US2643222A - Method of cathodically descalling and electrode therefor - Google Patents

Description

June 23, 1953 c, cox 2,643,222

METHOD OF CATHODICALLY DESCALING AND ELECTRODE THEREFOR Filed March 24, 1949 5 Sheets-Sheet l llll I June 23, 1953 G. c. COX

METHOD OF CATHODICALLY DESCALING AND ELECTRODE THEREFOR File d March 24, 1949 3 Sheets-Sheet 2 IN V EN TOR.

G. C. COX

June 23, 1953 METHOD OF CATHODICALLY DESCALING AND ELECTRODE THEREFOR Filed March 24, 1949 3 Sheets-Sheerv 3 INVENTOR.

Patented June 23, 1953 UNITED STATES PATENT OFFICE METHOD OF CATHODICALLY DESCALING AND ELECTRODE THEREFOR This invention relates to improved apparatus and methods for electrolytically treatin metal surfaces such, for example as areas of the side, bottom or deck surfaces of floating marine structures or the inner or outer surfaces of metal tanks, tank cars, etc. More particularly this invention relates to an electrode structure capable of effectively distributing an electric current at any desired current density up to several hundred amperes per square foot when using electrolytes such as sea Water or other electrolytes of equal or greater conductivity.

This electrode structure can be made to function completely as an anode with the structure undergoing treatment serving as a coacting cathode; or such a structure can be made to function as a cathode with the structure under treatment serving as a coacting anode; or a part can be made to act as an anode and another part as cathode with the adjacent metal surfaces acting respectively as a coacting cathode and a coacting anode.

An object of this electrode structure is to create a means and method which will efficiently descale or derust a large steel surface at a unit cost lower than other present-day equipment.

Another object is to produce an electrode structure which can be used when electrolytically depositing a protective coating on such surfaces under low cost controlled conditions.

Another object is to produce an electrode equipment which will effectively treat a metal surface by the use of an external power source the voltage of which is less than that required to form a destructive electric are.

A further object is to produce an electrode equipment the electrode elements of which galvanically coact with the metal surface under treatment to produce the required electric current for the operation without the use of an external current source.

Another object is to combine any of the above objects as required to meet a specific treating use.

The above and further objects will be apparent when the following specifications are read in conjunction with the accompanying drawings where- Figure 1 shows a plan view of a part of a woven mat type electrode in which the electrode elements are round rods suitably spaced by inter- Woven cords.

Figure 2 is a section on the line 22 of Figure 1.

Figure 3 is a section on the line 3-3 of Figure 1 and illustrates one method of leading current to or from the electrode elements.

Figure 4 is a plan view similar to Figure 1 except that the weaving is intermittently arranged along the electrode elements at desired intervals so that the elements will be held in position with a minimum of interwoven cords.

Figure 5 is a plan view of a part of a mat type electrode in which the individual electrode elements are spaced from each other by cords or other non-metallic separators. One or more separators may be used to get any desired spacing between the electrode elements.

Figure 6 is a section of a woven mat type electrode resting on a steel surface to be treated and shows the use of flattened bars or ribbon type electrode elements.

Figure '7 is a sectional view similar to Figure 2 but shows a section of a mat electrode in an operating position supported on the steel surface to be treated, the electrode weaving cords being several diameters smaller than the round electrode elements.

Figure 8 shows the plan view of a part of a mat type electrode in which the electrode elements are held in position by placing sheets of cloth or of non-metallic gauze on each side of the elements and sewing these sheets together between each element. If desired, more than one electrode element insert may be placed in the same pocket; or an electrode element may be omitted from every other pocket or otherwise, as required. An advantage of this arrangement is that new electrode elements may be inserted into these pocketlike spaces when the old ones become useless.

Figure 9 is a cross sectional view along the line 99 of Figure 8, showing the substantially tubular pockets.

Figure 10 is a sectional view similar to Figure 9 except that the replaceable electrode elements are flattened or ribbon-type bars. This figure shows these insert bars resting on and pressing against one of the sheets of porous non-conducting material which, in turn, is resting on and pressing against the steel surface to be treated.

