The manufacturing process control of flux cored welding wire is very strict

The manufacturing process control of flux cored welding wire is very strict. Due to the fact that the molten metal comes from the composition of the steel sheet and the flux, the dimensions and chemical composition need to be carefully checked before manufacturing to ensure quality.
Due to the limited internal space of the welding material, the size of the flux particles becomes increasingly important, forming a bird's nest like bond between the particles, resulting in uneven composition of the flux elements.
The vast majority of flux cored welding wires are rolled into a U-shaped cross-section by a flat metal thin strip, which is then filled with granular flux in the U-shaped metal groove. After the final sealing and rolling step, the flux is tightly rolled into the tubular welding wire
The welding wire rolled into a tubular shape is then subjected to a series of pulling actions to obtain the final required wire diameter. This pulling action can also ensure that the filled flux is uniformly fixed inside the welding wire material.
The key to the quality of flux cored welding wire production is how to prevent some wires from forming voids (without flux) due to poor control during the manufacturing/production process. In addition, the surface of the wire also needs to be smooth, smooth, and clean, otherwise it will affect the smooth wire feeding and the transmission of welding current. The welding wire is packaged in rolls or barrels to avoid entanglement or damage to the wires. Usually, the rolled wire is wrapped in a plastic sleeve and placed with a desiccant to prevent moisture. The wrapped material is then placed in a cardboard box and sent out.
When the skin material is thick, the cross-section is mostly in the BUTT mode and the amount of flux is small. The vast majority of carbon steel and low alloy steel have this shape of cross-section with a wire diameter of 2.8mm or less. For high alloys such as stainless steel and with a larger wire diameter, there needs to be a larger space inside the wire to accommodate the flux and alloy elements. The cross-section shape is often in the form of overlapping or heart-shaped (LAP and HEART SHAPED) joints.
As mentioned earlier, flux cored welding wire highlights the advantageous characteristics of many welding methods, such as the role of the flux part in improving the chemical composition and mechanical properties of the molten metal with the covered electrode. There are also characteristics of gas shielded metal arc welding and submerged arc welding in terms of production efficiency.
Flux cored welding wire can be used for welding carbon steel, low alloy structural steel, heat-resistant steel, high tension steel, high-strength quenched and tempered steel, stainless steel, and hard faced wear-resistant steel.
Flux cored welding wire is a promising new type of welding material
(1) Advantages:
1) For the welding of various steels, adaptability emphasizes the composition and proportion of the entire flux (commonly referred to as the flux core for general-purpose flux cored welding wires, and the term flux only appears in specific flux cored welding wires), which is extremely convenient and easy to provide the required chemical composition of the weld seam.
2) The process performance is good, and the weld seam is aesthetically pleasing. The gas slag joint protection is used to achieve good forming. Add arc stabilizer to stabilize the arc and ensure even transfer of molten droplets.
3) The deposition speed is fast and the production efficiency is high. Under the same welding current, the current density of flux cored welding wire is high and the melting speed is fast. Its deposition rate is about 85% -90%, and the productivity is about 3-5 times higher than that of electrode arc welding.
4) High welding current can be used for full position welding.
(2) Disadvantages
1) The manufacturing process of welding wire is complex
2) When welding, it is difficult to feed solid welding wires
3) The appearance of welding wire is prone to rusting, and the powder is prone to moisture absorption, so the requirements for the storage and management of flux cored welding wire are more stringent
3.1. The function played by the composition of the flux:
Similar to covered electrodes, manufacturers of flux cored wire have their own unique formula for the composition of the flux, and the composition of the flux varies depending on the applicable function of the welding material.
The basic functions of flux components are briefly described as follows:
(1) Oxygen and nitrogen removal agents
Due to the fact that nitrogen and oxygen can cause porosity or embrittlement in the weld metal, strong deoxidizers such as Al powder and weak deoxidizers such as manganese and silicon must be added to the flux. As for self-protection flux cored wire, AL needs to be added as a nitrogen removal agent in the flux. The purpose of adding deoxidizers and denitrification agents above is to purify the molten metal.
(2) Welding slag forming agent
Calcium, potassium, sodium and other silicosilicate substances are welding slag (also known as slag) forming agents. Adding them to the flux can effectively protect the molten pool from atmospheric pollution. Welding slag can provide a better appearance for the welding process, and after rapid cooling, it can also support the molten pool during full position welding. The coverage of welding slag can further slow down the cooling rate of the molten metal, which is particularly important for the welding of low alloy steel.
(3) Arc stabilizer
Sodium and potassium can keep the arc smooth and reduce splashing.
(4) Alloying elements
The addition of alloying elements such as manganese, silicon, molybdenum, chromium, carbon, nickel, and vanadium can improve the strength, ductility, hardness, and toughness of the molten metal.
(5) Gas forming agent
Fluorspar, limestone, etc. need to be added to the self protective flux cored welding wire to generate protective gas during combustion.
3.2 Types of welding slag
The composition of the flux determines the welding workability of the welding material and the mechanical properties of the molten metal. If the composition of the flux is mainly acidic, acidic welding slag will be generated after welding. Similarly, alkaline (calcareous) flux will be mainly used to produce alkaline welding slag. The welding process of acidic system welding materials is very good, with smooth and stable arc during the welding process, mostly through spray transition, and less spatter. It is widely favored by welding personnel in operation, and the mechanical properties of the molten metal can meet the requirements of AWS specifications.

Welding materials with alkaline systems can achieve excellent ductility and toughness in the molten metal, but their workability is much worse than that of acidic systems. The transition of molten droplets is mostly dominated by ball droplet transition, with more splashing.

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