US2086132A - Coated electrode for arc welding - Google Patents

Description

Patented July- 6, 1937 UNITED STATES PATENT OFFICE signor to The Lincoln Electric Company,

Cleveland, Ohio, a corporation of Ohio No Drawing. Application January 30, 1932,

- Serial No. 589,983

2 Claims.

The present improvements, having to do with coated electrodes for arc welding, have more particular regard to coatings suitable for metal and speciflcallyjiron electrodes known commercially as weld-rod. For certain uses it is found satisfactory to provide such weld-rod. simply with a wash coating, e. g., of a soap mixture, such coating making it easier to hold the arc. However, inother fields of use, it is essential and in practically all cases desirable to provide a coating on the weld-rod that will perform certain definite functions, .1. e., produce certain. desired effects in the welding operation. In particular it has been found desirable in many cases to sup;- ply an alloying ingredient to the weld metal as it is deposited in the seam or otherwise applied to the work, since it has been found that this will measurably increase the strength of the welded joint. Such ingredient can be more conveniently supplied in a coating on the rod than by including the alloying ingredient in the rod itself. It has alsobeen found important that a protective slag covering be deposited over the molten weld metal not only to prevent too rapid cooling of the latter, which may induce undesirable strains, but also to protect such metal before it sets from exposure to the atmosphere with consequent harmful absorption of oxygen and nitrogen. Such slag forming material, as well as ingredients which may act directly as deoxldizers of the molten metal, are likewise most conveniently included in the coating on the weldrod.

. Still other ingredients are desirably employed in such a coating in order to retard the rate of fusion or combustion of the coating as well as.

to mechanically bind the several ingredients into a hard durable coating which will withstand the handling to which the coated weld-rod is subiected during manufacture and transportation and incidentally to use. Kaolin or clay is generally used as such combustion retarding ingreclient and sodium silicate as such binder.

A certain minimum amount of each of the foregoing types of inorganic substances is necessary in the coating for best results. However, any amount in addition to this is detrimental, tending to form too much slag during thewelding operation, which results in slag inclusions in the weld, undercutting at the edge of the weld, depressions in the surface of the deposit and difficulty in cleaning off the resulting slag.

Finally, as-taught by Cravens (U. S. Patents Nos. 1,260,875 and 1,260,989), it has been recognized as desirable to surround the are by a nonoxidizing, insulating, gaseous vapor envelope, this not only to prevent lateral diffusion and dissipation ofheat but also to protect the highly heated molten metal, as it is transferred from the end of the rod to the work, against contact with the atmosphere with consequent objectionable absorption of gases. While the use of carbohydrate material, specifically in the form of a cotton cord wound upon the weld-rod, is described in the aforesaid Cravens patents, and while other equivalent organic materials such as paper pulp, wood pulp and wood flour, both in its natural state and chemically treated to remove the lignins, resins, etc., are described in various later patents, although not always with a full appreciation of the function of these materials in thus producing an insulating, non-oxidizing vapor in welding proximity to the work, I have discovered that there are other important conditions attending the use of such organic material, irrespective of its particular source or character.

More especially I have found that the volume per unit weight of such organic constituents is an important factor in the securing of satisfactory results from a coating of the type described. In addition I have found that the proper proportioning of such organic constituents to the several inorganic constituents employed, as well as the proportioning of the latter among themselves, is a factor of great importance in influencing the character of the slag deposited on the weld.

The object of the present invention, accord ingly, is to provide a coating composed of inorganic and organic materials of the types indicated which will'both provide an effective shielding atmosphere around the arc and produce a fluffy slag that will afford a satisfactory protec tion for the weld and at the same time be readily removable as well as eliminate slaginclusions, undercutting and other objectionable conditions. To the accomplishment of the foregoing and related ends, the invention, then, consists of the means hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail one approved combination of ingredients embodying my invention, such disclosed means constituting, however, but one of various forms in which the principle of the invention may be used.

