GB2317848A - Process and apparatus for producing foamed material slabs - Google Patents

Abstract

A process for producing foamed material slabs comprises feeding a reaction mixture to a feed region 4 of a conveying device 3 by depositing the mixture substantially transversely to the direction of conveying 'f'. This forms a reaction segment 8 which is then acted upon over its entire width by blast air jets which move substantially transversely to the direction of conveying and which impinge on (deform) the reaction segment surface . The rection segment with the deformed surface 9a is then moved further in the direction of conveying where it undergoes a reverse deformation. The deformed reaction segment surface is thereby converted into a smooth surface 9b and inhomogeneities resulting from air bubble inclusions are removed at the same time. The reaction segment is subsequently introduced into a double belt apparatus 10 which moulds the reaction segment into the finished foam slab.

Description

A continuous process for producing foamed material slabs in sheet form and an apparatus for carrying out the process This invention relates to a continuous process for producing foamed material slabs in sheet form, particularly foamed material slabs laminated with flexible facings or metal sheets wherein a freeflowing, foam-forming initial reaction mixture is deposited in sheet form on a conveying device and is fed on the conveying device, as a reaction segment which is reacting and which at the same time is foaming, to the inlet end of a double belt apparatus and is removed from the outlet end of the double belt apparatus as a finished foamed material slab. The invention also relates to an apparatus for carrying out the process according to the invention. In the context of the present invention, the term "foamed material" means a material with a foam structure which is distinguished by open and/or closed cells distributed over the entire mass of the material. In particular, the term "foamed material" means foamed plastics which are produced from foamable organic polymers, preferably polyurethanes. Within the scope of producing these foamed plastics, the starting components which polymerise to form polymers are preferably treated with foaming agents which are released for foaming, as what is termed the cell gas, by volatilisation and chemical reaction, and which thereby produce the foam structure. In the context of the present invention, the term "initial reaction mixture" means that foaming has not yet occurred or has not yet occurred to a significant extent in this mixture. Within the scope of the process according to the invention, foaming of this initial reaction mixture first takes place in the reaction segment which is conveyed on the conveying device. During the conveying of the reaction segment on the conveying device, the thickness of the reaction segment thus increases as a result of foaming, and the height of rise thereof changes continuously. The final thickness of the finished foamed material slab is set in the double belt apparatus, and the cured, finished foamed material slab is removed at the outlet end of the double belt apparatus. In practice, foamed material slabs of this type are used for various purposes. The foamed material slabs produced within the scope of the process according to the invention are preferably used as thermal insulation panels.

In the process of the type cited at the outset and from which the present invention stems, the initial reaction mixture is fed on to a point feed location, as it were, in a region which is in the middle with respect to the width of the feeder device. The build-up of initial reaction mixture which is thereby formed in the middle of the conveying device has to be distributed towards both sides by jets of air emerging from blast nozzles and by sizing rolls or runners. With these known measures, the distributing effect leaves something to be desired, since the adjustment of the foam film thickness is relatively difficult and sensitive. Moreover, in this known process the edge zones are generally not accurately limited to the product width as a result of the bottom facing being set on edge. In practice, the edge zones are generally of irregular form, so that an increased amount of waste arises when they are subsequently trimmed. In addition, a process for uniformly distributing a free-flowing initial reaction mixture on a continuously conveyed substrate is known (EP 0 374 558 B1), in which the initial reaction mixture is likewise fed on to what is a point feed location, as it were, ofthe substrate and is distributed towards the sides of the substrate by means of an air current. Ventilator rolls are provided for this purpose. The diameter of these ventilating rolls decreases from the mixture feed location to the sides, and they are driven coupled together.

Moreover, a process for continuously producing foamed material slabs is known (DE-OS 29 24 183) which employs a sloping feed table which descends in the direction of conveying of the initial reaction mixture which is fed, wherein a transverse distributing device, particularly a roller arrangement, for the initial reaction mixture is provided above this feed table. Distribution of the initial reaction mixture over the conveying device is substantially accomplished by means of the transverse distributing device. A process is also known (DE-OS 32 41 520) in which the initial reaction mixture is fed on to the conveying device by a mixer head which can move to and fro transversely to the direction of conveying, and wherein it is claimed that a uniform distribution of the initial reaction mixture can be achieved by employing a delimiting element having an elastically deformable surface above the conveying device. Furthermore, a deposition apparatus is known for depositing polyurethane foam on a continuously moving facing (EP 0 553 695). This apparatus employs a plurality of discharge nozzles which are attached to a mixer head which can travel transversely to the direction of conveying.

In contrast, a basic object of the present invention is to provide a process of the type cited at the outset with which unwanted surface structures and regions of unevenness in the reaction segment surface and in the foamed material slab surface can be prevented, and with which a homogeneous foam structure or cell structure of the finished foamed material slab can be obtained.

