Corrugated Tubing

Abstract

This disclosure teaches a helically corrugated two-layer tube made of strips of sheetmetal or plastic and this disclosure teaches further an apparatus and a method for manufacture of the tube. A leading and a lagging margin of an inner strip are folded over each other along the path of the helix. A leading margin of an outer strip overlaps a lagging margin thereof along a corrugation. That corrugation is pressed along with a mating corrugation of the inner strip to form a head-shaped or snap-button-shaped fold whereby the inner and outer strips are united.

Description

INVENTION

Helically wound, corrugated, flexible tubing formed of two layers of strips is known. In such tubing the two layers of strips are so wound over a winding mandrel that they overlap each other; in general the longitudinal edges of the strip of the one layer lie approximately in the center of the strip of the other layer. After the winding, this tubing is provided on the core of the winding machine with grooves and there is produced, so to say, an interlock by which the wound strips are held together in the wall of the tubing. The strength with which they are held together is, however, not very great and it may happen that the strips loosen from each other and unwind, particularly upon handling during processing or transporation. It has therefore already been proposed to impart the ribs or grooves of the tubing a special shape by which a better form-locked connection is obtained by undercutting or inclining the sides of the grooves. Aside from the fact that such a shaping of the grooves or ribs has certain difficulties inherent in it, other problems also arise; for instance, such a shaping is difficult when the material of which the strips consist is a metal sheet or a plastic of substantial thickness or strength.

In accordance now with the concept of the present invention, a helically grooved, flexible two-layer tubing of strips of sheetmetal or plastic is characterized by the fact that the edges of the strip forming the inner layer are folded together and the edges, lying spaced between each two folds, of the strip forming the outer layer are developed, together with the underlying rib of the inner layer, into a head-like or snap-fastener-like fold. An apparatus for manufacturing head-like or snap-fastener-like fold. An apparatus for manufacturing such tubing is characterized by the fact that three folding rollers are arranged around a winding mandrel behind the feed for a preshaped sheetmetal strip in the path of said strip at approximately equal distances apart, the first of said rollers pressing the rib formed by the overlapping edges to the side, the second pressing the laterally pressed rib more strongly against the winding mandrel, and the third being furthermore provided a second feed for a preformed sheet-metal strip which, covering the fold of the first strip, is wound on same, and folding rollers acting from the inside and outside which compress the rib on which the edges of the second strip overlap towards the outside, with the formation of a head-shaped or snap-button-shaped fold.

One method of producing helically grooved flexible tubes from sheetmetal strips preformed with grooves is characterized in accordance with the invention by the fact that first of all a sheet-metal strip is wound with overlapping edges on a winding mandrel and the edges are connected with each other by one or more shaping rollers forming a fold, and thereupon a second strip having the same preshaping is wound over the tube on the winding mandrel, its edges coming to lie approximately in the middle between the folds of the tube which is already wound and thereupon between shaping rollers acting from the inside and outside the rib is compressed on the overlap of the edges of the second strip to form a head-shaped or snap-button-shaped fold.

Tubing in accordance with the invention has the advantage that it can be made of stiffer materials, such as, for instance, alloy steels, metal plate or heavier plastics. By the double-layer embodiment and the fold connection between the edges of each individual layer, extremely high strength as well as gas imperviousness of the tubing is obtained, although its flexibility is retained.

The invention will be explained in further detail below on the basis of illustrative embodiments with reference to the drawings in which:

FIG. 1a is a diagrammatic view in perspective of a winding device.

FIG. 1b is a view of this device seen in the direction of the axis of the winding core.

FIG. 2 is a diagrammatic view of a wound tube.

FIG. 3 is a partial section through the winding of the first layer.

FIG. 4 is a partial section through the first folding of the first layer.

FIG. 5 is a partial section through the second folding of the first layer.

FIG. 6 is a partial section through the final folding of the first layer.

FIG. 7 is a partial section through the first and second layers.

FIG. 8 is a partial section through the folding of the first and second layers.

