US3353314A

US3353314A - Insulated panel having joined connectors

Info

Publication number: US3353314A
Application number: US560306A
Authority: US
Inventors: George W Melcher
Original assignee: BALLY CASE AND COOLER Inc
Current assignee: BALLY CASE AND COOLER Inc
Priority date: 1966-06-24
Filing date: 1966-06-24
Publication date: 1967-11-21
Anticipated expiration: 1984-11-21

Description

Nov. 21, 1967 e. w. MELCHE'R 3,353,314

INSULATED PANEL HAVING JOINED CONNECTORS 2 Sheets-Sheet 1 Filed June 24, 1966 l i l ATTORNEYS Nov. 21, 1967 c. w. MELCHER INSULATED PANEL HAVING JOIXQED CONNECTORS Filed June 24, 1966 INVENTOR &eo1:9c W Melclzer,

2 Sheets-Sheet 2 BY 9 V fa Zi/MA/k ATTORNEYS United States Patent C) 3,353,314 INSULATED PANEL HAVING J OINED CONNECTORS George W. Melcher, Bally, Pa., assignor to Bally Case and Cooler, Inc., Bally, Pa., a corporation of Pennsyl- Vania Filed June 24, 1966, Ser. No. 560,306 7 Claims. (Cl. 52127) ABSTRACT OF THE DISCLOSURE The present application is a continuation-in-part of my copending application Ser. No. 131,570 filed Aug. 15, 1961, now abandoned, entitled, Insulated Panel Assembly.

The present invention relates to an assembly of prefabricated insulated panels including a simple lock and novel supporting structure for permitting rapid and secore assembly of insulated panels to form a refrigerated compartment.

About twenty-five years ago, during the early days of mechanical refrigeration, cooling and freezing compartments, particularly of the walk-in type, were built-in and often made of cork insulation usually covered with plaster, wood or other materials. In recent years, the requirements for improved strength, sanitation, life and economy have resulted inall-metal sectional type refrigeration compartments formed from prefabricated panels so as to make possible a wide variety of sizes and shapes. Walkin refrigerators and coolers are now used throughout the food, medical and chemical industries for refrigerating a Wide variety of products. Modern refrigerating compartments of walk-in type size have achieved the important goal of complete sanitation by eliminating the possibility of penetration by insects and rodents. The metal panels have also prevented the accumulation of foods and juices which often can cause offensive odors.

In addition to steel, aluminum and other materials are available for large size compartments. Lower costs are achieved through the use of sectional construction involving mass production techniques with on-site assembly. The sections can be made in a variety of Widths, lengths and heights so that the assembly of proper sections can be accommodated to fit almost every users requirement.

Whilelocking devices for tightly assembling preformed panels to, form a large refrigerated compartment are known, many involve relatively complex constructions with a plurality of moving parts so as to substantially increase the cost of the over-all compartment. In addition to the very tight sealing required to avoid heat leakage at panel joints, it is essential that the locking device not only be simple of construction, and easy to actuate, but it preferably should provide no straight-through heat conducting path joining the inner and outer walls of the panel so that heat is not readily conducted and lost through the locking mechanism.

The present invention satisfies all of the above mentioned requirements by providing a panel assembly incorporating a simplified, easily and rapidly actuated locking device for joining insulated panels. The locking mechanism is formed of a minimum number of parts, and provides a tight and reliable seal between adjacent panels without setting up a thermal conduction path between the internal and external panel walls.

It is therefore a primary object of the present invention to provide an improved insulating panel assembly incorporating a simplified locking device of high strength and low thermal conductivity.

Another object of the present invention is to provide an insulating panel having low heat loss and incorporating a locking device which may be rapidly actuated so as to lessen the assembly time involved in the construction of a panel type refrigeration compartment.

Another object of the present invention is to provide improved construction for heat insulated panels.

Another object of the present invention is to provide a simple and reliable prefabricated insulating panel permitting the on-site assembly of large walk-in type refrigerated compartments such as food freezers and coolers.

Another object of this invention is to provide an improved construction for interlocking panels including locking means directly embedded in a mass of cellular insulating material having support means to prevent loosening of the joint between panels during use.

It is a further object of this invention to provide interlocking insulating panels having locking means rigidly supported in such a manner as to substantially eliminate the locking means and their supports as a source of thermal inefiiciency.