According to a first aspect of the present invention, there is provided a continuous process for producing foamed material slabs in sheet form, wherein a free-flowing, foam-forming initial reaction mixture is deposited in sheet form on a conveying device and is fed on the conveying device and optionally on the bottom facing, as a reaction segment which is reacting and which at the same time is foaming, to the inlet end of a double belt apparatus and is removed from the outlet end of the double belt apparatus as a finished foamed material slab, wherein the initial reaction mixture is continuously fed substantially transversely to the direction of conveying in a feed region of the conveying device, wherein the reaction segment which is thereby formed comprises surface structures resulting from the feeding, wherein following this the reaction segment is acted upon over its entire width and substantially transversely to the direction of conveying by blast air jets which impinge on the reaction segment surface, with the proviso that the reaction segment surface is deformed by the action of the blast air and the reaction segment surface which is moved further in the direction of conveying undergoes a reverse deformation, wherein the surface-structured reaction segment surface is converted, particularly in the edge zones, into a smooth reaction segment surface and inhomogeneities in the reaction segment resulting from air bubble inclusions are removed at the same time, and wherein the reaction segment is subsequently adjusted exactly to the respective product width and is introduced into the double belt apparatus.

Within the scope of the process according to the invention, the foamed material slabs are preferably manufactured from polyurethane foam. During the feeding of the initial reaction mixture transversely to the direction of conveying, a feeder device, e.g. a casting rake, is moved to and fro over the width of the conveying device, and an oscillating movement, as it were, of this feeder device thus takes place over the width of the conveying device. This results in a striated surface structure of the reaction segment which is formed, which comprises transverse ribs which are formed substantially transversely to the direction of conveying. Moreover, edge accumulations of the initial reaction mixture occur at the edges of the conveying device, in the region of the points of reversal of the reciprocating feeder device, due to the longer dwell time of the feeder device in these regions. As a result, a reaction segment surface with a relatively pronounced surface structure is accordingly formed. Surprisingly, very good smoothing of the reaction segment surface can be achieved by to the action of blast air on the reaction segment surface according to the invention and by the deformation and reverse deformation of this surface which results therefrom. The transverse ribs and edge accumulations in the reaction segment surface which are produced by feeding the initial reaction mixture can thereby be practically completely levelled out. The deformation and reverse deformation of the surface which are associated with the action of the blast air act as an stirring effect, as it were, due to which the surface is intensively mixed throughout and the reaction mixture is distributed effectively. According to the invention, extensive smoothing of the surface can be achieved without the action of additional mechanical components, such as rolls, rollers or runners, on the surface, and the problems and constraints associated with these mechanical components, such as unwanted build-ups of the reaction segment for example, are also avoided. As a result, an unexpectedly smooth surface of the foamed material slab is obtained. This is primarily advantageous when the foamed material slab is laminated with a top and a bottom flexible facing, preferably of paper or aluminium foil, since no regions of unevenness on the product surface can be copied on to these facings. Moreover, due to the stirring effect described above, unwanted air bubble inclusions which occur during the feeding of the initial reaction mixture are removed or destroyed. This is particularly surprising, since one skilled in the art would expect that additional unwanted air bubble inclusions would be formed due to the action of the blast air. However, the blast air jets can be adjusted so that even when there is an intense action of blast air on the reaction segment surface no additional air bubbles are formed, but instead the already-existing unwanted air inclusions can be removed.

Moreover, what are termed travelling bubbles at the interface between the foam and the top facing can also be significantly reduced without using an upper roller. Ifan upper roller is used, travelling bubbles such as these can even be removed completely, so that a velvet-like skin, as it were, is formed on the top surface of the reaction segment. As a result, an improvement in the foam structure or cell structure of the foamed material slab is achieved due to the stirring effect described above. A further contribution is made here in that mixture zones of different states of reaction or foaming which are present in the reaction segment can also be intensively mixed throughout due to the stirring effect. An effective and continuous distribution of the reaction mixture thus occurs, both in the direction of conveying and in the transverse direction of the reaction segment. As a result, foamed material slabs are obtained by the process according to the invention which have a surprisingly smooth, flat surface and which also have a particularly good foam structure, particularly in the edge regions.

According to one embodiment of the invention, the reaction segment is provided with a top and a bottom facing and the finished foamed material slab accordingly has a top and a bottom facing also. These facings are advantageously flexible facings of paper or foil, preferably metal foils, which may also be profiled to a greater or lesser extent. The free-flowing initial reaction mixture is preferably deposited on a bottom facing which is entrained on the conveying device. The bottom facing is preferably continuously preheated in a preheating oven before it enters the feed region.

