1. * GB780065 (A)
Description: GB780065 (A) ? 1957-07-31
Improvements relating to the manufacture of insulated cables
Description of GB780065 (A)
COMPLETE SPECIFICATION
Improvements relating to the Manufacture of Insulated Cables
We, SHARDLOVF ELECTRIC IWIRES LIMITED, a 'British .Company of Moseley
q3ui;Ldings, 516
Moseley Street, Manchester, Lancashire, and;
FRANCIS IGEORGE HARGREAVES, a British
Subject of 60, Moseley Road, Ashton-under-
Lyne, do hereby declare the invention, for which we pray that a patent
may be granted to us, and the method by which it is to be
performed, to be particularly described in and by the following
statentent: -
The present invention concerns thermo plastic insulated cables and in
particular multi-
core cables of the type wherein the individual conductors are of what
is known as; sector shape in cross section, each conductor being
insulated by embedding in a thermo-plastic material, the insulated
conductors being " laid on" or twisted prior to bmlding up into the
composite cable, so that the individual in sulated conductors have a
helical lay about the axis of the composite cable. The term sector
shape" used herein is! intended to in- clude cross-sectional shapes
which are fractions of the full section of the final cable.
In accordance wth the present invention, there is provided a method of
insulating individual conductors of sector lile cross-section for
forming into multi-core cables of the type above set forth and
utilising an extru- sion process which method consists in first
twisting the conductor to the desired lay, and thea in nonsotatabler
feeding said twisted conductor through a rotatable 'guide having an
outlet conforming with the sectional shape of the conductor whereby
the guide rotates in conformity with the lay of the conductor, and
finally feeding the conductor through a die head with the plastic

2. insulant and in coupling the die bead to the guide so that said head
and guide rotate together.
-It will be understood that as the conductor is prespiralled', it will
turn the guide member due to its passage through the 'outlet Rowever,
owing to the forcing in of the thermoplastic around the guide end, and
the resulting frictional drag, it will be necessary to drive the guide
member at a rotational speed in synchronism with the spiral lay of the
conductor.
Accordingly, a further feature of the in
Invention consists in additionally assisting the
rotation of the guide and die by power oper
ated driving means. This can be effected by a direct drive to the
guide from the driving
means for feeding the conductor through the
guide, but preferably, the drive is through a slipping clutch or other
frictional drive.
Also according to the invention, there is provided a means for
carrying out the process of the invention, said means comprising an
extrusion machine having an extruder head through which thermoplastic
insulant is forced, there being provided a guide member in the machine
body through which the conductor passes said member consisting of a
tubular body with am end formed with an outlet orifice conforming with
the cross-sectional shape of the conductor said guide member carrying
the die adjacent the guide end so that the conductor when fed into the
body passes first through the guide outlet and then through the die,
the thermoplastic insulant being forced through the die orifice around
the conductor, with the guide member and die mounted in the body so as
to be capable of rotation therein in accordance with the layer of the
conductor.
According to a further aspect of the inven tion, there is provided an
extrusion machine head for coating a sector or like section conductor
with thermoplastic insulant in accord ance with the method above set
forth, said machine having a cylindrical bore in which is rotatably
mounted a tubular guide, said guide carrying a coWaxiallr arranged die
at itsl front end, and having an outlet opening at this end which
conforms in shape and size with the cross-sectional shape of the
sector or like sectioned conductor which is arranged to be fed through
the guide, the die also having an orifice conforming in shape with the
said sec tion shape of the conductor but of a size larger to enable a
coated conductor to pass therethrough, means being provided whereby
thermoplastic insulant can be forced into the bore, and pass to the
conductor as it leaves the guide to pass out with the conductor as a
coating therefor through the die-orifice, the pre-spiral lay of the
conductor causing or con straining the guide and die to turn in

