Selection of electrode

Alloy type and wheel configuration are the primary factors that determine electrode selection.

Class 1 Copper.

  • Electrode wheels made of Resistance Welder Manufacturers Association (RWMA) class 1 copper (RWMA No. 1.16200) have been used for seam welding of aluminum and magnesium alloys, galvanized steel, and tinplated steel.
  • The minimum electrical conductivity of class 1 copper is 80% International Annealed Copper Standard (IACS). Recently, this material has been replaced by hot-forged and heat-treated RWMA class 2 copper in the overaged condition (RWMA No. 1.18200).
  • With adequate cooling and proper parameters, the high electrical and thermal conductivities of this material keep the electrode-workpiece interface at a temperature below the point where metallurgical discontinuities are formed near the weld surface.

Class 2 Copper:

  • Seam welding of low-carbon and low-alloy steel is usually done with electrodes made of hot-forged and heat-treated RWMA class 2 copper (RWMA No. 2.18200).
  • Minimum conductivity is 75% IACS. Minimum hardness is typically 65 HRB. Class 2 also works well with all types of coated steel, but the metallurgical optimization of weld parameters and provisions for wheel maintenance are critical to the success of welding coated steels.
  • For longer electrode life, premium class 2 wheels are available in the 20% coldworked form, where a minimum hardness of 75 HRB may be specified. Coldworked wheels show no appreciable loss of conductivity over the forged class 2 material.

Class 20 copper:

  • Class 20 copper (RWMA No. 20.15760) is also used for electrode wheels, with properties similar to those of class 2 premium wheels.
  • Class 20 wheels are made using a powder metallurgy process that produces a pure copper product, dispersion-strengthened with alumina. The alumina adds hot strength and tends to reduce pickup during welding of coated steels

Class 3 copper

  • Class 3 copper (RWMA No. 3.17510) is sometimes used for seam welding materials with lower electrical conductivities, such as stainless steel, Nichrome, and Monel alloys.
  • However, class 3 is used with special ventilation only because of the health hazard of atmospheric beryllium when welding or machining with class 3 material. (Beryllium-free class 3 alloy RWMA 3.18000 is also available.) Class 3 wheels have lower electrical conductivity (45% IACS), so they tend to run hot.

Sizes and Shapes

  • Electrode wheels range in diameter from 50 to 610 mm (2 to 24 in.). Popular sizes range from 100 to 305 mm (4 to 12 in.), with widths from 6 to 19 mm. Edge contours may be flat, radiused, beveled flat, or angled. In lap seam welding, weld quality seems to be easiest to control with a radius edge.
  • The need for nonradius contours is usually a matter of cosmetic appearance, or due to a tool access limitation. Mash seam welders very often use a flat-edge wheel

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