Split grooved sheath and method and apparatus for making same

A grooved tubular protective sheath (10) with a slot and a longitudinal flange. In particular, the flange (24) is provided on one edge (16) of the slot substantially at the bottom of the grooves (12) and positionable under the other slot edge (17). The grooves are closed at the edges (16, 17) of the slot by transverse walls (22). A method for manufacturing a grooved sheath includes extruding and molding an annular sheath with a longitudinal flat strip level with flute edge hollows, cutting the flat strip along one of its flute edges to form a tongue that is integral only with the other flute edge. The method further includes heating the sheath and cooling it, while passing it between cones or calenders to bring the flute edges together, whereby the tongue passes between the cut edge. A device for making a grooved sheath includes a molding machine with two series of symmetrical parallel shells. Internal faces of the shells are semi-cylindrical and ribbed transversely with a series of rainbow-shaped flutes forming a crenellated profile with flute hollows and flute ridges. Each shell in one of the series has a protuberance in form of a thin flat strip situated level with the flute ridges, wherein the strip is aligned from one shell to the next.

FIELD OF THE INVENTION 
The present invention relates to an annulate flexible tubular sheath, and 
more particularly to a sheath used for the protection and positioning of 
bundles of electrical wires and cables. 
BACKGROUND OF THE INVENTION 
Annulate tubular sheaths, that is to say those whose shape resembles a 
succession of interconnected rings, are usually produced from plastic, 
such as extruded polypropylene. These sheaths enable complex protection 
networks to be produced for bundles of electrical wires or cables within 
ships, aeroplanes or motor vehicles, and in the latter case notably in the 
engine compartment. This is because, given the limited space available, 
these sheaths or tubes need to be able to follow non-rectilinear walls 
very closely and skirt around the various components encountered. With 
such annulate sheaths, it is, indeed, possible to produce curves whose 
radius of curvature is less than three times their diameters, without 
their being deformed inwards or even breaking. 
One embodiment of such sheaths consists of extruding a plastic tube and 
pressing it as soon as it emerges against the annulate internal faces of a 
double series of shells situated opposite each other and progressing with 
the advance of the tube to a so-called "moulding" machine. It is thus 
possible to continuously produce long lengths of sheaths, which are then 
stored on transport drums. Such embodiments are described in greater 
detail for example in the documents FR 2 171 844, GB 1 250 639 and GB 1 
311 205. 
When these sheaths are used in a vehicle, the problem of inserting a strand 
of wires inside sections of sheaths is encountered. For a rectilinear 
section of sheath of around one metre, it is possible to insert the cables 
and then simply push them from one of its ends. This operation rapidly 
becomes more laborious for sections of greater length or for pre-installed 
sections with a number of curves. 
In relation to this, for example from the documents FR 2 264 649 or DE 24 
13 879, double-walled sheaths are known: an external one, annulate for 
flexibility, and a smooth internal one for the easy insertion of the 
cables. Also, for example from the document CA 1 302 310, annulate tubes 
are known manufactured with a factory-installed internal wire called a 
"wire puller" for the subsequent pulling of cables. However, these sheaths 
require additional material, and require costly conversions of the 
manufacturing equipment. 
More commonly, in the field of annulate protection sheaths, split sheaths, 
that is to say those which have been cut along a longitudinal straight 
line at the end of the manufacturing process, are being offered. It is 
then easy later on, in any area of the sheath, to insert electrical wires 
and cables directly through this slot which, normally, closes up again by 
virtue of the transverse rigidity provided by the flutes. Such sheaths 
remain inexpensive. 
Though satisfactory in the majority of cases, it is nevertheless found that 
these split sheaths can allow wires to escape in areas with a small radius 
of curvature where the slot tends to open up again. 
In order to overcome this drawback, the document DE-U-89 03 070 proposes a 
longitudinally split extruded sheath, the edges of whose slot are profiled 
in the form of two complementary longitudinal hooks. The hook edge facing 
outwards has a tongue above it for clamping and holding the other edge. 
