METHOD FOR PRODUCING A RIGID STRUCTURE BASED ON CURVED METAL TUBES FOR FORMING A REAR CANTILEVER SEAT

Abstract

The invention relates to a method for producing a rigid structure (5) based on curved metal tubes for forming a seat (1) of the rear cantilever type such as a chair or an armchair, characterized in that it comprises at least the steps involving forming two elongated one-piece lateral elements (10) by bending, each element at least being formed by a first base tubular portion (11) extending forwards, at a first bottom front bending zone (12), by a first front tube (13) erected upright and extending rearwards, at a first top front bending zone (14), by a lateral seating tube (15), said tubes used during bending by said method being made of a high carbon content, preferably between approximately 0.85 and 2.1%, steel alloy and the bending operations being performed cold before any type of subsequent heat treatment for hardening the steel that is used.

Claims

1. Method of producing a rigid structure based on metal tubes bent to form a seat of the rear cantilever type, such as a chair or an armchair, comprising the steps of: forming two one-piece elongated lateral members by bending said metal tubes, each of the two one-piece elongated lateral members made of a primary tubular foot portion extending forwardly and, at a level of a first lower frontal bending zone, extending as a front primary tube erected upwardly and, at a level of a first upper frontal bending zone, extending rearwardly as a lateral seat tube, said metal tubes used during the bending by said method being made of steel, and carrying out a subsequent heat treatment for hardening the steel after bending said metal tubes.

2. The method according to claim 1, wherein bending the metal tubes comprises bending the metal tubes which are made of steel having a carbon content between about 0.85 and about 2.1%.

3. The method according to claim 1, wherein bending the metal tubes comprises bending solid tubes having a diameter between about 10 and about 25 mm.

4. The method according to claim 1, wherein bending the metal tubes comprises bending the metal tubes forward and down and forward and up at approximately 90°, with a median bending radius of approximately 1.5 to 3 times the diameter of the metal tubes used.

5. The method according to claim 1, wherein the step of forming the two one-piece elongated lateral members by bending comprises forming a single continuous arc of approximately 180° between the primary tubular foot portion and the lateral seat tube.

6. The method according to claim 1, further comprising connecting the two one-piece elongated lateral members at the primary tubular foot portion of each of the two one-piece elongated lateral members to a third structural element which is formed of a hollow tube.

7. The method according to claim 6, further comprising producing the third independent structural element in the form of two secondary tubular foot portions connected respectively and in a parallel manner to the primary tubular foot portion of each of the two one-piece elongated lateral members and each extending in a second lower front bending zone into a front secondary tube erected upwards parallel to the front primary tube, each front secondary tube extending in a second upper front bending zone, into a single front transverse tube delimiting a seat structure with the two lateral seat tubes.

8. The method according to claim 7, further comprising providing the free ends of the solid tubes of the two one-piece elongated lateral members with undercut nipples having an external diameter identical to an internal diameter of the hollow tubes of the third independent structural element, then inserting said undercut nipples of the two one-piece lateral members into the hollow tubes of the third element over a length of 1 to 2 cm before soldering or welding the assembly to form the structure.

9. The method according to claim 8, further comprising forming, by bending, an arc of 180° at a free end of the primary tubular foot portion to connect the free end of the primary tubular portion with a free end of the secondary tubular portions.

10. The method according to claim 6, further comprising securing the front primary tube and the front secondary tube to each other with a reinforcing crossbar.

11. The method according to claim 10, further comprising arranging said reinforcing crossbar at mid-height of the front primary tube and the secondary tube.

12. The method according to claim 6, further comprising connecting, in extension of the lateral seat tubes, secondary lateral seat tubes, with rear tubes extending therefrom at a first high dorsal bending zone also belonging to the seat structure.

13. The method according to claim 12, further comprising bending the two rear tubes upwardly at a second dorsal bending zone to form a backrest.

14. The method according to claim 12, further comprising a subsequent step of attaching a rigid openwork plate or mesh or frame made of metal, between the front transverse tube, the lateral seat tubes, the secondary lateral seat tubes, and the rear seat tubes.

15. The method according to claim 14, further comprising a subsequent step of inserting a two-part seat pad, a top part and a bottom part, sandwiching and thereby hiding from outside said plate, mesh, or frame.

16. The method according to claim 2, wherein bending the metal tubes comprises bending the metal tubes which are made of steel having a carbon content between about 1.15% and about 2.0%.

