EP0070639B1

EP0070639B1 - Electrical crimp connection with anaerobic setting sealant

Info

Publication number: EP0070639B1
Application number: EP19820303481
Authority: EP
Inventors: Paul Eugene O'donnell; Michael Stephen Mamrick
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1981-07-20
Filing date: 1982-07-02
Publication date: 1986-02-26
Also published as: EP0070639A1; DE3269364D1; JPS5825090A; CA1189690A

Description

This invention relates generally to electrical connections and, more particularly, to an electrical crimp connection where a wire barrel is mechanically and electrically attached to a stranded wire conductor.
Electric terminals are commonly attached to the ends of electric cables by a crimp connection where an open U-shaped wire barrel of the terminal is crimped or deformed tightly around the exposed end of a stranded wire conductor of the cable. See for instance, US―A―3,032,602 granted to Samuel J. Farnell on May 1, 1962. This crimped wire barrel is both a mechanical and electrical connection of the terminal to the end of the stranded wire conductor. The terminals often have a second U-shaped barrel which is crimped around the cable insulation to enhance the mechanical connection.
Electrical terminals are commonly made of an oxidizable material, such as tin plated bronze and the stranded wire conductors are also commonly made of an oxidizable material such as copper. Consequently, the electrical crimp connection is subject to deterioration when exposed to an oxidizing environment because the electrical resistance increases due to oxides being formed at the interface between the crimped wire barrel and the stranded wire conductor. The useful life of the electrical crimp connection, therefore, depends among other things on the type of electrical circuitry involved and the environment to which the crimp connection is exposed.
A stable resistance of electrical crimp connections is particularly important in low voltage, low current applications such as electronic circuitry, and it is particularly challenging to achieve in harsh environments such as automobile engine compartments where electronic engine controls are becoming common.
A known way to stabilize the electrical resistance and thus improve the life of electrical crimp connections is to seal the electrical crimp connection by a solder reflow process. In this process, the exposed end of the stranded wire conductor is dipped in liquid solder which is allowed to solidify. The wire barrel of the terminal is then crimped tightly around the solder-coated end of the standard wire conductor. After the wire barrel is crimped, the crimp connection is then heated until the solder melts and flows to fill all the open spaces and voids inside the crimped wire barrel. The solder then cools and solidifies forming an air-tight seal for the interface between the crimped wire barrel and the stranded wire conductor.
The solder reflow process adequately stabilizes the electrical resistance of the electric crimp connection for use in electronic circuits. However, the solder reflow process is relatively expensive.
The object of this invention is to provide an electrical crimp connection which is stabilized by a method which is considerably cheaper and simpler than the solder reflow process.
US―A―2551 299 discloses a method of making an air-tight electrical crimp connection in which an open wire barrel is attached to a stranded wire conductor by means of crimping the open wire barrel around the stranded wire conductor after applying a polymeric material to one or more of the parts to be connected. The material to be used is a plastics material such as one of the known insulating plastics, and may be permanently plastic or may be convertible to a non-plastic material by heat or pressure.
A method of making an air-tight electrical crimp connection according to the present invention is characterised in that it includes the steps of applying an anaerobically-setting polymeric material, mainly composed of dimethacrylate ester, to a portion of the stranded wire conductor, crimping the open wire barrel around the portion of the stranded wire conductor so that the crimped wire barrel is mechanically connected to the portion of the stranded wire conductor and an electrical interface is produced inside the crimped wire barrel, while the anaerobically-setting polymeric material is retained inside the crimped wire barrel, said crimping operation producing a substantially air-free environment inside the crimped wire barrel whereby the anaerobically-setting polymeric material retained inside the crimped wire barrel polymerises and sets to provide an air-tight seal for the electrical interface.
A primary feature of the invention is the use of an anaerobically-setting polymeric material which forms an air-tight seal for the interface between the crimped wire barrel and the stranded wire conductor in an electrical crimp connection.
Another feature of the invention is the advantageous use of the air exclusion produced by the crimping process to polymerise and set the anaerobically-setting polymeric material which eliminates critical timing and greatly simplifies the processing of the electrical crimp connection in comparison to the solder reflow process.
Yet another feature of the invention is that the anaerobically-setting polymeric material removes native oxides on the wire barrel and the stranded wire conductor during the crimping process thus reducing the electrical resistance of the electrical crimp connection.
Yet another feature of the invention is that the anaerobically-setting polymeric material is a tenacious adhesive which improves the mechanical connection of the crimped wire barrel to the stranded wire conductor.
Still yet another feature of the invention is that the wire barrel may be slotted to lower the electrical resistance of the electrical crimp connection employing the anaerobically-setting polymeric material.
Other objects and features of the invention will become apparent to those skilled in the art as the disclosure is made in the following detailed description of a preferred embodiment of the invention as illustrated in the accompanying sheets of drawings in which:

Figure 1 is a perspective view of an electric cable and an apparatus for applying an anaerobically-setting polymeric material to an exposed end of the stranded wire conductor of the electric cable.
Figure 2 is a top view of a terminal having a slotted open wire barrel for crimping around the end of the stranded wire conductor after the anaerobically-setting polymeric material has been applied thereto.
Figure 3 is a side view of the terminal shown in Figure 1.
Figure 4 is a section taken substantially along the line 4-4 of Figure 2 and looking in the direction of the arrows.
Figure 5 is a perspective view of the terminal shown in Figures 2, 3 and 4 and an electric cable attached to each other by an electrical crimp connection according to the present invention.
Figure 6 is a transverse section through the crimped wire barrel taken substantially along the line 6-6 of Figure 5 and looking in the direction of the arrows.

