Arc welding uses two electrodes. The welder places one on the material to be welded, and an electric arc forms between it and the welding electrode. The heat this generates welds the metal. The strength of the electrode contributes to the overall strength of the weld, along with other factors, such as the width and length of the weld. You can normally take the electrode's strength from its written specifications, but if these are not available you can also calculate it from the weld strength.

Multiply the weld length by the weld width, both measured in inches. If, for instance, the weld length is 8 inches and the width is 0.2 inches, the formula would be 8 x 0.2 = 1.6.

Multiply your result by 0.525, which is the cosine of 45: 1.6 x 0.525 = 0.832.

Divide the weld's available strength, measured in kilopounds per square inch, by your answer. If, for instance, the weld has an available strength of 12 kilopounds per square inch, the formula would be 12 / 0.832 = 14.42. This answer is the weld electrode's nominal strength.

Divide your answer by 0.6, a constant coefficient. In this case, the formula is 14.42 / 0.6 = 24. This answer is the weld electrode strength, measured in kilopounds per square inch.
References
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