Process and device for the production of polyurethane components

Abstract

The invention relates to a method for producing polyurethane components, wherein a further component (5) is added to a first chemical component (1) before it enters a mixing chamber (3), and wherein the chemical component (1) is passed through a nozzle element (6) which is arranged in front of or on the mixing chamber (3) and which has a first flow path (7) for the chemical component (1), wherein the first flow path (7) for the chemical component (1) has a constriction (8), wherein the further component (5) is fed to the nozzle element (6) and is guided along a second flow path (9) through the nozzle element (6).In order to introduce a further material into the polyol stream in such a way that it can be mixed in and conveyed to the mixer with optimal conveying and the lowest possible shear stress, the invention provides that a gas (G) is fed into a container (10) for the further component (5) and / or into a flow path (11) for the further component (5), which extends from the container (10) to the nozzle element (6), and that means (12) for discharging the gas (G) are arranged in or on the nozzle element (6), and the gas (G) is discharged from the nozzle element (6) via the means (12). Furthermore, the invention relates to an apparatus for carrying out the method.

Description

The invention relates to a method for producing polyurethane components, in which at least two different chemical components, including at least one polyol component and one isocyanate component, are metered individually and then fed to the mixing chamber of a mixing head, in which they are mixed to form a polyurethane reactive mixture and are then discharged from the mixing chamber, in particular into an open or closed form, wherein at least one of the chemical components is added to the chemical component before entering the mixing chamber, a further component, in particular a filler, wherein the further component is present in liquid or solid form, in particular as a pulverulent, granular or particulate mixture, and wherein the chemical component to which the further component is added is passed through a nozzle element which is arranged upstream of or at the mixing chamber and which has a first flow path for the chemical component, wherein the first flow path for the chemical component has a constriction, wherein the further component is supplied to the nozzle element and the latter is guided through the nozzle element along a second flow path. The invention further relates to an apparatus for carrying out such a method.Known mixing devices for high-pressure polyurethane mixing-without additional addition of special components-are constructed in such a way that the at least two reactive components meet one another in a mixing chamber with high flow energy in the form of impulse energy and are thus mixed with one another. In the high-pressure mixing, there are generally no additional mixing elements present for further mixing of the reaction mixture, with the result that the mixing takes place exclusively by the flow energy contained in the reactive components. In practice, the countercurrent injection method has become established.The mixing takes place predominantly in a mixing chamber which is mechanically cleaned by means of a tappet. In the case of groove-controlled mixing heads, return grooves are provided in the control piston, via which the components in the circulation position circulate separately from one another from the inlet opening via the grooves without mixing taking place. In the metering position, the plunger is moved correspondingly, so that a mixing chamber is formed in the region of the inlet openings and the reactive components are mixed with one another.As an alternative to this, nozzle-controlled mixing heads are known which are designed without such circulation grooves. The component control is effected with controlled nozzles which are arranged in the inlet openings.The function of the nozzles is to generate the required flow energy and to convert the pressure energy into flow energy. In this case, narrow flow cross sections are required in the nozzle in order to produce the required aperture effect.Due to the properties imposed on the components produced, it is in part necessary to mix various additives into the reaction mixture. The additives can be present either in liquid or in solid, particulate or powdery form.The liquid additive components include, for example, activators, additives and paints. The liquid components are usually only fed to the reaction mixture in small amounts. These are either mixed in a batch predominantly in the polyol component or metered directly into the mixing chamber. When introduced directly into the mixing chamber, the problem often arises that, in the case of the minimum amount metering, an insufficient impulse is generated in order to be mixed sufficiently in the countercurrent injection. Processing as a polyol batch has the disadvantage that the partly corrosive properties of the additional component cause problems with regard to the useful life of the plant and partly require special components for conditioning and conveying. If colors are to be processed in batch, multiple rinsing processes are often required when changing the color, which makes a rapid change of the colors difficult.Solid fillers