Figure 11 is a sectional view similar to Figure 10 showing a modified form of insert in elongated pockets.

Various attempts have been made to produce an electrolytic equipment which can be used for descaling or otherwise treating metal surfaces such as the steel decks and sides of ships, storage tanks, etc., which are covered with corrosion products, old paint, films, etc.

Both from a practical consideration of availability without special preparation and an economic consideration of cost, the desirable electrolyte for treating marine structures is sea water. For treating inland structures, somewhat similar electrolytes may be used. However, the equipments can be adapted to use a wide variety of electrolytes for various specific applications.

Tests show that a commercial marine design of a 7,000 ampere moving type grid electrode made in accordance with applicants co-pending application No. 550,814 of August 23, 1944, now Patent Number 2,476,286, and operating with a sea water electrolyte required a minimum operating voltage of about 50 at the lower descaling current densities and a maximum of 140 volts for the higher current densities. Under normal operating conditions these secondary arc suppressor electrodes function perfectly but if one becomes broken and shorted to the main electrode, an arc can be set up between the broken electrode and the work.

An inherent design feature of such an externally powered grid electrode for rapid descaling is that the total gap between the input electrode and the work must be maintained at a distance which will safely prevent the formation of destructive arcs. Distances of one to four inches or more are common in the prior art; the shorter distance can be used with the arc suppressor electrodes and the longer distance is possible without such electrodes.

In this invention the gaps between the electrode elements and the work to be descaled or otherwise treated are comparatively so small that the required current density on the work surface can be obtained with a sea water electrolyte by the use of an applied voltage which is Well below the zone of transition from spark to arc. Depending on conditions, this transition from a spark to an are that will maintain itself begins when the applied voltage is raised above 25 to 30 volts. As the voltage is further increased the arc becomes more penetrating and destructive. Even with gap distances between electrode elements and the work surface up to one-fourth of an inch as herein disclosed, tests indicate that operating voltages in excess of fourteen are seldom necessary and usually the required voltages are below seven.

For example, when using normal sea water, one of these mat type grid electrodes gave a current dissipation when pressed against a steel surface equivalent to approximately one hundred amperes per square foot with an applied voltage of 2.10 volts. The grid was anodic and the work was cathodic. This electrode was constructed by weaving inch mild steel rods together with cotton cord of approximately inch in diameter. The current was fed to these steel elements by the arrangement shown in Figure 1.

A similarly constructed mat electrode using malleable magnesium elements produced, under similar conditions, a current density equivalent .to approximately 25 amperes per square foot even when no external voltage was applied. With an externally applied voltage of 2.05 volts the equivalent current density on the steel surface in contact with the magnesium mat electrode was more than 200 amperes per square foot. Depending upon the type of scale to be removed a current density not exceeding 100 amperes per square foot is generally suflicient for ordinary descaling with these electrodes.

Hence, for certain uses it is found that a magnesium mat type electrode will operate effectively without the application of an external current source. A study of other materials for the elements of these mat type electrodes showed that zinc and aluminum alloys give current densities generally between the values of the above examples. Electrode elements made of copper or other commercial metals or alloys may be necessary for specific applications, such, for example. as anodic descaling or similar treatments.

A study of electrolytes which may be used in addition to sea water and similar solutions showed that most sulphate or chloride brines of the alkali or alkaline earth groups would give useful descaling. When using dilute acid solutions of less than one-half of one percent efi'ectivedescaling has also been obtained. Similarly, these mat type electrodes have been found to be highly effective for electrocoating and electroplating with electrolytes compounded for a specific use.

