Patent Application
20220330703
This invention relates to a method of producing a rigid structure from curved metal tubes to form a seat of the cantilevered type, such as a chair or armchair.
Producing chairs or armchairs with a rear cantilever, i.e., with a seat that “floats” above the ground because of the absence of vertical rear legs is known. These seats have a particularly, aesthetic shape, with a comfortable and much appreciated “airy” structure.
Typically, these seats are made by bending hollow metal tubes with an external diameter of 20 or 30 mm and a material thickness of between approximately 2 and 3 mm, so that the tube, which is suspended in the hollow at the level of the seat, does not bend under the weight of the person who sits on the seat.
However, these seats are often massive/heavy because of the diameter of the tubes and the possibilities of different designs are quite limited. Indeed, because of the bending angles used, which are necessarily proportional to the diameters of the tubes used, the models all look the same, at least in terms of the legs and the general structure that results therefrom.
Furthermore, with respect to the processing technique used in the prior art, in order for a solid or hollow metal tube to be bendable, it must be made of a relatively ductile material For example, as a rule, for a hydraulic type tube (e.g., a gas pipe) made of low-alloyed basic steel with a low carbon content (on the order of 0.18%), this tube should have an external diameter of approximately 25 mm. Below this value, it bends too much to be stable, and it may even break under the weight of the user (due to the defects in its properties, i.e., it is ductile to be bendable, with the consequences that this implies for its mechanical strength).
Cold bending normally makes it possible to produce large quantities of identical parts with constant mechanical characteristics. With hot bending, this is not possible because the temperature rise alters the intrinsic mechanical characteristics of the steel. Moreover, as heating of the same piece and/or of one identical to another is hardly homogeneous, the bending radii are never exactly the same so that a process of this type is hardly industrial but rather reserved for implementation of a craft technique.
High-alloy steels, on the other hand, offer greater hardness after heat treatment, but they are not bendable at this level of hardness.
Finally, variants with solid and flat bars exist, for example those that are 40 mm wide and 15 mm high, but the resulting seats remain massive and quite similar in design.
Prior art processes for manufacturing this type of seat are therefore not optimized and do not allow, in particular, the creation of thin tubular structures, for example, those close to 15 mm in diameter, with a high resistance to bending and breaking to avoid breaking while remaining comfortable.
[00.10] The purpose of the invention is to remedy this problem and to be able to manufacture a cantilevered (rear) chair with thinner tube diameters (15 mm) than those used in previous technology (20-30 mm). For this purpose, it proposes to cold curve the lateral parts of the seat structure supporting the user's weight, i.e., tubes made of a steel with a high carbon alloy but in the annealed state (softened) in order to be cold bendable, and then to carry out a heat treatment of the curved structure thus obtained in order to obtain maximum hardness, so as to produce a thinner but highly mechanically-resistant part that keeps the seat from bending under the weight of the person sitting on the seat.
The present invention seeks to remedy these disadvantages with a completely novel approach.
To this end, according to a first aspect, this invention relates to a method of producing a rigid structure based on curved metal tubes to form a seat of the rear cantilever type, such as a chair or an armchair, characterized in that it comprises at least the steps consisting of forming, by bending, two elongated one-piece lateral elements, each consisting of at least one primary tubular portion of the foot extending towards the front, at a first low frontal bending zone, by an upright front primary tube extending towards the rear, at a first high frontal bending zone, by a lateral seat tube, said tubes used during bending by said method being made of alloy steel and bending being carried out before any type of subsequent heat treatment for hardening the steel used.
Thus, the load-bearing structure of the seat is reinforced, without it appearing either too massive or too fragile, and with a particularly high resistance to bending at the level of the overhang, supporting loads in excess of 120 kg without breaking or bending in an excessively pronounced manner.
The invention is implemented according to the following embodiments and variants set forth below, which are to be considered individually or in any technically operative combination:
Advantageously, the method consists of connecting the two one-piece elongated lateral members to at least a third hollow tube structural member at the level of the primary tubular foot portion.
Preferably, the method consists of producing a third independent structural element in the form of two secondary foot tube portions, connected respectively and in a parallel manner to the primary foot tube portions and each extending, in a second lower frontal bending zone, into a front secondary tube erected upwardly parallel to the front primary tube, each front secondary tube extending, in a second upper frontal bending zone, into a single front transverse tube delimiting the seat with the two lateral seat tubes.
This solution allows for the creation of a new style of cantilevered seat. The thinner diameter allows for different designs, especially with doubled tubular legs forming a symmetrical paperclip type seat flat on the floor instead of a U shape.
According to one particular embodiment, the process consists of providing the free ends of the solid tubes of the two lateral elements with undercut nipples having a diameter identical to the internal diameter of the hollow tubes of the third element, then inserting said undercut nipples of the first two lateral portions into the hollow tubes of the second portion over a length of 1 to 2 cm before soldering or welding the assembly to form the complete structure.
Preferably, the process consists of connecting the free ends of the primary and secondary tubular portions of each foot by bending a. 180° arc between said tubes.
According to particular embodiments:
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:
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.
Thus, this chair 1 comprises two first one-piece elongated side elements 10 (in dark gray in
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
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.
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.
According to this first embodiment shown in
Thus, a third internal element 20 of the structure 5 (light-colored in
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.
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.
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.
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.
As may also be seen in
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.
As illustrated in
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
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.
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
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.
According to a variant of the embodiment illustrated by
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.
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.
More specifically, as shown in the cross-section in
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
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).
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.
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.
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.
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.
In the embodiment shown in
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.
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.
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
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.
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.
The legs of the seat are not necessarily parallel to each other but may form a trapezoid.
The bending operations, in particular of the elongated side elements 10, may be performed under heat.
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.
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.
The ends of the feet do not necessarily form a 180° arc but may assume many other shapes.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR1903654 | Apr 2019 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/057485 | 3/18/2020 | WO |