Referring now to the drawing, Figure 1 shows an electric cable 12 comprising a stranded wire conductor 14 inside an insulation jacket 16. A length of the insulation jacket 16 has been stripped from the cable 12 to expose an end portion of the stranded wire conductor 14, which in the example illustrated, consists of seven substantially parallel copper wire strands 18.
Figure 1 also shows an apparatus for applying liquid material to the exposed end portion of the stranded wire conductor 14. The apparatus comprises a sponge pad 20 which is located in a shallow reservoir 22 by four corner braces 23. The bottom portion of the sponge pad 20 lies in liquid material 24 contained in the shallow reservoir and the sponge pad 20 is filled with this liquid material 24 by a wicking actio. The apparatus also includes an air cylinder which moves a ram plate 25 which presses the exposed end portion of the conductor 14 into the sponge pad 20 to apply the liquid material 24.
We have discovered that Loctite^@ AV, which is a non-conducting, anaerobically setting, polymeric material coposed mainly of a dimethacrylate ester, is an excellent material for stabilising the resistance of an electrical crimp connection particularly when a stranded copper wire conductor and tin plate bronze terminal are involved. Loctite^s AV is manufactured and marketed under Product Catalogue Number 87 by Loctite Corporation founded in 1954 which produces anaerobic polymeric materials of various formulations for use as adhesives and/or sealants.
The Loctite® AV, Product Catalogue Number 87, is a red liquid of mild odour. It has low solubility in water, a boiling point of approximately 300° F (149° C) and a specific gravity of 1.068 @ 80° F (26.7° C). The chemical composition comprises approximately 84% Dimethacrylate Ester, 6% Resin, 2.6% Tertiary Amine and 7% Catalyst.
The material is also believed to be described in the U.S. Patent 2,628,178 granted to Robert E. Burnett and Birger W. Nordlander of February 10, 1953.
Since Loctite® AV is anaerobic and does not set or polymerize until the material is in an oxygen or air-free environment, the liquid material 24 can be applied to the end portion of the conductor 14 without concern about premature solidification simply by keeping the electric cables 12 which have been treated with the Loctite^@ AV in a normal environment. Moreover, the exclusion of oxygen or air which is required for solidifying the Loctite^O AV is initiated at precisely the right time in the process as will hereinafter more fully appear.
As indicated above, Loctite^@ AV is a nonconductive material. We have not only discovered its surprising utility as a sealant for electrical crimp connections but we have also discovered that the electrical properties of the crimp connection can be enhanced by a tin plated bronze terminal 30, shown in Figures 2, 3 and 4, which has a unique wire barrel.
The terminal 30 has a female contact portion 32 at one end and a cable attachment portion 34 at the other end and generally conforms to the terminal which is disclosed in U.S. Patent 3,267,410 (Baer et al) and U.S. Patent 3,310,772 (Kirk).
The details of the contact portion 32 are not relevant to the present invention and, consequently, the contact portion 32 need not be described in detail.
The cable attachment portion 34 comprises an open wire barrel 36 and larger open insulation barrel 38. The open wire barrel 36 is generally U-shaped as shown in Figure 4 and the outer ends of the barrel are coined at 40 in accordance with standard practice. The wire barrel 36, however, is unique in that it has two slots 42 in each wing 44 of the open wire barrel 36 so that each wing 44 of the open wire barrel 36 has three narrow fingers 45. The fingers 45 deform independently of each other in the crimping process and each produces a tighter crimp while minimizing the danger of cutting wire strands 18.
In an actual example, a terminal 30 was made from tin plated bronze stock which was 0.016 inches (0.41 mm) thick. The slots 42 were about 0.020 inches (0.51 mm) wide and extended down from the coined ends of the open wire barrel 36 for about 0.040 inches (1.02 mm) so that the fingers 45 were each about 0.034 inches (0.86 mm) wide and 0.040 inches (1.02 mm) long. The insulation barrel 38 is conventional in design.
The terminal 30 is attached to the electric cable 12 with crimping dies generally of the form shown in the aforementioned Farnell patent so that the wire barrel 36 is tightly crimped around the end portion of the stranded wire conductor 14 (which has the Loctite^@ AV applied thereto) and the insulation barrel is tightly crimped around the insulation jacket 16 as shown in Figure 5.
The appearance of a typical transversely cross- sectioned electrical crimp connection made in accordance with our invention is shown in Figure 6. This schematic drawing made from a scanning electron micrograph correctly depicts the dimension of the tin plated bronze wire barrel 36 and a seven strand copper wire conductor 14. The hexagonal shape of the copper wire strands 18 and the predominance of boundaries intersecting at approximately 60° indicates that the copper wire strands 18 are under a high compressive stress while the areas designated 36d indicate that the tin plating on the interior wall of the crimped wire barrel 36 buckles severely.
The electrical crimp connections were also analyzed with an electron microprobe. The resulting micrographs of boundaries between the copper strands 18 (not shown) reveal a high concentration of carbon between adjacent copper strands which indicates that the Loctite® AV was not expelled by the crimping process.
The electrical properties of the electrical crimp connection, in this instance, are dominated by the interface between the copper wire strands 18 and the tin plating of the crimped wire barrel 36. Other micrographs (not shown) indicate that the Loctite° AV nearly forms a complete boundary layer between the tin plating and stranded copper wire conductor 14. The Loctite® AV thus reduces the effective contact area of the electrical crimp connection.
Cross-sections taken near the ends of the crimped wire barrel 36 show that the Loctite® AV fills the voids between the copper wire strands 18. This provides an effective seal protecting the interior surfaces from oxidation by air or other ambient gases.
The role of Loctite^* AV in the electrical crimp connection is believed to be as follows. Upon application, the Loctite® AV partially cleans the native oxide from the copper wire strands 18 and the wire barrel 36. This cleaning action may be facilitated by the temperature rise as the crimping process is initiated. As the crimp is formed, Loctite^a AV remains inside the wire barrel 36. The Loctite® AV is tenacious and reduces the contact area between the crimped wire barrel 36 and the copper wire strands 18. The slots 42 in the wire barrel 36 aid in establishing electrical contact by creating pressure gradients during the crimping process which encourage the flow of the unset Loctite° AV. The tin plating or layer buckles and increases the area of the interface between the crimped wire barrel 36 and the copper wire strands 18. It is also likely that the electrical contact between the crimped wire barrel 36 and the copper wire strands 18 can be enhanced by dispersing conductive particles in the Loctite^@ AV.
The crimping process also excludes air from inside the crimped wire barrel 36 so that the Loctite^* AV inside the tightly crimped wire barrel 36 is in an essentially oxygen or air-free environment. Consequently, the Loctite° AV starts to set up or polymerise when the wire barrel 36 is crimped.
When the Loctite^* AV is cured and forms a solid, it provides an air-tight seal for the interface between the crimped wire barrel 36 and the wire strands 18. This air-tight seal, formed by the Loctite® AV, is chemically inert and prevents oxidation of the contact interface. Consequently, the electrical resistance of crimp connection remains relatively constant over a prolonged life. The Loctite^@ AV is also a tenacious adhesive, so that it also counters the tendency of the crimped wire barrel 36 to relax. Thus, the cured Loctite® AV also enhances the mechanical connection between the crimped wire barrel 36 and the end portion of the stranded wire conductor 14.
The cure time of the Loctite® AV is two to six hours and the cure time is enhanced in this particular instance because the wire strands are copper. The cure time can also be substantially reduced to a matter of minutes by the use of a Loquic primer which is also marketed by the Loctite Corporation. However, since the terminals 30 are normally attached to the cables 12 several hours before the terminals 30 and cables 12 are used, a fast cure time is usually not necessary. Consequently, the use of Loquic@ or another accelerator is not necessary in most instances.

