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Title:
A FRAME STRUCTURE AND A METHOD FOR MANUFACTURING SUCH A FRAME STRUCTURE
Document Type and Number:
WIPO Patent Application WO/2008/141642
Kind Code:
A1
Abstract:
The frame structure, for instance a window sash or a frame for a window or door, includes top and bottom pieces and two side pieces (1). A core (2) includes a wooden core member and a plastic covering (3) encases the wooden core member. The wooden core member includes wood, which has been subjected to a treatment reducing the detrimental effects of the surroundings on the wood.

Inventors:
DANIELSEN HENRIK (DK)
Application Number:
PCT/DK2007/000234
Publication Date:
November 27, 2008
Filing Date:
May 18, 2007
Export Citation:
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Assignee:
VKR HOLDING AS (DK)
DANIELSEN HENRIK (DK)
International Classes:
E06B3/20
Domestic Patent References:
WO2007057029A12007-05-24
Foreign References:
EP1496189A22005-01-12
DE202004010345U12004-10-07
EP0251804A11988-01-07
EP0213252A11987-03-11
JPH0732313A1995-02-03
Other References:
None
Attorney, Agent or Firm:
CARLSSON, Eva et al. (Rigensgade 11, Copenhagen K, DK)
Download PDF:
Claims:

C L A I M S

1. A frame structure, such as a window sash or a frame for a window or door, including side, top and bottom pieces, said frame structure comprising a core including at least one wooden core member and a plastic covering encasing the core, and a weather-protecting shielding arrangement covering at least parts of the frame structure adapted to face outwards in a mounted position of the frame structure, c h a r a c t e r i z e d in that the at least one wooden core member includes at least one member of wood, which has been subjected to a treatment selected from the group consisting of heat- treatment, acetylation and impregnation, and that the core member made of treated wood constitutes a first shield of said shielding arrangement.

2. A frame structure according to claim 1, wherein the core includes a plurality of core pieces, each said core piece including at least one core member of treated wood.

3. A frame structure according to claim 2, wherein said plurality of core pieces totals four core pieces corresponding to the side, top and bottom pieces of the frame structure. 4. A frame structure according to claim 3, wherein at least one of said core pieces includes a plurality of core members.

5. A frame structure according to claim 4, wherein a first core member and a second core member of said core piece are connected with each other at a first set of mutually facing contact surfaces, said first or second core member being formed from treated wood.

6. A frame structure according to claim 5, wherein said core piece comprises a third core member connected with the first and/or the second core member at a second set of mutually facing contact surfaces. 7. A frame structure according to claim 6, wherein said third core member is made from the same material as the first core member.

8. A frame structure according to claim 6 or 7, wherein said third core member is connected with at least the second core member, said second set of contact surfaces extending substantially perpendicu-

larly to said first set of contact surfaces.

9. A frame structure according to any one of claims 5 to 8, wherein the first core member of each core piece faces inwards with respect to the frame opening and the second core member is made of treated wood and faces outwards, the second core member constituting the first shield of said shielding arrangement.

10. A frame structure according to any one of the preceding claims, wherein the plastic covering in cross section covers only part of the surfaces of the wooden core member. 11. A frame structure according to claim 10, wherein the plastic covering in cross section comprises two groups of each at least two parts provided on substantially opposite surfaces of said core member.

12. A frame structure according to any one of the preceding claims, wherein the plastic covering covers parts of the surfaces of the wooden core member visible to a user in a mounted state of the frame structure.

13. A frame structure according to any one of claims 10 to 12, wherein a second shield of said shielding arrangement covers at least the part of the surfaces of the wooden core member uncovered by the plastic covering.

14. A frame structure according to claim 13, wherein the parts uncovered by the plastic covering include surfaces substantially parallel to the roof in the mounted position.

15. A frame structure according to claim 13 or 14, wherein the parts uncovered by the plastic covering include surfaces substantially perpendicular to the roof in the mounted position.

16. A frame structure according to any one of claims 13 to 15, wherein the second shield includes a covering and/or a cladding.

17. A frame structure according to any one of claims 13 to 16, wherein the second shield includes a flashing.

18. A frame structure according to any one of the preceding claims, wherein the wooden core member is chamfered to the desired shape.

19. A frame structure according to any one of the preceding

claims, wherein the wooden core members are assembled with finger joints with a plurality of fingers, of which one finger joint is an interference fit, whereas the rest of the finger joints are loose fits.

