Exothermic Cutting Electrode

This invention pertains to exothermic cutting electrodes or burning bars of the type wherein a mass of metal is ignited in the presence of an oxidizing gas (e.g. oxygen) to form a flame or products of combustion which can be directed at a structural shape for cutting or piercing the structural shape.

Conventional burning bars which are used on land for cutting structural materials such as rock, stone, concrete, iron and steel are disclosed in any of U.S. Pat. Nos. 3,260,076; 3,507,231; 3,487,791; 3,500,774; 3,507,230; 3,570.419; and 3,738,288. These burning bars share a common feature in that they have an outer tube within which is placed a plurality of elongated rods or wires to make up a mass of oxidizable metal. Oxygen is conducted down through the outer tube to the end of the rod where combustion is initiated to produce a flame which is directed at the structural material. The prefered burning bars usually contain a readily oxidizable metal (e.g. magnesium or aluminum) as one or more of the rods to promote combustion.

The use of multiple strands in various configurations for arc welding electrodes is shown in U.S. Pat. Nos. 1,773,653, 2,345,758; 2,806,128 and 3,147,362 it being well known that welding electrodes are generally unsuitable for cutting operations.

Twisted wire or cable type burning bars or thermal ances are shown in U.S. Pat. Nos. 3,591,758; and 3,602,620.

Lastly, the multiple wire burning bar has been adapted to underwater use as shown in U.S. Pat. Nos. 4,069,407 and 4,182,947. The underwater rods of the aforementioned patents have an outer tube within which are disposed a plurality of elongated steel rods or wires the wire bundle including a readily oxidizable metal rod or wire which is preferably aluminum.

The present invention pertains to exothermic cutting electrodes or burning bars as they are known in the art. In particular the present invention provides an electrode having a central (inner) tube or oxygen passage around which is disposed a mass of similar metal. The mass of metal is held to the inner tube in a number of ways the most prevalent being the use of an outer tube. However, ferrules can be crimped to the mass of metal to hold it to the inner tube and the entire length between the ferrules can be covered with a water impervious electrically insulating coating to provide the outer surface of the electrode. The inner tube and mass of metal can be steel which is readily obtainable and easily fabricated which in the presence of oxygen conducted down the center tube will permit the establishment of a flame which can be directed against materials of construction to accomplish a cutting, boring, piercing or other severing operation. The inner or center tube insures that a jet of oxidizing gas and flame hits the workpiece with a concentrated force. According to the present invention the electrodes are constructed so that an electrical current passed down through the mass of metal can be used to heat the end of the electrode in the presence of the stream of oxygen, to its ignition temperature and thus start the progressive burning of the electrode mass producing a very high temperature flame. By proper selection of the metal and the proper relationship between the metal mass and metal surface in contact with the stream of oxygen (oxidizing gas), the current can be turned off once the flame from the burning mass of metal is established and the cutting can continue until the electrode is consumed.

Passage of the oxidizing gas can be enhanced by indenting the surface of the wire used as the mass of metal, grooving the outer surface of the inner tube and the means by which the outer tube or ferrules are fixed to the mass of metal.

Use of a particular coating can result in a visible indicator end on the electrode when it is in use underwater.

FIG. 1 is a partially fragmented perspective view illustrating an electrode for which the present invention can be used.

FIG. 2 is a view taken along the line 2--2 of FIG. 1.

FIG. 3 is a perspective view partially fragmented of an alternate embodiment of the electrode of FIG. 1.

FIG. 4 is a cross-sectional view taken along the line 4--4 of FIG. 3.

FIG. 5 is a perspective partially sectioned view of an electrode such as shown in FIG. 1 illustrating the present invention which features an inner tube the outer surface of which is provided with a series of parallel grooves to provide a means for facilitating flow of oxidizing gas between the outer surface of the inner tube and the inner surface of the helically wound wire mass.

FIG. 6 is a view taken along the line 6--6 of FIG. 5.

FIG. 7 is a fragmented elevational view of an alternate form of wire to be used in the electrode of FIGS. 1, 3 and 5.

FIG. 8 is a cross-sectional view of an electrode employing the wire of FIG. 7.

