U.S. patent number 3,705,257 [Application Number 05/231,840] was granted by the patent office on 1972-12-05 for electric cable and method of making.
This patent grant is currently assigned to Anaconda Wire and Cable Company. Invention is credited to Robert M. Wade.
United States Patent |
3,705,257 |
Wade |
December 5, 1972 |
ELECTRIC CABLE AND METHOD OF MAKING
Abstract
In an electric cable having a semiconducting jacket applied
directly over a wall of polymeric insulation, excessive bonding of
the jacket to the insulation is prevented by applying the curing
agent for the jacket only to its outer surface after extrusion, and
then effecting a vulcanization such that the inner jacket surface
remains thermoplastic.
Inventors: |
Wade; Robert M. (Wabash,
IN) |
Assignee: |
Anaconda Wire and Cable Company
(New York, NY)
|
Family
ID: |
22870824 |
Appl.
No.: |
05/231,840 |
Filed: |
March 6, 1972 |
Current U.S.
Class: |
174/115;
174/110PM; 427/118; 427/123; 174/120SC; 427/119 |
Current CPC
Class: |
H01B
9/028 (20130101); H01B 13/22 (20130101); H01B
7/29 (20130101) |
Current International
Class: |
H01B
13/22 (20060101); H01B 9/02 (20060101); H01B
7/29 (20060101); H01B 9/00 (20060101); H01B
7/17 (20060101); H01b 007/02 (); H01b 009/02 () |
Field of
Search: |
;174/12R,12C,12SC,12SR,115,11PM ;117/69,72,75 ;252/63.7,66 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Myers; Lewis H.
Assistant Examiner: Grimley; A. T.
Claims
I claim:
1. An electric cable comprising:
A. a conductor,
B. a wall of dielectric polymeric composition surrounding said
conductor,
C. a jacket of polymeric composition surrounding said wall,
comprising:
1. a thermoplastic inner surface directly adjacent to said wall,
and
2. a vulcanized outer surface, said jacket being homogeneous save
for a decreasing degree of vulcanization from said outer toward
said inner surface.
2. The cable of claim 1 wherein said wall comprises
polyethylene.
3. The cable of claim 1 wherein said wall comprises vulcanized
polyethylene.
4. The cable of claim 1 wherein said jacket is semiconducting.
5. The cable of claim 1 wherein said jacket comprises chlorinated
polyethylene.
6. The cable of claim 3 wherein said jacket comprises chlorinated
polyethylene.
7. The cable of claim 4 comprising drain wires embedded within said
jacket.
8. The method of making a jacketed cable comprising the steps
of:
A. extruding a polymeric jacket free from vulcanizing agent around
an insulated cable core,
B. applying a vulcanizing agent to the surface of said jacket, said
agent being sufficient to vulcanize said surface but insufficient
to vulcanize the entirety of said jacket,
C. heating said cable thereby vulcanizing said surface and
diffusing said agent into said jacket.
9. The method of claim 8 wherein said vulcanizing agent is applied
to said jacket in solution.
10. The method of claim 8 wherein said jacket comprises chlorinated
polyethylene blended with ethylene ethyl acrylate copolymer.
11. The method of claim 8 wherein said agent comprises an organic
peroxide.
12. The method of claim 8 wherein said agent comprises
di-.alpha.-cumyl peroxide.
13. The method of claim 9 wherein said agent comprises
di-.alpha.-cumyl peroxide.
14. The method of claim 9 wherein said solution comprises acetone
and said agent comprises di-.alpha.-cumyl peroxide.
15. The method of claim 8 wherein said heating is effected under
pressure.
16. The method of claim 15 wherein said heating is effected by
pressurized steam.
17. The method of claim 15 wherein said agent is applied to said
jacket in solution.
18. The method of claim 15 wherein said jacket comprises
chlorinated polyethylene blended with ethylene ethyl acrylate
copolymer.
19. The method of claim 15 wherein said agent comprises in organic
peroxide.
20. The method of claim 15 wherein said agent comprises
di-.alpha.-cumyl peroxide.
21. The method of claim 17 wherein said agent comprises
di-.alpha.-cumyl peroxide.
22. The method of claim 17 wherein said agent comprises
di-.alpha.-cumyl peroxide and said solution comprises acetone.
