IE851556L - Light weight extruded structural profile - Google Patents

Description

S8647 1 This invention is concerned with a method of manufacturing lightweight structural profile according to the preamble of claim 1. Such a method is known from GB-A-2028406. Profiles manufactured by a method 5 according to the invention are particularly but not exclusively suitable for use in the building or joinery industries instead of timber, for example in the construction of window and door frames and the like, but also for floor boards, joists, rafters and other 10 building components.

In WO 81/00588 there is described a method of manufacturing window and door frames from cored extruded plastics profiles in which the core material may be of high quality plywood or other suitable 15 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.

For such frames the core material is required to 20 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. Furthermore, as a timber substitute it may be desirable that the core material 5 should possess good screw-holding properties.

In GB-A-2028406 there is disclosed a method of manufacturing an extruded construction strip which is suitable for use in the manufacture of frames for windows and the like and which comprises a tubular 10 section of thermosoftening plastics material (specifically PVC) filled with a matrix of methylmethacrylate with hollow silicate spherules as a filler. As described, the construction strip may incorporate within the matrix a number of filaments 15 (specifically glass rovings) 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 20 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 25 extrusion by some means not 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 30 freely under pressure to fill the hollow section.

Furthermore, there is described in WO 82/03243 a method of making somewhat similar structural profile, in which method: (i) a core comprising an unsaturated polyester resin incorporating a silicate filler and an 3 additional mineral filler, thoroughly mixed and tightly compacted together, is extruded through a die, (ii) a sheath of a plastics material is extruded around the core, and (iii) the sheathed core is cured by means of 5 heat, so as to effect curing of the core and cross-linking between the core and the sheath. The preferred silicate filler for that process, as described therein, is in the form of lightweight hollow microspheres, and an acrylic coating is preferred for 10 the plastics sheath.

According to the process described in WO 82/03243, a very close packing of the selected fillers could be achieved, resulting in a considerable reduction in the amount of resin required. However, a further reduction 15 in the resin content can be desirable.

The invention provides a method of manufacturing lightweight structural profile in which a core comprising closely compacted and bonded particulate filler is formed in passage through a shaping die, characterised in that it comprises packing loose particulate filler into the shaping die by means of applied vacuum, progressing the packed filler by pulling it through the die, and causing the packed filler to become bonded by a bonding resin as it is progressed through the die in formation of the core.

Such a vacuum packing technique can enable particularly high packing densities to be achieved where the filler comprises a relatively coarse primary filler (e.g. layer mineral foam prills) and a relatively fine free-flowing additional filler (e.g. hollow silicate microspheres), the additional filler being drawn in separately to occupy interstices in previously packed primary filler.

To enable vacuum to be applied, the walls of the die can be provided with airways leading from the interior of the die. The airways may lead to one or more manifolds maintained at reduced pressure, a stream of air (or other gas) so being drawn into the die, and filler consequently being drawn into the die and packed. A suitable filter arrangement can prevent filler particles from entering or obstructing the airways in the die walls.

For certain products it might be desirable to arrange to have filler of a higher specific gravity towards the outside of the core than in the middle. This could be achieved by first packing by vacuum the heavier filler against the walls of the die and thereafter packing (also by means of vacuum) lighter filler into the middle.

Preferably, after initial packing by means of applied vacuum the packed filler is progressed through a convergent portion of the shaping die to achieve further consolidation of the packed filler. Introduction of the bonding resin into the packed filler preferably occurs as the filler is progressed through the convergent portion.

The manufacturing method can advantageously employ a pultrusion process similar to that described in GB-A-2143768. That is to say, glass fibre rovings, or equivalent materials, can be provided trapped between outer surfaces of the body of packed filler and walls of the shaping die, the rovings being pulled with the packed filler through the die as the profile is formed. Such use of glass fibre rovings can be of particular benefit in easing the process, serving to keep down the back pressure in the die with a consequent saving of wear in the apparatus generally and minimising any breakdown of the filler by crushing owing to excessive pressures. The fibres may provide a complete resin-bonded sheath for the core. If required, a plastics coating can be applied to the outside of the fibre-clad core, again as referred to in GB-A-2143768, though with suitable resins and pigments this may be unnecessary to provide finished profile with a fully satisfactory outer surface.

Advantage may be gained from at least the surface of the filler being at an elevated temperature when the bonding resin is introduced.

There now follows a detailed description, to be read with reference to the accompanying drawings, of a 15 method of making lightweight structural profile, which method illustrates the invention by way of example.

In the accompanying drawings: Figure 1 is a diagrammatic illustration of a packing section of pultrusion apparatus for 20 producing profile; Figure 2 is a diagrammatic cross-sectional view of the apparatus on the line II-II of Figure 1; and Figure 3 is a schematic illustration of the 2 5 apparatus as a whole.