17. The method according to claim 3, wherein the bending the metal tubes comprises bending solid tubes having a diameter between about 15 mm and about 20 mm.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0031] Further advantages, purposes and characteristics of this invention are apparent from the following description made, for the purpose of explanation and not limitation, with reference to the attached drawings, in which:

[0032] FIG. 1 is an isometric perspective view of a seat according to this invention,

[0033] FIG. 2 is an isometric perspective view of the tubular structure constituting the seat in FIG. 1,

[0034] FIG. 3 is a partial isometric and locally exploded view of FIG. 1,

[0035] FIG. 4 is a detailed view of FIG. 3,

[0036] FIG. 5 is an isometric perspective view of an embodiment of FIG. 1,

[0037] FIG. 6 is a side view of FIG. 5,

[0038] FIG. 7 is a perspective view of an alternative structure of FIGS. 1 through 4 and 5 through 6,

[0039] FIG. 8 is a cross-sectional view of FIG. 7 illustrating the connection between the different elements of the tubular structure,

[0040] FIG. 9 is another alternative embodiment of FIGS. 1 and 5, and

[0041] FIG. 10 depicts an alternative chair with an armrest.

DESCRIPTION OF THE EMBODIMENTS

[0042] FIGS. 1 to 4 represent a first embodiment of a chair 1 according to this invention.

[0043] This chair 1 has a rigid structure 5 based on tubes with an external diameter of 15 mm which are curved according to a well-known technology described later. This technology may also be used for tubes of different diameters, preferably in the range of approximately 10 to 25 mm, and more preferably between 15 and 20 mm.

[0044] Thus, this chair 1 comprises two first one-piece elongated side elements 10 (in dark gray in FIG. 2) a third structural element 20 (in light gray in FIG. 2) and a fourth back element 30 (in light gray in FIG. 2).

[0045] Each first elongated one-piece lateral element 10, thus realized in the form of a continuous tube, comprises a primary tubular foot portion 11 extending forward, at a first lower frontal bending zone 12, by a front primary tube 13 (or vertical post) erected upwardly and extending rearward, at a first upper frontal bending zone 14, by a lateral primary seat tube 15. This structure may also be seen in FIGS. 5 to 8.

[0046] As provided for in the invention, all the tubes of these first elongated side members 10 are solid and made of steel with a higher carbon content, preferably between approximately 0.85 and 2.1%, preferably between 1.15 and 2%, and the bending in zones 12 and 14 is carried out cold before any type of subsequent heat treatment for hardening the steel is used.

[0047] The front bottom 12 and front top 14 bending steps of the elongated side elements 10 are carried out at approximately 90°, preferably cold, on a rigid frame known per se, with a median bending radius (along the axis of symmetry of the tubes) of approximately 1.5 to 3 times the diameter of the tube used.

[0048] According to this first embodiment shown in FIGS. 1 to 4, certain zones of the structure 5 are “doubled”, or “paperclip-shaped”, which gives it a better grip on the ground on the one hand, and provides it with a very original aesthetic on the other hand.

[0049] Thus, a third internal element 20 of the structure 5 (light-colored in FIG. 2), made independently of the two elongated lateral elements 10, has two secondary tubular foot portions 21, connected respectively and in a parallel manner to the primary tubular foot portions 11 and each extending in a second lower front zone 22 of bending at 90°, by a front secondary tube 23 erected upwards parallel to the front primary tube 13, each front secondary tube 23 being extended, in a second upper front zone 24 of bending at 90°, by a single front transverse tube 25 delimiting a seat structure 8 with the two lateral seat tubes 15.

[0050] The free ends of each foot are formed by a curve 26 forming a 180° arc between said parallel tubes of the secondary portions 21, giving that particular shape of a paperclip previously indicated. This allows the “sliders”, formed by the primary and secondary tubular portions 11 and 21 and the curve 26 of each leg, to remain parallel to each other and to the ground, while contributing to the rigidity of the structure 5 and providing an aesthetically appealing appearance.

[0051] It should be noted that the third structure 30 has little or no effect on the weight-bearing capacity of the chair, since most of the weight rests on the two elongated solid tube side members 10, which are much stronger.

[0052] Alternatively (not shown), it is possible to add transverse bars between the primary 11 and secondary 21 tubular portions of each leg, at mid-length of the latter and/or close to the lower frontal bending zones 12 and 22. In this case, the purpose of these bars is to maintain portions 11 and 21 of the feet parallel to each other.

[0053] Likewise, the front primary tubes 13 and the front secondary tubes 23 are connected to each other by at least one reinforcing crossbar 28 placed at mid-height and/or close to one and/or the other of the lower front bending zone 12 and the second upper front bending zone 24. This bar 28 allows a better stability between the 2 front tubes 13 and 23 of the vertical posts of the structure 5.

