Submersible anode made of a resin matrix with a conductive powder supported therein

An anode for a cathodic protection system comprises a base portion or support structure which is shaped to receive a conductive element, or insert, within a cavity of the support structure. The conductive element is made of a polymer material, such as vinyl ester, with a conductive filler, such as graphite powder. The base is attachable to a marine vessel or other submersible component that is being protected by a cathodic protection system. The anode allows the use of a relatively inexpensive resin material with a graphite filler in place of a much more expensive platinum coated titanium element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to anode used in a marine environment and, more particularly, to an anode which is made of a polymer material, such as vinyl ester, that is impregnated with conductive particles, such as graphite powder.

2. Description of the Prior Art

It is well known that submersible components can suffer corrosion degradation as a result of galvanic currents between dissimilar metals. This type of galvanic corrosion can severely damage marine components, such as drive units. As an example, since the propeller of a marine propulsion system and the submerged housing of that same system are often made of dissimilar metals, a galvanic reaction can easily occur. This can result in severe damage to the marine drive unit.

U.S. Pat. No. 4,322,633, which issued to Staerzl on Mar. 30, 1982, discloses a marine cathodic protection system. The system maintains a submerged portion of a marine drive unit at a selected potential to reduce or eliminate corrosion thereto. An anode is energized to maintain the drive unit at a preselected constant potential in response to the sensed potential at a closely located reference electrode during normal operations. Excessive current to the anode is sensed to provide a maximum current limitation. An integrated circuit employs a highly regulated voltage source to establish precise control of the anode energization.

U.S. Pat. No. 4,528,460, which issued to Staerzl on Jul. 9, 1985, discloses a cathodic protection controller. A control system for cathodically protecting an outboard drive unit from corrosion includes an anode and a reference electrode mounted on the drive unit. Current supplied to the anode is controlled by a transistor, which in turn is controlled by an amplifier. The amplifier is biased to maintain a relatively constant potential on the drive unit when operated in either fresh or salt water.

U.S. Pat. No. 4,492,877, which issued to Staerzl on Jan. 8, 1985, discloses an electrode apparatus for cathodic protection. The apparatus is provided for mounting an anode and reference electrode of a cathodic protection system on an outboard drive unit. The apparatus includes an insulating housing on which the anode and reference electrode are mounted and a copper shield mounted between the anode and the electrode to allow them to be mounted in close proximity to each other. The shield is electrically connected to the device to be protected and serves to match the electrical field potential at the reference electrode to that of a point on the outboard drive unit remote from the housing.

U.S. Pat. No. 6,183,625, which issued to Staerzl on Feb. 6, 2001, discloses a marine galvanic protection monitor. The system uses to annunciators, such as light emitting diodes, to alert a boat operator of the current status of the boat's galvanic protection system. A reference electrode is used to monitor the voltage potential at a location in the water and near the component to be protected. The voltage potential of the electrode is compared to upper and lower limits to determine if the actual sensed voltage potential is above the lower limit and below the upper limit. The two annunciator lights are used to inform the operator if the protection is proper or if the components to be protected is either being over protected or under protected.

U.S. Pat. No. 3,953,742, which issued to Anderson et al on Apr. 27, 1976, discloses a cathodic protection monitoring apparatus for a marine propulsion device. The system monitor is coupled to an impressed current cathodic protection circuit used for corrosion protection circuit used for corrosion protection of a submerged marine drive. The cathodic protection circuit includes one or more anodes and a reference electrode mounted below the water line and connected to an automatic controller for supplying an anode current which is regulated in order to maintain a predetermined reference potential on the protected structure. A switch selectively connects a light emitting diode lamp or other light source between the controller output and ground so that the controller may, when tested, be used to operate the light source in order to confirm that power is available to the anode.