Reference will now be made to the drawings in .detail, in which similar numbers refer to similar parts:

In Figure 1, rod type electrode elements I are positioned and held in place by means of cords of any flexible non-conducting material 2. When it is desired to have the rod type elements of about three to ten feet long these elements may be fed into a loom from each side and are held by the warp. In this case the cords 2 comprise most of the warp. However, at least one edge of the warp consists of flexible strands of a good conductor such as copper. The combined crosssectional area of these flexible stranded conductors must be sufiicient to carry the electric current used in the operation, and are shown as flexible conductors 3 in Figures 1 and 3. The ends of these conductors 3 are clamped under the terminal blocks 4 to which is attached through the lugs 5 heavy current carrying cables 6 for leading the current to or from the mat type electrode. It is observed that such a flexible electric current connection may be easily woven on the electrode elements at any one or more desired 10- cations along their lengths.

When the electrode elements are continuous or more than about ten feet in length, the electrode elements I could be strung in the loom as the warp and the non-conducting cords 2 could be woven in by the shuttle. In this case the hexible stranded wires 3 sould be woven in place when required at suitable intervals along the electrode elements.

Various other methods of making suitable low resistance connections to the electrode elements may be used. For example, when such a mat electrode with comparatively long electrode elements is fastened in place against a surface to be treated, the ends of each of the elements could be clamped directly to one or more terminal lugs 4 as required. When using galvanic rod elements the ends of these rods could be connected directly to the work. It is often desirable to have a wire of malleable aluminum, copper or iron extruded in the center of such rods so that sufficient mechanical strength and low conductivity will be insured.

In order to produce a mat electrode with large mesh openings the weaving cords 2 may be spaced along the electrole elements I at intervals which will give the desired mesh openings as shown in Figure 4.

Figure 5 illustrates a method of spacing the electrode elements at greater distances than shown in the previous figures. This is accomplished by inserting one or more spacing cords 1 between the elements I. Instead of cords, nonconducting bars or rods may be used. This arr'angeinent would effect lower operating current densities than with the closely spaced elements and would be useful in electroplating or electrocoating large surfaces after they are descaled.

In many cases economics will require the use of flattened bars or ribbon type of electrode elements as shown in Figure 6. One example of such a use would be when galvanic or sacrificial anode elements are intended to have a limited life and cannot be recovered economically after being installed. For this use the ribbon elements 8 could be made of a suitable galvanic metal or alloy and could be designed for a limited amperehour life.

With electrolytes such as sea water and the like extensive experiment has demonstrated that, for a given applied voltage less than that required to form and sustain an electric arc, the current output per unit area of one of these mat type grid electrodes increases rapidly as the distance is decreased from about one-half inch to about one thirty-second inch or less. The arrangement shown in Figure 7 illustrates one way in which this may be accomplished. By the use of cords 2a which are several times smaller than the diameter of the electrode elements la, the distance between these elements and the surface of the sheet of steel 9 can be reduced to comparatively small values.

It is thus seen that the various arrangements shown may be defined as a mat type of electrode comprising a multiplicity of metallic electrode elements which are substantially longer in one dimension than the other and which have means for holding these elements side by side in a flexible relation to each other and substantially parallel, means for supporting these elements out of contact with the metal surface undergoing treatment, and means for electrically connecting these elements as required.

Another practical method of accomplishing the same thing is illustrated in Figures 8, 9, and 10. Two pieces of fabric Ill and II are held together by stitches l2, as shown. This stitching can be done on an automatic machine after the rods are assembled in place between the fabric. This procedure would lend itself to the manufacture of long mat electrodes by continuously feeding the fabric from rolls into an automatic stitcher while at the same time feeding the electrode elements from suitable coils. For smaller mat type grid electrodes in which the electrode elements are not more than about 10 to 14 feet long it is entirely practical to sew the two pieces of fabric together as shown at I2 and then slide the electrode elements into the individual tube-like jackets. In other words, this arrangement produces a multiplicity of substantially parallel non-conducting porous walled tubular pockets which are flexibly interconnected or interlaced along the sides of their long dimension in which the metallic electrode element inserts can be held.

