PatentDe  


Dokumentenidentifikation EP1211037 24.08.2006
EP-Veröffentlichungsnummer 0001211037
Titel Verfahren und Vorrichtung zum kontinuierlichen Herstellen von Schaumstoff zur Formung von Paneelen
Anmelder Impianti Oms S.p.A., Verano Brianza, Milano, IT
Erfinder Massarotto, Loris, 20050 Triuggio (Prov. of Milano), IT
Vertreter derzeit kein Vertreter bestellt
DE-Aktenzeichen 60121409
Vertragsstaaten AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LI, LU, MC, NL, PT, SE, TR
Sprache des Dokument EN
EP-Anmeldetag 22.05.2001
EP-Aktenzeichen 011119963
EP-Offenlegungsdatum 05.06.2002
EP date of grant 12.07.2006
Veröffentlichungstag im Patentblatt 24.08.2006
IPC-Hauptklasse B29C 44/34(2006.01)A, F, I, 20051017, B, H, EP
IPC-Nebenklasse B29B 7/76(2006.01)A, L, I, 20051017, B, H, EP   B29C 44/32(2006.01)A, L, I, 20051017, B, H, EP   

Beschreibung[en]

The present invention relates to a method and an apparatus for the continuous production of expanded plastic material for forming panels and the like.

It is known that expanded polyurethane foams are typically obtained by pouring a so-called reactive, liquid mixture, constituted by the reagents, i.e., isocyanate and polyol, water, catalysts and so forth, and by any blowing agents such as hydrocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, and the like.

In a few seconds, the reactive mixture starts to react, generating heat and carbon dioxide produced by the water-isocyanate reaction.

The carbon dioxide, together with the gases generated by the evaporation of any blowing agents, due to the heat generated by the chemical reactions, causes the expansion of the reactive mixture so as to generate the foam.

On the basis of this type of method, plants have been available for many years which allow the continuous production of low-density rigid foam panels for thermal insulation having, in cross-section, a rectangular shape or otherwise variously shaped; these panels can be produced in different lengths.

The foam of the lower and upper surfaces of the panels is coupled to substrates of various kinds, such as for example paper, bituminized paper, wood, metal plate and the like, which form outer claddings of said panel.

These panels are widely used, in particular, as insulators in the field of industrial building or in the field of industry or refrigeration.

Plants for manufacturing the panels generally have a series of dosage lines which dose out the components in the intended ratios to a fixed or movable mixing head which feeds the lower substrate of the cladding with the mixture produced by said lines, optionally by means of appropriately provided distribution units.

In another application, the reactive mixture can be applied by deposit on the upper substrate.

The reactive mixture enters a step of growth and polymerization and is conveyed, together with the upper and lower claddings, by appropriately provided movable conveyance and containment systems such as, for example, double conveyor belts, to a cutter for cutting the panels to the intended length.

A fundamental aspect in obtaining good-quality panels is the manner in which the reactive mixture is distributed by the mixing head onto the substrate of the cladding.

Accordingly, several systems have been proposed according to the type of panel to be produced and to the production rates; these systems use, for example, multiple fixed heads or a head which performs a reciprocating motion on a guide which is perpendicular to the panel production axis.

In the latter case, it is particularly important that the head be lightweight and compact, so as to allow easy placement of the injection head between the lower and upper substrates of the panel before entering the double containment belt.

In any event, however, containment of the weight and dimensions of the heads is a desideratum to achieve plant optimization.

In most cases, the production of thermal insulation panels requires the use of the cited blowing agents, and therefore such blowing agents are preferably added continuously at the time of production, with the advantage of being able to control their dosage according to the physical characteristics of the panel to be produced.

The addition can be performed directly in the mixing head or by premixing, in the exact amount required, by means of static or dynamic mixers, the blowing agent with one of the reactive components, for example the polyol, before said component, drawn from the storage tank, reaches the head in which final mixing occurs in order to prepare the reactive mixture to be deposited by pouring onto the substrate of the panel.

What has been described above for the blowing agent can in any case be extended to other components, catalysts and the like that are involved in the formation of the reactive mixture.

The concept already well known is that it is not convenient to perform the addition directly in the injection head, since an immediate consequence would be an increase in dimensions and weight, in addition to an increase in constructive complexity.

