EP0223312B1 - Method for covering objects, means therefor and products obtained - Google Patents

Abstract

The invention concerns a process for folding a flexible piece, in particular to upholster an object such as chair fitting with a flexible cover. The upholstering or covering process comprises cutting out a flexible piece (25) to a shape corresponding to that of the object plus a border on its contour, providing the edge of this border with a tensioning thread sliding within a passage preserved by auxiliary threads, covering the object with the piece so that the border provided with the tensioning thread project beyond the object contour, folding back the border and applying tractions in opposite directions on the two ends (5a, 5b) of the tensioning thread to tighten and to fold this border, lastly, after the tractions have been applied, locking the ends of the tensioning thread either by tieing them together or by stapling them to the back of the object or by crushing a punched-out clip (31) on the back of the object.

Description

The invention relates to a method of pleating a piece of flexible material, such as a textile piece, and its application to the covering of objects by means of flexible covers, in particular seat upholstery called upon to constitute the backrest, the seat or the armrests of a seat. It extends to the products obtained by implementing said process, as well as to means specially designed or modified to allow this implementation: modified sewing machine, self-dressing press, manual instrument to facilitate implementation of the process.

The seat covers are generally composed of a rigid support of appropriate shape and an elastic layer, in particular of foam, held on the front face of this support by a cover. The rigid support is generally made of wood or plastic (or similar material) but can also be metallic. (See BE-A-569937)

The covers are currently made from pieces of fabric which are cut to the shape of the fillings, with a very wide margin around the edge. This margin makes it possible to grasp each cover by its edges, to crease it around the periphery of the lining and to exert a traction ensuring the positioning of said cover around its lining; said margin is then fixed on the rigid support, either on the back thereof, or on its periphery. In the case of a wooden support, this fixing is usually ensured by stapling the fabric to the support. In the case of a metal support, this fixing is provided by a batten which is attached to the edge of the lining to pinch the margin of the fabric.

This dressing process has serious flaws. Firstly, it requires a large workforce to perform the manual operation of fitting the cover by successive pulls, and the operation of fixing the latter by stapling or using battens. In the case of a metal support, these operations are not only long, but also delicate and require great skill. In addition, the large width of the margins required around the periphery of each piece of fabric results in significant losses of material compared to that strictly necessary for dressing the linings; very often these margins must be overcut to remove the floating strip of fabric, and this operation increases the labor costs, while it entails risks of fraying of the edges of fabric, detrimental to the finished appearance of the product. . In addition, the folds of the cover around the edge of the lining are often distributed irregularly and it is impossible after fixing to modify them to improve the presentation of the finished product.

In addition, for certain fittings, the cover is fixed inside a groove formed on the periphery of the rigid support. In the case of a wooden trim, the fixing is ensured by stapling by means of a fine-pointed pistol and this operation is long and costly in terms of labor.

An object of the present invention is to alleviate the above-mentioned drawbacks and to provide a method of covering objects allowing considerable savings in labor.

Another objective is to allow significant savings in raw materials.

Another objective is to make it possible to make a finished product benefiting from improved appearance qualities.

More generally, the invention proposes to indicate an improved method of pleating a piece of flexible material, in particular textile, a method applicable in the above-mentioned context of the dressing of objects or in any other area.

• à découper une pièce en matière souple de forme correspondant à celle de la face antérieure de l'objet avec une marge supplémentaire sur le contour,
• à piquer sur cette marge en bordure de la pièce, au moins un fil auxiliaire agencé pour préserver un passage s'étendant le long de ladite marge et à mettre en place un fil de tension dans ledit passage de façon que ce fil puisse coulisser à l'intérieur et le long de ce passage avec des longueurs de dépassement à ses deux extrémités,
• à recouvrir la face antérieure de l'objet au moyen de la pièce de façon que la marge munie du fil de tension dépasse du contour de celui-ci,
• à replier ladite marge en bordure de l'objet et à exercer sur les deux extrémités du fil de tension des tractions en sens opposés tendant à raccourcir la longueur du fil engagée dans le passage précité et à resserrer et plisser ladite marge,
• et à bloquer les extrémités du fil de tension après tractions.

