Note: Descriptions are shown in the official language in which they were submitted.
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Impro~ements in or relating to the manufacture
of insulated electric cables
This invention concerns improYements in or
relating to the manufacture of insulated electric cables,
and more particularly concerns the manufacture of
insulated cables by a process wherein an extruded cable
insulation la~er is cured, that is to say vulcanized or
chemically cross-linked, by the applica*ion of heat
during passage of the cable through a tubular enclo6ure
formed at least in part as a catenary.
As is well known the use of such a catenary-
shaped curing enclosure enables the insulation of the
cable to be cured from a relatively soft and plastic state
as it exits from the extruder head at one end of the
catenary to a relatively firm and rigid state at the
oppos.ite end without there being any requirement to colltact
the insulation with supporting or guiding means at any
intermediate location, the cable simply being suspended
bet~een spaced apart locations so as to hang in a catenary
generally coaxial with the catenary-shaped curing
enclosure. Means are generally provided for controlling
the catenary position of the cable within the curing
enclosure to ensure that the still plastic cable insulation
does not come into contact w:ith the wall of the curing
enclosure and is not damaged thereby, such means
comprising for example a catenary position sensor within
~J~ 25 the curing enclosure coupled to control the catenary
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~ension in the cable by control oE the speed operation of
a cable haul ofE means external of the curing enclosure.
In the operation of such an apparatus using a
fluid, liquid or gas, with.in the curlny enclosure as a
medium for applying the re~uired heat to the insulation, a
difficulty arises on account o:E the action of the hydro-
static pressure of the curing fluid upon the cable which,
by virtue of the pressure differential between the inside
and the outside of the curing enclosure at the exit end
of the catenary tube, tends to extrude the cable through
the exit seal customarily provided at the exit end of the
enclosure. The tension applied to the cable externally
of the curing enclosure, that is to say the tension applied
by the haul off means for example, thus is not the same as
the tension experienced by the cable wi~hin the curing
enclosure, and under certain operating conditions, for example
wherein the cable has light-weight conductor(s) and a large
body of insulation and the curing fluid is relatively dense,
the situation can arise that the extrusion force developed
upon the cable at the exit end of the curing enclosure
exceeds the-normally required external tension leading to a
loss of.control of the cable catenary position within the
curing enclosure with attendant risk of damage to the cable
insulation.
To avoid or at least substantially reduce the risks
attendant upon the abovementioned problem, the present invention
proposes the provision of a cable restraining means at the
exit end of the catenary curing tube, or adjacent thereto
within the tube, for applying to the cable a restraint directed
opposi.tely to the forces ~developed by the hydrostatic pressure
of the curing fluid) which tend to extrude the cable through
the exit end of the catenary curing tube so as to nullify the
disadvantageous affects of such forces. The cable restraining
means comprises flexible means engageable with said cable
and adjustable means for pressing said flexible means toward
said cable and thereby vary the restraining force on the cable.
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Various means of applying such a restraint to the cable are
possible, particularly having regard to the fact that in the region of
the exit end of the catenary tube the cable insulation wlll be
virtually cured and is much less susceptible to damage. Thus the
restraining means might for example comprise braked ca-terpillars
acting on the cable, braking rollers or wheels~ or other frictional
devices. Ideally the restraining means will be adjustable for
accommodating different or varying cable dimensions, and will be
operable not only to nullify the effects of the hydrostatic forces
developed upon the cable but also to provide an excess restraining
force against which the cable tension control means can operate.
The presently preferred for~ of restraining means comprises a
plurality of generally flexible and resilient conical members which
are nested with each other and are arranged coaxially of the curing
tube, the conical members each being open at its apex for passage
therethrough of the cable in sliding frictional engagement with the
conical members, and the nested array of conical members being subject
selectively to the action of a pressure collar which can be urged
axially against the conical members so as by a degree of distortion
thereof tG vary the restraining effect of the conical members upon a
cable traversing their open apices~ The action of the pressure collar
can advan-tageously be made dependant upon the sensed tension applied
to the cable externally o~ the curing enclosure.
According to a further aspect of the present invention, a
method of curing an extruded insulation layer of an electric cable,
comprising passing the insulated electric cable along a catenary path
through a curing tube which conforms generally to said catenary path,
filling said curing tube with a heated fluid for effecting curing of
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the cable insulation layer, applying to the cable, at the exit end of
the curing tube or adjacent said exit end and within the curing tube,
a frictional restraining force directed oppositely to forces developed
by the hydrostatic pressure of the curing fluid which tends to extrude
the cable through the exit end of the curing tube, and selectively
varying said frictional restraining force as the cable is passed
through the curing tube so as to nullify the efEects of the forces
developed by the hydrostatic pressure of the curing fluidD
The invention, together with features and advantages thereof,
will best be appreciated from consideration of the following
description of exemplary embodiments given with reference to the
accompanying drawings wherein:
Figure 1 is a schematic showing of a plant for extruding
insulation onto a cable core and for curing the extruded -material in a
catenary tube;
Figure 2 is a scrap sectional view showing a
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restraining means embodying the present invention;
Figure 3 shows the restraining means of Figure
2 installed near to the exit end of a catenary tube;
Figures 4A to 4D show the sequence of operations
involved in setting up a catenary curing tube incorporating
a restraining means as in Figure 2; and
Figure 5 represen-ts a control system for
adjusting the restraining means of Figure 2 according to
variations in take-off tension.
