WO1982003243A1 - Manufacture of structural members and compositions for use therein - Google Patents

Abstract

A structural member, for example a profile for use in the manufacture of window frames or the like, has a plastic covered core, the core (50) comprising an unsaturated polyester resin filled with a silicate filler (preferably in the form of hollow microspheres) and an additional mineral filler such as calcium carbonate, mica, talc, kaolin and calcium silicate - preferably calcium carbonate coated with stearate - having particles of sizes in the range of about 2 to about 100 microns cup together and the sheath (52) comprising a thin coating (for example not exceeding 0.5 mm) of a homopolymer or a methacrylate copolymer methyl or ethyl methacrylate, crosslink with the core by heat polymerizing the covered core, preferably in an HS field. A method for continuously producing such a profile by the user of a plastic extrusion installation and a method for manufacturing window frames or the like using this method are described. The core is preferably reinforced by fiberglass wicks (18) arranged in layers.

Description

Manufacture of structural members and compositions for use therein.

Technical Field. This invention is concerned with the manufacture of structural members, particularly structural members suitable for use in the building or joinery industries (as a substitute for the traditional use of timber) and compositions for use therein. By way of example, but not of limitation, the invention will be hereinafter described with reference to the manufacture of structural members for use in the manufacture of frames for windows, doors and the like. Background Art. In the specification of my International Patent Application No.PCT/GB80/00133 there is described a method of manufacturing such frames from cored extruded plastics profiles in which the core material may be of high quality plywood, or other suitable material, for example a cement-bonded fibrous material such as cement-bonded chipboard or cement-bonded glass fibres, provided with a cladding of plastics material e.g. polyvinylchloride. In such frames the core material is required to possess a high degree of dimensional and shape stability and to be of adequate strength to bear the loads encountered by the frames in use in various weather conditions.

In the specification of UK Patent Application No.2028406 (European Patent Application No.0007431) there is disclosed a sectional construction strip suitable for use in the manufacture of frames for windows and the like which comprises a tubular section of thermosoftening plastics material (specifically PVC) filledwith a matrix of methylmethacrylate with hollow silicate spherules as a filler. The construction strip preferably incorporates a number of filaments (specifically glass ravings) extending lengthwise of the strip for reinforcement purposes. In manufacturing the strip the plastics sheath forming the hollow section is extruded by a first extruding machine and the sheath is filled by extruding thereinto (by a second extruding machine) the plastics matrix of methylmethacrylate incorporating the silicate spherules being extruded in the cold state into the hollow sheath whilst the latter is still hot. The glass rovings are drawn into the matrix during its extrusion by some means hot disclosed. Curing of the matrix takes place as the strip is fed through a sizing bush of considerable length. It is apparent that the matrix must comprise a relatively high proportion of resin (methylmethacrylate) enabling the matrix to flow freely under pressure to fill the hollow section. Furthermore the cold curing process used in the production of the strip is likely to entail a relatively low rate of extrusion due to the low cure rate, and the need to employ a relatively long sizing bush to ensure that the desired shape of the section is maintained. The use of a cold curing process is also likely to involve difficulties if a temporary breakdown of machinery occurs in that curing of material in the machine(s) continues causing setting of the material and consequently difficulty in clearing the machine(s) involved. An object of the present invention is to effect further improvements in the production of structural members, such as, for example, profiles suitable for use in the manufacture of frames for windows and the like, whereby the disadvantages above referred to are likely to be avoided or substantially diminished, and the resulting product may be produced at a relatively high rate and at an economic price. Disclosure of Invention. According to the invention a structural member comprising a plastics sheathed core is characterized in that the core comprises an unsaturated polyester resin incorporating a silicate filler and an additional mineral filler having particle size in the range of from about 2 to about 100 microns thoroughly mixed and tightly compacted together and cured. More preferably the particle size of the additional filler is in the range of from about 2 to about 25 microns and the silicate filler is in the form of lightweight hollow microspheres having a size range from about 30 to about 100 microns. While suitable substances for the additional filler may comprise at least one of the following, viz. calcium carbonate (e.g. in the form of chalk or calcite) mica, talc, china clay and calcium silicate or the like, I find that good results are given when calcium carbonate in a stearate-coated form is used. Preferably compositions for use in making the core comprise, to each 100 parts by weight of silicate filler, from about 30 to about 85 parts by weight of polyester resin, and from about 60 to about 20 parts by weight of said additional filler. Furthermore I prefer to reinforce the core by incorporating filaments comprising glass fibre rovings extending lengthwise of the structural member and arranged in one or more layers therein.