are usually present in particulate, short-fibre or powdery form. These are often abrasive and produce severe wear on the conveying devices and in the line systems. In addition, some fillers, such as expandable graphite, are particularly shear-sensitive and generate further challenges in handling and in mixing into the reaction mixture.A method of the above-mentioned generic type is known from DE 33 35 787 A1. A similar solution is disclosed in DE 10 2010 031 958 A1.For conveying powdery fillers, DE 27 50 938 A1 proposes the use of an internal pressure of a filler container charged with gas. This represents a particularly gentle conveying possibility, since no pumps or other dynamic conveying devices have to be used. In this case, the gas pressure can be used in a targeted manner as delivery pressure via a regulating system and thus serve for setting the desired flow rate. Since solid fillers tend to flow defects such as well and bridging, it is necessary to keep the bulk material free of flow.Fluidization of bulk materials by means of air loosening is known in silo technology. The cited DE 27 50 938 A1 addresses this approach in the field of the processing of polyurethanes. A fine air distribution is produced via a porous cone in the filler container and the bulk material is kept flowable. The mixing in in the region of the mixing chamber is not described.Various methods are known for adding solid fillers, such as chalk, expandable graphite or similar materials, to the reaction mixture:First, the filler can be added to one of the main components.Furthermore, the addition of the filler to the reaction mixture can take place within the outflow system after the high-pressure mixing.Finally, the filler can be added via a separate feed into the mixing chamber.When the filler is added to one of the reaction components, the filler is injected together with the main component into the mixing chamber, i.e. the fillers must be conveyed together with the main component under high pressure via a metering pump. The disadvantageous effect here is that the liquids filled with fillers tend to demix and form deposits in the pipelines. Abrasive fillers frequently lead to increased wear on the surfaces which are subjected to severe mechanical and flow conditions, for example within the nozzles, metering pumps and valves. Sensitive fillers can be damaged to an unacceptably high degree by processing at high pressure.In particular, the processing of expandable graphite presents great challenges to machine technology. In polyurethane processing, expandable graphite is used as flame retardant. The mode of action, advantages and problems in the processing of shear-sensitive fillers such as expandable graphite are explained, for example, in EP 3 892 432 A2.One problem in the processing of expandable graphite is that the expandable graphite particles can be destroyed if they are subjected to mechanical loads, such as in particular shear forces in pumps or nozzles. On the one hand, their flame retardant effect is impaired as a result; on the other hand, the acid released negatively impairs the chemistry during the foaming process.It is therefore problematic if expandable graphite, as is customary in other fillers, is mixed as a filler-polyol mixture in a container, is kept in suspension there by means of stirrer and must additionally be circulated so that no expandable graphite can settle in the lines.A method for reducing the circulation time of the expandable graphite-polyol mixture under high pressure is described in the cited EP 3 892 432 A2.An addition downstream of the mixing chamber is proposed, for example, in EP 0 037 523 A1, in DE 27 50 938 A1 and in DE 10 2009 011 900 B3, which, however, disadvantageously leads to inadequate mixing. The additive component is added to the reaction mixture in these previously known solutions. A further mixing element is not present in these cases; this procedure cannot be implemented in self-cleaning mixing heads.DE 42 16 943 A1 describes a method in which the filler is fed directly to the mixing chamber. However, the arrangement described here has insufficient mixing for many applications. It has been found in experiments that the impulse energy is usually not sufficient to add the additive component sufficiently well to the reaction mixture.Similar solutions are disclosed in AT 519 978 A4, DE 25 44 559 A1, DE 690 15 821 T2, DE 10 2010 018 946 A1, DE 10 2011 002 881 A1, FR 1 496 800 A and US 2012 / 0 178 895 A1.In the light of the above-described problems, the object of the present invention is to provide a process of the generic type and a corresponding device with which both liquid and solid, particulate or powdery additives are introduced into a reaction mixture which is mixed by means of the countercurrent injection process in such a way that the additive is mixed in as well as possible. In this context, particular care should be taken to ensure that filler particles can be mixed in as gently as possible and with low shear stress and liquid additives in small amounts with low pre-pressures. Furthermore, an essential requirement according to the task is to convey the additive as well as possible from its storage container up to its mixing into one of the chemical components from which the reaction mixture is produced.The effect of this object by the invention is characterized according to the