SE452868B - Reinforced plastic semi-mfd. prod. mfr. - Google Patents

Abstract

Continuous manufacture of reinforced plastics in semi-finished condition, the laminate thus produced and the plant used. The method involves conveyor belts onto which a thixotropic gel coat of unreinforced plastic is deposited by an extruder. One or more layers of thixotropic reinforced plastic are then added in stations along the conveyor, and then a final layer is deposited on a smooth surface to form the gel coat of the other side. The reinforced core contains at least one tier of cellulose or foam plastic, not in polymerized or foamed condition but with a foaming agent added for the subsequent curing. At least one layer of a water emitting thermosetting resin is included together with plaster of Paris in proportion to absorb the water given off during the setting. On completion the semi-finished laminate is wrapped in plastic foil with the air evacuated to make a rigid prod.

Description

4s2fs6s plastic and reinforcement must be handled simultaneously. In particular, the handling of reinforcement in the form of carpets and weaves is time-consuming and cumbersome because this cannot be done with simple mechanical methods but must be done by hand or by means of robots.

In order to reduce the aforementioned disadvantages, products have been developed in the form of semi-finished products where plastic in a curable but non-self-curing form is combined with a reinforcement. Such materials are laid out in suitable shapes cut out over the surface, for example a mold surface, to be clad. A cohesive layer can be formed by overlapping the pieces. After cladding, the plastic hardens and encloses the reinforcement so that the cohesive hard plastic construction is obtained. However, these semi-finished products marketed to date have had some disadvantages. They have not been possible to cure to thick layers and have not been able to give constructions with a smooth and / or colorable surface. Nor has it been possible to give these materials varying density and thickness. These previously known semi-finished products have therefore only been used in simpler constructions where the requirements for appearance and strength have been small.

The object of the present invention is to provide a rational process for the manufacture of reinforced plastic, which can also be used in constructions where the requirements are large with regard to smooth surfaces, coloring possibilities, integrated (a cross-section varying) density and a requirement corresponding to high requirements. strength.

A further object of the invention is to provide a semi-finished product with the above-mentioned properties and produced by the process.

It is also an object to provide a plant for carrying out the process; The object of the invention is achieved by carrying out the method according to the features stated in claim 1 or carrying out the semi-finished product with the features specified in claim 8 and carrying out the plant with the features specified in claim 14.

The accompanying drawings show a plant for the production of the semi-finished product and also the semi-finished product itself, whereby the process and the semi-finished product are described in connection with a description of the plant. Fig. 1 shows a schematic view of the 452 868 plant; and Fig. 2 shows a section through a semi-finished product in one embodiment.

Fig. 1 shows the plant and it consists according to the figure of a conveyor track 1 in the form of endless belts 2, 3, the upper transport parts of which run from left to right in Fig. 1. At the beginning end of the track is located a tank 4 for a preferably thickened plastic mass with unreinforced viscosity above 1000 cp, which is to form a yoke layer on the manufactured product, a so-called gelcoat consisting of e.g. an unsaturated ester plastic thickened with magnesium hydroxide.

Through this or other additives, thixotropy of the gelcoat can be achieved, which means an advantageously high viscosity in the applied condition but still good flowability during the application.

This thickened gelcoat can be extruded, whereby the viscosity is reduced by the processing, after which the previously high viscosity is regained faster than by the chemical maturation process of the liquid plastic, which is only used today. Gelcoat can be thickened in containers outside the manufacturing process where it is then used. The mass from the tank 4 is conveyed to an extruder 5, which is arranged to deposit a layer of the plastic mass on the conveyor web 1 during its movement to form said surface layer. The conveyor belts 2, 3 of the conveyor belt are designed to form a smooth surface for the layer. The band can e.g. be made of reinforced chloroprene rubber.

In a next station, a surface reinforcement 7 is laid down from a roll 6 in the extruded layer and pressed into it by means of a roller 8. The surface reinforcement must be open and permeable, so that the later applied plastic layer is connected to the gelcoat which is on belt 2. A suitable material is a sparse fiberglass fabric. An additional tank 9 is provided for the plastic mass which is to form the load-bearing part of the semi-finished product inside the said surface layer. The plastic mass can be unsaturated polyester and it is compact and free of gas inclusions. Like the gel coat, it is not self-curing but of such a nature that it can be cured by physical means. impact. Also this plastic mass, which is then reinforced (see below), is thickened and extruded in the same way as the gelcoat here by means of an extruder 10, which has the advantage that the thickening process goes faster here too, 4521868 Med 13 denotes a roll with reinforcement 14, which is passed down towards the plastic layer applied by means of the extruder 10. The reinforcement layer in the form of e.g. fabric, mat or rowing is pressed down into the plastic layer by means of rollers 15. Also connected to a tank 12 is at the next station on the transport path 1 a spray device 17 for plastic mass.

