Electrical steel strip for large magnets used in radiation equipment (hero image)
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High-performance electrical steel strip with outstanding magnetizability for large magnets used in medical radiation equipment

Radiation therapy plays an integral role in the treatment of cancer, with state-of-the-art proton therapy equipment increasingly becoming the standard of care. This treatment method uses special high-performance magnets to generate a precisely aligned proton beam that targets tumor cells without damaging healthy tissue. As a result, medical technology companies rely on high-performance electrical steel strip materials from Waelzholz to manufacture the large magnets used in this radiation equipment.

Medical treatment centers that perform proton therapy often consist of entire building complexes and are equipped with sophisticated systems technology that generates protons and accelerates them to 60% of the speed of light (180,000 km/sec (111,847 miles/sec)). The radiation units used in these facilities consist of a particle accelerator known as a cyclotron and vacuum tubes that guide the protons to the precise spot on the body receiving the radiation treatment. Large magnets positioned on the tubes use strong magnetic fields to ensure that the radioactive proton beams specifically target only the cancer cells in the body (see Figure 1: Proton therapy).

Waelzholz manufactures high-performance electrical steel strip within the tightest tolerances featuring excellent magnetizability for large magnets used both in cyclotrons and on the vacuum tubes of proton therapy equipment. In this context, it is crucial that our material’s properties meet the highest standards and remain constant even over large batch sizes. This is due to the fact that a considerable quantity of our material is needed for these large magnets – the magnets used in such a system weigh between 15 and 25 metric tons each.

Electrical steel strip with high polarization for powerful magnetic fields

Daniel Dunker, responsible for the special product electrical steel strip in Waelzholz’s Material Technology Department, explains: “The electrical steel strip has to generate extremely powerful magnetic fields for this application. Due to the size of the magnets, a large amount of iron is also required. This is why electrical steel strip with a thickness of approximately one millimeter (0.039 inch) is the standard material used to manufacture these special magnets. We supply various versions of it in accordance with the EN 10106 standard.” In addition to its excellent magnetizability, the large material thickness also offers advantages during the subsequent production steps, as it reduces the number of steel plates required for each magnet and therefore the time and effort required for the necessary punching processes.

Stable and low-vibration lamination stacks thanks to bonding varnish technology

For magnet-based medical technology applications, Waelzholz offers electrical steel strip with a coating of bonding varnish. Marco Baptista from the Sales Department explains the benefit for the customer: “Large magnets consist of lamination stacks, which in turn are made up of many individual electrical steel strip plates. Thanks to the special varnished surface, customers can efficiently join these plates together into a stable stack via a bonding process. This eliminates the need for additional welding operations.” According to Dunker, in addition to the increased stability of the lamination stacks, joining the plates using bonding varnish has another key advantage for the final application in the state-of-the-art radiation equipment: “This method creates low-vibration stacks that ensure the proton beam is guided reliably and the magnetic field is constantly generated. In addition, magnets whose lamination stacks are connected via bonding varnish operate more quietly, reducing noise pollution and thus stress for the patient. Conventional mechanical connections involving welding or riveting of the steel plates can result in extremely fine gaps, which can lead to vibrations and thus to “frequency hum.”

Coating the electrical steel strip with bonding varnish thus fulfills several requirements simultaneously when it comes to manufacturing large magnets and their subsequent use in medical radiation equipment:

  • High stability of the lamination stacks
  • Undisturbed magnetic flux for maximum magnetizability by eliminating damaging connections between the steel plates
  • Low-vibration stacks for precise beam guidance

Figure 1: Proton therapy

First, the protons are generated by a particle source and then accelerated with the aid of a magnetic field on a spiral path up to 180,000 km/sec (111,847 miles/sec) in what is known as the cyclotron (1), the particle accelerator. Immediately after leaving the cyclotron, the protons are reduced to a predetermined velocity, which is used to precisely determine the later depth of the particles’ penetration into the human body. The highly accelerated protons are directed from the cyclotron via a vacuum tube (2) to the treatment sites (3) and (4), where they are subsequently discharged and destroy the cancer cells. Powerful magnets along the beam tube (shown in orange -5) force the positively charged particles in the desired direction. For certain treatment situations, such as the irradiation of tumors in the eye, static treatment units are also available (4).

Illustration of a proton therapy system with large magnets made from electrical steel strip

Figure 2: Detailed view of a proton treatment system

The protons are accelerated in the cyclotron and directed to the treatment sites via vacuum tubes. The gantry is a swiveling treatment unit on a patient table. The proton beam can be positioned to within fractions of a millimeter via the gantry.

Waelzholz electrical steel strip suitable for a wide range of medical technology applications

For more than ten years, Waelzholz has been supplying electrical steel strip materials used to manufacture high-performance large magnets for radiation therapy. In addition, the magnetic material is suitable for other fields of application in medical technology, such as mechatronic magnet-driven intramedullary rods for bone-preserving leg lengthening procedures.

In this way, we also meet the requirements of the most state-of-the-art technologies for international cutting-edge medicine thanks to the exceptional, customized material properties and precision of our steel strip materials.