In manufacturing structural members in accordance with the invention I prefer to use as the plastics sheath an acrylic coating comprising a methyl methacrylate or ethyl methacrylate homopolymer or copolymer which is cross-linked with the core during curing thereof by means of heat.

By incorporating an additional filler as above referred to, particularly a stearate-coated calcium carbonate, in the core material in addition to the silicate filler in the form of microspheres, it is possible to achieve a very close packing of the microspheres with the additional filler occupying a considerable proportion of the space which would be otherwise left between the microspheres if silicate filler were used alone. This results in a considerable reduction in the amount of resin required enabling the core material to be produced in a closely compacted semi-dry condition which facilitates the maintenance of a stable shape to the core material during the curing process. While, by the use of an appropriate catalyst, it is possible to cure the core material either by a cold-curing process or by a hot-curing process, I prefer to use a hot-curing process since the use of such a process shortens the curing time and enables a relatively higher rate of production than would otherwise be the case. Use of a hot-curing process also minimises trouble which might be encountered in the event of a temporary breakdown of equipment used in the production of structural members from the core material since the heat can be turned off to avoid unwanted curing of material in the equipment. Furthermore, using an acrylic coating for the core incorporating polyester resin as above referred to and curing the material by heat is likely to effect very strong bonding of the coating to the core by cross linking between the coating and the core material. While it is possible to produce a structural member as set out in the last preceding paragraph but two by thoroughly mixing and compacting the core ingredients in the desired proportions (including any appropriate catalyst) and tamping the composition to pack it into an appropriately shaped mould, followed by the removal of the mould, applying the sheath by any suitable coating process and curing the member, I prefer to use a continuous method of production which comprises the steps of thoroughly mixing and compacting together the constituents of the core, extruding the core through an appropriately shaped die, extruding a sheath of plastics material

(preferably an acrylic coating as hereinbefore referred to) around the core and curing the sheathed core by means of heat so as to effect curing of the core and cross-linking between the core and the sheath. Preferably the acrylic coating is extruded around the core as it leaves the die through which the core is extruded. The extrusion of the core may conveniently be effected at a temperature such that the core emerges from the shaping die at a temperature in the order of 40ºC, while the acrylic coating may conveniently be extruded around the core at a temperature of the order of 230º - 240ºC so that the curing process is initiated at the interface between the coating and the core material, resulting in cross-linking therebetween and very strong bonding between the coating and the core material. The curing process is preferably completed by passing the sheathed core through a high frequency electro-magnetic field arranged to maintain a temperature of some 200ºC in the material. By applying the coating material in the manner just referred to it is possible to obtain a very uniform and effective protective coating of the core, even with coatings of a thictaiess no greater than 0.5 mm. thus enabling the production of structural members such as a profile for use in the manufacture of frames for windows and the like at an economic price.

I have found that very effective mixing and compacting of the core components can be achieved by metering the appropriate quantities of the components into a hopper arrangement of a machine employing a rotating and oscillating feeding screw, particularly good results being likely to be obtained by the use of a machine of the type known as a Buss-Kneader, supplied in the U.K. by Buss-Hamilton limited. The mixed and compacted core material is then fed to a first plastics extrusion machine which extrudes the core through the shaping die, a second plastics extruding machine being employed to extrude the coating around the core. The coated core is then caused to pass through a tunnel of appropriate cross section to complete the curing process. ϊhe tunnel conveniently comprises a pair of spaced polished stainless steel electrodes, conveniently arranged so that opposite (e.g. upper and lower) surfaces of the formed member move in contact with the electrodes, while the remaining surfaces of the formed member (e.g. the opposite side surfaces thereof) are supported by ceramic or PTFE spacers between the electrodes, the ceramic spacers having smooth walls for engaging the member as it travels jthrough the tunnel. Alternatively the tunnel may be made of PTFE having a shape to engage the profile on all surfaces, with upper and lower generally flat parallel electrodes spaced from the upper and lower surfaces of the profile by the PTFE material. The various parameters such as frequency of the electric field, strength of field, length of tunnel, and speed of extrusion of the material will be chosen to ensure that adequate curing takes place. The curing of the material immediately after the application of the acrylic coating is likely to produce a finished product having excellent finish requiring little or no maintenance, good bonding between the coating and the core of the structural member. By the addition of the appropriate pigments to the acrylic coating material different colour finishes may be readily obtained. Reinforcement of the core by the incorporation therein of glass fibre rovings at one or more levels in the extruded structural member, as hereinbefore referred to, may be conveniently effected by splitting the die through which core is extruded into the desired number of component parts so as initially to extrude the core composition in a number of separated streams which are then caused to converge to form the completed section. For example, assuming it is desired to introduce the glass fibre rovings at two different levels, the die may comprise three parts extruding an upper layer, a middle layer and a lower layer respectively of the structural member. Then as the three layers are caused to converge to form the structural member, the desired number of glass fibre rovings are introduced into the die arrangement in the regions between the layers, the rovings being drawn into the die at the desired speed as the core of the structural member is extruded from the die.

