Storage of welding electrodes

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Storage of welding rods ⒈ Principles ⑴ When storing welding rods, special attention must be paid to environmental humidity. The higher the relative humidity and temperature in the air, the higher the water vapor partial pressure, and thus the flux is more prone to absorbing moisture. When the water vapor partial pressure in the air is ≤5 mmHg, the moisture absorption of the coating is very low. However, it is generally recommended that the relative humidity in the air be below 60%, and that the equipment be kept at a certain distance from the ground and walls (about 30 cm). ⑵ Make sure to distinguish between the types and specifications of welding electrodes; mistakes must not be made. ⑶ When transporting welding electrodes, care should be taken during stacking to avoid damaging the coating; this is especially important for electrodes with a coating of poor strength ； Be especially careful with things such as high-strength steel electrodes, stainless steel electrodes, surfacing electrodes, cast iron electrodes, and so on. The welding rods should not be stacked too high. ⒉Effects of moisture on welding electrodes: When welding electrodes become moist, the color of their coating turns black. There is no sharp metallic sound when the electrodes come into contact with each other. Additionally, if the surface of the electrodes remains moist for an extended period, \"white spots\" may appear on it. In some cases, although there are no visible changes on the surface of the electrodes, the arc becomes stronger and more spatter is produced during welding. Impact of moist electrodes on process performance: (1) Intense arc with unstable combustion. ⑵A lot of splashing, large particles. ⑶It has a large penetration depth, making edge chipping likely. ⑷The slag coverage is uneven, and the weld bead shape is rough, resulting in indentation. ⑸Slag removal is difficult, and low-hydrogen slag has many surface pores. Effect of moist electrodes on weldability: The water absorbed by moist electrodes turns into gas under the heat of the welding arc, releasing hydrogen, which causes the formation of welding cracks and pores. The moisture absorption of welding electrodes is related to the way they are stored; for example, whether they are stored with their openings exposed or bundled together, or placed in electrode holders, all these factors affect the level of moisture absorption. To limit moisture absorption, welding electrodes are generally sealed in polyethylene plastic bags during packaging. However, even with this measure, complete protection from moisture over the long term is not possible. Therefore, limits on the maximum allowable moisture content of welding electrodes have been established, as shown in the table below: Coating type – Percentage of moisture content requiring re-drying: Titanium type: above 3%; Titanium-calcium type: above 2%; Cellulose type: above 6%; Low-hydrogen type: above 0.5%. There is a linear relationship between the moisture content of low-hydrogen welding electrodes and the amount of diffused hydrogen in the weld. According to available data, when the coating contains 0.2% moisture, the diffused hydrogen level measured using the mercury method is 5 ml/100g (for E7018). Thus, the necessary baking temperature can be determined based on the amount of diffused hydrogen in the weld. ⒊Redrying of welding rods: Welding rods absorb moisture over a long period of time from the time of manufacture until they are used. If the core of the rod does not rust and the coating does not deteriorate, redrying the rod can restore its original properties. The drying temperature is set in accordance with the specifications provided in the electrode manual; too low a temperature fails to remove moisture, while too high a temperature can cause the binder to decompose, leading to cracks in the coating. When welding and the molten metal approaches these cracks, the coating may peel off. Moreover, as the drying temperature increases, the alloying elements within the coating get oxidized, which affects the proper transition of the alloys. To dry welding rods, special ovens with automatic temperature control are generally used. It is advisable to dry only the amount of rods that will be used immediately; after drying, they should not be left outside for more than four hours. When stacking the rods in the oven, the number of layers should not exceed 3 for rods with a diameter of φ4 mm, and 5 for those with a diameter of φ3.2 mm. Otherwise, excessive stacking will lead to uneven temperature distribution and localized overheating, which can cause the coating to peel off. The drying oven must be equipped with a moisture exhaust device. The number of times it can be redried is generally 2 times. If it exceeds 2 times, the opinion of the electrode manufacturer must be sought. ⒋Discarded electrodes: For structural steel electrodes, especially low-hydrogen electrodes as well as those for heat-resistant and low-temperature steels, if the core is severely rusted (by bending the electrode to expose the core inside the coating), if the coating is heavily dampened with significant surface discoloration, if the coating sticks together in clumps or falls off in powder form (as is the case with cast iron electrodes), or if, in electrodes where alloying elements are delivered through the coating, the coating peels off, such electrodes can be considered unusable. If the core is valuable, such as in stainless steel or nickel-based electrodes, it may still be possible to remove the coating, re-coat it, and use the electrode again.