EP1580387A2

EP1580387A2 - Thermal-break section for door and window frames or the like and associated method for assembling said section

Info

Publication number: EP1580387A2
Application number: EP05075675A
Authority: EP
Inventors: Maurizio Hydro Building Systems S.p.A. Dampierre
Original assignee: Norsk Hydro ASA
Current assignee: Norsk Hydro ASA
Priority date: 2004-03-23
Filing date: 2005-03-22
Publication date: 2005-09-28
Also published as: EP1580387A3; ITMI20040551A1

Abstract

A thermal-break section (21) is described, said section comprising: a first half-shell (22), a second half-shell (23), and at least one body (24) of heat-insulating material, said first half-shell and said second half-shell comprising longitudinal teeth forming a seat for said at least one body of heat-insulating material, characterized in that said first and second half-shells (22,23) comprise at least one fixed longitudinal locating tooth (229,239) and at least one longitudinal tooth (228,238) which can be folded from a first open position into a closed locking position for locking said at least one body (24) of heat-insulating material. The solution according to the present invention can be used for the production of solid and strong thermal-break window and door frames having a thermal-break chamber which is substantially symmetrical and not staggered.

Description

The present invention relates to the sector of aluminium sections used for the production of door and window frames. In particular, it relates to a so-called thermal-break section and a method for assembling said section.
Various aluminium sections used for the production of door and window frames are known. In particular, non-insulated sections are known in which there exists metallic continuity between the section parts which are exposed to the external environment and the section parts inside a substantially closed environment (for example an apartment). Since aluminium is a good heat conductor, non-insulated sections therefore have the drawback that they allow heat exchange between the inside and the outside.
In order to overcome these drawbacks, for some time "thermal-break" sections have been known. In thermal-break sections, the aluminium part exposed to the exterior is separated from the internal part by means of heat-insulating bodies. In these sections a thermal-break chamber with walls made of heat-insulating material is formed. Usually, this material is a plastic material. Typically, this plastic material is polyamide, ABS, PVC or the like. This chamber partially made of plastic material interrupts the transmission of heat due to conduction between the outer part and the inner part and provides the section with an optimum heat-insulating property.
CH 654 897 A discloses a composite profiled rod which is used, for example, for forming a window frame. It has two metal profiled rods and an insulating profiled rod which connects them together. The insulating profiled rod has two insulating strips which are provided in the vicinity of their longitudinal edges with undercuts in which limbs of the metal profiled rods engage. Two insulating webs connect the two insulating strips to one another in the region of the undercuts. These webs divide the intermediate space existing between the strips into three parts.
DE 29 11 832 A discloses a heat-damming compound profile for window or door frames or similar components in which there is provided two metal profile rods and an intermediate layer connecting these profile rods. The intermediate layer is composed of a profiled shape-retaining insulating strip. Each profile bar is provided with a forcible guide for the insulating strip and are connected by oppositely located lugs outside the insulating strip. Each lug is provided with a small continuous cam which is movable against a corresponding projection of the insulating strip. DE 29 11 832 A also provides a method of making a heat-damming compound profile by pushing the insulating strip into the forcible guides and into the lateral pins of the profile bars, and exerting pressure from the exterior by means of rollers or pressure gliders upon the metallic lugs at simultaneous directed support of the profile bars at the sides opposite the lugs.
DE 3221 218 A discloses a profiled body which comprises two profiled rails, in particular such rails of metal, arranged at a distance parallel to each other.
Other thermal-break section arrangements are known from DE 30 25 706 A and DE 26 08 299 A.