It is an additional object of this invention to provide interlocking insulating panels for on-site assembly into large walk-in refrigerators or the like having inner and outer shells separated by a thick layer of cellular insulating material with locking means embedded in the cellular material the locking means being supported by a series of vertical and/or horizontal bands to provide great structural rigidity with a minimum of heat loss.

These and further objects and advantages of the invention will be more apparent upon reference to the following specification, claims and appended drawings wherein:

FIGURE 1 is a perspective view with parts in section showing one construction which has been utilized for joining adjacent insulated panels to overcome various of the above mentioned difliculties;

FIGURE 2 is an exploded view showing the various elements of an insulated panel using the locking structure of FIGURE 1;

FIGURE 3 is a horizontal section through the locking device of FIGURE 1;

FIGURE 4 shows a typical panel assembly using the locking structure of FIGURE 1;

FIGURE 5 is a front elevation of the locking mechanism of FIGURE 1;

FIGURE 6 is a perspective View with parts in-section of the novel locking mechanism of the present invention as incorporated in an improved insulated panel construction;

FIGURE 7 is a perspective view of a portion of the improved panel of FIGURE 6;

FIGURE 8 is a horizontal section through the improved pauel taken along lines 8-8 of FIGURE 7; and

FIGURE 9 is a vertical section taken along line 9-9 in FIGURE 7.

Referring to the drawings, one approach which has been employed to overcome the above noted longstanding problems is shown in FIGURE 1. A locking device 10 is employed to connect adjacent insulated panels 12 and '14.

Panels

12 and 14 are of identical construction as illustrated in FIGURE 2 and comprise an outer shell 16 and an inner shell 18 typically dieformed from steel or aluminum. Each of the

shells

16 and 18 is formed with a

peripheral flange

20 and 22 overlying a wooden frame 23 comprising

sides

24 and 26, top 28 and bottom 30. Received within the frame 23 is a thick layer of fiberglass or like insulation 32. A pair of neoprene rubber

gasket sealing strips

34 and 36 are secured to the outer edge of frame member 23.

Formed along side 24 and top 28 are a plurality of slots 38. Similar slots 40, one of which is illustrated in FIGURE 3, are formed in the opposite side members 26 of the wooden frame. Received within each of the slots and extending transversely thereacross is a locking pin 42 having its opposite ends embedded in the

spaced walls

44 and 46 of the slots 40. For ease of insertion, locking pins 42 may be driven into side members 26 prior to the application-of the

shells

20 and 22.

Received within the slots 38 in side member 24 and top 28 are lockiung arms 50 terminating in hooks 52 adapted to engage locking pins 42 in adjacent panels. Locking arms 50 are rigidly secured between a pair of

circular bearing plates

54 and 56 by a pair of rivets 58 and '60-. The thickness of the locking arm and bearing plates are substantially equal to the width of the slot 40 so that maximum use of the insulating material is employed at the joints between adjacent panels.

Locking arm 50, as well as

bearing plates

54 and 56, are provided with mating hexagonal apertures receiving one end of a hexagonal rod '62. Rod 62 passes completely through the locking arm and plates and is tightly received in a circular hole indicated by dashed lines 62 in FIG- URE '3, which hole communicates with the slot 38.

During the assembly of a refrigerated compartment such as 'a walk-in freezer or cooler, adjacent panels 12 'and 14 are brought into engagement with

gasket strips

34 and 36 contacting

flanges

20 and 22 of the adjacent panel and the

respective slots

38 and 40 in alignment. A hex wrench, indicated by dashed lines at 64 in FIGURE 1 is then slipped over the exposed end 66 of each of the hex rods '62 so that the locking arm is pivoted from the solid line to the dashed line position in FIGURE 1 with the hook 52 engaging locking pin 42 to pull the adjacent panels into tight heat sealing engagement. Inner shell 18 is provided with suitably placed apertures 68 through which the hex rods 62 extend. FIGURE 4 illustrates a plurality of

panels

70, 72, 74, and 76 in edge-to-ed'ge engagement forming what might be the side wall of a walk-in refrigerating unit. Each of these panels is constructed in the manner of

panels

12 and 14 previously described, with the exception that panel 74 includes an additional frame member 78 secured to the top and bottom frame members of the panel and provided with suitable slots and locking arms for engagement with the locking pins of a further panel "80. Panel 80 is in turn connected in series with

additional panels

82 and 84 which latter panels may form a portion of a dividing 'wall for the refrigerated compartment. While the above construction has been described in conjunction with wall elements, it 'is apparent that it is equally applicable to partition panel junctions such as that illushated by panels 74 and '80 in FIGURE 4 as well as ceil- 'ing'and floor panels if desired.

