The present invention relates to a method of manufacturing oblong articles of polyurethane integral foam or a corresponding hardenable material, which is injected into a mould and is caused to harden under pressure therein. Articles of integral foam show surfaces of solid, non-foamed material, while the articles other¬ wise consist of a heat insulating foam material, and such articles are found to have a high mechanical strength and stability, whereby they are usable as entirely or partially self carrying construction elements for many different purposes. It is hereby advantageous that they are mouldable with complex shapes and may form light and cheap castings, but for many purposes they are attractive even with less complex shapes, e.g. as tubular or rod shaped products.

Such integral foam products might be produced by extrusion, but the material is unsuited for conventional extrusion, because a rather high pressure is required in the mould inasfar as the foaming up material, in order to form the compact surface layer, shall seek to expand to a volume, which is considerably larger than the mould cavity. Moreover, the setting of the moulding material takes places slowlier than e.g. the cooling setting as enabling an extrusion shaping of metal and thermo- plastics, and it seems to be a fact that integral foam articles have so far been produced in closed moulds, even such articles, the shape of which could otherwise condition a production by extrusion.

It is the purpose of the invention to provide a

method, which enables the production of an integral foam material by an extrusion like process.

The invention is based on the recognition that this purpose can be fulfilled by a modified application of a rather special extrusion technique, which is already known from other fields of the art, and by which the moulding material is successively injected into a forwardly moved moulding chamber as formed by opposed mould parts on endless belts or chains which engage each other along a common forward run, whereby the material, e.g. concrete, reaches to get shape stabilized before it is delivered from the forward run of the mould parts. The forwardly moving mould parts are then moved away from each other and from the material under ^" delivery, and they are returned, through outer return runs, so as to be successively rejoined adjacent the area of material introduction. For the invention it is of course not sufficient that a stabilization of the cross sectional shape of the material is thus obtainable before the material is delivered from the forwardly moving mould system, because for the formation of integral foam articles it is still necessary that a considerable over¬ pressure should reside in the mould. According to the invention, however, this condition may be fulfilled by adapting the length and the velocity of the said forward run of the mould parts in such a manner that the foam material, before its delivery from the mould run, gets time to form a rigid plug, which, itself, may resist the high pressure in the effective mould cavity. Once the process has been started, such a plug will be created continuously as a rear end portion of the product as pushed forwardly from the mould run with a velocity as given by the motion of the mould run.

Also at the entrance to the mould chamber a "plug" should be provided for enabling the necessary build-up or maintenance of the overpressure, but such a plug may

be natuarlly formed by a nozzle head, through which the injection of the foam material takes place, as this nozzle head may simply fill out the cross section of the mould chamber. On this background the invention is primarily characteristic by the features or method steps as recited in claim 1.

In claim 2 is indicated a very significant possibility, viz. a continuous introduction of one or more reinforcing strings in the material. Because the strings will be anchored in the said material plug and in the hardened material in front thereof, they may be introduced under tension, whereby the products may in a simple manner be provided with a pre-tensioned reinforcement.

In the following the invention is described in more detail with reference to the drawing in which:-

Fig. 1 is a perspective view of a system according to the invention, Fig. 2 is a longitudinal section through a part thereof.

Fig. 3 is a sectional view of the outer portion of the nozzle head, and

Fig. 4 is a sectional view of a modified nozzle head, The system shown in Fig. 1 comprises a pair of endless chains 2 and 4, each made of heavy chain links in the form of blocks 6, which are brought to abut each other along a common forward run 8 of the two chains. The blocks 6 are provided with exterior, longitudinal grooves 10, which, for the two chains is common, will form a longitudinal channel through the forward chain run 8. Along this run the blocks 6 of the two chains are forced sealingly against each other, e.g. by means of opposed rows of stationary pressure rollers 12. In the left hand end - the introduction end - of

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the common forward run 8 is shown a stationary injector unit 14 having an inlet tube 16, and a pair of reincorcing strings 18 as supplied from supply reels 20; . these strings may be glass fibre roving. In the right hand end is shown a rod 22 as under delivery from the run 8 and constituting the final casting.