In the currently known thermal-break sections, the thermal-break chamber is formed by inserting the ends of two polyamide strips into special cavities provided in two half-shells of the section. Alternatively, tubular shaped heat-insulating bodies are used. Engagement of the polyamide strips or the tubular body is performed plane-wise. In other words, the fixing points are situated in two parallel planes. Each of the abovementioned special cavities is delimited by a pair of longitudinal folding teeth or by a longitudinal folding tooth and a fixed shoulder. During insertion of the strips or the tubular body, the teeth are all open so as to allow precisely easy insertion of the strips or the tubular body, respectively. After insertion of the strips or the tubular body into the respective cavities, the semi-finished section (comprising the two half-shells and the polyamide strips loose inside the respective cavities) is processed by a rolling machine. The rolling machine compresses the teeth of both cavities and makes fast the joint between the strips, or the tubular body, made of heat-insulating material and the half-shells.
The rolling machines used to compress the teeth comprise in turn facing rollers which compress the longitudinal teeth when the semi-finished section passes between them. In order to perform this tooth compression operation, the rolling machine must have sufficient space to allow the parallel passing movement of the compression rollers on the two opposite sides of the section thus assembled. This requirement, in turn, means that the section must be square or at least only slightly rounded.
However, at present many door and window frames are currently required with particularly rounded forms and very deep glass-gripping flanges, primarily in order to satisfy new aesthetic requirements. In these cases, the glass-gripping flange of the section limits the space where the compression roller must pass into the glass insertion cavity of the section. In other words, the flange (typically the glass-gripping flange) projects and "covers" (when the section is seen in a cross-section) the teeth which can not be folded.
Necessarily, this has meant that in the current thermal-break sections with particularly rounded forms and very deep glass-gripping flanges the strips of heat-insulating material are positioned staggered, so as to nevertheless allow the passing movement of the rollers inside the glass insertion cavity.
However, owing to this staggered position of the strips, during folding of the tooth, the section tends to twist and become distorted owing to the uneven pressure of the rollers. Because of this, it is difficult, if not impossible, to assemble the sections in a precise manner in order to form a frame or a leaf, for example.
In an attempt to overcome this problem, some manufacturers tend to reduce the pressure exerted by the rollers. In this case, however, the problem arises of not ensuring a strong and reliable joint between the half-shells and the strips of heat-insulating material because the teeth are not compressed sufficiently. In this case also, assembly of a frame or a leaf is difficult because the strips of heat-insulating material tend to slip, in particular during cutting of the sections.
In addition to the above, the staggered positioning of the strips of heat-insulating material has the effect that the surface in contact with the external atmosphere is located in a position set further back from a hypothetical middle axis of the section. As a result, the external atmosphere affects a larger surface area of the section and therefore the thermal transmittance value of the door or window frame increases.
In the light of the above problems, the main object of the present invention is to provide a thermal-break section in which the strips of heat-insulating material substantially face each other and may be rigidly fixed to the half-shells of the section even when the position of the glass insertion cavity prevents the use of facing rollers.
These and other objects are achieved by means of a section in accordance with Claim 1 and a method according to Claim 13. Further advantageous features are set forth in the dependent claims. All the claims are understood as forming an integral part of the present description.
According to a first aspect, the present invention provides a thermal-break section comprising: a first half-shell, a second half-shell, and at least one body of heat-insulating material, said first half-shell and said second half-shell comprising longitudinal teeth forming a seat for said at least one body of heat-insulating material, each of said first and second half-shells comprising one fixed longitudinal locating tooth and one longitudinal tooth which can be folded from a first open position into a closed locking position for locking said at least one body of heat-insulating material inside the seat. According to the invention, the second half-shell comprises a flange projecting over its fixed longitudinal locating tooth when the thermal-break section is seen in a cross-section. In a particularly advantageous embodiment, the body of heat-insulating material comprises two bodies of heat-insulating material, each having a cross-section substantially identical to the other one and being situated symmetrically opposite each other in an interlocking arrangement.