If high-pressure injection heads are used, problems are encountered in relation to the premixing of the various components, which is performed in the low-pressure part of the circuit, i.e., upstream of the high-pressure delivery pump.

This aspect causes considerable problems, since an inevitable seepage of the polyol high-pressure pump occurs which, exactly in the case of low-pressure premixing, can cause continuous changes in the ratio among the various components.

It is also known, in polyurethane foaming technology, that precise dosage and optimum thermostatic control of the components fed to the mixing head throughout the process are extremely important for obtaining products having optimum and constant characteristics.

For this purpose, for example, it is useful to provide, before the step of pouring the reactive mixture begins, a recirculation of the components which allows to obtain the required temperature, flow-rate and pressure conditions, thus avoiding transients, in the initial periods of the pouring process, in which these parameters are not ideal, consequently producing panels which do not have the intended quality characteristics.

In the current state of the art, therefore, the possibility to provide effective recirculation becomes an important factor in ensuring that the physical conditions of the components of the reactive mixture remain constant both during the pouring steps and during the recirculation steps.

DD 133 642 A discloses a device (4) for mixing gas in a polyol. A polyol feed circuit (1-3,6-7) feeds and recirculates the polyol to a mixing device (5) at which a reciprocating cone (8) is arranged and about which there are disposed mixing grooves (10-12). A gas is also fed to one of the mixing grooves (10) through a gas line (16-19).

The aim of the invention is to eliminate the above noted drawbacks, by providing a method for the continuous production of expanded plastic material for forming panels and the like which allows to perform a step of recirculation in the head at high pressure which allows to avoid altering the ratios among the various components, maintaining at all times the optimum ratios and preventing the occurrence of incorrect mixing.

Within this aim, a particular object of the invention is to provide a method in which it is possible to perform high pressure recirculation despite having a mixing head or pouring assembly in which only two injection assemblies are available, thus reducing to a minimum the dimensions and volume of the mixing head.

Another object of the present invention is to provide an apparatus for the continuous production of expanded plastic material which thanks to its particular constructive characteristics is capable of giving the greatest assurances of reliability and safety in use.

Another object of the present invention is to provide an apparatus which can be easily obtained starting from commonly commercially available elements and materials and is furthermore competitive from a merely economical point of view.

In accordance with the invention, there is provided a method for the continuous production of expanded plastic material for forming panels and the like, as defined in the appended claims.

Further characteristics and advantages will become better apparent from the description of a method for the continuous production of expanded plastic material for forming panels and the like and of the apparatus for carrying out the method, illustrated with the aid of the accompanying drawings, wherein:

  • Figure 1 is a schematic view of the apparatus during the recirculation step;
  • Figure 2 is a schematic view of the apparatus during the pouring step.

With reference to the figures, the apparatus for the continuous production of expanded plastic material for forming panels and the like comprises a mixing head, generally designated by the reference numeral 1, which in a per se known manner defines internally a pouring channel 2 in which a self-cleaning piston 3 can move hermetically, with recirculation slots 4 which are arranged at a first injection assembly 5 and at a second injection assembly 6.

The piston 3 can perform a translation movement by means of a piston 7 in order to position the slots 4 in the recirculation position, as shown in Figure 1, or in the pouring position, in which the piston 3 releases the injection assemblies in order to perform mixing and pouring of the foam.

The first injection assembly 5 is connected to a duct 10 for introducing a mixture of components which can include, for example, polyol mixed with blowing reagents, catalysts and the like.

For this purpose, there is a polyol tank 20, downstream of which there is a high-pressure pump 21 which introduces the polyol in a first delivery branch 22 and a second delivery branch 23, respectively controlled by a first two-way valve 24 and by a second two-way valve 25.

The first branch 22 is connected, with the interposition of a first calibrated one-way valve 26, to the delivery duct 10 in close proximity to the mixing head, while on the second delivery branch 23 there is a mixer 30 for introducing the remaining components of the mixture.

The second branch 23, downstream of the mixer 30, has a second calibrated one-way valve 31 connected to the delivery duct 10, which is also in close proximity to the mixing head 1.

At least one duct for introducing the remaining components, such as blowing agents, catalysts and so forth, is connected to the mixer 30.