20. A frame structure according to any of the preceding claims, wherein the plastic material encasing has a thickness in the interval of 1 to 8 mm, preferably at least 2 mm and maximum 5 mm.

21. A frame structure according to any one of the preceding claims, wherein said at least one wooden core member has further been subjected to a treatment with a fungicide. 22. A method for manufacturing a frame structure comprising the steps of: providing a core member of treated wood, pre-treating the surface of the core member to facilitate adherence, assembling a core piece of a plurality of core members, placing a set of assembled core pieces in a mould, injecting a setting plastic material in the mould, removing the finished frame structure from the mould, and providing a shielding arrangement to cover at least parts adapted to face outwards in a mounted position of the frame structure.

23. The method according to claim 22, wherein the core member is machined in the appropriate shape by moulding, chamfer, or the like.

24. The method according to claim 22 or 23, wherein ends of the core members are machined to provide engaging finger joints with a plurality of fingers of which one set of fingers are adapted to provide an interference fit, whereas the rest of the finger joints are loose fits.

25. The method according to any of the claims 22-24, wherein the step of pre-treating the surface of the core member is a step of roughening the surface.

26. The method according to claim 25, wherein the setting plastic material is polyurethane.

Description:

A frame structure and a method for manufacturing such a frame structure

The present invention relates to a frame structure, such as a window sash or a frame for a window or door, including side, top and bottom pieces, said frame structure comprising a core including at least one wooden core member and a plastic covering encasing the core and a weather-protecting shielding arrangement covering at least parts of the frame structure adapted to face outwards in a mounted position of the frame structure.

There is a growing interest for robust and aesthetically pleasing frame structures, especially caused by positive economical development in the western world in recent years, increased building activity and increased building renovation. Great efforts are being made to protect such frame structures from the weathering, as the window or door is traditionally installed with an expected lifetime of approximately 15 or 20 years.

Frame structures for windows meeting these demands are known in a number of different configurations and have proven to function very well in a number of different uses. However, when the room inside the window is used for purposes, where the humidity is extremely high over extended periods of time, such as bathrooms, laundry rooms etc., condensation is known to be a problem as it causes the growth of mould or alga, particularly on the bottom sash and frame member and on the bottom portion of the sealing strip. Over time this causes tarnishing and possible deterioration of the material of the sash and frame members. This is particularly the case in roof windows. To avoid these drawbacks roof windows for bathrooms and like have been made from plastic or from plastic covered wood. Plastic has excellent resistance to humidity, as it is by nature non-hygroscopic and as it may contain fungicides.

However, plastic windows have some drawbacks that prevent wide use thereof. Initially, the raw material and the tools utilized for providing the plastic covering are relatively expensive. As it is

furthermore difficult to provide a plastic material fulfilling all of the strength and insulating requirements set to such frame structures, reinforcing and/or insulating material such as wood must be used.

Applicant's patent EP-Bl-O 251 804 discloses a frame structure of the kind mentioned in the introduction. The frame structure is in the form of a window structure, for instance a window frame or sash. The plastic covering of the frame structure disclosed in this document is obtained by encapsulating the core at least partly by moulding a layer of for instance polyurethane on the core. The core may be made of wood or wood-based material, such as pine, chipboard or plywood. This construction is a success and provides a number of advantages, especially with regard to weatherproofness, while at the same time providing some possibility of letting the natural water contents of the wood migrate and evaporate to the surroundings. With regard to insulating properties and the resistance against deterioration of the wood of the construction, there is, however, room for improvement.

It is an object of the invention to provide a frame structure of the above kind having improved properties with respect to deterioration of parts of the frame structure due to influences of the surroundings, while still providing a weatherproof and robust construction.

To achieve this object the frame structure outlined in the introduction is characterized in that the at least one wooden core member includes at least one member of wood, which has been subjected to a treatment selected from the group consisting of heat-treatment, acetylation and impregnation, and that the core member made of treated wood constitutes a first shield of said shielding arrangement.

By including at least one wood member that has been subjected to such a treatment into the core of the frame structure, a number of advantages have been obtained. First, the risk of deterioration of the treated wooden core member itself has been reduced or even eliminated. Without being bound by theory, it is believed that some of the deterioration that such a frame structure is subjected to from the surroundings during its lifetime is due to detrimental effects resulting from the water contents of the wood. Second, it has proven possible to

utilize the treated wooden core member as a part of the shielding arrangement. Traditionally, the shielding arrangement is an external shielding arrangement including coverings, claddings and/or flashings connected to the pieces of the frame structure. By providing the first shield of such an arrangement in the frame structure itself, an increased protection is obtained in a simple manner.

