Foam Core Panel With Interlocking Skins and Thermal Break

Overhead doors in which a series of door panels are hinged together, each panel having steel inner and outer skins and a foam insulating core, are well known in the art. Typically, such panels are manufactured by foaming the cores in place, usually in continuous production runs where one web of steel is unrolled from a supply roll, advanced through a forming station where its sides are folded inwardly, and coating with a liquid which upon further treatment and heat becomes the plastic foam core. A similar web of steel is unrolled from another supply roll to become the opposite skin. The inturned sides of the two steel webs are sometimes joined directly together but, more frequently, are connected to the core but not directly to each other so that a direct path of thermal conductivity between the skins is avoided. The spaces between the two skins are often bridged by resilient spacers that serve to provide a "thermal break" as well as a protective joint seal between the skins. A common characteristic of such constructions is that where a thermal break is provided the inner and outer metal skins are seldom if ever physically interlocked together. The integrity of the steel-foam-steel sandwich of such a panel is therefore maintained primarily by the bond formed between the inner surfaces of the skins and the plastic material of the core. Reference may be had to the following patents illustrative of the prior art: Nos. 4,183,393, 4,123,885, 3,336,713 (metal skins spaced apart from each other and bonded to foam cores); No. 3,786,613 (skins bonded to and interlocked with foam core without thermal break); U.S. Pat. Nos. 3,992,837, 3,830,027, 2,008,325 (inner and outer skins joined together directly or by means of splines without thermal break).

In the earlier constructions in which the side edges of the inner and outer metal skins are joined directly together, or are coupled by splines or other connecting strips, the requirements of strength, rigidity, and durability have been achieved at the expense of poor thermal barrier performance. More recent constructions in which the side edges of the skins are spaced apart, even though they may be bridged by joint seals of low thermal conductivity, function more effectively as thermal barriers but sacrifice long-term durability and strength. Over extended periods, some foam disintegration or weakening necessarily occurs with such changes often being accelerated by the gradual escape of inert gases from the foam structure and the replacement of such gases by outside air. As degradation of the foam core occurs, the forces maintaining the integrity of such a panel are diminished. Such problems are more serious where the plastic cores are foamed in place since consistency of cellular structure and uniformity of contact between the foam and the inner surfaces of the skins are difficult to achieve and control. The presence of voids or spaces where foam may be absent within the panel cannot be readily determined and such voids obviously reduce the strength of such a panel and increase the possibilities of delamination and failure.

In the door panel of this invention the inner and outer skins are interlocked together to provide a unit of high structural rigidity and durability. Even though they are physically interlocked, the skins are separated from direct contact by a resilient barrier element of low thermal conductivity. The result is a panel that has effective thermal barrier properties and also exceptional rigidity, strength, and durability.

The foam core is pre-formed rather than being foamed in place and is retained between the metal skins by bonding the core to the skins and mechanically interlocking the inner and outer skins to each other. Being pre-formed, the core material may be inspected prior to assembly to insure uniform and consistent quality. Compression of the core during assembly results in forceful adhesive contact between the core surfaces and the inner surfaces of the skins, thereby assuring secure bonding of the components.

Briefly, the panel includes a pre-formed resilient foam core sandwiched between a pair of inner and outer metal skins, the respective skins having side flanges with interlocking hook portions that physically interlock the two skins together. A resilient thermal barrier element or member is interposed between the hook portions to provide a joint seal between those skins and also to provide a resilient weatherstrip or cushioning bead for engagement with the similar strip of an adjacent panel in a complete door assembly.

During manufacture, the two skins are pressed towards each other to compress the pre-formed foam core and to position the hook portions of the side flanges for interlocking engagement when the compressive forces are relieved. The flanges may be incompletely formed at the commencement of such an assembly operation to permit clearance between the hook portions as the skins are urged towards each other during the compression step. Thereafter, the flanges are bent so that their hook portions are disposed in direct alignment. When the compressive forces are released, such hook portions, with the thermal barrier elements interposed therebetween, then shift into secure interlocking relation.