According to a preferred embodiment of the invention, the free-flowing initial reaction mixture is continuously fed in the feed region by a multiplicity of feed nozzles which are disposed in series substantially in the direction of conveying, wherein the multiplicity of feed nozzles is moved to and fro transversely to the direction of conveying. Within the scope of the invention, a casting rake is preferably provided as a feeder device for this purpose. This casting rake has a distributor pipe which is disposed substantially parallel to the direction of conveying, which is attached to a mixer head for the initial reaction mixture, and on which the multiplicity of feed nozzles which are disposed in series in the direction of conveying is provided. A casting rake of this type constitutes a nozzle unit which operates reliably and which is simple to manipulate. In principle, however, other nozzle units such as fan and film nozzles can also be used. It is essential that the liquid foam mixture is deposited in a sufficiently sheet-like form. The feed nozzles may also be provided in two or more mutually parallel rows on the distributor pipe, or in two rows which are displaced by a defined angle in relation to each other. As has already been mentioned above, during the feeding of the initial reaction mixture the feeder device executes an oscillating movement substantially transversely to the direction of conveying. The frequency of oscillation of this oscillating movement is preferably adjustable.

According to a preferred embodiment of the process according to the invention, which is particularly important within the scope of the invention, the free-flowing initial reaction mixture is fed continuously in a feed region which rises in the direction of conveying. It should be understood that the feed region is disposed directly underneath the feeder device. The rising feed region forms a run-off slope, as it were, for the initial reaction mixture which is fed in striated form, so that the striations can flow into one another, as it were, over the run-off slope, and the result is thus an effective preliminary distribution of the reaction mixture, and moreover mixture zones of different states of reaction are mixed with each other. In this manner, the transverse rib structure of the reaction segment surface which results from the feeding thereof is already partially levelled out in the feed region. In this connection, the combination of the rising feed region on the one hand and the action of blast air according to the invention on the other hand assumes a particular importance within the scope of the invention, not least, moreover, because the bottom facing is pulled flat by a roller deflection. The angle of inclination of the rising feed region is advantageously adjustable in relation to the direction of conveying, and amounts to 2 to 50 for example.

The action of the blast air on the reaction segment surface preferably takes place directly behind the feed region in the direction of conveying. The blast air is directed on to the reaction segment surface in the form of defined, spike-like air jets which are sharply focused, as it were, which defined air jets each produce separate deformations in the reaction segment surface. Within the scope of the process according to the invention, a blowing apparatus is employed which comprises at least one blast air distributor pipe, which has a multiplicity of blast air nozzles and which is disposed substantially normal to the direction of conveying and extends over the entire width of the reaction segment. The blast air nozzles are preferably disposed linearly in a row, with substantially the same blast air nozzle spacing. The blast air nozzle spacing is advantageously 5 to 40 mm. The blast air nozzle diameter is 1 mm to 3 mm, depending on the viscosity, surface tension, amount of feed and rate of throughput of the film of foam mixture. It also falls within the scope of the invention for the blast air nozzles in the blast air distributor pipe to be offset in relation to each other in a linear double or triple row. The spacing between the blast air nozzles in the region of the edge zones of the reaction segment is preferably less than or greater than the spacing in the other sections of the blast air distributor pipe. The blast air distributor pipe is advantageously disposed above the conveying device so that the vertical distance between the blast air nozzles and the reaction segment surface is 8 to 30 mm, preferably 18 to 20 mm. The vertical distance between the blast air distributor pipe and the conveying device is preferably continuously adjustable. Within the scope of the invention, dry blast air at room temperature can be blown on to the reaction segment. However, it also falls within the scope of the invention to preheat or even to cool the blast air, depending on the reaction behaviour of the foam system and on the ambient temperature in the production shop. Providing the blast air at a controlled temperature does not result in any impairment of the uniform foam structure or cell structure of the foamed material slab. The mass flow of blast air and the blast air pressure are set according to the type of initial reaction mixture used and on the thickness of the reaction segment. The blast air preferably emerges from the blast air nozzles at a blast air pressure of 3 to 6 bar.

According to a preferred embodiment of the invention, the reaction segment is acted upon by blast air jets which impinge substantially vertically on the reaction segment surface. If a fixed blast air distributor pipe is employed in this embodiment, the mass flow of blast air emerging from the blast air nozzles and the blast air pressure are set so that craters are formed in the reaction segment surface at the place of impingement of the blast air jets, which craters can be described as "air indents" and which undergo a reverse deformation as the reaction segment is conveyed further.

In this manner, effective mixing of the reaction mixture throughout and smoothing of the reaction segment surface are achieved. According to a preferred embodiment of the invention, the process is conducted so that the blast air jets are produced by blast air nozzles which oscillate transversely to the direction of conveying. For this purpose, the blast air distributor pipe is advantageously designed so that it can oscillate transversely to the direction of conveying. The frequency of oscillation is preferably 10 to 50 Hz, depending on the physical properties of the foam mixture and on the production rate. The oscillation amplitude is advantageously 5 to 15 mm, preferably 5 to 35 mm. The term "oscillation amplitude" means the maximum excursion, transverse to the direction of conveying, of the blast air distributor pipe from its rest position.