However, the complexity of the profile of these hooks in association with 
the tongue makes the extrusion nozzle and the forming shells particularly 
costly. Furthermore, closure of the slot by engaging hooks all the way 
along the slot is difficult, with the risk of being poorly executed in 
many places. The documents EP 0 114 213 and DE 34 05 552 describe variants 
of even more complex slot closure devices. 
SUMMARY OF THE INVENTION 
The aim of the present invention is a split annulate protective sheath 
comprising a means of efficaciously closing the slot, that is to say a 
means which opens easily when cables are inserted, closes immediately 
afterwards, and remains so thereafter whatever the shape of the subsequent 
path given to the sheath once installed, and this despite the presence of 
any vibrations. Such a sheath should also remain inexpensive to produce. 
The objectives are attained by a split annulate tongued sheath by virtue of 
the fact that a simple continuous longitudinal tongue is formed on one of 
the edges of the slot substantially level with the hollow of the flutes, 
and that this tongue lodges under the other edge of the slot. 
By virtue of the presence of the flutes, the profile of a slot edge takes 
the form of a wavy line which can be defined, by analogy with the teeth of 
a rack, by a flute hollow, a flute top and a flute depth. 
When the strand is inserted into the sheath according to the invention, the 
tongue functions in the manner of a shutter. Then, if this sheath is 
called upon to describe very severe radii of curvature, which in normal 
sheaths gives rise to a slight re-opening of the slot, the tongue keeps 
the slot closed. The cables, by exerting a pressure against the walls of 
the sheath, actually push the corresponding tongue area against the other 
edge, thereby confirming the locking of the closure. Deterioration of the 
cables against the slot is thus avoided. 
According to a preferred embodiment, the thickness of the tongue represents 
substantially the thickness of the wall of the annulate tube, and its 
width represents between 1/10 and 1/2 of the internal diameter of the 
sheath, preferably between 1/6 and 1/3 of the internal diameter. 
This width of the tongue constitutes a good compromise between easy opening 
of the slot when a cable is inserted and effective closure of the slot 
under the condition of extreme curvature of the sheath. 
The flutes are usefully closed at the edges of the slot by transverse 
walls. This arrangement provides additional sealing at the slot against 
dust and other undesirable substances, and also renders the slot less 
aggressive to cables. 
If required, the flute edge walls can be oblique and oriented towards the 
outside to facilitate the insertion of the bundle of cables. 
One advantageous embodiment of a sheath according to the invention consists 
of: 
extruding and then moulding an annulate sheath having a longitudinal flat 
strip level with the flute edge hollows, 
cutting the flat strip along one of its flute edges to form a tongue 
integral only with the other flute edge, 
heating the sheath and then cooling it by passing it through restriction 
means, such as cones or calenders, so as to bring the flute edges 
together, the tongue passing beneath the cut edge. 
Compared with the method of manufacturing a standard split annulate sheath, 
this method requires only a modification to the initial profile of the 
sheath in the moulding machine and an extra heat shrinking operation, 
which means that the sheath according to this invention remains 
inexpensive to produce. 
A device specially designed for implementing the method described above, 
this device comprising, at the outlet of an extruder, a moulding machine 
with two series of symmetrical parallel shells whose internal faces each 
have a semi-cylindrical shape ribbed transversely with a series of 
rainbow-shaped flutes, is particularly remarkable in that each half-shell 
in one of the series has a protuberance in the form of a thin flat strip 
situated level with the flute ridges, these strips being aligned from one 
shell to the next.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The left-hand half of FIG. 1 illustrates a conventional device for 
manufacturing annulate tubes 10. This device notably comprises, at the 
outlet of an extruder 66, a moulding machine comprising two series of 
symmetrical parallel shells 50 each driven upstream and downstream by a 
pair of toothed return wheels 56. The internal face of each shell 50 is 
semi-cylindrical in shape, ribbed transversely with a series of 
rainbow-shaped flutes with an apex angle of 180 degrees. Thus two shells, 
one from each series, situated opposite each other, together form the 
complete periphery of an annulate sheath portion 10. 