Treated wood has been found to possess a large number of properties equal to or better than those of ordinary wood which has not been subjected to treatment within the context of the present invention, i.e. for instance only traditional seasoning. Until now there has been a reluctance or even prejudice to use treated wood, which is traditionally a relatively expensive and high-class material as a core member in such constructions. However, despite the higher price of treated wood compared to ordinary, untreated wood, the overall lifetime price of the resulting frame structure is surprisingly not significantly raised when using treated wood. This is, i.a., due the superior properties of treated wood, so that the risk of exchange of parts is very low.

In order to facilitate the manufacture and make it possible to optimize the properties, the core may include a plurality of core pieces, each said core piece including at least one core member of treated wood.

Conveniently, said plurality of core pieces may total four core pieces corresponding to the side, top and bottom pieces of the frame structure. In a further development of this embodiment, at least one of said core pieces includes a plurality of core members. Each core piece may have its individual configuration of core members in dependence of the need for strength, weatherproofing properties and/or aesthetical appearance. The configuration of each individual core piece may vary. For instance, a first core member and a second core member of said core piece may be connected with each other at a first set of mutually facing contact surfaces, said first or second core member being formed from treated wood.

In order to obtain further advantages during manufacture and/or in use of the frame structure the core piece may comprise a third core member connected with the first and/or the second core member at a second set of mutually facing contact surfaces. In one further development of this embodiment, the third core member is made from the same material as the first core member. This makes it possible to obtain similar properties and appearance on several faces of the frame structure.

In an advantageous further development of the embodiment relating to core pieces formed by a plurality of core members, the first core member of each core piece faces inwards with respect to the frame opening and the second core member is made of treated wood and faces outwards. This makes it possible to achieve a harmonized appearance on the side which is visible to the user in the mounted state of the frame structure, whereas the external or outwards facing sides most exposed to the weathering are duly protected by the inherent properties of the treated wood.

Depending on the intended field of application of the frame structure, the plastic covering may in cross section cover only part of the surfaces of the wooden core member. This makes it possible to optimize the use of the plastic material, which is relatively costly.

Preferably, the plastic covering in cross section comprises two groups of each at least two parts provided on substantially opposite surfaces of said core member. The plastic covering may cover parts of the surfaces of the wooden core member visible to a user in a mounted state of the frame structure. The plastic covering provides protection and a smooth surface, which in addition to being aesthetically pleasing is advantageous from a practical point of view. Such a plastic covering provides for a surface which is easy to clean and demands almost no maintenance in the form of e.g. painting, lacquering, oil treatment etc..

In a preferred embodiment, a second shield of said shielding arrangement covers at least the part of the surfaces of the wooden core member uncovered by the plastic covering. The configuration of such a

second shield may be optimized with respect to the need for protection depending on the particular exposure to the weathering.

Preferably, the parts uncovered by the plastic covering include surfaces substantially parallel to the roof in the mounted position. This makes it particularly easy and reliable to provide the second shield.

Alternatively or additionally, the parts uncovered by the plastic covering include surfaces substantially perpendicular to the roof in the mounted position.

The second shield may include a covering and/or a cladding. Furthermore, the second shield may include a flashing.

The wooden core member may be shaped by any suitable process, but according to an embodiment the wooden core member is chamfered to the desired shape. The resulting outline or cross section of the core member is relatively smooth with rounded edges, whereby flow of the plastic materia! is facilitated, the production time reduced, and a high quality coated frame structure may be achieved.

Jointing of wooden core members of different pieces of the frame structure may be accomplished by any suitable joining means, such as nails, screws, fittings, glue etc. In an embodiment of the invention the wooden core members are assembled with finger joints with a plurality of fingers, of which one finger joint is an interference fit, whereas the rest of the finger joints are loose fits. Hereby the frame structure may be assembled quickly and with relative ease without need for special tools. The interference fit holds the members together during moulding of the plastic encasing, and the loose fit allows for the plastic material to flow into the gaps between the fingers during manufacture, and when the plastic is set, the joint is effectively fixed. As the joint is completely encased in plastic material, the surface of the frame structure is closed and impervious making the frame structure weatherproof and robust.