method in that a gas is supplied into a container for the further component and / or into a flow path for the further component, which extends from the container to the nozzle element, and in that means for discharging the gas are arranged in or on the nozzle element and the gas is discharged from the nozzle element via the means.The nozzle element preferably has a chamber into which the further component to which gas is added is introduced, wherein the means for discharging the gas are arranged on the chamber and the gas is discharged via the latter. The gas is preferably supplied at overpressure (compared to the ambient pressure).The second flow path preferably ends in the region of the constriction, so that the further component can be mixed in with the chemical component, wherein the flow rate of the chemical component to which the further component is added is increased by the constriction and thus a local negative pressure is generated in the chemical component, and wherein the further component is supplied to the chemical component in the region of the local negative pressure.The constriction in the first flow path of the chemical component can be designed as an annular gap and the further component can be supplied concentrically behind the annular gap in the flow direction of the components. In this case, it can be provided in particular that the further component is supplied behind the annular gap in the direction of an axis of the nozzle element.The chemical component is preferably accelerated to a speed of at least 20 m / s after flowing through the constriction.The chemical components are mixed in the mixing chamber preferably by means of countercurrent injection. They are preferably injected into the mixing chamber by means of nozzles.The further component is preferably expandable graphite.The nozzle element is preferably arranged close to the mixing chamber.The device for producing polyurethane components comprises at least one metering pump for metering a chemical component in the form of a polyol component, at least one metering pump for metering a chemical component in the form of an isocyanate component, a mixing head having a mixing chamber for mixing the polyol component and the isocyanate component, at least one container for storing a further component, in particular expandable graphite, wherein a nozzle element is arranged upstream of or on the mixing chamber, which nozzle element is designed for mixing the further component with at least one of the chemical components, wherein the nozzle element has a first flow path for the chemical component, which flow path has a constriction, and a second flow path for the further component, wherein it is provided according to the invention that the second flow path for the further component ends in the region of the constriction, gas supply means for supplying gas into the container for the further component and / or into a flow path for the further component, which extends from the container to the nozzle element, are arranged, and means for discharging the gas are arranged on the nozzle element.The nozzle element preferably has a chamber into which the further component to which gas is added can be introduced, wherein the means for discharging the gas are arranged on the chamber.The means for discharging the gas are preferably designed such that they are permeable to gas, but are impermeable to solid or liquid constituents of the further component. In this case, it is particularly envisaged that the means for discharging the gas have openings and / or gaps with small dimensions, the diameter or inside width of which is less than 0.5 mm, preferably less than 0.25 mm. For this purpose, porous materials can also be used, for example, via which the gas can escape from the chamber, which, however, is not permeable to solid particles.In a line which is in fluidic connection with the means for discharging the gas, an adjustable throttle for adjusting the volume flow of gas can be arranged. This throttle can optionally also be arranged directly on the means for discharging the gas.The constriction in the first flow path of the chemical component is preferably designed as an annular gap, wherein the second flow path for the further component ends behind the annular gap in the flow direction of the components. In this case, it is provided in particular that the second flow path for the further component extends at least in sections in the direction of an axis of the nozzle element.The second flow path for the further component is preferably formed at least in sections by a cylindrical opening, on which a piston-like, axially displaceable slide is arranged, which slide is designed for entry into the opening in order to close the latter.The nozzle element preferably has a nozzle housing and a nozzle needle that is axially displaceable relative to the nozzle housing, wherein the constriction, in particular the annular gap, is formed between the one axial end of the nozzle needle and the nozzle housing. Preferably, means are arranged for influencing the position of the nozzle needle relative to the nozzle housing, wherein the means can be designed in particular as electrical, hydraulic or pneumatic control and / or regulating means.It is also possible for spring means to be arranged in order to generate a pressing force of the one axial end of the nozzle needle