Process and apparatus for manufacturing telecommunication cables filled with expansible powder

A process and apparatus for filling multi-conductor cables, particularly a telecommunication cable with several insulated wires surrounded by a covering and a sheath, with a mixture of powders which expand with the absorption of moisture. The conductors are fed in spaced relation into the entrance of a casing having an interior, frusto-conical wall which decreases in diameter from its entrance to its exit. The exit is small in diameter compared to the entrance so that the conductors converge as they pass from the entrance to the exit. Intermediate the entrance and the exit, the conductors are subjected to the powders which are caused to follow a helicoidal course by a screw which directs them toward the exit. Due to the shape of the casing wall, the powders are forced toward the conductors.

The present invention relates to a process and apparatus for manufacturing 
telecommunication cables, and particularly, cables comprising 
substantially a bundle of insulated conductors. 
Henceforth, in this text, the term `conductor` shall mean a conductive wire 
having insulation thereon, and the term "powdered expansible material" 
shall include the use of several substances, in the form of powders, which 
have the characteristic of expanding when subjected, for example, to the 
absorption of water. Hence, due to this latter characteristic, such 
powdered expansible material, when introduced between the sheath and the 
conductors of a telecommunication cable and disposed in such a way as to 
swell up as a consequence of the entry of water into the cable due to 
accidental causes produces a blockage which prevents any such water from 
spreading throughout the entire cable. 
As an example of these substances, mixtures of various powders can be 
mentioned, such as those disclosed in the U.S. Pat. No. 4,002,819 or, yet 
as another example, carboxymethylcellulose, and bentonite. 
Certain of the known cable manufacturing processes are based upon the 
operation of causing a bundle of conductors, that are already cabled 
together, to pass into a container having an internal diameter 
corresponding to that of a bundle, and in sending a mixture of powders by 
means of pressurized air, towards the annular aperture of the container 
traversed by the conductors in such a way as to force the powdered 
material or the powdered mixture in-between the conductors. 
This process includes the operation of winding certain tapes around the 
cable core, for preventing the leakage of the powders, and finally, the 
step of extruding a protective sheath over the tape covered core. 
Unfortunately, during the cabling of the conductors--which is effectuated 
before these enter into the container, a canal or channel can be formed 
between the conductors. Consequently, when the conductors pass into the 
container, there is the drawback that the air, used under pressure at 
times up to 10 atmospheres, can pass along the canal to the outside of the 
container, and hence, this could tend to expel the powders that are 
already introduced in-between the conductors. 
A further known process, consists in applying the powdered material 
electro-statically in-between the conductors before assembling them 
together. This procedure has the drawback of being rather slow, and 
moreover, the structure is unsuited for processing in the standard cabling 
machines used for the actual manufacture of telecommunication cables. 
Moreover, the powder disposed on the conductors results, in certain cases, 
in being insufficient with respect to the quantity that is desired, and 
the further operation of predisposing oil in the surface of the 
conductors, for permitting the deposition of the powders, in the 
successive electrostatic phase brings about, as is known to those skilled 
in the art, damage to the conductor insulation, due to the presence of the 
oil when the cable is subjected to electrical tension. 
Therefore, one object of the present invention, is to provide a process and 
apparatus for manufacturing telecommunication cables, which comprise 
expansible material in powder form, said process or apparatus not having 
any of the above-mentioned drawbacks. 
In accordance with the object of the present invention, the process for 
manufacturing a telecommunication cable, comprising a bundle of 
conductors, a covering sheath disposed around the conductors, and material 
in expansible powder form disposed in-between sheath and conductors, is 
characterised by the fact of comprising the steps of: 
(a) causing the conductors to advance inside means having a truncated-cone 
shaped cavity, means extending all around the longitudinal axis of the 
cavity, from an entrance section to an exit section, while maintaining the 
conductors separated, one from the other, but converging as they move 
towards the exit section; 
(b) causing the material in powder form to advance under pressure, 
according to a helicoidal course, with mechanical thrusts, for urging said 
material in powder form in-between the conductors as they pass through the 
truncated-cone shaped cavity; and 
(c) covering the conductors with a sheath, upon their exiting from the said 
cavity. 
The distinguishing characteristic of the above-described process, is the 
guiding and the remixing, under pressure, of powders inside a helicoidal 
channel, from which the said powders issue and are subjected to a 
mechanical thrust which suffices to cause them to become well-distributed 
around and in-between the conductors. 
In one form of operation, the process is characterized by the fact of 
causing the said material in powdered form to advance between the entry 
and the exit sections of the cavity, along a helicoidal course disposed 
all around the conductors, and to move said powdered form material from 
the helicoidal course towards the centre of the cavity, and around the 
conductors themselves. 