The method of the invention can be applied to provide an object with a cover in order to dress it on its front face. The dressing process according to this application is characterized in that it consists of a combination:

• to cut a piece of flexible material of shape corresponding to that of the front face of the object with an additional margin on the contour,
• to stitch on this margin at the edge of the workpiece, at least one auxiliary thread arranged to preserve a passage extending along said margin and to place a tension thread in said passage so that this thread can slide at the inside and along this passage with protruding lengths at its two ends,
• to cover the front face of the object by means of the part so that the margin provided with the tension thread protrudes from the outline thereof,
• folding up said margin at the edge of the object and exerting pulls in opposite directions at the two ends of the tensioning wire, tending to shorten the length of the thread engaged in the aforementioned passage and tightening and pleating said margin,
• and to block the ends of the tension thread after pulling.

This process is applicable, as well in the case of a cover whose border must be positioned on the back of the object opposite its rear face, as in a cover whose border must be inserted in a groove made on the periphery of the object. In the first case, the margin provided with the tension thread is folded back towards the rear face of the object, then the thread is tightened in the vicinity of said rear face during the pulling operation. In the second case, the tension thread is positioned so as to come opposite the groove after folding the margin and is tightened to fit into said groove.

In the process of the invention, the margin can be provided at the width strictly necessary since it no longer has to be grasped to pull on the fabric and since it no longer serves to fix the fabric on the object. On the contrary, it is the ends of the tension thread that are pulled and the fabric is held by the tightening of it behind or around the object. It is thus possible to save material by cutting more strict parts. In addition, no excess is no longer necessary and the edge of the fabric provided with the overlock has a perfect appearance which contributes to giving the finished product a quality appearance. In addition, the cover is not blocked along the perimeter of the object as it is when it is stapled, fixed by strip, glued or welded. After blocking the ends of the tension thread, the operator can, if necessary, distribute the folds by sliding the margin along the tension thread in the circumferential direction.

This dressing process according to the invention can be applied in a particularly profitable manner to the manufacture of seat upholstery composed of a rigid support and an elastic layer (foam or other). It conditions considerable savings in labor. It should also be noted in this case that the cutting of the piece of fabric can be very easily adapted as a function of the contour of the lining to obtain, after tensioning, a desired final shape.

The ends of the tension wire can be blocked by any means and in particular by a knot joining them. For wooden or similar supports, these ends can be stapled to the back of the trim or in the groove around its periphery. For metal supports, it is advantageous to provide the support with at least one lug intended to protrude at the location of the ends of the tension wire; the blocking of the ends of this wire is then ensured by closing this or these lugs towards the support to wedge them.

Furthermore, the invention extends to a modified sewing machine to allow the implementation of the previously defined process. This machine is of the well known type, comprising a crowbar, at least one needle, at least one hook, means for driving these members and means for supplying auxiliary threads, with a view to making stitches. overlock; according to the present invention, it is equipped with means for supplying tension thread, means for guiding said thread towards the presser foot and a guide tunnel formed longitudinally in the presser foot and opening under it. ci, said tunnel being transversely positioned relative to the presser foot, needle and hooks, so as to guide the tension thread at an intermediate level between the stitching line and the overlock hooking line.

The tension thread is thus brought to unwind continuously, and is guided towards the presser foot to align it at the edge of the piece, the overlock being produced above and on either side of it.

Such an inexpensive modification of the overlocking machine makes it possible to automatically place the tension thread on the edge of the pieces of fabric (or ribbons if an auxiliary ribbon is used).