The specific example illustrates two ducts 40 on which a respective three-way valve 41 is arranged which connects a product delivery duct 42 and a recirculation duct 43.

The second injection assembly 6 is connected to a second delivery duct 50 for introducing, for example, the isocyanate or in any case another component of the mixture.

A first recirculation duct 60, located at the first injection assembly 5, and a second recirculation duct 61, located at the second injection assembly 6, are further provided on the mixing head.

In practical operation, when the apparatus is in the initial recirculation conditions, the polyol is drawn from the storage tank 20 and is introduced, by means of the high-pressure pump 21, toward the delivery branches 22 and 23.

In recirculation conditions, the valve 25 is closed and the valve 24 is open, and therefore the polyol flows through the first branch 22 and, by means of the one-way or check valve 26, it is introduced in the mixing head, where by flowing through the correspondingly arranged slot 4 it is introduced in the first recirculation duct 60, which returns the polyol into the tank 20

The one-way or check valve 31 prevents from flowing the polyol toward the mixer 30, thus isolating it and the corresponding delivery branch from the mixing head, which is of the self-cleaning type.

Clearly, instead of the one-way valves 26 and 31, manually- or automatically-operated isolator valves can be used.

In this manner, a complete recirculation is obtained which occurs through the head for mixing the polyol alone without blowing agents, catalysts or other components of the reactive mixture, which are recirculated by means of the three-way valve or equivalent valves, which provide to divert the flow that arrives from the delivery duct 42 toward the corresponding recirculation duct 43 before introduction in the mixer.

It should also be added that the apparatus can return the polyol directly at the intake of the high-pressure pump 21 instead of directly into the storage tank 20, thus excluding from the recirculation the storage tank and any possibility of introducing blowing agent, catalysts and/or other components in the reactive mixture.

Clearly, the other component of the reaction, i.e. the isocyanate, is also in the recirculation step and is recycled in a conventional manner by means of the second delivery duct and the second recirculation duct 61 with the passage through the corresponding slot 4.

In order to pass from the recirculation step to the pouring step, shown in Figure 2, first the mixing head is opened by the action of the self-cleaning piston 3, which is translated by the piston 7, thus opening the valve 25 and then closing the valve 24, so that the polyol is introduced in the second branch, which sends it toward the mixer 30.

The three-way valves 41 also switches, so that the other components of the mixture, such as blowing agents, catalysts and the like, are mixed with polyol.

The beginning of this sequence, with the opening of the mixing head, interrupts the step of recirculation of the polyol before the blowing agent, the catalysts or the components of the reactive mixture to be premixed with the polyol are introduced in the mixer, thus making it impossible for said components to reach the storage tank 20.

Opening the valve 25 before closing the valve 24 provides protection from the danger of overpressures due to the simultaneous closure of both valves.

At the end of this sequence of operations, the polyol is taken from the storage tank 20 and is sent, by means of the high-pressure pump 21 through the valve 25 to the mixer 30, which also receives the blowing agent, the catalysts and any other components of the reactive mixture through the respective three-way valves 41.

The polyol, after being premixed with the blowing agent, the catalysts or any other components of the reactive mixture by the mixer 30, through the second one-way valve 31, which is also arranged very close to the mixing head, is introduced in the first injection assembly 5, which injects the mixture into the pouring channel simultaneously with the isocyanate introduced by the other injection assembly, thus providing the reactive mixture, which exits from the pouring channel 2.

The one-way valve 26 in practice isolates the first branch 22 from the flow of premixed polyol.

The above disclosed sequence of operations must be performed as quickly as possible, optionally even with a partial overlap of the execution times of some consecutive operations, insofar as this is allowed by the components used, following in any case the described sequence, in order to minimize the amount of reactive mixture that is poured without having optimum quality.

At the end of the pouring time, in order to return the plant to the initial recirculation conditions, first the three-way valves 41 that introduce the blowing agents, the catalysts or the other components to be added are switched and the valve 24 is simultaneously opened; then the valve 25 is closed.

The mixing head is then closed by moving the self-cleaning piston 3, which places its slots 4 at the injection assemblies.

This transition to the recirculation step can optionally be performed with a short delay in order to flush with pure polyol the delivery duct 10, which is common for the polyol and the remaining components.

