TPT September 2012

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September 2012 151
Article
SMS Elotherm GmbH – Germany
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the tube to protect the inner surface against oxidation in the
annealed area.
After a short soaking zone, the red-hot tube is rapidly cooled
below the oxidation threshold by special cooling elements in
three stages. This cooling process also takes place with the
exclusion of oxygen. Residual cooling of the tube to room
temperature takes place in a water spray chamber.
Induction tube hardening and
tempering with EloMatTM
multi-zone technology
Innovative solutions from SMS Elotherm offer higher flexibility
than conventional furnace systems for induction hardening
and tempering of long products, especially with small batch
sizes.
In just a few minutes, tube hardening and tempering lines
can be ramped up or down and reconfigured for the next
material batch. In situations where materials of different sizes
and batches with different steel grades need to be hardened
and tempered at different temperatures on a daily basis,
output capacity can sometimes be increased by more than
half compared to hardening and tempering in a conventional
furnace.
In induction tube hardening and tempering systems, thermal
energy is induced directly in the material to achieve maximum
throughput for the entire range of tube products. This avoids
lost time due to conductive heating, which requires longer
process times.
A significant feature of modern tube hardening and tempering
systems is the high homogeneity of the tempered structure,
with uniform Rockwell hardness (variation ±1 HRC or better)
measured over the entire tube length.
Due to the very short heating times achieved with induction
heating, surface decarburisation does not occur and scale
formation is minimal compared to furnace hardening. The
negative effect of tempering brittleness with various material
grades that are preferably used for hardening and tempering
does not occur with induction technology.
Precise process management with high reproducibility in
conjunction with specific material handling during transport,
induction heating with controllable multi-zone technology,
effective quenching and a special cooling bed allow a high
degree of tube straightness to be achieved after hardening
and tempering. The straightness corresponds to that of
the input material and usually does not exceed 2mm/m;
sometimes it is even better.
SMS Elotherm offers to customers complete quench & temper
system solutions with comprehensive process expertise.
Induction tube heating
Induction heating processes have been the key technology for
round tubes and tubular sections for decades.
Cost-effective heating solutions for coating, bending and
cutting have delivered an optimal performance in practice.
Tube end heating before sizing or compression moulding in
several steps is also a precise and cost-effective induction
process.
In cooperation with a renowned German customer, SMS
Elotherm has developed a modern tube end joining technology
and has already delivered the first production systems. Unlike
conventional friction welding of round tubes, this new induction
pressure welding method also allows pressure-welded joints
to be made with oval or square tubes. The new process
avoids irritating material bulging at the joint as commonly seen
with friction welding.
Layout of a typical induction equipment for heat treating of tubes
(Quench & Temper)
Seamless, thick walled tubes after
the quench & temper process
Tube end heating prior
to a sizing press