The thickness of the plastic material encasing the wooden core member is a balance of integrity of the resulting frame structure, material cost, insulation properties etc. A suitable interval of the average thickness of the plastic material is 1 to 8 mm, preferably at

least 2 mm and maximum 5 mm. The plastic material is relatively expensive, and hence the thickness should be kept at a minimum, but practical problems relating to moulding of the plastic sets a lower value of about 1 mm. Although the treatment selected for the core member or members provides a protection against fungus which will be sufficient for most applications of the frame structure, it is possible to subject the at least one wooden core member to a treatment with a fungicide.

Another aspect of the invention relates to a method for manu- facturing a frame structure comprising the steps of; providing a core member of treated wood, pre-treating the surface of the core member to facilitate adherence, assembling a core piece of a plurality of core members, placing a set of core pieces in a mould, injecting a setting plastic material in the mould, removing the finished frame structure from the mould, and providing a shielding arrangement to cover at least parts adapted to face outwards in a mounted position of the frame structure. This method can be performed with a limited degree of manual labour, thereby resulting in a relatively efficient and low cost method for manufacture when producing such frame structures in large numbers.

The core member may be shaped in any suitable way, such as by sawing, planing and milling or the like, however according to an embodiment the core member is machined in the appropriate shape by moulding, chamfer, or the like. Hereby the resulting core member has an outline with a relatively smooth contour, which is advantageous with regard to moulding of the plastic around the core member, as the flow of plastic in the mould is facilitated.

The core members may be joined at corners by any suitable means, such as screws, nails, fittings etc., but according to an embodiment ends of the core members are machined to provide engaging finger joints with a plurality of fingers of which one set of fingers are adapted to provide an interference fit, whereas the rest of the finger joints are loose fits. Hereby jointing is facilitated, and there is no need for special tools are separate elements. Further metal elements

will have the disadvantage that due to the thermal conductivity of metal there is a risk of cold bridges in the construction and poor insulation property of the construction. The interference fit of some fingers will hold the construction assembled in the mould, whereas the loose fit providing gaps between other fingers will allow plastic material to flow into the gaps during moulding and securely fix the joint when the plastic sets.

Pre-treating of the surface of the core member to facilitate adherence may be accomplished in a number of ways, such as by etching the surface, applying a suitable primer or the like. According to an embodiment the step of pre-treating the surface of the core member is a step of roughening the surface, to provide a non-smooth surface having improved adherence characteristics. The roughening entails an increase in the area of the contact surface between the core and the plastic covering. Such roughening may also include e.g. a chamfering or grooving operation, in which the surface is provided with a number of grooves of identical or varying depth and width. This operation is carried out by an appropriate tool, such as a gouge or moulding iron, which may have e.g. a zigzag pattern of valleys and troughs to form grooves of a depth of e.g. 1 mm in the surface of the core member. The advantageous effect may be due to facilitated wetting of the surface, so the plastic material will get in intimate contact with the surface during moulding, and hence form a strong bond between the core member and the plastic material. According to an embodiment, the setting plastic material is polyurethane, which is a well-known material with suitable properties with regard to weatherproofness, insulation, mouldability etc.

In the following the invention will be described in more detail by way of. example and with reference to the drawing, in which: Fig. 1 is a perspective view showing a window incorporating a frame structure in a first embodiment of the invention;

Fig. 2 is a cross-sectional view of a detail of the frame structure, along the line II-II in Fig. 1;

Fig. 3 is a photo of a cross-sectional slice of a window frame

prototype, said photo corresponding to the cross-sectional view of Fig. 2 of the first embodiment of the frame structure shown;

Fig. 4 is a cross-sectional view corresponding to Fig. 2 of a second embodiment of the frame structure according to the invention; Fig. 5 is a cross-sectional view of a third embodiment of the frame structure according to the invention;

Fig. 6 is a perspective view showing a detail of a frame structure in a fourth embodiment of the invention;

Figs 7 to 9 are cross-sectional views along the lines VII-VII, VIII-VIII and IX-IX, respectively, in Fig. 6;

Fig. 10 is a photo of a corner joint in the window frame prototype shown in Fig. 2;

Fig. 11 is a front view photo of a core of a window frame prototype corresponding to a fifth embodiment of the frame structure according to the invention;

Fig. 12 is a side angle view photo of the prototype window frame core of Fig. 11;

Fig. 13 is a front view photo of a core of a window sash prototype corresponding to a sixth embodiment of the frame structure according to the invention; and

Fig. 14 is a side angle view photo of the prototype window sash core of Fig. 12.

