GB2287491A

GB2287491A - Hollow structural member with internal stiffening

Info

Publication number: GB2287491A
Application number: GB9505217A
Authority: GB
Inventors: William Henry Topham; Alfred David Ganderton
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-03-15
Filing date: 1995-03-15
Publication date: 1995-09-20
Also published as: GB9404949D0; CA2144550A1; DE19509330A1; GB9505217D0; FR2717558A1

Description

2287491 METHOD OF-MAKING A STRUCTURAL MEMBER, AND THE PRODUCT OF SAID

METHOD This invention relates to a method of making a structural member, and also to the product of said method.

Structural members which are of hollow section and made by extrusion are very widely used; these may be of aluminium or of a plastics material. The extrusions are customarily made in the lengths of up to 5 or 6 metres.

Such structural members are used a great deal in the construction of, for example, conservatories. When used as glazing bars (standard length of the order of only 2.8 to 3.0 metres) in the conservatory roof, there is often unacceptable downward bowing of the glazing bar due (a) to the length of the bar and (b) to the weight of the glazing (whether this be glass or, for example, polycarbonate), said weight being a considerable problem when double-glazed untis are employed. The incidence of snow, wind and violent down-draughts only exacerbates matters.

Moreover, in other buildings, such structural members are used as components in curtain walling where the effect of wind can cause either inward bowing or outward bowing of mullions and transoms depending upon the direction of the wind in relation to the particular face of the building containing said curtain walling.

Furthermore, in the field of domestic and industrial buildings, roofs comprise trusses which themselves include rafters; rafters help to support the weight of the tiles or other roofing materials. Rafters could, in time, sag under the weight of the roofing material alone and, even more, when snow has fallen or when wind-pressure is exerted on the roof spasmodically over a period of years. The rafters could be moved.

The problem of unacceptable bowing stems from the inherent rigidity (stiffness) of the extruded lengths of the mentioned materials not being great enough, and the principal object of the present invention is to try to increase the rigidity (stiffness) of the structural members without unacceptably increasing the weight of them.

According to the present invention a structural member comprises a hollow section structural element made of a first material and whose inherent rigidity (stiffness) has been improved by the inclusion, within the void of the hollow section, of an elongate body of substantially the same length as the structural element, said elongate body filling all or part of said void and including a second material which has a density lower than that of the first material, and said elongate body further including at least one stiffening member which is of substantially the same length as the structural element and which is made of a third material and which is bonded to said second material.

The structural member maybe straight or may have had a curve imparted to it.

The second material may be a foamed plastics material; for example polyvinyl chloride, polyurethane or styrene, and can be of the kind which becomes foamed as a result of the action of the moisture in the ambient air or as the result of the interaction of the constituents of a two-part chemical mix.

Other suitable materials may be used such as (a) chopped up wood (or sawdust) bonded by an adhesive and (b) chopped up word (or sawdust) plus cement/concrete and aerated.

The stiffening member may be, for example, made of metal or carbon fibre and preferably has a high modulus of elasticity for the material concerned, thus for aluminium the modulus would be typically 70 G.Pa and for steel typical 204 G.Pa appropriate value being employed for other materials.

Four stiffening members may be included each of which is of angle section, the elongate body having the cross-sectional shape of a rectangle and said stiffening members being located at or in the proximity of the rectangular corners of the body. In another embodiment two L-shaped stiffening members may be included which are arranged in relation to one another as to form, in cross-section, a rectangular figure whose sides are parallel to the walls defining the void in the structural element. In yet other embodiments, at least one pair of strip-like stiffening members may be disposed at or in the vicinity of an opposed pair of faces on the inner walls of said hollow section element.

The invention also includes a structural member as set forth about which is carried in one or nor directions over its length.

The elongate body may be a preformed unit which is inserted into said void.

Alternatively, said elongate body may be bonded to the structural member as a result of having been treated in situ in the void.

The present invention also includes a method of making a structural member which includes filling all or part of a hollow section structural element made from a first material with an elongate body of substantially the same length as the hollow section structural element and of a second material of a density lower than the first material, and incorporating into said elongate body a stiffening member of substantially the same length as the elongate body and made of a third material, and bonding said stiffening member to said second material. Thus the method may include extruding a hollow element, preforming said elongate body with a cross-sectional area which is substantially the same as a void in said hollow section element and incorporating at least one stiffening member therein, and inserting said elongate body into said void of said hollow section element.

