US1674576A - Welding electrode - Google Patents

Description

Patented June 19, 1928.

UNITED STATES PATENT OFFIKCE,

ARTHUR STBOHKENGEB, OI IONDON, ENGLAND, ASSIGNDB TO THE QUASI-ABC OOIPANY- LIMITED, OF LONDON, ENGLAND.

WELDING ELECTRODE.

Io Drawing. Application filed June 17, 1928, Serial No. 116,730, and in Great Britain September 18, 19.5.

This invention relates to electrodes such as are employed in the fusion deposition of metals b the process known as arc welding an for cutting or preparing metal I surfaces preparatory to welding or other operations.

For many years past it has been realized that in order to effect electric welding with the deposition of fused metal the deposit should be as free as possible from oxide or other impurities. It is of great importance to select a suitable covering material for the metallic electrode which shall form a slag during the welding operation and will tend to remove impurities from the metal while also protecting the metal from ox1dation during deposition and cooling. Various forms of covering materials have been proposed and used from time to time for' his purpose, some of these being applied as a paste, while in recent years other forms of coverings have been developed, one which has ha a very large use being a covering of blue asbestosyarn or fibre wound spirally around the electrode. It has been recognized that blue asbestos contains a substan tial' proportion of iron in the form of ferrous silicate, and its favourable effects have been attributed to the reducing action which iron in the ferrous state is capable of exertin in the slag. In order to increase this e ect, aluminium on an equivalent material havin a high afiinity for oxygen has-been use generally wound in with the covering in the 85 form of a wire, stri or plating on the metallic core of the e ectrode, and'electrodes made in this manner, as described for example in the specification of in United States Patent No. 1,144,390, have en very successful in practlce.

I have found, in comparing the results obtained from electrodes covered with various mixtures of blue asbestos with white asbestos and other materials, that the higher the percentage of iron, that is to say the nearer the covering material is to being pure blue asbestos of high iron content, the more effective in neral is the slag covering in producing t e results desired. These re sults, however, depend according to my researchnot only upon the Ereducing action of the slag which melts with the core of the electrodes during the welding, and covers the surface as the welding progresses, but also upon thevarious other characteristics of the slag material. For example, it is most important that the slag should flow evenly and regularly over the surface of the inolten metal covering it completely, and forming a layer of suflicient thickness to insure that the rate of cooling of the metal deposited will be favourable to the ultimate structure of the weld junction between the deposited metal and the body of the metallic article on which the deposit is being effected. The fusion temperature of the covering material is also important, and the fusion temperatur e of blue asbestos has been found to make it more suitable as a covering material for electrodes than most other substances, while the possibility of applying it spirally around the electrode as a yarn is a matter of very great practical importance because it insures the even and regular fusion of the covering as the electrode core melts.

The slag resulting from some covering materials does not fuse evenly as the electrode core is melted, and the slag forms an indifferent or irregular covering on the surface of the deposited metal, with the result that not only is oxidation liable to occur, but the metal cools in such a way that the junction between the welding metal and the metallic structure to which it is applied is liable to have a coarse crystalline formation which tends to produce serious weaknesses in this zone. Welds made with blue asbestos as a covering material upon the electrodes are strikingly superior to welds made with other kinds of slags applied to the electrode, but the research has shown that there is room for further improvement in this respect. Attempts to increase the amount of iron by incorporating as'olid ferrous, oxide in the covering material, have not proved successful, possibly because of the necessity of applying such material as a paste involving other constituents which render the added oxide of iron inefiective for the purpose in view.

