Fluxes for submerged Arc Welding (SAW Fluxes)
The main function of the flux for welding with Flux Clad Welding Wire (SMAW) One of the main functions is to protect the weld pool from the air. But there are several different things:
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- SAW Fluxes are granular.
- SAW Fluxes are not designed to be extruded and do not contain any flux to coat cores, wires.
- SAW Fluxes can be used with a wide range of welding currents. In some cases, a welding current of up to 2000 amps may be used.
- SAW Fluxes do not need to produce gas to cover the melt well like SMAW does. Organic materials such as cellulose are not used with SAW Fluxes.
Mineral fluxes are composed of oxides of calcium, silicon, manganese and other elements. The flux must have a lower melting point than the weld. so that the molten slag can float above the weld before the weld hardens. Slacks are melted in the temperature range of 1,100 – 1200 ℃. When hardened, slag has a greater shrinkage rate than steel so slag shrinks faster and can be easily knocked out of the weld. The flux at the displacement will come off on its own without knocking. And cleaning welds does not require chisels or grinding stones. If welding with good flux
2.2.1 Flux production method
There are two methods of producing SAW Fluxes.
Method 1 Use all the mixtures of melting flux together. Subsequently, it is grinded to the desired size.
Method 2 Mix all the flux ingredients together and dry them. For this method, it can also be divided into 2 types according to baking temperature: Agglomerated or Bonded Fluxes.
2.2.2 Type of Fluxes
SAW Fluxes are classified according to the flux production method. Each type of flux has certain properties. and influencing the mechanical and chemical properties of SAW Fluxes can be divided into the following types:
1) Fused Fluxes are produced by drying all flux mixtures. Then melted at a temperature of 1500 – 1700 Cº by melting in an electric furnace with direct current flowing through the flux. When the flux melts, it conducts electricity. Subsequently, the molten flux is poured into water or on a plate to cool (Chill Plate) and grind to the desired size. The last step is to separate the size of the flux beads.
The advantages of this type of flux are
- The ingredients in the flux are homogeneous.
- Flux is not hygroscopic.
- Used flux can be reused.
- Suitable for high speed welding.
- Deoxidizer and Ferroalloys cannot be added to the flux. This is because the production of this type of flux uses high temperatures. This will cause the elements to lose and dissociate during the flux production process.
2) Agglomerated and Bonded Fluxes
Both fluxes are produced by combining different ingredients. The flux is mixed together, including ferrosilicon, ferromanganese, sodium silicate, titanium, etc., and then bake until small particles stick together into small globules. and later to grind to size Curing temperature for Agglomerated Fluxes 800 – 1000 Cº For Bonded Fluxes, the production process is the same as for Agglomerated Fluxes, the difference is that the curing temperature of Bonded Fluxes is lower.
- This type of flux is produced at low temperatures. Therefore, Deoxidizer and Ferroalloys can be added to the flux.
- The flux density is low so it can be used to cover the weld thicker.
- The flux melted into slag can be easily knocked out.
- Once used, it cannot be recycled because the chemical composition has changed.
- Easy to absorb moisture. Storage must be careful.
Agglomerated Fluxes are denser than Fused Fluxes by weight and in welding Agglomerated Fluxes are approximately 20% less than Fused Fluxes by weight.
The flux must be stored in low humidity. For transportation, it must be packed in moisture-proof packaging. If the flux is wet, it must be baked at approximately 400 °C for 1 hour. will cause the weld to become porous or cracked and to store used flux for reuse Should be careful of impurities mixed with flux, such as iron rust, oil, etc., because the impurity causes porosity.
2.2.3 Flux Chemical Reaction
The main purpose of the flux is to cover the weld wells without air. and the flux itself reacts with the weld The important thing that will have consequences is
- The composition of the weld is not necessarily the same as that of the weld wire, as the flux may add elements to the weld. and may reduce another element from the weld as well
- The flux may transfer oxygen to the weld.
Changes in the weld composition depend on the type of flux, the chemical composition of welding wire and the melting ratio of slag to A wire in which the flux transfers an element, meaning elemental silicon or manganese, to the weld. Flux with less elemental transfer to weld is called “Neutral” or “Inactive Type”, for flux with more elemental transfer to weld is called “Active Type”.
The oxygen content of the weld flux can be further divided into 2 levels, which is the level of high oxygen content of the weld called “Acidic”, while the flux with less oxygen is added to the weld. called “Basic”
It is very important to know the influence of flux on the weld mixture. Because it affects the properties of the weld as well. For this reason, we have to choose a welding wire. If the flux contains a large percentage of silica (SiO), the silicon content in the weld is higher than that. Similar electrodes, the chromium content in the weld may be lower than that in the weld wire, and care must be taken in the selection of stainless steel fluxes.
Minimal loss of chromium
As mentioned above, the advantages of Agglomerated or Bonded Fluxes can be added with Deoxidizer and Alloys.
The amount of deoxidants transferred to the weld It depends on the amount of melted flux. and electromotive force Some fluxes are sensitive to changes in welding parameters (Welding Parameter) and in some cases they are recommended for use only for single-line welding. Figure 4 shows the effect of the electromotive force on the silicon content in weld meat. By comparing Active and Neutral fluxes, when choosing a flux it is important to consult the manufacturer’s recommendations. The recommendations may indicate limitations in use. or require a special process in order to provide the most efficient use
– When using Active Fluxes, the amount of silicon and manganese transfer to the weld depends on the amount of melted flux or electromotive force applied.
– When using Neutral Fluxes, the gain and loss of manganese and silicon of the weld It has no effect on the melting amount of flux or electromotive force.