Another method of performing the invention includes extruding a hollow section element and creating within a void in said hollow section element an elongate body to substantially fill said void and including a stiffening member.

Another object of the present invention is to tackle the problem, which was reviewed in the opening paragraphs in a different way from those already suggested. Thus, instead of trying to ameliorate the inherent rigidity (stiffness) of a hollow-section structural member which is already in existence and which may, for example, have been bought in from a supplier or stockist of such structural members is to manufacture a structural member ab initio.

Thus the method can include (1) continuously and simultaneously feeding into an extrusion head (a) a heated plastics material (b) at least one stiffening member, and (c) another material whose density is lower than (2) (3) (4) that of the plastics material and of the stiffening member; extruding said plastics material to form a hollowsection structural element within whose void the or each stiffening member is positioned; cooling the extrusion by means of a cooling jacket which forms part of the extrusion head; and thereafter introducing said other material whose density is lower than those of the plastics material and of the or each stiffening member into the void in order to fill said void and to become bonded both to the plastics material and to the or each stiffening member.

The method also includes bending or forming the hollow section structural element to form a curve or curves in one or more directions over its length before filing with said elongate body.

Some exemplary embodiments of a hollow-section structural member according to the present invention, and of a method of making such a member, will now be described by way of example and with reference to the accompanying diagrammatic drawings in which:

Figure 1 represents a section through a typical structural member of extruded material (e.g. PVC) with a U-shaped stiffening member positioned in its void; Figure 2 represents the ideal positioning, within the void of a structural member which is the same as the one shown in Figure 1, of four stiffening members; Figure 3 represents the same section as Figure 2 but after injection of a foam plastics material; Figure 4 represents, schematically, a split-mould for the manufacture of a pre-formed elongate body; Figure 5 represents the pre-formed body after removal from the split- mould; Figure 6 represents the same typical structural member of extruded PVC as before and in whose void are positioned two stiffening members; Figures 7 and 8 show in elevation and section, respectively, one of the stiffening members shown in Figure 6; Figure 9 illustrates one manner in which two stiffening members may be positioned within the void of a structural member by a spacer prior to foam plastics material being injected into the void; Figure 10 represents a side elevation of one such spacer, outside the structural member, with the two applied stiffening members; Figure 11 represents the same typical structural member as before, this time stiffened in separate planes X-X and Y-Y by incorporated stiffening members which are arranged in pairs; Figure 12 illustrates diagrammatically a structural member supported underneath prior to foam plastics material being injected; Figure 13 illustrates the same kind of structural member as shown in Figure 12 but subjected to one upward force and two downward forces; Figure 14 is a diagrammatic illustration of apparatus for making a structural member according to the invention; and Figure 15 is a cross-sectional view on the line XV-XV of Figure 14.

Figure 1 shows a structural member according to the invention which comprises a hollow section structural element in the form of an extrusion 10 (for example, of PVC) for use as a glazing bar or other structural member which is of hollow section and has a principal void 11 (other small voids, if provided, being ignored). In order to stiffen the extrusion 10, an elongate body is made in the following manner:- A stiffening member 12 made of a suitable U-shaped section is positioned in the void 11 in the attitude shown; the stiffening member 12 consists of parallel limbs 13,14 and a connecting piece 15 which keeps the limbs 13,14 spaced apart. When the stiffening member 12 is in position, foam plastics material (not shown) is injected into the void 11 in order to fill said void and create said elongate body. The foam plastics material becomes bondedto -the-,gxtrusion 10 and to the stiffening member 12. Thus the foam provides a second material which has a density lower th4n that of the first material in the extrusion 10 and the stiffening member 12 which is made from a metal, for example aluminium or steel, or from a carbon reinforced plastic (CRP) provides a third material. The stiffening member is arranged to have a high modulus of elasticity, that is for example if aluminium typically 70 G.Pa or if steel typically 204 G.Pa and appropriately for other materials.

The inherent stiffness or rigidity of the extrusion 10, which may be 3 metres or more in length, is greatly increased by the elongate body which comprises the stiffening member 12 and the foamed plastics material.

Figure 2 shows an extrusion 20 having a void 21 in which four stiffening members 22 are positioned in the positions shown, foam plastics material 23 (Figure 3) is injected into the void so as to fill it and thereby create an elongate body which comprises the members 22 and the foamed plastics material 23. The foamed material surrounds some of the members 22 or pushes all or some of them into the adjacent corners of the extrusion 20.

