Frames for windows and other panels

In a composite section for making up window frames and the like, and comprising interengaging sections of metal and of plastics, there are at least two spaced-apart pairs of interengaging hook formations on the two sections, forced into tight engagement by the insertion of a wedging strip between the sections, the spacing apart of the formations ensuring stability against tilting. There are furthermore abutment surfaces on at least one of the hook formations on the plastics section and on the metal section to define accurately the relative positions of the sections. The purpose is primarily to ensure the front and back faces of the composite section are truly parallel and correctly spaced apart.

This invention relates to frames, primarily for windows, although such 
frames may be applied also to other forms of panel used in building 
construction. 
A known drawback of extruded aluminium alloy or other metal frames is their 
high thermal conductivity, the effect of which partially negates the value 
of using double glazing to restrict loss of heat. Frames made of extruded 
plastics material are known, especially in continental Europe, but in 
order to have adequate rigidity they have to be of relatively heavy 
section, making them expensive in terms of material cost, and anyway there 
can be a danger of distortion that may create problems when the corners 
are mitred. 
Composite frames are also known, comprising inner and outer extruded metal 
sections separated by a so-called `thermal break` in the form of a section 
of plastics material that is either bonded to the metal, or mechanically 
keyed to it, or both. Finally, it is known to have simply two extrusions, 
one of plastics and one of metal, keyed together. In both these composite 
forms of frame, the keying together of the rigid metal section and the 
less rigid plastics extrusion can be a problem and despite the use of 
relatively complex interlocking sections with various ribs, flanges and 
rebates, there is the danger that the frames may come apart, especially 
when subjected to the very rough handling that they may receive during 
delivery and erection. 
In particular, proposals have been made involving hook-like projections on 
the metal section and on the extruded plastics sections, which 
interengage, and then the two parts are held together by the insertion of 
a series of spaced apart wedges held in by friction, or in some cases a 
single continuous wedge section held in place by screws. However, these 
known arrangements do not allow for any tolerances in the dimensions of 
the parts. 
There are two important factors to be taken into account in practice in the 
assembly of rectangular frames from composite sections of combined metal 
and plastics section. In the formation of such frames, lengths of the 
composite section are cut to the required length, with mitred ends, and 
then joined together at the corners by special L-shaped connecting pieces. 
If the front and back surfaces of the composite section are not truly 
parallel the corner joint is distorted, so that the two sides of the 
rectangle that meet at that corner fail to lie in a common plane, and the 
whole frame takes on a twisted state. Secondly, if the front and back 
faces are, due to tolerance variations, not exactly the right distance 
apart, the result is likewise an overall distortion of the frame. These 
two factors are not adequately dealt with in the known constructions. 
The aim of the invention is to provide a composite section for use in the 
formation of frames, which section takes the above-mentioned factors into 
account and ensures truly parallel and correctly spaced front and back 
faces despite possible tolerance variations in the metal and plastics 
section that go to make up the composite section. 
According to the invention, in a composite section suitable for forming 
rectangular frames and made up of at least one rigid metal section and at 
least one less rigid plastics section mechanically keyed together by the 
use of interengaging hook formations on the two sections, in co-operation 
with wedging means to hold them together, there are at least two separate 
spaced-apart hook formations on each of the two interengaging sections, 
both hook formations facing in the same direction and at least one of the 
hook formations is of tapering profile to provide a wedging action and at 
least one of the hook formations (it may be the same one) has an abutment 
surface engaging a co-operating abutment surface on the other section to 
define accurately the relative positions of the interengaging hook 
formations, the two spaced sets of hook formations being simultaneously 
locked in position by the insertion of a continuous wedge profile that is 
held locked in place by co-operation of its own shape with one of the 
sections. 
By the provision of two spaced sets of hook formations we ensure that there 
can be no relative tilting of the metal section on the one hand and the 
plastics section on the other hand, so that their external faces remain 
truly parallel, and the provision of the abutment surfaces on one of the 
sets of hook formations ensured that those faces are the correct distance 
apart.