[0054] As may also be seen in FIGS. 1 through 4, a fourth structural member 30 is provided on the back of the overall structure 5. More specifically, these are secondary lateral seat tubes 31 that are attached to the primary lateral seat tubes 15 and that extend, at a first upper back zone 32 of bending at 90°, into two rear tubes 33 also belonging to the seat structure 8.

[0055] The two rear tubes 33 are then bent upwards at the level of a second 90° bent dorsal zone 34 to form a backrest 35 closed upwards by a 180° bend forming an inverted “U” and covered with a backrest lining 36 of a known type.

[0056] As illustrated in FIGS. 3 and 4, a rigid plate or mesh 40, preferably metallic, is fixed (preferably by welding and/or brazing) between the front transverse tube 25, the lateral seat tubes 15 and 31, and the rear seat tubes 33 together defining the seat structure 8.

[0057] A seat pad 50 is then incorporated into the seat structure 8. Preferably, this seat upholstery 50, made for example of leather or padded imitation leather, consists of two independent parts 51 and 52. More precisely, the upper part 51 and the lower part 52 sandwich the said plate/mesh 40 in such a way as to make it completely invisible from the outside (see FIG. 1 for example). The front edge 50a of each of the parts 51 and 52 is preferably flush with the front cross tube 25.

[0058] The upper part 51 of the seat upholstery 50 comprises front protrusions 54 which are integrated between the tubes 13 and 15 on the one hand, and the tubes 23 and 25 on the other hand, at the level of bends 14 and 24.

[0059] Similarly, the lower part 52 of the seat upholstery 50 has a rear housing 53 that engages a rear protrusion 55 of the upper part 51 of the seat upholstery 50, as seen in FIG. 4. This allows the seat upholstery 50 to be integrated as well as possible with the seat structure 8 of the overall tubular structure 5. In particular, this type of assembly gives the impression, at least from the front as well as from the sides, that the seat 50 forms a single element because the peripheral joining lines of the two parts 51 and 52 are actually hidden by tubes 25 and 15.

[0060] As contemplated by this invention, all of the tubes of the third structural member 20 and the fourth dorsal member 30 have the same outside diameter as the tubes constituting the elongated side members 10.

[0061] According to a variant of the embodiment illustrated by FIGS. 5 and 6 and presenting a different aesthetic, the overall structure 5 is constituted by only two long lateral elements 10 (in grey) identical to those of FIGS. 1 to 4, i.e., composed of a continuous doubly bent tube comprising a primary tubular portion of the foot 11 extending towards the front, at the level of a first lower frontal zone 12 of bending at 90°, by a front primary tube 13 (or vertically upright) drawn upwards and extending towards the rear, at the level of a first upper frontal zone of bending at 90° 14, by a lateral seat tube 15.

[0062] This chair 1 also comprises a third tubular structure 20 (light colored) “which closes the legs towards the rear” and which is constituted for this purpose by two secondary tubular portions of legs 21 respectively extending the two primary tubular portions of legs 11, these two secondary tabular portions of legs 21 being bent at 90° in lower rear bending zones 26b in order to form a rear tube 29 disposed substantially in line with the backrest upholstery 36.

[0063] Similarly, the chair comprises a fourth tubular structure 30 (light colored) comprising two secondary lateral seat tubes 31 attached to the primary lateral seat tubes 15, said secondary lateral seat tubes being this time bent upwardly at 90° in the upper dorsal bending zones 32 and are extended by rear tubes 35b forming the support of the backrest upholstery 36.

[0064] FIGS. 7 and 8 illustrate the mode of connection of the elongated side elements 10 made of solid tube (shaded tubes) with a third structural element 20 and a fourth dorsal element 30 according to an intermediate variant (without a backrest structure) between FIGS. 1 to 4 (so-called “double slide” structure) and FIGS. 5 to 6, both of which are made of hollow tube (light-colored tubes).

[0065] More specifically, as shown in the cross-section in FIG. 8, the upper and lower free ends 10a of the solid (black colored) tubes of the two elongated side members 10 are provided with undercut nipples 10b having an outer diameter D1 identical to the inner diameter D2 of the hollow tubes of the third (gray colored tubes) and fourth (light colored tubes) structural members 20 and 30.

[0066] To build the entire structure 5 of chair 1, it is sufficient to insert said undercut nipples 10b of the two elongated side members 10 into the hollow tubes of the third structural member 20 and the fourth structural member 30 for a length of 1 to 2 cm before brazing or welding the assembly. This method of attachment is the same as that used for the overall structures 5 of chair 1 in FIGS. 1 to 4 and 5 to 6.

[0067] The structure thus formed is therefore particularly thin, light, airy, and aesthetically pleasing, without compromising its strength and resistance to bending due to the design and shaping of the elongated elements made of solid tubes cold curved in a soft state before thermal hardening in order to have a very high degree of hardness (63HRC).