The above described construction represents a substantial improvement over those previously employed since it is quite simple, and eliminates to a large extent, thermal conduction between the inner and outer shells through the latch mechanism. Further, such construction provides adequate support for the latch whereby it will not separate from the panel during use, causing failure of both the insulating and structural properties of the panel.

However, there are a number of disadvantages in the use of a wood frame, or other wood components, to provide sufiicient structural strength for use in walk-in ref-rigerators. Wood commonly has a thermal conductivity "K" factor ranging from about 2.7 to 4 which is 20 to 40 times greater than the K factor of 0.11 for urethane foam, and the K factor of 0.24 for fiberglass, which are used for insulating material in making panels for walk-in type refrigerators and the like. Furthermore, the K factor of wood varies considerably with the moisture content of the wood. Thus, newly cut lumber has a rather high moisture content with a higher K factor and thermal conductivity. If the wood is dried to lower the K factor and improve the thermal efficiency of the' insulating panels, this is not only expensive, but the wood will later reabsorb moisture in use, thus greatly increasing the K factor and thermal conductivity (to more than twenty times the thermal conductivity of the porous insulating material within the panel). This causes loss of efiiciency and sweating of the walk-in refrigerator panels in the region incorporating the wood, due to short circuit transfer of heat from the outside to the inside of the refrigerator compartment via the wood. Moisture will commonly condense and collect on the panels in the region of the wood frame or other wood components under common refrigerator operating conditions (e.g., 30 F.) with common ambient external temperature (e.g., 7090), and this problem is particularly acute on a humid day with even a relatively high internal refrigerator temperature.

Further, use of a wood frame for walk-in refrigerator panels involves additional complications in design, production and use because of wide variance of the K factor for different woods from different geographical areas.

Furthermore, the wood frame or other wood components incorporated in insulating panels for Walk-in refrigerators often absorb moisture to a degree where these wood components warp significantly. This not only further penalizes the thermal efficiency of the refrigerator but creates problems of sanitation by adversely affecting the seal between panels.

Thus, as a practical matter, since wood has a K factor 20 to 40 times greater than the K factor of cellular plastic and like insulating materials, wood is considered as a thermal conductor in the walk-in refrigerator field.

An alternative approach 'to the construction of insulating panels of high strength and low thermal conductivity is typified by the structure shown in Canadian Patent No. 563,849 of Fred S. Lee, issued Sept. 30, 1958. The approach of the Canadian patent is to embed within the insulating material between the panel surfaces the locking devices for joining adjacent panels to assemble a refrigerator or like compartment. However, the insulating materials used in making these panels have low tensile strength which include particularly the urethane foams, fiberglass and other porous or foam plastics suggested in the Canadian patent (column 2.). Accordingly, when the locking devices joining panels are merely embedded within the insulating material itself, structural stresses are transmitted from thelocking members directly to the insulating materials. This generally results in the locking receptacles becoming separated from the insulating material, and in any event provides inadequate structural rigidity for a walk-in refrigerator. This literally renders such a walk-in refrigerator construction commercially unsatisfactory, and sometimes even inoperative. Further, the structure described in this Canadian patent not only involves a number of disadvantages including the requirement for an assortment of blocks, frames, etc., but it also has the basic shortcoming of stresses between the weak panel insulating material and the supporting member for the panel interlocks. Thus, whatever number and configuration of wood or other inserts are embedded within the low strength insulating material, that Canadian patent system provides no method for relieving the load on the insulating material itself. Thus, an insulated panel refrigeration compartment according to the Canadian patent does not have requisite structural strength and integrity.

In accordance with the present invention the various problems detailed above can be substantially overcome through the use of the improved construction shown in FIGURES 6-8 of the attached drawing. Here, the locking structure of the present invention is incorporated in laminated insulating panels such as 90 and 92. The locking mechanism is essentially the same as that described in connection with FIGURES 1-5 and for convenience, like parts bear like reference numerals.

Panels

90 and 92 are formed with outer shells 94 and inner shells 96 having a layer of rigid but highly cellular insulating material 98 bonded in place between the shells.

