ISO 18275:2011 pdf free download – Welding consumables – Covered electrodes for manual metal arc welding of high-strength steels – – Classification.
C.1 General
The properties of a covered electrode, i.e. both its welding characteristics and the mechanical properties of the weld metal, are decisively influenced by the covering. This homogeneous mixture of substances generally contains the following six main components:
— slag-forming materials; deoxidants
— shielding-gas-forming materials; ionizing agents;
— binders;
— alloying elements (if necessary).
In addition, iron powder may be added to increase the weld metal recovery, which may affect the positional welding properties.
Certain electrode designs, while usable on both a.c. and d.c. (either or both polarities), may be optimized by their manufacturer for one particular current type for a particular market need.
C.2 Type 10 covering
Electrodes of this type contain a large quantity of combustible organic substances, particularly cellulose, in the covering. Owing to the intensive arc, such electrodes are especially suitable for welding in the vertical downward position. Arc stabilization is primarily by sodium, so the electrodes are mainly suitable for d.c. welding, normally with the electrode positive [d.c.(+)].
C.3 Type 11 covering
Electrodes of this type contain a large quantity of combustible organic substances, particularly cellulose, in the covering. Owing to the intensive arc, such electrodes are especially suitable for welding in the vertical downward position. Arc stabilization is primarily by potassium, so the electrodes are suitable for both a.c. and d.c. electrode positive [d.c.(+)] welding.
C.4 Type 13 covering
Electrodes of this type contain a large quantity of titanium dioxide (rutile) and are heavily stabilized with potassium. They produce a soft quiet arc, even at low currents, and are especially suitable for sheet metal.
Other methods of collection and measurement of diffusible hydrogen may be used for batch testing, provided they possess equal reproducibility with, and are calibrated against, the method given in ISO 3690. The hydrogen content is influenced by the type of current.
Cracks in welded joints may be caused or significantly influenced by diffusible hydrogen. The risk of hydrogen- induced cracks increases with rising alloy content and stress level. Such cracks generally develop after the joint has become cold and are therefore termed cold cracks.
Assuming that the external conditions are satisfactory (i.e. weld areas clean and dry, no excessive air movement), the hydrogen in the weld metal stems from hydrogen-containing compounds in the consumables; in the case of basic covered electrodes, the water taken up by the covering is the main source. The water dissociates in the arc and gives rise to atomic hydrogen which is absorbed by the weld metal. Under given material and stress conditions, the risk of cold cracking diminishes with decreasing hydrogen content of the weld metal.
In practice, the appropriate hydrogen level depends on the particular application and, to ensure that this is achieved, the relevant handling, storage and drying conditions recommended by the electrode manufacturer should be followed.