In the first embodiment of the frame structure shown in Fig. 1, the frame structure is a window frame having two side pieces 1 and Ia, a bottom piece Ib and a top piece Ic. As will be described in further detail below, the structure of the individual pieces may vary within the general principle underlying the invention, i.e. that a core including a core member comprising treated wood is encased by a plastic covering.

However, in the following reference will be made only to the right-hand side piece 1.

In the drawing of Fig. 2 and the photo of Fig. 3 a cross- sectional view of a detail of a window frame side piece according to the invention can be seen. The side piece 1 comprises a core consisting of a core member 2 of treated wood encapsulated in a plastic covering in the

form of a surface layer 3 of plastic material. The surface layer 3 is formed of foamed polyurethane. The wooden core is machined into shape by moulding or chamfer in long units, and can even make up an entire side piece of the window if considered advantageous. Hence the cross-section shown comprises recesses 4 and 5, which are not used at this position, but has a function elsewhere along the frame side piece. The recess 6 is adapted for taking up a lining.

In the embodiment shown in Fig. 3, the single core member 2 is made of wood which has been heat-treated. The growth rings of the heat-treated wood can be seen, and it is also seen that the heat-treated wood is relatively dark in colour. Research work on heat treatment of wood has been performed e.g. in Finland for some years, and reference is made to the previously mentioned publication. In this context heat treatment processes are processes in which the physical properties of the wood are changed permanently, i.e. moisture content, but also strength, insulation property etc. Such changes are effected when wood is subject to temperatures above 150 0 C. In the embodiment shown, the heat-treated wood has been subjected to a temperature in the interval of 150-240 0 C for 0.5-4 hours. The temperature may have been constant during this interval or vary within the limits of the speed of temperature adjustment of the kiln. Other heat-treatments are of course conceivable as well, as long as they provide the properties aimed at. The heat- treated wooden core member preferably has a density between 350 and 500 kg/m 3 . The wood species of the heat-treated part of the core may be any species suitable to the purpose, examples being softwood species such as pine or spruce.

The effect of heat treatment of wood depends on a number of parameters, such as • the maximum temperature and the length of the actual heat treatment period

• the temperature gradient

• the length of the entire heat treatment

• the use and amount of water vapour

• the kiln drying process before the actual heat treatment

• the wood species and its characteristic properties.

As mentioned temperatures over 150 0 C alter the physical and chemical properties of wood permanently, for example the colour of the wood darkens, the shrinkage and swelling of the wood is reduced, and the equilibrium moisture content of the wood is improved. It is also found that the strength is reduced, but the insulation property is enhanced. The heat treatment process is normally divided in a preheating period, an actual heat treatment period and a cooling period. During preheating and cooling the temperature gradient is controlled to avoid excessive splitting or cracking of the wood.

Heat treatment reduces and lowers water uptake, which is advantageous with regard to durability of the wood and resistance to deterioration. However, this effect also lowers the adherence of the plastic material during moulding, and hence it has till now been considered very difficult to encapsulate heat-treated wood in plastic.

Swelling and shrinking of heat-treated wood is reduced, so the risk of cracking of the plastic covering is reduced.

A disadvantage of heat-treated wood is that the strength de- crease by 10-30% in bending and pulling, and the wood becomes more brittle, but it is surprisingly found that the reduction in strength is not a problem in the frame structure according to the invention.

Figs 4 and 5 schematically show alternative embodiments of the frame structure according to the invention. Fig. 4 shows a cross sectional view of a window frame side piece, and Fig. 5 correspondingly shows a cross sectional view of a window sash side piece. In Figs 4 and 5 a plastic covering in the form of a surface layer 103, 203 of plastic material covers only part of the surfaces of a wooden core member 102, 202 seen in cross section. The surface layer 103, 203 comprises two groups of each at least two parts provided on substantially opposite surfaces of said core member. As previously described large binding forces are achieved between the surface layer 103, 203 and the core member 102, 202 because the plastic material adheres well to treated wood. However, additional safety from separation of plastic from treated

wood is achieved by this particular provision of surface layer parts.