From what has been said hereinbefore it will be appreciated that the structural members in accordance with the invention may be produced with a minimum of waste since they may be formed in their desired final shape without the necessity of machining operations. Furthermore they can be produced economically at a relatively high rate. Structural members in accordance with the invention are likely to have (a) a density of the order of 800 Kgm/c.meter; (b) a high stability against dimensional changes under a wide temperature range (of the order of 0.2 - 0.5% for a temperature change from -10ºC to 100ºC); (c) a very low moisture take-up (of the order of 2%) ; (d) a high load-bearing capability; (e) a screw-holding capacity of up to about twice that of timber and (f) low heat transmission (providing good thermal insulation) enhanced by the use of silicate filler in the form of hollow microspheres. There will now be given, with reference to the accompanying drawings, a more detailed description of a method provided by the invention and illustrative of certain aspects thereof, of manufacturing a structural member, in the form of a profile for a frame for a window or the like, from a glass-fibre reinforced composition comprising a polyester resin incorporating a silicate filler in the form of hollow microspheres, and calcium carbonate, said profile being illustrative of other aspects of the invention. It is , however, to be clearly understood that said method and profile are selected for description merely by way of exemplification of the invention and not by way of limitation thereof. Brief description of the drawings.

In the accompanying drawings, Figure 1 is a sketch showing, rather schematically, a layout of machinery suitable for use in carrying outthe illustrative method;

Figure 2 is a cross sectional view of the illustrative profile for use in the manufacture of a window or the like frame;

Figure 3 is a view, largely diagrammatic, indicating how a die arrangement may be provided for manufacturing said profile;

Figure 4 is a cross sectional view of an electrode system suitable for use in an RF heater for curing the illustrative profile;

Figure 5 is a cross sectional view through an inner frame member and the associated outer frame member of a frame for a window or the like made from the illustrative profile; and

Figure 6 is a detail view (drawn to an enlarged scale as compared with Figure 5) showing a weather proofing arrangement.

Best mode of carrying out the invention. Figure 2 shows, in cross section, a structural member in the form of a profile suitable for use in the manufacture of frames for windows or the like comprising a plastics-sheathed core 50, the. sheath being indicated at 52. The core 50 comprises an unsaturated polyester resin incorporating a silicate filler and an additional mineral filler which have been thoroughly mixed and compacted together and cured. Suitable compositions for the core comprise, to each 100 parts by weight of silicate filler, from about 30 to 85 parts by weight of polyester resin, and from about 60 to about 20 parts by weight of additional filler. The silicate filler is preferably in the form of hollow microspheres (giving components of, relatively light weight and low thermal conductivity) a suitable material being supplied in the U.K. under the trade name Finite by Messrs. Finite (Runcorn) Limited. While different grades of Finite are available a grade having microspheres in a range from about 30 to about 100 microns in diameter is found to be particularly suitable. The additional filler may comprise at least one of the following substances viz. calcium carbonate (e.g. in the form of chalk or calcite), mica, talc, china clay and calcium silicate I have obtained good results by using calcium carbonate in a stearate- coated form conveniently in a particle size in the range of from about 2 to about 100 microns, but preferably in the range of from about 2 to about 25 microns, such, for example as is available, in the U.K., from Blue Circle Cement Company Limited under the designation Snowcal type CW₁. Suitable resins are available in the U.K., for example from Messrs. Scott-Bader Limited.

The sheath 52 comprises an acrylic coating comprising a methylmethacrylate or ethyl methacrylate homopolymer or copolymer. Appropriate pigments may be incorporated in the coating to provide coloured finishes when desired. Curing of the coated core, preferably by means of heat, effects cross linking between the coating and the core resulting in very strong bonding between the coating and the core. Adequate performance of the sheath, as to durability and providing a good finish to the product, may be achieved with relatively thin acrylic coatings, for example coatings no more than 0.5 mm thick.

