Alkaline electrodes often use marble (calcium carbonate) as a gas generating agent. When heated, CO2 is generated and becomes a protective gas. Therefore, there is very little hydrogen in the welding zone and the hydrogen content of the weld metal is low. Therefore, alkaline electrodes are also called low hydrogen. welding rod. The acid welding electrode is usually made of starch, wood flour, cellulose and other gas-generating agents. After thermal decomposition, more H2O is generated in the welding area, which significantly increases the hydrogen content of the weld metal. There are several reasons why alkaline electrodes must be reverse connected:
① Because the coating of alkaline electrode contains more fluorite, fluorine with a higher ionization potential is decomposed in the arc atmosphere, so that the stability of the arc is reduced.
② If an AC welding machine is used, a stable arc cannot be established. If DC direct connection is used, when the droplet transfers to the molten pool, it will be impacted by the positive ion current emitted from the direction of the molten pool, which will hinder the transfer of the droplet and cause splash and arc instability.
③ When using DC reverse welding, not only can reduce the phenomenon of splashing, but also because the molten pool is located at the cathode, the hydrogen positive ions emitted from the direction of the welding rod and the electrons on the surface of the molten pool are neutralized to form hydrogen atoms, reducing hydrogen holes.
