Device For Bending Metallic Tubes And In Bent Metallic Tubes

Abstract

The device enables metallic tubes to be bent round acute curves. Two coplanar grooved rollers support the tube and a tool is forced downward on the intermediate section of the tube, so bending the tube and deforming its cross-section. The active surface of the tool has a median groove and two ribs bounding the groove, extending longitudinally of the tube. The bent tube thus has a concave portion including a median rib and two longitudinal shoulders.

Description

The present invention relates to devices for bending or curving metallic tubes in the cold around a relatively sharp angle, that is to say around a curve of small radius of curvature, comprising, on one hand, two members intended to receive a tube and, on the other hand, a tool adapted to be supported under the action of an external force, on a portion of the tube comprised between said two support members, so as to bend this tube whilst deforming its cross-section.

The invention relates also to metallic tubes bent around a curve of small radius of curvature by means of these devices, as well as assemblies or frameworks composed at least in part of such bent tubes.

The invention applies more particularly, but not exclusively, to the case where the bent tubes concerned serve for constituting frame works for beds, tables, seats or other articles, and especially frame works for vehicle seats.

By "small radius of curvature" of the bend is meant a radius of curvature which is of the same order of magnitude as that of the tube, that is to say generally comprised between one half and double this diameter. The corresponding bends form relatively sharp angles, which frees their inner zones and reduces their incurved zones: this advantage being often sought, for example when it is desired to fix springs or other accessories on the tube in the immediate proximity of the apex of one of its angles, generally on the inside of this angle.

When a metallic tube is bent along such a curve of small radius of curvature, the metal of the tube located in the convex portion of the bend is stretched whilst the metal located in the concave portion is on the other hand compressed; there is hence produced a deformation of the cross-section of the tube and, to facilitate bending, this deformation is guided by means of a tool.

Hitherto, the tool concerned forced the metal of the tube located in the concave portion of the bend towards the inside of said tube so as to give the transverse cross-section of this concave portion the form of an inset V. Tubes thus bent and deformed have small mechanical strengths, especially to torsion and to flexion, particularly in the direction of reopening the angle of bending, by reason of the tendency to tearing and cracking of the zones, of the concave portion of the bend, which have been rendered fragile by the deformation (zones generally located at the tip and at the apices of the V).

It is an object of the invention, in particular, to reinforce the mechanical strength of the concave portion of the bend.

According to the invention there is provided a device of the type concerned, wherein the tool is arranged so that the surface of its active portion coming into contact with the tube on bending has a median groove and two ribs bounding this groove, the said groove and the said ribs extending around the longitudinal direction of the tube after bending.

According to another aspect of the invention, there are provided metallic tubes, bent so as to comprise at the concave portion of their elbows, a longitudinal median rib bounded by two ledges.

In tubes thus bent, the constituent metal of the concave portions of the tubes has not undergone flow or accentuated forcing on its deformation, but only relatively moderate flexions; moreover, the total cross-section resulting in the bend zone is relatively large. As a result, excellent mechanical strength is obtained of the said curved zone to torsions and flexions.

According to further and preferred features of the invention, the sections of the tube which are attached to its bent portion have a circular cross-section; the width of the groove fashioned in the active portion of the tool, (and hence that of the rib formed in the elbow of the tube) may be of the order of one third of the outer diameter of the tube.

In order that the invention may be more fully understood, a preferred embodiment thereof is described below, purely by way of illustrative but non-limiting example, with reference to the accompanying drawing in which:

FIG. 1 shows diagrammatically in section a device for bending tubes, constructed according to the invention, in its position corresponding to the beginning of the operation of bending a tube;

FIG. 2 is a view, from above of the embodiment of the device shown in FIG. 1;

FIG. 3 shows, in side view, the same embodiment at the end of the bending operation;

FIG. 4 shows, in side view, a metallic tube, bent, according to the invention; and

FIG. 5, lastly, is a partial section along the line V--V of FIG. 3 of the tool and of the bent tube spaced from one another.

With regard to the bending device as a whole, this includes:

two support members 1, such as cradles, or again grooved rollers mounted on parallel axes of rotation 2, located at an adjustable distance D from one another (FIG. 1), which members are arranged transversely with regard to one another, that is to say both corresponding to a same transverse plane of symmetry P,

a tool 3 located generally at an equal distance from the members 1, above these members, corresponding to two planes of symmetry: a first plane merging with the plane P and a second plane Q equidistant from the axes 2 and perpendicular to the intersection of the plane P and the plane containing the said V axes,

and means for ensuring relative displacement of the members 1 and of the tool 3 along a direction denoted by a double arrow F, parallel to the intersection of the two planes P and Q.

The operation of such a known device is as follows.