In addition, the invention extends to an instrument intended to facilitate the execution of the pulling operation on the ends of the tension thread. This instrument is characterized in that it comprises a support, two rotary studs mounted on said support, means for wedging wire on each stud, a manual rotary drive member and a transmission mechanism interposed between said member. drive and said rotary studs and adapted to ensure rotation in the opposite direction thereof from a rotation of said manual member.

The invention also extends, as such, to a ribbon capable of constituting an auxiliary for the implementation of the pleating method defined above, this ribbon being characterized in that it comprises a tension wire running along of the latter, this tension wire being retained by auxiliary threads stitched onto said strip so as to allow longitudinal sliding of said tension thread.

To facilitate the dressing of a lining having angles, the rigid lining support is preferably manufactured by providing on its rear face at least one lug in the vicinity of each angle: the tension wire is tightened so as to come to bear against these lugs in order to better distribute the tightening effect and limit it at the corners.

The lining covering process defined above can in particular be implemented on a press of the type comprising a plate, a movable compression plate located opposite said plate, means of displacement of said plate making it possible to separate it or to bring it closer to the plate, and a form of holding the lining, carried by the plate and having raised edges. According to a characteristic of the present invention, said press is equipped, on two sides of the plate and in the vicinity thereof, with two grippers for gripping the ends of the tension wire, said grippers being located opposite one of the other and mounted on jacks capable of bringing them closer or apart in a plane substantially parallel to that of the plate, in order to exert traction on said ends of the tension wire.

Such a press makes it possible to dress the seat upholstery in remarkable conditions of economy on labor costs.

The present invention extends, as such, to the seat upholstery produced, comprising a rigid support, an elastic layer, a flexible cover covering one side of the upholstery and having a margin folded over the periphery of this face or towards the opposite face, and characterized in that said cover is held by a tension thread held by auxiliary threads stitched along the aforementioned margin, said tension thread being stretched and blocked so as to crease said margin and tighten it on the around the trim or towards the back.

• la figure 1 est une vue schématique en perspective d'une machine à coudre modifiée conformément à l'invention,
• la figure 2 en est une coupe de détail du pied de biche par un plan transversal,
• la figure 3 en est une coupe schématique,
• la figure 4 est une vue de détail, illustrant le fonctionnement de ladite machine,
• la figure 5 est un schéma d'une housse préparée au moyen de ladite machine, en vue de l'habillage d'une garniture de siège, cependant que la figure 6 illustre en coupe de détail la texture du bord de ladite housse,
• la figure 7 est une vue schématique en perspective d'un ruban auxiliaire réalisé conformément à l'invention à l'aide de ladite machine,
• la figure 8 est une vue schématique en perspective d'une presse d'habillage conforme à l'invention,
• les figures 9a, 9b, 9c, 9d et 9e sont des vues schématiques illustrant le procédé d'habillage conforme à l'invention,
• la figure 10 est une vue en perspective d'une garniture de siège obtenue par mise en oeuvre dudit procédé,
• la figure 11 est une vue en coupe d'une variante de garniture, obtenue par le procédé de l'invention,
• la figure 12 est une vue de détail en perspective d'une autre variante,
• la figure 13 est une vue de détail en perspective d'un autre mode de réalisation en cours d'habillage,
• les figures 14 et 15 sont des vues en coupe d'un dossier ou assise de siège habillé conformément à l'invention sur ses deux faces, respectivement, avant assemblage et après,
• enfin, les figures 16, 17 et 18 sont des vues d'un instrument accessoire conforme à l'invention, respectivement en perspective et en coupes par deux plans perpendiculaires.