23. The method of claim 15 wherein said agent is applied within a
chamber containing said pressure.
24. The method of claim 16 wherein said agent is applied within a
chamber for said steam.
Description
BACKGROUND OF THE INVENTION
Economies in high-voltage cables have recently been effected by
eliminating the separate shielding system, making the protective
jacket semiconducting, and applying it directly onto the wall of
cable dielectric. Such a cable construction, wherein the jacket
comprises embedded drain wires is described in Plate et al. U.S.
Pat. No. 3,474,189, the disclosures of which are included herein by
reference. Although it would be desirable to increase the toughness
and tensile strength of the jacket material by vulcanization, this
has not proven feasible because of the necessity of avoiding
adhesion between the semiconducting jacket and the outer surface of
the wall of insulation. Such adhesion would make it difficult to
free stripped ends of cable from residues of the electrically
conducting jacket composition at terminations and joints.
SUMMARY
I have invented a cable and method of cable manufacture that allows
the jacket of the cable to be strengthened by vulcanization without
increasing its adhesion to the cable insulation. My new cable is
thus provided with a jacket that can withstand the expansion of
such high-thermal-coefficient insulating materials as vulcanized
polyethylene, at higher cable temperatures than cables previously
known. My improved cable will also more affectively resist any
explusion of drain wires from cable jackets by electrical forces
during high fault currents.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 shows a section of a cable made to my invention
FIG. 2 shows the steps of a method of my invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to FIG. 1, a cable of my invention, indicated generally
by the numeral 10, has a conductor 11, a heavy wall 12 of
insulation, and a semiconducting jacket 13 in which are embedded a
plurality of drain wires 14. The wall 12 comprises cross-linked
polyethylene, but my invention has application to cables with
insulation walls of other compositions such, for example, as
ethylene-propylene rubber, polyvinyl chloride, and unvulcanized
polyolefin. However, my invention has particular advantages for
cross-linked polyethylene insulated cables since cross-linked
polyethylene has a particularly high thermal coefficient of
expansion, and this places an extra strain on the jacket 13. The
jacket 13 comprises chlorinated polyethylene blended with ethylene
ethyl acrylate and a high proportion of carbon black to increase
its electrical conductivity. A preferred thermoplastic jacket has
been described in application Ser. No. 167,741 assigned to the
assignees of the present invention, which has the advantage, that,
being thermoplastic, it does not bond unduly to the wall 12. In the
present invention an inner surface 16 of the jacket 13 remains
thermoplastic but an outside surface 17 has been vulcanized to
provide greater toughness and tensile strength. Vulcanization of
the outer portion of the jacket 13 is achieved by diffusion of
vulcanizing agent through the surface 17 so that the jacket 13 is
homogeneous except for radial differences in the degree of
vulcanization or cross linking. This vulcanization decreases
gradually through a radial section of the jacket 13 so as to leave
the inner surface 16 free from vulcanization. Chlorinated
polyethylene has been employed in the composition of the jacket of
the cable 10 principally to reduce its combustibility. However, my
present invention can also be efficaciously applied to a
semiconducting polyethylene jacket.
Although it will be understood that the inclusion of drain wires is
not essential to the present invention, where such drain wires are
included, vulcanization of the surface 17, and of a layer of the
jacket surrounding the wires helps to confine the wires 14 within
the jacket in two ways. The higher tensile strength of the
vulcanized composition resists radial expulsion of the wires by
electrical forces during surges of current, and the higher
softening temperature of the vulcanized composition prevents the
surface from melting during short periods of high ambient
temperature.
In FIG. 2 I have diagrammed a method of making the cable 10 whereby
a reel 21 of the conductor 11 is continuously paid through an
extruder 22, a vulcanizing tube 23, and cooling section 24 for
application of the dielectric wall 12. The insulated core then
passes through a second extruder 26 wherein it receives the jacket
13 and drain wires 14.
So far the description of my method has been previously disclosed
for the manufacture of cables with thermoplastic jackets. I now
provide a novel step of coating the jacket 13 with a suitable
curing agent by passing the cable 10 through a chamber 28 wherein
it is sprayed or otherwise coated with di-.alpha.-cumyl peroxide.
