Patent Application
20180282880
The invention generally pertains to structure components, and more particularly to a sacrificial collar that is placed on an underwater structural component of a sea vessel to protect against stray current or galvanic corrosion.
Two of the most significant problems that affect submerged components of a sea/water vessel are stray current corrosion and galvanic corrosion. Stray current corrosion is a serious destructive occurrence and results from a metal with an electrical current flowing into it submerged in water that is grounded, such as a lake, river or ocean. The current can leave the metal and flow through the water to ground. This will cause rapid deterioration of the metal at the point where the current leaves. Stray direct current is particularly destructive.
Galvanic corrosion (also called “dissimilar metal corrosion”) refers to corrosion damage induced when two dissimilar materials are coupled in a corrosive electrolyte. The corrosion occurs when two (or more) dissimilar metals are brought into electrical contact usually under water. When a galvanic couple forms, one of the metals in the couple becomes the anode and corrodes faster than it would by itself, while the other becomes the cathode and corrodes slower than it would alone. Either (or both) metal in the couple may or may not corrode by itself. When contact with a dissimilar metal is made, however, the self-corrosion rates will change. Corrosion of the anode will accelerate and corrosion of the cathode will decelerate or even stop.
The major cause for corrosion is a potential difference between the different materials. The bimetallic driving force was discovered in the late part of the eighteenth century by Luigi Galvani in a series of experiments with the exposed muscles and nerves of a frog that contracted when connected to a bimetallic conductor. The principle was later put into a practical application by Alessandro Volta who built in 1800, the first electrical cell, or battery, a series of metal disks of two kinds, separated by cardboard disks soaked with acid or salt solutions. This is the basis of all modern wet-cell batteries, and it was a tremendously important scientific discovery, because it was the first method found for the generation of a sustained electrical current.
One of the most prevalent problems associated with stray current or galvanic corrosion is the deterioration of submerged structural components on sea vessels. This is especially pronounced on components that are made of a soft metal, which will deteriorate more quickly than components made of a hard metal. In addition to the cost incurred to replace or fix damaged/destroyed components, there is also a significant safety risk that occurs when certain components are damaged/destroyed.
The corrosion potential of any metal is a voltage that can be measured by a reference electrode. Such measurements in water commonly are made with a silver/silver chloride reference electrode. The corrosion potential is a characteristic value for that metal, and it does matter if you have one metal component or 100, the corrosion potential stays the same.
There have been attempts to address the problem of stray current or galvanic corrosion. The most common solution is to add what is typically referred to as a sacrificial anode. The anodes are made of a metal that will attract electrolytes faster than a metal to which it is attached, thereby causing the anode to experience the destructive impact. While prior art sacrificial anodes are usually effective, many of the designs are not entirely practical and can be difficult to implement.
What is needed is a sacrificial anode that can be quickly and easily attached, and that will protect any structural component to which it is attached. Optimally, a sacrificial collar design, as disclosed herein, would be provided. A collar design would be easy to attach could be manufactured in a variety of shapes and sizes for use on many types of components both submerged in seawater and in other environments.
A search of the prior art did not disclose any literature or patents that read directly on the claims of the instant invention. However, the following U.S. patents are considered related:
The U.S. Pat. No. 3,024,183 discloses a method producing sacrificial or consumable zinc anodes for use in inhibiting corrosion by galvanic action, and sacrificial zinc anodes that are use for the protection of metal structures and equipment such as heat exchangers, pipe lines, ship hulls, storage tanks and the like. In some instances, anodes are made in the form of cast blocks or slabs, with steel inserts to provide electrical contact between the anode and the metal structure to be protected, and also to provide means for fastening the anode to the metal structure to be protected.
The U.S. Pat. No. 3,152,059 discloses a method of making sacrificial or consumable zinc anodes for use in inhibiting corrosion by galvanic action and sacrificial zinc anodes produced for the protection from corrosion of metal structures and equipment such as heat exchangers, pipe lines, ships' hulls, storage tanks and the like. Sacrificial or consumable anodes are made in the form of cast blocks or slabs with steel inserts to provide electrical contact between the anode and the metal structure to be protected and, also, to provide means for fastening the anode to the structure.
The U.S. Pat. No. 4,391,567 discloses a corrosion preventing device for mounting in seawater on an electrically conductive propeller shaft supporting a marine propeller composed of a metal having a first galvanic potential. The device includes an annular washer having a generally circular periphery, composed of a metal having a second galvanic potential not greater than the first galvanic potential. The device further includes a generally toroidal anode having a circular periphery concentric with the axis, composed of a metal having a third galvanic potential greater than the first galvanic potential. The galvanic cell formed by the washer cathode and the toroidal anode maintains the propeller at a relative cathodic potential, thereby preventing the corrosion thereof in the seawater.
For background purposes and indicative of the art to which the invention relates, reference may be made to the following remaining patents found in the patent search.