An exothermic electrode or burning bar according to the present invention provides a mass of oxidizable metal that in the presence of an oxidizing gas (e.g. oxygen) and a source of ignition will produce a flame which can be directed against a workpiece which may be part of a fixed land structure or marine structure or similar object so that in the hands of the skilled operator a cutting, piercing or burning operation can take place. Electrodes according to the present invention can be used to burn, cut or pierce structural materials in air or water such as cast iron, steel, concrete and rock, the latter being either natural or synthetic.

One form of the invention is shown in FIGS. 1 and 2, the electrode shown generally as 10 comprising an inner tube 12 the inner tube being of a low carbon steel 171/2 inches (.about.44.45 cm) long having a 0.187 inches (.about.4.74 mm) outside diameter and a 0.130 inches (.about.3.30 mm) inside diameter. Wrapped around tube 12 in a helical fashion is a continuous length of low carbon steel wire 14 having a nominal diameter of 0.62 inches (.about.1.57 mm). The steel wire is wound in such a fashion as to define a tube having a 0.305 inches (.about.7.75 mm) outside diameter and a 0.192 inches (.about.4.88 mm) inside diameter with an overall length of 173/4 inches (.about.45.09 cm). Wire 14 is wound so that it projects approximately 0.125 inches (.about.3.18 mm) over the ends of inner tube 12. Disposed around the wire 14 is an outer tube 16 having an outside diamter of 0.375 inches (.about.9.53 mm) and an inside diameter of 0.319 inches (.about.8.10 mm) with an overall length of 18 inches (.about.45.72 cm). As shown in the drawing on the torch end of the electrode, the outer tube 16, projects beyond wire 14 and wire 14 beyond inner tube 12. On the burning end the three components can be flush.

The entire electrode 10 can then be coated with 0.015-0.020 inches (.about.3.81 mm-.about.5.08 mm) of an electrically insulating material such as a vinyl sold by Michigan Chome and Chemical Company under the trade name MICRON 455 Vinyl. In use a portion of one end of the plastic coating can be stripped away so that the electrode can be clamped in a torch (not shown) such as disclosed in U.S. Pat. No. 3,780,258 for use under water. Alternatively, the electrode can be fabricated by clamping the outer tube in a fixture which will prevent adherence of the coating as it is applied.

Set forth in Table I are a series of tests performed under water wherein electrodes according to that shown in FIGS. 1 and 2 were tested against electrodes shown in U.S. Pat. No. 4,069,407.

From the foregoing Table it is apparent that ectrodes according to the present invention and in particular to FIGS. 1 and 2 resulted in significantly better performance than those of the prior art. In the category of Cut Per Inch of Electrode Consumed the inventive electrodes were unanimously better than those of the prior art. All tests except for number 3 were run with electrical current being fed to the electrode during the entire test. In the case of test number 3 after cutting began on the test sample the power was turned off and cutting continued. In test number 3 it is apparent that the inventive electrodes were superior since they had a significantly better overall performance for the length of electrode consumed. It is believed the inner tube insures that a jet of oxygen and flame of burning metal hits the workpiece with concentrated force thus the inventive electrodes performed better than the prior art electrodes.

FIGS. 3 and 4 disclose an alternate embodiment of the present invention wherein the electrode 20 includes a central tube 22 of low carbon steel having a 0.187 inches (.about.4.75 mm) outside diameter and a 0.130 inches (.about.3.30 mm) inside diameter. Wrapped around tube 22 is a continuous helix of 0.062 inches (.about.1.57 mm) diameter steel wire 24. On either end of the electrode 20 a steel ferrule 26 is crimped over the wound wire 24 the ferrule having an axial length of 1.5 inches (.about.3.81 cm), a 0.375 inches (.about.9.53 mm) outside diameter and a 0.319 inches (.about.8.10 mm) inside diameter. Between the ferrules covering the exposed wound wire 24 is a plastic coating 28 similar to the coating used on the electrode of FIG. 1. Electrodes according to FIGS. 3 and 4 were tested and found to perform satisfactorily. As long as the hot metal spatter was not excessive and did not adhere to and burn through the plastic coating an electrode of this type will perform satisfactorily.

If the outer coating of the electrode is formulated with a red dye (Michigan Chrome and Chemical Company -MICRON 455-Red Vinyl) so the coating is red throughout its cross-sectional thickness, as the electrode is consumed a cone of coating is formed that projects beyond the consumed metallic portions of the electrode. The heat of the arc between the workpiece and the electrode causes the projecting coating to transmit a red glow thus facilitating positioning of the electrode by the diver/welder. The glowing tip aids the diver/welder (user) in maintaining the proper arc length between the workpiece and the electrode.