Other characteristics, objects and advantages of the invention will emerge from the description which follows with reference to the appended drawings, which present non-limiting examples of embodiment thereof; on these drawings which form an integral part of this description:

• Figure 1 is a schematic perspective view tive of a sewing machine modified in accordance with the invention,
• FIG. 2 is a detail section thereof of the crowbar by a transverse plane,
• FIG. 3 is a diagrammatic section thereof,
• FIG. 4 is a detail view, illustrating the operation of said machine,
• FIG. 5 is a diagram of a cover prepared by means of said machine, for the dressing of a seat upholstery, while FIG. 6 illustrates in detail the texture of the edge of said cover,
• FIG. 7 is a schematic perspective view of an auxiliary ribbon produced in accordance with the invention using said machine,
• FIG. 8 is a schematic perspective view of a covering press according to the invention,
• FIGS. 9a, 9b, 9c, 9d and 9e are schematic views illustrating the dressing process according to the invention,
• FIG. 10 is a perspective view of a seat upholstery obtained by implementing said method,
• FIG. 11 is a sectional view of a variant of packing, obtained by the method of the invention,
• FIG. 12 is a detailed perspective view of another variant,
• FIG. 13 is a detailed perspective view of another embodiment during dressing,
• FIGS. 14 and 15 are sectional views of a seat back or seat dressed in accordance with the invention on its two faces, respectively, before assembly and after,
• finally, FIGS. 16, 17 and 18 are views of an accessory instrument according to the invention, respectively in perspective and in sections through two perpendicular planes.

• deux de ces fils sont travaillés par les deux crochets 3 afin de serpenter sur une face et sur l'autre, en s'accrochant ensemble le long d'une ligne d'accrochage -La- proche du bord de la pièce de tissu,
• l'autre fil est travaillé par l'aigui 1 le 2 afin de réaliser à travers la matière une ligne de piqure -Lp- maintenant les deux autres fils.

The sewing machine shown by way of example in FIGS. 1, 2 and 3 is an overlocking machine of the traditional type comprising a presser foot 1, a needle 2 (or possibly several) and hooks (in the example by number two), one of which is visible at 3 in FIG. 1. These means are associated with means for supplying auxiliary wires 4 and with conventional drive means, capable of moving them appropriately to make stitches. overlocking. In FIG. 1, it has been assumed that the machine was supplied by means of three auxiliary wires 4 in order to make an overlock with three wires:

• two of these threads are worked by the two hooks 3 in order to meander on one side and on the other, by hanging together along a hanging line -La- close to the edge of the piece of fabric,
• the other wire is worked by the needle 1 the 2 in order to achieve through the material a line of sting -Lp- holding the two other wires.

These means and their operation are in themselves well known and will not be described in more detail.

According to the present invention, the machine is provided with a coil for supplying an additional wire, known as tension wire 5, of larger diameter than the auxiliary wires 4 (in particular the coil for supplying itself of the conventional type. , which was not shown).

In addition, a rigid descending tube 6 is fixed to the front of the machine by a tab 7. This tube is arranged to guide the tension wire coming from the supply reel to the vicinity of presser foot 1, opposite from the upstream part of it.

A flexible tube 8 of smaller diameter than the previous one is secured to the presser foot 1 by a holding part 9, so that one of its ends penetrates into the rigid tube 6.

The other end of this flexible tube 8 is located opposite a tunnel 10 which is formed longitudinally in the presser foot so as to open below it. The flexible tube 8 thus forms a continuous passage between the rigid tube 6 and the tunnel 10, and its flexibility allows it to lend itself to the movements of the crowbar.

The tunnel 10 is formed by a notch formed under the crowbar at the edge thereof; this notch is laterally closed by a square-shaped piece 11 fixed to the presser foot using a screw 12. The tunnel is thus transversely positioned relative to the presser foot, needle and hooks, so as to guide the tension thread 5 at an intermediate level between the stitching line Pq and the hooking line Pa of the overlock.

Thus, as illustrated in FIGS. 4, 5 and 6, the tension thread 5 unwinds continuously and is guided to align itself at the edge of the piece of fabric (referenced 25 in these figures), so that the overlock is made above the thread 5 and traps it in the longitudinal passage -P- preserved between the stitching line Lp and hooking line La. In this passage, the tension thread 5 remains free to slide longitudinally. It should be noted that no difficulty is encountered at the angles: it suffices to turn the piece of fabric in the usual way with respect to the machine.