The switching, as a first operation, of the three-way valves 41, and the closure, with optional delay, of the mixing head, as final operation of the sequence, together with the action of the second one-way valve 31, which in practice isolates the second branch 23 from the mixing head, prevents the recirculation to the storage tank 20 of amounts of blowing agents, catalysts and other components of the reactive mixture.

The above disclosed operations must of course be performed as quickly as possible, optionally also with partial overlaps of the times of some consecutive operations, so as to minimize the amount of reactive mixture that is poured, at the end of production, without the necessary requirements that ensure optimum quality of the produced panel.

Another important aspect is that the one-way valves 26 and 31 must be fitted as close as possible to the mixing head or directly on said mixing head, thus minimizing the path shared by polyol and other components of the mixture, so as to minimize said flushing time and the amount of reactive mixture that is poured before the mixing head closes.

It should also be added that it is possible to provide other structural solutions for the apparatus, such as for example the replacement of the first and second isolator or cut off valves 24 and 25 with a single three-way valve, without altering the types of the operating steps being performed.

From the above description it is evident that the invention achieves the intended aim and objects, and in particular the fact is stressed that the described solution allows to have a high-pressure mixing head with recirculation in the head which allows to always have optimum component dosage despite having a mixing head with only two injection assemblies, and allows to perform mixing of the polyol with the other components of the mixture downstream of the high-pressure pump, so as to always maintain precise values of the percentages of the various components.

The system has also the advantage that during production, if the percentage of the components of the reactive mixture varies, the effect is immediately evident on the panel being produced; whereas with the conventional system the transient would be longer and therefore more finished product would be rejected.


