GB2418391A

GB2418391A - Forming grooves on a tube

Info

Publication number: GB2418391A
Application number: GB0421439A
Authority: GB
Inventors: Peter David Jenkins; Daniel Owen Jenkins
Original assignee: Miniflex Ltd
Current assignee: Miniflex Ltd
Priority date: 2004-09-27
Filing date: 2004-09-27
Publication date: 2006-03-29
Anticipated expiration: 2024-09-27
Also published as: GB2418391B; GB0421439D0

Abstract

An apparatus for forming grooves 18 in the exterior surface of a plastics tube 10, the apparatus comprising two opposed rollers 132, 134 that form the grooves 18 within the tube 10 and two opposed positioning means 142, 144 that hold the tube in position relative to the roller 132,134. The rollers 132,134 and positioning means 142, 144 are arranged around an aperture 122 through which an extruded tube 10 may pass for the formation of the grooves.

Description

APPARATUS

The present invention relates to an apparatus for processing the outer surface of cylindrical members, such as tubes and conduits, and in particular to the processing of such members to form a series of annular grooves.

EP 765 214 discloses an apparatus suitable for forming a series of parallel grooves in the outer wall of a smooth bore tube. The apparatus comprises three rollers which are disposed around the tube as it is passed through the apparatus. One or more of the rollers are grooved and the rotation of the grooved roller(s) forms the sequence of grooves within the outer surface of the tube.

One of the limitations of the apparatus disclosed in EP 765 214 is that the triangular arrangement of the rollers form an interstice through which the tube is passed. The geometry of this arrangement means that it is difficult to process small tubes, for example tubes having a diameter . of 2 mm or less. deco

I

According to a first aspect of the present invention there . is provided an apparatus for forming parallel grooves in a....

the outer wall of a tube, the apparatus comprising first roller and second roller and first positioning means and second positioning means, wherein: the first roller comprises a ridges the first roller is disposed in opposition to the second roller about an aperture; the first positioning means is located next to the aperture and between the first and second roller; and the second - 2 positioning means is located next to the aperture, between the second and first rollers in opposition to the first positioning means. Preferably, the first roller, first positioning means, second roller and second positioning means are located substantially equidistantly around the periphery of the aperture.

The second roller may comprise a ridge. The ridge of the first roller may have a different height to the ridge of the second roller. Preferably the first and second positioning means are resiliently biased.

According to a second aspect of the present invention there is provided method of forming parallel grooves in the outer wall of a smooth-bore plastic tube, the method comprising the steps of: passing the tube along a passage through an apparatus, the passage defined by passage surfaces, the passage having an axis; mounting first and second opposed rollers adjacent the passage through the apparatus) arranging a ridge formed on the circumferential surface of .

one or both of the rollers to extend from the . ... circumferential surface and to project into the passage; mounting first and second opposed positioning means rollers adjacent the passage through the apparatus the first ee..

positioning means being located between the first and I.. second rollers and the second positioning means being located between the second and first rollers; and forming a groove in the outer wall of the tube by the contact between the ridge of the roller(s) and the tube. - 3

The invention will now be described, by way of example, with reference to the following Figures, in which: Figures la & lb show schematic depictions of tubes which have been processed by an apparatus according to the present invention; Figure 2 shows a schematic depiction of the tube shown in Figure lb under bending; and Figure 3 shows a schematic depiction of an end view of an apparatus according to the present invention.

The sheathing 10 shown in Figure 1 is extruded, as a plain- walled tube, from a plastics material such as polypropylene. The tube has an outer wall 12 and an inner wall 14 which defines an internal bore 16.

A plain-walled tube can be bent to virtually any radius and the amount of applied force necessary to do this bending, especially as the radius of curvature becomes smaller, increases progressively and steplessly up to the point at which the tube wall kinks and the tube cross-section :e . collapses. In order to prevent over bending of an optical ë . fibre located in the bore 16, a plain-walled tube is modified so that the tube can be bent up to a pre determined radius by application of a relatively low force, but can only be bent beyond this radius, if at all, by .e ... application of a significantly higher force. To achieve . this, the outer wall 12 of the tube is formed, subsequent to extrusion, with annular grooves 18. The grooves are formed primarily by locally compressing the wall material, although it is within the scope of the invention for the grooves to be formed by cutting of the wall material.

Figure la shows a tube where all the grooves 18 are of equal depth; Figure lb shows a tube where the grooves 18 are alternately deeper and shallower.

The function of the grooves 18 is best illustrated in Figure 2 from which it can be seen that on the inner side of the curve, the grooves 18a close up and the peripheral edges of the grooves come into contact to limit further bending. On the outer side of the curve, the grooves open up as shown at 19. Up to this point, bending takes place by flexing "hinges" 20 formed by the material remaining at the bases of the grooves 18. Beyond this point, application of extreme force can result in further bending but when this happens, there will be distortion of the plastics material.

One of the desirable results of forming the grooves by compressing the wall material is that the "hinges" 20 will be formed of heavily compressed plastics material which .

. will be more dense locally than the surrounding plastics and in this dense area there will be some advantageous 2.[ alignment of polymer chains. This process can be assisted by stretching the tube during the groove-forming process. ë . . . :

. Figure 3 shows a schematic depiction of an end view of an apparatus 100 according to the present invention. The invention comprises an end plate 120 in which an aperture 122 is disposed. Around the aperture are arranged first - 5 and second rollers 132, 134 and first and second positioning means 142, 144. The first roller 132 is opposed to the second roller 134, with the aperture being located between the first and second rollers. Similarly, the first positioning means is opposed to the second positioning means with the aperture being located between the first and second positioning means. The first positioning means is located inbetween the first and second rollers and the second positioning means is located between the second and first rollers. Preferably the rollers and positioning means are equidistantly located around the periphery of the aperture, i.e. the rotational displacement of the first positioning means relative to the first roller is substantially 90 .