3. accordance with the lay of the conductor.
It will be seen in accordance with this invention both guide and die
rotate, the speed rotation being in conformity with the spiral
conductor lay. The die orifice is of course such that the coated
conductor issuing therefrom is of desired cross section, which will be
the cross-section of the conductor enlarged by an even coating of
insulant.
The guide outlet conveniently is of the conductor cross section, so
that as the conductor (which is not rotating) passes through the
outlet, the guide and die are caused to rotate, as mentioned above
however, owing to frictional drag due mainly to the thermoplastic
material around the guide, the turning of guide and die is
power-assisted.
For a clear understanding of the invention to be obtained, reference
will now be made to the accompanying drawings illustrating preferrecl
embodiments, and in which
Figure 1 is a longitudinal section through one form of head.
Figure 2 is a transverse section showing the die orifice and
Figure 3 is a view similar to Figure 1 of a second and preferred
embodiment.
Referring firstly to Figures 1 and 2, the extrusion machine includes a
barrel like part 10 in which the extruder screw 11 rotates to feed the
thermoplastic material into the bore 12 through the head. The head is
arranged so that the material is fed around a guide member comprising
a tubular body 13 disposed at a right angle to the barrel and suitably
supported. The one or front end of the tubular body carries the end 14
'which consists of a tubular member having a tapering outer surface 15
and co-axial with the tubular body, with a sector shaped aperture or
orifice 16 axially therethrough. The tubular body 13 extends beyond a
rear support and is coupled at this rear end by gearing 17 to the
drive for the conductor through the tube whereby as the conductor is
fed the tube rotates.
-Mounted in front of the guide end is the die member 18 which has a
recess 19 into which the tapered nose end of the guide projects, the
recess including a conical or tapering part conforming with the nose
of the guide.
Said die also has a number of slots 20, arranged therearound and
leading from the space around the guide to the die aperture or orifice
21 through which the conductor is fed, whereby the conductor is bedded
into a sheath of or coated with the material as it passes through the
die orifice.
The die is mounted in a hollow plug like member 22, the one end of
which is retained in a recess in the head, the plug member being
arranged co-axially with respect to the guide and die therein.

4. Suitable adjustable packing members and glands will be provided at the
front end of the plug member and at the rear end of the head to
prevent leakage from around the tube and die.
The die is mounted so as to rotate with the guide member. This
conveniently is achieved by means of a key and keyways as shown at 23
which couple the die and guide.
In order to ensure that the thermoplastic material is homogeneous a
flow ring 30 is provided this having concentric groups of holes 31
which ensure that the thermoplastic under pressure is completely
masticated and envelopes the core as a homogeneous mass.
In operation, the sector section conductor is fed through the guide
members and the die at a constant speed, the said conductor being
pre-formed by twisting. The guide member is turned (and with it the
die) in synchronism with the spiral lay of the conductor whereby the
guiding outlet aperture or orifice maintains correct orientation with
respect to the sectional shape position passing therethrough at any
instant.
In the construction of Figure 3, which shows simply the body, guide
and die, the guide consists of the tapering hollow tube 24 (i.e. the
guide and apertured end are as a single unit) the die 18 being carried
at the front end of the tube by spoke-like members 20. It will be
noted that this arrangement is simplified as compared with the first
described embodiment. The guide member and die are mounted in ball
races 25, 25, and suitable packings not shown, will be provided.
Reference numerals, otherwise than in above, conform in their
application to the same or equivalent parts of the first embodiment.
A preferred method of drive is shown in
Figure 3, wherein the guide 24 is assisted in rotation through a
sprocket wheel and chain drive 26, torque being applied through an
electric motor 27 and an adjustable pressure frictional drive 28.
What we claim is: -
1. Method of insulating individual conductors of sector-like
cross-section for forming into multi-core cables of the type set
forth, and utilising an extrusion process, which method consists in
first twisting the conductor to the desired lay, and then in
non-rotatably feeding said twisted conductor through a rotatable guide
having an outlet conforming with the sectional shape of the conductor
whereby the guide rotates in conformity 'with the lay of the
conductor, and finally feeding the conductor through a die head with
the plastic insulant and in coupling the die head to the guide so that
said head and guide rotate