In one embodiment, the flange also projects over the fixed longitudinal locating tooth of the first half-shell when the thermal-break section is seen in a cross-section. Possibly, the flange is a curved glass-gripping flange.
Advantageously, the thermal-break section according to the present invention comprises a spacer with interlocking elements for joining with said two bodies of heat-insulating material. Possibly, the spacer is cross-shaped.
Preferably, the heat-insulating material is a plastic material, preferably polyamide.
Preferably, between the longitudinal locating tooth and the longitudinal folding tooth there is a continuous and substantially flat bottom surface.
The longitudinal locating tooth may comprise an angled surface inside the seat and a substantially flat surface outside the seat, the angled surface forming an acute angle with the bottom surface and the external surface being substantially perpendicular to the bottom surface.
The fixed and foldable teeth have substantially the same shape. In particular, the longitudinal locating tooth comprises a connection surface between said angled surface inside the seat and the flat surface outside the seat, the connection surface forms an acute angle with the flat surface outside the seat. The folding tooth comprises an angled surface inside the seat and a surface outside the seat provided with a longitudinal weakening groove.
When the section is assembled, the bottom surfaces of the first and second half-shells are substantially parallel and the substantially flat external surfaces of the locating teeth lie in a same plane. The plane in which the substantially flat external surfaces of the locating teeth lie coincides substantially with the bottom surface of a glass cavity.
According to a second aspect, the present invention provides a method for manufacturing a thermal-break section. The method comprises the steps of: providing a first half-shell, a second half-shell and at least one body of heat-insulating material, each of the half-shells comprising longitudinal teeth forming a seat for said at least one body of heat-insulating material; inserting said at least one body of heat-insulating material inside the seat, folding only one of the longitudinal teeth of each half-shell towards said at least one body and keeping the other one of said longitudinal teeth of each half-shell substantially fixed. According to the present invention, the step of providing a second half-shell comprises providing a second half-shell with comprises a flange projecting over its fixed longitudinal locating tooth when said thermal-break section is seen in a cross-section. According to the present invention, the step of inserting said at least one body of heat-insulating material comprises the step of inserting two bodies of heat-insulating material, each having a cross-section substantially identical to the other one and being situated symmetrically opposite each other in an interlocking arrangement.
According to one embodiment, a spacer is inserted between a first heat-insulating body and a second heat-insulating body.
Preferably, the heat-insulating material is a plastic material, preferably polyamide.
The method advantageously comprises the step of arranging the tooth of each half-shell to be kept fixed against a corresponding locating surface. The locating surface should be relatively thin in order to operate between the projecting flange and the fixed teeth. Possibly it is substantially "L" shaped.
Preferably, the method according to the invention comprises the step of providing the folding tooth of each half-shell with a longitudinal weakened groove.
According to a third aspect, the present invention provides a half-shell for the manufacture of a section as set forth above which comprises a longitudinal tooth which is substantially fixed and a longitudinal folding tooth for locking at least one body of heat-insulating material, between the fixed tooth and the longitudinal tooth there being formed a bottom surface which is substantially flat and continuous. Preferably, the half-shell comprises a flange projecting over its fixed longitudinal locating tooth when said thermal-break section is seen in a cross-section.
A detailed description of the invention now follows, said description being provided purely by way of a non-limiting example, to be read with reference to the accompanying illustrative plates in which:

