GB2112218A - Insulating ends of electrical conductors - Google Patents

Abstract

An electrical conductor 1 is an insulating tube 2 is further insulated by forming at least one groove 12 around tube 2 adjacent the end of conductor 1 and then molding a body 16 of cohesively incompatible insulating material around the grooved part of the tube to form a corresponding ridge 20. This ridge creates a tortuous arcing path and also inhibits the displacement or withdrawal of the insulated conductor from the body 16. The end 1a of conductor 1 may be soldered to another electrical conductor 14, so that the joint is encapsulated by body 16. <IMAGE>

Description

SPECIFICATION Jacketted electrical conductor terminal end and method of making same This invention pertains to insulating the terminal end of an electrical conductor wire that is already insulated with the usual insulating tube around it. The terminal end of the conductor wire may or may not have a component such as an electrical terminal or connector soldered to it, but in either case, the purpose of adding an insulative jacket is to enclose the exposed terminal end or component of the insulated electrical conductor wire.

Molding an insulative jacket around the terminal end of an already insulated electrical conductor wire is old in industry. In the past, the insulating tubes around electrical conductor wires have been made with thermoplastic material, which is to say matter that becomes plastic on being heated, thermoplastic material being a resin that can be melted by heat and then cooled, with the process being able to be repeated any number of times without appreciable change in properties, as is exemplified by cellulose acetate, vinyl resins, polystyrenes and acrylic resins.

Recently, thermoplastic insulating tubes around electrical conductor wires have been replaced with insulating tubes made of thermosetting compositions, as when it is desirable that the insulating tube not be prone to softening by reheating, a thermosetting composition being matter in which a chemical reaction takes place while it is being molded under heat and pressure resulting in an entire change of appearance, chemical and physical properties, and with the end product being resistent to further applications of heat. Some examples of thermosetting compositions are phenolics, urea resins and irradiated polyhalocarbon as sold by ITT Supernant Division of Clinton, Massachusetts.

A usual problem with thermoset material, such as irradiated polyhalocarbon for the insulating tube around an electrical conductor wire, however, is that it is cohesively incompatible with thermoplastic insulating material such as polyethylene or polypropylene that is used to form an insulative jacket. Consequently, a poor seal is formed between the insulative jacket and the conductor insulation, leaving no appreciable grip on the wire insulation to hold against twisting, displacement and axial withdrawal from within the insulative jacket.

Furthermore, upon injection into a mold, thermoplastic material hardens to form a thin outer skin at that point where it is next to the cold mold, but where the thermoplastic material is least cooled, nearest the conductor, the thermoplastic material remains fluid and tends to shrink as it cools further. In order to compensate for the shrinking, air is sucked in along the wire insulation thereby forming air pockets on the straight path along the insulation inside the jacket from the atmosphere to the terminal end of the wire, precisely at the place where such air pockets are not desired because air pockets reduce the breakdown voltage rating of the path below that of the insulating jacket.

It is an object of the present invention to provide a seal for a jacketted conductor with secure encapsulation of the terminal end of the conductor even by a cohesively incompatible insulative body.

It is another object of the present invention to provide an insulative seal that will increase the tortuous leakage or arcing path where air pockets previously decreased the path.

According to the invention a doubly insulated and electrically conductive article comprises an elongate conductor with a terminal end, an insulating tube around the conductor, the tube having at least one groove around it adjacent the end of the conductor, and an insulative body molded closely around the insulation tube, the body having a ridge extending into the groove in the tube, thereby to seal and secure the conductor to the insulative body.

Also, according to the invention, a method of attaching a body on a conductor enclosed in a tube of insulation that is cohesively incompatible with said body comprises forming at least one annular groove around the insulation tube, and molding a body of insulative material on the grooved part of the insulation so that the insulative material forms a ridge extending into said groove thereby to define a tortuous conductive path along the exterior or of the insulation tube and inhibit axial withdrawal of the conductor and insulation from the body.

The invention may be understood more readily and various other features of the invention may become apparent from consideration of the following description in conjunction with the accompanying drawings, wherein: Figure 1 is a side elevation of an insulated electrical conductor insulation; Figure 2 is an end view of a jig for grooving the conductor insulation; Figure 3 is a side view of the jig; Figure 4 is a side elevation of the conductor grooved and attached to a component; Figure 5 is a plan view of the conductor in a mold shown in cross section; and Figure 6 is a cross sectional view of the encapsulated conductor according to the invention.

Figure 1 shows an elongate insulated electrical conductor 3 comprising an electrical conductor wire 1, a conventional tube of insulating material 2 shown in partial cross section enveloping the wire 1, and an uninsulated terminal end 1 a of the wire 1. The tube of insulating material 2 is made of a thermosetting composition such as the aforementioned irradiated polyhalocarbon sold by ITT Supernant Division of Clinton, Massachusetts.

Furthermore, said thermosetting insulating material 2 is cohesively incompatible with thermoplastic material such as that used to form an encapsulating insulative jacket 1 9 as shown in Figure 6.

In Figures 2 and 3 a jig for grooving the wire insulation, a V-trough 4 having a stop wall 6 and a V-bottom 4a is shown holding the insulated electrical conductor wire 3 in position for having tube 2 grooved by abrasive discs 7 rotated on a shaft 8 driven by a motor M. The stop wall 6 has a slot 6a which allows the uninsulated terminal end 1 a of insulated wire 3 to extend through unobstructed as the end of the insulating tube 2 butts up against the inner surface of the stop wall 6. Just above and in rotational engagement with the insulated conductor wire 3 is a holddown roll 9 that is attached to a swinging arm assembly 11.