The stiffening members 22 are supported by a series of spacers (not shown in Figures 2 and 3) whose function is to enable the required lengths of stiffening members to be fed into the extrusion in their appropriate positions in which they will be maintained prior to the foam injection. The spacers can be set, for example, at intervals of 1 metre or 0.5 metre.

Figure 4 shows, in schematic form, a split-mould 30 in which four stiffening members 31 have been placed using a series of spacers (not shown) for the same purpose as described above. The mould 30 is then closed and foam plastics material is injected into the mould with the result that said material, indicated by the reference numeral 32, either surrounds some of the members 31 or pushes all or some of them into the adjacent corners of the mould 30.

-g- The resultant product, when removed from the mould 30, is a pre-formed elongate body 33 (Figure 5) which comprises the four stiffening members 31 which have been incorporated in and bonded to the foamed plastics material 32. The product is made to the same length as that of the extrusion which is to be stiffened, and is inserted into the void of said extrusion (for example, a void similar to the void 11 of the extrusion 10). The product is made in such a mould as will ensure that the product has a cross-sectional shape and a cross-sectional area which is the same as those of the void of the extrusion which is to be stiffened.

Figure 6 illustrates an extrusion 40 having a void 41 in which two stiffening members 42 are positioned. Each stiffening member 42 is of the form shown in Figures 7 and 8, namely, approximately L-shaped in section and having perforations 43 in the limb 44 thereof. The foam plastics material when injected will complete envelop the limbs 44 of the members 42 by passing through the perforations 43. The perforations 43 ensure lightness of the members 42 and also enable good integration of said members with the foamed plastics material.

The same is true if the stiffening members 42 are placed in a split-mould of the kind shown in Figure 4.

Figure 9 shows an extrusion 50 having a void in which two stiffening members 51 are positioned; said members are supported by a series of spacers 52 (see also Figure 10) which are set at intervals of, 0.5 metre along the length of the members 51. The spacers 52, which may be moulded or otherwise produced at low cost, ensure that the separate stiffening members 51 are held in approximately their required final positions. Each spacer 52 has a large opening 53 so that the foam plastics material, can flow freely throughout the void and create an elongate body.

Figure 11 illustrates an extrusion 60 having a void in which four stiffening members 61,62,63,64 are placed, said members having been incorporated (in situ or in a split mould) in foamed plastics material 65 to create an elongate body. The pairs of stiffening members on opposite faces of the elongate body stiffen the exrusion in two different planes X-X and Y-Y.

Figure 12 shows an extrusion 70 which is supported on a flat surface prior to injection of foam plastics material into its void 71. If stiffening members have been positioned in the void in the manner described above with reference to Figures 1 to 3 and 6 to 11 before foam injection, the stiffened extrusion will (after foam injection) be a straight stiffened extrusion.

The structural member can be made however with one or more curves along its length.

For some applications, however, it may be of considerable advantage for the stiffened extrusion to have bden given a curve for the purpose of being able to support a heavy load; if any load on a stiffened extrusion which is upwardly curved is such that there is downward deflection of the extrusion, such deflection would only result in the upwardly curved stiffened extrusion becoming a straight (or slightly less curved) stiffened extrusion. This is illustrated, with considerable exaggeration, in Figure 13 in which an extrusion 80 is subjected to an upward force F2 at,or near its mid-length point and downward forces F1 at or near each of its ends. If the pre-curved extrusion (which preferably already lias within its void an has been known or formed arrangement of- stiffening member(s) as described above with reference, for example, either to Figure 2 or to Figures 911-0) and foam plastics material injected into its void to create an elongate body, the extrusion 80 retains its curvature (completely or partially) when the forces are removed. An alternative way of achieving the same effect is to manufacture, using an appropriately curved split-mould, a product similar to the one shown in Figure 5 but curved lengthways; thus curved product is then slid into the pre-curved extrusion and said extrusion will retain its curvature (completely or partially) when the forces which created the curvature of the unstiffened extrusion are removed.

Referring to the preceding paragraph and to the discussion of Figure 13 in particular, it must be stressed that almost any pre-set curved may be produced by varying the number and magnitude (and points of application) of the forces applied to the extrusion.

Figure 14 shows a construction of an extrusion head for a mould which can conveniently be used for making a structural member according to the invention.

