99% of the Stud Welding completed for Field Heat Treating purposes is Capacitor Discharge Pin Welding. Regularly 12Ga Pins are used to fasten the Flexible Ceramic Heaters to different work pieces. 3” 12 Ga Mild Steel pins are the most used item for this purpose. Blunt Point pins have become the new industry standard for safety purposes, although some people still prefer the regular point (sharp point) pins.
These Pins are available in other alloys depending on the base metal of the work piece. In situations where the PWHT is required at higher temperatures or in PWHT furnaces that are susceptible to multiple heat cycles Stainless Steel pins are used.
4” – 6” 10Ga stainless steel pins are also used for insulating PWHT furnaces, although Drawn Arc Stud Welding of Insultwist Pins has proven to be much more durable.
This process uses a powerful capacitor to store energy at a specific voltage determined by stud size and material. When a weld is initiated, this energy is “discharged” through an “ignition tip” at the base of the stud, creating an instantaneous arc which creates a pool of molten metal in the work piece. The operator of the welding gun keeps tension on the stud which sinks into the work piece, resulting in a permanent bond as the molten material solidifies… all in fractions of a second!
Drawn-arc stud welding is a method of attaching fasteners primarily to steel by using a constant-current DC power supply. These power supplies are typically a 3-phase transformer-rectifier, equipped with controls to operate a special drawn-arc stud welding gun. When the weld is initiated, current begins to flow through the stud while the weld gun simultaneously lifts the stud to “draw an arc”, which melts the base of the stud and surface of the work piece. Upon completion of the weld time, the gun plunges the stud back to the work piece, resulting in a permanent bond as the molten material solidifies…all within fractions of a second.