CA1244206A - Manufacture of lightweight extruded structural profile - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

In the manufacture of lightweight extruded structural profile comprising a resin-bonded core of closely compacted particulate filler, loose filler is packed into an extrusion die by means of applied vacuum. The filler is packed within a sheath of glass rovings which is used to draw the packed filler through the die. As the sheath and packed filler are progressed through the die, a liquid bonding resin is introduced to permeate and bond together the packed filler and the sheath. The filler comprises layer mineral foam in a coarse particulate form and a free-flowing relatively fine material (such as hollow silicate microspheres) as an additional filler, the additional filler being vacuumed in to occupy the interstices of previously packed foam filler.

Description

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T~ MAN111;`/\CTURE OF LIG~l'rWE CGHT E~XTE~IJDED Sl'RUCTUl~AI, PROFII,F:

This invention is concerned with the manufacture o~
lightweigh-t extruded struc-tural profile, particularly but not exclusively profile 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 building components.

In International patent specification No. 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 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 possess a high degree of dimensional and shape stability and ~o 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 should possess good screw-holding properties.

In U.K. patent specification No. 2 028 406 B there is disclosed a method of manufacturiny an extruded construction strip which is suitable for use in the manufacture of frames for windows and the like and which comprises a tubular section of thermosoftening plastics material ~specifically PVC) filled with a matrix of me~hylmethacrylate with hollow silicate spherules as a filler. As described, the construction strip may 'IL'ZV~

incorporate with:in the matr:ix a number of fi]arnents (specifically glass rovlngs) extend;ng leng-thwise of the strip for reinforcement purposes. In manufacturing -the strlp the plastics sheath forming the hollow section is extruded by a first extruding machine and the sheath is Eilled by extruding -thereinto (by a second extruding machine) the plastics matrix of methylmethacrylate incor-porating 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 matri~
during its extrusion by some means not disclosed. Curing of the matrix takes place as the strip is fed through a sizing bush of cons:iderable length. It is apparent that the matrix must comprise a relatively high propor-tion of resin (methylmethacrylate) enabling the matrixto flow freely under pressure to fill the hollow section.

Furthermore, there is described in International patent specification No. WO 82/03243 a method of making somewhat similar structural profile, in which method:
(i) a core comprising an unsaturated polyester resin incorporatin~ a silicate filler and an 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 haat, 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 thereinr is in the form of lightweight hollow microspheres, and an acrylic coating is preferred for the plastic~ sheath.

According to the process described in specification No~ WO 82/03243, a very close packin~ of the selected fillers could be achieved, resulting in a considerable reduction in the amount of resin required. However, a ~2442V~

Eurther reducl:ion ~ he re.qin content can be clesirable.
Furthermore, there coul.d be an advanta~e in usincJ, at leas-t as the primary filler for the core of such str~ctural profile, a reaclily manufacturable material that could reduce the dependence on commercially supplied fillers.

There are known, and described for example in European patent specification No. 0 0~6 489 ~A1), rigid inorganic foams of cellular structure comprising one or more layer minerals (hereinafter referred to as layer mineral foams). The term "layer minerals" includes vermiculite, kaolinite, kaolin-containing clays such as ball clays, china clays and fire clays, montmorillonite and sepiolite. Mixtuxes of layer minerals may be employed in making foams, as also may mixtures of one or more layer minerals with one or more materials other than layer minerals. Where the foam comprises at least a major proportion of clays (hereinafter referred to as a clay foam) it may be sintered to confer improved strength and water~stability.

Such rigid foams have been proposed for various uses, including insulation uses and the fire-protection of substrates. Whilst often produced in the form of extruded board or slab-stock, the foams are also produced in a coarse particulate extruded form known as prills, the prills comprising short extruded strands of the foam material. Production of such foams can be effected utilising readily available materials and relatively simple machinery.

It has now been found by the applicant that such rigid foam materials can be used most effectively and advantageously in a method of manufacturing lightweight extruded structural profile in which there is formed in : .
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an extruc.lon process a core compr:ising close:L~ compacted alld bonded part:iculate fi]ler compr;sing Lay~r mineral Eoam in a coarse part:iculate Eorm.