Figure 1 is a cross-sectional view of a square thermal-break section according to the known art;
Figure 1.1 is an exploded view of the section according to Figure 1;
Figure 2 is a cross-sectional view of a first embodiment of the invention associated with an heat-insulating body consisting of two parts;
Figure 2.1 is an exploded view of the section according to Figure 2;
Figures 2.2, 2.3 and 2.4 are enlarged details of Figure 2;
Figure 3 is a cross-sectional view of a second embodiment of the invention associated with an heat-insulating body consisting of three parts;
Figure 3.1 is an exploded view of the section according to Figure 3; and
Figures 3.2, 3.3 and 3.4 are enlarged details of Figure 3.

With reference initially to Figure 1, a cross-sectional view of a known thermal-break section 11 is shown. In particular, Figure 1 shows a shutter section with a square shape. The known shutter section comprises a first inner half-shell 12 and a second outer half-shell 13 and a pair of strips 141, 142 of heat-insulating material. Usually said heat-insulating material is polyamide, PVC, ABS or another plastic material.
The first half-shell 12 of the section 11 in Figure 1 comprises a substantially rectangular main chamber 121 with two larger sides 122 and two smaller sides 123. A seal holder flange 124 extends in a direction from one of the larger sides 122. One of the smaller sides 123 has hooks 125 for fixing a glass stop flange (not shown). On the other large side 122 there are two grooves 126 for inserting the ends of the heat-insulating strips 14.
Each of the grooves 126 for the ends of the strips 14 comprises an inclined shoulder 127 and a rotatable locking tooth 128. For the purposes of the present invention, the shoulder 127 is not considered to be a tooth.
The second half-shell 13 of the thermal-break section shown in Figure 1 comprises a main chamber 131 which is substantially rectangular. Along a larger side 132 of said main chamber 131 there are two respective grooves 136 for inserting the other ends of the heat-insulating strips. Each groove 136 is delimited by an inclined shoulder 137 and by a rotatable locking tooth 138. A glass-gripping flange 134 extends from an extension on the opposite side to that of the grooves 136. A seat for a seal is located at the end of the glass-gripping flange 134. When the section 11 is assembled, combining the two half- shells 12, 13 and the heat-insulating strips 141, 142, the glass-gripping flange 134 and the glass stop flange form a space which is called "glass cavity". The glass is also not shown for the sake of clarity.
Assembly of the two half- shells 12, 13 of the leaf section 11 according to Figure 1 is performed by rotating all four teeth 128, 138 towards the polyamide strips 141, 142. Typically, this rotation is performed by a rolling machine with facing rollers 15 which engage with the teeth 128, 138 on the glass cavity side and on the opposite side. It is obvious that this operation would be particularly difficult if the glass-gripping flange 134 were curved, as shown in Figures 2, 2.1, 3 and 3.1, and covered (at least partially) the rotatable teeth 128, 138 because there would not be space (on the glass cavity side) for the passing movement of the facing rollers of the rolling machine. The rolling operation would moreover be unreliable if the strips 141, 142 were arranged in a staggered manner since the rollers 15 would not operate opposite to each other and all the abovementioned drawbacks would arise.
A first embodiment of the section 21 according to the present invention is shown in Figure 2 and in Figures 2.1 to 2.4. It will be noted that the section according to Figure 2 is substantially similar to the section according to Figure 1 and a detailed description thereof will not be repeated. In order to indicate the same components, reference numbers similar to those used in Figures 1 and 1.1 have been used, but with the first digit "1" being replaced by the digit "2".
The section according to Figure 2, however, differs substantially from the section in Figure 1 in that it has a very curved glass-gripping flange 234 which prevents the use of facing rollers 25 in a roller machine.
According to the present invention, each half- shell 22, 23 comprises two longitudinal teeth 228, 229, 238, 239 which are separated by a substantially flat and continuous bottom surface 226', 236'. The term "continuous" is understood as referring to a surface which is not interrupted by other teeth, projections or shoulders. However, the present invention also contemplates other embodiments with teeth or projections which interrupt this flat bottom surface 226', 236', but which in practice do not play a part in locking the heat-insulating material.
One longitudinal tooth 229, 239 of each half- shell 22, 23 is substantially rigid and is not folded during assembly of the half- shells 22, 23 and the bodies of heat-insulating material 241, 242. Typically, in a leaf section 21, the substantially rigid teeth 229, 239 are those on the glass cavity side. In fact, on the opposite side, there are generally no particular space restrictions. In any case, according to the present invention, the presence of a pair of teeth which are substantially fixed and rigid also in sections where there are no problems of limited space may be envisaged.