FIG. 9 is a partial section through the finished tube.

The winding device of FIGS. 1a and 1b consists of a winding mandrel 1 which is driven in rotation in the direction indicated by the arrow A. On this winding mandrel 1 there is arranged a first folding roller 2 which is rotated in synchronism in the direction indicated by the arrow B. In front of this first folding roller 2 there is arranged the feed (not shown in detail here) for a strip 3 which as been preshaped with grooves. In the direction of the winding pitch and spaced about 120.degree. from the first folding roller 2 there is arranged on the winding mandrel a second folding roller 4 which is also driven in the direction indicated by the arrow C. Another folding roller 5 is arranged on the winding mandrel 120.degree. away from the second folding roller 4 in the direction of the winding pitch, it also being driven in the direction indicated by the arrow D. Just behind the end of the winding mandrel 1 there are arranged two folding rollers, namely an inner folding roller 6 and an outer folding roller 7, in such a manner that the point of contact of their cylindrical surfaces lies in the extension of the cylindrical surface of the winding mandrel. Of these two rollers, the outer folding roller 7 is driven. Directly in front of these two folding rollers there is a feed (not shown here) for the strip which has been preshaped with grooves for the second layer of the tube.

In order to give an idea of a helically grooved flexible tube, reference is had to FIG. 2.

The development and shaping of the tube in accordance with the invention as well as details of the apparatus will be described below with reference to FIGS. 3 to 9. In FIG. 3 there is shown a cross section through the wall of the first layer, helically wound on the winding mandrel 1 of the strip which has been preshaped with grooves. This cross section lies at a point of the winding mandrel in front of the first folding roller 2 but behind the feed of the strip 3 for the first layer. It can be noted that the edges of the helically wound strip overlap in such a manner that the flank of the groove which extends upward on one edge is covered by the flank of the groove which extends downward on the following edge of the strip. This place of overlap is widened, as shown in FIG. 4, by the first folding roller 2 and pressed to one side. For this purpose the folding roller 2 is provided on its cylindrical surface with a shaping portion, protruding ribs 9 and 10 of which engage into adjacent grooves on both sides of the point of overlap of the strip wound into a tubing and between the ribs 9 and 10 it is developed with an asymmetric groove 11 which places the covered overlap rib with the two edges of the strip somewhat to the side and compresses it. For this purpose the groove 11 is made somewhat shallower than the general depth of the grooves of the strip.

This preformed fold is further compressed, as shown in FIG. 5, by a second folding roller 4. For this purpose, this folding roller 4 is provided on its cylindrical surface with two ribs 12 and 13 which are the same distance apart and have the same height as the ribs 9 and 10 of the folding roller 2. The groove 14 between these two ribs 12 and 13 is, however, substantially flatter and less curved so that the overlap rib which has already been bent to one side is compressed further in the direction of the deflection.

In the case of the third folding roller 5, as shown in FIG. 6, the distance between and the height of the ribs 15 and 16 developed on the cylindrical surface is the same as in the preceding folding rollers 2 and 4. The space between these two ribs 15 and 16 is developed as merely a slightly curved recess so that the fold of the overlap point of the strip edges which has been preformed in the two preceding folding rollers is tightly and securely compressed. The first layer of the strip wound on the winding mandrel 1 has been developed, upon passing the third folding roller 5, into a finished, firmly folded, one-layer tube. Tests in actual practice have shown that under special conditions, for instance where the strip material is readily deformable, it is possible to shape and completely fold the first, single-layer tube also with only a single folding roller on the winding mandrel. Thereupon another strip 8 which has been preformed with grooves is wound on this finished tube in such a manner that its grooves enter the grooves of the tubing and its edges are about equal distance at both sides from the folds of the tubing. This strip 8 which forms the second layer is so wound up that its edges also overlap in the same way as has been described above in connection with the winding of the first strip. The upward extending groove flank on the one edge of the strip therefore engages over the downward extending groove flank on the other edge of the strip.