The chains 2 and 4 are driven by suitable driving and guiding means at a predetermined, uniform speed, this speed as well as the length of the common run 8 being adjusted according to the expansion and stetting characteristics of the moulding material.

As shown in Fig. 2 the injector unit 14 consists of a nozzle head 24, which fills out the cross section of the moulding channel 26 as formed by the juxtapposed block grooves 10 along the chain run 8. The nozzle head 24 has a centrait injector opening 28, which is connected with the inlet tube 16 and continues forwardly in a hopperlike widening inlet nozzle 30, in the wall of which admission holes 32 for the reinforcing strings 18 are provided.

Through the inlet tube 16 and the injector opening 28 is introduced a foaming up moulding material, which starts to expand immediately by its entrance into the conical inlet nozzle 30. The shape of this nozzle favours the foam material, during its introduction into the forwardly moved moulding channel 26 of the chain run 8, to expand for the achievement of isotropic flow and pressure conditions, which seems to be important for obtaining a perfect moulding result. The expanding material produces a considerable pressure in the moulding channel 26 and is, besides, brought along by or in the forwardly moving channel. By its pressure against the walls of the moulding channel the material soon forms a solid skin layer 34 of increasing thickness, and after a while also the central foam material will set, e.g. at

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or just adjacent the line a as shown.

In front of the line a, i.e. to the right thereof, the moulding material will thus form a rigid plug in the moulding channel 26, and this plug - which is created successively and continues towards the right in the final product rod 22 - will constitute a ridig wall towards that part of the moulding channel 26, in which the moulding material is still under initial setting under a high pressure, the said material plug being able to resist this high pressure. At the other end of the moulding channel 26 the moulding chamber is confined by the nozzle head 24, which is materially sufficiently tightly engaging the inner wall of the moulding channel 26. It should be emphasized that ^' ihe nozzle head 24 need not show any complete mechanical sealing against the wall of the moulding channel 26, beceause the moulding material itself will contribute to create the required sealing. In case of a small escape around the nozzle head the moulding material as under high pressure will seek to penetrate into or rearwardly through the associated ring gap, but at the same time the material will get moved forwardly by the forward movement of the moulding channel walls, whereby the result will be an effective sealing without rearward escape of the moulding material.

Thus, the moulding material will here get the same opportunity to expand under pressure against the sides of the mould as when moulded in a stationary, closed mould, but the result will be a continuously delivered product rod 22, which can be cut at desired lengths, whereby these single lengths will show a rigid skin formation on those parts thereof, which are in practice the more interesting" or relevant, viz. _the outer longitudinal surface portions.

The finished moulding product 22 is liberated from

the chain run 8 by outward pivoting of the link blocks 6, and to this end it may be important that a slip agent has been applied to the walls of the moulding grooves 10. Such an agent may be supplied from a nozzle system 36 cooperating with the exterior sides of the blocks 6 during the return run of the blocks. Prior to the application of the slip agent the blocks, during their return run, may pass a brushing station 38, in which the moulding grooves 10 are cleaned for possible remaining moulding material therein. Such a brushing cleaning may be supported by means of compressed air from a nozzle system 40, and the brushed off material rests may be sucked away through a suction nozzle 42.

The reinforcing strings 18 as introduced through the holes 32 will get rigidly anchored in the set moulding material to the right of the line a and will thus automatically be pulled into the mould product by the very movement of the chains 2 and 4. At theintroduct¬ ion-: ■ '-.-I side of the reinforcing strings these strings may be held by a certain friction or introduction resistance, whereby the introduction will take place with an established pull tension in the strings, such that they will be incorporated in the final product in a pre-tensioned condition. If desired, the final product may of course be further reinforced by way of short, suitable reinforcing fibres being mixed into -the injected moulding material.