U.S. Pat. No. 6,251,308, which issued to Butler on Jun. 26, 2001, describes a highly conductive molding compound and fuel cell bipolar plates comprising the compounds. A conductive polymer is disclosed which is suitable for use in applications which require corrosion resistance including resistance to corrosion when subjected to acidic flow at temperatures ranging from −40 degrees Fahrenheit to 140 degrees Fahrenheit and which can be molded into highly intricate and thin specimens which exhibit consistent conductivity, sufficient strength and flexibility, and appropriate surface characteristics. In particular the invention involves molding unsaturated prepolymer resin composition which have high loadings of conductive fillers. Further to enable the necessary characteristics, the composition includes rheological modifies such as Group II oxides and hydroxides; carbodiamides; aziridines; polyisocyanates; polytetrafluroetheryle (PTFE); perfluoropolyether (PFPE), and polyethylene. Ostensibly, these modifiers act to alter the apparent molecular weight and three dimensional prepolymer network structures correcting rheological deficiencies which otherwise lead to excessive resin particulate separation during the molding process and large variances in bulk conductivity across the plate surface. The composition is disclosed for use in electrochemical cells, such as fuel cells.

U.S. Pat. No. 6,365,069, which issued to Butler et al on Apr. 2, 2002, describes a process of injection molding highly conductive molding compounds and an apparatus for this process. A technique and apparatus are disclosed for injection molding highly filled conductive resign compositions. These compositions include one or more unsaturated polyester and vinyl ester resin; a copolymer having a terminal ethylene group; and at least about 50 weight percent of an inorganic particulate conductive filler, an initiator, and a rheological modifier to prevent phase separation between the resin and the conductive filler during molding. The method allows these compositions to be molded into highly intricate and thin electrically and thermally conductive specimens without significant post process machining. The method involves the use of an injection molding apparatus that has a hopper with an auger having a vertical component in its positioning to feed into the feed throat of an injection molding machine which has a phenolic screw that has been modified to have a constant inner diameter and a constant flight depth.

The material described in U.S. Pat. Nos. 6,251,308 and 6,365,069 have been used in certain devices, such as fuel cells. The high electrical conductivity of the material and its resistance to corrosive elements allows it to be used as a conductive material in certain environments that would otherwise attack many other types of material. The material is available in commercial quantities from Quantum Composites, Inc. which is a subsidiary of Premix, Inc. One such material is referred to as “Pemtex”.

Marine anodes have been made from expensive materials, such as platinum and titanium, in order to provide a useful life when they are submerged for use as an anode in a cathodic protection system. It would be useful if a marine anode could be made of a less expensive material that can withstand rough treatment in a corrosive environment.

SUMMARY OF THE INVENTION

A submersible anode, made in accordance with a preferred embodiment of the present invention, comprises a support structure with a conductive element comprising a polymer-based matrix material and conductive particles supported within the matrix material. It further comprises a conductor connected in electrical communication with a conductive element, the conductor being connectable to an electrical power supply. The conductive element comprises a matrix of vinyl ester with graphite particles disposed within the matrix in a particularly preferred embodiment of the present invention. The support structure is attachable to a component of a marine vessel and shaped to contain the conductive element. The component of the marine vessel, in a preferred embodiment, is the transom of the marine vessel. The support structure is a polymer in a preferred embodiment and, in certain embodiments, the present invention further comprises a sealing material disposed proximate the conductive element to prevent moisture to from contacting the conductor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A system known to those skilled in the art as the MerCathode system is commercially available from Mercury Marine, a division of Brunswick Corporation. The MerCathode system provides automatic protection against galvanic corrosion. It is a solid state device that operates with a marine vessel's 12-volt battery and provides protection by impressing a reverse blocking current that stops the destructive flow of galvanic currents. It is particularly useful on marine vessels that have stainless steel propellers or other submerged stainless steel hardware. One important element of the MerCathode system, or any other impressed current cathodic protection system, is the anode. In order to increase the useful life of the anode, it is typically manufactured with a titanium element that is coated with platinum. This material is costly and easily damaged by abrasion.

FIG. 1shows an anode that is well known to those skilled in the art and is typically incorporated as part of the MerCathode system. It has a plastic base10which is shaped to support a platinum-coated titanium insert12. Two holes,16are provided to allow the base10to be attached to a transom of a marine vessel, or other component, so that it can hold the insert12at a preselected position, relative to a device to be protected, under the surface of water in which the marine vessel is operated.