As an alternative to the above-mentioned heat-treatment, the wooden core member or members may have been subjected by acetylation. Acetylation, in general, is a process that introduces an acetyl functional group into an organic compound. Mores specifically, the free hydroxy! groups of the wood are converted into acetyl groups, e.g. by making the wood react with acetic anhydride. In this manner, the hydroxyl groups, which are known to adsorb water from the surroundings and are furthermore believed to be the source of decay of the wood, are eliminated. This has the advantage that the strength and adhesion properties of natural wood are maintained. However, the negative aspects of untreated wood having natural water content are reduced, as the weathering does virtually not influence a core member treated by acetylation. As a further alternative the wooden core may be treated by impregnation. Impregnation is a well-known process and may be carried out in a variety of different steps. One particularly efficient method is disclosed in WO 2003/095165, the contents of which are incorporated herein by reference. The above-mentioned treatments all provide a protection against the formation of fungus, which will be sufficient for most applications. However, as an additional treatment the wooden core member or members may further be subjected to a treatment with a fungicide. This eliminates completely or at least reduces to a very large extent the risk of fungus formation in the frame structure.

In the embodiment of Fig. 4 the first group comprises parts 103a - 103i, parts 103a - 103c being disposed on surfaces of the core member 102 facing a window sash of the window, and parts 103d, 103e being disposed on opposite surfaces of the core member, i.e. the surface of the core member, which in a mounted state of the window is facing a roof into which the window has been integrated. The second group comprises parts 103f - 103i, parts 103f - 103h being disposed on surfaces of the core member 102 in a mounted state of the window facing the inside, i.e. a room of a building into which the window has

been built, and part 103i being disposed on an opposite surface of the core member 103, i.e. the surface of the core member 103, which in a mounted state of the window is facing the outside.

Correspondingly, in the window sash of Fig. 5 the first group comprises parts 203a - 203c, part 203a being disposed on a surface of the core member 202 facing a windowpane of the window sash, and parts 203b, 203c being disposed on opposite surfaces of the core member 202, i.e. surfaces of the core member, which in a mounted state of the window are facing a window frame of the window, e.g. the window frame of Fig. 4. The second group comprises parts 203d - 203f, part 203d being disposed on a surface of the core member 202 in a mounted state of the window facing the inside, and parts 203e, 203f being disposed on opposite surfaces of the core member 203, i.e. the surfaces of the core member 203, which in a mounted state of the window are facing the outside.

In the embodiment of Fig. 4 the parts 103d, 103e are separate parts disposed on a mutual surface of the core member 102, thus forming a discontinuation of the surface layer 103 on the surface of the core member 102, which surface in a mounted state of the window is facing and hidden by the roof. Since this surface is hidden, it serves no aesthetic purpose to let the surface layer 103 cover this surface. Similarly, in the embodiment of Fig. 5 the surface layer 203 does not cover the surfaces of the core member 202 hidden, during normal use in a mounted state of the window, to a user inside the building. This saves plastic material, which is relatively costly in comparison with the material of the core. Moisture protection and weather resistance of naked treated wood is typically sufficient, even on surfaces of treated wood facing the outside and acting as a first shield against the weathering. Even other materials utilized as core members may have sufficient properties to face the outside.

In the embodiment shown in Fig. 4 one of basically three different types of sheath-like elements is used for providing a second shield in the shielding arrangement for waterproofing of the construction; a first type of elements known as flashings proof the meeting between the

roofing and the window, a second type of elements known as claddings proof the frame and sash profiles themselves and a third type of elements known as coverings proof space between the sash claddings and the pane or glassing beads. In Fig. 4, the outwards facing side 102a of the single core member 102 acts as a first shield, and a covering (i.e. of the above- mentioned third type) 501 acts as a second shield. The covering 501 extends substantially in parallel with the face 102 facing upwards and outwards in the mounted position of the frame structure and hence substantially in parallel with the roof surface in the mounted position.

In alternative embodiments the core of the side pieces, the top piece and/or the bottom piece comprises further core members of heat- treated wood, non-heat-treated wood or wood treated by any other method, or any other suitable material such as an insulating foamed material. The strength requirements of the top and bottom pieces are typically lower such that these pieces may comprise core members with improved insulating properties, but poorer strength properties, such as an insulating foam material. Such core members are preferably completely encased by more durable core members such as wooden core members.

While core members visible from the inside of a building into which the frame structure has been built, as mentioned in the above, are preferably covered by a surface layer, core members only visible from the outside of the building can be manufactured from another material such as not encased heat-treated or otherwise treated hardwood to provide a compromise between appearance and costs. Heat-treated hardwood has a lighter colour than heat-treated softwood. The hardwood may be in the form of birch or European aspen.