[0068] The choice of steel used is also important. It is, as mentioned earlier in the description, a high carbon steel, typically approximately 1.15 to 2%, so that it is rigid enough not to bend under the weight of the user but also flexible enough to bend without breaking, while keeping a permanent and almost identical stability regardless of its weight.

[0069] Thus, a solid tube made of Z160 CDV12 (1.55% carbon), a steel known to be brittle (steel for machine tools, sheet metal cutting tools, etc.) but in fact sufficiently elastic to provide a slight, comfortable spring effect (coax. 2-2.5 cm of bending range), might be chosen.

[0070] The solid tube of Z160 CDV12 in the annealed (soft) state is bent according to known techniques (on a rigid frame) with a median radius (at the transverse axis of the tube) of approximately 35 mm in bending zones 12 and 14 for a tube with an outside diameter of 1.5 mm.

[0071] Hardening at a temperature above 900° C., e.g., 1000-1050° C., followed by tempering and then cooling, e.g., by cryogenics, are carried out after bending in order to stiffen the resulting structure and achieve a service hardness of approximately 63HRC.

[0072] In the embodiment shown in FIG. 9 the bending steps of the elongated side members 10 form a single continuous 180° arc 12 (rather than two independent 90° arcs) between the primary foot tube portion 11 and the seat tube 15.

[0073] The same is true for bending arc 22 of the third structure 20 at the level of tubes 23 which follows the same curvature as tubes 13 of the first elongated side members 10.

[0074] Of course, only the primary foot tubular elements 11, the primary front tubes 13 and the primary side seat tubes 15 are made of solid high carbon steel tube.

[0075] The resulting chair 1 remains extremely stable and strong, with a design very different from the two previous models, but retaining a solid tubular portion (part of the legs, of the front and of the seat) in the areas requiring increased resistance to flexing and breaking. Of course the structure 5 is similar to that of FIGS. 1 to 4, with the first elongated side members 10 made of solid high carbon steel tube to support the weight and all the rest of the structure 5 (third and fourth structural members 20 and 30) made of hollow tube.

[0076] FIG. 10 shows a chair 1 in which the elongated side elements 10 are substantially the same as in the previous embodiments (tube bent and then heat-treated, bending 12 and 14 at approximately 90°), with the difference that side tubes 15 no longer form a lateral part of the seat structure 8 but an armrest 60. Likewise, the front transverse tube 25 of the third structure 20 no longer forms a front part of the seat structure 8 but only serves to connect the lateral upright members constituted by front tubes 13 and 23. Each armrest 60 also has a side tube 27 of the third structure 20 that is parallel to the side tube 15 of each elongated member 10. The upholsteries of the seat 50 and the backrest 36 form a single upholstery, for example, in the form of a fabric or leather cloth stretched between the seat structure 8 and the fourth structural element 30. As in the previous variants, the user's weight continues to be supported mainly by the lateral elongated elements 10 which are more rigid than the rest of the structure.

[0077] It should be understood that the detailed description of the subject-matter of the invention, which is given for illustrative purposes only, does not in any way constitute a limitation, as the technical equivalents are also included within the scope of this invention.

[0078] Thus, the 180° angle or the 90° angles of the upper and lower front bends may be slightly larger than these values, to give the seat a particular shape with a slight tilt.

[0079] The legs of the seat are not necessarily parallel to each other but may form a trapezoid.

[0080] The bending operations, in particular of the elongated side elements 10, may be performed under heat.

[0081] Steels other than the one mentioned might be considered, the principle being to find a steel that is cold bendable according to the desired radius of curvature and that will have the same characteristics of stiffness without breaking after hardening under the weight of the person sitting on the chair.

[0082] The tubes may be hollow or solid, square, or rectangular in cross-section, and the elongated side members 10 may be made with hollow tubes, preferably from 2 to 6 mm, for example with an internal diameter of approximately 5 mm. In this case, an intermediate sleeve-like part will need to be provided instead of the nipples 10b to connect the elongated side elements 10 to the third and fourth structural elements 20 and 30.

[0083] The ends of the feet do not necessarily form a 180° arc but may assume many other shapes.

[0084] The lattice or sheet 40 may be replaced by a simple frame connected around the inner perimeter of the seating structure 8 and covered, for example, by a sheet of wood or other material to support the upholstery.

[0085] It is possible for the paperclip-like structure 5 to comprise not only two parallel tubes, but three parallel tubes to form the legs and extend into three front tubes, one of which forms the front post 25 of the seating structure 8, another forms the side posts 15 of the seating structure 8, and a last one is directed upwards to form armrests.