Abstract:
A cap for protecting an electrical terminal from corrosion having a base which is insertable upon the terminal, a tapered section designed to guide and surround a mate to the terminal as it is being connected, and a removable top which protects the terminal before connection. The tapered section deforms during the connection operation to surround the mating terminal and seal the connection from corroding species.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a cap which fits over one electrical terminal and which seals itself to a mating electrical terminal to inhibit corrosion. 
     2. Description of Related Art 
     The concept of an information highway is now developing into hardware which will provide wide bandwidth service to every home and office in the telephone loop plant. The location of this hardware places environmental burdens upon network interface units, particularly with respect to corrosion and its effect upon error free operation. These units, which interconnect the loop plant to interior circuitry must withstand wide temperature excursions and the effects of contamination and moisture. The contaminating species may be air-borne, such as corrosive gases, or they may be particulate contamination, which may become dissolved in water from rain or condensation. Temperature excursions which permit early morning condensation have been found to be particularly offensive because the amount of water is small and the concentration of contaminants is high. Dissolution of some of the contaminate material then forms an acid which corrodes electrical terminals. 
     Reducing cost is another factor to ensure the universal acceptance of wide-bandwidth systems, so inexpensive connectors have been developed which are intended for indoor use. These are commonly known as “F-type” connectors, and because of their low cost and wide availability; they have also been used in external applications, with unreliable results. 
     Attempts have been made to protect these connectors by covering them with a cap to exclude the environment, particularly during shipment and installation. The caps are removed upon installation, but corrosive gases and ionic contamination still seep through the threads of the F-type connector and corrode the center conductor. This corrosion layer increases the resistance of the conduction path and causes interference in video or data signals. 
     Accordingly, there is an increased need in the art for an inexpensive connector which provides reliable, error-free operation over a range of environmental conditions which are to be encountered in the loop plant or any corrosive environment. It would be particularly desirable to use the same inexpensive connector in both interior and exterior applications to minimize cost and inventory. Further, it is desirable to continue using a connector which is already in widespread use by protecting it with an inexpensive cap which will provide corrosion protection before installation and during extended use. In addition, there is a need to minimize the amount of material which is discarded when the connector is mated. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an electrical terminal which is protected from corrosive environments by a cap which seals elements which are sensitive to corrosion from gases or electrolytes. 
     In one embodiment of the invention, a base, tapered section, and top define a volume which is open at the base end. The inner dimension of the base is slightly smaller than the terminal it is intended to protect from corrosion. The base is forced part-way onto this terminal thereby creating an interference fit and seal. When the terminal is to be connected to its mate, the top is removed leaving the tapered section and base attached to the terminal. The mate is guided by the tapered section and forced into the base to create another interference fit and seal. The base, tapered section, and top are made from a polymer, typically polyethylene, and preferably a corrosion intercept reactive polymer. A scored section may be added between the tapered section and the top to ensure separation at that section. An extension section may also be added adjacent to the top to provide more space for the terminal during storage and shipment. The terminal and its mate may provide connection to a battery, an electronic circuit, or a radio frequency circuit. The terminal may be any shape, but more frequently it is rectangular or circular, and it may comprise single or multiple pins. 
     In another embodiment of the invention, one portion of a connector, either a plug or a receptacle, is capped with the apparatus described above, and they are provided together as an assembly. On installation, the top is removed and the mate is forced into the body to make the connection and create the seal against corrosion. 
     In still another embodiment of the invention, a polymer cap comprising an annular base, a tapered section, an extended section, and a top define a volume which is open at the base. The base of the cap is adapted to deform around the plug and receptacle of a radio frequency connector. 
     With this cap, the same inexpensive radio frequency connectors are capable of both indoor and outdoor use, minimizing cost and inventory. The cap provides corrosion protection to the connector in both the mated and unmated condition. The amount of discarded material is also limited to the top of the cap. 
    
    
     These and other features and advantages of the invention will be better understood with consideration of the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of one embodiment of the invention; 
     FIG. 2 is a cross sectional view of another embodiment of the invention; 
     FIG. 3 is a cross sectional view of still another embodiment of the invention; and 
     FIG. 4 is a cross sectional view of a mated connector pair protected by the invention. 
     The drawings are not to scale. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The distribution of wideband communications facilities to provide universal service to homes and offices in the telephone loop plant may be accomplished with coaxial or other cables which terminate in a network interface unit. Hardware exists which meets military specifications to resist environmental conditions, but to promote universal service and meet competition, this hardware must also be provided at relatively low cost while ensuring error-free operation. This invention is not limited to connectors adapted to radio frequency operation, because there is also a need to protect terminals in apparatus such as batteries from the effects of corrosion. 