The cords 2 and lid for weaving the electrode elements into mats as shown in Figures 1 to 7 and the cord 01 thread for weaving the fabric l9 and H shown in Figures 8 to 10 should ordinarily be porous and highly absorbent to water. Loosely twisted cotton cord or loosely woven cotton cloth have given excellent results. For acid electrolytes good results were obtained when using a commercial grade of flexible plastic waterproof window screen for the fabric sheets l0 and II. In general, a lower cell resistance and better results are obtainecl when using a fabric 6 having water absorbent porous filaments. Obviously the use of a waterproof or absorbent filament will depend on the reaction products and intended life of the mat.

When using a fabric having either absorbent or waterproof filaments the size of the mesh or the closeness of the weave should be such that the electrolyte will freely pass through the mat, also that any gas generated at the work surface or electrode surface will easily escape and not remain as small trapped gas bubbles in the interstices. The occurrence of either of those situations causes an undesirable rise in the electrical resistance of the cell. A felt of high porosity gives good results as the fabric sheets Ill and II. Other materials of the desired characteristics may be used, as impregnated fabrics.

When a mat type grid electrode having highly porous fibers is resting on a flat steel surface, for example, the steel deck of a ship, the weight of the electrode elements press the fabric ll against the deck surface along the areas immediately under the electrode elements. Now if sea water or other desired electrolyte is sprayed or otherwise poured over the mat the electrolyte will be quickly absorbed in all the pores and meshes of the fabric and the internal electrical resistance across this cell will drop to values approaching those obtained if the cell components were submerged in the same solution. Under these conditions with a sea water electrolyte, excellent descaling can be obtained when the external circuit is properly completed through an external power supply when using non-galvanic anodes, or direct to the surface under treatment when suitable galvanic anodes are used.

The materials which have given excellent results as galvanic or self-generating electrode elements are the commercial magnesium alloys containing small percentages of aluminum and zinc, and aluminum alloys containing a small percentage of zinc. Electrode elements of pure zinc are useful in certain applications requiring only moderate current densities.

The materials which have given excellent results as anode elements when driven from an external low voltage power supply are the alloys of aluminum of commercial cell grade purity. The least expensive grade of mild steel reinforcing rods have given good results as electrode elements when driven from an external power supply. Copper or its alloys are sometimes required particularly when used for cathodes.

The use of galvanic anodes with an external power supply will give an extremely high current output for a limited period. This arrangement has been found useful for treating a surface covered with a firmly attached hard scale.

In general, ordinary round rods or ribbon type electrode elements are used. However, for an electrode having a large current output and a short life, the electrode elements may be made of strips of perforated, expanded or crimped metal which are held between fabric sheets ill and l 1, similar to the procedure described above. Such an arrangement is shown in Figure 11 in which the inserts 13 are held in the elongated pockets by sewing the fabric sheets Ill and H together at suitable distances by stitches l2. For heavy current output, the exposed surface of these inserts per unit weight is made comparatively large by using perforated, expanded or 'crimped metal. When very large electrodes areconstructed, these elongated pockets may be made sufficiently wide and sufficiently long to hold a commercial size sheet of expanded, crimped or perforated metal in one pocket. When using the rod or ribbon type elements, a lower current density may be obtained by leaving every other pocket empty, etc. This action would be similar to that shown in Figure 5. Depending upon the use, these mat type grid electrodes can be made in sizes ranging from about one square foot to several thousand square feet of total eifective area.

The novel features of these mat type electrodes are: (1) rod or wire type electrode elements are surrounded by a sufficient amount of non-conducting fibrous material either in the form of filaments, cords, or fabric to prevent the electrode elements from coming in direct contact with the work under treatment; (2) these electrode elements are held away .from the work surface a sufficient distance to cause a layer of electrolyte to be retained in the pores and meshes of the cords or fabric between the electrode elements and the work; (3) the combined pores and meshes of the mat must be sufficient to allow the exhausted electrolyte to drain away or be replaced either constantly or intermittently by a fresh solution; (4) the electrode elements can be constructed from the alloys which form effective galvanic couples with the work under treatment and therefore act as a self-generating current source; (5) the same galvanic type of electrode elements can be operated as driven electrodes when necessary, therefore the storage of more than one type of mat electrode element is not essential; (6) the device is highly flexible in one dimension, is comparatively light in weight and can be rolled up into a long roll like a carpet for easy storage and handling; (7) the entire device is simple to manufacture and easy and foolproof to operate.

