WO 96/14176 describes methods and apparatus for manufacturing helical products and provides a discussion of earlier methods of making such products. The present application relates to particular products that can be made in helical form and discusses methods of using or adapting the apparatus and methods of W096/14176 to making such products.

Helical devices as shown in WO 96/14176 have some minor drawbacks. The first is that the free end of the helix can dig into optical cables when the cables are under tension and this is undesirable due to the relatively fragile nature of optical cables. The second drawback is that once the helical device is in place about a cable, whether optical or otherwise, it is difficult to get the free end of the helix away from the cable to unwind the helix. It is known with wire helical devices to flare the ends of a helix by forming the helix and then manually flattening its end in a press but, so far as the applicants are aware, such a method has not been used for metal strip helical devices.

GB 2303503 discloses, in the drawings only, flared ends to the helical strips. There is no disclosure as to the nature of this flaring nor as to how such flaring may be made.

GB 2308752 arguably shows a flared end to a helical unit. There is no disclosure as to the nature of the flaring end nor is there any disclosure as to the material of the helical unit.

GB 2234830 discloses a spiral helix used as a damper in which the helix"has an overall diameter which increases smoothly towards this end".

In a first aspect, the present invention provides a helical device for engagement with a cable, the helical device comprising a single length of metal strip comprising a first helical section, a second non-helical section, and a third helical section, the end of either or both the first and third helical sections remote the second helical section being flared away from the longitudinal axis of the helix,. the flaring being in the form of a section of spiral helix form.

The inner surface of the helical sections may be knurled and it is advantageous that the knurling occupy only a part of the width of the strip material leaving the edges essentially free of knurling.

To produce these devices one may follow the steps of :- i) feeding strip material to an apparatus ii) within the apparatus automatically activating helix forming means to form a first section of the strip material into the shape of a helix iii) within the apparatus automatically inactivating the helix forming means so as not to form a second section of the strip material into the shape of a helix

iv) within the apparatus automatically activating the helix forming means to form the third section of the strip material into the shape of a helix v) selectively controlling the helix forming means to produce between helical sections of adjacent devices sections of increasing and then decreasing diameter, the strip being cut between the sections of increasing and then decreasing diameter, either prior or subsequent to the formation of the section of decreasing diameter, to provide the flared ends of the two adjacent devices vi) repeating steps i) to v) to produce further devices.

Further features of the invention will be apparent from the following description and the claims.

The invention is illustrated by way of example in the following with reference to the drawings in which:- Fig. 1 is a part schematic view of a device in accordance with the invention; Fig. 2 is a part schematic view of apparatus as claimed in WO 96/14176 Fig. 3 is a view of a helical device in accordance with WO 96/14176 Fig. 4 is a view of a further helical device in accordance with WO 96/14176 Fig. 5 is a view of a still further helical device in accordance with WO 96/14176 Fig. 6 is a view of a yet further helical device in accordance with WO 96/14176.

In Fig 1. a helical section 1 is shown of relatively constant pitch and diameter and lying between lines I-I and II-II.

End 2 of the helical section 1 is connected to other parts of the device not shown. The whole device may be of the general form shown in any of Figs. 3-6.

The other end 3 of the helical section 1 is of spiral helix form being generally helical but of varying and increasing diameter so that it flares away from the longitudinal axis III- III of helical section 1.

The end of section 3 remote helical section 1 forms a tab 4. As the section 3 flares away from the longitudinal axis III-III of the helical section 1 it can be seen that it lies outside lines I-I and II-II so that the tab 4 cannot dig into a cable wound into the helical section 1.

Tab 4 will lie free of the surface of a cable wound into the helical section 1 and so it is relatively easy to get a digit or a tool under the tab to prize the helical section away from the cable.

Advantageously the inner surface of the helical section 1 is knurled and yet more advantageously the knurling occupies only a part of the width of the strip material leaving the edges essentially free of knurling (as indicated at 5 in Fig. 1). Knurling improves the grip of the helical section to the cable and by only occupying a portion of the width of the strip the edges of the strip are not rough and so will not abrade the surface of a cable when the helical device is engaged with the cable.

The helical devices may be formed, for example, by using apparatus capable of making helixes and of selectively varying the diameter of the helix during production of a single article so as to produce a flared end to a helix of a given diameter where it changes to a helix of a larger diameter. Suitable apparatus is disclosed in WO 96/14176. The apparatus disclosed in WO 96/14176 may be programmed to produce between helical sections of adjacent devices a section of increasing diameter and cutting the material.

The succeeding device is then made by producing a section of decreasing diameter leading on to the helical section of the succeeding device. Alternatively a section may be provided between adjacent helical devices comprising a section of increasing and then decreasing diameter, increasing from the diameter of the helical section and then decreasing to the diameter of the following helical section, this section being cut about the region of greatest diameter to provide the flared ends of the two devices.

Preferably this section can comprise a pair of spiral helixes joined at their widest diameter directly, by a helix of constant diameter, or otherwise. Using such a method avoids the need to have a separate flattening step as used in relation to wire formed helical devices.

The apparatus of WO 96/14176 is versatile and can be programmed as required and, as described in WO 96/14176, variation of the pitch and diameter of a helix being formed can be selectively varied. As shown in Fig 2 a pair of rollers or other forming members 42A and 42B are used to bend and twist incoming strip material 26 to form a helix 46.

By varying the angle and spacing of rollers 42A and 42B the pitch and diameter of the helix can be varied as required even during the formation of a helix so that switching from a helix of constant diameter to a helical spiral of increasing diameter is straightforward.

The knurling can be applied by a separate knurling wheel in the apparatus or one of the forming members bending the strip to shape may comprise a knurling surface.