In its basic design the sacrificial collar is comprised of a first section having a half-circle cavity and a matching second section having a half-circle cavity. The collar is preferably square or rectangular but can be any geometric shape, and is made of metal such as zinc, aluminum or magnesium, with zinc currently preferred. The first section and the second section are secured together around a structural component, with the component located within the cavities on the two sections. Typically, the structural component will be located on an environment where galvanic corrosion occurs such as within seawater. Therefore, the sacrificial collar is especially effective for use on sea vessel components that are submerged in seawater. Although this is the primary use, the sacrificial collar can also be utilized in other environments where corrosion can occur.
Once the two sections are secured together and onto a structural component, the sacrificial collar will attract the stray current or galvanic corrosion, instead of the stray current or galvanic corrosion being subjected to the structural component. The sacrificial collar will literally sacrifice itself to the stray current or galvanic corrosion, thereby protecting the structural component to which the collar is secured.
In view of the above disclosure, the primary object of the invention is to provide a sacrificial collar that is secured on a structural component to protect the component against stray current or galvanic corrosion.
In addition to the primary object, it is also an object of the invention to provide a sacrificial collar that:
These and other objects and advantages of the present invention will become apparent from the subsequent detailed description of the preferred embodiment and the appended claims taken in conjunction with the accompanying drawings.
The best mode for carrying out the invention is presented in terms that disclose a preferred embodiment of a sacrificial collar. Two of the most serious problems associated with the use of metal components are; first, stray current corrosion, and second, galvanic corrosion which is also known as bimetallic corrosion or dissimilar metal corrosion. These problems are especially prevalent for metal components that are located in seawater, such as submerged parts of a boat or other sea vessel.
Stray current corrosion occurs when metal with an electrical current flowing into it is immersed in water that is grounded (such as in any lake, river or ocean). The current can leave the metal and flow through the water to ground. This will cause rapid corrosion of the metal at the point where the current leaves. Stray direct current is particularly destructive. Stray current corrosion can cause rapid deterioration of the metal. If the metal happens to be aluminum, it can be destroyed in a matter of days.
Galvanic corrosion occurs when there are two different metals are physically or electrically connected and immersed in seawater, effectively creating a battery. Some amount of current flows between the two metals, and the electrons that make up that current are supplied by one of the metals giving up bits of itself in the form of metal ions to the seawater. The most common casualty of galvanic corrosion is a bronze or aluminum propeller on a stainless steel shaft, but metal struts, rudders, rudder fittings, outboards, and stern drives are also at risk. An example of this is a ship propeller that is made of bronze and zinc. When corrosion occurs the zinc in the propeller will deteriorate first, leaving zinc molecules in the bronze, which results in the remaining bronze being extremely fragile.
The way to counteract stray current or galvanic corrosion is to add a third metal into the circuit, one that is quicker than the other two to give up its electrons. The instant sacrificial collar can function as the third metal. While the sacrificial collar is predominantly used in seawater applications, there are instances of corrosion occurring in other locations. The design of the sacrificial collar allows the collar to be effectively utilized in many of these other instances. Additionally, the sacrificial collar can be secured on many types of structural components. For the purpose of this disclosure, the sacrificial collar is disclosed and shown secured on a circular object such as a shaft. Any modifications that would be necessary to facilitate the use of the sacrificial collar on other sizes/shapes of structural components is anticipated and thereby intended to be covered by this disclosure.
The sacrificial collar 10, as shown in
As shown in
A square or rectangular lower section 42 is a mirror image of the upper section 12, and is also comprised of a front surface 44, a rear surface 46, a right surface 48, a left surface 50, an upper surface 52 and a lower surface 54. Extending along the upper surface 52 is a half-circle cavity 58. It should be noted that the half-circle cavities 28,58 are only one possible shape. Other shapes such as square or triangular can also be utilized depending on the requirements of the application/function.
When the upper section 12 is mated to the lower section 42 the two respective half-circle cavities 28,58 create a single circular opening 60 that extends through the sacrificial collar 10 from the front surfaces 14,44 to the rear surfaces 16,46. Extending through one of at least two angularly opposed corners of the lower section 42 from the lower surface 54 to the upper surface 52 is a bore 64. The bores 34 on the upper section 12 are aligned with the bores 64 on the lower section 42.
The sacrificial collar 10 is secured on a circular structural component such as a shaft 86 by placing the upper section 12 on the shaft 86 such that one-half of the shaft's diameter is within the upper section's cavity 28 and then placing the lower section 42 on the shaft 86 such that the other half of the shaft's diameter is within the lower section's cavity 58. The sacrificial collar's two sections 12,42 are then secured on the shaft 86 by attachment means 70 that preferably comprise inserting a bolt 72 into each of the bores 34,64 and screwing a nut on the end of the bolt. Once the nut is tightened on the bolt, the two sections 12,14 are secured on the shaft 80, as shown in
In addition to the bolt and nut combination 72, the attachment means 70 for attracting the upper section 12 to the lower section 42, and that facilitates the securing the sacrificial collar 10 on a structural component, can be comprised of a screw 74, as shown in
Also, as shown in
As previously disclosed, the sacrificial collar 10 is preferably square or rectangular, as shown in
While the invention has been described in detail and pictorially shown in the accompanying drawings it is not to be limited to such details, since many changes and modification may be made to the invention without departing from the spirit and the scope thereof. Hence, it is described to cover any and all modifications and forms which may come within the language and scope of the claims.
