Due to the special influence of the thermophysical properties of carbon dioxide gas, it is impossible to form the axial free transition of metal liquid balance at the end of welding wire when using conventional welding power supply, and short circuit and droplet necking explosion are usually needed. Therefore, compared with the free transition of MIG welding, the splash is more.
However, if a high-quality welder is used and the parameters are properly selected, a very stable welding process can be obtained and splashing can be minimized. Due to the low price of shielding gas used, the weld seam is well formed when short-circuit transition is adopted, and high-quality welded joints without internal defects can be obtained by using welding wire containing deoxidizer. Therefore, this welding method has become one of the most important welding methods for ferrous materials.
Extended data:
1, preparation of flux-cored wire
The manufacturing process of (1) flux-cored wire is strictly controlled. Because the filler metal comes from the components contained in the steel plate and flux, the size and chemical composition must be carefully checked before manufacturing to ensure the quality.
Due to the limited internal space of solder, the size of flux particles becomes more and more important, the particles form a nest-like combination, and the flux composition is uneven.
Most flux-cored wires are rolled into a U-shaped cross-section by a strip of flat metal, and granular flux is filled in the U-shaped metal groove, and then the flux is tightly rolled in the tubular welding wire through the final sealing rolling step.
(2) The welding wire wound into a cylinder will become the final required wire diameter through a series of drawing actions, and this drawing action can also fix the filled flux evenly in the welding wire sheath.
How to prevent some welding wires from becoming hollow (flux-free) due to poor control in the manufacturing/production process is the key to the production quality of flux-cored welding wires.
In addition, the welding wire surface should be smooth and clean, otherwise it will affect the smooth wire feeding and welding current transmission. The welding wire is packed into coils or barrels to avoid winding or breaking of the welding wire. Usually, the coiled wires are wrapped in plastic sleeves, and desiccant is placed to prevent the materials from getting wet, and the wrapped materials are sent out in cartons.
When the leather material is thick, the cross section is mostly butt joint and the welding dose is less. Most carbon steel and low alloy steel have this shape of cross section, and the diameter of steel wire is 2.8 mm or less. When the diameter of welding wire is large, such as stainless steel and other high alloy materials, the cross-sectional shapes of flux and alloy elements are mostly overlapping or heart-shaped joints.
2. Features
As mentioned above, flux-cored wire highlights the advantages of many welding methods. For example, the flux part plays a role in improving the chemical composition and mechanical properties of the filler metal with covered electrode coating. Production efficiency is also characterized by gas shielded metal arc welding and submerged arc welding.
Flux-cored wire can be used to weld carbon steel, low-alloy structural steel, heat-resistant steel, high-strength steel, high-strength quenched and tempered steel, stainless steel and hard-faced wear-resistant steel.
Flux-cored wire is a promising new welding material.
(1) Advantages:
1) has strong welding adaptability to various steels, and it is very convenient and easy to adjust the composition and proportion of flux (commonly used flux-cored wires are often called additives as flux cores, and the word flux only appears in specific flux-cored wires), which can provide the required weld chemical composition.
2) Good process performance and beautiful weld. The combined protection of gas and slag is adopted to obtain good forming. The arc stabilizer is added to stabilize the arc and make the droplet transition uniform.
3) fast deposition speed and high production efficiency. Under the same welding current, flux-cored wire has high current density, fast melting speed, deposition rate of about 85%-90%, and productivity is about 3-5 times higher than that of covered electrode arc welding.
4) Large welding current can be used for all-position welding.
(2) Disadvantages
1) The manufacturing process of welding wire is complicated.
2) When welding, wire feeding is more difficult than solid welding wire.
3) The appearance of welding wire is easy to rust and the powder is easy to absorb moisture, so the storage and management requirements of flux-cored welding wire are more stringent.
3. The function of flux composition:
Like coated covered electrode, flux-cored wire manufacturers also have their own unique formula for flux composition, which varies with the different functions of welding materials.
The basic functions of flux components are summarized as follows:
(1) deoxidizer and denitrifier
Because nitrogen and oxygen can cause porosity or embrittlement of weld metal, it is necessary to add strong deoxidizer such as aluminum powder and weak deoxidizer such as manganese and silicon into flux. For self-shielded flux-cored wire, Al should be added to the flux as nitrogen remover. The purpose of adding deoxidizer and nitrogen remover above is to purify molten metal.
(2) welding slag forming agent
Silicate substances such as calcium, potassium and sodium are slagging agents (also known as slag), which can effectively protect the molten pool from air pollution by adding flux. The slag can make the welding props look better, and support the molten pool for full posture welding after rapid cooling. Covering with welding slag can slow down the cooling rate of molten metal, which is especially important for welding of low alloy steel.
(3) Arc stabilizer
Sodium and potassium can keep the arc soft and smooth and reduce splashing.
(4) Alloy elements
Adding alloying elements such as manganese, silicon, molybdenum, chromium, carbon, nickel and vanadium can improve (improve) the strength, ductility, hardness and toughness of the filler metal.
(5) gas forming agent
Fluorite, limestone, etc. It needs to be added to the self-shielded flux-cored wire to make the combustion produce protective gas.
4. Type of welding slag
The composition of flux determines the weldability of welding materials and the mechanical properties of filler metals. If the flux composition is mainly acidic, acidic slag will be produced after welding, and similarly, alkaline (calcium) flux will also produce alkaline slag.
The welding process of welding materials in acid system is very good, the arc is smooth and stable during welding, and spray transition is mostly used, with little splash, which is widely liked by welders in operation, and the mechanical properties of cladding metal can meet the requirements of AWS specification.
The flux in alkaline system can make the solder obtain excellent ductility and toughness, but its machinability is far less than that in acidic system. The droplet transfer is mainly spherical droplet transfer, with more splashing.
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