Adhesive bonding and miscellaneous chemical manufacture – Methods – Making electrical conductors of indefinite length
Reexamination Certificate
1995-04-13
2001-08-14
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Making electrical conductors of indefinite length
C156S244120, C156S244270, C174S1170FF
Reexamination Certificate
active
06273977
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method and apparatus for bonding two separate independent insulated electrical wires together. This is done in a manner that maintains the concentricity of each electrical conductor with respect to the insulation. The invention uses heated thermoplastic material that surrounds each electric conductor. When the insulation has set, the insulated conductors are touched together and are bonded to each other by the heated thermoplastic insulation.
BACKGROUND OF THE INVENTION AND PROBLEM PRESENTED TO INVENTOR
Modern twisted pair cable consists of two separate insulated wires paired through twisting means. Ideally, the insulation of each conductor is applied in such a manner that the concentricity of the conductor with respect to the insulation is maintained. When the conductors are paired, the electrical properties of the cable are maintained at a desirable level.
During installation and handling of the cables, the cables are bent, twisted and stretched, and this changes the geometry of the conductors with respect to each other and it adversely affects critical electrical properties such as attenuation, crosstalk and transmission. In recent years, with improved signal processing speeds and increased data rates, the need for high performance cables, up to 100 mbps, has greatly increased the use of twisted pair cables and has brought to light the importance of these inherent problems.
These installation and handling problems can be eliminated by joining the two conductors together by fusing the pair of conductors along its longitudinal axis, while maintaining each conductor's electrical properties, such that the geometry of the cable cannot change during installation or handling. This will maintain the electrical integrity of the cable.
Post extrusion chemical bonding is one method currently being used to make the cable. A chemical or solvent is applied to the surface of each individually insulated conductor such that, when they are brought into contact with each other and a catalyst is applied, the two separately insulated conductors are fused together. The product of this process is a cable of two insulated conductors joined along an axially extending groove and having desirable electrical properties. This approach offers limited processing speeds which are caused by an additional chemical or solvent application step, and a limited control of bonding characteristics because it is limited to the bond characteristics of the applied chemical or solvent. There also are limited material choices. Many thermoplastics have a very high resistance to some chemicals and solvents, which makes adhesion very difficult or impossible using these thermoplastics.
Another method currently used to negate the problem is parallel extrusion. In this process the two conductors are insulated by extruding the insulation onto the two conductors simultaneously, through the same head and tooling, while they are kept in close proximity to one another, such that the electrical properties of each individual conductor are maintained. The product of this process is a cable of two insulated conductors joined along an axially extending groove and having desirable electrical properties. This approach also offers limited processing speeds because of the nature of the extruder head tools used. It has a limited concentricity control because there is no way to adjust for normal tool wear and pressure variations in the extrudate. It has limited color coding capabilities because using one unmanifolded head limits the number of colors possible.
SUMMARY OF THE INVENTION
The present invention produces a cable of two insulated conductors joined along an axially extending groove and having desirable electrical properties with faster processing speeds, increased concentricity, increased control of bonding characteristics, increased color coding capabilities and increased material choices over the prior art. The present invention is directed to a method and apparatus for producing a pair of individually insulated wires joined by thermal bonding means.
The cable of the present invention includes separate metallic conductors, such as copper, spaced an equal distance from each other in the same plane. Each conductor is concentrically surrounded by an insulating material, such as a thermoplastic elastomer, and the conductors are joined along an axially extending groove such that the geometry of the cable cannot change during further processing and handling, thereby maintaining the electrical integrity of the cable.
In the method of making such a cable, at least two moving electrical conductors are provided in a spaced relationship to one another. The conductors are moved through an extruder means where each is independently coated with a heated thermoplastic electrical insulation material. The independently insulated conductors are kept in a spaced relationship for a period of time to allow the heated insulation on each conductor to set independent of the other conductor. After they are set, the conductors are then brought into touching contact with each other, whereby they are fused and joined by the heated thermoplastic insulating materials surrounding each conductor. The fused conductors are cooled by a cooling means and taken up as a single electrical cable that has been thermally bonded.
In a preferred embodiment of the method, a tension means is applied to uninsulated conductors before they enter the extruder means which equalizes and maintains the tension in the conductors, insuring equal tension on all conductors throughout the system. In the extruder means each conductor is coated independently through separate extruder heads and tooling, or by a single manifolded extruder head with multiple tooling, with a heated thermoplastic electrical insulation, such that the concentricity of the conductor with respect to the surrounding thermoplastic insulation is maintained. The independently coated conductors are brought into touching contact after the thermoplastic coating has set by passing the conductors to a pair of cooled, grooved pinch rolls, by which the coated conductors are joined and fused. The newly joined cable is then cooled by an air and/or liquid quench bath means.
The apparatus of the present invention includes means for providing a first and a second moving uninsulated conductor. The apparatus also includes a tension means for receiving and exiting each conductor and creating equal tension on each conductor as it exits the tension means. An extruder means is included for receiving the conductors from the tension means, the extruder means coating the conductors independently with heated thermoplastic insulation material and in a spaced-apart relationship while maintaining the concentricity of each conductor with respect to the surrounding thermoplastic insulation. The apparatus further comprises means for moving the heated thermoplastic insulated conductors together so as to touch the heated thermoplastic material of each conductor together and join them. The apparatus also includes means cooling the joined thermoplastic insulated conductors.
The present invention for producing a pair of individually insulated wires which are joined by thermal bonding provides significant advantages over the prior art. In particular, the present method allows for increased production and efficiency due to a decrease in the number of steps. There is no chemical or solvent application step. The speed of the system is increased due to the lack of single tooling in the head(s). The method of the present invention offers greater control of concentricity due to an ability to account and adjust for normal tool wear and pressure variations in the extrudate. The present method involves greater control of bonding characteristics due to the lack of solvents. The bond characteristics are set by the amount of tack in each conductor and the pressure supplied to the individual insulated conductors by the pinch rolls and not by the characteristics of a chemical or solvent applied. It is for this
Harden David R.
Harden Scott W.
Ball Michael W.
Cable Design Technologies, Inc.
Paul A. Beck & Associates
Tolin Michael A.
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