It is often desirable to use only one or two of the electrode elements in a suitable pocket type mesh covering for descaling or otherwise treating small, narrow or otherwise difficult places.

For descaling the deck of a ship an electrode as shown in Figure 1 would be laid flat down against the steel deck. For rapid cathodic descaling the cables 6 would be connected to the positive terminal of a low voltage power source and the other terminal of the power source would be connected to the deck. The mat is then sprayed continuously or intermittently with a suitable electrolyte, which may be sea water. After the required period the mat is moved and the scale is either scraped off mechanically or hosed off with a pressure hose. When desirable, anodic descaling can be carried out with exactly the same arrangement except that in this case the deck is connected to the positive terminal and the electrode to the negative terminal of the power source.

Excellent cathodic descaling of such a deck surface can be effected without the use of an external power source by the use of magnesium rod electrode elements. In this case the cable 6 or its equivalent is connected directly to the deck.

A similar procedure is used for descaling the vertical sides of a ship or storage tank. The only precautions are that the mat must be held firmly against the surface to be treated and in general a greater quantity of electrolyte must be sprayed or hosed onto the mat. A fine mesh mat, having good absorbent properties-is generally preferable for this work.

For descaling the bottom of a ship a mat with a large open mesh construction as shown in 'Figure 4 is highly desirable and is held against the bottom while the ship is at anchor or tied at a wharf. This open mesh construction allows free :gas movement and escape which in turn causes a slight stirring of the water in which it is immersed.

Although such electrodes have been found useful for various other descaling and coating applications, theabove examples illustrate the general types of equipment and methods of operation of these novel procedures. However, it is intended that the invention is not to be limited to theapparatus and method illustrated, but is to be broadly inclusive of any and all equivalents both of method and apparatus such as fall within the scope of the appended claims.

I claim:

1. A flexible mat adapted to be'placedcontiguous with a surface of an iron or steel structure which is -to be electrolytically treated comprising a plurality of substantially parallel slender elongated bars of a metal selected from the group consisting of magnesium, magnesium base alloys, aluminum or aluminum base alloys; and flexible means mechanically interconnecting all of the elongated bars at intervals along the sides of their long dimension; said flexible means including at least two parts one of which parts is a flexible porous non-conductive fabric in mechanical contact with the coacting surface of the bars on at least one side of the mat for spacing said bars from the surface of said structure at a distance equal to the thickness of the fabric, and the other of which parts is a flexible metallic low resistance conductor electrically interconnecting the bars and adapted to be electrically connected to the structure to be treated.

2. A flexible mat as defined in claim 1 in which the flexible conductor interconnects the bars adjacent the ends thereof which form one end of the mat and in which the flexible fabric extends over a limited area of the bars located between the flexible conductor and the end of the mat opposite to the flexible conductor.

3. A flexible'mat as defined in claim 1 in which said flexible means constitutes the only means for interconnecting the bars, whereby the mat maybe rolled up, the bars being semi-rigid.

4. An electrode comprising a plurality of slender rods of a metal selected from the group consisting of magnesium, magnesium base alloys, aluminum or aluminum base alloys; means for holding the rods in essentially parallel relationship comprising cords interwoven with the rods substantially at right angles to the rods, said cords being composed of flexible non-conductive flbers; a terminal; and flexible low resistance means electrically interconnecting the rods and the terminal.

5. A mat electrode for treating contiguous metal surfaces of an iron or steel structure consisting of a plurality of slender rods of a metal selected from the group consisting of magnesium, magnesium base alloys, aluminum or aluminum base alloys, means for spacing the rods from the metal surfaces and for holding the rods in flexible and essentially parallel relationship comprising sheets of fabric respectively extending over the galvanically coacting area of the rods on both sides of the mat and including means mechanically interconnecting the sheets (at intervals in 9 thespaces between the rods, a terminal and flexible low resistance electrical conducting means interconnecting the rods and the terminal.