An extrusion head 100 is supplied with moulten plastic 101 which is continuously fed under pressure. The pressurised moulten plastic exits through an aperture 102 and in the case of a hollow extrusion 103 this is formed between the face 104 of the extrusion head and a bridge piece 105.

Simultaneously to the extrusion of the moulten plastic 101 from the shaped aperture 102 stiffening members 105 are fed continuously through the head and out through the aperture 102 with the extruded molten plastics material 101. The stiffening members 106 are guided internally (not shown) so that they line the insides of the faces of the extruded walls 107 of the extension 103.

As the semi-moulten extrusion 103 and stiffening members 106 combination proceeds through and out of the extrusion head 100 it passes a cooling station or stations indicated by reference numeral 108 (only one station is shown).

At an appropriate point inside the extrusion 103 after the plastics has solidified, liquid material 109 is injected under pressure into the centre of the extrusion 103 via a supply tube 110 passing right through the extrusion head 100. This liquid changes state to become a foamed core 111 at a point further along the combined extrusion stiffener foam combination, this point being illustrated by reference numeral 112.

Figure 15 shows a section through the finished material which comprises a rigid plastic outer wall 107 containing stiffeners 106 (two being shown) and cured foam 111 all bonded together to form a homogeneous whole.

It will be seen that the stiffeners 106 are fed through sealing means 113 arranged in the wall of the extrusion head 1.

Although glazing bar extrusions have been described above it will be appreciated that other members, for example mullions, transoms and rafters or other structural members can be made according to the present invention, whether such structural members support glazing or anything else, and whether such structural members are extruded or moulded.

Although the above constructions have made use of a foam plastics material in the creation of the elongate body; other materials (for example, the chopped wood/sawdust bonded by an adhesive, or the aerated chopped wood/sawdust plus cement/concrete already mentioned) can be used to provide good results.

Moreover, as employed in this specification, the word "curved" includes not only what is represented and exemplified in Figure 13 but also what is not illustrated and which consists of three or more conjoined straightline portions (a Mansard roof is a well-known example of a curved roof which, as seen in cross-section, consists of three conjoined straight roof portions). Imparting curvature to structural members in order to make them curved (as just hereinbefore defined) is important for those members which are laid horizontally and not only for those which are laid other than horizontally.

Some of the advantages obtained by the carrying into effect of the present invention are:- For conservatories, (a) the invention permits the use of the whole length of an extruded glazing bar which, when reinforced traditionally, would "bow" unacceptably under its own weight; (b) the invention provides a significantly lighter glazing bar than the traditional method, thus facilitating fitting and working; (c) the invention permits the use of glass sealed units at greater spans by the pre-stressing of the glazing bar to compensate for the weight of the glass unit, whereby, when the sealed unit is fixed into the glazing bars, the appearance of the roof is level when viewed front and back at whatever pitch the roof is set (e.g. 100 or 30'); (d) at least when a foamed plastics material is used, the foam which bonds the stiffening member(s) to the extrusion has excellent insulating qualities, thus improving the 'lull value of conservatory roofs and with particular regard to the incidence of condensation.

For curtain walling, at present, to support a pvc curtain wallinq system requires a substantial steel substructure bdt the stiffening of pvc mullions in accordance with the present invention provides not only better deflection properties but also better insulation properties due to the fact that there is not steel front to back.

Claims

1. A structural member comprising a hollow-section structural element made of a first material and whose inherent rigidity (stiffness) has been improved by the inclusion, within the void of the hollow section, of an elongate body of substantially the same length as the structural element, said elongate body filling all or part of said void and including a second material which has a density lower than that of the first material, and said elongate body further including at least one stiffening member which is of substantially the same length as the structural element and which is made of a third material and which is bonded to said second material.

2. A structural member as claimed in claim 1 in which said second material is a foamed plastics material.

3. A structural member as claimed in claim 2 in which said foamed plastics material is polyvinyl chloride,. polyurethane or styrene.

4. A structural member as claimed in claim 2 or claim 3 in which said plastics material is of the kind which becomes foamed as a result of the action of the moisture in the ambient air or as a result of the interaction of the constituents of a two part chemical mix.

5. A structural member as claimed in any one of the preceding claims 2,3 or 4 in which said stiffening member is incorporated in and bonded to said foamed plastics material.

6. A structural member as claimed in claim 1 in which said second material is a chopped-up wood or sawdust bonded by an adhesive or a chopped-up wood or sawdust plus cement/concrete and aerated.