In the manufacture of lightweight structural profile comprising a core of closely compacted resin-bonded particulate filler within a sheath of resin-bonded reinforcing fibres, a shaping die 10 lined with continuously supplied reinforcing fibres in the form of glass rovings 12 is packed from one end with loose particulate filler, from feeding means comprising a conduit 14, as the rovings are continuously drawn through the die (in the direction of the arrow E in Figure 1). Reference can be made to U.K. patent specification No. 2 143 768 A for a further example of the manufacture of profile comprising a fibre-sheathed core in such a pultrusion process.

A nose portion 16 of the conduit 14 is received within an entry portion 18 of the die 10 and is shaped similarly to the interior cross-section of the die in that region to define a suitable gap (all around the nose portion) to permit and control introduction of the glass rovings 12 on to the wall surfaces defining the die cavity 20. The glass rovings are fed in, in continuous lengths, from supply drums 21 (Figure 3) and are caused to line the die cavity 20 substantially uniformly over all its wall surfaces.

A generally annular array of airways, comprising fine radial bores 22 in the walls 24 of the die 10, connect the die cavity 20 with the interiors of low pressure manifolds 26. The manifolds are connected to a vacuum pump 27, whereby air can be drawn from the manifolds to reduce air pressure within the die cavity. By this means, particulate filler supplied to the die cavity from the feeding means through the conduit 14 can be vacuumed into a packing region 28 of the cavity (within the array of airways) and so packed within the sheath of glass rovings 12 in that region. The sheath of rovings itself serves to some extent as a filter preventing filler particles from entering or obstructing the airways 22, but additional filtering 7 means (not shown) can be provided to prevent the passage of fine filler particles.

In the construction shown in Figures 1 and 2, a resin feeding tube 30 of resin feeding means extends 5 longitudinally through the conduit 14 and the die cavity 20 substantially to the limit of the packing region 28 (which is to say, it extends to the limit of, or very slightly beyond, that portion of the die 10 provided with the bores 22). Alternatively, and as 10 indicated in Figure 3, resin can be introduced through a feeding tube 31 through the die wall to a feeding channel 33 in the die wall extending in a loop around the die cavity.

At the start of operation, a plug 32 (Figure 1) is 15 positioned to occupy the die cavity 20 immediately beyond the packing region 28. The plug 32 is shaped similarly to the interior cross-section of the die in that region to define a suitable gap to accommodate and hold the glass rovings 12 against the interior die wall 20 surfaces. The plug provides, in effect, a dummy section of core which together with the sheath of rovings around it blocks the die to permit initial vacuum packing of the filler. Once filler has been packed by vacuum into the packing region 28, continuous 25 formation of profile can commence by withdrawal (in the forwards direction) of the plug 32. The plug is of a compressible foam material which permits it to be drawn through the convergent die. The plug is drawn from the die in a similar manner to that in which the profile 30 will thereafter be drawn through and from the die, which is to say by applying a pulling force in the direction of passage to the glass rovings 12 held to the plug/core (in a similar manner to that described in U.K. patent specification No. 2 143 768 A, hereinbefore 8 referred to) . Liquid resin is fed through the feeding tube 30 or 31 to permeate the packed filler and the glass rovings 12, the resin thereafter being caused or allowed to cure or set to provide a shaped body of predetermined cross-section of sheathed resin-bonded filler.

More or less immediately following the packing region 28, there is a compressing region 34 within the die 10 in which a convergence of the die walls causes compression and further consolidation of the core as it passes to a final forming region 36 of the die.

With particular reference to Figure 3, the feeding means for supplying particulate filler to the shaping die 10 comprises two feed shutes 38 and 40 leading into the feed conduit 14. Each of the shutes is valved to enable measured portions of filler materials to be delivered into the conduit 14 as required. The vacuum pump 2 7 in operation draws an air stream through the conduit 14, and heating means 42 within an entry portion of the conduit enables the air to be heated if required. Resin is supped to the resin feeding tube 30 or 31 by means of a supply pump 44. The resin supply can be controlled by monitoring the pressure in the feeding tube. Profile drawing means 46, of a kind well known in the pultrusion art, acts continuously to draw the glass rovings 12 (and the profile core) through the shaping die 10.

The particulate filler comprises layer mineral foam in a coarse particulate form as a primary filler. Suitable clay foam prills (being short extruded strands) are as promoted in the U.K. by Imperial Chemical Industries PLC as "K4 Inorganic Foam". The prills may, for example, have a mean extruded length of around 5 mm and a diameter of about 2 mm, and their specific gravity can fall (at choice) anywhere within as wide a range as 0.1 to 0.6; partly reflecting that, the proportion (by weight) of filler in the resin-bonded product can vary between, Sciy, 25% and 80% (depending also on the type of resin used}.