In a technique developed by the applicant for the purpose of enabling loose particulate layer mineral foam (i.e. not pre-mixed with liquid resin) to be introduced into an extrusion die in an efficient manner, applied vacuum is utilised to draw in and pack the ~iller. This technique could Pind wider application in use with other fillers in manufacturing lightweight extruded structural profile, and the invention provides in one of its aspects a method of manufacturing lightweight extruded structural profile in which there is formed in an extrusion process a core comprising closely compacted and bonded particulate filler, the method comprising packing loose particulate filler into an extrusion die by means of applied vacuum and progressing the packed filler through the die to become bonded in formation of the core.

It is to be clearly understood that any references herein to extrusion (e.g. to an extrusion process and die, and to the core and profile being extruded) are intended to be read broadly as applicable to a pultrusion process, in which it may be that only pulling forces are applied to move the profile, in formation, thxough the die.

Such a vacuum packing techni~ue 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 addi~ional filler ~e.g. hollow silicate microspherest, the additional filler being drawn in separately to occupy lnterstices in previously packed primary filler.

~2 ~ 3 To enclble vacuum to be c~ppliecl, t,he~ walls o~ the di,e can be provided with airways leaclinq rom khe 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 suitab]e filter arrangement can prevent filler particles ~rom 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.

The manufacturing method can advantageously employ a pultrusion process similar to that described in U.R.
patent specification No. 2 143 768 A. That is to say, glass fibre rovings, or equivalent materials, can be provided trapped between outer surfaces of a body of packed filler and walls of the extrusion die, the rovings being pulled with the packed fiIler through the die as the profile is extruded. Such use of glass fibre rovings can be of particular benefit in easing the extrusion process, serving to keep down the back pressure in the die with a consequent saving of wear in the apparatus generaIly 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 outsid~ of the fibre-clad core, again as referred to in patent specification No. 2 143 768 A, though with suitable resins and pigments this may be unnecessary to ~ , .

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provlde Einlshed profile with a fully satisfactory outer surface.

In a preferred method, after the loose filler has been vacuum packed within the extrusion die a bonding resin is caused to permeate the interstices of the packed filler (and the surrounding sheath of fibres, if present) the xesin thereafter being caused or allowed to cure or set. Advantage may be gained from at least the surface of the filler being at an elevated temperature when the bonding resin is introduced.

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

The coaxse particulate layer mineral foam can conveniently be in the form of short extruded strands ("prills"). An additional filler, being of a less coarse particulate form, can be introduced; a preferred such additional filler comprises (primarily if not exclusively) a silicate filler in the form of hollow microspheres.

The densities and strengths of layer mineral foams can vary over a wide range but can be readily controlled.
Their use, together with careful selection of secondary fillers as appropriate, affords a corresponding versatility in determining the properties of structural profile so manufactured.

2()6 'I'here now :Eollows a cle~ai.:Lecl de~cription, to be re~acl with refer~nce to the accompany.i.n~ draw:irlgs, of a method of making lightwel~ht extruded s-tructural profile which illus-trates the invention by way o~ exarnple.

In the accompanying drawings:

Figure 1 is a diagrammatic illustration of a packing sectiorl of pultrus.ion apparatus for producing extruded profile;

Figure 2 is a diagrammatic cross-sectional view of the apparatus on the line II-II of Fiyure 1; and Fi~ure 3 is a schematic illustration of the apparatus as a whole.

In the manufacture of lightweight extruded structural profile comprising a core of closely compacted resin-bonded particulate fill.er within a sheath of resin-bonded reinforcing fibres, an extrusion die 10 lined with continuously supplied reinforcing fibres in the form of glass rovings 12 is packed from one end wi-th 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 extruded profile comprising a fibre~sheathed core in such a pultrusion process.

A nose portion 1~ 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 .~, .

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rovings 12 on to tlle wall surEace~ defining the die cavity 20. The CJla5S rovings are ~ecl in, itl COlltillllOU~
lencJ-ths, Erom supply dru~s 21 ~Figure 3) and ~re caused to line the clie 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 mani~olds 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 o glass rovings 12 in that region. Ths sheath of rovings itself serves to some extent as a filter preventing filler particles from entering or obstructing the airways 22, but additional filtering means (not shown) can be provided to prevent the passage o fine filler particles.

In the construction shown in Figures 1 and 2, a resin feeding tube 30 of resin feeding means extends longitudinally through the conduit 14 and the die cavity 20 substantially to the limlt of the packing region 28 ~which is to say~ it extends to the limit of, Qr very slightly beyond, that portion o the die lO
provided with the bores 22~. Alternatively, and as 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.