7. A structural member as claimed in any one of the preceding claims in which said stiffening member is made of metal or carbon fibre.

8. A structural member as claimed in claim 7 in which said stiffening member has a high modulus of elasticity for the material concerned.

9. A structural member as claimed in any one of the preceding claims in which four stiffening members each of which is of angle section is included.

10. A structural member as claimed in claim 9 in which said elongate body has a rectangular cross-section, said stiffening members being located at or in the proximity of the rectangular corners of the body.

11. A structural member as claimed in any one of preceding claims 1 to 8 in which two L-shaped stiffening members are included which are arranged to form in cross-section a rectangular figure whose sides are parallel to the walls defining said void in the structural element.

12. A structural member as claimed in any one of preceding claims 1 to 8 in which a pair of strip-like stiffening members are included which are disposed at or in the vicinity of an opposed pair of faces on the inner walls of said hollow section element.

13. A structural member as claimed in any one of the preceding claims in which said elongate body is a preformed unit which has been inserted into said void.

14. A structural member as claimed in any one of the preceding claims 1 to 11 in which said elongate body is bonded to the structural element as a result of having formed in situ in said void.

15. A structural member as claimed in any one of the preceding claims which is carried in one or more directions over its length.

16. A method of making a structural member which includes filling all or part of a hollow section structural element made from a first material with an elongate body of substantially the same length as the hollow section structural element and of a second material of a density lower than the first material, and incorporating into said elongate body a stiffening member of substantially the same length as the elongate body and made of a third material, and bonding said stiffening member to said second material.

17. A method as claimed in claim 16 which includes extruding a hollow element, preforming said elongate body with a cross-sectional area which is substantially the same as a void in said hollow section element and incorporating at least one stiffening member therein, and inserting said elongate body into said void of said hollow section element.

18. A method as claimed in claim 16 which includes extruding a hollow section element and creating within a void in said hollow section element an elongate body to substantially fill said void and including a stiffening member.

19.

(1) A method as claimed in claim 16 which includes continuously and simultaneously feeding into an extrusion head (a) a heated plastics material (b) at least one stiffening member, and (c) another material whose density is lower than that of the plastics material and of the stiffening member; (2) (3) (4) extruding said plastics material to form a hollowsection structural element within whose void the or each stiffening member is positioned; cooling the extrusion by means of a cooling jacket which forms part of the extrusion head; and thereafter introducing said other material whose density is lower than those of the plastics material and of the or each stiffening member into the void in order to fill said void and to become bonded both to the plastics material and to the or each stiffening member.

20. A method as claimed in any one of preceding claims 15 to 18 which includes using a foam plastics material as said second material.

21. A method as claimed in claim 20 in which said foamed plastics material is polyvinyl chloride, polyurethane or styrene.

22. A method as claimed in claim 20 which includes using chopped-up wood or sawdust bonded with an adhesive or chopped-up wood or sawdust plus cement/concrete and aerated.

23. A method as claimed in any one of preceding claims 16 to 22 in which said stiffening member is made of metal or a carbon fibre.

24. A method as claimed in claim 23 in which said stiffening member has a high modulus of elasticity for the material concerned.

25. A method as claimed in any one of the preceding claims 16 to 24 in which four stiffening members are included, so disposed as to be at or in the proximity of the rectangular corners of the void of the hollow section element, which void is rectangular in cross-section.

26. A method as claimed in any one of the preceding claims 16 to 24 in which two L-shaped stiffening members are included which are arranged to form in cross-section a rectangular figure whose sides are parallel to the walls defining said void in the structural element.

27. A method as claimed in any one of the preceding claims 16 to 24 in which a pair of strip-like stiffening members are included which are disposed at or in the vicinity of an opposed pair of faces on the inner walls of said hollow section element.

28. A method as claimed in any one of the preceding claims which includes bending or forming the hollow section structural element to form a curve or curves in one or more directions over its length before filling with said elongate body.

29. A method as claimed in claim 28 which includes bending the structural element into a curve or curves by applying appropriate forces and then filing with said elongate body.

30. A method as claimed in claim 29 in which said bending forces are applied with said stiffening member or members in positions prior to filling with said elongate body.

32. A stiffened structural member substantially as described herein with reference to and as shown in the accompanying drawings.

33. A method of making a stiffened structural member substantially as described herein and with reference to and as shown in the accompanying drawings.