In use, the tube 10 to be processed will pass through the aperture 122 and then pass between first roller 132 and second roller 134. In one embodiment of the present invention, the first roller 132 is a grooved roller that comprises a helical cutting ridge. As the tube is passed through the aperture and then between the rollers, the first roller is rotatably driven, with a the rotation of . the roller causing the helical cutting ridge to form a : groove within the outer surface of the tube. The second roller 34 does not comprise such a ridge but is free to . rotate. The positioning means 142, 144 are resiliently ..

... biased and act to retain the tube between the two rollers :: such that the action of the rollers act to form grooves in the tube. The positioning means may be, for example, knife edge blades or any other element that is sufficiently thin to be arranged to co-ordinate with the rollers. - 6

For the sake of clarity, Figure 3 does not show a tube passing through the aperture, but the positioning means are shown in a position that would be adopted when a tube was received within the aperture. The resilient biasing of the positioning means may be such that in the absence of a tube the positioning means make contact with each other, in a position at the middle of the aperture. Alternatively, the resilient biasing of the positioning means may be variable so that the rest position of the positioning means can be controlled. Such a feature allows the lateral forces of the positioning means to be limited.

The diameter of the aperture may be varied, either by the use of aperture plates having apertures of different sizes or through the use of an aperture having an adjustable diameter. This allows the apparatus to be used with tubes of different diameters. To accommodate tubes of different diameters, one or both of the rollers may be movable (in the context of Figure 3, the rollers may be moved up or down) or alternatively the rollers may be replaced by substitute rollers having a different diameter and/or a . different cutting ridge height. *

2.t In an alternative embodiment of the present invention, both the first and the second rollers comprise a helical cutting .

... ridge. The rollers can be configured such that the first . roller forms one groove in a series of grooves whilst the second roller forms the subsequent groove in the sequence.

Alternatively, the two rollers may be configured such that - 7 the action of one ridge reinforces the action of the other, with both ridges forming the same groove.

The different ridges can be of different forms, for example different heights. The tube of Figure lb is formed by using a roller having two ridges of different heights to produce the shallower and deeper grooves. Alternatively one of the rollers could have the lower ridge and the other roller could have the taller ridge. The ridges do not have to be of a shape which forms grooves in the tube surface; exactly the same principle of operation could be used with a suitably formed grooving roller to apply any embossed pattern to a cylindrical surface.

If the tube 10 is not drawn directly from an extrusion die, it may be desirable to heat the tube before it passes through the apparatus 100, in order to soften the plastics material.

It will be clear to the skilled man that the pitch of the groove-forming ridges on the surface of the roller(s) will determine the pitch of the grooves in the tube 10 and . therefore the apparatus can produce grooves at different : pitches by using different rollers. .

It is significant that the apparatus has no reciprocating ...' components. The apparatus can therefore be accurately :: balanced and this allows it to be rotated at high speed with no vibration problems. This enables economic manufacturing speed for a production line to be achieved. - 8

For the purposes of the present invention, there is no restriction on the end use to which the tube or rod may be put. Although this specification describes particularly the preparation of a tube surface, it will be obvious to the skilled man that a rod surface could be prepared in the same way. The invention thus provides a simple and effective way of continuously forming a series of independent annular grooves in the surface of a tube or rod. The resulting product is particularly suitable as a bend limiting tube for use with optical fibre, since it can protect the fibres inside and prevent them being bent through too sharp a radius. It is also within the scope of the invention to prepare the outer surface of a thin- walled tube using this apparatus. It may then be necessary to pressurise the interior of the tube to force the tube walls to conform to the shape of the groove- forming ridges on the roller(s).

Successful trials have been carried out on tubes of polypropylene, polybutylterephthalate (PBT), nylon, polyethylene and plastics which are blends of PET and :. acrylonitrilebutadienestyrene (ABS). It will be understood - - . that other plastics materials having similar properties may . e.

also be used with the present invention. 2t a... . .

....e - 9

Claims

1. An apparatus for forming parallel grooves in the outer wall of a tube, the apparatus comprising first roller and second roller and first positioning means and second positioning means, wherein: the first roller comprises a ridge; the first roller is disposed in opposition to the second roller about an aperture; the first positioning means is located next to the aperture and between the first and second roller; and the second positioning means is located next to the aperture, between the second and first rollers in opposition to the first positioning means.

2. An apparatus according to claim 1, wherein the first roller, first positioning means, second roller and second positioning means are located substantially equidistantly around the periphery of the aperture.

3. An apparatus according to claim 1 or claim 2, wherein the second roller comprises a ridge. :.

4. An apparatus according to any preceding claim wherein . the first and second positioning means are resiliently : biased.

5. An apparatus according to claim 3, wherein the ridge of the first roller has a different height to the ridge of :: the second roller.

6. An apparatus according to any preceding claim, wherein the first roller comprises a helical cutting ridge. -

7. An apparatus according to any of claims 3 to 6, wherein the second roller comprises a helical cutting ridge.

8. A method of forming parallel grooves in the outer wall of a smoothbore plastic tube, the method comprising the steps of: passing the tube along a passage through an apparatus, the passage defined by passage surfaces, the passage having an axis; mounting first and second opposed rollers adjacent the passage through the apparatus; arranging a ridge formed on the circumferential surface of one or both of the rollers to extend from the circumferential surface and to project into the passage; mounting first and second opposed positioning means rollers adjacent the passage through the apparatus the first positioning means being located between the first and second rollers and the second positioning means being located between the second and first rollers; and forming a groove in the outer wall of the tube by the . contact between the ridge of the roller(s) and the tube.

.-.e : ce . A.