The tool 3 occupying the position shown in FIG. 1, or high position, a cylindrical metallic tube 4 to be bent is placed under the said tool 3, on the members 1 where it rests by two contact zones. Between these zones extends a portion 6 of the tube, of length substantially equal to the distance D, which is free of any support. The middle line 7 of the tube is hence situated in the plane P.

Means provided to cause relative movement of the tool 3, the members 1 and the tube 4 are then actuated so that the said tool comes to bear on the median region of the portion 6 of the tube and to bend, in the cold, this tube 4 at this spot whilst deforming its section. The middle line 7 of the tube curves inward but remains in the plane P.

In the following there is denoted by longitudinal direction of the tube, the direction of the middle line of this tube; just as there will be designated by transverse direction, a direction orthogonal to the middle line of the tube and by transversal section, a section through a plane perpendicular to the middle line of the tube.

Hitherto, the form of the tool 3 was such that it produced a single very deep hollow, elongated longitudinally in the central zone of the concave portion of the bent tube and the elbow thus obtained was relatively fragile, cracking or breaking fairly easily in its very deformed zones.

To overcome this drawback, according to the invention, there is made to comprise at the surface 8 of the active portion, of the tool, coming into contact with the tube 4, a median groove 9 and two ribs 10 and 11 bounding this groove, said groove and said ribs being oriented along the longitudinal direction of the tube 4.

The median groove 9 may have a transverse section of various shape but has preferably the shape of an arc of a circle, as shown in FIG. 5, which shape avoids sharp angles. The ribs 10 and 11 have a transverse section of small curvature, of sign opposite to that of the curvature of the groove 9. The widths of the groove and of the ribs are substantially equal and for example of the order of one third of the outer diameter of the tube each. There are given to the connecting beads 12 and 13 of the ribs 10 and 11 with the groove 9 the smallest possible curvatures compatible with good mechanical strength of the bent tube.

The cross-sections of the surface 8 of the tool through the plane P, which contains the middle line 7 of the tube before and after bending, and through planes parallel to this plane P, having advantageously the shape of circular arcs and the surface of the groove 9 is then constituted by a portion of a toric surface.

The whole of the active portion of the tool 3 coming into contact with the tube may have the shape of a grooved pulley.

The depth of the groove 9 may be such that after bending there exists a free space between the bottom of the said groove and the surface of the tube 4 included in this groove, but it is preferred that said bottom of the groove is closely applied against the tube after bending to avoid any risk of folding of this tube opposite this bottom by guiding it completely until the end of deformation.

The form of the tool 3 is selected so as to facilitate or at least to render possible disengagement of this tool out of the concave portion 14 of the bent tube: it is also to enable this disengagement that the angle of bending will be limited in practice to 160.degree.-170.degree. or, in other terms, that the angle of the elbow obtained will not be less than 10.degree. or 20.degree. .

The tube 4 obtained after bending has, in the concave portion 14 of its elbow, the impression of the surface 8 of the active portion of the tool, that is to say a longitudinal median rib 15 bounded by two ledges 16 and 17.

Generally the arms of the elbow form an angle equal to 90.degree. .

Mostly, the tube used is of steel and, for example, its outer diameter is equal to 20 mm and its thickness to 1.5 mm.

As stated above, the average order of magnitude of the radius of curvature R of the middle line of the bent portion of the tube is the same as that of the diameter D of the tube: the said radius of curvature is preferably comprised between the said diameter and double this diameter.

As a result, there is obtained a bending device for metallic tubes which responds well to the objective which it was sought to attain and which enables the obtaining in a simple manner, economically and rapidly, of a tube bent around a relatively sharp angle and having nontheless good mechanical strength in its bent zone.

As is self evident, and as results already also from the preceding description, the invention is not at all limited to those of its methods of application and of production, which have been more particularly described; it embraces, on the contrary, all variations, especially :

those in which the tool 3 is constituted by two flanges, particularly circularly, of which the periphery forms ribs 10 and 11, said flanges being held parallel and separated from one another by a distance equal to the width of the groove 9;

those where the sections of the surface 8 of the tool through a family of planes parallel to the plane P have variable radii of curvature, the smallest corresponding to the median zone of the active surface of the tool and the greatest to the longitudinal ends of this surface, so as to facilitate disengagement of the tool.

Claims

What I claim is:

1. A metallic tube bent into an elbow around a curve of small radius of curvature, said curve having a concave portion including a median rib extending towards the center of curvature of said curve and bounded laterally by two shoulders, the cross-section of the tube on each side of the elbow being circular.

2. A metallic tube bent into an elbow around a curve of small radius of curvature according to claim 1, said median rib being of about the same width as the width of each said shoulder.

3. A metallic tube according to claim 1, its diameter being comprised between the radius of curvature of its bend and half of said radius of curvature.

4. A metallic tube according to claim 2, its diameter being comprised between the radius of curvature of its bend and half of said radius of curvature.

5. A metallic tube according to claim 1, bent into an elbow of about 10.degree. to about 90.degree. .