When the overlock has been made on the entire edge of the piece of fabric, the tension thread is cut, leaving protruding lengths 5a, 5b at its two ends (Figure 5).

The piece of fabric can then be pleated by pulling in opposite directions over these lengths, in order to shorten the length engaged in the aforementioned passage.

In the example of FIG. 5, the piece of fabric is directly equipped with the tensioning thread 5, by stitching the auxiliary threads directly into the material thereof, with said tensioning thread being placed simultaneously.

It is also possible to use an auxiliary ribbon 13 as shown in FIG. 7. This ribbon comprises, at the edge, a tension wire running along it; this tension wire is retained as previously by auxiliary threads stitched by means of the machine described above.

Thus, ribbons such as 13 can be made available to users in order to avoid them having to equip themselves with a modified overlock machine: a simple traditional sewing machine is then enough to stitch the ribbon at the edge of the affected piece of fabric.

Furthermore, the pleating of a piece of fabric 25 provided with a tension thread as explained above is described below in the context of the application of the method to the dressing of a seat upholstery.

This pleating and this covering are carried out by means of a press as shown in FIG. 8.

Said press comprises a frame 14 which carries a horizontal plate 15, in the circular example. This plate is mounted on pivoting means such as a ball stop 16, allowing its rotation about a central axis perpendicular to its plane (in the example vertical axis).

Above the plate 15, there is a mobile compression plate 17 which is carried by a jack 18 so that it can be moved vertically opposite the plate; in the same way as the plate, pivoting means such as ball stop 27 are inserted to allow the plate to rotate around the same vertical axis as the plate.

In addition, the press is equipped on two sides of the plate and above it, with two gripping claws such as 19. Each claw 19 is, in the example, of the known type comprising a blocking plate 19a to front toothed edge, articulated in a frame 19b: it is thus able to block one end of wire which has been engaged in said claw as shown in the detail in FIG. 8.

The two claws 19 are located opposite one another and mounted on double-acting cylinders 20 capable of bringing them closer or apart in a plane substantially parallel to that of the plate. These jacks are preferably fixed on supports 21 making it possible to adjust the position as a function of the type of lining to be dressed.

The cylinders 20, in the example of a pneumatic nature, are controlled synchronously by means of a pedal 22.

Figures 9a to 9e illustrate the process implemented by means of said covering press.

A holding form 23 is placed in the center of the plate 15; it has raised edges 23a and its shape is adapted to that of the lining 24 to be dressed.

This lining 24 is composed of a rigid support 24a and an elastic layer of foam 24b. Its cover referenced 25 is formed by a piece of fabric of the type of that of FIG. 5. Said piece previously cut to the shape of the lining with an additional margin 25a is therefore provided with the tension thread 5 at the edge of this margin.

The piece of fabric 25, the layer of foam 24b and the rigid support 24a are superimposed in the shape 23 as illustrated in FIG. 9a, the margin 25a of the piece being raised by the edges 23a of the shape. The operator turns the plate 15 to place the two ends of the tension wire on the side of the claws 19.

The plate 17 is then lowered by the action of the jack 18, until the elastic layer 24b is compressed (FIG. 9b).

The claws 19 are then brought closer to each other by the action of their pneumatic cylinder 20 (FIG. 9c). The operator crosses the ends of the tension thread to hang each of them on the opposite claw.

The claws 19 are then moved apart by the action of the jacks 20 (FIG. 9d). During their movement, they exert on the ends 5a, 5b of the pulls which tighten and fold the margin 25a, which comes to fall back against the rear face of the rigid support. Excellent regularity of the folds is obtained by subjecting the plate 15 to small rotational movements in one direction and the other (arrow R in FIG. 5d: the ball thrusts 16 and 27 allow this rotation in the compression position).

