How are oxides in slag classified? How to determine the slag acidity and alkalinity? What are long slag and short slag?

According to molecular theory, the oxides in the slag can be divided into three types according to their properties: acidic oxides such as SiO2, TiO2, P2O5, etc .; basic oxides such as K2O, Na2O, CaO, MgO, BaO, MnO, FeO, etc .; Al2O3, Fe2O3, Cr2O3 and so on. When there are many alkaline oxides in the slag, the slag appears alkaline. Conversely, when there are many acidic oxides, the slag appears acidic. Generally, the “alkaliness” is used to indicate the strength of the alkalinity of the slag:

K = total mass of various basic oxides / total mass of various acid oxides

In the formula, K represents the basicity of the slag. When K> 1.5, the chemical properties of the slag are alkaline and are called alkaline slag; when K <1.5, the chemical properties of the slag are acidic and are called acid slag. For example, the slag of E4320 electrode is mainly composed of FeO, SiO2, MnO, etc. It is mainly acidic oxide, which is called acidic electrode. The slag of E5015 electrode is mainly composed of CaO and CaF2. It is mainly based on alkaline oxides and is called alkaline electrode. Viscosity is one of the important physical properties of slag. The viscosity of welding slag depends on the composition and temperature of the slag. During the cooling process of the welding pool, the viscosity of the slag will gradually increase. According to the increase of slag viscosity during cooling, welding slag can be divided into two types: long slag and short slag. As the temperature decreases, the slag solidifies very slowly and the solidification interval is wide. This type of slag is called long slag. As the temperature decreases, the slag solidifies rapidly and the solidification interval is very narrow. This type of slag is called short slag. Short slag is characterized by low viscosity at high temperature, good fluidity and good metallurgical effect. The slag has a narrow solidification temperature range during solidification, which is suitable for vertical welding and overhead welding. When welding in all positions, short slag should also be used.