Referring to Figure 1, a cable core 1 is fed by
metering caterpillar device 2 through the cross head 3 of
an extruder ~here a layer of elastomeric insulation is
extruded continuously onto the cable core lo The outlet
of the e~truder leads directly into the inlet end of a
catenary shaped curing tube 4 which, in operation,
contains hot ~luid under a predetermined pressure. As
shown, the cable follows a catenary path through the
catenary tube 4, its position within the catenary tube
being controlled through a detec*or 5 which determines
the operating speed of a haul-off caterpillar 6 to det~
ermine the tension in the cable. The exit end of the
catenary tube 4 is sealed by ~eans of a seali~g arrange~
ment 7.
Figure 2 shows a scrap sectional ~iew of a
restraining means 8, embodying the invention, fitted
within the bore of a catenary curing tube such as that
designated 4 in Figure 1. The restraining means 8
comprises a set of frusto-conical members 9 nested or
stacked together as shown and defining by their aligned
open apices a through passage ~or the cable 10. The
members 9 are formed of rubber, natural or synthetic
depending upon the temperatures to ~hich they are to be
subjected, and are selected to be of a size nominally
to suit the dimensions of the cable 10. The members ~
are securely clamped to the wall 11 of the catenary tube
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4, and are arranged to be subject to the action of a
pair of pressure rings or collars 12, 13 the former 12
of which is secured to the catenary tube and the latter
13 of which is ~ovable axially of the catenary tube~ As
will be appreciated, movement of pressure collar 13
towards the left (as ~iewed in Figure 2) will cause a
deformation of the members 9 such as to cause the~ to
grip more strongly the cable 10, whereas the opposite
movement will reduce the restraining effect of the
members 9.
Figure 3 is an examplary showing of the
restraining means 8 of Figure 2 installed adjacent to
the exit end of a catenary curing tube 4. A pressure
bypass 14 is provided around the res*raining ~eans 8,
and there is also provided downstream of *he restraining
~eans 8 a pneumat.ic seal 15 and a quick release hawser
seal 160 Figures 4A to 4D show the sequence of
operations i~volved in setting up a catenary vulcaniza~
tion line such as that of Fi~ure 3. In Figure 4A, the- .
cable start 20 is pulled through the catenary tube 4
with a small d.iameter hawser 21 which gives rise only
to a very small hydrostatic force acting at the quick
release seal 16. Under these conditions, the sensed
haul off tension is relatively high and this causes the
pressure collar 13 (Figure 2) of the restraining means
o to be adjusted towards the right so as to minimize
the action of the restraining means 8 and permit
relativel~ free passage of the cable start 20. Figure
4B shows the cable start 20 engaged with the restraining
mea~s 89 but otherwise the conditions are as for Figure
4A since the restraining means 8 is bypassed by bypass
line 14. When, as shown in Figure 4C, the cable start
20 plugs the seal 15, the pressure between seal 15 and
hawser seal 16 reduces towards atmospheric and- the
hydrostatic force developed upon the cable by virtue of
the pressure of the curing medium increases dramaticallyO
The haul off tension of the cable drops correspondingly,
and in response to this fall, the restraining means 8 is
actuated by corresponding leftwards movement of pressure
collar 137 In Figure 4D, the hawser seal 16 has opened
preparatory to the cable start 20 exiting from the
catenary tube 7 and the restraining device 8 adopts a
normal operating condition where, in dependence upon
varying haul off tension, it applies to the cable a
variable restraining action.
Figure 5 shows a control system for adjusting
the restraining means 8 of Figure 2 according to
variations in the sensed haul-off tensionr The rubber
cones 9 of the restraining means 8 are compressed in
order to provide the required braking force by means of
a pair of hydraulic cylinders 30, 31. The degree of
compression, and hence the magnetude of the braking
force, is determined by the displacement of these
cylinders. This displacement is determined by a three
position hydraulic valve 32 providing a clamping, a
neutral and a releasing mode. This valve is controlled
automatically by an electronic logic system 33 fed by a
signal from a ~ad cell which monitors the haul off
tension via the turn round wheel (Figure 1). Two set
points are selected, a low and a high. If the haul off
tension is below the low level the brake 8 is put into
clamp until such time as the displacement is sufficient
to generate enough braking force to increase the haul
off tension to the ~ow level where it will then change
to neutral, i.e. no further displacement will take
place. Should the cable size increase for a given
displacement, the braking force will increase and hence
so will the haul off tension; if the tension increases
above the high limit the brake will release in a
similar manner~ This control system is totally
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independent of the catenary position detector 5 which
con~rols the speed of the haul off device 6.