6. The device of claim in which the fabric is thinner than the rods.

'7. A mat electrode for treating contiguous metal surfaces of an iron or steel structure consisting of a plurality of slender rods of magnesium, .means for spacing the'rods from the metal surfaces and for holding the rods in flexible and essentially parallel relationship comprising sheets of fabric respectively extending over the galvanically coacting area of the'rods on both sides of the mat and including means mechanically interconnecting thesheets at intervals in the spaces between the rods, a terminal, and flexible low resistance electrical conducting means interconnecting the rods and the terminal.

81A mat electrode for treating contiguous metal surfaces of an iron or steel structure consisting of a plurality of slender rods of a magnesium base alloy, means for spacing the rods from the metal surfaces and for holding the rods in flexible and essentially parallel relationship comprising sheets of fabric respectively extending over the galvanically coacting area of the rods on both sides of the mat and including means mechanically interconnecting the sheets at intervals in the spaces between the rods, a terminal, and flexible low resistance electrical conducting means interconnecting the rods and the terminal.

9. A mat electrode for treating contiguous metal surfaces of an iron or steel structure consisting of a plurality of slender rods of aluminum, means for spacing the rods from the metal surfaces and for holding the rods in flexible and essentially parallel relationship comprising sheets of fabric respectively extending over the galvanically coacting area of the rods on both sides of the mat and including means mechanically interconnecting the sheets at intervals in the spaces between the rods, a terminal, and flexible low resistance electrical conducting means interconnecting the rods and the terminal.

10. A mat electrode for treating contiguous metal surfaces of an iron or steel structure consisting of a plurality of slender rods of an aluminum base alloy, means for spacing the rods from the metal surfaces and for holding the rods in flexible and essentially parallel relationship comprising sheets of fabric respectively extending over the galvanioally coacting area of the rods on both sides of the matand including means mechanically interconnecting the sheets at intervals in the spaces between the rods, a terminal, and flexible low resistance electrical conducting means interconnecting the rods and the terminal.

11. The method of cathodically descaling the surface of an iron or steel structure at a current density of at least 25 amperes per square foot which comprises the steps of: holding one side of a thin flexible non-conducting porous electrode separator against the surface of the structure under treatment by pressing against the separator with the sides of a multiplicity of slender substantially parallel rods of a metal selected from the group consisting of magnesium, magnesium base alloys, aluminum or aluminum base alloys; connecting the rods through a low resistance flexible conductor to the said structure; then repeatedly filling the voids between the rods and the coacting surface of the structure with an electrolyte suitable for the specific descal ng 10 action and for a sufiicient time to descale the surface.

12. The method of cathodically descaling the surface of an iron or steel structure at a current density of at least 25 amperes per square foot which comprises the steps of holding one side of a thin flexible non-conducting porous electrode separator against the surface of the structure under treatment by pressing against the separator with the sides of a multiplicity of slender substantially parallel rods of a metal selected from the group consisting of magnesium, magnesium base alloys, aluminum or aluminum base alloys; connecting the rods through a low resistance flexible'conductor to the said structure; then repeatedly filling the voids between the rods and the coacting surface of the structure with a brine-suitable for the specific descaling action and fora sufficient time to descale the surface.

13. The method of cathodically descaling the surfaceof an iron. or steel structure at a current density of at least 25 amperes per square foot which comprises the steps of: holding one side of a thin flexible non-conducting porous electrode separator against the "surface of the structure under treatment by pressing against the separator with the sides of a multiplicity of slender substantially parallel rods of a metal selected from the group consisting of magnesium, magnesium base alloys, aluminum or aluminum base alloys; connecting the rods through a low resistance flexible conductor to the said structure; then repeatedly filling the voids between the rods and the coacting surface of the structure with an electrolyte consisting substantially of sea water and for a sufficient time to descale the surface.