Figs 6 to 9 show an embodiment, in which the pieces 301, 301a, 301b, 301c constituting the core of the frame comprises a number of core members manufactured from different materials. In the embodiment shown, the core may form the core of a frame structure of a window frame, but the principle is fully adaptable to other frame structures, such as a window sash or a frame of a door. It is even

possible to let the core form a substantial part of the frame structure.

In Figs 7 and 9 a first core member 302 and a second core member 303 of the side core piece 301 are connected with each other at a first set of mutually facing contact surfaces 311, the second core member 303 being formed from treated wood, such as for instance heat treated wood, acetylated wood or impregnated wood, having improved deterioration resistance properties than the first core member 302. The material of the first core member 302 may be any material fulfilling the aesthetically and practically convenient demands. For instance, the material may be lacquered pine.

As shown in Fig. 8, the top core piece 301c comprises a third core member 304c connected with the first and second core members 302c, 303c at a second set of mutually facing contact surfaces 312c. In the embodiment shown, the third core member 304c is made from the same material as the first core member, viz. a wooden material in the embodiment shown. The third core member 304c is connected with at least the second core member 303c, said second set of contact surfaces 312c extending substantially perpendicularly to said first set of contact surfaces 311c. The bottom core piece 301b shown in Fig. 9 has substantially the same configuration as the side core piece 301, and comprises a first core member 302b and a second core member 303b.

As in the embodiment shown in Fig. 4 the frame structure provides for a second shield of a shielding arrangement, the parts 303, 303c and 303b acting as a first shield. The second shield is shown only in respect of the piece 301 shown in Fig. 7 but similar configurations are conceivable in connection with the frame pieces 301b and 301c. The second shield thus includes a covering 501 corresponding to the covering in Fig. 4. Furthermore, the shield includes a cladding 502 having a first part substantially parallel with the upper and outwards facing side and a second part substantially perpendicular to the first part. Thus, the second part of cladding 502 covers the outwards and sidewise facing part of core member 303 not covered by either another core member 302 or a plastic covering. Eventually, the shield includes a

flashing 503 comprising a first part along the outwards and sidewise facing side of core member 303 and a second part substantially perpendicular to the first part and adapted to be positioned substantially in parallel with and below the roofing in the mounted position. In all of the above embodiments, the first core member of each core piece faces inwards with respect to the frame opening. However, other configurations are of course conceivable. It is, of course, conceivable to treat the surface or surfaces uncovered by the plastic covering by any suitable coating. In Fig. 10 a photo of a corner joint of the window frame can be seen. A part of the plastic coating 3 has been cut away for illustration of the finger joint. One core 2 comprises three fingers 2a, 2b and 2c, engaged with four fingers 7a, 7b, 7c and 7d of another core. The joint between fingers 7b, 2b and 7c is an interference fit, so this joint will be able to fix the mutual position of the two cores. This means that at manufacture, the cores may be assembled and placed in a mould. The joint between other fingers is a loose fit, so there is a gap into which the plastic coating material may flow and set to fix the joint, as can be seen at reference numeral 8. As will be clear to the skilled person the finger joint should not be considered restricted to the embodiment with core member of treated wood, e.g. heat treated, acetylated or impregnated wood, as the advantages of the joint is evidently also present with core members of other materials, such as untreated wood, plywood etc. In Figs 11 and 12, an embodiment of an assembled frame core

12 can be seen prior to moulding of the plastic coating around the members of the frame core 12. The frame core 12 is assembled of straight pieces of treated wood having uniform cross-section along the length thereof. At a comer joint auxiliary wedge parts 13 may be provided as can be seen to strengthen the joint and provide a smooth transition between the jointed members, if the core members differ in size. The wedge parts 13 are not necessarily made of treated wood, but may be made of for example plywood.

An embodiment of an assembled sash core 20 can be seen in

Figs 13 and 14. The construction of the sash core 20 is a little more complicated and comprises additional plywood parts 21, 22 and 23 attached to the core parts of treated wood.

A prototype of the frame structure was made using a polyure- thane foam of the integral type as the plastic material. The polyurethane was foamed in the mould, and the density of the resulting layer of PUR depending on the free space available in the mould, as e.g. a void will result in a lower density. It will be evident to the skilled person that other types of plastic material could be used with good results.