I have now found that it is possible to attain the desired result with the use of minerals other than crocidolite, but which occur ina long crystallineor fibrous form and which contain a higher percentage of iron. One of these minerals is a'variety of hornblende known as amositeF; Whereas crocidolite contains generally from 24 to 28% or thereabouts -of iron, amosite contains generally well over 30% or iron, and sometimes nearly 40%. It is essentially an iron silicatebut the proportion of ferrous to ferric oxide in its composition is liable to vary substantially. In experiments which I have made with this material, using it alone or in a mixture with blue asbestos as a covering for electrodes I have discovered that it has substantial advantages over any other covering material, not only in the directions mentioned already but in otherrespects, as hereinafter set forth. The slag resulting from this material has a high iron content and itsco-efli'cient of expansion is substantially different from that of deposited metal, with the result that as the. metal cools, the slag covering tends to separate from the deposit, and is easier to remove than the slag resulting from blue asbestos alone. The slag formed does-not tend to separate from the deposited metal until this latter has cooled down to a point well below that at which there is risk of oxidation, probably about from 200 ,to 150 (1, so that the surface of the metal deposited is not deleteriously affected even if the slag flies off on its own account at or below this temperature. The improvement in the crystal -structure at the weld joint when the covering material contains the higher iron content is mosthnarked, the

crystals as shown byflphotomicrographs of sections of the weld at the weld junction being comparatively small and very uniformly distributed. Iran only attribute this result to an improved annealing effect due to the use of this new covering material.

Although amosite, when'used as the main constituent of the covering material, has all the advantages set forth, yet certain inci dental difficulties arise in connection with its use. Amosite fibres are "found to be considerably more brittle than those of blue asbestos, so that the 'material is more difficult to card and to spin into yarn. Further, when amosite is used as the covering material, the slag is more viscous than that from blue asbestos, probably owing to its -7 high iron content, and this renders the operation of welding with amosite-covered .electrodes rather more diflicult. The operator has ,to'be particularly careful to avoid trapping slag in the .weld metal. For these reasons I prefer to use a mixture of blue asbestos and'amositefibres, which can be carded and spun together, the spun mixture being very suitable for use as an electrode covering material. It has the requisite strength for winding, and the slag flows more freely so that welding is facllitated, and the results are more uniform and reliable. I find that a mixture of about equal parts of blue asbestos and amosite is very suitable for all purposes, as the yarn has the necessary strength, the addition of the amosite substantially increases the iron content in the slag, and the welds havea high resistance to fracture, as tested by alternating impact and bending stresses, or in any other effective manner.

Although amosite ,has been referred to as the material preferably used to increase the iron content of the electrode covering, it is to be understood that any mineral consisting essentially of silicate of iron crystals in a long fibrous form, so that it can be spun into yarn or otherwise applied as a fibrous covering to the core of an electrode, may be used provided that its percentage content of iron is sufficient for the purpose in view. The improvements which I have noted are most marked when forms f amosite con- ,taining f om 35% of iron upwards are used,

but a s' bstantial improvement over anything obtainable with bli1e asbestos and other covering materials aloneis noticeable even when the iron content of the covering material is but little more than 30%. v The covering material or mixture of materials is preferably spun into yarn and applied to the electrode core by winding spirally thereon with' the use of sodium silicate or other material of a similar. character to secure the turns of the yarn upon the electrode and to make a paste or cement which may be added to by impregnating the electrode with any other materials in solution or suspension. Although it is preferable to apply the material as a yarn, the fibrous material may be lapped around the electrode in any suitable manner, and the invention is not limited to spinning the material into yarn before its ap licatlon.

he invention is also not limited to the" use of electr des covered with amosite alone or mixtures thereof with blue asbestos, for the-deposition of iron and ,steel, as the same covering material may be employed for electrodes made of any of the metals which are capable of being deposited by fusion depo- I I claim as new and desire to secure by ters Patent is 1'. An electrode adapted for use in the weldin and cutting of metals, comprising a meta lic core with a covering of fibrous material wrapped around it, said fibrous material consisting essentially of e mixture on, said composite yarn consisting of a. mixof fibrous crocidohte and amosite in the proture of fibrous crocidolite and amosite so portion of about one-halfQach. proportioned that the iron content is be- 10 2. An electrode adapted for use in the ..tween 30 and 40 per cent. 5 welding or cutting 0m metals comprising In witness whereof, I hereto -subscribe my a metallic core with a covering in the form name this 7th day of June,- A. D. 1926. of a composite yarn wrapped spirally there- ARTHUR PERCY STBOHMENGER.