     Referring now to FIG. 1, there is shown apparatus  5  which is one embodiment of the invention wherein a polymer base has a sidewall  12 , a first end  13 , and a second end  14 . The second end of the base supports a tapered section having a sidewall  20 , a first end  21 , and a second end  22 . The second end of the tapered section supports top  30 . The inner dimension of the base is selected to provide an interference fit around a terminal (not shown) which is to be protected from corrodant species, either gaseous or in dissolved ionic form. In the discussion which follows, the terminal may be rectangular or circular, it may be a single post or it may comprise a multiplicity of pins, it may be a plug or a receptacle, and it may be designed to transmit any signal from DC to radio frequency or microwave frequency. The terminal could therefore be a post of a battery, the connector to an electronic circuit, or a coaxial type connector to a microwave circuit. Typically, the base is an annulus, the tapered section is the frustum of a cone, and the top is circular. The base, tapered section, and the top define a volume which is open at the first end  13  of the base. The base may be selected from the class of any thermoset or thermoplastic materials. An example is polyethylene, and a preferred embodiment is a corrosion intercept reactive polymer. This material is described in U.S. Pat. No. 4,944,916 given to Franey, Jul. 31, 1990, the description of which is incorporated herein. The advantageous property of a corrosion intercept reactive polymer is that it neutralizes corrosive gases by chemical reaction between a sacrificial material in the polymer matrix and corrosive gases such as sulfur or chlorine based compounds. Accelerated tests have shown that a connector which would otherwise be corroded has an expected life of 20 years when protected by the cap. 
     To protect the terminal before installation and in shipment, apparatus  5  is pushed on to the terminal by placing first end  13  over the terminal. A force is required to slightly expand the inner dimension of the base and to slide it over the terminal. The thickness of sidewall  12  may range from 30 to 100 mils. The dimensions are selected to provide a secure interference fit over a particular terminal thereby protecting it from corrosive species. Apparatus  5  is forced on to the terminal until about half of the sidewall is in contact with the terminal. When a connection is to be made to the terminal, top  30  is torn away from second end  22  of the tapered section. The thickness of sidewall  20  of the tapered section is selected so that the break occurs at second end  22 , and the thickness may range from 10 to 40 mils, with a 25 mil thickness being typical. The thickness of the top may range from 50 to 100 mils. The mate to the terminal is then guided by the tapered section toward the base and forced into that portion of the base which is not in contact with the terminal. The mate also makes an interference fit with the base so that the base surrounds both the terminal and its mate and seals their connection from corroding species. A typical interference between the base and the side of the terminal being 5 to 10 mils for a 250 mil diameter terminal. 
     Referring now to FIG. 2, there is shown apparatus  6  in accordance with another embodiment of the invention comprising a base and top section whose elements numbered from 12 to 22 have been described above and are incorporated here. Second end  22  of the tapered section terminates at scored section  40 . In this section the thickness of the sidewall is reduced by 30% to 70% to ensure that separation of the tapered section from first end  51  of extension section  50  occurs at the scored section. Second end of the extension section supports top  30 . The operation and materials of apparatus  6  is similar to that of apparatus  5 . About half of the base is forced over the terminal and the mate is guided by the tapered section toward second end  14  of the base and forced down into the base in an interference fit. 
     Referring now to FIG. 3, there is shown capped connector assembly  7  comprising a cap whose elements numbered  12  through  52  have been described in the description of apparatus  6  and are incorporated here. Sidewall  12  of the base surrounds plug  60  which is shown as one component of a connector, in this figure it is shown as a coaxial connector, and the component protected by the cap may be either a plug or a receptacle. Element  60  could also be the terminal of a battery or a multipin connector leading to an electronic circuit. The cap is inserted over plug/receptacle  60  so that portion  15  of sidewall  12  does not contact plug/receptacle  60 . When the connection is to be made, top  30  and extension section  50  are removed from tapered section  20  at scored section  40 . The mate ( 91  in FIG. 4) to plug/receptacle  60  is then guided toward second end  14  by the tapered section and it is forced into the base so that portion  15  is expanded to fit around the mate, seal the connection, and protect it from corroding species. 
     Referring now to FIG. 4 there is shown by way of example a mated coaxial connector pair comprising plug  90  which is screwed into receptacle  91 . Surrounding both of these elements is body  12  which is expanded slightly to create an interference fit between itself and both the plug and receptacle. Corroding species, whether gaseous or ionic, are thereby prevented from reaching and attacking the center conductor and threaded portions of the connector. 
     The advantages of this structure are that inexpensive connectors which are already in wide use for indoor applications may be applied to outdoor hardware minimizing cost, inventory, and the amount of material discarded. 
     Changes and modifications in the specifically described embodiments can be carried out without departing from the scope of the invention. In particular, a plug may be used for a receptacle, and vice versa, a terminal may refer to a single pin terminal or to a multipin terminal, and all the aforementioned connectors may be designed to operate from direct current to microwave frequencies. In addition, the cap may be used to protect non-electrical connections such as bolts which are used in mechanical or-civil engineering applications.