According to a preferred embodiment of the process according to the invention, the reaction segment is acted upon by blast air jets which impinge obliquely on the reaction segment surface in the direction of conveying or opposite thereto, or it is acted upon by blast air jets which impinge vertically. The relative blowing angle between the blast air nozzles which are set obliquely, or the blast air jets which emerge obliquely, and the vertical setting of the blast air nozzles, or ofthe blast air jets, is preferably plus or minus 10" to 15 Within the scope ofthe process according to the invention, a blast air distributor pipe is preferably employed for this purpose with which different relative blowing angles can be set. Due to the oblique impingement of the blast air jets on the reaction segment surface, a standing wave, as it were, is formed on the reaction segment surface, and contributes to the very effective distribution and mixing throughout of the reaction mixture. However, depending on the nozzle spacing and the amount of air, and on the foam formulation and the production rate, a standing wave such as this can also be produced when vertically aligned air jets and a fixed air grid or blast air distributor pipe are used. In any event, the reaction segment subsequently undergoes a reverse deformation. The smoothing of the reaction segment surface is optimised in this manner. Due to the standing wave in particular, unwanted air bubble inclusions are also held back and destroyed. This applies in particular when a double- or triple-row air grid or blast air distributor pipe is employed. It should be understood that the action of the blast air is adjusted so that the reaction mixture is not held back and banked up to such an extent that the onset of complete reaction has already occurred. Types of air grids which are suitable in each case are used for different production conditions (foam system, product density and production rate). The amount and velocity of the air can be adjusted without difficulty so that the individual craters or "air indents" have as much basal contact as possible, without foam splashes being formed or a standing wave which is too pronounced being formed and the material thereby being excessively banked up.

An embodiment which is particularly important within the scope of the invention is one in which the blast air jets are produced by blast air nozzles which oscillate transversely to the direction of conveying. For this purpose, the blast air distributor pipe or air grid concerned is designed so that it can oscillate transversely to the direction of conveying. When using an oscillating blast air distributor pipe, considerably greater amounts of air can be conveyed than when using a stationary blast air distributor pipe. The oscillation stroke is preferably somewhat greater than the spacing between the blast air nozzles. The frequency can be adjusted so that, irrespective of the spacing between the blast air nozzles, an excessive pile-up does not occur if the material is displaced laterally to a sufficient extent. The diameters of the blast air nozzles are preferably sized and matched to each other so that when the blast air distributor pipe is stationary and there is basal contact between the "air indents" the crater edges almost touch each other. The distance of the blast air distributor pipe from the reaction segment or the bottom facing thereof is advantageously selected so that no foam splashes occur under the conditions discussed above. Moreover, a multirow blast air distributor pipe satisfactorily removes any small air bubbles which may possibly be present on the foam surface, and accomplishes this better than a single-row blast air distributor pipe. In order to achieve an optimum setting, the distance of the blast air distributor pipe from the bottom facing or from the reaction segment, the amount of air, and the oscillation stroke and frequency, are continuously adjustable.

Moreover, it falls within the scope ofthe invention for the blast air distributor pipe to be provided with blast air nozzles distributed over its circumference, and for this blast air distributor pipe to be rotated about its longitudinal axis. The blast air nozzles here are preferably disposed helically on the blast air distributor pipe. It also falls within the scope of the invention to provide a multiplicity of blast air distributor pipes which are distributed over the width of the reaction segment and which preferably rotate about their longitudinal axes.

According to the teaching ofthe invention, separate air grids or air distributor nozzles, which are vertically and horizontally adjustable and which can swivel horizontally, are provided in the edge region of the reaction segment, so as to be able satisfactorily to level out edge accumulations which occur in the edge region of the reaction segment. Moreover, the use of blast tubes and sheet nozzles is not ruled out. Outstanding results are obtained with short air grids, because not only can edge accumulations be levelled out completely with air grids such as these, but a precise width of feed with a straight edge formation can also be achieved at the same time. Furthermore, it is possible to correct, by means ofthe casting rake, any "serrated edges" which may be formed.

One skilled in the art can determine, within the scope of simple tests, the manner in which the number of blast air nozzles, the blast air nozzle spacing and the blast air nozzle diameter, as well as the mass flow of blast air and optionally the frequency of oscillation and the amplitude of oscillation of the blast air distributor pipe are to be set, depending on the type, the amount and the properties of the initial reaction mixture which is to be fed, in order to achieve the optimum smoothing effect and the effective destruction of air bubbles. In this connection, however, reference is also made to the examples of embodiments which are described in detail below.