Each thermal barrier element takes the form of an extruded section of resilient plastic or rubber that is extended about one of the hook portions early in the assembly operation. Specifically, the resilient strip is attached to the outwardly-facing hook portion of one of the side flanges prior to the compression step. As the skins are then urged together to compress the resilient foam core therebetween, the side flange of the other skin with its inwardly-facing hook is forced into alignment with the opposing outwardly-facing hook so that when the compressive forces are released the two hook portions will be forced by the resilient foam core into tight interfitting relationship with the thermal barrier strip locked securely and sealingly therebetween.

Other advantages, objects, and features of the invention will become apparent from the specification and drawings.

FIG. 1 is a fragmentary sectional view of a door panel showing the interlocking relationship of the metal skins, barrier element, and foam core.

FIG. 2 is a fragmentary sectional view showing two such door sections and the sealing relationship between the thermal barrier elements of those sections.

FIG. 3 is a reduced sectional view further illustrating the relationship between two adjacent door sections.

FIG. 4 is an exploded perspective view showing the several components of a door panel.

FIG. 5 is a somewhat schematic sectional view illustrating an early step in a manufacturing operation with one flange of each skin being incompletely formed.

FIG. 6 illustrates the compression step in which the two skins are urged towards each other to compress the resilient pre-formed core therebetween.

FIG. 7 depicts the step of urging the flange with its inwardly-facing hook into a final position at right angles to the remainder of the skin of which it is a part.

FIG. 8 illustrates the final step of relieving the compressive forces to allow outward expansion of the foam core and secure interlocking of the hook portions of the respective flanges with the thermal barrier elements secured therebetween.

Referring to the drawings, the numeral 10 generally designates a door panel for a sectional overhead door. As is well known, a plurality of such panels are joined together by hinges of the type designated by numeral 11 in FIG. 3, such hinges being equipped with rollers that ride in tracks for raising and lowering the door. Since this invention is concerned only with panel construction, further discussion of the associated elements of a complete door assembly is believed unnecessary herein.

The main elements of panel 10 are shown in exploded relation in FIG. 4. The panel includes an insulating core 12 formed of any suitable resilient plastic foam. Expanded polystyrene has been found particularly effective. The core is generally rectangular in outline with parallel planar faces 12a and 12b. The upper and lower side edge surfaces 12c and 12d are stepped and, as shown most clearly in FIG. 5 the stepped configuration along opposite longitudinal (upper and lower) side edges is dimensionally the same but reversed in direction. Thus, surfaces 13 are set inwardly from surfaces 14 to define longitudinal shoulders 15 therebetween, the shoulder along one longitudinal edge facing in a direction opposite from that of the shoulder along the other longitudinal edge.

The panel also includes a pair of protective skins or shells 16 and 17 formed of sheet steel or other material (preferably metal) having similar properties. The two skins are designated by different numerals (16 and 17) to facilitate discussion and because, in the finished product, one skin 16 will define the outer surface of the panel and the other 17 the inner surface; however, both skins are identical except for their orientation. Specifically, each rectangular skin has first and second longitudinal flanges 18 and 19 extending at right angles in the same direction from the principal plane of the skin. The first flange is preferably smaller or narrower than the second and terminates along its edge in an inwardly-turned-longitudinally-extending hook portion 18a. The larger second flange 19 has an outwardly-turned longitudinal hook portion 19a. In the finished panel, hook portions 18a and 19a are interlocked with a resilient thermal barrier element 20 interposed therebetween (FIGS. 1-3).

The thermal barrier element 20 may be extruded from vinyl (i.e., polyvinyl chloride) or any other tough, durable, and resilient thermoplastic material having low thermal conductivity. As shown most clearly in FIG. 1, element 20 when viewed in transverse section has an enlarged generally C-shaped portion 20a that merges along one edge with a smaller C-shaped portion 20b nested within the first, the two C-shaped portions together enclosing the outwardly-projecting hook portion 19a of longitudinal flange 19. When the skins 16 and 17 are locked together, the C-shaped portions 20a and 20b of the thermal barrier element or member 20 prevent direct contact between the two hook portions. One leg of the smaller C-shaped portion 20b extends outwardly or externally from the interlocking zone and terminates in a longitudinally-extending hollow bead or cushion 20c that in an undeformed state is generally circular in cross sectional outline (FIG. 1).