As mentioned above, urethane foam insulation is preferred. However, as also noted above, such material in a form suitable for insulating purposes provides little tensile support for objects embedded therein. Thus, in accordance with this invention, and as shown particularly in FIG- URES 7-9, the panels of the present invention include a plurality of horizontal metal support bands 100 embedded in the insulation 98. Welded or otherwise attached to one end of the horizontal bands 100' are metal locking cups 104; similar locking pin cups 106 are secured to the opposite end of the same supports. In addition there may be provided vertical supports 102 embedded in each panel. Similar locking cups 104 and 106 are secured to the opposite ends of vertical bands 102 to permit attachment of the insulated wall sections to floor or ceiling panels in the refrigerated enclosure. This construction has been found highly advantageous since

bands

100 and 102 extend through the walls to provide a closed metal framework and a rigid support construction which does not load the weak insulation material of the panels. Further, since the

structural elements

100 and 102 are embedded within the plastic foam insulation, there is no thermal loss through the structural bands and the associated locking

cups

104 and 106.

Received in cups 106 are locking pins 42 which pass through the side walls of the cups and are rigidly supported therein, but which locking pins do not extend entirely through the panel, Similarly, passing through the side walls of cups 104 are hex bars 62 which actuate the locking arms 50 in a manner identical to that previously described with respect to FIGURE 1. As in FIGURE 1, because the hexagonal rod 62 is received eccentrically through the

plates

54 and 56 and locking arm 50, rotation of the hex rods 62 causes the locking arms 50 to rotate into engagement with the locking pins 42 of adjacent panel to draw the panels into tight sealing engagement. The

cups

104 and 106 are provided with flanges around three sides such as the

flanges

110 and 112 for attachment to the support members. The cups may be welded or otherwise attached by means of these flanges to the

metallic support elements

100 and 102.

Hex rods 62 are tightly received through circular apertures in the inner shell 96 and in the cups 104 and may be rotated by means of a wrench or other device to lock and unlock the panels in tight heat sealing engagement. Rotation of the hex rod 62 in a clockwise direction brings the hook 52 into the dashed line position in FIGURE 6 and in engagement with the locking pin 46. Subsequent clockwise rotation of the hex rod 62 returns the locking lever 52 to the solid line position and disconnects the locking mechanism. The frictional engagement of the hex rod 62 with the apertures in the shell and cup in the embodiment of FIGURE 6 and with the inner surface of circular aperture 62' formed in the wood frame shown in FIGURE 3, in conjunction with the tight engagement of the hook over the locking pin 42 assures a tight and permanent joint between the two panels. As can be seen in FIGURE 6, the hook 52 preferably slightly overlies the locking pin 42 and acts to draw the two panels together into tight engagement. At the same time the lever arm 50 is supported by the hex rod 62 which passes completely through the locking arm and bearing

plates

54 and 56 and into the opposite side of the panel. It is an important feature of the present invention, however, that the hex rod 62 does not extend entirely through the panel but stops short of the front shell 94 in FIGURE 8 so as not to provide a good heat conductive path completely through the panel.

The novel walk-in refrigerator insulated panel construction of FIGURES 6-9 eliminates peripheral wood frame members, or other wood components like wooden blocks for mounting locking devices for joining adjacent panels. Commercial usage shows this novel arrangement has very satisfactorily solved the long-standing problem of thermal loss and inefficiency due to incorporation of high K factor wood frames, or like wood components, Within such insulating panels. Further, this invention provides addi-' tional advantages of a remarkably simplified construction which not only vastly improves the thermal efficiency of the walk-in refrigerator panels but also provides increased structural integrity and strength, rapid fool-proof insulation, elimination of warpage, etc. This novel construction of FIGURES 69 has proven very successful in commercial use since its introduction to the trade in mid-1962, and applicants assignee has abandoned prior long-standing systems of insulated panel construction using wood framing, or other wood components, in favor of this new invention.

