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148
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.
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)
Contact welding unit