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 My present invention relates to a frame member of low thermal conductivity, serving as a heat-transfer-limiting member, especially for windows, doors, facades and the like. More particularly, the invention relates to a heat-transfer-limiting composite member, which may be referred to as a profile, and which is comprised itself of two structural shapes or profiles which preferably are composed of metal, bridged by two thermal conductivity-limiting ribs which space the structural shapes apart.
 Frame members of low thermal conductivity are provided in a great variety of shapes and configurations and serve as members of low thermal conductivity in frames for windows, doors, facades and the like which are to have insulating capability, i.e. are capable of blocking the flow of heat from one side to the other of the window, door or other member provided with the frame. The panel or panels of the window or door, e.g. a double-pane window, are thermally insulated between two zones and by utilizing frame members or profiles of low thermal conductivity to support the panel or panels, the heat flow across the structural element can be greatly limited.
 One of the more common constructions of such composite frame members has a pair of structural shapes or metal profiles which can be extruded from aluminum or some other light metal or light metal alloy and which can be held apart by the aforementioned conductivity-limiting webs. These webs, in turn, may be formed at their edges engageable with the structural shapes, with formations that mate with and engage in complementary formations of the structural shape. In a typical construction of this type, the formations on the webs are cleats or beads which are engageable in grooves of the structural shapes and preferably have dovetail cross sections.
 While such composite frame members are effective in providing structural support in door, windows, facades and the like and have low thermal conductivity, at least in part because of the low conductivity cross sections of the webs, it is desirable to further improve the thermal properties of such members, i.e. to reduce the heat flow thereacross still further.
 While theoretically such further reduction in heat flow could be reduced by reducing the thicknesses of the webs, there is a limit to the extent to which the thicknesses can be reduced without loss of mechanical and structural strength.
 It is, therefore, the principal object of the present invention to provide a frame member or composite profile of low thermal conductivity, i.e. thermal barrier properties, whereby drawbacks of earlier systems are avoided and whose thermal and mechanical properties are optimized.
 Another object of this invention is to provide an improved composite profile for windows, doors, facades and the like which is free from the drawbacks of earlier composite profiles for these purposes.
 These objects and others which will become apparent hereinafter are attained, in accordance with the invention, in a frame member of low thermal conductivity for use as described and which comprises:
 two spaced apart mutually parallel structural shapes each having a pair of connecting formations along sides of the structural shapes facing one another;
 a pair of mutually spaced conductivity limiting webs each formed along respective opposite edges with a connecting formation mating with a respective one of the connecting formations of a respective one of the structural shapes whereby the conductivity limiting webs bridge between and interconnect the structural shapes, the webs being of substantially uniform thickness between the connecting formations thereof; and
 a plurality of substantially planar ribs of substantially uniform thickness interconnecting the webs between the connecting formations thereof and running substantially perpendicular to the webs or at an inclination thereto, a sum of the wall thicknesses of the webs and all of the ribs being no less than 3.8 mm where the ribs are perpendicular to the webs and no less than 1.6 mm where the ribs are inclined to the webs.
 When I refer to ribs which are inclined to the webs, I intend to so describe ribs which may not intersect or cross and are so inclined as well as crossing pairs of ribs.
 The advantages of the frame member of the invention reside in the combination of thin wall webs which have low thermal conductivity with connecting ribs which provide good mechanical properties with respect to compressive strength, tensile strength, transverse torsional strength, shear stress resistance and rigidity, as well as other strength parameters, together with good heat-blocking characteristics.
 Advantageously the wall thicknesses of the individual conductivity-limiting webs is in a range between 0.5 and 1.5 mm, and more preferably between 0.6 and 1.0 mm. The wall thicknesses of the individual webs can also be between 0.8 and 2.0 mm. Best results are obtained with frame members which have two such ribs and each of the ribs has a wall thickness between 0.8 and 2.0 mm and preferably between 1.0 and 1.5 mm. A particularly effective combination of parameters in the case of the thickness of the individual webs can also be between 0.8 and 2.0 mm.
 In the case of frame members with three such ribs, each of the ribs can have a wall thickness between 0.3 and 2.0 mm and preferably between 0.8 and 1.5 mm.
 The ribs can run perpendicularly to the webs or can be inclined, e.g. can cross. According to another feature of the invention a spacing between each of the formations of a respective one of said webs and a rib proximal thereto is 20 to 40% of a spacing between structural shapes and preferably 25 to 30% thereof. Furthermore, it has been found to be advantageous in the case of inclined ribs to have them adjoin the webs at transverse segments connected to the respective formations or cleats of the ribs.
 The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:
 The frame member or composite profile shown in the drawing can be utilized for windows, doors, facades and wherever structural strength is required in a frame but transmission of heat between opposite sides of the frame is to be suppressed. A composite profile according to the invention can comprise two preferably metallic structural shapes or profiles
 To provide structural strength while limiting thermal conductivity, the webs are bridged by a plurality of connecting ribs
 In the embodiment of
 It has been found to be important, for the purposes of the invention, that the sum of the thicknesses S
 The maximum wall thickness sum can be 10 mm and preferably is around 6 mm.
 The wall thicknesses of the webs
 For the three rib embodiment of
 The distance