In the spray device 17, glass fiber can be supplied to the plastic mass, so that a reinforced composition can be sprayed out. In addition to the plastic mass, such a composition contains reinforcing fibers of such a short length that the composition becomes sprayable. The spraying device 17 is followed by a station for the application of additional reinforcement. The station consists of a roller 18 for the reinforcing material and rollers 19 for pressing the same into the applied plastic mass.

In a subsequent station, a plastic layer can be applied which constitutes a core material of low density. A suitable material is foam plastic or cellular plastic in already foamed form from a roll 21 or application in sheet form. Rollers 22 are arranged to press the layer into the underlying mass. Alternatively, a thin layer of non-foamed plastic mass in non-polymerized form can be applied from a tank 23 by means of a nozzle 24. The plastic mass, which is to form the foam or cellular plastic at a later stage, is for this purpose added with blowing agent or otherwise arranged to ferment under the influence of heat.

This station is followed by a station for laying stretched reinforcing fibers in the plastic mass, a so-called fiber harp 25. In this, dry fibers of varying lengths are fed which are laid down in any orientation and parallel to each other into one or more layers. The fiber harp 25 is followed by a further spraying device 27 of the same type as the spraying device 17. This is followed by another station for laying down reinforcement from a roller 28 and with rollers 29 for leveling the applied reinforcement layer (compare stations 13, 15).

In the next station, thickened plastic mass is applied from a tank 30 by means of an extruder 31 in the same way as in the station 9, 10.

This is followed by laying an additional surface fabric 32 from a roll 33 by means of rollers 34. Compare stations 13-15.

Next, after the conveyor track 1, a degassing station 35 is placed. It consists of a hood 36 which forms a chamber over the material on the conveyor track. The chamber is connected by means of a line 37 to a vacuum pump, so that negative pressure is formed in the chamber.

After the degassing station 35, the conveyor belt 2 merges into the second conveyor belt 3. In its entirety, the conveyor track 1 is thus divided in that it is formed with two endless loops of conveyor belts which meet at a breaking roller 39 for the belt 2 and a breaking roller 41 for the belt Release from the belt 2 of the highly viscous gelcoat layer can be facilitated by a tensioned wire or belt 40, which abuts the belt 2 where it bends over its end roll.

Between the two conveyor belts, 2, 3 running over the rollers 39, 41, there is a narrow gap through which a plastic foil 42 is passed from a roller 43. In the gap there can be a soft roller 44 which abuts against both endless belts. This plastic foil will thus be fed onto the subsequent conveyor belt 3 in connection with the transfer of the web of material formed in the previous stations. In this case, the plastic foil will settle closest to the conveyor belt and thus form a base for the material web.

Above the conveyor belt 3 after the breaking roller 41 is placed a second conveyor track 45, the upper belt path of which is opposite the first conveyor belt and the lower belt part thus runs in the same direction as the opposite conveyor belt 3. Next to the conveyor belt 45, above it is arranged a station for plastic foil from a roll 46 and it will form the upper cover of the semi-finished product. The plastic foil is held against the conveyor track 45 by means of a soft roller 47.

What now remains to form a complete semi-finished product, which gives a smooth, colorable surface on both sides, is the addition of an additional surface layer. This surface layer is first formed on the surface of the plastic foil on the conveyor belt 45 and is then laid down on the web of material conveyed on the conveyor belt 3. Thickened plastic mass, gel-coat, from a tank 48 is passed by means of a line to an extruder 49, which is arranged to deposit a layer of the plastic mass on the plastic foil during its movement to form said surface layer. The material webs are joined between the conveyor belt 45 and the conveyor belt 3.

The material web, after production if all stations have been used, consists of at least one plastic foil and then a surface layer of thickened plastic mass with a surface fabric followed by layers of plastic mass supplied with reinforcement, whereby the reinforcement can consist of 452 868 several layers and of different types of reinforcement. Manufacture with different types of reinforcement forms is possible by inserting the corresponding, described stations in a suitable selection. In some product forms there is also the mentioned layer of core material in cellular or foam form, which enables lower density of products manufactured in the semi-finished product. A complete semi-finished product, which can give a smooth, colored surface on both sides, has a surface layer of thickened plastic mass covered with plastic foil on both sides.

