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 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. In recent years, the variety and dosage of domestic flux-cored wire are increasing. Compared with solid wire, flux-cored wire has the following advantages and disadvantages.
(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, which can provide the required weld chemical composition.
2) The process performance is good, and the candle seam forming is beautiful. Using the combined protection of gas and slag, good molding is obtained. 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. 1, the role 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 embrittlement of pores or weld metal, deoxidizers such as manganese and silicon must be added to the flux. For self-shielded flux-cored wire, AL should be added into flux as deoxidizer. The purpose of adding deoxidizer and nitrogen remover above is to purify molten metal.
(2) welding slag forming agent
Calcium, potassium, sodium or silicon are all slagging agents, which can effectively protect the molten pool from air pollution by adding flux. After rapid cooling, the slag can make the welding props look better and support the molten pool during full posture welding. 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 molybdenum, chromium, carbon, manganese, 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.
3.2 Types 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 material in acid system has good weldability, the arc is smooth and stable when welding, the shape is similar to jet arc, and the splash is small, which is widely loved by welders in operation. The mechanical properties of molten metal are average, but it 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.
In recent years, the development of flux system for low alloy steel welding materials combines the machinability of acidic system with the excellent mechanical properties of alkaline system.
Covered electrode coating refers to the coating coated on the surface of welding core. During the welding process, the coating decomposes and melts to form gas and slag, which plays the role of mechanical protection, metallurgical treatment and improvement of process performance.
The coating consists of minerals (such as marble and fluorite), ferroalloy and metal powder (such as ferromanganese and ferrotitanium), organic matter (such as wood powder and starch) and chemical products (such as titanium dioxide and water glass).
Commonly used coating covered electrode coating has titanium calcium type (J422 coating covered electrode, acidic slag) and low hydrogen type (J507 coating covered electrode, alkaline slag).