Although I prefer to use di-.alpha.-cumyl other peroxides are known
for curing compositions comprising chlorinated polyethylene and
polyethylene and these may be used within the scope of my
invention, including tertiary peroxides in which the valences of
the carbon atoms not linked to oxygen are attached to alkyl,
cycloalkyl, alkylcycloalkyl, cycloalkyl-alkyl, aryl or aralkyl
radicals, and also quinhydrone dimerides as disclosed in U.S. Pat.
No. 3,036,982. Solvents other than acetone may be used, less
volatile solvents having the advantage of holding the vulcanizing
agent on the surface 17 through the entrance to a curing chamber.
It is not essential to my invention, however, to apply the curing
agent in solution. As detailed in an example hereinbelow, I have
successfully applied the molten agent directly to the jacket.
Curing agents can also be applied as suspensions or emulsions, such
as water suspensions or emulsions.
On leaving the chamber 28 the cable 10 is passed into a vulcanizing
tube 29 wherein vulcanization of the surface and diffusion of the
curing agent beneath the surface is effected. Following passage
through a final cooling zone 31, the cable 10 is taken up on a reel
32.
The tube 29 has a steam supply entrance 33 and a condensate drain
34 but a hot inert pressurized gas such as nitrogen or helium may
be used instead of steam within the scope of my invention. The
latter method has the advantage that it is easier to keep the
application chamber relatively cool. To counteract the pressure in
the tube 29 a pump 36 is used to meter the vulcanizing agent into
he chamber 28. In lieu of the continuous process shown, the entire
cable can be removed to a curing chamber after the surface has been
coated with peroxide in solution. I have found that acetone works
well as a solvent for di-.alpha.-cumyl peroxide in this application
but other solvents, which have been known, can also be used.
EXAMPLE 1
A cable made in accordance with the description of FIG. 1,
hereinabove, with a jacket 13, 0.080 inch thick was brush coated
with a 50 weight percent solution of di-.alpha.-cumyl peroxide in
acetone. The acetone permitted to evaporate. Thereupon the cable
was vulcanized in a steam chamber at 225 pounds per square inch in
pressure for one minute. Specimens cut from the outer surface of
the jacket with thicknesses from 0.022-0.032 inch were found to
have an average tensile strength of 1,586 psi compared to a tensile
strength of 1,373 psi for an unvulcanized jacket specimen and an
average elongation of 183 percent compared to 327 percent for an
unvulcanized specimen.
EXAMPLE 2
A length of the cable 10 was coated with molten di-.alpha.-cumyl
peroxide at 75 psi. Specimens 0.020-0.024 inch thick were sliced
from the outer surface of the jacket and found to average 2,783 psi
tensile strength and have 120 percent elongation. Specimens
0.018-0.020 inch thick were then sliced from the underlying
thickness of jacket for testing to determine the depth of diffusion
of the curing agent. These averaged 2,870 psi in tensile strength
and 207 percent elongation. The much greater elongation indicates
presence of some thermoplastic composition at the deeper level.
EXAMPLE 3
A cable with 250 MCM conductor, a 0.175 inch wall of cross-linked
polyethylene insulation and an 0.080 inch thick chlorinated
polyethylene, ethylene ethyl acrylate jacket was coated with
di-.alpha.-cumyl peroxide and cured in steam at 200 psi for 1
minute. A specimen 0.015-0.020 inch thick was sliced from the outer
surface of the jacket and found to have a tensile strength of 2,056
psi and an elongation of 162 percent. The conductor of a length of
this cable was raised to 135.degree.C for 24 hours to determine if
the expansion of the insulation would cause cracks to appear in the
jacket. No cracks appeared. The conductor temperature was raised to
155.degree.C for 24 hours without causing any cracks to appear in
the jacket. The conductor was raised to 200.degree.C for 1 hour
without causing any cracks to appear over the drain wires. A
circumferential crack did appear next to a holding clamp. For
comparison, cracks appeared over the drain wires of a cable with an
unvulcanized jacket at a conductor temperature of 135.degree.C
after 2 hours.
I have invented a new and useful cable and method of making the
same of which the foregoing description has been exemplary rather
than definitive and for which I desire an award of Letters Patent
as defined in the following claims.
* * * * *