The core 50 of the profile shown in Figure 2 incorporates a number of reinforcing filaments extending throughout the length of the profile, the filaments comprising glass fibre rovings which are conveniently arranged in a number of layers (two as shown in Figure 2) in the core. A method of effecting a continuous production of structural members in accordance with the invention will now be described with reference to Figure 1, which shows, schematically, a plant suitable for the production of the profile shown in Figure 2, and indicates various stages in the assembly of frames for windows or the like therefrom.

Thorough mixing and compaction of the core ingredients is effected in a mixing machine 10 preferably of the type known as Buss-Kneader supplied in the U.K. by Buss-Hamilton Limited. The machine includes a hopper 12 to which the ingredients are fed in the desired proportions by feed hoppers, feed tanks and proportioning pumps or other devices of known type. The Buss-Kneader machine employs a feed screw (not shown) on the rotation of which is superimposed a reciprocating motion to effect thorough mixing and kneading of components and tight compaction of the microspheres of the Finite material and interspersed calcium carbonate particles.

The kneaded composition is fed from the Buss-Kneader machine into a screw type plastics extrusion machine of known type (indicated generally in Figure 1 by the reference numeral 14). At the output end of the extrusion machine is a multi-part die arrangement 16 which is arranged to extrude the composition in a plurality of portions (e.g. layers) which are initially separated but are arranged to converge, by converging walls of the die arrangement, to provide an extrusion of the desired overall cross-sectional shape at the outlet of the die arrangement.

As the composition travels through the die arrangement 16, glass fibre rovings 18 supplied from a plurality of drums 20 are introduced (after being drawn through baths, not shown, of polyester resin) via separate channels into the die arrangement 16 so as to enter between the several initially separate portions of the composition so as to become firmly embedded therein by the convergence of those several extruded portions to form the completed section of the core of the structural member.

The core material may conveniently be extruded at a temperature in the order of 40ºC so that (although any necessary catalyst for use in the heat curing of the core material will have been added in the Buss-Kneader machine) little or no curing takes place until the material is subsequently heated to curing temperature.

On leaving the die arrangement 16 the extruded core (which emerges in a continuous length) passes through a second die arrangement 22 of a second plastics extrusion machine 24 which is arranged to extrude around the core a sheath comprising a thin coating of acrylic material, as above referred to. The acrylic coating may conveniently be extruded at a temperature in the order of 230° - 240°C so that on contact with the core material curing at the interface between the coating and core is initiated, the curing process being continued by passing the coated core, as it emerges from the die arrangement 22, through a supporting tunnel in an RF heater 26 to effect thorough curing of the core and cross linking between the acrylic coating and the core material. As the cured profile emerges from the RF heater it may be cut up into appropriate lengths by a suitable cutting machine 28 and the several lengths conveyed away by a suitable conveyor 30.

Figure 3 shows, in cross section, a portion of a die arrangement 16 suitable for use with the extruding machine 14 for forming initially three separate layers of the core of the profile so that the glass fibre rovings can be introduced between the layers as they are caused to converge and form the complete section of the profile. As shown, the die arrangement comprises an upper die portion 70 which is shaped to provide an upper layer or portion of the profile, a middle die portion 72 which is shaped to provide a middle layer or portion of the profile, and a lower end portion 74 which is shaped to provide a lower layer or portion of the profile. As hereinbefore referred to, the glass fibre rovings may be introduced into the die arrangement by channels (not shown) extending into the regions 73 and 75 between the die portions 70 and 72, and 72 and 74 respectively. The die arrangement 22 of the plastics extruding machine 14 for extruding the acrylic coating will be slightly larger than the outlet of the die arrangement 16 and arranged therearound preferably to provide a coating of constant thickness (conveniently some 0.3 mm thick) around the core of the profile. (In Figure 2 the relative thickness of the coating is exagerated in order that it can be clearly shown). The tunnel of the RF heater 26 through which the profile passes during the curing operation is shaped (in cross section) to support the profile on all sides and conveniently comprises upper and lower electrodes 80, 82 respectively (see Figure 4) made of polished stainless steel (providing low friction surfaces for engagement with the profile) extending along the length of the tunnel (conveniently in pairs, each of some 1½ to 2½ metres long) separated by insulators 84, 86 of ceramic or PTFE material providing smooth side walls 88, 90 adapted to support the side walls of the profile. An RF field of appropriate frequency (e.g. some 27

Megahertz) and power is applied continuously across the electrodes 80, 82 during the curing operation. As shown in Figure 4 the upper and lower electrodes 80, 82 are respectively contoured to follow the outline shape of the corresponding portions of the profile.

