Welding Materials

Welding Materials

 

fluxes, electrodes, and shielding gases used in welding to obtain welded joints by means of a specified process.

Welding fluxes are nonmetallic materials used for various purposes, depending on the welding method. In arc welding, the flux shields the arc and the weld puddle from the effects of the atmosphere, prevents spatter, and physically and chemically affects the metal in the weld puddle. In electroslag welding, the flux forms an electrically conductive melt with specific engineering properties. In gas welding, the flux cleans the surfaces of the base metals.

The fluxes used in resistance welding and electroslag welding are granular; those used in gas welding are powders or pastes. A distinction is made between fusible granular fluxes, made by melting the components, and nonfusible fluxes (also called ceramic or agglomerated fluxes). The latter are made by mixing powder materials with a binder. In composition, fusible fluxes are alloys of silicate oxides and silicate salts; nonfusible fluxes are mixtures of pulverized ores, minerals, ferrous alloys, metals, and other materials held together by a binder, which is usually an aqueous solution of liquid glass or, less frequently, sodium aluminate or some other substance.

Welding electrodes are made of an electrically conductive material and conduct electric current to the weld. Electrodes may be consumable or nonconsumable. Consumable electrodes include welding wires, rods, plates, and strips with a solid cross section, wires and tapes with powdered cores and covered or combination electrodes (fusible tips). Nonconsumable electrodes include rods and electrodes used in resistance welding. Consumable electrodes also provide the filler metal of the weld puddle. The use of consumable electrodes of appropriate composition makes it possible to change the composition of the weld, alloy the weld with specific components, and lower the content of undesirable impurities. Depending on their purpose, consumable electrodes may be made of a variety of metals or alloys, including steel, aluminum, titanium, and copper.

A covered electrode consists of a rod and a covering. The rod may be fabricated from welding wire, or it may be cast. The covering is made from a mixture of materials that promote the ionization of the atmosphere near the welding arc, provide shielding against the undesirable effects of the atmosphere, and are effective in the metallurgical treatment of the melt puddle. Powder-filled tubes and strips consist of a metal shell filled with a powdered substance. Such substances include gas-forming and slag-forming materials, ferrous alloys, and metals.

Nonconsumable electrode rods are made of tungsten (either pure or containing ionizing additives, such as lanthanum oxide or yttrium oxide), high-grade carbon, or synthetic graphite. Carbon and graphite electrodes sometimes have a channel filled with a substance that promotes the ionization of the atmosphere near the welding arc. Electrodes used in resistance welding are interchangeable elements that carry electric current and transmit forces to the parts beingjoined.

Shielding gases, whether inert or active, affect the metal in the weld puddle in various ways. Inert gases, such as argon, helium, or a mixture of the two, form a shielding gas envelope in the weld zone that protects the weld from the effects of the surrounding atmosphere. Active gases also change the chemical composition of the weld. Active shielding gases used in welding include carbon dioxide (either pure or mixed with oxygen and argon) and argon mixed with carbon dioxide and oxygen.

REFERENCE

Tekhnologiia elektricheskoi svarki metallov i splavov plavleniem. Moscow, 1974.

V. V. PODGAETSKII

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