a drive to bring technical advantage and reduce production costs, the
steel parts using magnetic field techniques for improved environment and
in-line manufacture project took an innovative approach to the heat
treatment process used to lend strength and durability in many steel products.
For the first time, the partners succeeded in using magnetic fields -
rather than conventional furnaces - to generate the high temperatures
needed. This consumes less energy, is more environment-friendly and is
economically viable for adoption by SMEs.
performance steel components are heat treated to optimise their strength
and durability. Today, this is performed mainly in batch furnaces housed
in separate steel plant departments, or - especially for smaller producers
- undertaken by specialised independent companies.
As a result,
the process typically involves costly and time-consuming transport of
the parts, and creates a need for manufacturers to carry larger stocks.
Another disadvantage is that the heated metal is usually cooled rapidly
by quenching in mineral oils, with the attendant environmental and fire
hazards. Until recently, however, no viable alternative method had been
found whereby steel could be through-heated up to the required temperatures
of 900°C and above.
with French research institution Cedrat Recherche prompted Sweden's
Magnetteknik International to propose exploring the use of magnetic
field heating technology (MFHT) to achieve the desired result. This
offered the prospect of substantial cost savings and a more environment-friendly
The result was the creation of a CRAFT
project, in which the consortium also included the Swedish
Institute of Production Engineering Research (IVF), two component
manufacturing SMEs - Uppakra from Sweden and Mölbro from Denmark
- and Rübig,
an Austrian specialist in heat treatment under protective atmospheres.
objectives were to build two prototype machines based on MFHT with
integrated water/gas quenching and tempering, and to test them on-line
at the two SME plants.
back the boundries
had previously concentrated on developing and supplying magnetic
field systems for applications such as the rapid pre-heating of
plastics moulding tools and shrink-fit parts. Here, the maximum
temperatures required were only in the region of 600°C.
steel hardening, we would be working above the so-called Curie point
of the metal, at which it loses its magnetic properties," explains
Magnetteknik's Erik Naslund. "This was unknown territory for
us, and we were not certain what results we could expect."
the project goals meant pushing back the boundaries of current knowledge,
using mathematical modelling, simulation and the investigation of
magnetic core materials. This would determine how the process temperature
limit could be raised while retaining uniformity of heating throughout
the body of the treated metal.
this end, Cedrat developed special calculation software, and trained
the other partners to use it. A key element was determining the
optimum frequency to be used, which depends on the nature of the
components being treated and the level of hardness required. This
was important because the manufacturing project partners were making
distinctly different types of product. Uppakra, a sub-contractor
to the SKF organisation, was producing bearing parts, while Mölbro's
output was agricultural implements such as ploughshares.
extensive trials with Mölbro, we learned a great deal about
the process. Ultimately, we proved that we could satisfactorily
harden the products, but were not able to meet their commercial
requirements in terms of cost," Mr Naslund observes. "With
Uppakra, however, we did reach a successful conclusion." For
the annular ball-races that were the subject of the investigation,
the working frequency proved to be above 2,000 Hz, compared with
the 50 to 900 Hz used in previous generations of equipment.
order to prevent the parts oxidising during hardening, we drew on
Rübig's experience to develop a prototype machine in which
the heating took place under vacuum," Mr Naslund notes. "In
this case, the speed of treatment proved to be such that this protection
was unnecessary. However, inert gas or vacuum chambers will certainly
be required for some applications. Other customers will require
further refinements such as pick-and-place robots, so we will need
to provide for these in our eventual system designs."
the end of the two-year project, the ball-races had been approved
by SKF as a basis for further testing. Uppakra subsequently took
delivery of the first MFHT production heater. Magnetteknik and Rübig
now plan to market the equipment throughout Europe, and foresee
its adoption for a far wider range of components.
of the new process include substantial manufacturing economies as
a result of the rapid throughput and smaller inventories. The environment
will be enhanced through energy savings and reduced transport requirements.
And, as the heaters handle single components rather than batches,
variations in properties after hardening can be controlled more
effectively by in-line inspection and statistical process control.
manufacturers of high-performance steel components now have access
to an advanced process of steel-hardening, which will help them
better compete with rivals from low wage economies, safeguarding
European jobs. The overall annual saving for European industry is
20 million, with the major benefit accruing to SMEs handling smaller