against the nozzle housing, wherein the spring means are preferably designed as a mechanical spring or as a pneumatic spring.By adding a gas (air being in particular, but not necessarily; carbon dioxide may also be used, for example), optimum delivery of the further component, in particular the expandable graphite, from its storage container to the nozzle element and through the latter can be ensured. The flowability thereof can thus be ensured in a simple manner.Generally, a readily soluble gas (such as the carbon dioxide mentioned) with which the further component is flooded is suitable as gas. The gas pressure can optionally also be used to regulate the discharge quantity from the nozzle element.The introduction of a compressed gas can also be provided in order to flow through the region of the second flow path and thus keep the further component flowable. For this purpose, corresponding gas inlet and outlet openings can then be provided between the axial end regions of the second flow path in order to pass gas through the second flow path.The introduction of the gas into the further component is preferably effected directly in the region of the container for the further component. In combination with the discharge of the gas from the chamber in the region of the nozzle, a flow of the gas from the container to the nozzle is generated. This has the advantage that the solid filler can be conveyed into the mixing chamber without problems via the nozzle. By means of the selected gas pressure in the further component and within the nozzle, the amount of filler introduced into the one chemical component, in particular into the polyol, can be adjusted.The continuous overflow of the gas ensures that the filler is kept flowable within the line system.The amount of the outflowing gas can be regulated via an adjustable throttle in order to use as small an amount of gas as possible for overflowing.The outlet opening of the gas at the nozzle is designed such that although gas can escape, the filler remains within the metering line and cannot escape to the outside.Solid fillers can thus be conveyed into the mixing chamber in an improved manner via the internal pressure of the filler container to which gas is applied. The means for discharging the gas (overflow opening) in the region of the nozzle ensure that particulate, granular or powdery fillers are kept flowable and that no outflow disturbances of the solid fillers occur. The overflow opening can be designed as a valve, as a bore or as a diaphragm. Furthermore, the use of a porous material, a screen, a perforated plate or a filter is also possible here. Finally, a combination of the elements mentioned is also possible. Thus, although gas can escape from the chamber, no solid component can escape from the chamber.According to the proposed concept, a liquid, particulate or powdery additive component is thus preferably mixed in concentrically by means of the nozzle element in the form of a multicomponent nozzle of at least one of the two reaction components, wherein the nozzle element is arranged in the region of the line of a main component immediately before it enters the mixing chamber and the additive component is injected into the mixing chamber only during the mixing process with the main component. In combination with the addition of gas to optimize the delivery of the additional component, there is the possibility of significantly improved processing of polyurethane to which expandable graphite has to be added.The mixing is preferably effected in such a way that the additional component is guided within one of the two counter-streams and meets one another at the same point as the high-pressure component.The concentric addition causes an acceleration of the additional component and thereby increases its impulse force.A separation of polyol and isocyanate and of the additive component takes place until shortly before the mixing chamber.The additional component is therefore preferably introduced concentrically within the main component stream. It is preferably not supplied at high pressure.The inlet opening of the additional component into the mixing chamber can be closed by a tappet (see the above-mentioned axially displaceable slide). This makes it possible to produce a reaction mixture with and without an additional component. In addition, the plunger prevents the additional component from leaking into the reaction components or the additional component from being added with reaction mixture. In the circulatory mode (using recirculation grooves), the slide closes the opening, while in the shot mode it selectively releases or keeps it closed, depending on whether or not the additive is to be introduced into the mixing chamber during this shot.In addition, active vibrators (vibration generating means) can result in improvement of the flow behavior.The nozzle element is preferably designed with a drilled nozzle needle, in which the additional component is guided into the mixing chamber. The nozzle needle has an annular throttle gap. Via the throttle gap, the pressure energy of the reaction components is converted into flow energy and thus into mixed energy. The throttle gap can be adjusted either as a function of the travel or as a function of the component pressure upstream of the nozzle. As pressure-dependent adjusting elements, preferably mechanical and gas pressure