A further object of the invention, is an apparatus for manufacturing a 
telecommunication cable, comprising a bundle of conductors, at least one 
sheath covering the conductors exteriorly, material in expansible powder 
form in-between the the bundle of conductors, said apparatus being 
characterized by the fact of comprising means for helicoidally advancing 
the material, in expansible powder form, into a truncated-cone shaped 
cavity having an entry and an exit section and means for separately 
guiding each conductor into the cavity causing them to converge in a 
direction towards the cavity exit. 
Said frusto-conical cavity, in which the conductors advance separately, can 
be the same cavity wherein the powders advance in helicoidal fashion. 
In this form of realization, the apparatus is characterized by the fact 
that said means for advancing the material in powder form along a 
helicoidal course comprises a frusto-conical casing, a hopper for the 
entry of the material in powder form into the inside of the casing, a 
hollow screw disposed inside of the casing and having a helicoidal thread 
that rotates around its own axis, said thread having an external profile 
in proximity to and along the casing surface and an inner profile defining 
the limits of a frusto-conical chamber into which the conductors pass, and 
means for rotating the screw itself.

The invention will now be described with reference to the manufacture of a 
telecommunication cable 1 (FIG. 1) comprising a plurality of conductors 2, 
insulated--for example, with thermoplastic resins, such as polyolefins or 
vinylic resins, two spiralled overlapped tapes 3,4 an external sheath 5 of 
metal, plastics or rubber, expansible material 6, in the form of powder 
and in-between the conductors 2 and between the conductors 2 and the tapes 
3. 
For example, the tapes may be made of polyester, the sheaths, polyethylene, 
and the expansible material comprises carboxyl-methyl-cellulose. 
In a particular cable constructed according to this invention, the 
inter-spaces between the conductors and around the conductors, can be 
filled at least partially, by means of a suitable dosage, with the 
expansible material adapted for forming a blockage against any penetration 
of water. For example, this material can occupy 30% of the spaces present 
in the cable-core, and then if there be any present water, the material 
will swell and thus, block the water from spreading along the cable. 
The apparatus 7 (FIG. 2) for the manufacture of cable 1, comprises a 
station 8 with a plurality of bobbins 9 around which are wound the 
conductors 2, a group 10 of the guide-pulleys 11 for the conductors 2 
during the unwinding, an apparatus 12 for the application of the 
expansible material, a group 13 for applying spiralled tapes 3 and 4 
around the cable-core, an extruder 14 for covering the core with the 
sheath 5, a winching drum 15, and a drum 15' for collecting the cable. 
The drums 15 and 15' respectively, rotate around their own axis for pulling 
and collecting the cable, and simultaneously, they also rotate around the 
axis A-A for causing, in a known way, the cabling of the conductors 2 at 
the exit of the apparatus 12. 
The principal part of the invention, is constituted by an apparatus 12, and 
the other parts of the apparatus 7 are constituted by known devices and 
hence, hereinafter, for simplicity sake, these known devices will simply 
be mentioned whenever necessary. 
The apparatus according to the main concept of the invention, is based upon 
means adapted to urge the material 6 in powder form (FIG. 1) forward and 
along a helicoidal path within a frusto-conical cavity defined by two 
sections and upon further means for guiding the conductors 2 separately, 
one from the other, into the cavity. 
In a preferred form of embodiment, these means are constituted 
respectively, by an Archimedean screw device 16, that rests upon a base 
16' (FIG. 3) and by a special element 17, referred to hereinafter as the 
`die`. 
The spiralling device 16 comprises a frusto-conical casing 18, a hopper 19 
for the entry of the expansible material, in powder form, towards the 
inside of the casing 18, a hollow screw 20 disposed within the casing 18 
and having a helicoidal thread rotating around its own axis 21 that 
coincides with the axis A-A of the plant and means 22 for rotating the 
screw 20. The exit of the casing 18 comprises a plug 18', preferably made 
out of stainless steel, and having a central hole for the passage of the 
conductors 2. 
Said helicoidal thread of the screw 20 is disposed with its external 
profile 23 in proximity to, and extending along the inner surface 24 of, 
the casing, and with its inner profile 25 defining a frusto-conical 
chamber 26, inside which the conductors 2 pass and which is in 
communication with the spaces between the threads of the screw 20. 