If all the described stations for applying plastic mass and reinforcement are used, a symmetrical product is obtained around said foamed or foamable layers which are applied in stations 21, 24. namely similar stations placed symmetrically from stations 17 and 27 for spraying plastic mass to the stations 4, 5 22 and 23, respectively, On both sides of these stations are and 4ä, 49 for extrusion of the two surface layers. With respect to 18, 19 for laying down reinforcing fabric and the station 25 for laying down reinforcing fibers, full symmetry does not prevail.

However, either these two stations can be made equal according to either embodiment - also here the design is made symmetrical, so that it is doubled or doubled for loading of both types of reinforcement alternatively or complementary to each other. If you do not want full symmetry of the product, certain stations can be excluded. It is also possible to vary the content of the different layers on both sides of the semi-finished product. There are thus separate tanks 4 'and 48 for the surface layers, so that the surface layers can be differentiated, for example, in their color. The tanks 9 and 30 are also separate and their contents can be varied. The semi-finished product is thus surrounded by foil and these are joined together by e.g. welding or an adhesive in a station 50 which joins the edges of the two foils. There is also a station 51 for cutting the material in order to be able to obtain an overlap without increasing the thickness for splicing. In the station there is also a device 52 for closing the ends of the foils, so that the plastic material is completely enclosed between the foils. After the station S2, a soft feed roller 53 is arranged, which provides an evening of the foils and a tight abutment against the plastic material. All stations or selected parts of the stations at the conveyor belt 3 and the conveyor track 45 are covered by a hood 54, which forms a negative pressure chamber, which is connected to the vacuum line 37. 452 868 This can, for example by means of reduction valves, be arranged to give different negative pressures in hoods 36 and 54. When the closure of the plastic foils is made under negative pressure, the packaging of the semi-finished product is given special properties such as increased stiffness due to the external pressure of the air. I, '_. Fig. 2 shows the semi-finished product produced, thus a reinforced laminate with the plastic in uncured form. The semi-finished product is shown in the form of two pieces 60 and 61, which are laid against a surface 63, which may belong to a mold. As mentioned in connection with the station 51, the two pieces 60 and 61 are slanted so that an overlapping joint 65 is formed. They are surrounded by plastic foils, a foil 66 facing the surface 63 and a second foil 67 on the opposite side of the laminate designated 68 in pieces 60 and 61. The laminate consists of a first surface layer 70, which was laid on the conveyor belt 2 by means of the extruder 5. The the other side towards the foil 67 is formed by the second surface layer, which is piled by means of the extruder 49 and which is denoted by 71.

Between the two surface layers 70, 71 is a core 72, which consists of uncured plastic mass and the reinforcement laid by using one or more of the described stations.

A layer of foam / cellular plastic or foamable plastic mass 73 is also laid in the stations 21 and 23, respectively, and shows how a sandwich material is formed, if any, when the layer 73 forms foam in connection with the completion of the material at its final formation.

If you choose to have pre-foamed material in the core, you can choose a rigid foam, which gives a pressure against the surrounding mold surfaces.

This results in good mold filling and good adhesion of the gelcoat layers to the mold surfaces. In connection with the curing of the material in general, a molding can be obtained by compressing the foam, so that the material retains its shape and thickness after removal from the mold. In the case of non-foamed core material, the foaming in connection with the hardening will give an expansion to the semi-finished product and through this the mentioned effect can be achieved with a good pressure of the surfaces of the semi-finished product against the mold surfaces. After foaming and during the polymerization, the material acquires the shape and thickness determined by the shape.

When joining pieces 60 and 61 and any additional pieces, the foils must be cut at the edges where the pieces are to be joined to each other, so that the laminate_. 452 868 68 between the foils come into contact with each other. The pieces are designed according to the surface to be covered and which usually has a three-dimensional shape. The cutting of the pieces can take place already in the manufacturing process through controlled cutting means or in connection with the cladding of the surface. In many cases, however, at least evenly wide strips can be used.