springs are used.The quantity of the component flow can be adjusted as a function of displacement and / or pressure via the position of the nozzle needle, since the size of the annular gap can be changed in a targeted manner. This can be done either manually or by means of a control or regulation.The proposed solution permits particularly gentle processing of fillers. These need not be mixed into one of the two main components beforehand. Thus, particularly shear-sensitive solid fillers are not subjected to the otherwise necessary pumps and nozzles.Abrasive or corrosive additional components can be conveyed up to the mixing chamber in a separate metering line and have no negative influence on the longevity of the production plant.Problems with deposits and the separation of solid particles in a liquid main component can be prevented with the proposed solution.As a result of the mixing in of the additional component into the main component stream with high impulse energy, the additional component is entrained and therefore does not have to be conveyed with high energy itself until it enters the mixing chamber.The drawings illustrate an embodiment of the invention. FIG. 1 schematically shows a device for producing a molded part made of polyurethane, in which a high-pressure mixing head is used, into which polyol and isocyanate and a further component in the form of expandable graphite are injected by means of component nozzles, FIG. 2 shows the section through a nozzle element which is arranged on or in the mixing head, wherein the working position of the nozzle element is outlined, in which the further component in the form of expandable graphite is fed to the polyol, and FIG. 3 shows the nozzle element in the illustration according to FIG. 2, wherein the position of the nozzle element is now outlined, in which both the supply of the chemical component and the supply of the further component is blocked.FIG. 1 outlines a device for producing a molded part (not shown) made of polyurethane. For this purpose, in the present case, the reactive mixture is applied in a form (not shown).A container for polyol 1 and a container for isocyanate 2 can be seen. Each container is connected via a line to a metering pump 14 and 15, respectively. The metering pumps 14, 15 then convey the respective component to a mixing head 4 which has a mixing chamber 3. Both the polyol 1 and the isocyanate 2 are injected via a nozzle element 6 and via a nozzle (not shown) with high pressure into the mixing chamber 3 and are mixed here, as a result of which the reactive mixture is formed.The mixing head 4 has an axially displaceable control slide and recirculation grooves in order to guide the components in the circuit. The technology in this respect is of interest only at the edge here and is sufficiently known as such in the prior art.A container 10 for a further component 5 in the form of expandable graphite is also provided. It is true to mix the further component 5 as well as possible in a distributed manner into the polyol 1 without subjecting it to high stresses, in particular in the form of shear. Furthermore, a satisfactory conveyance of the further component is to be ensured.This is achieved by the special nozzle element 6, which in the embodiment is arranged directly on the mixing chamber 3.FIGS. 2 and 3 show the nozzle element 6 in more detail, wherein FIG. 2 outlines a position of the nozzle element open for the further component 5, while FIG. 3 blocks the supply for both the chemical component 1 and for the further component 5. The components of the nozzle element 6 correspond to one another, so that only a few reference numerals, which are mentioned in FIG. 2, are also entered in FIG. 3.The nozzle element 6 has a nozzle housing 21. In the nozzle housing 21, a nozzle needle 22 is arranged so as to be displaceable in the direction of an axis a. The nozzle housing 21 has a feed 24 for the further component 5. Furthermore, an outlet 25 for the mixture, which consists of the polyol 1 and the further component 5, is provided in the nozzle housing 21.In the present case, it applies that the nozzle element 6 is arranged directly in front of the mixing chamber 3 and via this the further component 5 is mixed into the polyol 1 (additive or alternatively also into the isocyanate 2). The nozzle element 6 has a first flow path 7 for the polyol 1, wherein the first flow path 7 has a constriction 8 in the form of an annular gap. Furthermore, the further component 5 is supplied to the nozzle element 6, wherein said component is guided along a second flow path 9 in the nozzle element 6. The second flow path 9 ends in the region of the constriction 8, the flow paths 7 and 9 being illustrated in FIG. 2 by dotted lines.By the corresponding position of the nozzle needle 22 relative to the nozzle housing 21, the size of the annular gap 8 can be adjusted. For this purpose, an adjusting device 27 is provided.By a corresponding adjustment of the size of the annular gap 8, the polyol 1 is correspondingly accelerated, so that the static pressure in the material is reduced. In the region of the reduced pressure, the second flow path 9 opens out, so that when the further component 5 is added, it is mixed into the polyol 1 in an optimum manner. As can be seen from FIG. 2, the annular gap 8 and the end of the second flow path 9 are arranged concentrically