FLEXIBLE CORRUGATED TUBE
This invention relates to a flexible corrugated tube consisting of a succession of axially displaced convolutions obtained by spirally coiling a thin metal strip 5 formed with longitudinally extending corrugations which in the finished tube are transformed into spirals coaxial with the tube. Tubes of this kind are known.
The invention relates in particular to a tube in which the borders of successive tube convolutions overlap 10 each other.
In the tube according to the invention the corrugations formed in the strip are substantially of wave form, the waves having arcuate crests alternating with similarly shaped troughs. 15
It is an object of the present invention to provide a flexible corrugated tube as described above in which successive convolutions are firmly secured to each other along their overlapping borders without the use of special connecting means, adhesives or the like. 20
According to the present invention there is provided a flexible corrugated tube consisting of a succession of axial displaced convolutions obtained by spirally coiling a thin metal strip formed with longitudinally extending corrugations, the corrugations being substan- 2^ tially of wave form, the waves having arcuate crests alternating with similarly shaped troughs, the borders of successive tube convolutions overlapping each other, with at least one corrugation in the overlapping border portion of a convolution fitting into a corrugation of 30 the overlapped border portion of an adjoining convolution so that the two corrugations are locked to each other in the manner of hooks or teeth which engage each other.
In accordance with a preferred embodiment of the ^5 invention a cross-section of at least those corrugations which fit into each other is substantially that of the waves in a maeander, with the width of the corrugations at their crests and at their troughs being greater than between their flanks. 40
According to a further feature of the invention a plurality of corrugations in the overlapping border portion of a convolution is fitted into an equal number of corrugations in the border portion of an adjoining convolution; the overlapping border portions of the convolu- 45 tions may extend in some cases substantially over half the width of the strip from which they are formed.
The invention relates further to a method of producing a flexible corrugated tube as described above and ^ to apparatus for carrying out this method.
Accordingly the invention provides a method of producing a flexible corrugated tube as set forth in the proceeding paragraphs in which spirally coiling of the thin metal strip is performed in such a way that at least one 55 corrugation in the overlapping border portion of a convolution is fitted into a corrugation in the overlapped border portion of the adjoining convolution and in which simultaneously with or immediately after the fitting of one corrugation into another the corrugations 6Q are reduced in height by compression in such a way that the cross-section of at least those corrugations which fit into each other is substantially that of the waves in a maeander, with the width of the corrugations at their crests or at their troughs being greater 65 than in-between crests and troughs.
The compression may be produced by applying substantially at the apex of the wave troughs a pressure in
the direction of the wave crests. The compression may also be produced by applying a tensile force to the strip in its longitudinal direction whilst the strip is spirally coiled on a mandrel. Alternatively the compression may be produced by applying substantially at the apex of the wave crests a pressure in the direction of the wave troughs.
A sealing strip may be coiled between corrugations whilst they are being fitted into each other. This strip may be made of plastics material or of paper. The sealing strip may be heated whilst the corrugations are reduced in height and the strip may be used or bonded to the walls of corrugations inbetween which the sealing strip is coiled.
A sealing tape extending in the longitudinal direction of the metal strip may be bonded to at least one of the two lateral edges of said metal strip, the sealing strip projecting laterally beyond the strip edge; and between or after coiling of the metal strip into convolutions the sealing tape bonded to one convolution is bonded to the border portion of the adjoining convolution.
The tube may be formed by spirally coiling a corrugated metal strip, the height of the corrugations in the strip being larger than the width of the corrugations. The height of the corrugations may be at least twice as great as their width.
Apparatus for carrying out the method set forth for producing a flexible metal tube comprises preferably a rotatable mandrel onto which the strip is coiled and at least one pressure roller adapted to cooperate with the mandrel and arranged from the mandrel at a distance corresponding to the thickness of the metal strip, the pressure roller being provided with grooves for receiving the corrugations of the strip.
At least over part of the axial length of the pressure roller the grooves may be shallower and at least at their bottom wider than the corrugations in the metal strip prior to its compression and in which the width of ridges situated between the grooves may at least at the bottom of the grooves be less than the width of the corrugations prior to their compression.
One of the pressure rollers may be arranged facing the mandrel and at the place where the oncoming metal strip makes first contact with the mandrel, the pressure roller being axially offset in the direction of that area of the mandrel surface onto which the convolutions of the strip are coiled and in which that surface area of the offset pressure roller which is in contact with the oncoming strip has grooves of a depth which is at least as great as the unreduced height of the corrugations.
The pressure roller may be arranged at an angle to the mandrel which is equal to the angle of pitch of the convolutions.
In a preferred form of the apparatus three pressure rollers are provided, the latter being distributed around the periphery of the mandrel and spaced-apart from each other by an arc subtended by an angle of 120°.
The pressure roller may be made from an elastically yielding material.
A tube according to the invention as well as a method and apparatus for producing it will described by way of example with reference to the accompanying drawings.
FIG. 1 is a cross-section of a thin metal strip, formed with longitudinally extending corrugations from which a tube according to the invention is produced,
FIG. 2 is a section through part of a wall of a tube, produced from the metal strip shown in FIG. 1, prior