It should be common for production to take place in a mold and the surface 63 is in such cases a mold surface. In connection with the molding and during a part of the curing process, the laminate may be enclosed, a second mold half being required, which forms a second surface, which is moved towards the first, so that the laminate is squeezed. Alternatively, an airtight bag can be formed, which is pressed against the laminate by high gas pressure over the bag or by evacuating trapped air between the bag and the laminate and thereby allowing the air pressure to press the laminate against the mold surface. There are also other methods of holding a laminate layer to a mold wall. Å There are also cases where a body is to be covered with a layer of plastic, a body that belongs to the finished product. In this case, the foil on this side, which is to rest against the body, is suitably removed, whereby a direct contact is obtained between the laminate and the body to be covered. In the production of a reinforced plastic construction in a mold, on the other hand, the plastic foil can remain until the mold is removed, thereby forming a release foil, which facilitates the removal of the laminate from the mold. After curing, the foil is peeled off.

Curing of the plastic laminate can take place by starting the curing process by means of heating. The laminate must then be heated to a temperature adapted to the respective plastic material.

For polyesters, organic peroxides are often used as thermosets and usually those which are cured at 60 ° C and above. These peroxides and inhibitors are added from the beginning when the plastic mass is mixed. The heating. can be done by conduction from the mold, through-air blowing or by irradiation with infrared light. Curing can also take place by activation by means of short-wave radiation such as ultraviolet light to initiate the curing reaction. For some plastic systems ultraviolet light is sufficient,. which is present in solar radiation, which is why curing can be initiated without special devices if it is possible to expose the structure to solar radiation. Electron radiation and microwave radiation 452 ¶868 are additional possibilities to supply the energy needed to initiate the curing reaction. k During curing, the interaction between light curing and heat curing can be achieved. The penetration depth of UV radiation is limited by reinforcement and absorption in fillers and in the plastic itself. However, when the photocurable layer is cured, a lot of heat is emitted and this heat will initiate the underlying thermosetting layer, which can initiate additional layers.

An interesting embodiment is to select a radiation-curing composition for the reinforced layer inside the surface layers, while the surface layers, the gelcoat, are of the thermosetting type. Instead of radiation-curing composition, a compression can also be used which is heat-curing but is initiated at a lower temperature than the surface layers are initialized. Since the surface layers, which lack reinforcement, are relatively permeable to radiation, the intermediate layers can be initiated to be cured by radiation from the outside. During curing, heat is formed, which initiates curing of the surface layers. In this way, the intermediate, reinforced layer can be hardened first while the surface layers are still malleable. Also expansion of the core layer, if such an occurrence can be obtained before the surface layers have even become dimensionally stable.

In this way it is possible to obtain a smoothing of the surface layers while they are still malleable in the otherwise hairy material. The leveling can take place by a mechanical processing, for example with rollers, after the reinforced layers have become sufficiently hard. The mold can at least partly consist of radiation-permeable material or consist of a permeable cloth, inside which the plastic is enclosed under vacuum. In the case of thermosetting materials, heat is applied, the surface layers initiated at a higher temperature hardening last. When the material is enclosed, the pressing from the hardening and expanding intermediate layer will give an impression of the still moldable surface layers against the mold walls and thus a good surface smoothness.

In the case of water-splitting plastic, gypsum can be included in the product, which absorbs the water and forms a solidified mass. This can occur with thermosets. Thus, urea, melamine and phenolic resins can be used and e.g. heat-cured or light-cured with a candle-hardener, which forms an acid when illuminated. In connection with these polymers and others such as imide resins, which on curing form water, the said combination with gypsum can be made. Without special measures, it is a disadvantage as it forms pores where the excess water passes out. In addition, these resins shrink during curing. With gypsum additive it is achieved that the pores do not form, because the water stays in the material. per the mixture of plastic and gypsum, as the gypsum expands during solidification and compensates for the shrinkage.A mixture of thermosetting plastic and gypsum can be added harder and water and thus a material that does not shrink is obtained.

Because the laminate is provided from the outset with a surface layer, a gelcoat, which can be colored in any desired color, in many constructions the plastic body itself is finished with the removal of the mold. In other cases, sanding is required, especially of existing joints, and often also polishing. However, these are jobs that are easy to perform in that the surface layers are finished in their structure and only require a lighter surface treatment. During molding and. curing protects the foil environment from harmful fumes. No spreading of dust from the reinforcement or any handling of the reinforcement material, which can be troublesome, is required during the forming work. The semi-finished product according to the invention thus provides an exceptionally good working environment in the production of reinforced plastic constructions and enables these to be produced to a great extent with a reduction in the manual work at the manufacturing site.