14. The method of cathodically descaling the surface of an iron or steel structure at a current density in excess of 25 amperes per square foot which comprises the steps of: holding one side of a thin flexible non-conducting porous electrode separator against the surface of the structure under treatment by pressing against the separator with the sides of a multiplicity of slender substantially parallel rods of a metal selected from the group consisting of magnesium, magnesium base alloys, aluminum or aluminum base alloys; flexibly connecting the rods to the said structure through a means for generating an additive polarity low voltage direct current supplementing the galvanic potential; then repeatedly filling the voids between the rods and the coacting surface of the structure with an electrolyte suitable for the specific descaling action and for a sufificient time to descale the surface.

15. The method of cathodically descaling the surface of an iron or steel structure at a current density in excess of 25 amperes per square foot which comprises the steps of: holding one side of a thin flexible non-conducting porous electrode separator against the surface of the structure under treatment by pressing against the separator with the sides of a multiplicity of slender substantially parallel rods of a metal selected from the group consisting of magnesium, magnesium base alloys, aluminum or aluminum base alloys; flexibly connecting the rods to the said structure through a means for generating an additive polarity low voltage direct current supplementing the galvanic potential; then repeatedly filling the voids between the rods and the coacting surface of the structure with a brine suitable for the 1 1 specific descaling action and for a sufiicient time to descale the surface.

16. The method of cathodica'lly descaling the surface of an iron or steel structure at a current density in excess of 25 amperes per square foot 5 which comprises the steps'of: holding one side of a thin flexible non-conducting porous electrode separator against the surface of the structure under treatment by pressing against the separator with the sides of a multiplicity of slender substantially parallel rods of a metal selected from the group consisting of magnesium,

magnesium base alloys, aluminum or aluminum. base alloys; flexibly connectin the rodsto the.

said structure through a means for. generating an additive polarity low voltage directcurrentt supplementing thegalvanic potential; then re-- peatedly filling the voids between the rods and the coacting surface of the structure withanelectrolyte consisting substantially of sea water and for a sufficient time to descale the surface.

GEORGE CHANDLER COX.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Craney June 13, 1899 Wisnom Dec. 3, 1907 Jenkins Feb. 20, 1912 Payne Oct. 3, 1922 Giffen May 17, 1927 Edelman July 3, 1929 Hesse Sept. 17, 1940 Taylor Feb. 17, 1948 T'arr June 29, 1948 Butler Oct. 12, 1948 Thomas Feb. 6, 1951.

FOREIGN PATENTS Country Date Great Britain of 1852 Great Britain of 1873 Great Britain Aug. 10, 1893 Great Britain of 1899 Great Britain Aug. 22, 1930

Claims (1)

1. A FLEXIBLE MAT ADAPTED TO BE PLACED CONTIGUOUS WITH A SURFACE OF AN IRON OR STEEL STRUCTURE WHICH IS TO BE ELECTROLYTICALLY TREATED COMPRISING A PLURALITY OF SUBSTANTIALLY PARALLEL SLENDER ELONGATED BARS OF A METAL SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM, MAGNESIUM BASE ALLOYS, ALUMINUM OR ALUMINUM BASE ALLOYS; AND FLEXIBLE MEANS MECHANICALLY INTERCONNECTING ALL OF THE ELONGATED BARS AT INTERVALS ALONG THE SIDES OF THEIR LONG DIMENSION; SAID FLEXIBLE MEANS INCLUDING AT LEAST TWO PARTS ONE OF WHICH PARTS IS A FLEXIBLE POROUS NON-CONDUCTIVE FABRIC IN MECHANICAL CONTACT WITH THE COACTING SURFACE OF THE BARS ON AT LEAST ONE SIDE OF THE MAT FOR SPACING SAID BARS FROM THE SURFACE OF SAID STRUCTURE AT A DISTANCE EQUAL TO THE THICKNESS OF THE FABRIC, AND THE OTHER OF WHICH PARTS IS A FLEXIBLE METALLIC LOW RESISTANCE CONDUCTOR ELECTRICALLY INTERCONNECTING THE BARS AND ADAPTED TO BE ELECTRICALLY CONNECTED TO THE STRUCTURE TO BE TREATED.

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