Alternatively, the tunnel .through which the profile passes during the curing process can be formed entirely in PTFE material having parallel upper and lower surfaces engaging generally plane, parallel electrodes which, because they are not engaged by the travelling profile, need not be of polished stainless steel, but can be made of less expensive aluminium.

The profile shown in Figure 2 is of generally rectangular cross sectional shape with a glass or other panel-retaining member 54 upstanding from an upper surface 56 of the profile and extending along the profile and having a first inclined face 58 and a second inclined face 60. The height h of the portion 54 is at least substantially equal to its width w. The portion 54 has a panel-facing surface 62 disposed perpendicularly to the surface 56. The surfaces 58, 60 are of equal widths and are respectively inclined at the same angle θ to the vertical and horizontal respectively as seen in Figure 2 for a purpose hereinafter described. The profile has such additional flanges, protuberances or the like 64, 66 as may be required for weather-proofing or other purposes.

A profile having a cross sectional shape as shown in Figure 2 may be used in a very economical method of manufacturing frames for windows or the like (as disclosed in the specification of my International Patent Application No.PCT/GB80/00133 hereinbefore referred to) in which sawing means are arranged to make a series of transverse cuts at 45° across the profile so as to sever therefrom successively frame members of appropriate lengths for assembly alternately into, an outer, static, frame and an inner, opening, frame for a window or the like, the panel-retaining members being severed from those frame members which are to be assembled into the outer frame. The alternate frame members are then assembled to form said inner frame and said outer frame and, after cutting the panel-retaining members severed from the frame members for the outer frame to the appropriate lengths, they are utilised as glazing strips in assembling said inner frame with a glass or other panel.

Figure 5 shows, in cross section, a frame member of an inner, opening, frame 100 and an adjacent frame member of an outer, static, frame 102 of a window frame, the inner and outer frames of which are both made from the illustrative profile by following such a method which may be practised by using a plant outlined in Figure 1. Conveniently the sawing machine 28 first cuts the profile into appropriate lengths (by means of transverse cuts at 45 as indicated in Figure 1), the action of the sawing machine being initiated by engagement of the previously sawn end of the profile with an end gauge 29. (It will be understood that, in order not. to interrupt the extrusion process, the sawing blade and the end gauge 29 will be caused to travel, during the actual cutting operation with the moving profile). While the sawing machine 28 could be arranged to cut off lengths of profile sufficient to provide the four outer frame members and the four inner frame members of a single window frame, in order to avoid the need for handling unduly long lengths of profile, it is more convenient to cause the sawing machine to cut the profile into lengths each of which is sufficient to provide two of the inner frame members and two of the outer frame members so that the two lengths of profile required to assemble a single window frame travel together along the conveyor 30 as shown in Figure 1.

The pairs of lengths of profile are then fed from the conveyor 30 to a station 31 at which the lengths are severed (by 45 transverse cuts) alternately to provide frame members for the inner and outer frames. Also at the station 31 the panel-retaining member 54 is severed from the frame members which are to be assembled into the outer frame by means of a saw-cut along the dotted line 104 indicated in Figure 5 the saw-cut lying parallel and close to the adjacent surface of the profile. Also at the station 31 any necessary holes or slots may be formed in the frame members which are required in assembling the frames. The frame members are then assembled to form the inner and outer frames of a window at stations 33 where corner joints may be formed by injection of plastics material into appropriate cavities in the adjacent ends of the frame members, or, alternatively by simple screwing operations because of the good screw holding property of the core material of the profile as above referred to.

At station 35 the inner and outer frames are assembled together by the addition of the necessary pivots, hinges, stays and any other fittings required. The arrow 37 indicates the supply of a glass or other panel of appropriate size (e.g. a double glazed unit P, as indicated in Figure 5) for assembly in the opening frame, an appropriate mastic being used to seal the panel in the frame. The panel is secured in place by means of glazing strips 54' provided by cutting to appropriate lengths the panel-retaining members 54 which have been severed from the outer frame members as above described, and securing them by screws 106 to the inner frame as shown in Figure 5. In fitting the glazing strips the members 54' are turned so that the cut faces are positioned against the glass (or other panel). It will be appreciated that, since (as hereinbefore explained with reference to Figure 2) the width w of the panel-retaining member 54 is equal to its height h, turning the member 54' on its side as above described ensures that the height of the glazing strip is the same as that of the panel-retaining member 54. If the member 54' were mounted on the frame member with the cut face facing downwards the loss of material produced by the saw cut 104 would result in the glazing strip being of less height than the panel-retaining member 54 with a consequent lessening of the visual appearance of the window frame. A further advantage arising from assembling the glazing strips as above described is that the holes for the screws 106 can be drilled before the panel-retaining member 54 used for the glazing strips is severed from the profile.