According to a preferred embodiment which falls within the scope of the process according to the invention, a top facing is applied to the reaction segment, in front of the double belt apparatus in the direction of conveying, via a height-adjustable deflection roller disposed in front of the double belt apparatus. The term "height-adjustable" means that the vertical distance of this deflection roller from the reaction segment or from the conveying device is adjustable, and in fact can be adjusted depending on the foaming behaviour of the reaction mixture and thus depending on the thickness of the reaction segment. The process is preferably conducted so that the reaction segment reaches the top facing conveyed on the deflection roller at 50 % to 75 % of its final height of rise. The flexible top facing is then entrained on the reaction segment lying on the rising foam and following the angle of inclination of the foam. The reaction segment advantageously reaches its final height of rise as it enters the double belt apparatus. This embodiment has the advantage that no additional measures are necessary in order to stabilise the top facing, e.g. by holding-down devices acting on the facing. The immersion of the upper roller or upper deflection roller at 50 % to 75 % of the height of rise has a decisive effect. The distance of the upper roller or deflection roller from the double belt inlet then follows automatically, depending on the reaction times of the foam mixture and on the production rate. Depending on the distance from the double belt apparatus, stabilising measures for the top facing are then possibly required.

According to the invention, the deflection roller for the top facing, in combination with the measures described above for smoothing, gives rise to an additional effective smoothing effect with respect to the reaction segment surface. In particular, residual air bubble inclusions which are still present in the reaction segment, and air inclusions which arise due to the bow wave of the rising foam on the top facing, which bow wave is otherwise customary and which results from transverse fold formation, are removed in an operationally reliable manner.

According to a second aspect of the invention, there is provided an apparatus for carrying out the process in accordance with the first aspect, comprising a feeder device for feeding the free-flowing initial reaction mixture, a conveying device having a feed region for the initial reaction mixture, a blowing apparatus for the action of blast air jets on the reaction segment which is conveyed on the conveying device, a double belt apparatus for pressing the finished foamed material slab, wherein the feeder device comprises a multiplicity of feed nozzles which are disposed in series substantially in the direction of conveying, wherein the feeder device with the multiplicity of feed nozzles is designed so that it can move to and fro transversely to the direction of conveying.

Preferred embodiments of this apparatus according to the invention are claimed in claims 6 and 7.

The process according to the invention is explained below with reference to an apparatus for carrying out the process and to schematic illustrations thereof, where: Figure 1 is a side view of an apparatus for carrying out the process according to the invention; Figure 2 shows another embodiment of the subject of Figure 1; Figure 3 shows area A from Figure 1 on an enlarged scale; Figure 4 is a plan view of the subject of Figure 3 in the direction of arrow B; Figure 5 shows area C from Figure 3 on an enlarged scale; Figure 6 is a plan view of the subject of Figure 5 in the direction of arrow D; Figure 7 shows another embodiment ofthe subject of Figure 6; Figure 8 is a view of the subject of Figure 7 in the direction of arrow E; Figure 9 shows another embodiment of the subject of Figure 5; and Figure 10 is a plan view of the subject of Figure 9.

Figures 1 and 2 illustrate an apparatus for carrying out the process according to the invention for producing foamed material slabs. The apparatus comprises a feeder device 1 for feeding a freeflowing, foam-forming initial reaction mixture 2 in sheet form on to a conveying device 3 in a feed region 4 of said conveying device 3. The feeder device 2 has a distributor pipe 6 attached to a mixer head 5 for the initial reaction mixture 2, on which distributor pipe 6 a multiplicity of feed nozzles 7 is provided, which are disposed in series in the direction of conveying (Figure 3). The feeder device 1 with the multiplicity of feed nozzles 7 is designed so that it can move to and fro transversely to the direction of conveying f, so that the initial reaction mixture 2 is continuously fed substantially transversely to the direction of conveying fin the feed region 4. This oscillating movement air and the reaction segment surface 9 which is moved further in the direction of conveying f subsequently undergoes a reverse deformation. The surface-structured reaction segment surface 9, which comprises transverse ribs, is thereby converted into a smooth reaction segment surface 9, and inhomogeneities in the reaction segment 8 resulting from air bubble inclusions are removed at the same time. The embodiments of the action of blast air according to the invention are explained in more detail below in connection with Figures 5 to 10.

According to a preferred embodiment of the invention, and in the embodiment exemplified, the conveying device 3 has a feed region 4 which rises in the direction of conveying f, in which the initial reaction mixture 2 is continuously fed (Figure 3). In this rising feed region 4, the initial reaction mixture 2 which is fed in striated form can flow back, as it were, as indicated in Figure 3, so that a preliminary levelling-out can already occur ofthe transverse rib structure which results from the feeding. The angle of inclination of the feed region 4 is preferably adjustable, as in the embodiment exemplified. Moreover, the vertical distance of the distributor pipe 6 from the feed region 4 is advantageously designed so that is adjustable, as in the embodiment exemplified. This is indicated in Figure 3 by a double arrow. In addition, the angular setting of the distributor pipe 6 is preferably designed so that it is adjustable vertically in relation to the conveying device, as in the embodiment exemplified. This is likewise indicated in Figure 3 by a double arrow.

