Technology News
102
M
arch
2014
Benefits of induction heat
treatment for tube and bar
By Guido Opezzo and Dirk M Schibisch
of SMS Elotherm
INDUCTION quench and temper (Q&T)
has now become firmly established
practice, particularly in applications
that require precise, fast, flexible and
repeatable heat treatment of tubular and
bar material. A process in successful use
for heat treatment of bar material for many
years, induction quench and temper has
recently been extended to cover tubular
products. The new processes developed
include technologies for pipes with upset
ends, creating special demands on the
induction heating processes used.
Induction quench and temper was
initially used only in the production
of automotive components such as
stabilisers, which for the cold-bending
process require a consistent hardness
and microstructure along the workpiece,
properties that could not be achieved
with conventional combustion furnaces.
After the induction quench and temper
of bar steel had gradually prevailed in the
industry, the process was also developed
for tube material such as seamless tubes
and inductively longitudinally welded
tubes. Compared with the conventional
processes using combustion furnaces
and supported also by the booming
market of OCTG products (oil country
tubular goods) for the exploration of oil
and gas, the results were so convincing
that the induction quench and temper
process for tube material has within the
last two years prevailed completely.
Compared with conventional methods
using furnaces with fossil firing systems,
the induction quench and temper of long
products is beneficial to owners in several
respects. The main differences that lead
to sustained savings in production are
outlined briefly in the following. Current
demands for a reduction of stocked
material and the large number of different
materials lead to a flexible just-in-time
production strategy in heat-treatment
shops, with small batch sizes of just 30
to 50 tons.
In many cases this means that batches
with different material dimensions and
grades need to be heat-treated at dif-
ferent quench-and-temper temperatures
several times a day. The limits of
conventional combustion furnaces are
quickly reached here, as these furnaces
are unable to respond flexibly enough to
varying batch sizes, and temperatures
can be adjusted only very slowly.
Especially where flexible production
lots are concerned, the benefits of the
induction technology become clearly
recognisable. For a change of the batch,
the whole induction line can be run
empty within a few minutes and set up
again for the next batch with a minimum
work effort. To do so, the owner has at
his disposal high-speed tool changing
systems to ensure that operation can be
changed over to energy-efficient heating
coils with a suitable diameter within a
few minutes.
Another benefit of induction in this
context is the rapid and easy identification
of heat treatment recipes for new
materials or component geometries. This
allows test production runs or quality
tests to be performed at a minimum cost
for customers who, in turn, will thus gain
a competitive edge – a classical win-win
situation for all parties involved.
Whereas conventionally heated
chamber or continuous furnaces always
require the entire furnace space to be
heated to the necessary temperature,
thus achieving a good efficiency only
with fully loaded furnace, an induction
quench and temper line will respond
flexibly to different batch sizes and
dimensions. An induction quench and
temper line which, for example, is
rated for a maximum throughput of 13
tons/hour and can process workpieces
with outside diameters from 3 to 9", is
capable of achieving these 13 tons/hour
with 3" tubes or with 9" tubes.
This is possible because induction
generates the heat directly in the
workpiece and does not need to be
supplied from outside. Long material
passes through the induction coils at
the speed adjusted to the respective
diameter and is thus heated to or soaked
at the material-specific austenitisation
or temper temperature within a few
seconds.
It is only by induction quench and
temper that owners are able to always
fully utilise their equipment, as material
can be produced at a maximum
throughput, irrespective of the material
dimensions. Still, if smaller batches
need to be run because of small
production lots, a matured converter
technology as used by the Elotherm
iZone™ system also allows certain coil
sections to be cut off. This ensures that
only the minimum amount of energy
needed to heat a defined amount of
material is always consumed, which will
have a lasting positive effect not only
on the direct reduction of production
costs, but also on the reduction of CO
2
emissions.
SMS Elotherm GmbH
– Germany
Website:
Shaping roller made
of GP4M hardened to
58-60 HRC