The outer end of the nozzle head 24 may be designed as shown in Fig..3, viz. so as to have a rearwardly oriented scraper edge 44 capable of scraping off possible rests of moulding material from the mould blocks 6.

Optionally, the injector opening 28 may be shaped as a ring nozzle about a large inlet opening for a pipe, which may then form a central portion of the moulded product, e.g. a conductor pipe as hereby provided

with a coating of a heat insulating foam material, whether a hard or a soft foam. Normally the foam material will adhere to the pipe surface in such a manner that in the area around the latter and inside the wall of the moulding channel 26 ^" the moulding material may still successively build up a "plug area", which can resist the considerable overpressure in the forming area of the final foam layer on the pipe.

In connection with the invention it may be important that the mould blocks 6 be heatabie or coolable during the moulding process, and the blocks, therefore, may be designed so as to have interior heating or cooling channels, which, particularly along the forward chain run 8, are connectable with outer inlet and outlet means for a heating or cooling medium, though such an arrangement should not here be described in more detail.

Optionally the hopper shaped material inlet 30 may be dispensed with, whereby the nozzle head 24 as illustrated in Fig. 4 may consist of a simple nozzle plate 46 having, if relevant, inlet holes 32 for reinforcing strings 18.

The invention is not limited to the production of profiles of a polyurethan material or a foam material,, generally, inasfar as the method and the system according to the invention may well be used or adapted for many other usable materials, with or without reinforcement.

A particularly important example is polyester concrete, from which it may be desirable to produce profiles as reinforced by a unidirectional long fibre reinforcement and/or random distributed short fibre reinforcement, or even without fibre reinforcement at all. In connection with a conventional moulding of polyester concrete and similar materials it can be extremely difficult to remove the air, which is

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inevitably present in the concrete, and the moulded articles, therefore, normally show undesired interior air pockets as well as pores or craters in the surface thereof. Air may often be removed by subjecting the moulded article to a moderate vacuum, but with polyester concrete such a treatment would be demolishing, because the manomer as dissolved in the polyester will boil away under the temperature conditions as necessary for ^• the setting process. Moreover, with conventional moulding of polyester concrete and several corresponding materials it is rather difficult to produce entirely uniform castings, since already a faint non-uniformity in the start and stop phases of the discontinuous production of the castings may give rise to changes of the mechanical properties of the castings.

With the use of the method according to the invention articles or profiles of polyester concrete and the like may be produced with a high degree of uniformity, and also here it will be an important environmental advantage that the moulding material is constantly contained in closed surroundings, endwise by the set material itself. The use of the reasonably tightly sealing injection plug or plate and the successive firm forcing together of the mould parts ^" involve that the moulding material may be injected under a relatively high pressure, e.g. 5-10 bars, and this again means that possible air pockets in the material will be substantially compressed, whereby they will play a smaller role in the finished product. The finished product is comparable to an extruded product, though, as mentioned, with the possibility of many variations of the cross sectional shape, including the provision of a uniformly corrugated surface of the profile. It will even be possible to guide the joined mould parts along a curved path, whereby length curved profiles are produceable in a well controllable manner. Moreover, it will be possible to adjust the mould

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cross sections and the chain length in such, a manner that long products such as masts having an evenly varying cross section may be produced successively, when as mentioned the injector plug is yieldably designed such that it may steadily fill out the by-passing moulding cross section.

Optionally the injector plug may be provided with short or long rods projecting axially forwardly through the moulding channel at least to the area of initial setting of the moulding material, whereby the produced profiles may be provided with through-going channels. The moulding material should hereby slide along the rods, but for certain materials this will be possible without further, and otherwise a slip agent may supplied outward- ly through small radial holes in the particular rod core or cores.

Along the chain run 8 the blocks 6 may be held together in a direct manner by suitable lock means, which are actuated at the injection end and released at the delivery end of the chain run.