US1871257A - Welding electrode - Google Patents

Description

Aug. 9, 1932. v Q A, CADWELL 1,871,257

' WELDING ELECTRODE Filed Oct. 19, 1925 METALLIC PENCIL.

VA RIV S/Y SURI'A SILICON cane/v. x7 CLAY COATING SlL/cArE5 G UM I INVENTOR. I z I Char/a6 A. C'aawe/Z A TTOR Patented Aug. 9, 1932 UNITED STATES PATENT OFFICE CHARLES A. CAD'WELL, OF CLEVELAND HEIGHTS, OHIO, ASSIGNOR TO THE ELECTRIC RAILWAY IMPROVEMENT COMPANY, OF CLEVELAND, OHIO, A CORPORATION OF OHIO WELDING ELECTRODE Application filed October 19, 1925. serial No. 63,299.

The present improvements, relating, as indicated, to metallic electrodes, have more particular regard to coated metallic pencils (rods or wires) of the type used in arc weld- It has been the practice for some time in metal working by electricity to employ what are known as coated metallic pencils in order either to introduce alloying and reducing ingredients into the weld or to secure certain other desirable results in the manipulation of the pencil. For example, a bare metallic pencil or electrode if not carefully handled is apt to stick to the work with consequent damage and delay. Accordingly, the coatings heretofore used have been composed of materials that when highly heated form a slag adapted to protect the metal of the weld from oxidation and from too rapid chilling, and such materials have also been selected with a view to their insulating character, which is of value to the operator in certain cases. Asbestos and chalk are examples of the materials just referred to. The purpose in employing an alloying or reducing agent in the coating is of course obvious and this has been introduced, for example, in the form of a fine wire interwoven with the material of the coating or of a metallic powder added to such material.

The object of the present improved coating is to overcome difficulties of a different character, for the meeting of which none of the coatings heretofore employed or proposed, so far as I am aware, is suited. To this end I employ a com osition differing radically from any heretofore employed in coatings of the type in question. For example, instead of an insulating material, I employ one that is a fairly good conductor even when cold. Furthermore, the coating instead of melting at a temperature lower than that of the metal of the electrode, melts at a higher temperature and so tends to assume the form of an annular extension or sleeve that projects beyond the point of the electrode so as to retard the deposition of metal and generate a higher temperature to a corresponding greater penetration or depth of weld. Furthermore, the coating material inknown cold shot weakness.

cludes an ingredient which under the heat of the arc is decomposed into a reducing element or elements which react with the metal of the weld to overcome oxidation and to improve the quality of such metal.

To the accomplishment of the foregoing and related ends, the invention, then, consists of the ingredients and resultant coated product hereinafter fully set forth and particularly pointed out in the claims, the an The invention will be first describedwith particular reference to coated copper are weld pencils such as are employed, for ex ample, 1n certain known methods for attaching copper bonds to steel rails. In such case, a bare metallic copper electrode deposits metal in large globules which fall intermittently from the point of the electrode and which amalgamate with each other only in case the temperature of the work is high enough to prevent a chill of the first drop before the next shall have fallen. Inasmuch as copper is a metal of relatively low melting point, a chilled or cold shot condition is always found at the bottom of a copper are weld made with bare pencil. Particularly is this true in the application of this method of welding to rail bonding, where the first drops from the cou er electrode may fall on the cold copper of the conductor.

Even if a mold or dam be used in an effort to puddle the mass of the metal deposited into a molten lake, the critical part of the weld, that is, the contact, where the first metal from the electrode falls, will show the well If the bare copper electrode is used to deposit metal in strings or layers, as for instance on top of the lower flange of a rail, the mass deposited will be found to resemble a conglomerate of nodules poorly bonded together.

The difficulties attendin the use of a bare copper electrode for rail onding, resulting from cold shot effect, are greatly increased by the condition of the surface of the rail to be bonded. Any reducing agent introduced as an alloy into the copper metal of the electrode, capable of reacting with the oxide found on the surface of the average rail, requires more heat for a good reaction than can ossibly be obtained from the cold shot metal dropped intermittently from a bare copper electrode, although it must be said that the chilling effect of a steel body is much less than one of copper and that on a comparatively clean rail, copper are metal from a bare electrode makes better contact with the steel than it does with the copper of the bond conductor. The greatest difliculty from poor rail contact in using a bare copper electrode results from an adverse polarity. The common practice on electric railways of using trolley current direct through a rheostat, without transformation, for bonding, dictates that a positive electrode be used on track rail and a negative electrode on third rail. The greatest difference exists in the action of a bare copper electrode in the two cases. A drop of metal falling from the end of a ositive electrode drops downwards, while rom the end of a bare negative pencil, working on third rail, the drops of metal are propelled with force by a. flickering, fitful arc flame that sends the successive drops in unexpected directions.

