Welding slag is mainly based on the alkalinity, ie basic oxide slag and by the ratio of acid oxides.
(1) acid electrode
Coating contains large amounts of TiO2, SiO2 and other acidic material and a certain amount of slag forming carbonate, etc., strong oxidizing slag, slag basicity coefficient is less than 1. Good acid stainless steel welding wires , arc stability, can be AC ​​and DC dual-use, small splash, slag slag fluidity and good, mostly glassy slag, loose, good performance slag, weld aesthetic appearance. Acid electrode coating contains more silica, iron oxide and titanium oxide, is strong, weld metal oxygen content is high, burning more alloying elements, alloy transition coefficient is small, deposition metal hydrogen content is higher, and thus lower weld metal ductility and toughness.
(2) basic (low hydrogen) electrodes
Coating contains large amounts of basic slag forming materials (marble, fluorite, etc.), and contains a certain amount of deoxidizing agent and alloying agent. Electrode depends mainly on alkaline carbonate (such as CaCO3, etc.) for the decomposition of the CO2 shielding gas, arc atmosphere, the lower the hydrogen partial pressure, and calcium fluoride in fluorite at high temperatures and hydrogen combine to form hydrogen fluoride (HF), reduce the hydrogen content in the weld, so the basic low hydrogen type electrode also called welding rod. Determined by glycerol, each 100g of deposited metal diffusible hydrogen content, basic nickel welding rod  welding rod for the 1 ~ 8mL, acid electrode for the 17 ~ 50mL. CaO quantity of basic slag, slag desulfurization capacity, thermal deposited metal cracking ability. Moreover, the basic oxygen electrode and the weld metal hydrogen content is low, less non-metallic inclusions with high plasticity and impact toughness. As basic electrode coating contains more fluorite, arc stability is poor, generally use more DCRP, only when the coating contains more amount of stable arc agent, we can pay, DC. Generally used for the more important basic electrode for welding structures such as dynamic load or rigid to withstand the larger structure.