Anspruch[de]
Verfahren zur kontinuierlichen Herstellung von Schaumstoffmaterial zum Formen von Paneelen, bei dem während des Gießschrittes mindestens eine Reaktionskomponente und ein Gemisch der übrigen Komponenten bei hohem Druck in einen Gießkanal (2) eines Mischkopfes (1) mittels zwei Injektionsvorrichtungen (4, 5) eingeleitet werden, wobei das Gemisch der übrigen Komponenten ein mit Treibmitteln und Katalysatoren vermischtes Polyol enthält und auf der stromabwärts gelegenen Seite der Hochdruckpumpe (21) bereitgestellt wird, die räumlich von dem Mischkopf (1) getrennt ist und während des Gießanhalteschrittes das mit Treibmitteln und Katalysatoren vermischte Polyol für sich in einem Rezirkulationsschritt zugeführt wird, wobei das Polyol während des Rezirkulationsschrittes von einem ersten Zufuhrzweig (22) gespeist wird, der von einem zweiten Zufuhrzweig (23), in dem der Mischer (30) vorgesehen ist, verschieden und getrennt ist und während des Gießschritts das Polyol in den zweiten Zufuhrzweig (23) eingeleitet wird, damit es durch den Mischer (30) strömt, in den mindestens eine Leitung (40) zum Einleiten der Treibmittel und Katalysatoren übergeht. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die mindestens eine Reaktionskomponente aus Isocyanat besteht. Verfahren nach einem oder mehreren der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass der erste Zufuhrzweig (22) und der zweite Zufuhrzweig (23) an einer Versorgungsleitung (10) des Mischkopfes (1) zusammenlaufen und dass Einwegventile (26, 31) vorgesehen sind, die auf den ersten Zufuhrzweig (22) und den zweiten Zufuhrzweig (23) wirken. Verfahren nach einem oder mehreren der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Treibmittel rezirkuliert und katalysiert werden, bevor sie in den Mischer (30) geleitet werden. Verfahren nach einem oder mehreren der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass das Polyol während des Rezirkulationsschritts in den Polyol-Speicherbehälter (20) zurückgeführt wird. Verfahren nach einem oder mehreren der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass im Übergang vom Rezirkulationsschritt zum Gießschritt der Gießkanal (2) im Mischkopf (1) geöffnet wird, dann der Durchgang zum zweiten Zweig (23) zuerst für das Polyol geöffnet wird und dann der Durchgang durch den ersten Zweig (22) geschlossen wird, wobei die übrigen Komponenten des Gemischs nach dem Durchgang des Polyols in dem Mischer (30) eingeleitet werden. Verfahren nach einem oder mehreren der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass im Übergang vom Gießschritt zum Rezirkulationsschritt der Fluss des Polyols durch den Mischer (30) unterbrochen wird, nachdem die Leitungen (40) zum Einleiten der Treibmittel und Katalysatoren auf Rezirkulation eingestellt worden sind. Vorrichtung zur kontinuierlichen Herstellung von Schaumstoffmaterial zum Formen von Paneelen und dergleichen, umfassend einen Mischkopf (1), der intern einen Gießkanal (2) bildet, in dem sich ein selbstreinigender Kolben (3) bewegen kann, wobei der Kolben (3) Rezirkulationsschlitze (4) hat, die jeweils an einer ersten Injektionsvorrichtung (5) und an einer zweiten Injektionsvorrichtung (6) angeordnet sein können, für mindestens eine erste Komponente und die übrigen Komponenten des Gemischs, wobei die Injektionsvorrichtung (5) für die übrigen Komponenten des Gemischs mit einer Versorgungsleitung (10) verbunden ist, in der ein erster (22) und ein zweiter (23) Zufuhrzweig zusammenlaufen, wobei der erste Zufuhrzweig (22) von dem zweiten Zufuhrzweig (23) verschieden und getrennt ist, wobei die Zufuhrzweige (22, 23) auf der stromaufwärts gelegenen Seite durch Ventilmittel (24, 25) gesteuert werden, die auf der stromabwärts gelegenen Seite der Hochdruckpumpe (21) angeordnet sind, deren Einlass mit einem Speicherbehälter (20) für Polyol verbunden ist, wobei auf dem zweiten Zufuhrzweig (23) ein Mischer (30) vorgesehen ist, der räumlich vom Mischkopf (1) getrennt ist und mit mindestens einer Leitung (40) verbunden ist, um Treibmittel und Katalysatoren einzuleiten, wobei ferner ein erster Rezirkulationskanal (60) vorgesehen ist, der mit der Injektionsvorrichtung (5) verbunden ist, um die Komponente in den Polyol-Speicherbehälter (20) zurückzuleiten. Vorrichtung nach Anspruch 8, dadurch gekennzeichnet, dass sie auf dem ersten Zufuhrzweig (22) und auf dem zweiten Zufuhrzweig (23) ein erstes (26) und ein zweites (31) Einwegventil umfasst, wobei die Ventile geeignet sind, die Rückführung des Materials zu verhindern, und wobei der erste und der zweite Zufuhrzweig (22, 23) an dem Zuführungskanal (10) des Mischkopfes (1) zusammenlaufen. Vorrichtung nach einem oder mehreren der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass sie auf dem ersten Zufuhrzweig (22) und auf dem zweiten Zufuhrzweig (23), auf der stromaufwärts gelegenen Seite des Mischers (30), ein erstes (24) und ein zweites (25) Zweiwegeventil umfasst. Vorrichtung nach einem oder mehreren der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass sie an dem mindestens einem Rohr (40) zur Verbindung mit dem Mischer (30) ein Dreiwegeventil (4) umfasst, um das entsprechende Treibmittel und die Katalysatorkomponente zu rezirkulieren. Vorrichtung nach einem oder mehreren der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass sie an der Zufuhr der Hochdruckpumpe (21) ein Dreiwegezufuhrventil umfasst, das den ersten (22) und den zweiten (23) Zufuhrzweig steuert.