with respect to the axis a. In the preferred embodiment, the further component 5 is guided radially on the inside and the polyol 1 is guided radially on the outside, and the two components are combined downstream of the annular gap 8 in the conveying direction and thus mixed together in an optimum manner.Whether and how much material is supplied to the polyol 1 to the further component 5 can be influenced by an axially displaceable slide 20 with a drive 26, wherein the slide 20 can enter a cylindrical opening 19 in the nozzle needle 22 (this takes place in the illustration according to FIG. 3 ).In the second flow path 9 for the further component 5, a chamber 13 is formed, which is provided with means for discharging a gas G.In this regard, reference is made to FIG. 1, which shows that the container 10 for the further component 5 is in fluidic connection with gas supply means 16. A gas under pressure (increased with respect to ambient pressure) is introduced into the container 10 via the gas feed means 16. The gas G flows through the further component 5 and thus assists in conveying the component 5 from the container 10 via a flow path 11 as far as the nozzle element 6.In FIG. 2, the path taken by the gas G is indicated by dot-dash lines when the component 5 loaded with gas G enters the nozzle element 6 via the feed 24. The mixture of gas G and component 5 passes into the chamber 13, to which the means 12 for discharging the gas G are attached. Accordingly, the gas G escapes from the chamber 13 in the direction schematically shown by an arrow.For example, by means of a component with a very small gap (with a few tenths of a millimeter dimension) or by using porous material, it can be ensured that the gas G can escape from the chamber 13, but the component 5 (in particular the expandable graphite present in solid form) is retained in the chamber 13 and conveyed further.In FIG. 1, it is too schematically shown here that a throttle 18 can be arranged in the line 17, via which the gas G is discharged from the chamber 13, with which throttle the volume flow of the escaping gas G can be adjusted.The gas G always maintains the further component 5 in a readily conveyable state, so that in particular a precise metering of the further component 5 is problem-free.List of reference numbers:1 Chemical component (polyol) 2 Chemical component (isocyanate) 3 Mixing chamber 4 Mixing head 5 Further component (filler, expandable graphite) 6 Nozzle element 7 First flow path 8 Constriction (annular gap) 9 Second flow path 10 Container for the further component 11 Flow path for the further component 12 Means for discharging the gas 13 Chamber in the nozzle element 14 Metering pump for polyol 15 Metering pump for isocyanate 16 Gas supply means 17 Line 18 Throttle 19 Cylindrical opening 20 Axially displaceable slide 21 Nozzle housing 22 Nozzle needle 23 Supply of chemical component (polyol) 24 Supply of further component 25 Outlet for mixture of chemical component together with further component 26 Drive for slide 27 Adjusting device for constriction (annular gap) G Gas a Axis of the nozzle element

Claims

Method for producing polyurethane components, in which at least two different chemical components (1, 2), including at least one polyol component (1) and one isocyanate component (2), are metered individually and then fed to the mixing chamber (3) of a mixing head (4), in which they are mixed to form a polyurethane reactive mixture and then discharged from the mixing chamber (3), in particular into an open or closed form, wherein at least one of the chemical components (1, 2) is added to the chemical component (1, 2) before entering the mixing chamber (3), a further component (5), wherein the further component (5) is present in liquid or solid form, and wherein the chemical component (1, 2) to which the further component (5) is added is passed through a nozzle element (6), which is arranged upstream of or on the mixing chamber (3) and which has a first flow path (7) for the chemical component (1, 2), wherein the first flow path (7) for the chemical component (1, 2) has a constriction (8), wherein the further component (5) is fed to the nozzle element (6) and this is guided through the nozzle element (6) along a second flow path (9), characterized in that a gas (G) is fed into a container (10) for the further component (5) and / or into a flow path (11) for the further component (5) which extends from the container (10) to the nozzle element (6), and in that means (12) for discharging the gas (G) are arranged in or on the nozzle element (6) and the gas (G) is discharged from the nozzle element (6) via the means (12).Method according to Claim 1, characterized in that the nozzle element (6) has a chamber (13) into which the further component (5) to which gas (G) is added is introduced, wherein the means (12) for discharging the gas (G) are arranged on the chamber (13) and the gas (G) is discharged via said chamber.Method according to Claim 1 or 2, characterized in that the gas (G) is fed in at superatmospheric pressure.Method according to one of Claims 1 to 3, characterized in that the second flow path (9) ends in the region of the constriction (8), with the result that the further component (5) can be admixed with the chemical component (1, 2), wherein the flow rate of the chemical component (1, 2) to which the further component (5) is