire extrusion system has to be carried out less precisely, since corresponding compensation options can be achieved by the reaction medium.
The small parts, which lie close together in the outer zone, result in a particularly smooth and, for example, water-repellent outer surface.
The density of the higher-density outer layer can be determined relatively freely by the amount and depth of penetration of the reactant. Since this layer in turn has a greater strength, strands produced according to the invention can be used not only as pressure-resistant spacers, but also as particularly tensile, pressure-resistant and torsion-resistant supports or beams.
Since the reactant reacts immediately, the control of the weights is sensitive and precise.
The uniformity of the compression is significantly better than in the previously known active systems shown.
In contrast to the passive systems described, there is advantageously no need to pull out the mandrels or walls.
However, the advantages of the invention are not yet exhausted.
For particularly highly stressed components, an additional binder in liquid or vapor form can also be fed to the reactor instead of water or steam, which in turn additionally improves the strength of the strand.

Fig. 1

Einen Längsschnitt durch eine Strangpresse.

Fig. 2

Einen Querschnitt durch einen Reaktor auf der Linie I-I gem. Fig. 1.

Fig. 3

Einen Querschnitt durch einen Reaktor.

Fig. 4

Ein Strangprofil.

Of course, water / steam, binder or even only parts of the binder, for example hardener or NH₃ or uric acid, can be introduced through the inlet openings of the reactor at the same time.
The application of the invention is therefore diverse. For the purpose of special results, other teachings on controlling compaction can be advantageously combined with the invention. The introduced steam or water is by no means to be regarded as process steam, through which the binding agent is to be set.
The amounts of steam or water used in the invention are too small for this.
For various extruded profiles, it is conceivable to design the reactor in a length in which the entire curing takes place. In this version, it is no longer necessary to attach a curing channel to the reactor. According to the invention, the reactor can expediently be provided in whole or in part with movable, adjustable side walls.
Details are shown for example and schematically in the drawings:
It shows:

Fig. 1

A longitudinal section through an extrusion press.

Fig. 2

A cross section through a reactor on line II acc. Fig. 1.

Fig. 3

A cross section through a reactor.

Fig. 4

An extruded profile.

Fig. 1 shows a longitudinal section through an extrusion device. 1st

Here, the filling and pressing room 2 with the closing slide 3 and the inlet shaft 4 for the batch 5 from small parts and binders according. the previously unpublished application P 38 44 192 trained.
The end face 6 of the ram 7 has the position at a distance 8 to the end 9 of the filling and pressing space 2 is equal to the length of the compressed strand 10 .
The reactor 11 connects to the filling and pressing chamber 2 . In the exemplary embodiment, its inner profile is cylindrical.
The first of here 6 inlet openings 13 for the reactant, in the exemplary embodiment steam, faces the end 9 of the filling and pressing space 2 and is made at a distance 14 in the reactor 11 . This distance 14 is greater than the length of the compressed strand part, which corresponds to the distance 8 . The length 15 between the first inlet opening 13 and the last inlet opening 16 for the reactant is approximately five times the distance 8 in the example. The fact that the intermediate inlet openings are evenly distributed over the length 15 , but the distances do not correspond to the length 8 , means that the binder is introduced particularly evenly.
In a steam boiler 17 , water vapor is generated as a reactant, which increases the moisture in the outer layer of the strand 18 .
The flow rate of the reaction steam is controlled by the flow control valve 20 . The steam pressure is set by a regulation by the pressure reducing valve 21 and not by the pressure in the steam boiler 17 .
The time of steam entry determines the check valve 22 , which is in the open position according to the position of the ram 7 during the extrusion of the strand 10 , otherwise in the blocked position.

This valve can be switched via limit switches, for example. In order to prevent locally too much steam from getting into the reactor 11 , the check valve can be switched to the open position.
The type of control described above enables a particularly precise and uniform determination both the weight of the strand 18 and the depth of penetration of the steam into the outer zone of the strand 18 .
The strength of the strand 18 can therefore also be determined precisely.
If, for any reason, the type, the composition, the size or the moisture of the batch 5 filled into the extrusion press changes, the reaction of the strand 18 in the reactor 11 can be adapted in this way by simply changing the setting of the valves 20 , 21 or 22 that a strand 18 with the desired properties is nevertheless produced. In any case, the invention results in a particularly good surface and, depending on the setting of the valves 20 , 21 , 22, an outer layer that is more or less densified as required.