FIG. 2is a section view of the device shown inFIG. 1. As can be seen, the holes16are formed through the base10. In addition, the base10is shaped to have a recess20formed in it which is sized to receive the insert12. InFIG. 2, the insert12shown inFIG. 1is not present. An opening24is formed through the base10to allow an electrical conductor to pass therethrough, as will be described in greater detail below.

FIG. 3is a section view ofFIG. 1. The insert12is shown disposed within the recess20of the base10. An electrical conductor30, such as a wire, extends through the opening24. The electrical conductor is shown with an insulative sheath36surrounding it, except for an end portion of the conductor30itself which is physically and electrically connected to a portion38of the insert12. An encapsulant39is disposed around the sheath36of the electrical conductor30and in the space of the cavity20below the insert12.

The anode shown inFIGS. 1–3works in a satisfactory manner to provide an important component that is necessary to the galvanic protection system by impressing a current in the water near a device to be protected, such as a stern drive unit. However, in order to provide an anode having a long useful life, expensive components are normally required. The insert12is typically made of a titanium element that is coated with platinum. It would therefore be significantly beneficial if the reliability and long life of a MerCathode anode, such as that illustrated inFIGS. 1–3, could be provided at less expense than is required when a platinum-coated titanium element12is used.

FIG. 4shows an anode40made in conjunction with a preferred embodiment of the present invention. The cavity20serves the basic purpose of the cavity described above in conjunction withFIGS. 1–3, although certain modifications are possible in a preferred embodiment of the present invention. An element42is made of a polymer matrix having an electrically conductive filler. This element42replaces the platinum-coated titanium element12described above. The element42is a conductive plastic material that is highly resistant to corrosion and chemical attack while also being highly conductive, both electrically and thermally. This material is generally similar to the material discussed in U.S. Pat. Nos. 6,251,308 and 6,365,069 described above.

With continued reference toFIG. 4, a contact element44is urged toward the underside46of the insert42by a spring48. An electrical conductor,30is connected in electrical communication with the contact element44. The cavity20below the insert42can be filled with encapsulant, such as the encapsulant39described above in conjunction withFIG. 3. This encapsulant inhibits the intrusion of water into the space under the insert42and in the region of the contact element44and spring48. In some embodiments of the present invention, a dam50can be provided to isolate the spring48and contact element44from the encapsulant which is inserted into the remaining portions of the cavity20. The electrical conductor30allows a power supply60to be connected in electrical communication with the contact element44and, in turn, with the insert42because of the intimate contact between the contact element44and the underside46of the insert42.

InFIG. 4, the base10is shown attached to a transom64of a marine vessel. It should be understood that although the transom64is shown in a generally horizontal position inFIG. 4, it is typically disposed in a near vertical configuration at the rear of a marine vessel.

With continued reference toFIG. 4, the present invention provides a support structure, such as the base10, and a conductive element, such as the insert42, that comprises a polymer matrix material with conductive particles supported within the polymer matrix material. The matrix material is typically a polymer such as vinyl ester and the conductive particles are typically a graphite filler or powder supported within the vinyl ester material. The present invention further comprises a conductor30that is connected in electrical communication with the conductive element42which allows the conductor30to be connected in electrical communication between a power supply60and the conductive element42. In the embodiment shown inFIG. 4, the contact element44provides the intimate electrical contact between the conductor30and the conductive element42.

As described above, the conductive element42comprises a matrix of vinyl ester with graphite particles disposed within the matrix. The support structure, or base10, is attachable to a component, such as the transom64, of a marine vessel. The support structure is made of polymer in a preferred embodiment of the present invention and the encapsulant which is disposed in the cavity20prevents moisture from contacting the conductor30within the space of the cavity20.

Although the present invention has been described to show a particular embodiment and illustrated with specific detail, it should be understood that alternative embodiments are also within its scope.