An analysis of the described method in the described plant suggests that a large number of advantages are gained in relation to what has been achieved so far through known methods. Thus, the surrounding environment is not affected by odor and by harmful fumes during application and the anti-curing effect of air on the surface layer of the material can be avoided. The semi-finished product has a good surface on both sides, which can be dyed and it can occur in thick layers. During the process, thickened gelcoat can be extruded, whereby the viscosity is reduced by the processing, after which the previously high viscosity is recovered faster than what is done by thickening of liquid plastic in conventional working methods. The gelcoat and plastic mass for the load-bearing layer can be thickened in containers outside the actual production line in which it is used. The same also applies to other constituent plastic materials such as the polyester, which is usually used in the reinforcement of plastic. The plant can be expanded to apply various coatings such as plastic or metal foil or textile materials. i452isea ll The semi-finished product produced is excellent for further processing, for example pre-cutting, controlled material application in three-dimensional forming, and for this purpose the material can be adapted to extensibility and strength in different directions. In the case of semi-finished products which contain the described core material in unfoamed form, during the molding while heat is supplied for the curing, a foaming with expansion of the layer is obtained, which gives a good mold filling. If the material is foamed already at the molding, a material is obtained which is compressed, shaped and hardened by the action of heat. The semi-finished film enclosing the foil may be for packaging purposes only, or may be included in the product, or may be a release film. When the foil is closed under negative pressure, a special product is formed, a rigid package of the semi-finished product that is easy to work with and does not need to be thickened, but can be used directly or stored for a long time with retained properties.

The thickened material needs to be stored for a certain time at a certain temperature and can then be used for a relatively short time, which limits the use of now known materials. Precisely this thickening process is a problem that has not yet found its solution. With the above-mentioned vacuum packaging, the problem is circumvented, so that it is the foil that determines the elongation instead of, as before, the thickened polyester with reinforcement.

The plant described can be adapted for the manufacture of non-semi-finished products for the formation of plastic shells, as indicated. For example, continuous laminates for e.g. the construction industry is produced. In this case, the material described with plaster added can be used. The advantage is a cheap material that is more fire resistant than plastic.

The plant can also be used for the production of sub-products such as only a gelcoat layer. Gelcoat can then be extruded and sold as a stand-alone product. In use, one foil is removed and the layer is worked down against the mold with rollers or with vacuum suction between the tensioned frame and the mold. This layer is cured in other ways than with short-wave light. On top of this layer, wet application or other methods can then be used when applying the reinforced layer. The advantage is that the exposure to styrene vapor is completely avoided and that the next layer can be applied directly without having to fit the exact time when the gelling has reached the stage when the application is to be made of the next layer without dissolving the layer or getting poor adhesion. If an external pressure is applied here and the hardener is adapted to a gel that is slightly later than the gel of the reinforced layer, the desired effect is achieved, as for the semi-finished product, that the gelcoat layer flows out and evens out the irregularities that all gelcoat surfaces have had so far. . w

Claims (15)