It is apparent from the above that the present invention provides a novel locking mechanism and panel construction for sectional type compartments of structural integrity, particularly suited for use in walk-in type refrigerating units used in the commercial preservation of food, medicines, chemicals and a wide variety of related products. The locking device and strap of the present invention makes it possible for the mass production of similar interlocking insulating panels to be used in a variety of combinations to form different size constructions conforming to specific buyer requirements. On-site' assembly of a strong refrigerator compartment comprising interlocked insulating panels is expedited by the rapid and reliable embedded strap and associated locking mechanisms which may be simply and rapidly effected through a partial turn of the hex rod elements projecting from the interior edges of the assembled panels. If desired, rubber plugs or other seals may be placed over the projecting ends of the hex rods to avoid contact with the projecting ends. A simple quarter turn of the hex rod brings the locking arms into tight engagement with the locking pins of adjacent panels and acts to tightly seal the entire unit against heat loss and moisture, with stress being transferred through the associated straps. Disassembly for enlargement or modification of the compartment is just as rapidly and easily effected by a quarter turn of the hex rod in the opposite direction to disengage the locking levers with the locking pins.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments aretherefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. A rectangular heat insulating panel comprising: a pair of side shells with a relatively thick layer of heat insulating material therebetween, said insulating material having a low thermal conductivity and relatively low tensile strength; at least one elongated member of relatively high tensile strength material embedded within and surrounded by said insulating material and extending through the panel so that opposite ends of said member are adjacent two ditferent edges of said rectangular panel; locking means for interconnecting said panel with other insulating panels, including first and second thin receptacles connected to the respective ends of said elongated member, each of said receptacles being embedded in said layer of insulating material; an extensible latching device mounted in one of said receptacles, a catch mounted in the other of said receptacles for interlocking with an extensible latching device, each said receptacle comprising a cup having spaced walls defining a slot in the edge of the panel insulating layer and so located that the slots in adjacent heat insulating panels are aligned when two panels are interconnected, said cup walls extending substantially parallel to the plane of each of said shells, a flange extending from at least one edge of said cup and lying in a plane intermediate said cup walls, said elongated member comprising a substantially fiat strap secured at each end to the flanges of said cups, said strap lying at least substantially within an area bounded by the planes of the outer surfaces of said cup walls whereby said strap and cups are all spaced a substantial distance from said panel shells by heat insulating material.

- 2. A heat insulating panel as defined in claim 1 comprising: a plurality of said elongated members disposed at spaced positions within said panel layer of insulating material with ends thereof adjacent to opposite edges of the panel, each of said ends being connected to cups in said insulating material adjacent opposite edges of the panel.

- 3. A heat insulating panel as recited in claim 1 wherein said strap is a flat metal strip welded to the flange of each of said cups.

4. An insulating panel as set forth in claim 1 wherein said catch compirses a locking pin secured to the spaced walls of the cup adjacent said one panel edge, said latching device having a hook shaped portion for engaging with said locking pin in an adjoining panel when two panels are interconnected, said latching device further including a pivotally mounted rod, a locking lever secured to the rod and including said hooked-shaped portion for engaging said locking pin, one of said shells having an aperture formed therein communicating with one end of said pivotally mounted rod whereby a tool may be inserted into the aperture to rotate the rod and thereby cause the lever to rotate into hooking engagement with said locking pin.

5. A refrigeration compartment comprising a plurality of prefabricated rectangular heat-insulating wall panels adapted for convenient site assembly, each panel comprising a pair of side shells with a relatively thick layer of heat insulating material therebetween, said insulating material having a low thermal conductivity and relatively low tensile strength; at least one elongated member of relatively high tensile strength material embedded within and surrounded by said insulating material and extending through the panel so that opposite ends of said member are adjacent two dilferent edges of said rectangular panel; locking means for interconnecting said plurality of insulating panels, including first and second thin receptacles in each panel connected to the respective ends of said elongated member, each of said receptacles being embedded in said layer of insulating material; an extensible latching device mounted in one of said receptacles, a catch mounted in the other of said receptacles and interlocking with the extensible latching device of an adjacent panel, each said receptacle comprising a cup having spaced walls defining a slot in the edge of the panel insulating layer and so located that the slots in adjacent heat insulating panels are aligned, said cup walls extending substantially parallel to the plane of each of said shells, a flange extending from at least one edge of said cup and lying in a plane intermediate said cup walls, said elongated member comprising a substantially fiat strap secured at each end to the flanges of said cups, said strap lying at least substantially within an area bounded by the planes of the outer surfaces of said cup walls whereby said strap and cups are all spaced a substantial distance from said panel shells by heat insulating material.

6. Apparatus according to claim 5 wherein said straps are made of a flat metal strip and said layer of heat insulat ing material comprises a thick layer of urethane foam bonded in place between said side shells.