As examples of the alloying ingredients which may be desirably, although not necessarily, in-

the latter purpose more specifically, titanium dioxide is desirably employed. In addition to the foregoing ingredients, a substantial amount of a compound such as kaolin, capable of forming a slag of high viscosity under the arc temperatures, is employed, together with a suitable refractory binder such as asbestos fiber and sodium silicate or water-glass, the latter in the form of a solution in water.

For the organic constituent, as indicated above, a variety of materials are available, these being preferably carbohydrates. Cotton of course is substantially pure alpha-cellulose and is a most satisfactory ingredient, whether employed in the form of a cord wound around the electrode or as cotton lint or chemically prepared alpha-cellulose. The same is true of paper pulp or wood pulp or flour where such wood pulp or flour has been chemically treated to eliminate the resins, etc., although where the other conditions hereinafter set forth are observed, such elimination is not as important as has heretofore been assumed.

The amount of shielding atmosphere produced by the organic constituents thus incorporated in the coating I have found depends upon the weight of such constituents. A certain minimum amount of shielding atmosphere is of course essential in order to prevent oxidation of the weldmetal and to shield it from the nitrogen. of the air. However, an excess of organic constituents is detrimental in that the latter do not burn completely and tend to cause the formation of gas holes in the weld.

On the other hand, since-a definite thickness of coating on the weld-rod is necessary in order properly to confine and direct the arc, it is evident that the proportion of organic to inorganic constituents in the coating depends not only upon their proportion by weight in the mixture, but" also to a great extent upon their respective volumes per unit of weight. Accordingly, since the volume per unit weight of the inorganic constituents is fairly constant, I have concluded that it is of the utmost importance in theproper design of a coating to pay particular attention to the volume per unit weight of the particular organic material used. Now, the materials generally used for this purpose vary in volume per unit weight from about 1 cubic centimeter per gram to about 3 cubic centimeters per gram' in their air-dried state. This may be conveniently measured by weighing a given amount of the material into a graduated cylinder and tapping the bottom of the latter on a block of wood until the surface of the material settles down to its minimum height. The volume may then be read directly in cubic centimeters. Organic materials which are suitable as fiux constituents can be produced in a light fiuffy fibrous form which, when measured in the manner outlined above, will have volumes per gram weight as high as 20 cubic centimeters. I have found, however, that best results are obtained if the organic material used in the coating has a volume of 3.5 to 6 cubic centimeters per gram weight, when such material contains approximately 10% moisture. An organic material having this volume per unit weight prorluces a coating which enables the correct weight of such material to be employed without increasa lesser volume per gram than that indicated above as desirable.

If wood pulp is selected as the organic material for use in the foregoing mixture it should have a density corresponding with a volume of from 3.5 to 6 cubic centimeters per gram weight determined in the manner set forth above. In place of such wood pulp, alpha-cellulose in its ordinary commercial form may be obtained having substantially the same density, and this is als true of certain grades of cotton lint.

The foregoing organic and inorganic ingredients may be added to each other in any desired order as most convenient and then thoroughly intermixed. It should be stated that the-sodium silicate solution will contain approximately 40% of such silicate but more or less water may be used in such solution, or, if necessary, additional water may be added to the mixture in order to produce a paste of the proper consistency to permit its extrusion or application to the metal wire or rod. The coating after being dried. at ordinary or slightly elevated temperatures in the air will firmly adhere to the metal without baking and be sufficiently hard and resistant to withstand such handling as is ordinarily encountered in the handling and use of these coated electrodes.

Other modes of applying the principle of'my invention may be employed instead of the one explained, change being made as regards the materials employed, provided the ingredients stated by any of the following claims or the equivalent of such stated ingredients be employed.

I therefore particularly point out and distinctly.

cellulosic material characterized by the fact that substantially all of the cellulosic material present in the covering before being combined with the remaining ingredients of the covering is in. such state that when settled together in an air dried state and containing approximately 10% moisture, one gram of the material will have a. volume of approximately 5 cubic centimeters.

THEOPHIL E. JERAB-EK.