Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to splices in telephone
cables and more particularly to encapsulation of splices using
low pressure injection molding techniques.
A telephone distribution system from the
central office to the subscribers has the general form of a
tree network. A tree ne-twork comprises a main trunk which
divides into a number of main branches which further subdivide
into branches and thence into sub-branches. This process
may carry on for many further subdivisions and in the telephone
network often does. The main trunk in the telephone network
is a number of multi-thousand pair of cables that run out of
the central office. These trunks, depending on their length,
may include splices with no division. The cables branch
numerous times before the final branch, the customer drop wire,
branches off. Each of the branching points or nodes necessitates
splicing one cable to another, a pair at a time.
Currently the opened cables, once the wires
are spliced in place, are wrapped with many layers of sealing
tape and closed in with a heat shrinkable split sleeve. The
splice is baked to melt the tapes and shrink then onto the
cables and exiting wires.
Prior to the above system, and still in use in
some areas, the cable opening was taped and a split sleeve
was placed around the cable. The ends of the split sleeve
were sealed with a number of layers of sealing tape. The
sleeve was then flooded with a pouring type encapsulating
sealant, such as polyurethane.
The invention provides an air tight and water
tight seal around a telephone cable that has been opened and
has a number of pairs selected and spliced to wires or cables
exiting from the splice. The seal extends over and around
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the cables exitiny from the spliced joint. This is accomplished
by encapsulating -the cable with a molten plastic material which
seals to the cable sheaths.
The advantages of the invention are that it
provides a seal that is not as susceptible to the possibility
of human error as can be expected when applying several layers
of tape, because the encapsulation is injected by machine,and
in certain circumstances a bonding occurs between the injected
plastic and the cable sheath. Cost per splice can be greatly
reduced.
The physical size of the sealed splice is much
smaller than the current system, allowing for easier handling
of the cables and splices, and the splice can easily be made in
the field as well as in a factory setting.
The invention is accomplished by using an
injection molding die with a mold cavity specifically designed
to hold the various wires and cables. The mold cavity has an air
space around the cables and wires. This air space is filled
with the molten plastic material injected under low pressure.
The mold cavity has small ports exiting from the die that allows
air and the molten plastic to exit from the cavity. This
allows the injected material to wash the surfaces of the cables
and wires and ensures a seal between the injected material and
the cables wire sheaths. The injection gun is removed and a
pressure ram is attached to the mold. During the cooling
period, the splice is kept under pressure to ensure a good
seal.
The invention will be better understood with
reference to the following diagrams for example in which:-
Figure 1 is a perspective view of a completed
four drop wire splice;
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Figure 2 is a partial cross-section of the
splice of Figure 1;
Figure 3 is a cross-section along the line A-A
of Figure 2;
Figure 4 is a plan view of one half of the
mold;
Figure 5 is a cross-section of the mold.
As illustrated in the drawings, the four drop
wires 11, 12, 13 and 14 emerge from the encapsulation 15
parallel to the main cable 10. Pip 16 is the remnant of the
injection point and may be removed at a later date.
A long slit 20 is made through the outer sheath
21 and the metallic sheath 22 for access to the inner cable pairs
23. A ground lug 24 is installed through both the outer
sheath 21 and the metallic sheath 22 with electrical connections
to the metallic sheath 22. A ground wire 25 from drop wire
12 is connected to the ground lug 24. Ground wires are likewise
connected from the other drop wires 11, 13 and 14. Each drop
wire is cut to give seven or eight inches of slack. A
~u polyethylene liner 26 is installed in the slit opening 20
between the cable pairs 23 and the metallic sheath, with the
selected pair 27 exiting through a hole in the liner26. Pair
27 is spliced, using splice element 28, to the pair of conductors
29 comprising drop wire 12. Drop wires 11, 13 and 14 are
connected to other pairs from the main cable 10 in a likewise
manner. The entire area except the drop wires 11, 12, 13 and
14 is wrapped in a layer of tape 30 to secure the splices to
the main cable 10.
The mcld is comprised, for example, of two
plexi-glass layers 41 and 42 each which is hollowed out to
form one half of the mold cavity 43. Extensions 44 of the
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cavity hold the main cable, having an inner diameter correspond-
ing to the outer diameter of the main cable. Likewise
extension 45 hold the drop wires. Ports 46 are provided to
allow air and molten plas-tic to escape and to ensure that a
seal occurs between the cable sheath and the molten plastic.
The two halves of the mold 41 and 42 are
sandwiched together between base plate 47 and top plate 48.
The unit is held together by release bolt and wing nut
combinations 49 which extend through bolt holes 49a.
Alignment pins 50 assure proper mating of the two plexi-glass
layers 41 and 42. Attached to the top plate 48 is plate 51 which
contains the bayonet type attachment 52 for the attachment of
the injection molding gun. The injection port 53 runs centrally
through the plate 51, the top plate 48 and the top layer 41 to
allow the injected plastic to enter the mold cavity.
One of the major problems that the present
invention overcomes is the problem of a good seal to cables
that have polyethylene sheaths. The adhesive used with tapes
does not bond well to polyethylene and a poor moisture barrier
can exist. The same problem is true of pouring type encapsulants
as they must be poured at normal temperatures that are well
below the temperature at which polyethylene will bond.
The use of molten polyethylene as the encapsulant
obviates the above problems.
The molten polyethylene for the encapsulant is
injected into the mold cavity under an injection pressure of
approximately 10-50 psi and the injection temperature, at
approximately 300C., is such that the cable sheath melts and
~a bond occurs between the polyethylene sheath and encapsulant.
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