Furthermore, a mandrel 60 emerging from the outlet of the extruder 66 bears 
at its end a closing plug 62 isolating the downstream annulate sheath part 
10. An atmospheric overpressure can then be applied between this closing 
plug and the outlet of the extruder by injecting compressed air emerging 
from openings 64 in the mandrel. Thus a plastic tube which is still hot on 
leaving the extruder is immediately pressed into the flutes of the shells 
50 so as to take the final annulate shape thereof. 
More particularly according to the invention, each half-shell in one of the 
series, for example the top series in FIG. 1, has a protuberance in the 
form of a flat plane strip situated level with the flute ridges, these 
strips being aligned from one shell to the next. 
As illustrated in FIG. 2a, the annulate sheath 10 leaving the shells 50 has 
a continuous flat strip 20 level with its internal face, that is to say 
level with its flute hollows 12. This flat strip forms a recess defined by 
two flute edges 16 and 17. These flute edges therefore take the form of 
crenellated lines oscillating between flute hollows 12 and flute ridges 
14. By virtue of the mode of distributing the plastic material by means of 
overpressure, the thickness of this flat strip 20 is substantially equal 
to the thickness of the tube as, for example, measured in a flute hollow 
or ridge. It will also be noted that the edges of the flutes 16 and 17 are 
blocked, that is to say the flute ridges are closed off by transverse 
radial walls 22. 
As an alternative, and as can be seen better in FIG. 3, the protuberance on 
the shells can have a trapezoidal cross section. The walls 22' of the slot 
edges are then oblique and oriented towards the outside. 
In the following station, the sheath 10, brought by rollers or other guide 
means 72, is held with its strip 20 oriented very precisely upwards by an 
upper orientation disc 70 engaged in this strip. A disc or other cutting 
means 74 immediately downstream can then effect a continuous separation 18 
(FIG. 2b) exactly between the strip and the second flute edge 17, thereby 
producing a tongue 24 which is integral only with the flute hollow 12 of 
the first edge 16, as can be seen better in FIG. 2b. The sheath 10 thus 
split is still held downstream with its tongue oriented upwards by a disc 
or other upper holding means 75, which, being slightly lower than the 
first guide disc 70, simultaneously lowers the tongue 24 below the second 
edge 17. 
In the following station, the split sheath is then heated by thermal means 
80 such as hot-air nozzles or radiant plates up to a temperature allowing 
permanent plastic deformation, this temperature depending on the 
composition of the plastic forming the sheath. During cooling, the sheath 
then passes through a series of cones or calenders 82 with smaller and 
smaller output diameters, these cones or calenders squeezing the sheath 
until the flute edges 16 and 17 come to be adjacent, the tongue 24 being 
passed fully beneath the second edge 17. The sheath, fully cooled at the 
output, then definitively retains the shape of the cross section 
illustrated in FIG. 2c. 
When the sheath is used, the operator easily understands that he simply 
needs to press on the first edge 16 to open the slot, the tongue 24 
integral with this edge 16 also moving away from the second edge 17. It is 
thus possible to insert a first loop of cables and, step by step, press on 
the adjacent areas of edges 16 in order to carry on inserting the cable 
over a required length. Once the cable enters the sheath sufficiently in 
order to pass beyond the tongue 24, the latter closes up automatically in 
the manner of a shutter by virtue of its elasticity and that of the edge 
16. 
Thereafter, if the sheath is to be given a curvature such that the flute 
edges 16 and 17 move apart, it is found that the tongue 24 holds the 
sheath closed at this point, thereby preventing the cables from emerging. 
Numerous improvements can be made to this sheath and to its method of 
production within the scope of the claims. For example, the flat 
protuberance on the shells 50 in the manufacturing device modified 
according to the invention can have a sharp edge along one of its 
longitudinal edges to prepare the subsequent cut 18. The cooling of the 
split sheath can be accelerated by a jet of cold air or by passage through 
a tank of cold water.