Claims

1. A method of making an air-tight electrical crimp connection in which an open wire barrel (36) is attached to a stranded wire conductor (14) by means of crimping the open wire barrel (36) around the stranded wire conductor (14) after applying an acrylic polymer to one or both parts to be connected characterised in that the method comprises the steps of:

applying an anaerobically-setting polymeric material (24), mainly composed of dimethacrylate ester, to a portion of the stranded wire conductor (14),

crimping the open wire barrel (36) around the portion of the stranded wire conductor (14) so that the crimped wire barrel is mechanically connected to the portion of the stranded wire conductor and an electrical interface is produced inside the crimped wire barrel, while the anaerobically-setting polymeric material (24) is retained inside the crimped wire barrel (36),

said crimping operation producing a substantially air-free environment inside the crimped wire barrel whereby the anaerobically-setting polymeric material (24) retained inside the crimped wire barrel Polymerises and sets to provide an air-tight seal for the electrical interface.

2. A method of making an electrical crimp connection according to claim 1, characterised in that the anaerobically-setting polymeric material (24) is non-conducting.

3. A method of making an electrical crimp connection according to any one of the preceding claims, characterised in that a metallic, open wire barrel (36) is provided which has a tin layer on an interior surface, and during the crimping step the tin layer (36d) is buckled to produce the electrical interface inside the crimped wire barrel.

4. A method of making an electrical crimp connection according to claim 3, characterised in that the stranded wire conductor (14) is made of copper.

5. A method of making an electrical crimp - connection according to any one of the preceding claims, characterised in that the open wire barrel (36) has a tin layer on an interior surface and slots (42) forming a plurality of narrow fingers in each wing of the open wire barrel.