7. A rectangular heat insulating panel comprising: a pair of side shells with a relatively thick layer of foam heat insulating material therebetween, said insulating material having a low thermal conductivity and relatively low tensile strength; said foam layer having a projecting tongue along at least one edge and a corresponding groove along at least the edge opposite from said tongue for mating with the tongue of an adjacent panel; at least one elongated member of relatively high tensile strength material embedded within and surrounded by said insulating material and extending through the panel so that opposite ends of said member are adjacent said tongue and groove; locking means for interconnecting said panel with other insulating panels, including first and second receptacles connected to the respective ends of said elongated member, each of said receptacles being embedded in said layer of insulating material; an extensible latching device mounted in one of said receptacles, a catch mounted in the other of said receptacles for interlocking With an extensible latching device, each of said receptacles comprising a thin metal cup having a flange and spaced walls defining a slot in the edge of the panel insulating layer and so located that the slots in adjacent heat insulating panels are aligned when two panels are interconnected, said cup walls extending substantially parallel to the plane of each of said shells, said elongated member comprising a substantially flat metal strap secured at each end to said thin cups, said strap and cup walls all being spaced a substantial distance from said panel shells by heat insulating material.

References Cited UNITED STATES PATENTS 1,254,417 1/1918 Leonard 52583 1,271,708 7/1918 Horstman 52583 2,136,431 11/1938 Gardaile 52587 2,340,263 1/ 1944 Dodson 52227 2,635,450 4/1953 Orzel 52587 2,647,287 8/1953 Jones 292-111 2,738,211 3/ 1956 Schlueter 2921 11 2,741,341 4/1956 Anderson 52585 2,920,475 1/ 1960 Graham 52587 FOREIGN PATENTS 563,849 1958 Canada. 187,751 1922 Great Britain. 634,877 1950 Great Britain.

56,227 1924 Sweden.

JOHNE. MURTAGH, Primary Examiner.

R. A. STENZEL, Assistant Examiner,

Claims

1. A RECTANGULAR HEAT INSULATING PANEL COMPRISING: A PAIR OF SIDE SHELLS WITH A RELATIVELY THICK LAYER OF HEAT INSULATING MATERIAL THEREBETWEEN, SAID INSULATING MATERIAL HAVING A LOW THERMAL CONDUCTIVITY AND RELATIVELY LOW TENSILE STRENGTH; AT LEAST ONE ELONGATED MEMBER OF RELATIVELY HIGH TENSILE STRENGTH MATERIAL EMBEDDED WITHIN AND SURROUNDED BY SAID INSULATING MATERIAL AND EXTENDING THROUGH THE PANEL SO THAT OPPOSITE ENDS OF SAID MEMBER ARE ADJACENT TWO DIFFERENT EDGES OF SAID RECTANGULAR PANEL; LOCKING MEANS FOR INTERCONNECTING SAID PANEL WITH OTHER INSULATING PANELS, INCLUDING FIRST AND SECOND THIN RECEPTACLES CONNECTED TO THE RESPECTIVE ENDS OF SAID ELONGATED MEMBER, EACH OF SAID RECEPTACLES BEING EMBEDDED IN SAID LAYER OF INSULATING MATERIAL; AN EXTENSIBLE LATCHING DEVICE MOUNTED IN ONE OF SAID RECEPTACLES, A CATCH MOUNTED IN THE OTHER OF SAID RECEPTACLES FOR INTERLOCKING WITH AN EXTENSIBLE LATCHING DEVICE, EACH SAID RECEPTACLE COMPRISING A CUP HAVING SPACED WALLS DEFINING A SLOT IN THE EDGE OF THE PANEL INSULATING LAYER AND SO LOCATED THAT THE SLOTS IN ADJACENT HEAT INSULATING P ANELS ARE ALIGNED WHEN TWO PANELS ARE INTERCONNECTED, SAID CUP WALLS EXTENDING SUBSTANTIALLY PARALLEL TO THE PLANE OF EACH OF SAID SHELLS, A FLANGE EXTENDING FROM AT LEAST ONE EDGE OF SAID CUP AND LYING IN A PLANE INTERMEDIATE SAID CUP WALLS, SAID ELONGATED MEMBER COMPRISING A SUBSTANTIALLY FLAT STRAP SECURED AT EACH END TO THE FLANGES OF SAID CUPS, SAID STRAP LYING AT LEAST SUBSTANTIALLY WITHIN AN AREA BOUNDED BY THE PLANES OF THE OUTER SURFACES OF SAID CUP WALLS WHEREBY SAID STRIP AND CUPS ARE ALL SPACED A SUBSTANTIAL DISTANCE FROM SAID PANEL SHELLS BY HEAT INSULATING MATERIAL.