Each of the rigid teeth 229, 239 has an angled surface 229', 239' inside the seat 226, 236 and a substantially flat surface 229", 239" outside the seat 226, 236. The angled surface 229', 239' forms an acute angle with the bottom surface 226', 236' and the external surface 229", 239" is substantially perpendicular to the bottom surface 226', 236'. When the section 21 according to the invention is assembled, the external surfaces 229", 239" of the fixed teeth 229, 239 of the first and the second half- shells 22, 23 lie in a same plane and the bottom surfaces 226', 236' are substantially parallel.
Then, the half- shells 22, 23 of the section 21 according to the invention are extruded with a tooth 229, 239 having a predefined angle and an opposite tooth 228, 238 extruded with a weakening line 228', 238'. This weakening line favours compression with the passing movement of one of the rollers 25 of the rolling machine which performs joining together of the half- shells 22, 23 and the heat-insulating strips 24 and produces the thermal-break area or chamber 26. Typically, the weakening line 228', 238' is in the form of a longitudinal weakened groove. It will also be noted that the foldable teeth 228, 238 have an end nose and are joined to the bottom surface 226', 236' by means of a weakened base in order to reduce the thickness of the foldable teeth 228; 238 in the region of the base.
Owing to this arrangement, the part of the section directed towards the glass insertion cavity acts only as a bearing/opposition surface while the compressive force is exerted solely on the opposite side by means of a single roller 25.
In Figure 2 (as well as in Figures 2.1, 2.2 and 2.4), the body of insulating material comprises a body of insulating material consisting of two parts 241, 242 which are substantially symmetrical and mounted facing each other and substantially in an interlocking manner. Basically, the two interlocking heat-insulating bodies 241, 242 form a tubular heat-insulating body. By means of the body of heat-insulating material (for example polyamide) an interruption is created between the half-shell 23 directed towards the outside and the half-shell 22 directed towards the inside. The two bodies 241, 242 of heat-insulating material joined together have an overall form which is approximately rectangular viewed in cross-section with shaped corners such as the teeth 228, 229, 238, 239. Preferably, the body of heat-insulating material delimits an internal area. As is conventional, the bodies of heat-insulating material may be provided with grooves 243 for a bead of hot-melting glue (not shown).
It will be noted that the section according to Figure 3 is substantially similar to the section of Figure 2 and a detailed description thereof will not be repeated. Reference numbers similar to those used in Figures 2 and 2.1 to 2.4 have been used to indicate the same components, but the first digit "2" has been replaced with the digit "3". The section 31 according to Figure 3 is wider and longer than that of Figure 2. In the case also of the section 31 according to Figure 3, the shape of the glass-gripping flange 334 prevents the passing movement of the facing rollers 35. According to the present invention, each groove 326, 336 which houses the body of heat-insulating material 34 comprises a longitudinal locating tooth 329, 339 and a rotatable tooth 328, 338 for locking the heat-insulating body 34. The fixed tooth 329, 339 and the rotatable tooth 328, 338 are separated by a bottom surface 326', 336' which is substantially flat and continuous.
In addition to two separate heat-insulating bodies 341, 342, a cross-shaped spacer 344 is preferably provided. The spacer 344 is also made of heat-insulating material and has a shape complementing that of the two heat-insulating bodies 341, 342. In this way, a chamber is formed inside the heat-insulating body 34, being substantially divided into four equal portions by two longitudinal perpendicular partitions. Advantageously, this internal division of the chamber limits the convective movements inside it.
Various advantages are obtained by the present invention. Firstly, assembly of the half-shells and strips of plastic material is secure, strong and reliable. Moreover, the thermal-break section in which the strips substantially face each other is stronger than the sections with staggered strips and therefore less subject to twisting during processing.
Advantageously, the Applicant has found that, in the thermal-break section according to the present invention, the thermal transmittance line passes substantially along the axis of the thermal-break chamber. In other words, the transmittance line passes along a longitudinal plane parallel to the bottom surface of the seats for the heat-insulating material and situated at the same distance therefrom. On the other hand, the presence of staggered strips moves this thermal transmittance line towards the part of the section directed towards the internal environment and therefore diminishes the effectiveness of the thermal-break characteristic. The result is a high dispersion of heat in the known sections.
Other not insignificant advantages of the present invention consist in the fact that extrusion of the fixed locking teeth is performed with greater precision. This results in an increased strength of the section and an improved product compared to the known products. Finally, the extrusion dies are simpler than those used for extruding half-shells with both the teeth rotatable.
Thanks to the substantially identical shape of the foldable and fixed teeth and to the shape of the two bodies of insolating material which mate together the thermal-break section according to the present invention can be assembled in a very efficient and economical way.