The parts are proportioned and dimensioned so that cushion 20c is only slightly offset from the longitudinal midplane of the finished panel (FIG. 1). When two panels are fitted together as shown in FIG. 2, the cushion or bead of one engages that of the other to provide an effective weather-tight seal between the adjacent panels. The thermal barrier element 20 therefore performs the multiple functions of (a) preventing direct contact between the inner and outer skins of each panel in the area of interlock between those panels, thereby providing a thermal break between the inner and outer skins notwithstanding the interlocking relationship of their hook portions 18a and 19a, (b) sealing the interior of the panel against the entry (and exit) of gases and particulates, and (c) providing a resilient external bead or cushion that engages a similar bead of an adjacent panel to form a weather-tight seal.

In the finished panel, the remaining two side edges are closed off by suitable steel side plates 21 as illustrated in FIG. 4. The side plates may be bonded or connected to the skins by rivets, screws, adhesives, or any other suitable connecting means, it being understood that the side plates are not in contact with the outer skin 16, but rather isolated from this skin by a suitable rigid plastic or other material of low thermal conductivity 22, being inserted between the outer flange of the side plate and the outer skin 16, and that a suitable sealant material (which may be a material used for adhesive bonding) may be disposed between the flanges of the side plate and the inner and outer skins to block the passage of gases and pollutants.

In the best mode known for practicing the invention, the foam core 12 is pre-formed rather than being foamed in situ. Its initial cross sectional configuration at the commencement of an assembly procedure is as shown in FIG. 5. During assembly, the resilient core is compressed (FIG. 6) and then, after the hook portions of the metal outer skins are disposed in alignment, the compressive forces are relieved, the foam core is allowed to expand. As the foam core expands, the metal skins move apart and their hook portions shift into tight interlocking relation with the thermal barrier elements clamped therebetween (FIG. 8).

The compressive forces exerted upon the skins and core during the assembly procedure may be applied by any suitable means. Where each panel is formed individually in a batch operation, such compressive forces may be exerted by a pair of platens. In a continuous operation, flanges 18 and 19 are continuously formed and interlocked. The compressive means preferably comprises a series of rollers. To facilitate interlocking of the hook portions of the respective flanges, and to allow flange clearance during the compression step, it has been found desirable to form each skin with the smaller first flange 18 turned inwardly to an angle less than 90.degree., preferably about 75.degree. (such angle being measured in relation to the principal plane of the skin externally of that skin). Thus, as shown somewhat schematically in FIG. 5, just prior to the compressing step the larger flanges 19 with their outwardly-turned hook portions 19a extend at right angles to the primary plane of each metal skin but the smaller flanges 18 with their inwardly-turned hook portions are disposed at angles less than 90.degree. so that the compression step may proceed without interference between the hook portions of the respective skins 16 and 17 and without resistance between the foam core and inwardly-turned hook portions 18a. When compression of the core has been achieved to the desired extent, step-down rollers or other suitable means (not shown) force flanges 18 with their inwardly-turned hook portions into right-angled positions (FIG. 7) so that the opposing hook portions 18a and 19a may interlock when external compressive forces are relieved.

The use of pre-formed core stock has several advantages, a major one being that inspection of the core prior to assembly is possible. Voids and malformations which might occur and remain undetected when a core is foamed in place are therefore avoided. Also, the use of a pre-formed core permits the use of an aggressive adhesive for securely bonding the core to the inside surfaces of the metal skins, the result being that a more secure and stable bonding of the core material with the skins is possible when the core is pre-formed rather than being foamed in place. Any of a variety of well-known and commercially-available contact adhesives stable up to temperatures of at least 150.degree. F. may be used.

While in the foregoing, an embodiment of the invention has been disclosed in considerable detail for purposes of illustration, it will be understood by those skilled in the art that many of these details may be varied without departing from the spirit and scope of the invention.