TPT September 2012

Article

Precise, energy-efficient induction systems for the tube and pipe industry By Gerd Ommer, co-author: Dirk M. Schibisch, SMS Elotherm GmbH

HFI/HFC longitudinal seam welding of tubes and tubular sections Elotherm is the only manufacturer to offer customers both constant-current and constant-voltage high-frequency welding generators. Constant-current welders using a parallel resonant circuit with MOSFET transistors are designed for welding powers up to 800kW and frequencies from 100 to 600kHz. Effective solutions for induction welding and heating processes are a basic requirement for modern, cost- effective tube production. SMS Elotherm combines comprehensive skills in tube production systems with advanced process expertise and achieves low energy consumption through intelligent technology. This results in highly efficient and economical induction solutions.

Contact welding unit

The EloWeld TM constant-voltage HF generator with a series resonant circuit and IGBT transistor modules, introduced by Elotherm in the mid-1990s, offers welding power up to 2,000kW. Both EloWeld TM systems feature convenient and reliable load adaptation using reproducible capacitor switching with pneumatic switches, either manually or automatically from the control cabinet. A drawback of variable frequency adjustment, eg retuning the resonant circuit for different jobs, is the need for readjustment to restore the original frequency, voltage and current settings, which may be very time-consuming. To reduce service costs, easily replaceable standard modules with a single MOSFET or IGBT are used instead of expensive power units in the form of compact modules with many transistors. The digitally configurable converter features modern diagnostics and visualisation with online status and fault indications in plain text. Separation of the converter from the external resonant circuit offers additional decisive advantages. The external resonant circuit contains no unprotected electronic power units liable to cause problems due to vibration and moisture. There are no sensitive components, such as transistors or driver boards, in the direct vicinity of the welding line. They are located in the converter cabinet behind the line or in a central control room for easy servicing. The HF output transformer is designed as an isolating transformer, and pneumatic inductor clamps protect the external resonant circuit against deformed tubes (risk of being dragged along) and simplify safe inductor changes.

Pneumatic inductor clamps to simplify safe inductor changes and to protect the external resonant circuit against deformed tubes (dragging risk)

148

www.read-tpt.com

September 2012