In order tb provide a weather-proof seal between the flanges 66 of the inner and outer frames the flanges 66 may be provided with draught-proofing seals 67 of flexible PVC (as seen in Figure2) which can be extruded during the extrusion of the profile by providing a further plastics extrusion head and a modified die arrangement. However, I prefer to use a draught-proofing arrangement as shown in Figure 6 in which each of the flanges 66 is provided with a generally rectangular sealing strip 69 of EPDM cellular rubber arranged to be secured to faces 71 inclined, preferably at 45º, to the general plane of the window frame, and to abut: in overlapping relationship with a considerable amount of compression as shown in Figure 6 when the window frame is in closed condition. Such an arrangement allows for a considerable amount of misalignment or deflection under extreme wind conditions before loss of effective sealing occurs.

Claims

Claims:-

1. A structural member comprising a plastics sheathed core characterized in that the core comprises an unsaturated polyester resin incorporating a silicate filler and an additional mineral filler having a particle size in the range of from about 2 to about 100 microns thoroughly mixed and tightly compacted together and cured.

2. A structural member as claimed in claim 1 characterized in that the silicate filler is in the form of lightweight, hollow microspheres having a size range of from about 30 to about 100 microns and in that said additional filler has a particle size in the range of from about 2 to about 25 microns.

3. A structural member as claimed in claim 2 characterized in that the composition of the core comprises, to each 100 parts by weight of silicate filler, from about 30 to about 85 parts by weight of polyester resin, and from about 60 to about 20 parts by weight of said additional filler.

4. A structural member as claimed in claim 3 characterized in that said additional filler comprises at least one of the following substances namely calcium carbonate, (e.g. in the form of chalk or calcite), mica, talc, china clay and calcium silicate.

5. A structural member as claimed in claim 3 characterized in that said additional filler comprises calcium carbonate in a stearate coated form.

6. A structural member as claimed in claim 1 characterized in that the plastics sheath of the core is provided by an acrylic coating comprising a methylmethacrylate or ethyl methacrylate homopolymer or copolymer, cross-linked with the core during curing thereof by means of heat.

7. A structural member as claimed in claim 1 characterized in that the core incorporates reinforcing filaments comprising glass rovings extending lengthwise of the structural member and arranged in one or more layers in the core.

8. A method of forming a structural member as claimed in claim 1 which comprises the steps of thoroughly mixing and compacting together the constituents of the core, extruding the core through an appropriately shaped die, extruding a sheath of plastics material around the core and curing the sheathed core by means of heat so as to effect curing of the core and cross linking between the core and the sheath.

9. A method of forming a structural member as claimed in claim 8 characterized in that the sheath is formed by extruding an acrylic coating comprising a methylmethacrylate or ethylmethacrylate homopolymer or copolymer around the core as it leaves the die through which the core is extruded and in that curing is effected by passing the sheathed core through a high frequency electromagnetic field.

10. A method of forming a structural member as claimed in claim characterized in that said die is a multipart die organised so as to allow the introduction of reinforcing filaments comprising glass rovings into the core in one or more layers as it is extruded therethrough.

11. A structural member as claimed in claim 1 in the form of a profile for use in the manufacture of frames for windows or the like characterized in that the profile is of generally rectangular cross-sectional shape with a panel-retaining member (54) upstanding from, and extending along, one surface (56) of the profile, said panel-retaining member having a panel-facing face (62) disposed. perpendicularly to said surface (56) and a pair of inclined faces (58,60) extending along the profile between said surface (55) and the panel-facing surface (62), said faces being of substantially equal widths and being equiangularly inclined to the panel-facing surface (62) and said surface (56) of the profile, and the height and width of the panel-retaining member being at least substantially equal, whereby, in the manufacture of frames for windows or the like from the profile, the profile may be sawn, by a series of transverse cuts arranged at 45 across the profile, into frame members of appropriate lengths for assembly alternately into an outer, static frame and an inner, opening frame, the panel-retaining members being severed from those frame members which are to form the outer frame and being used as glazing strips in assembling the inner frame with a glass or other panel.