Since the reactor 11 , in the exemplary embodiment is heated by heating sleeves 23 , the reactant introduced evaporates without being further disadvantageous. Due to the small amount of steam introduced, there is no fear of steam tensions in the binder or even steam cracks in the strand 18 .
As described, water or additional liquid or vaporous binder can of course also be introduced into the strand 18 via the reactor 11 instead of the steam.
It goes without saying that steam, water and binding agents can also be mixed together.
Since the reactor 11 can be made very long, the curing channel adjoining it will be kept correspondingly short or even completely eliminated.
The walls 25 , 26 of the curing channel 24 need, since the strand 18 has already partially set due to the length of the reactor 11 and has sufficient internal strength and dimensional stability, to be leaned against the strand only in such a way that the heat can escape from them , but not so far from the strand that additional liquid or vaporous binder up to for the final curing of the strand 18 can be entered in this without major gap losses.
As described, it is of course possible to use the invention, ie the reactor, in combination with other systems for controlling the weight of the strands. The teaching DE - 29 32 405 is conceivable as a combination.

Fig. 2 shows a cross section through a reactor on the line II acc. Fig. 1.
The exemplary embodiment uses a reactor cross section for a circular strand.
An annular steam inlet opening 28 is machined into the reactor jacket 27 . The reactant passes from the hose 29 through the bore 30 into the steam inlet opening 28 . In order to prevent condensation from accumulating, the bore 30 is provided on the underside of the steam inlet opening 28 . As a result, condensed water can possibly flow back through the hose 29 .
A heating jacket 31 is placed around the reactor jacket. This can be designed, for example, as an electric resistance heater.
However, all other heating systems are also conceivable and possible.
Fig. 3 also shows a cross section through a reactor, here for a rectangular strand.
In this exemplary embodiment, the invention uses a circumferential channel 37 from which the reactant, here water, which is supplied from the motor pump 33 via the line 34 and evaporates due to the temperature in the reactor and via the inlet nozzles 36 located on the circumference of the inner reactor surface 35 the strand penetrates under positive pressure. According to the amount of feed Water and pressure of the water vapor forming in the reactant is the penetration depth of the water vapor until it condenses again into water in the strand.
The valves 20 , 21 and 22 already described can also be used in this system.
They are installed in line 34 .

Fig. 4 finally shows a square extruded profile with chamfered corners.
Here the reactant has penetrated into the strand according to the depth dimension 38 . The strand has a higher density outer zone 39 with a particularly smooth and flat surface 40 .
This smooth surface 40 protects the strand against damage. At the same time, the more highly compressed edge zone can be subjected to a particularly high tensile and compressive load, while the lowly compressed inner strand zone 41 , in which the molded parts have largely retained their shape - that is to say not lie very close together - gives the strand a certain elasticity and, for example, good nail connections enables.
In this invention, the depth 39 and the strength of the strand can be determined largely freely and in a simple manner to suit the application.

Claims (8)

1. Method of controlling the compression and/or of creating a subsurface zone having a higher density and an improved surface in the bar extrusion of particles, in particular vegetable particles, with bonding agents, wherein the mixture is compressed in the compressing compartment (2) of a bar extruder (1), characterized in that the compressed mixture (5), which presents a low moisture, is transferred in a reactor (11) joining said bar extruder (1), in which reactor the moisture in said subsurface zone (12) of the strand (10) is increased by means of water, steam or an additional liquid or vaporous bonding agent in a way that

   - the particles in said subsurface zone (12) use their interior strength and adhere tightly to each other at a low force,

   - the particles in said subsurface zone (12) change their position within said strand (10) so as to reduce the pressure acting upon the inner walls of said reactor (11),

   - a more strongly compressed subsurface zone (12) having a smooth surface is formed in said strand (10, 18),

   - the compression and the specific weight may be controlled and precisely determined via the quantity, the temperature and the depth of penetration of the reagent into said subsurface zone (12).
2. Method according to Claim 1,
   characterized in that an agent influencing the friction, such as wax, is used in a liquid or vaporous form, either alone or in a mixture with water or steam.
3. Device for the bar extrusion of particles, in particular vegetable particles, with bonding agents, wherein the mixture is compressed in a compressing compartment (2) by means of a ram (7) and the mixture so compressed is expelled into a setting channel (11), characterized in that for carrying out the method according to Claim 1 a reactor (11) is provided which joins said compressing compartment and having an inside contour which largely corresponds to the section of the strand, and having inside surfaces wherein inlet openings (13) are provided for the supply of water, steam or an additional liquid or vaporous bonding agent.
4. Device for carrying through the method according to Claim 3, characterized in that the inside surface of said reactor (11) extend in parallel to each other in the direction of compression.
5. Device according to Claim 3 or 4,
   characterized in that a plurality of spaced openings (13) is provided along the direction of compression.
6. Device according to Claim 5,
   characterized in that the spacing of said openings (13) is different from the length (8) of the strand segment (10) formed by each compression cycle.
7. Device according to the Claims 3 to 6,
   characterized in that said reactor (11) is heated by means of heating sleeves (23, 31) and that its temperature is higher than the boiling temperature of said reagent.
8. Device according to Claim 7,
   characterized in that said reactor (13) presents an extension so long that set-up will take place therein completely.

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