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Research > Growth > Research projects > Steel technologies projects > Magnets prove hot prospect for steel treatment

Graphic element Magnets prove hot prospect for steel treatment

In a drive to bring technical advantage and reduce production costs, the Hardening 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.

Most high 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.

Magnetic field heating

Discussions 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 process.
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.

The 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.

Pushing back the boundries

Magnetteknik 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.

"For 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."

Achieving 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.

  Special calculation software

To 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.

"In 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.

"In 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."

  Savings for SMEs

At 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.

Advantages 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.

European 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 estimated at 20 million, with the major benefit accruing to SMEs handling smaller production volumes.

Magnetic field heating technology
Pushing back the boundries
Special calculation software
Savings for SMEs

Key facts

Steel is a basic commodity touching most aspects of our daily lives - from housing and transport to industrial plant, agricultural machines and defence equipment. The New materials and production technologies in the steel industry generic activity is aimed at helping European companies regain ground from competitors in the lower-wage economies. This CRAFT project was designed to bring particular benefits to SMEs (small and medium sized enterprises) by developing a more effective method of heat treatment.

Project: Hardening steel parts using magnetic field techniques for improved environment and in-line manufacture (BRST-CT97-5133)

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