According to a preferred embodiment of the invention, and in the embodiment exemplified, the reaction segment 8, and thus the finished foamed material slab also, is covered by a bottom facing 15 ad a top facing 16. These are flexible facings in the form of metal foil. In principle, the reaction segment 8 itself can also form the bottom facing. The two facings 15, 16 are preheated in a preheating oven 17 before they come into contact with the reaction segment 8. The initial reaction mixture 2 is preferably deposited on the bottom facing 15 which is entrained on the conveying device 3 or as the conveying device, as in the embodiment exemplified. In the embodiment which is illustrated in Figures 1 and 2, the initial reaction mixture 2 and the reaction segment 8 are conveyed by the bottom facing, which is guided via suitable rollers or rolls. The bottom facing 15 here is therefore a component of the conveying device 3. The top facing 16 is preferably deposited on the reaction segment, in front ofthe double belt apparatus 10, via a height-adjustable deflection roller 18 disposed in front ofthe double belt apparatus 10, as in the embodiment exemplified. The process is advantageously conducted as in the embodiment shown in Figures 1 and 2, so that the reaction segment 8 reaches the top facing 16, which is conveyed on the deflection roller 18, at about 50 % to 75 % of its final height. According to a preferred embodiment, and as shown in Figure 1, the deflection roller 18 is disposed in front of the double belt apparatus at a distance with respect to 50 % to 75 % of the height of rise which results from the reaction behaviour of the foam system and from the production rate. The stabilising elements which may possibly be necessary are denoted in Figure 2 by reference numeral 19. The reaction segment has advantageously reached its final height of rise as it enters the double belt apparatus, as in examples 1 and 2. At the same time, the top facing is preferably just pressed flat against the upper belt of the double belt apparatus.

As indicated in Figure 4, the reaction segment surface 9a, which is structured due to the feeding conditions and comprises a transverse ribbed profile, is converted into a smooth reaction segment surface 9b by the blowing apparatus 11 and the action of the blast air. In addition, the edge accumulations 20 of the initial reaction mixture 2 which result from the feed conditions are levelled out by the action of the blast air, as is also indicated in Figure 4. However, additional blast air distributors 21 can also be provided in the region of the edge accumulations 20, as illustrated in Figure 4. It also falls within the scope of the invention for the blast air distributor pipe 13 to be provided with blast air distributor pipe sections 22, as indicated by the dashed lines in Figure 4, in the region of the edge accumulations 20 and parallel to the direction of conveying, and preferably angled in the direction of conveying. The edge accumulations 20 can be levelled out very effectively and in an operationally reliable manner by these additional measures. According to a preferred embodiment of the invention, and in the embodiment shown in Figures 5 and 6, the reaction segment 8 is acted upon by blast air which impinges on the reaction segment surface 9 substantially vertically. Craters 23 are formed here as deformations of the reaction segment surface 9, due to which the reaction mixture of the reaction segment surface 9 is distributed particularly effectively, as indicated by arrows in Figures 5 and 6. Figure 5 also shows the reaction segment surface 9b which is conveyed further downstream of the cavity in the direction of conveying, and which is subjected to reverse deformation and is smoothed. As a result, thorough mixing and distribution of the reaction mixture is achieved, and both an effective smoothing of the reaction segment surface 9 and the removal of unwanted air bubble inclusions 28 are effected, as indicated in Figure 5. This effect can be intensified even further if the blast air jets which act vertically on the reaction segment surface 9 are produced by blast air nozzles 14 which oscillate transversely to the direction of conveying. For this purpose, the blast air distributor pipe 13 is designed so that it can oscillate or move to and fro substantially normal to the direction of conveying f, as indicated by a double arrow in Figure 4. However, the blowing apparatus can also be moved periodically on an oval or circular path above the reaction segment 8 for this purpose.

The result of this embodiment of the action of blast air is illustrated in Figures 7 and 8. At the points of reversal of the oscillation or to and fro movement of the individual blast air nozzles 14, the craters 23 are formed in the reaction segment surface 9, which craters 23 are joined by connecting channels 24 as a result of the oscillation of the blast air distributor pipe 13. The thorough mixing, distribution and stirring effects which were described above are effectively intensified due to this oscillation.