. As previously indicated, I have discovered that if there be applied a coating to such a copper welding pencil, which is not only an agent for the reduction of any oxides of iron or copper that might occur at or in the weld, but which under the action of the are becomes a plastic tube encasing the copper at the pointof the electrode and draws somewhat over the point like a glass tube softened by heat for sealing, not only is the actual welding operation facilitated, but a much more homogeneous juncture is obtained between the parts being welded together, e. g. bond and rail. By employing for this coating a material that not only becomes thus plastic upon heating, but is also a good conductor with a melting point considerably higher than copper, the deposition of molten copper is greatly retarded with a corresponding increase in the amount of heat introduced into the weld. In fact, the action of this coated pencil is more that of an ideal selffeeding, non-metallic are, under which the molten copper is deposited more as a continuous spray of highly superheated metal than as a succession of the large drops from a bare metallic electrode. The absence of large drops and a spraying action as from an atomizer results from the constricted, plastic and overshot envelope of the electrode end which exercises a capillary attraction for the molten metal before it can collect in large drops, and also from the volatilization of certain elements in the coating which help to break up metallic globules.

The thickness and composition of the coat ing may be varied to secure any degree of heat, with accompanying slower rate of deposition desired, the limit being a coating so refractory that after the first few drops of copper have fallen, the end of the copper rod will have retreated to a distance above the end of the electrode, which end, from the material of the coating alone, becomes a very stable non-metallic electrode, with the result that no more, or very little, copper will fall and only a heating are will remain.

I have found that carborundum or silicon carbide, SiC, constitutes, when subjected to the action of the arc flame, a satisfactory material for the reduction of the oxides that occur in welding and at the same time prevents oxidation from the air and insures a sound set in the copper deposited. This compound or material also introduces elements for deoxidation which, if they occur in excess of oxidation needs, will alloy with both the copper and steel of the weld, while such material is also a conductor of the current of the are and thus when the coating projects as an overshot envelope at the end of the electrode, it will carry the current where the heat intensity is greatest and thus retard the flow of metal and consequently introduce more heat into the weld. Finally,it is refractory under heat with a melting point considerably above that of the ordinary metals.

In order to impart to the coating composition a plastic condition when it approaches the melting point, so that it will not fall off in crumbs, it is desirable to admix with such silicon carbide a binding material such as high silica clay, in which the binding quality is developed by the addition of water.

It is also desirable to include in the composition a certain amount of volatile matter to assist in breaking up large globules of molten metal as well as provide a fluid slag for floating off refractory crumbs, and for this purpose the fusible silicates comprised in common bottle glass, for example, may be added to the clay binder.

Finally, in order that the composition may be quickly and cheaply applied to the metallic pencil and be secured against dislodgment from handling, a suitable water soluble gum is added, a relatively small quantity of this in combination with the clay binder being sufficient for the purpose. The following is typical of a satisfactory composition including the ingredients named above, viz

Per cent Silicon carbide 68.5 Clay 10.5 F usible silicates 16.5 Gum 4.5

The foregoing percentages are based on the weight of the materials when dry, the materials being mixed in this condition and then made into a thin paste by'the addition of water and applied to the rod or pencil with a brush. After drying a coat of varnish may be added to toughen the skin of the coating.

7 In the process of welding the varnish and I form of the are as it attaches to thepoint of the electrode in the onecase or the other. Thus, as shown in Fig. 2, where the electrode is on the positive side, the adjacent portion of the arc is more or less confined to the exposed end of the metallic pencil, while, as shown in Fig. 3, where the electrode is on the negative side, the arc assumes a more spreading form and attaches to the projecting coating envelope as well as to the end of the metallic pencil; 'however, such envelope tends to close more or less across such end. In both cases the metal will lie back of the end an appreciable distance and will always present a clean appearance when the arc is discontinued, showing that there is no tendency for the metal to oxidize before it is deposited.

In case the deposition of the metal is unduly retarded, the projecting envelope or the outer portion thereof may be readily broken ofl by lightly striking the same against the parts being welded; while, on the other hand, if a coating of sui'ficient thickness is employed, by propermanipulation the arc "may be struck entirely from. such projecting envelope portion and used as a cutting arc.

While the melting point of iron or steel is considerably higher than that of copper, the

temperature at which the-envelope will melt is still higher and substantially the same operative results. are obtained where my improved coating is used on such iron or steel my invention may be employed instead of the one explained, change being made as regards the materials employed, provided the ingredients or elements stated by any of the following claims or the equivalent of such stated in redients or elements be employed.

I there ore particularly point out and distinctly claim as my invent1on:

1. An electrode for electric arc weldin which comprises a copper containing metal .lic rod and an envelope thereon containing silicon carbide in substantial proportion.

2. An electrode for electric arc weldin which comprises a copper containing metal lic rod and an envelope thereon containing about 68 per cent of silicon carbide.

Signed by me, this 13th day of October,

' CHARLES A. GADWELL.

pencil as with a copper pencil. Obviously it may be employed with equal advantage as a coating for pencils composed of other metals or alloys having the same relationship in the matter of temperature of fusion.

Other modes of applying the principle of

Images