The means 22 for the rotation of the screw, comprise an annular flange 27 
secured to the right extremity 28 of the helicoidal thread in the 
proximity of the entry section of the conductors 2 into the casing 18, a 
pulley 29 open at its center and connected laterally to the flange 27, and 
a driving group 30 comprising a motor 31, a pulley 32 and a belt 33 which 
drives the screw 20 by way of the pulley 32 and the pulley 29 
respectively. 
The screw 20 is supported and centered with respect to the casing 18, by 
suitable supporting means which, in the preferred embodiment comprises a 
plurality of rollers 34 on the arms 35 extending from the casing 18 with 
the axis of each roller 34 parallel to the axis 21 of the screw 20, the 
rollers 34 being distributed around the periphery of the flange 27 (see 
FIGS. 3 and 4). 
Each of said plurality of rollers 34 presses, at its periphery 36, against 
the wall of a special annular well 37 of the flange 27 in such a way that 
the rollers 34 are caused to rotate by the flange 27 itself, and these 
rollers 34 prevent any mis-alignment of the screw 20 with respect to the 
casing 18. 
The entry section of the Archimedean screw device 16, is limited by the die 
17 sustained by a structure 38 and provided with a plurality of holes 39, 
distributed along circles of various diameters, the conductors 2 passing 
through the holes 39. 
The apparatus 12 is completed by the presence of sealing means between the 
stationary die 17 and the face of rotating pulley 29. These sealing means 
can be several, and they are made out of materials which are adapted to be 
sealed in fixed relation either to the pulley 29, or to the die 17, in 
such a manner that during the relative motion between pulley 29 and die 
17, there is a sliding contact and simultaneously a sealing. For example, 
this material can be comprised of an elastomeric annular gasket 40 having 
its periphery 41 attached to the pulley 29, and in a lip-sealing contact 
with a circular protuberance 43 on the die 17 and having a pointed edge 
engaging the gasket 40. 
The apparatus further includes a sealing means between the casing 18 and 
the opposed rotating pulley 27, for example, an annular elastomeric gasket 
44 applied, as is shown in FIG. 3a, in contact with the surfaces of the 
casing 18 and of the pulley 27 and preferably, chrome plated for reducing 
friction to the minimum. 
Upstream and downstream of the apparatus 12, suitable containers (not 
illustrated) may be attached for receiving and holding, if necessary, 
small quantities of powder which can come out nevertheless, from the 
apparatus 12. 
The sealing means, made as described, prevents almost all of the powder 
material from escaping thereby permitting the elimination of any 
subsequent operations for the recovery of such material, and more 
important still, maintaining the air surrounding the apparatus practically 
free of great quantities of powder dispersed therein. In this manner the 
health of the workers is also safeguarded. 
The operation of the apparatus will now be described. The conductors 2 
(FIG. 2), subjected to the pull exercised by the drum 15, are gradually 
unwound from the bobbins 9 and guided from group 10 of pulleys 11 toward 
the screw device 16 of FIG. 3. The conductors 2, which are separated one 
from the other as they enter the device 16 converge within the device 16 
owing to the action of the separating and guiding that is imposed upon 
them by the holes 39 (FIG. 4) of the die 17 through which they pass and to 
the cabling action to which they are subjected when exiting from the 
casing 18. 
During their passage through the screw device 16, the various conductors 2 
cross the frusto-conical chamber 26, remaining inside the helicoidal 
threads of the screw 20 that is rotated around its axis 21 by means of the 
driving group 30 (FIG. 3). 
The screw 20 continuously pushes the expansible material 6, loaded in 
powder form into the hopper 19, toward the plug 18' along a helicoidal 
course or path and as the powders gradually approach the exit at the left 
extremity of the casing 18, they are forced to occupy even smaller volumes 
with the result that the powders are forced inwardly toward the axis 21. 
As a consequence, said powders fully penetrate in-between the conductors. 
This action is further favoured by the fact that the conductors 2 are 
squeezed together as they move towards the exit, with the result of 
compressing and more tightly enclosing the powders within the bundle of 
conductors 2. 
Thereafter, as the bundle of the conductors 2, containing the powdered 
material, issues from the Archimedean screw device 16, there takes place 
the further and following usual steps for manufacturing the cable 1 (FIG. 
2): 
(1) firstly, the cabling of the conductors is effectuated by rotating the 
drums 15 and 15' around the axis A-A; 
(2) then, the tapes 3 and 4, are applied by means of the group 13; 
(3) thereupon, the cable-core is covered with an external protective layer 
5, by means of the extruder 14; 
(4) finally, there takes place the winding of the cable under the form of 
turns--with the help of the winch drum 15 and the collecting drum 15. 