According to a further preferred embodiment of the invention, which is particularly important within the scope ofthe invention, the reaction segment 8 is acted upon by blast air jets 12 which impinge obliquely on the reaction segment surface 9 in a direction opposite to the direction of conveying f This gives rise to a standing wave 25 on the initial reaction mixture 2 transverse to the direction of conveying, wherein the associated wave crests 26 are formed in front of the impinging blast airjets 12 (Figure 9, Figure 10). Very effective distribution and thorough mixing ofthe initial reaction mixture are obtained due to this standing wave, as indicated in Figure 9 by arrows within the reaction segment 8. Unwanted air bubble inclusions 28 generally burst at the wave crest, particularly when an air rake or blast air distributor pipe 13 is used which has two or three rows of blast air nozzles 14. The smoothed reaction segment surface 9b which has undergone reverse deformation can be seen behind the standing wave 25 in the direction of conveying fin Figure 9. According to a preferred embodiment, and in the embodiment shown in Figure 9, the blast air nozzles 14 are additionally equipped with extension tubes 27 which convey the blast air jets directly on to the reaction segment surface 9. Air turbulence effects at the reaction segment surface 9 are thereby prevented. According to a preferred embodiment of the invention, the blast air jets 12 are also produced by blast air nozzles 14 which oscillate transversely to the direction of conveying when the reaction segment surface 9 is acted upon obliquely by the blast air, for which purpose the blast air distributor pipe 13 oscillates transversely to the direction of conveying fat a predetermined frequency of oscillation. In this embodiment, the wave crests 26 ofthe standing waves 25 are formed at the points of reversal of the oscillating movement of the individual blast air nozzles 14. This embodiment, which is quite particularly important within the scope of the invention, is distinguished by the optimum results as regards the smoothing of the reaction segment surface and as regards the removal of deleterious air bubble inclusions 28.

The process according to the invention is explained in more detail below with reference to examples of embodiments: Example 1 A finished foamed material slab with a thickness of 30 mm was produced by the continuous process according to the invention, which foamed material slab was laminated with a bottom and top facing made of a length of paper. The process according to the invention was carried out using an apparatus as shown in Figure 1. The bottom facing was fed to the double belt apparatus.

The initial reaction mixture was fed by a feeder device comprising a mixer head and a distributor pipe attached thereto parallel to the direction of conveying, in a feed region ascending at 5. The initial reaction mixture consisted of customary starting material components, which are known to one skilled in the art, for producing a polyurethane foamed material. The setting time of the initial reaction mixture was 29 seconds. Feed nozzles with a feed nozzle diameter of 1.4 mm were disposed on the distributor pipe at a spacing of 5 mm. The distributor pipe was moved to and fro transversely to the direction of conveying, and a reaction segment with a width of 1250 mm was formed in the feed region. The speed of conveying of the reaction segment was 7 m/minute. In the feed region and directly behind the feed region, the reaction segment had a surface with a relatively pronounced structure, in which transverse ribs were formed on the reaction segment surface due to the feed conditions in particular. A blast air distributor pipe with a length of 1250 mm was disposed above the conveying device, normal to the direction of conveying, at a distance of about 350 mm behind the distributor pipe in the direction of conveying. The thickness of the reaction segment at the location of the blast air distributor pipe was about 1.5 mm. The blast air distributor pipe had 128 blast air nozzles at a spacing of 10 mm, which were arranged linearly in one row in the blast air distributor pipe and which had a blast air nozzle orifice diameter of 1.2 mm. The blast air nozzles and the blast air distributor pipe were aligned vertically. The total mass flow of blast air was about 850 Minute. The blast air nozzles were disposed at a distance of 15 mm above the reaction segment surface. Furthermore, additional air grids or blast air distributors were disposed in the edge regions of the reaction segment, and were vertically and horizontally adjustable and could swivel vertically. The blast air distributor pipe was moved to and fro transversely to the direction of conveying at a frequency of oscillation of 23 Hz, and with a maximum excursion (oscillation amplitude) of 20 mm. A standing wave was observed transverse to the direction of conveying in the reaction mixture at the place of action of the blast air, and the wave crests of this standing wave were formed on the reaction segment surface directly in front of the points of impingement of the individual blast air nozzles. A deflection roller for depositing the top facing on the reaction segment was disposed in front of the double belt apparatus, which deflection roller was at a distance of 1450 mm from the distributor pipe of the feeder device and was disposed at a height of about 25 mm above the bottom facing. The reaction segment reached the deflection roller at about 75 % of its height of rise, i.e. at 75 % of the thickness of the completely reacted reaction segment, and about 5 seconds before its setting time had elapsed.

Example 2 A foamed material slab with a thickness of 60 mm, which had a top and bottom facing of aluminium foil, was produced by the process according to the invention The process was conducted substantially as in Example 1, except that the speed of conveying of the reaction segment on the conveying device was 5.5 m/minute. In addition, the blast air nozzles in the blast air distributor pipe were at a nozzle spacing of 5 mm and the blast air was directed on to the reaction segment surface at a mass flow of 1150 1/mien.