Whilst the particulate layer mineral foam alone may constitute the filler, it is usually preferable that a suitable secondary filler be incorporated. This additional filler should be a relatively fine filler, and to permit efficient incorporation by the vacuum packing technique it should be a free-flowing material. A preferred secondary filler comprises (at least as the primary constituent) silicate material in the form of hollow microspheres; such material is widely known as a filler and is available commercially either as recovered from power station waste or as manufactured "glass bubble" filler.

Chopped glass strands may also be introduced in addition to the foam clay and hollow silicate fillers.

Employing the vacuum packing technique (hereinbefore described) the primary and secondary fillers are introduced into the shaping die separately in discrete measured portions. A first of the feed shutes 38 is used to supply the primary filler (the prills) , and the second feed shute 40 is used to supply the secondary filler (the microspheres), measured portions of the two fillers being supplied alternately. Accordingly, a portion of primary filler is first released from the first feed shute 38, and the filler is drawn by vacuum into the packing region 28 of the shaping die. A portion of secondary filler is then released from the second feed shute 40 and drawn into the packing region 28 and into the interstices of the packed portion of primary filler. A next measured portion of primary filler can be released from the first feed shute 38 at a suitable time, bearing in mind that forming is taking place continuously, with the glass rovings 12 being drawn continuously through the die 10 by means of the profile drawing means 46.

Further consolidation of the initially vacuum packed primary and secondary fillers occurs as the core material is progressed next through the compressing region 34 of the die 10. With the resin-feeding arrangement as shown in Figure 3, a bonding resin is introduced through the feeding tube 31 shortly before the end of the compressing region of the die. The resin (whether introduced at the centre of the packed filler as from the tube 30 in Figures 1 and 2, or at the periphery as from the tube 31) permeates the remaining interstices of the packed filler (and the glass fibre rovings 12) by capillary attraction and the effects of increasing pressure as the material moves through the die. A non-foaming phenolic resin system which has been used successfully is one available in the U.K. from BP Chemicals under the trade marks Cellobond J25/425L resin and Phencat 10 catalyst. Typically, in use of that resin system, with about 5% of the catalyst, the heating means 42 is utilised to result in the foam clay filler having a surface temperature of around 70 °C when the resin (i.e. mixed resin and catalyst) is introduced, the shaping die 10 itself being at a temperature ranging from not more than about 90 °C at its entry end to around 130 °C towards its outlet end. 11 In the finished profile the proportions of the constituents (by volume) can be within the following ranges: Layer mineral foam prills (primary filler) : 50%-60% Hollow silicate filler (additional filler) : 28%-.32.5% resin : 12%-17.5% The finished sheath thickness may typically be 0.5 mm to 0.75 mm. 12

Claims (13)

1. A method of manufacturing lightweight structural profile in which a core comprising closely compacted and bonded particulate filler is formed in passage through a shaping die, characterised in that it comprises packing loose particulate filler into the shaping die by means of applied vacuum, progressing the packed filler by pulling it through the die, and causing the packed filler to become bonded by a bonding resin as it is progressed through the die in formation of the core.

2. A method according to claim 1 in which the bonding resin is introduced to permeate the packed filler after packing of the filler.

3. A method according to claim 2 in which the resin is introduced into the packed filler when the filler has an elevated surface temperature.

4. A method according to any one of claims 1, 2 and 3 in which after initial packing by means of applied vacuum the packed filler is progressed through a convergent portion of the shaping die to achieve further consolidation of the filler.

5. A method according to claim 4 in which the bonding resin is introduced to permeate the packed filler as the packed filler is progressed through the convergent portion of the die, the resin thereafter being caused or allowed to cure or set.

6. A method according to any one of claims 1 to 5 in which by means of applied vacuum a primary and an additional filler are introduced successively into the die, the additional filler being a relatively fine free-flowing filler which is drawn in to occupy interstices of packed primary filler.

7. A method according to any one of claims 1 to 5 in which the filler comprises layer mineral foam in a coarse particulate form.

8. A method according to claim 6 in which the primary filler is layer mineral foam in a coarse particulate form and the additional filler is a silicate filler in the form of hollow microspheres.

9. A method according to any one of claims 1 to 8 in which the filler is packed within a sheath of reinforcing fibres within the shaping die, the sheath and the packed filler together being drawn through the die.

10. A method according to claim 9 in which the reinforcing fibres are of glass.

11. A method according to either of claims 9 and 10 in which the bonding resin is caused to permeate also the sheath of fibres.

12. A method according to claim 1 of manufacturing lightweight structural profile, substantially as hereinbefore described with reference to the accompanying drawings.

13. Lightweight structural profile whenever manufactured by a method claimed in a preceding claim. F. R. KELLY & CO., AGENTS FOR THE APPLICANTS.