As with the electrode of FIGS. 1 and 2 the ferrule 26 project beyond one end of the wire 24 and wire 24 projects beyond one end of inner tube 22 thus defining the torch end of the electrode.

FIG. 5 shows another embodiment of the electrodes of FIGS. 1 and 3 wherein the electrode 30 encircles a grooved central or inner tube 32. Wrapped around inner tube 32 in a helical fashion is a continuous length of low carbon steel wire 34. Wire 34 is wound to project over the ends of inner tube 32. Disposed around wire 34 and of like dimensions (FIG. 1) is an outer tube 36. As shown in the drawing on the torch end 38 of electrode 30 the outer tube 36 projects beyond wire 34 and wire 34 beyond inner tube 32. On the burning end 40 the three components can be flush. The three components are held in place by a series of random indentations 42, 44, 46, 48 made in outer tube 36. The use of random indentations on the outer tube permits oxidizing gas to flow easily between the outer tube 36 and the outer surface of helically would wire 3 thus assuring an adequate flow of oxidizing gas is present at the burning end 40 of electrode 30. A particularly effective arrangement results from having four randomly spaced indentations near the torch end 38 of the eleotrode 30 and two randomly spaced indentations at the burning end 40 of electrode 30. Dimensionally electrode 30 can be the same as electrode 10.

The ferrule 26 of the electrode 20 of FIG. 3 can also be held in place by random indentations such as used with the electrode of FIG. 5.

FIG. 6 is a cross-sectional view of the electrode of FIG. 5 wherein the outer surface of inner tube 32 is provided with a series of parallel grooves to provide means for facilitating flow of oxidizing gas between the outer surface of tube 32 and the inner surface of helically wound wire 34.

FIG. 7 shows a wire 50 which has a plurality of random surface dents disposed around its circumference. Thus, for example, when wire 50 is used in the electrode of FIG. 1 the surface dents 52 help oxidizing gas to be conducted between the inner surface of outer tube 16 and the wire helix and between the outer surface of inner tube 12 and the wire helix 50 to assure adequate oxidizing gas at the burning end of the electrode.

FIG. 8 shows a cross-section of another electrode similar to FIG. 5 using the wire 50 of FIG. 7 to form the internal helix. This produces passages 52 for flow of oxidizing gas down through the electrode without the need for longitudinal surface grooves on inner tube 32.

As stated above, the electrodes according to the present invention can be provided with a continuous electrically insulating water impervious cover so that they can be used either above or below the surface of a body of water. In particular, the electrodes have been found to be very effective for under water use.

Using a construction according to the present invention assures that the steel components at the projecting end of the electrode (end opposite that clamped in the torch) are bathed in a stream of high-pressure oxygen. As the electrode is consumed, this intimate relationship between the mass of metal and the oxygen stream must remain for consistent performance. This is assured in the electrodes of the present invention by utilization of the inner tube which is heretofore not shown in the electrode constructions delineated in the prior art.

As described above, each electrode is constructed so that the outer tube or ferrules project over one end of the mass of metal (e.g. spring wound wire) which in turn projects over the inner tube. This construction defines a torch end of the electrode that acts as a manifold so that the oxidizing gas flows mainly through the inner tube. Oxidizing gas is also directed through passages between the inner wall of the outer covering (tube or vinyl) and the mass of metal and between the outer surface of the inner tube and the adjacent surface of the mass of metal.

In some cases it may be advantageous to provide a like recess on the burning end of the electrode to: provide space for oxygen coming through the center tube to diffuse laterally into an annular ring which facilitates ignition of the end of the electrode.

In the case of the embodiment of FIGS. 1, 2, 3, 4, and 5 both the tube and the helical wrap around the inner tube may be recessed from the projecting end of the electrode in order that all parts of the electrode are bathed in oxygen making it easy to initiate the flame and maintain consistent performance of the electrode as it is consumed.

Electrodes according to the present invention can be used on dry land but find excellent utility for under water use. As is well known in the trade, divers performing under water cutting operations are paid premium wages and must have reliable electrodes. They must also have electrodes which will cut efficiently per unit of electrode consumed. Such electrodes are disclosed in the foregoing specification which have been shown to out perform current state of the art electrodes of the multiple wire type.