Anspruch[en]
A method for the continuous production of expanded plastic material for forming panels, consisting, during the pouring step, in introducing at least one reaction component and a mixture of the remaining components at high pressure in a pouring channel (2) of a mixing head (1) by means of two injection assemblies (4,5), said mixture of the remaining components comprising polyol mixed with blowing agents and catalysts, said mixture being provided downstream of the high-pressure pump (21) spatially separated from the mixing head (1), and during the pouring hold step said polyol mixed with blowing agents and catalysts are individually placed in a recirculation step, during the recirculation step the polyol is fed by a first delivery branch (22) which is distinct and separate from a second delivery branch (23) in which the mixer (30) is provided, and during the pouring step the polyol is introduced in said second delivery branch (23) in order to flow through the mixer (30), into which at least one duct (40) for introducing the blowing agents and catalysts merges. The method according to claim 1, characterized in that said at least one reaction component is constituted by isocyanate. The method according to one or more of the preceding claims, characterized in that said first delivery branch (22) and said second delivery branch (23) merge at a supply duct (10) of said mixing head (1) and in that one-way valves (26,31) are provided which affect said first (22) and second (23) delivery branches. The method according to one or more of the preceding claims, characterized in that it recirculates said blowing agents and catalysts before they are introduced in said mixer (30). The method according to one or more of the preceding claims, characterized in that, during the recirculation step, the polyol is returned to the polyol storage tank (20). The method according to one or more of the preceding claims, characterized in that in the transition between the recirculation step and the pouring step, the pouring channel (2) in the mixing head (1) is opened and then the passage toward said second branch (23) is first opened to the polyol and then the passage through said first branch (22) is closed, the remaining components of the mixture being introduced after the passage of the polyol in the mixer (30). The method according to one or more of the preceding claims, characterized in that during the transition between the pouring step and the recirculation step the flow of the polyol through said mixer (30) is interrupted after the ducts (40) for introducing the blowing agents and catalysts have been set to recirculation. An apparatus for the continuous production of expanded plastic material for forming panels and the like, comprising a mixing head (1) which internally forms a pouring channel (2) in which a self-cleaning piston (3) can move, said piston (3) having recirculation slots (4) which can be arranged at a first injection assembly (5) and at a second injection assembly (6) respectively, for at least one first component and the remaining components of the mixture, the injection assembly (5) for the remaining components of the mixture being connected to a supply duct (10) in which a first (22) and a second (23) delivery branch merge, said first delivery branch (22) being distinct and separate from said second delivery branch (23), said delivery branches (22,23) being controlled upstream by valve means (24,25) arranged downstream of a high-pressure pump (21) the intake of which is connected to a supply tank (20) for polyol, a mixer (30) being provided on said second delivery branch (23) spatially arranged from said mixing head (1) and being connected to at least one duct (40) for introducing blowing agents and catalysts, a first recirculation duct (60) being further provided which is connected to said injection assembly (5) for return into the polyol storage tank (20) of the component. The apparatus according to claim 8, characterized in that it comprises, a first (26) and a second (31) one-way valves on said first delivery branch (22) and on said second delivery branch (23), said valves being adapted to prevent the return of the material, said first and second delivery branches (22,23) mutually merging at the supply duct (10) of said mixing head (1). The apparatus according to one or more of the preceding claims, characterized in that it comprises on said first delivery branch (22) and on said second delivery branch (23), upstream of said mixer (30), a first (24) and a second (25) two-way valves. The apparatus according to one or more of the preceding claims, characterized in that it comprises, on said at least one duct (40) for connection to the mixer (30), a three-way valve (4) for recirculation of the corresponding blowing agent and catalyst component. The apparatus according to one or more of the preceding claims, characterized in that it comprises, on the delivery of said high-pressure pump (21), a three-way delivery valve which controls said first (22) and second (23) delivery branches.
Anspruch[fr]
