Exploring Types of Welding Rod Flux Coatings

Table of Contents

Metal Ore

The most commonly used metal ores are ilmenite and hematite, and occasionally hematite. Currently, synthetic hematite and reduced ilmenite are used to replace natural hematite. Both are used to reduce TiO2 from titanium iron ore (TiO2+FeO+Fe2O3).

Synthetic hematite is produced through reduction in a liquid state, while reduced ilmenite is produced under solid-state powder conditions (TiO2≥45%), thus containing reduced iron powder (approximately 30%), along with unreduced FeO (5%~9%).

Titanium iron ore is divided into selected titanium ore (FeTi)O3 and titanomagnetite (FeTi)O4. (FeTi)O4 can be transformed into (FeTi)O3+Fe2O3, containing TiO2 8%~11%, FeO 30%~34%, and Fe2O3 46%~50%. Selected titanium ore comes in high-grade and low-grade varieties.

The former contains about TiO2 60%, FeO 9%~19%, Fe2O3 8%~21%; the latter contains approximately TiO2 45%~48%, FeO 30%, and Fe2O3 no more than 20%. In China, the low-grade selected titanium ore is generally used in the flux formula for welding rods.

Welding rods primarily made of TiO2 exhibit good operational performance because TiO2 can reduce slag viscosity and surface tension, which is advantageous for improving weld formation and slag removal. However, the flux has a relatively high melting point, and when the formulation is inappropriate, it may easily form larger sleeves, which is unfavorable for re-arc initiation.

Although the arc is stable, the blowing force is low, resulting in shallow penetration.

Rocks

Common rocks include carbonates, silicates, and fluorides, with the most diverse and complex types being silicates. The purest form is quartz, consisting of pure SiO2. Feldspar, kaolin, mica, and talc are all silicate aluminate, containing not only SiO2 and Al2O3 but also other oxides, such as K2O+Na2O in feldspar, K2O in mica, and MgO in talc.

Particularly, silicate aluminate often contains crystalline water or compound water, which can easily lead to hydrogen increase in the weld. Any material containing K2O has a stabilizing arc effect.

Carbonates can both form slag and generate gas, while also stabilizing the arc. As the decomposition temperature of CaCO3 and Mg-CO3 differs, attention must be paid during the drying of welding rods. Limestone is commonly used in basic electrodes, requiring a higher drying temperature of 400~450℃, while various types of carbonates can be used in acidic electrodes.

Fluorides are mostly used in basic electrodes dominated by carbonate, primarily serving to lower the melting point, dilute the slag, but their effect on reducing viscosity in high alkalinity is not significant. Fluoride can also remove hydrogen.

However, fluoride easily forms large negative ions, which is unfavorable for stable arc combustion, necessitating the use of direct current power supply. Furthermore, fluoride dust can become soluble in water, posing health risks to the human body.

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