Daily Question: March 2, 2011 – Multiple Choice

I’m here to support you; choose ③ first, okay

My answer is "2"; welds made with basic electrodes have lower crack resistance compared to those made with acidic electrodes.

This post was last edited by SuperFree2316 on 2011-3-2 08:39. It should be better now!

The welds produced by alkaline electrodes have better crack resistance than those produced by acidic electrodes.③

Reply 1# gzf7390637lv 3 What is the difference between acidic welding electrodes and alkaline welding electrodes? Based on the properties of their coatings, welding electrodes can be divided into two main categories: acidic welding electrodes and alkaline welding electrodes. (1) Electrodes whose coating contains large amounts of acidic oxides (such as TiO2, SiO2, etc.) are called acidic electrodes. Acidic electrodes can be used with both direct current and alternating current; they exhibit good welding properties, with a low level of arc noise and spatter, good fluidity of the slag, easy slag removal, and an attractive appearance of the weld seam. Due to the presence of large amounts of silicates, iron oxide, and titanium oxide in the coating, they have strong oxidizing properties. However, the mechanical properties of the weld seam, especially its impact toughness, are relatively poor. These electrodes are suitable for welding ordinary low-carbon steels and low-strength low-alloy structural steels, and they are the most widely used type of electrode. (2) Welding electrodes that contain large amounts of basic oxides (such as CaO, Na2O, etc.) in their coating are called basic welding electrodes. Welding electrodes rely primarily on the decomposition of carbonates (such as CACO3 in marble) to produce CO2 as a shielding gas. The partial pressure of H in the arc column atmosphere is low, and CAF2 in fluorite combines with H at high temperatures to form hydrogen fluoride HF, thereby reducing the hydrogen content in the weld. Hence, alkaline welding electrodes are also known as low-hydrogen welding electrodes. The basic slag contains a high amount of CAO, which gives it strong sulfur removal capacity and good resistance to thermal cracking. Due to its low oxygen and hydrogen content, it has few non-metallic impurities; as a result, it possesses high plasticity and toughness, as well as good resistance to cold cracking ； However, since the flux contains a high amount of CAF2, which affects gas ionization, alkaline electrodes generally require a DC power supply and are welded using the reverse polarity method. AC power can be used for welding only when a arc-stabilizing agent is added to the flux. Alkaline electrodes are mainly used for welding important structures such as boilers, pressure vessels, and alloy structural steels. Comparison table of acidic and basic welding electrodes. J422 boasts excellent welding process properties, including easy arc initiation, stable arc, comfortable welding experience, easy slag removal, attractive weld bead shape, high deposition efficiency, and wide applicability. J38 (J421) not only exhibits the superior welding process characteristics of titanium-type slag systems, such as a stable and gentle arc, low spatter, good slag coverage, easy rod control, automatic lifting of the slag skin, attractive weld bead shape, and easy arc re-initiation, but also possesses good mechanical properties.