Claims

A thermal-break section (21; 31) comprising: a first half-shell (22; 32), a second half-shell (23; 33), and at least one body (24; 34) of heat-insulating material, said first half-shell (22; 32) and said second half-shell (23; 33) comprising longitudinal teeth forming a seat for said at least one body of heat-insulating material, each of said first and second half-shells (22, 23; 32, 33) comprising one fixed longitudinal locating tooth (229, 239; 329, 339) and one longitudinal tooth (228, 238; 328, 338) which can be folded from a first open position into a closed locking position for locking said at least one body of heat-insulating material (24, 34) inside the seat, wherein:

a) said second half-shell (23; 33) comprises a flange (234) projecting over its fixed longitudinal locating tooth (239, 339) when said thermal-break section (21; 31) is seen in a cross-section;

b) said at least one body of heat-insulating material (24; 34) comprises two bodies of heat-insulating material (241, 242; 341, 342), each having a cross-section substantially identical to the other one and being situated symmetrically opposite each other in an interlocking arrangement.
The thermal-break section according to claim 1, wherein the flange (234) also projects over the fixed longitudinal locating tooth (229, 329) of the first half-shell (22; 32) when said thermal-break section (21; 31) is seen in a cross-section.
The thermal-break section according to claim 1 or 2, wherein the flange (234) is a curved glass-gripping flange (234).
The thermal-break section according to any of previous claims, wherein it also comprises a spacer (344) with interlocking elements for joining with said two bodies of heat-insulating material (241, 242; 341, 342).
The thermal-break section according to Claim 4, wherein said spacer (344) is cross-shaped.
The thermal-break section according to any one of the preceding claims, wherein said heat-insulating material is a plastic material, preferably polyamide.
The thermal-break section according to any one of the preceding claims, wherein between said longitudinal locating tooth (229, 239; 329, 339) and said longitudinal folding tooth (228, 238; 328, 338) there is a continuous and substantially flat bottom surface (226', 236'; 326', 336').
The thermal-break section according to Claim 7, wherein said longitudinal locating tooth (229, 239; 329, 339) comprises an angled surface (229', 239'; 329', 339') inside the seat (226, 236; 326, 336) and a substantially flat surface (229", 239"; 329", 339") outside the seat, the angled surface (229', 239'; 329', 339') forming an acute angle with the bottom surface (226', 236'; 326', 336') and the external surface (229", 239"; 329", 339") being substantially perpendicular to the bottom surface (226', 236'; 326', 336').
The thermal-break section according to Claim 8, wherein said longitudinal locating tooth (229, 239; 329, 339) further comprises a connection surface between said angled surface (229', 239'; 329', 339') inside the seat and said flat surface (229', 239"; 329", 339") outside the seat, said connection surface forming an acute angle with the flat surface (229", 239"; 329", 339") outside the seat.
The thermal-break section according to any one of the preceding claims, wherein said folding tooth (228, 238; 328, 338) comprises an angled surface inside the seat and a surface outside the seat provided with a longitudinal weakening groove (228', 238'; 328', 338').
The thermal-break section according to any one of the preceding claims, wherein, when the section (21; 31) is assembled, the bottom surfaces (226', 236'; 326', 336') of the first and second half-shells are substantially parallel and the substantially flat external surfaces (229", 239"; 329", 339") of the locating teeth (229, 239; 329, 339) lie in the same plane.
The thermal-break section according to Claim 11, wherein the plane in which the substantially flat external surfaces (229", 239"; 329", 339") of the locating teeth lie coincides substantially with the bottom surface of a glass cavity.
A method for manufacturing a thermal-break section (21; 31), the method comprising the steps of: providing a first half-shell (22; 32), a second half-shell (23; 33) and at least one body of heat-insulating material (24; 34), each of the half-shells comprising longitudinal teeth forming a seat for said at least one body of heat-insulating material (24; 34); inserting said at least one body of heat-insulating material inside the seat, folding only one (228, 238; 328, 338) of the longitudinal teeth of each half-shell (22, 23; 32, 33) towards said at least one body (24; 34) and keeping the other one (229, 239; 329, 339) of said longitudinal teeth of each half-shell (22, 23; 32, 33) substantially fixed, wherein:

c) the step of providing a second half-shell (23; 33) comprises providing a second half-shell which comprises a flange (234) projecting over its fixed longitudinal locating tooth (239, 339) when said thermal-break section (21; 31) is seen in a cross-section;

d) the step of inserting said at least one body of heat-insulating material comprises the step of inserting two bodies of heat-insulating material (241, 242; 341, 342), each having a cross-section substantially identical to the other one and being situated symmetrically opposite each other in an interlocking arrangement.
The method according to Claim 13, wherein the step of inserting two bodies of heat-insulating material (241, 242; 341, 342) inside the seat comprises the step of inserting a spacer between a first heat-insulating body (242; 342) and a second heat-insulating body (243; 343).
The method according to any one of Claims 13 to 14, wherein said heat-insulating material is a plastic material, preferably polyamide.
The method according to any of claims 13 to 15, wherein it comprises the step of arranging the tooth (229, 239; 329, 339) of each half-shell (22, 23; 32, 33) to be kept fixed against a corresponding locating surface.
The method according to Claim 13, wherein it further comprises the step of providing the folding tooth (228, 238; 328, 338) of each half-shell with a longitudinal weakened groove (228', 238'; 328', 338').
Half-shell for the manufacture of a section (23; 33) according to any one of Claims 1 to 13, which comprises a longitudinal tooth (239; 339) which is substantially fixed and a longitudinal folding tooth (238; 338) for locking at least one body of heat-insulating material (24; 34), between the fixed tooth and the longitudinal tooth there being formed a bottom surface (236'; 336') which is substantially flat and continuous, wherein said half-shell (23; 33) comprises a flange (234) projecting over its fixed longitudinal locating tooth (239, 339) when said thermal-break section (21; 31) is seen in a cross-section.