The ends of the tension wire are then blocked, for example by stapling by means of a staple 26, on the back of the rigid support when this support is made of wood or the like (FIG. 9e). These ends can then be cut in the vicinity of the clip 26.

The method described above allows savings in labor which can be estimated at around 50% compared to the conventional method of pulling the cover manually behind the rigid support, then stapling it over the whole around.

A packing is obtained as shown from the back in Figure 10, which has remarkable finishing qualities. The process of the invention makes it possible to leave only a very narrow margin M behind the lining, in order to reduce the consumption of fabric. In addition, the serged edge of the fabric benefits from perfect clarity without any risk of fraying. It is possible, if necessary, to move the peripheral folds of the cover subsequently to further improve their distribution. Nothing prevents then fixing a few staples around the cover to freeze it in its best configuration.

The tension thread 5 can be of any type: thread, synthetic, natural or, if appropriate, metallic thread. In the latter case, a protruding length can be left waiting to be fixed later on a metal part of the seat such as its foot: the invention thus provides a simple means to avoid the accumulation of electrostatic charges on the seat.

Figure 11 shows in section a lining similar to the previous one, but in which the rigid support 28 is provided on edge with a groove 29. The cover is made so that its tension wire comes to be positioned opposite this groove after folding of the margin. During the pulls on its ends, this tension wire is inserted into said groove and comes to tighten therein. End blocking can be provided by any means and in particular by a staple if the support is made of wood or the like.

Furthermore, FIG. 12 represents, in partial perspective, another variant of the lining, in which the rigid support is previously provided, during its manufacture, with a lug 30, projecting on its rear face, in the vicinity of each angle. . This pin can be added by nailing, screwing ... in the case of a wooden support or come from a stamped cutout in the case of a metal support. When it is tightened, the tension wire comes to bear against these lugs 30 (on the external side) so that the tightening effect is limited at the angles. This avoids too much tension on the piece of fabric in areas of very strong curvatures.

FIG. 13 shows a possible method of blocking the ends of the tension wire in the case of a rigid metal support (where stapling is not possible). This support is previously provided during its manufacture with one (or more) lug 31 protruding at the location of the ends of the tension wire (stamped cut). At the point where the ends cross, the margin of the fabric is caused to pass under this lug and the latter is closed towards the support (arrow F) to wedge said ends after pulling.

The method of the invention is particularly well suited for producing seat backs or seat covers coated on their two faces, as shown in FIGS. 14 and 15. A lining 32 of the preceding type is produced with a rigid support provided on its periphery with nesting means, in particular of a peripheral nesting molding 33; this lining is dressed by the method of the invention, in particular by tightening the tension thread of its cover in the molding 33.

A plate 34, provided on its periphery with interlocking means combined with those of the lining (in the example interlocking collar 35 of suitable shape and elasticity), is dressed in a similar manner by means of a cover. The tension wire can be tightened on the rear face of the interlocking collar.

The lining 32 and the plate 34 are then presented back to back so that their dressed faces are in opposition, and are fitted and crimped by causing their fitting means to cooperate.

Furthermore, the pulling operation on the ends of the tensioning thread can be carried out in certain applications (dressing carried out without using a press, or any other pleating of fabric) by means of an instrument of the type shown in Figures 16, 17 and 18.

This small accessory to be able to be held in hand comprises a support 36 which may be constituted by a flat-shaped casing. On this, are mounted two rotary studs 37, 38 arranged opposite one another. Each stud is provided with means for wedging one end of the wire.

In the example, each pad is made of a slightly elastic material and these wedging means consist of a simple diametrical slot 39 formed in each pad. The two slots of the pads are initially arranged in parallel (or even slightly divergent) planes as illustrated in FIG. 16, with a cutaway on the facing halves, so as to be able to guide and perfectly block the ends of the wire in positions crossed.