Referring first to FIG. 1, and extruded metal section 1 of aluminium alloy 
is basically in the form of a rectangular hollow box section but with an 
extended front flange 2 having a flat front face 3. On one side of the box 
section there are two L-shaped hook formations 4 and 5, widely spaced 
apart in a direction perpendicular to the plane of the face 3. Both hook 
formations point in the same direction, i.e. towards the face 3. One limb 
of each hook is parallel to that face and the other limb, which points 
towards it, has a rounded nose and has one side, 4a, 5a perpendicular to 
the face 3 and the other side 4b, 5b inclined at 15.degree. to that 
perpendicular. This inclined side has a step or shoulder, 4c, 5c, directed 
away from the face 3. 
Co-operating with the metal section 1 is a section 6 of plastics material, 
preferably unplasticised PVC. It is of complex form, comprising two linked 
hollow box sections, and a flat face 7 which defines the rear face of the 
overall composite section that is formed by the sections 1 and 6. The 
section 6 has two spaced-apart L-shaped hook formations 8 and 9, both 
facing in the same direction, i.e. towards the face 7, and co-operating 
respectively with the hook formations 4 and 5 on the metal section 1. The 
free limb 8a, 9a of each hook formation 8, 9 tapers towards its free end 
(for example with its inner face inclined at 5.degree. to a line 
perpendicular to the face 7) and terminates in a rounded nose. 
When the two sections 1 and 6 have been caused to interengage, with the 
hook formations 4 and 5 engaging the hook formations 8 and 9, a continuous 
resilient wedge section 10 of unplasticised PVC is forced into the gap 
between a face 11 on the back of the hook 9 and a face 12 on the inside of 
the front flange 2. A rebate 13 on the wedge section 10 engages under a 
shoulder defined by a head 14 on the flange 2, so as to hold the wedge 
permanently and virtually irremovably in place. 
The insertion of the wedge 10 causes the respective hook formations to 
become tightly engaged and the lateral dimensions of the free limbs of the 
hooks 4 and 5 are such, in relation to the width of the channels defined 
by the free limbs of the hooks 8 and 9, that they distort these hooks 8 
and 9 at least to some extent, and so ensure complete freedom from play in 
both sets of hook formations, despite possible tolerance variations in the 
plastics section or the metal section, or both. Moreover the nose of at 
least the hook 9 engages a face 15 on the one limb of the hook 5 to define 
the degree of engagement of the hook formations, the face 15 being in a 
plane parallel to the faces 3 and 7. 
Thus the spacing apart of the pairs of hook formations, combined with the 
wedging action, ensures freedom from play or tilt between the sections 1 
and 6, and so the faces 3 and 7 are truly parallel. Secondly, the abutment 
of the nose of the hook 9 against the face 15 on the hook 5 defines 
accurately the relative positions of the sections 1 and 6 in a direction 
perpendicular to the planes of the faces 3 and 7, and so the spacing apart 
of those faces, i.e. the overall front-to-back thickness of the composite 
section, is accurately determined. These two factors ensure that a frame 
built up from lengths of this composite section, is free from distortion 
and that its front and back faces are flat. 
It will be understood that the flanges, undercuts and rebates that are 
visible in FIG. 1 but have not been described are for the purpose of 
receiving glazing, and other mounting and sealing strips, not shown. 
FIG. 2 illustrates a symmetrical composite section, suitable for forming 
mullions within a rectangular frame made from the section of FIG. 1. An 
aluminium alloy extrusion 16 comprises a box section with a front face 17, 
and with two hook formations 18 and 19, spaced apart and lying on opposite 
sides of the box but both pointing towards the plane of the face 17. An 
extrusion 20 of unplasticised PVC is based on a combination of two 
back-to-back mirror image versions of the extrusion 6 of FIG. 1, but with 
one hook formation from each omitted, so there is a total of only two hook 
formations 21 and 22, co-operating respectively with the hook formations 
18 and 19 of the section 16. The plastics extrusion has a flat rear face 
23. The wedge section 10 that holds the two extrusions together is 
substantially the same as that of FIG. 1 but in this case two lengths of 
this wedge sections are used. In the version of FIG. 2 there are shallow 
beads 24 and 25 on the plastics extrusion to engage the backs of the hook 
formations 18 and 19. These beads help to define accurately the effective 
widths of the channels which the hooks 18 and 19 enter, and ensure that 
they become wedged, distorting the plastics and free from play. Like the 
hook 9, the nose of each hook 21 and 22 engages an abutment face 26 and 27 
on the co-operating hook of the metal section to define accurately the 
spacing between the faces 17 and 23. The parallelism of these faces is 
ensured by the wide lateral spacing of the two pairs of co-operating hook 
formations, in combination with their wedging action. 
Additional stability is provided by beads 28 and 29 on the plastics 
section, engaging opposite sides of the inner end of the metal section 16.