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Basic knowledge of welding materials

gdzhxc.com     2021-11-01     520

Because the development of welding technology in different countries is not the same, the development and application of various welding materials are also different.

1. Fusion welding material

The consumable materials used for welding during fusion welding are called welding materials. Commonly used welding materials include four types of welding rod, flux, welding wire, and shielding gas.

1) Welding rod

The welding rod is composed of two parts: the core and the coating.

On the one hand, the metal core can be used as an electrode to conduct welding current and generate an arc. On the other hand, the core is melted and used as a filler metal for the weld. Therefore, the chemical composition of the weld core directly affects the quality of the weld, and it is usually a special metal wire with low carbon, sulfur, and phosphorus content.

The coating is a coating layer that is press-coated on the surface of the welding core. It is made up of various raw materials such as mineral powder, ferroalloy powder and binder in a certain proportion. Its main functions are:

(1) Improve the manufacturability of the electrode, such as making the arc easy to ignite, keeping the arc burning stably, conducive to the formation of the weld, and reducing spatter.

(2) Mechanical protection function Under the action of high-temperature arc, the coating will decompose to produce a large amount of gas and form slag, which protects the molten metal.

(3) Metallurgical treatment effect Remove harmful impurities (such as oxygen, hydrogen, sulfur, phosphorus, etc.) through metallurgical reactions, while adding beneficial alloying elements to improve the quality of welds.

 According to different types of coatings, welding electrodes can be divided into two categories: acid electrodes and alkaline electrodes. The commonly used acid electrodes in production are calcium-titanium electrodes, and the commonly used alkaline electrodes are low-hydrogen mainly based on carbonate and fluorite. Type electrode. The arc of the acid electrode is relatively stable and adaptable. Both AC and DC welding machines are applicable. However, the mechanical properties of the weld are general and the crack resistance is poor. It is difficult to start the arc with alkaline electrode, the arc is not stable enough, and the adaptability is poor. It is only suitable for DC arc welding machine. However, the mechanical properties and crack resistance of the weld are better, and it is suitable for the welding of medium carbon steel and high carbon steel. 

2) Flux

Flux is a granular substance with a certain particle size. If the electrode coating is separated from the core, and the coating is granulated and applied, it can actually be considered as a flux. According to the manufacturing method of flux, it can be divided into two categories: melting flux and non-melting flux (ceramic flux and sintered flux). In order to make granular flux, a smelting method can be used. The powder is mixed according to the proportion, then heated to melt, granulated and dried to obtain the so-called smelted flux; if a similar electrode coating is used, only the adhesive is used to bond the powder and dried at low temperature (generally <400℃). The flux is called bonding flux. If it is sintered at higher temperature (400~600℃) or high temperature (700~900℃), it is called sintered flux. To distinguish it from smelting flux, bonding flux and sintered flux are collectively referred to as Non-melting flux.

3) Welding wire

There are two types: solid-cored wire and flux-cored wire. Solid-core welding wire is formed by drawing and processing hot-rolled welding rod steel wire, generally only called welding wire. There are many kinds of commonly used steel welding wires, and their composition varies depending on the welding object and the welding method used.

There are many types of solid wire, which can be selected according to the material of the welding structure and the welding method. Flux-cored welding wire can be used alone or in combination with flux or shielding gas.

4) Protective gas

Commonly used protective gases include CO2, Ar or CO2 Ar.

2. Brazing material

1) Solder

According to the basic composition of its alloy components, solders can be divided into gallium-based, bismuth-based, indium-based, tin-based, lead-based, cadmium-based, zinc-based, and other solders with a melting point lower than 450°C, and aluminum with a melting point higher than 450°C. Brazing filler metal, copper-based, silver-based, manganese-based, gold-based, nickel-based, and palladium-based alloys.

2) Flux

When brazing, generally use flux, which is the flux used in brazing. Its function is to remove the oxides on the surface of the solder and base metal, and protect the solder and the liquid solder from oxidation during the brazing process, and improve the wettability of the solder with the liquid solder. When brazing, the commonly used fluxes mainly include alkali, alkaline earth metal halides, fluorides, borax, boric acid, etc.; when soldering, the commonly used fluxes include organic and inorganic fluxes, such as organic acids (rosin acid), organic Amine salts, amines and amides, as well as inorganic acids (hydrochloric acid), inorganic salts (zinc chloride solution), etc.

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