A manual member such as handle 40 makes it possible to drive these studs by means of a transmission mechanism housed in the support 36; this mechanism consists in the example of a pinion 41 secured to the handle, a pinion 42 secured to the pad 37 and arranged in direct engagement with the pinion 41, and a pinion 43 secured to the other pad 38 and arranged in engagement with an intermediate pinion 44. The two studs 37 and 38 thus rotate in opposite directions when the handle is rotated. The pinions are dimensioned so that these opposite rotations are performed at equal speed.

In addition, a non-return member, such as ratchet wheel 45 and ratchet 46, allows the rotation of the mechanism only in one direction in order to avoid a return after pulling on the ends of the wire.

The above-described instrument makes it possible to exert, in a practical and effortless manner, well-defined pulls on the ends of the tension thread when the latter must be tightened to cause wrinkling.

Claims (23)

1. Method for covering an object by means of a flexible cover, said object having a front face to be covered, characterised in that it jointly consists:

in cutting out a piece of flexible material (25) of a shape corresponding to that of the front face of the object, with an additional border (25a) on its contour,

in stitching to said border (25a) auxiliary threads (4) so as to form at the edge of the piece an overcast seam comprising a stitched line (Lp) in the material and an outer hook-up line (La), with a passage (P) between the two threads extending along the border,

in positioning within passage (P) of the overcast seam a tensioning cord arranged in such a way that said cord can slide within and along said passage, with excess lengths at its two ends (5a, 5b),

in covering the front face of the object with said piece so that the border provided with the tensioning cord goes beyond the contour of said object,

in folding over said border at the edge of the object and in subjecting the two ends (5a, 5b) of the tensioning cord to pull in opposite directions tending to reduce the length of the cord engaged in the above passage and to contract and pleat said border,

and in blocking the ends of the tensioning cord after pulling.

2. Method according to claim 1, whereby tensioning cord (5) is positioned at the same time as auxiliary threads (4) are stitched, by carrying out said stitching above the tensioning cord, the latter being guided at the edge of the piece in step with the stitching process.

3. Method according to claim 2, characterised in that one unwinds tensioning cord (5) continuously, guides the latter so as to align it at the edge of the piece, and produces the overcast seam above said cord, so that stitch line (Lp) in the material and hook-up line (La) of the auxiliary threads are, one and the other, located on one side and the other of said tensioning cord.

4. Method according to one of claims 1, 2 or 3, characterised in that one positions tensioning cord (5) directly on the piece of flexible material by stitching auxiliary threads (4) directly within the material of said piece and locates tensioning cord (5) within the above passage (P).

5. Method according to one of claims 1, 2, 3 or 4, characterised in that tensioning cord (5) is positioned on an auxiliary tape (13) by stitching auxiliary threads (4) to said tape and locating said tensioning cord along said tape, whereby said auxiliary tape is then attached, in particular by sewing, to the edge of the piece of flexible material.

6. Method according to one of claims 1 to 5 for covering an object having a rear face opposite the front face, whereby the tensioning cord is positioned so as to be opposite the rear face after folding over the border, said cord being contracted in the vicinity of said rear face during the operation of pulling.

7. Method according to one of claims 1 to 5 for covering an object having a circumference provided with a recess (29) on the periphery of the front face, characterised in that the tensioning cord is so positioned as to be opposite the recess after folding over the border, said cord being inserted into said recess during the operation of pulling and being contracted within the latter.

8. Method according to one of claims 1 to 7 for covering a seat back composed of a rigid support (24a) and an elastic layer on the front face, whereby the elastic layer (24b) is maintained in a compressed state during the operation of pulling at the ends (5a, 5b) of the tensioning cord.

9. Method according to claim 8, whereby the rigid support of the back consists of wood or an analogous material and whereby blocking of the two ends of the tensioning cord consists in hooking (26) them to the support.

10. Method according to claim 8, whereby the rigid support of the back consists of metal, characterised in that said rigid support is made with at least one projecting catch (31) at the location of the ends of the tensioning cord, blocking of said ends being ensured by closing said catches towards the support so as to clamp said ends.

