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Design and Construction Benefits

Conventional glass fridge and freezer display doors require the initial construction of an insulated glass unit. This consists of two or more glass panes separated with aluminium spacer bars, sealed with butyl rubber and requires 24 hours to cure. This insulated glass unit is then transferred to a second production line where a metal frame with electrical heating is constructed about it using corner stakes, screws and the like. The Eco Door™ combines both these assemblies in the one operation, significantly reducing manufacturing time and costs.

Utilising extruded thermal plastics, a frame is extruded and constructed by mirror-welding the sides together. The extruded frame incorporates mounting surfaces which both hold and optimally space the glass and plastics panes. The panes are set into the frame using a ultra-violet adhesive⁵ which provides rigidity to the extruded plastics frame and the entire door unit (Figure 1). The need for a separate assembly line of the insulated glass unit in conventional doors is completely eliminated.

This new concept in display door construction utilises extruded thermal plastics, a far superior insulator some 1000 times more efficient than the metal frames currently employed. Figures 2a and 2b show typical extrusion sections. Mirror-welding the frame members, solves the common problem of saw-toothing or door-sag occurring in conventional doors due to the use of mechanical fasteners. Combined with the removal of electrical heating circuits, all servicing and maintenance costs are eliminated. Figures 3a and 3b compares the design of conventional heated glass doors with The Eco Door™.

Removing the need for butyl seals reduces the cure time significantly from the 24 hours of conventional doors to only 2 seconds with The Eco Door™. This allows far greater production as well as reducing construction space.

Also significant is the reduction in parts and stock-holding from 50 components in a conventional door to just 19 components in The Eco Door™ - a reduction of 60%!  Tables in Appendix 1 compare the manufacturing time and parts between a conventional door and The Eco Door™.

Assembly time is similarly reduced from 57 minutes in a conventional door to just 12.5 minutes with The Eco Door™ (see Appendix 1 for details).

Using the new design, production requires substantially less labour, machinery, assembly time, and parts, as well as eliminating one entire production line - the manufacture of an insulated glass unit - saving the manufacturer millions of dollars per year.

A further feature of removing the separate construction of the insulated glass unit (IGU) is the ability to use optimum thermal spacing between the glass/plexiglass panels. Figure 4 highlights the dramatic loss in thermal resistance once the spacing of glass panes decreases from the optimum of 13mm. The spacings of 6mm to 9mm, common in conventional doors, provide significantly less thermal resistance.

Manufacturers of conventional doors have been unable to utilise the benefit of optimal spacing due to the bulk and thickness of the metal frame required to support the IGU. Now inefficient doors requiring both maintenance and electrical heating can be replaced with The Eco Door™.

Where humidity conditions are critical, argon gas may be inserted into the cavities between the panes - providing a further improvement of approximately 2% relative humidity before condensation occurs.

Figure 2a: The Eco Door™ frame standard extrusion profile

Figure 2b: The Eco Door™ frame extrusion profile with full length handle

Figure 3a: Conventional door with insulated glass unit, metal frame, corner stakes, and heating wires and strips

Figure 3b: Back-view of The Eco Door™ - an extruded thermoplastics frame incorporating pane-mounting surfaces and constructed by mirror-welding

Figure 4: Optimal Spacing for Thermal Performance⁶