After the second strip 8 has been wound in this manner on the tube, the tube leaves the winding core and passes by two additional folding rollers 6 and 7. The points of contact of the cylindrical surfaces of these two folding rollers lie in the extension of the cylindrical surface of the winding mandrel. The inner folding roller 6 is rotatably supported and is provided on its cylindrical surface with a recess which corresponds approximately to the recess of the cylindrical surface of the first folding roller 2. As can be noted from FIG. 8, two ribs 17 and 18 are so arranged that they engage from the inside into the ribs which are adjacent the overlap groove of the edges of the outer strip. Between these ribs 17 and 18 there is formed a wide groove 19 with approximately parallel flanks and an arch which has a depth equal to about two thirds of the depth of the grooves of the tube. Opposite this inner folding roller 6 and partially extending into its cylindrical surface is an outer folding roller 7 which is driven, in the same way as the folding rollers 2, 4 and 5. The cylindrical surface of this outer folding roller 7 is provided with two outer ribs 20 and 21 which extend into the grooves of the tube which are adjacent the overlap groove. Between them is a considerably lower rib 22 which engages into the overlap groove. From FIG. 8 it can be noted that the two-layer tube is guided by the ribs 17 and 18 of the inner folding roller 6 and the ribs 20 and 21 of the outer folding roller 7. These ribs or the folding rollers which engage from the inside into the ribs or from the outside into the grooves of the tube also prevent a deformation of the ribs or grooves of the tube which are adjacent the overlap groove. Only the overlap groove, i.e. the groove of the tube on which the strip edges of the second strip wound on the outside of the tube overlap, is formed by the interengaging folding rollers 6 and 7, this taking place in such a manner that the groove is compressed from the inside to a shallower depth by the arched groove 19 on the cylindrical surface of the folding roller 6, and from the outside the groove is retained in smaller shaped depth by the rib 22 of the folding roller 7 but the compressed part is shaped so that this groove assumes a head-shaped or snap-button shape and thus a folding. In this way there is produced at this overlap rib a firm, dependable folding together of the overlapping edges of the outer strip. After leaving the cooperating folding rollers 6 and 7, the inner and outer layer of the two layer tube are connected by folds which are independent of each other and located spaced from each other and furthermore a firm connection of the two layers is obtained by the head-shape or snap-button shape of the fold of the second outer layer. The width of the strips used in practice for an advantageous embodiment is 10.5 ribs or grooves, the dimension of the strip depending on the shape of the grooves. It is, of course, also possible to use strips having a larger or fewer number of grooves. From FIG. 8 it can be noted that a two-layer tube in accordance with the invention must be formed from at least strips having 41/2 grooves. Such a tube, however, has less flexibility since the folds closely follow each other on the inside and outside. A cross section through the wall of the preferred embodiment of a tube in accordance with the invention is shown in FIG. 9.

Claims

I claim:

1. A tube comprising in combination:

an elongated inner strip having an inner leading margin and an inner lagging margin each substantially parallel to the other,

the inner strip having inner corrugations running substantially parallel to the inner margins,

the inner strip wound along a helical path with the inner leading margin and the inner lagging margin folded over each other along the helical path,

an elongated outer strip having an outer leading margin and an outer lagging margin each substantially parallel to the other,

the outer strip having outer corrugations running substantially parallel to the outer margins,

the outer strip wound along the helical path with the outer corrugations overlaying substantially the inner corrugations,

at least one of the corrugations of the inner strip pressed along its length with at least one of the corrugations of the outer strip in the form of a head-shaped fold to join the inner and outer strips together,

the outer leading margin overlapping the outer lagging margin under the head-shaped fold,

the corrugations having a substantially uniform height,

the head-shaped fold having a height substantially less than the height of the corrugations,

and the head-shaped fold spaced from the folded margins of the inner strips.

2. The tube of claim 1 with the inner and outer strips of sheetmetal.

3. The tube of claim 1 with the inner and outer strips of plastic.

4. The tube of claim 1 with one of the strips of plastic and the other of sheetmetal.