11. Method according to claim 8, whereby blocking of the two ends of the tensioning cord consists in tying said ends together.

12. Method according to claims 6 and 8 jointly, with a view to covering a back with corners, characterised in that the rigid support of the back is made with at least one projecting peg (30) on its rear face and in the vicinity of each corner, and in that the tensioning cord is contracted so as to rest against said pegs with a view to limiting the effect of contraction in the region of the corners.

13. Sewing machine modified so as to enable the implementation of the method according to one of claims 1 to 12, of the type comprising a presser foot (1), at least one needle (2), at least one hook (3), means for driving these devices and means for feeding auxiliary threads with a view to making overcast seam stitches, characterised in that it is provided with means for feeding a tensioning cord, means (6, 8) for guiding said cord towards presser foot (1) and a guide duct (10) produced longitudinally within presser foot (1) and opening out on the underside of the latter, said duct (10) extending transversely in relation to the presser foot, the needle and the hooks so as to guide the tensioning cord at an intermediate level between stitch line (Lp) and hook-up line (La) of the overcast seam.

14. Sewing machine modified according to claim 13, characterised in that the means for guiding the tensioning cord comprise:

a rigid tube (6) designed to guide the cord emanating from the feeding means to the vicinity of presser foot (1), opposite the upper part of the latter,

a flexible tube (8), one end of which is inserted in said rigid tube, firmly connected with the presser foot so that its end is located opposite duct (10) with a view to forming a continuous passage towards said duct.

15. Sewing machine modified according to one of claims 13 or 14, characterised in that duct (10) is formed by a cut-out provided on the underside of the presser foot at the edge of the latter, as well as by an angle piece (11) attached to said presser foot.

16. Press for automatic covering of a back, enabling the implementation of the method according to one of claims 1 to 12, comprising a platen (15), a movable compression plate (17) situated opposite said platen, means for displacing said plate (18) enabling it to be retracted from or approached to the platen, and a form for holding the back (23) supported by platen (15) and having raised edges (23a), said press being characterised in that it is provided, on two sides of platen (15) and in the vicinity of the latter, with two grippers (19) for gripping the ends of the tensioning cord, said grippers being situated opposite one another and mounted on jacks (20) capable of approaching or retracting them within a plane substantially parallel to that of the platen, so as to apply a pull to said ends of the tensioning cord.

17. Press according to claim 16, characterised in that platen (15) and plate (17) are mounted on means (16, 27) enabling their rotation about a central axis at right angle to their plane.

18. Appliance specially designed to facilitate the implementation of the method according to one of claims 1 to 12, characterised in that it comprises a support (36), two rotary devices (37, 38) mounted on said support, means (39) for clamping cord to each device, a manual device for rotary driving (40) and a transmission device (41-44), interposed between said driving device and said rotary devices and capable of causing the latter to rotate in opposite directions, as a result of rotating said manual device.

19. Appliance according to claim 18, characterised in that with each device (37, 38) the clamping means consist in a diametrical slot (39) provided within said device.

20. Appliance according to one of claims 18 or 19, characterised in that transmission mechanism (41-44) is associated with a ratchet device (45, 46) permitting rotation only in one direction.

21. Seat back capable of being produced by the method according to claims 1 to 12, comprising a rigid support (24a), an elastic layer (24b), a flexible cover (25) covering one face of the back and comprising a border folded over on the circumference of said face or towards the opposite face, characterised in that said cover (25) is held by a tensioning cord (5) retained by auxiliary threads (4) stitched so as to form an overcast seam at the edge of said border, said tensioning cord being stretched and blocked so as to pleat said border and contracted about the circumference of the back or towards the rear face.

22. Tape enabling the implementation of the method according to one of claims 1 to 12, characterised in that it comprises a tensioning cord extending along the latter, said tensioning cord being retained by auxiliary threads stitched to said tape (13) so as to enable longitudinal sliding of the tensioning cord.

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