One particular advantage of the apparatus just described, lies in the 
possibility of filling-up the inter-spaces between the conductors, with 
powders even when, for some reason or other, the feeding of the material 
6, by way of the hopper 19, is interrupted. In fact, inside the casing 18, 
within which the screw rotates, there is deposited a certain quantity of 
powder 6 having a volume that is higher than that immediately required by 
the bundle of conductors 2 exiting from the apparatus. Consequently, the 
screw 20 is able to push, for a certain period, this powdered material 6 
independently of the feed of the powder from the hopper 19 towards the 
exit, in this way guaranteeing (at least for the period sufficient for the 
hopper to be refilled) a correct manufacturing of the cable. 
In a further embodiment according to this invention, the apparatus for 
applying the powders comprises means separated from the frusto-conical 
cavity where the conductors 2 pass for pushing the powdered material into 
the cavity. With reference to FIGS. 5 and 6, such means include: 
(a) a first frusto-conical casing 45, resting on the base 45', inside which 
the conductors 2 pass separatedly, while being dragged by appropriate 
pulling means (not illustrated) from the entry section--represented by a 
die 46, to the exit section 47 of the casing; 
(b) a second frusto-conical casing 48, inside which a frusto-conical screw 
49 rotates, the screw 49 having a full-core 50 and a thread 51. Said screw 
49 is rotated around its own axis 52 by a motor 53 through a known per se 
connection means 54 and 55 which may, for example, be an end-less screw 
54, and gears within a casing 55 for rotating the shaft of screw 49. 
This second casing 48 is fed with expansible material in powder form coming 
from a hopper 56 and comprises at its exit, an extension 57, the end 
section of which lies between the conductors 2 of the bundle adjacent to 
the section exit 47 of the casing 45, or in a more distant position the 
feed of the powders being varied as a function of the position of the end 
section of the said extension 57 with respect to the conductors 2 that are 
convergent one to the other. 
Preferably, the first casing 45 further comprises adequate systems for the 
exhausting of a part of the powders when the pressure, to which they are 
subjected inside this casing in the vicinity of the hole in the exit 
section 47, becomes excessive and may cause a risk of bringing about a 
rupture of the conductors 2 themselves. 
For example, the apparatus could be provided with an exhaust valve that is 
set for a pressure value of the powder. Alternatively, it could comprise a 
conduit between the first casing 45 and the hopper 56 in such a way as to 
return a certain quantity of powders to the hopper 56, and in this manner, 
to maintain the pressures of the powders in the vicinity of the exit 47 at 
correct functioning values. 
The apparatus of FIGS. 5 and 6, forms part of apparatus for manufacturing a 
cable (FIG. 1), which is illustrated in FIG. 2 and is a substitute for the 
apparatus 12. Even in this embodiment, the powders are forced to follow a 
helicoidal course, caused by the turns of the screw 49 at the exit from 
the extension 57, with a mechanical thrust that pushes the powders towards 
the exit 47 and the frusto-conical part of the casing 45 having a 
diminishing diameter. 
Let it be assumed that the casing 45 is half-filled with expansible 
material in powder form. As a consequence of the continuous rotation of 
the screw 49, there is a further inflow of powders coming from the hopper 
56 and directed from the exit section of the extension 57 in such a way as 
to continually fill the upper free space in the proximity of the exit 
section 47 of the casing 45, thereby providing a mass of powders, in the 
form of a frusto-conical `block` inside which the conductors 2 pass. 
The solutions provided by the present invention prevent the formation, in 
the powders accumulated in the vicinity of the exit of the casing, of 
canals or channels caused by the passage of the conductors 2, such canals 
having walls delimiting areas having sections that are greater than the 
transverse dimension of the conductors. This situation, if occuring, would 
become extremely undesirable since the conductors 2 would pass through the 
canals without receiving or dragging the powders along with them. 
The solutions illustrated in the FIGS. 3 and 5 eliminate to good advantage, 
these drawbacks. In fact, the continuous inflow of the new quantities of 
powders--pushed by the screw 20 (FIG. 3) or by the screw 49 (FIG. 5) 
causes the collapsing and the continuous re-mixing of the canal walls 
which may be formed by the passage of the conductors and therefore, this 
guarantees the contact and the dragging of the powders among the 
conductors. 
Although preferred embodiments of the present invention have been described 
and illustrated, it will be apparent to those skilled in the art that 
various modifications may be made without departing from the principles of 
the invention. For example, the invention is applicable to 
telecommunication cables having parts that are different from those which 
are described and illustrated in FIG. 1. Also, for example, the screw 30 
can have a single or a multiple-thread, as desired.