The coating of these electrodes contains organic materials that turn into gases in the arc. About 30% of the coating weight is cellulose. In some countries, paper pulp and wood powder are added to the coatingrterg in certain ratios to reduce the amount of pure cellulose. These organic compounds in the coating decompose in the arc to form carbon monoxide, carbon dioxide and hydrogen, which increase the arc tension and thus, the welding arc becomes stronger and harder. Compared with other types of electrodes, with the same current values, a 70% deeper penetration is obtained with cellulosic electrodes.
This type of electrode is generally produced with thin or medium coating thicknesses. When the coating is thin, a light amount of slag is formed on the welding beam and the spatter loss is high. On the other hand, the gap filling and vertical down welding capability as well as penetration of the weld obtained by this electrode is good. Since this electrode can be used in every position (particularly in vertical down), it has a wide range of applications in the ship building industry and in the welding of pipelines with a wall thickness of less than 12.5 mm. The cellulose that burns during welding forms a very good protective gaseous atmosphere.
Application
The main features of cellulosic electrodes are as follows:
The titanium compounds in the coating provide arc stability as well as help clean the slag easily. Adding a certain amount of ferromanganese to the coating makes it possible to compensate for the manganese that is lost through oxidation during welding and to deoxidize the weld pool. Since these electrodes are generally manufactured using a sodium silicate binder, they can best be used with DC(+).