Method of producing coaxial cable

Details Method of producing coaxial cable Method of producing coaxial cable

2000-02-28

2002-11-26

Arbes, Carl J. (Department: 3729)

Metal working

Method of mechanical manufacture

Electrical device making

C029S728000, C029S03300H, C174S1020SP

Reexamination Certificate

active

06484392

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coaxial cable producing method and a coaxial cable and particularly, to a method of producing a coaxial cable of which the metal plating layer formed by impregnating a metal woven shielding conductor layer with a molten metal is improved at its inner surface in the smoothness and thus its adhesivity to an insulated cable is increased and to such a coaxial cable.
2. Description of the Prior Art
As high frequency coaxial cables enhanced in the electric characteristics including the suppression of reflection and attenuation in a high frequency range, semi-rigid type coaxial cables are known in which an insulated cable produced by coating a center conductor with an insulator layer is coaxially covered at its outer surface with a metal pipe made of, for example, copper or aluminum.
The semi-rigid type coaxial cables using the metal pipe are however high in the production cost and poor in the flexibility, hence making the wiring operation difficult.
Alternatively, modified coaxial cables which are decreased in the production cost and improved in the flexibility although their electric characteristics including the suppression of reflection and attenuation are lower than those of the semi-rigid type coaxial cables using the metal pipe have been proposed comprising an insulated cable produced by coating the outer surface of a center conductor with an insulator layer and covered with a metal woven shielding conductor layer and a metal plating layer produced by passing the insulated cable through a molten metal plating solution to impregnate the metal woven shielding conductor layer with a molten metal.
FIG. 10
is an explanatory view showing a process of forming the metal woven shielding layer in a modified coaxial cable producing method using the molten metal plating.
An insulated cable W formed by coating the outer surface of a center conductor (
102
in
FIG. 11
) with an insulator layer (
103
in
FIG. 11
) with the use of a common means at the previous step is released from a supply reel
20
, passed on a guide roll
21
, and directed into a dice
24
.
Also, a group of metal conductor wires
14
are woven with reels
25
, on which the metal conductor wires
14
are wound, spinning about the insulated cable W at the entrance of the dice
24
to form a metal woven shielding conductor layer (
104
in
FIG. 11
) over the outer surface of the insulated cable W.
A resultant intermediate cable
111
having the metal woven shielding conductor layer (
104
in
FIG. 11
) covered over the outer surface of the insulated cable W is drawn by the action of a drawing capstan
22
and taken up on a take-up reel
23
.
FIG. 11
is a cross sectional view of the intermediate cable
111
.
The metal woven shielding conductor layer
104
of the intermediate cable
111
is closely bonded to the outer surface of the insulated cable W.
FIG. 12
is an explanatory view showing a process of forming a metal plating layer in the method of producing a coaxial cable using the molten metal plating.
The intermediate cable
111
is released from a supply reel
51
, coated with a flux by a flux coating apparatus
52
, guided by a guide roller
53
A, and directed into a molten metal plating solution
55
in a molten metal plating tub
54
. Then, the cable is guided by a guide roller
53
B in the molten metal plating tub
54
, moved out from the molten metal plating solution
55
, passed through a plating solution squeezing dice
56
disposed above the molten metal plating solution
55
for adjusting to a desired thickness of the plating, cooled down by a cooling apparatus
57
to complete a coaxial cable
101
, guided by a guide roller
53
C, and taken up on a take-up reel
58
.
FIG. 13
is a cross sectional view of the coaxial cable
101
produced by the coaxial cable producing method using the molten metal plating.
The coaxial cable
101
comprises the insulated cable W formed by coating the center conductor
102
with the insulator layer
103
and the metal plating layer
105
formed on the insulated cable W by impregnating the metal woven shielding conductor layer
104
with the molten metal.
FIG. 14
is an exemplary diagram of the attenuation and reflection characteristics of a transmission signal on the coaxial cable
101
.
A one-meter length of the coaxial cable
101
was prepared and its reflection and attenuation characteristics at a high frequency range from 0.045 GHz to 18 GHz were measured with a network analyzer.
Peaks of the reflection and the attenuation which may result from the effect of a winding pitch of the metal woven shielding conductor layer
104
are shown at about 10 GHz of a transmission frequency.
Also, the standing wave ratio of a reflected voltage at a high frequency range from 0.045 GHz to 18 GHz is 1.4.
SUMMARY OF THE INVENTION
In the conventional method of producing a coaxial cable using the molten metal plating, the metal woven shielding conductor layer
104
is adhered closely to the outer surface of the insulated cable W during the step of forming the intermediate cable
111
as shown in FIG.
11
. When the intermediate cable
111
is immersed in the molten metal plating solution
55
, for example, at 260° C., the insulator layer
103
made of a resin material is thermally expanded hence biting into the metal woven shielding conductor layer
104
. This causes the metal woven shielding conductor layer
104
to be hardly impregnated with the molten metal. Accordingly, when the insulator layer
103
is cooled down and returns to its original size, portions of the metal woven shielding conductor layer
104
are exposed from the inner surface of the metal plating layer
105
thus generating gaps and undulations of the surface.
If there are generated gaps and undulations of the inner surface of the metal plating layer in which a high frequency current runs, the high frequency characteristic may be declined. More particularly, peaks of the reflection and attenuation which may result from the effect of a winding pitch of the metal woven shielding conductor layer
104
appear about at 10 GHz of the transmission frequency, hardly ensuring the effectiveness within a frequency range including 10 GHz.
In addition, the adhesivity between the insulated cable W and the metal plating layer
105
is poor, causing the metal plating layer
105
to be easily slipped out.
It is an object of the present invention to provide a coaxial cable producing method and a coaxial cable of which the metal plating layer formed by impregnating a metal woven shielding conductor layer with a molten metal is improved at its inner surface in the smoothness and its adhesivity to the insulated cable is increased.
As a first aspect of the present invention, a method of producing a coaxial cable is provided comprising the steps of covering with a metal woven shielding conductor layer an insulated cable formed by coating the outer surface of a center conductor with an insulator layer, and passing the cable through a molten metal plating solution to impregnate the metal woven shielding conductor layer with a molten metal to have a metal plating layer, said step of covering with the metal woven shielding conductor layer being arranged in which the insulated cable is accompanied with one or more solder or tin wires while the metal woven shielding conductor layer is being woven.
In the method of producing a coaxial cable as the first aspect, when the intermediate cable having the insulated cable associated with one or more solder or tin wires is immersed in the molten metal plating solution, the solder or tin wires are dissolved into the molten metal plating solution thus generating a spatial margin between the insulated cable and the metal woven shielding conductor layer. This prevents the insulator layer from biting into the metal woven shielding conductor layer when it is thermally expanded. Accordingly, as the metal woven shielding conductor layer is impregnated deeply with the molten metal, there are generated no gaps or undulations on the

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