In material development, I work on compressed magnetic powder cores for the iron cores of motors, transformers and the like. At present, many power devices operate with a drive frequency below several hundred Hz. However, it is certain that power devices featuring higher-speed and larger-output drive will be strongly needed in the near future. Specifically, power devices that operate in a high-frequency zone, around 1 kHz, will be particularly important. Compressed magnetic iron powder is currently attracting attention as an iron core material that could replace laminated steel sheet in such power devices. In order to minimize energy loss (iron loss) in the high-frequency zone, laminated steel sheets must be extremely thin, which increases cost, while compressed magnetic powder cores can be manufactured by sintering and molding iron powder, providing considerable leeway in forming. Therefore, the new material, which can more easily accommodate the growing need for downsizing, as in the case of automobile motors, is expected to replace laminated steel sheet.

At the same time, compressed magnetic powder cores still pose a challenge: if left as originally developed, the cores are not very advantageous in comparison to laminated steel sheets, because the cores cause considerable iron loss during electro-magnetic conversion in the low-frequency zone, where many currently available power devices operate. If it becomes possible to reduce iron loss in the low-frequency zone, while maintaining existing strength in the low-frequency zone, compressed magnetic powder cores will be superior to laminated steel sheet in all aspects, including greater flexibility to its shape, and will replace them without any doubt. This is why we are trying to improve their properties.

The key to reducing iron loss was to properly process iron powder, the material of compressed magnetic iron powder cores. Distortion that occurred during iron powder processing had to be eliminated by thermal treatment, which becomes more effective as the treatment temperature rises. However, higher temperatures deteriorate the 100-nanometer-or-so insulated film that must be formed on the iron powder surface. So, another problem arose: how to enhance the heat resistance of the insulated film.

To solve this problem, we adopted a layered structure, in which a wet coating of binder resin was applied to the surface of the insulated film of phosphoric glass. This method enabled us to obtain a two-layer film evenly spread on the iron powder surface, with the first layer 20 to 30 nanometers thick, and the second layer 100 to 150 nanometers thick. Moreover, compared to the thermal resistance of up to 673 K obtained in the conventional process, the new method realized an increase of about 150 K to 823 K. As a result, we were able to reduce iron loss by one-third, even under such conditions as magnetic flux density of 1 T and frequency of 1000 Hz, comparable to the target conversion loss of laminated steel sheets.

I think that those who are involved in R&D tend to make the error of closing ourselves up in our individual research themes, and forgetting the rest. At SEI, however, we have very close ties with other research teams and other divisions. For example, in the research area of power devices where I work, the team studying coil wires and another team in charge of overall product design cooperate with each other in a very natural way. So when researchers hit a wall, they can turn to other teams for advice and inspiration, for unexpected clues and solutions. We can also undertake our research while being aware of market trends, customer requests and other factors that could affect the target product when it is commercialized, such as mass production potential and cost. As a researcher, it is still possible for me at SEI to feel directly involved in manufacturing, in which it is essential to be conscious of what the finished product will be like. This is a strong point particular to this company.

At present, we are trying to improve the compressed magnetic powder core further, so as to realize its mass production while guaranteeing stable quality. The need for more compact, lighter-weight and larger-output power devices continues to grow. I hope that at the earliest possible time we will be able to develop a product that responds to society’s expectations, and thereby contribute to society.