The hold-down roll 9 presses the insulation tube 2 against the V-bottom 4a as the abrasive discs 7 extend up through an opening 5 shown in Figure 3 and cut grooves in the insulation tube 2.

In Figure 3, the arrow R shows the rotation of the insulated wire 3 in relation to the V-trough 4 and the swinging arm assembly 11 when the insulating tube 2 is cut by the rotating abrasive discs 7 so as to form grooves 12 as shown in Figure 4. In Figure 4 the elongate electrical conductor wire 1 enveloped by the grooved insulating tube 2 has 3600 annular grooves 12 adjacent the uninsulated terminal end 1 0. Two or more 3600 annular grooves completely around the conductor insulating tube 2 are preferred, if not necessary. In any case, when two or more equally spaced grooves are formed, a square walled annular land 10 is created between each adjacent pair of grooves.The grooves 12 shown in Figure 4 are square walled, that is, their radial walls 13 are parallel to each other and perpendicular to the wire 1 and the bottom of each groove is perpendicular to the walls.

Figure 5 shows the insulated electrical conductor wire 3 and the soldered electrical conductor 14 placed within a mold 1 6 having an encapsulant entrance 17. In Figures 4 and 5 the terminal end 1 a of the wire 1 is soldered to an electrical connector 14 although according to the invention the terminal end 1 a may be unconnected. When a molten thermoplastic encapsulant (not shown) such as polyethylene, polypropylene or nylon is injected into the mold 1 6 via the encapsulant entrance 1 7 the encapsulant will flow into the grooves and into an insulative jacket forming space 1 8 to form an encapsulating insulative jacket 19, shown in Figure 6, having annular ridges 20 formed in the grooves 12 of the insulation 2.As the molten thermoplastic encapsulant (not shown) cools down and forms the encapsulating insulative jacket 19, linear shrinkage of said insulative jacket 19 occurs along the insulating tube 2 within the mold 16 causing the adjacent annular ridges 20 of the insulative jacket 1 9 to pinch or grip the intermediate lands 10 shown in Figure 6 and tighten the seal between the jacket 1 9 and the insulation 2. The pinching annular ridges 20 not only increase the tightness of the seal between the insulative jacket 19 and the insulating tube 2 but prevent relative rotation of the electrical conductor 14 and the insulation 2 which would twist and break the wire 1.Moreover, the extension of the jacket ridges 20 into the annular grooves 12 mechanically prevents withdrawal of the insulating tube 2 from the insulative jacket 1 9 shown in Figure 6 despite the cohesive incompatibility between the thermoplastic material comprising the jacket ridges 20 and the thermosetting material comprising the insulating tube 2.Previously, when a molten thermoplastic encapsulant cooled down to form a ridgeless insulative jacket air would be sucked or drawn in from outside the mold being used as the jacket material shrunk, thereby to create undesirable air pockets between the insulative jacket and a grooveless insulating tube. Presentiy, however, and according to the invention, the combined structure of the annular jacket ridges 20 fully lodged in the annular grooves 12 seals out the air previously drawn in and provides a tortuous path between the insulative jacket 1 9 and the insulating tube 2 that is much longer than the previous straight path where air pockets would decrease the insulative effect of the path and increase the likelihood of high voltage leakage or arcing.

In laboratory tests on jacketted conductors wherein the insulative jackets were made of thermoplastics such as polypropylene, polyethylene or nylon and the electrical conductors were insulated with cohesively incompatible thermosetting material such as irradiated polyhalocarbon, both of the prior ungrooved type and conductors grooved according to the present invention, otherwise identical specimens of jacketted conductors were formed in the same mold, in the same molding run, with the same molding time and involving the same parts. For conductors with ungrooved insulation the breakdown voltage from the atmosphere to the wire end 1 a was 1 5-200 KvDC. For conductor insulation grooved according to the present invention the breakdown voltage was 50-60 KvDC (which was the limit of the power supply). The jacketted length of the conductor was 3/8 inch in both cases, but the breakdown voltage of the present conductor was over twice that of prior conductors.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

Claims (12)

Claims

1. An insulated electrically conductive article comprising: an elongate conductor with a terminal end; an insulating tube around the conductor, the tube having at least one groove around it adjacent the end of the conductor; and an insulative body molded closely around the insulation tube, the body having a ridge extending into said groove in the tube, thereby to seal and secure the conductor to the insulative body.

2. An article according to Claim 1 wherein the tube has two or more grooves defining a land between each pair of grooves.

3. An article according to Claim 2 wherein two ridges of the body pinch an intermediate land in order to inhibit the rotation and dislocation of the insulating tube relative to the body.

4. An article according to Claim 2 or 3, wherein the or each land has the same diameter as the insulating tube.

5. An article according to any one of Claims 1 to 4, wherein the or each groove has parallel walls extending radially of the tube.

6. An article according to any one of Claims 1 to 5, wherein the or each groove is 3600 in circumference.

7. An article according to any one of Claims 1 to 6, wherein the ridge extending into said groove is annular.

8. An article according to any one of Claims 1 to 7, wherein the insulative body and the insulating tube are cohesively incompatible.

9. An article according to Claim 8 wherein the insulating tube is made of thermosetting plastic material.

10. A method of attaching a body on a conductor enclosed in a tube of insulation which comprises: forming at least one annular groove around the insulation tube; and molding a body of insulative material on the grooved part of the insulation so that the insulative material forms a ridge extending into said groove thereby to define a tortuous conductive path along the exterior of the insulation tube and inhibit axial withdrawal of the conductor and insulation from the body.

11. A method substantially as hereinbefore described with reference to the accompanying drawings.

12. The product of Claim 10 or 11.

1 3. An article substantially as described with reference to Figure 6 of the accompanying drawings.