Procédé pour la production en continu de matière plastique expansée pour la formation de panneaux, consistant, pendant l'étape de coulée, à introduire au moins un réactif et un mélange des autres constituants sous une forte pression dans un canal de coulée (2) d'une tête de mélange (1) à l'aide de deux systèmes d'injection (4, 5), ledit mélange des autres constituants comprenant du polyol mélangé à des agents d'expansion et des catalyseurs, ledit mélange étant acheminé en aval de la pompe à haute pression (21) espacée de la tête de mélange (1) et, pendant l'étape d'attente de coulée, ledit polyol en mélange avec des agents d'expansion et des catalyseurs sont individuellement placés dans une étape de recirculation, étape de recirculation au cours de laquelle le polyol est fourni via une première banche d'alimentation (22), distincte et séparée d'une seconde branche d'alimentation (23) dans laquelle est présent le mélangeur (30), et, pendant l'étape de coulée, le polyol est introduit dans ladite seconde branche d'alimentation (23) pour passer par le mélangeur (30) dans lequel débouche au moins un conduit (40) servant à introduire les agents d'expansion et les catalyseurs. Procédé selon la revendication 1, caractérisé en ce que ledit au moins un réactif est constitué par de l'isocyanate. Procédé selon une ou plusieurs des revendications précédentes, caractérisé en ce que ladite première branche d'alimentation (22) et ladite seconde branche d'alimentation (23) se rejoignent au niveau d'un conduit d'alimentation (10) de ladite tête de mélange (1) et en ce que des clapets anti-retour (26, 31) sont prévus pour agir sur lesdites première (22) et seconde (23) branches d'alimentation. Procédé selon une ou plusieurs des revendications précédentes, caractérisé en ce qu'il met en oeuvre une recirculation desdits agents d'expansion et catalyseurs avant leur introduction dans ledit mélangeur (30) . Procédé selon une ou plusieurs des revendications précédentes, caractérisé en ce que, pendant l'étape de recirculation, le polyol est renvoyé dans le réservoir de stockage (20) de polyol. Procédé selon une ou plusieurs des revendications précédentes, caractérisé en ce que, lors de la transition entre l'étape de recirculation et l'étape de coulée, le canal de coulée (2) dans la tête de mélange (1) est ouvert, puis le passage en direction de ladite seconde branche (23) est ouvert d'abord pour le polyol, puis le passage dans ladite première branche (22) est fermé, les autres constituants du mélange étant introduits après le passage du polyol dans le mélangeur (30). Procédé selon une ou plusieurs des revendications précédentes, caractérisé en ce que, pendant la transition entre l'étape de coulée et l'étape de recirculation, l'écoulement du polyol dans ledit mélangeur (30) est interrompu après que les conduits (40) pour l'introduction des agents d'expansion et des catalyseurs ont été amenés à permettre la recirculation. Dispositif pour la production en continu de matière plastique expansée afin de former des panneaux et analogues, comprenant une tête de mélange (1) qui définit intérieurement un canal de coulée (2) dans lequel peut se déplacer un piston autonettoyant (3), ledit piston (3) comportant des fentes de recirculation (4) qui peuvent être ménagées respectivement au niveau d'un premier système d'injection (5) et au niveau d'un second système d'injection (6), pour au moins un premier constituant et pour les autres constituants du mélange, le système d'injection (5) pour les autres constituants du mélange étant relié à un conduit d'alimentation (10) dans lequel débouchent une première (22) et une seconde (23) branches d'alimentation, ladite première branche d'alimentation (22) étant distincte et séparée de ladite seconde branche d'alimentation (23), lesdites branches d'alimentation (22, 23) étant commandées en amont par des moyens formant clapets (24, 25) disposés en aval d'une pompe à haute pression (21) dont l'entrée d'admission est reliée à un réservoir d'alimentation (20) pour polyol, un mélangeur (30) étant disposé sur ladite seconde branche d'alimentation (23), physiquement espacé de ladite tête de mélange (1) et relié à au moins un conduit (40) servant à introduire des agents d'expansion et des catalyseurs, un premier conduit de recirculation (60) étant en outre prévu, lequel est relié audit système d'injection (5) pour faire revenir le constituant dans le réservoir de stockage (20) de polyol. Dispositif selon la revendication 8, caractérisé en ce qu'il comprend un premier (26) et un second (31) clapets anti-retour sur ladite première branche d'alimentation (22) et sur ladite seconde branche d'alimentation (23), lesdits clapets servant à empêcher le retour de la matière, lesdites première et seconde branches d'alimentation (22, 23) se rejoignent l'une avec l'autre au niveau du conduit d'alimentation (10) de ladite tête de mélange (1). Dispositif selon une ou plusieurs des revendications précédentes, caractérisé en ce qu'il comprend, sur ladite première branche d'alimentation (22) et sur ladite seconde branche d'alimentation (23), en amont dudit mélangeur (30), une première (24) et une seconde (25) soupapes à deux voies. Dispositif selon une ou plusieurs des revendications précédentes, caractérisé en ce qu'il comprend, sur ledit au moins un conduit (40) à relier au mélangeur (30), une soupape (4) à trois voies pour la recirculation de l'agent d'expansion et du catalyseur correspondants. Dispositif selon une ou plusieurs des revendications précédentes, caractérisé en ce qu'il comprend, du côté refoulement de ladite pompe à haute pression (21), une vanne de refoulement à trois voies qui commande lesdites première (22) et seconde (23) branches d'alimentation.






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