The finished foamed material slabs which were removed from the outlet end of the double belt apparatus in examples 1 and 2 had a surprisingly smooth surface, and no deleterious regions of unevenness could be ascertained in the top facing. When the foamed material slabs were cut at various places, a very homogeneous foam structure was ascertained, and no unwanted air bubble inclusions could be identified therein.

As a result, a better distribution, surface smoothing and reduction of bubbles are achieved by the blast air distributor pipe and the air grid when the liquid foam mixture is deposited in front of the double belt inlet. The edge accumulation produced by the deposition of the foam can be levelled out, particularly for thin foamed material slabs, by the use in addition of short, adjustable air grids in the edge region ofthe reaction segment. Moreover, the outside edges of the reaction segment or foam segment can be pulled straight and can be accurately adjusted to the lateral limit. An improved cell structure in the edge region is thereby obtained also, a reduced width of trimming is required and less waste is produced. Even travelling bubbles at the top facing can be reduced by the blast air distributor pipe, and these can even be completely removed by means of the upper roller or deflection roller which is used in addition.

Claims (11)

1. A continuous process for producing foamed material slabs in sheet form, particularly foamed material slabs laminated with facings, wherein a free-flowing, foam-forming initial reaction mixture is deposited in sheet form on a conveying device and is fed on the conveying device, as a reaction segment which is reacting and which at the same time is foaming, to the inlet end of a double belt apparatus and is removed from the outlet end of the double belt apparatus as a finished foamed material slab, wherein the initial reaction mixture is continuously fed substantially transversely to the direction of conveying in a feed region of the conveying device, wherein the reaction segment which is thereby formed comprises surface structures resulting from the feeding, wherein following this the reaction segment is acted upon over its entire width and substantially transversely to the direction of conveying by blast air jets which impinge on the reaction segment surface, with the proviso that the reaction segment surface is deformed by the action of the blast air and the reaction segment surface which is moved further in the direction of conveying undergoes a reverse deformation, wherein the surface-structured reaction segment surface is converted into a smooth reaction segment surface and inhomogeneities in the reaction segment resulting from air bubble inclusions are removed at the same time, and wherein the reaction segment is subsequently introduced into the double belt apparatus.

2. A process according to claim 1, wherein the free-flowing initial reaction mixture is fed continuously and in an oscillating manner over the width of the reaction segment in a feed region which rises in the direction of conveying.

3. A process according to either one of claims 1 or 2, wherein the blast air jets are produced by blast air nozzles oscillating transversely to the direction of conveying.

4. A process according to any one of claims 1 to 3, wherein a top facing is deposited on the reaction segment at 50 % to 75 % of the height of rise of the latter, in front of the double belt apparatus in the direction of conveying, via a height-adjustable deflection roller disposed in front of the double belt apparatus.

5. An apparatus for carrying out the process according to any one of claims 1 to 4, having a feeder device for feeding the free-flowing initial reaction mixture, a conveying device having a feed region for the initial reaction mixture, a blowing apparatus for the action of blast air jets on the reaction segment which is conveyed on the conveying device, a double belt apparatus for pressing the finished foamed material slab, wherein the feeder device comprises a multiplicity of feed nozzles which are disposed in series substantially in the direction of conveying, wherein the feeder device with the multiplicity of feed nozzles is designed so that it can move to and fro transversely to the direction of conveying, wherein the blowing apparatus comprises a multiplicity of blast air nozzles disposed transversely to the direction of conveying, wherein the blast air nozzles are aligned so that the reaction segment surface can be acted upon by blast air jets over the width of the reaction segment.

6. An apparatus according to claim 5, wherein the conveying device has a feed region which rises in the direction of conveying.

7. An apparatus according to either one of claims 5 or 6, wherein the blowing apparatus is designed so that it can oscillate transversely to the direction of conveying.

8. An apparatus according to any one of claims 5 to 7, characterised in that the amount of air, the oscillation stroke, the frequency, and the distance of the blowing apparatus (11) from the reaction segment are continuously adjustable.

9. An apparatus according to any one of claims 5 to 8, characterised in that the blast air distributor pipe (13) comprises one or more rows of blast air nozzles and the blast air nozzles (14) are disposed vertically or at a predetermined angle up to 30 in or opposite to the direction of conveying or production.

10. An apparatus according to any one of claims 5 to 9, characterised in that blast air distributors (21), e.g. air grids, air distributor nozzles or the like, are disposed in the edge regions of the reaction segment (8), and are horizontally and vertically adjustable and can swivel in a horizontal plane.

11. An apparatus for carrying out the process of any one of Claims 1 to 4, substantially as hereinbefore described, with reference to the accompanying drawings.