added is increased by the constriction (8) and a local reduced pressure is thus generated in the chemical component (1, 2), and wherein the further component (5) is fed to the chemical component (1, 2) in the region of the local reduced pressure.Method according to one of Claims 1 to 4, characterized in that the constriction (8) in the first flow path (7) is designed as an annular gap (8), and the further component (5) is fed concentrically downstream of the annular gap (8) in the direction of flow of the components (1, 2).Method according to Claim 5, characterized in that the further component (5) is fed in the direction of an axis (a) of the nozzle element (6) behind the annular gap (8).Method according to one of Claims 1 to 6, characterized in that the chemical component (1, 2) is accelerated to a speed of at least 20 m / s after flowing through the constriction (8).Method according to one of Claims 1 to 7, characterized in that the chemical components (1, 2) are mixed in the mixing chamber (3) by means of countercurrent injection.Method according to one of Claims 1 to 8, characterized in that the chemical components (1, 2) are injected into the mixing chamber (3) by means of nozzles.Method according to one of Claims 1 to 9, characterized in that the further component (5) is expandable graphite.Device for producing polyurethane components, in particular for carrying out the method according to one of Claims 1 to 10, comprising - at least one metering pump (14) for metering a chemical component in the form of a polyol component (1), - at least one metering pump (15) for metering a chemical component in the form of an isocyanate component (2), - a mixing head (4) having a mixing chamber (3) for mixing the polyol component (1) and the isocyanate component (2), - at least one container (10) for storing a further component (5), wherein a nozzle element (6) is arranged upstream of or on the mixing chamber (3), which nozzle element is designed for mixing the further component (5) with at least one of the chemical components (1), wherein the nozzle element (6) has a first flow path (7) for the chemical component (1), which has a constriction (8) and a second flow path (9) for the further component (5), characterized in that the second flow path (9) for the further component (5) ends in the region of the constriction (8), in that gas feed means (16) for feeding gas (G) into the container (10) for the further component (5) and / or into a flow path (11) for the further component (5) which extends from the container (10) to the nozzle element (6) are arranged, and in that means (12) for discharging the gas (G) are arranged on the nozzle element (6).Device according to claim 11, characterised in that the nozzle element (6) has a chamber (13) into which the further component (5) to which gas (G) is added can be introduced, wherein the means (12) for discharging the gas (G) are arranged on the chamber (13).Device according to claim 11 or 12, characterised in that the means (12) for discharging the gas (G) are designed such that they are permeable to gas (G) but are impermeable to solid or liquid constituents of the further component (5).Device according to claim 13, characterised in that the means (12) for discharging the gas (G) have openings and / or gaps of small dimensions, the diameter or inside width of which is less than 0.5 mm, preferably less than 0.25 mm.Device according to one of Claims 11 to 13, characterized in that an adjustable throttle (18) for adjusting the volume flow of gas (G) is arranged in a line (17) which is in fluidic connection with the means (12) for discharging the gas (G).Device according to one of Claims 11 to 15, characterized in that the constriction (8) in the first flow path (7) of the chemical component (1) is designed as an annular gap (8), and the second flow path (9) for the further component (5) ends behind the annular gap (8) in the flow direction of the component (1).Device according to claim 16, characterised in that the second flow path (9) for the further component (5) extends at least in sections in the direction of an axis (a) of the nozzle element (6).Device according to one of Claims 11 to 17, characterized in that the second flow path (9) for the further component (5) is formed at least in sections by a cylindrical opening (19), on which a piston-like, axially displaceable slide (20) is arranged, which is designed for entry into the opening (19) in order to close said opening.Device according to one of Claims 11 to 18, characterized in that the nozzle element (6) has a nozzle housing (21) and a nozzle needle (22) which is axially displaceable relative to the nozzle housing (21), it being possible for the constriction (8) to be formed between the one axial end of the nozzle needle (22) and the nozzle housing (21).Device according to claim 19, characterised in that means are arranged to influence the position of the nozzle needle (22) relative to the nozzle housing (21), wherein the means are in particular designed as electrical, hydraulic or pneumatic control and / or regulating means, or that spring means are arranged to generate a pressing force of the one axial end of the nozzle needle (22) against the nozzle housing (21), wherein the spring means are preferably designed as a mechanical spring or as a pneumatic spring.

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