15 », 2452 ses PATENTKRAV A method of making reinforced plastic in the form of a web (50, 51) and comprising continuously making at least one reinforced plastic layer (72) and at least one reinforced plastic layer (70), intended to form an optionally colored surface layer on the surface of the web with both kinds of plastic layers of such plastic material that its curing can be initiated by a physical factor, characterized in that the plastic layers, which are intended to form a semi-finished product, which is intended to be given its final shape in a forming work separate from the production and after which the curing of the plastic material is initiated, are selected to be initiated for the curing by various physical factors, so that the reinforced plastic layer (70) is of such a nature that its curing is initiated by radiation, and the unreinforced surface plastic layer (70) is of such , that its curing is initiated by heat and at the temperature which arises during the curing of the reinforced plastic layer, which is initiated by about the radiation. 2. A method according to claim 1, characterized in that during manufacture a layer (70) of said unreinforced plastic is deposited on a smooth, movable surface such as a conveyor belt (2), on which one or more further layers (72 ) of said reinforced plastic is applied, after which an additional, final layer is laid on a smooth surface (45) to be transferred to the challenged part of the semi-finished product to form the outer layer of its remaining side. 3. A method according to claims 1 and 2, characterized in that the plastic material for the surface layers (70, 71) is given a thixotropic shape when applied to the conveyor tracks (2, 45). 452 868 W A method according to claim 1, 2 or 3, characterized in that the plastic material for at least a part of the reinforced layer (72) is given a thixotropic shape when applied to said surface layer. 5. ¿5. A method according to claim 1, 2, 3 or 4, characterized in that at least one layer (73) of a foam or cellular plastic is inserted into the reinforced plastic layer (72). A method according to claim 5, characterized in that the layer (73) of the foam or cellular plastic is inserted into the reinforced plastic layer (72) in non-foamed and non-polymerized form but added with foaming agent for activating it and polymerizing of the plastic during said subsequent curing. 7. A method according to any one of the preceding claims, characterized in that at least one layer of a thermosetting plastic which emits during curing is applied together with gypsum, the amount of thermosetting plastic being so adapted to the amount of gypsum that the gypsum is able to absorb the water for crystal formation. , which is generated during the curing of the plastic. A method according to any one of the preceding claims, characterized in that the needle fabric (SO, 61) after its preparation is enclosed in a casing (66, 67) of plastic foil, which is evacuated on air, so that the external air pressure compresses the semi-finished product into a rigid form. A semi-finished product prepared according to the method according to any one of claims 1-8, wherein in continuous production at least one reinforced plastic layer (62) is made in uncured form and of such a plastic material that its curing can be initiated by a physical factor such as heat or radiation and forming the web-shaped semi-finished product (60, 61), which is intended to be given its final shape in a forming work separate from the production, after which the curing of the plastic is initiated, characterized in that it comprises on both sides a layer (70, 71) of an unreinforced plastic, arranged to form a possibly colored surface layer, a so-called gel-coat, and between the surface layers one or more layers (72) of reinforced plastic in uncured condition._ »ß 452 see Semi-finished product according to claim 9, characterized in that said surface layers (70, 71) are of the thermosetting type and at least partially permeable to radiation, and that the intermediate layers (72) are at least partially of the radiation-curing type, so that the curing of the semi-finished product can be initiated by means of radiation which penetrates the surface layers, the heat generated by the initiated curing initiating curing of the surface layers. 11. ll. Semi-finished products according to claim 9, characterized in that said surface layers (70, 71) are of the thermosetting type and that intermediate layers (72) are arranged to be initiated with heat at a lower temperature than that at which the surface layers are initiated. , whereby curing is initiated in intermediate layers by applied heat and the heat thus formed together with the applied heat initiates curing of surface layers. Semi-finished product according to claim 9, 10 or 11, characterized in that the reinforced plastic layer (72) encloses at least one layer (73) of a foam or cellular plastic, which in the semi-finished product has not foamed and not polymerized form, but is added with foaming agent for activating this and polymerizing the plastic during said subsequent curing. A semi-finished product according to any one of claims 9-12, characterized in that it comprises at least a layer of a thermosetting plastic which emits during its curing and is added with gypsum, which is arranged to absorb the water formed during the curing of the plastic. for crystal formation. A plant for carrying out a process according to any one of claims 1-8 for the production of reinforced plastic in the form of a semi-finished product (60, 61) according to any one of claims 9-13 and comprising the continuous production of at least one reinforced plastic layer (72) in non-reinforced plastic. hardened form and of such a plastic material that its curing can be initiated by a physical factor such as heat or ultraviolet radiation and forming the web-shaped semi-finished product, which is intended to be given its final shape in a forming work separate from the production, after which the curing of the plastic is initiated. a first conveyor track (2) with a smooth surface, at 452 868 w the conveyor track an extruder (5) for laying a surface layer (70) on an upper part of the conveyor track, along the conveyor track, then devices for applying the reinforced plastic (72) on the surface layer, then a second conveyor track (45) with a smooth surface and with an upper part and a lower part, of which the latter is opposite to the upper part of the first conveyor track, at the upper part of the second conveyor track an extruder (49) for laying down a second surface layer (71), so that this accompanies the second conveyor track to its lower part, where the surface layer (71) is laid down in the reinforced plastic (72), soul is carried by the first surface layer (70) on the first conveyor track. Plant according to claim 14, characterized in that before the second conveyor track (45) the first conveyor track is divided into two sections (2, 3), each having said upper part in such a way that these upper parts follow one another . in the joint between the sections a device for erecting a plastic foil (42) on the second section whereby the plastic layer (70, 72) formed on the first section will be placed on the plastic foil when transferred from one section to the other, after the second conveyor track (45) a device (46, 47) for laying a second plastic film (67) on top of the formed semi-finished product, so that it will be enclosed between the two plastic films, and devices (50, 52) for joining the plastic foils to a tight casing around, by means of a cutting device (51) along the second section (3) of the first conveyor track separated pieces (60, 61) of the formed semi-finished product. L)