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~ -t th~ start of operation, a plucJ 32 (Figure L) i3 positloned to occupy the die cavlty 20 immedia~ely beyond the packincJ 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 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 :Lnitial vacuum packing of the filler. Once filler has been packed by vacuum into the packing region 28/ continuous formation of profile can commence by withdrawal (in the forwards direction) of the plug 32 at noxmal extrusion speed. 1'he 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 will thereafter be drawn through and from the die, which is to say by applying a pulling force in the direction of extrusion 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 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 allo~ed to cure or set to provide an extruded body of predetermined cross-section of sheathed resin-bonded filler.

More or less im~ediately 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 extrusion die 10 comprises two feed shutes 38 and 40 leading into z~

the feed conduit 14~ Each o~ the shute~ :Ls valved to enable measured portiGns of filler materlals to be delivered into the conduit 14 as required. The vacuum pump 27 in operation draws an air stream through the conduit 14, and heating means 42 within an entry portic,n of the conduit enahles 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 extrusion die ]0.

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 ~ithin 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 hetween, say~ 25~ and 80~ (dependiny 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 :~24~

filler and :is avai:lable comrnarcially eit,ller as recovered from power station waste or as manllfactured "cJlass bubble" E:i:Ller.

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

Employing the vacuum pack.i.ng techni.que lhereinbefore descri.bed) the primary and secondary fillers are introduced into the extrusion dle 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 porti.on 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 extrusion die. A portion of secondary filler is then released from the second feed shute ~0 and drawn into the packing region 2~ 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 extrusion is taking place continuously, with the glass rovings 12 being drawn continuously through the die 10 by means of the profil2 drawing means 46.

Further consolidation of the inltially 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) .

~LZ~ 6 permeates the rem.~ ing interstices of~ the packed fi:Ller (and the glass Eibre rovings 12) by capillary attraction and the eEfec-ts of increasiny pressure as the material moves through the die. A non-foaming phenoli.c resin system which has been used successfully is one available in the U.K. from BP Chemicals under the trade marks Cellobond J25/4251, resin and Phencat lO 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 70C when the resin (i.e. mixed resin and catalyst) is introduced, the extruding die 10 itself being at a temperature ranging from not more than about 90C at its entry end to around 130C towards its outlet end.

In the finished profile the proportions of the constituents (by volume) can be within the following ranges:

Layer mineral foam prills (prirnary filler) : 50% 60%
Hollow silicate filler (additional filler) : 28%-32.5 resin : 12%-17.5~

The finished sheath thic~ness may typically be O.S rnm to 0.75 mm.

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; the method comprising packing loose particulate filler into the shaping die by means of applied vacuum, causing a bonding resin to permeate the packed filler and progressing the packed filler through the die to become bonded by the resin in formation of the core.

2. A method according to claim 1 in which, the resin is introduced into the packet filler when relative to the ambient temperature the filler has an elevated surface temperature.

3 . A method according to claim 1 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.

4. A method according to claim 3 in which the bonding resin is caused 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.

5. A method according to claim 1 in which by means of applied volume 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.

6. A method according to claim 1 in which the filler comprises layer mineral foam in a coarse particulate form.

7. A method according to claim 5 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.

8. A method according to claim 1 in which the packet filler is pulled through the shaping die in a pultrusion process.

9. A method according to claim 8 comprising packing the filler within a sheathing of reinforcing fibres within the shaping die, the sheathing and the packed filler together being drawn through the die by means of A pulling force exerted on the fibres in the direction of passage 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 cause to permeate also the sheathing fibres within which the filler is packed

12. A method of manufacturing lightweight structural profile in which there is formed in passage through a shaping die a core comprising closely compacted and bonded particulate filler comprising a primary filler and a relatively fine additional filler, the method comprising packing loose particulate filler into the shaping die by means of applied vacuum and progessing the packed filler through the die to become bonded in formation of the core, the primary filler and the additional filler being introduced successively into the die, and the additional filler being a relatively fine free-flowing filler which is drawn in to occupy interstices of packed primary filler.

13. 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, the method comprising packing loose particulate filler within a sheathing of reinforcing fibres within the shaping die by means of applied vacuum and progressing the packed filler through the die to become bonded in formation of the core, the sheathing and the packed filler together being drawn through the die by means of a pulling force exerted on the fibres in the direction of passage through the die.