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ENOMOTO Yuji (Center for Technology Innovation – Materials / Electrification Component & Material Research Dept. / Senior Researcher)
Electric motors are machines that convert electric energy into rotary motion. Development began in the early 19th century, and research to achieve even higher efficiency and performance continues to this day.
Hitachi’s first product as a company in 1910, was a 5-horse power motor to be used in mines. Today, Hitachi produces industrial motors that are used at production sites such as factories. With industrial motors, energy efficiency is an extremely important performance indicator. Highly efficient motors do the same job with even less electricity. Saving on the electricity bill contributes to reducing production costs for the entire factory, which translates to increasing price competitiveness of the product. Furthermore, in Japan, as much as 75 percent of Japan's industrial electricity is consumed by motors. This means that increased efficiency of industrial motor will have a major impact in reducing electricity consumption in Japan as a whole.
(Publication: November 8, 2018)
In 2008, Hitachi succeeded in developing a high-efficiency motor with amorphous metals, and in 2014, Hitachi announced the development of a prototype IE5-class efficiency standard amorphous motor. IE5 is a standard set by the International Electrotechnical Commission (IEC), an international standardization body for electrotechnology, in its guideline on motor efficiency. The first commercial product that utilized a motor with this technology, is the scroll air compressor of Hitachi Industrial Equipment Systems Co.
We knew that amorphous metals would increase the efficiency of motors. However, it is extremely difficult to process amorphous metals, and it was anticipated that this would cause large difficulties for use in motors.
What does amorphous mean in the first place? Its element is iron and its chemical element symbol is Fe. There are also traces of other elements that are added. However, it is the same as other iron based materials.
Despite this, the atomic structure inside amorphous metals is different from normal metals.
In the process of cooling heated iron, crystals are formed. Thus, if you look at the surface of iron through a microscope after polishing the surface, you can see that it is an ensemble of small crystals. However, if the iron is cooled quickly, crystals do not form, and it becomes amorphous with a non-crystalline structure.
If electric wire is wound, it becomes a coil. When electrical current passes through this coil, a magnetic field is generated. If an iron core is placed inside the coil, the magnetic field that is generated becomes stronger. Thus, coils used in motors have an iron core.
Electromagnetic induction is a physical phenomenon where magnetic fields are generated by flows of electrical current, and when the magnetic field changes, flows of electrical current are generated. When the coil generates a magnetic field, the current runs through the iron core. When this happens, the electrical current energy inside the iron core becomes heat, which tries to escape to the outside. This is called core loss. When amorphous metals are used for the iron core, this core loss decreases by up to a tenth. In addition, amorphous metals also have a high ability to strengthen magnetic fields.
However, there are also downsides to amorphous metals. Amorphous metals are made by rapidly cooling hot iron. After being molded into a thin foil that is 25 µm thick, the iron is cooled immediately. For this reason, amorphous metals are formed in a foil like state, just like aluminum foil that you might use at home. The "soul of amorphous metals" is cannot be crafted because it is impossible to rapidly cool the center portion.
Moreover, amorphous metals are hard and brittle, making them difficult to work with and process. At present, the only feasible processing method is using shearing machines. This type of processing is almost like cutting with scissors. While there are other types of processing available, they are impractical in terms of cost incurred.
The performance levels of motors when amorphous metals are used for the iron core are extremely high. Therefore, almost all motor technicians would like to use amorphous metals for their motors. However, these are too difficult to process, and making products at a realistic price is something we've been unable to achieve.
Normally, iron cores are made from iron plates created from electromagnetic steel sheet. Iron cores are made by stacking several dozen thin plates that are punched out with molds. We laminate multiple thin plates to limit the flow of electrical current inside the iron core which causes energy loss, increasing the performance of motors. Simultaneously, the processing cost is not as expensive because once the mold is made, we can simply punch out shapes without worrying about incurring further costs. However, because amorphous metals are so hard, brittle, and thin, we cannot use the molds to punch out and create the shapes.
This is where we thought that we should use a different type of motor.
There are various types of motors. The development target here was a motor which places a permanent magnet on the rotating part of the motor (rotor) and an electromagnet on the motor case side (stator). Conventionally, we employ a motor called the radial-gap motor where the stator is enclosed around the cylindrical rotor. With this motor, the iron cores are formed by stacking several electromagnetic steel plates that are made by punching out the shapes.
In contrast to this, for motors which use amorphous metals, we used the axial-gap motor, where the stator is located between two disk-shaped rotors. In this motor, the iron core that has been cut out looks like a baumkuchen. Just like the "annual rings" found on baumkuchen, by stacking the thin foils of amorphous metals, we can manufacture the iron core.
Specifically, we create a mold that is shaped like a baumkuchen and stack the amorphous pieces that are cut from above during the shearing process. If the length of the cut amorphous metals is lengthened little by little, an iron core with "annual rings" like a baumkuchen is formed. With this shape, there is no need to punch out shapes. Iron cores can be made simply by cutting the amorphous metals that are provided as a long roll. In addition, the inexpensive ferrite magnet can be used as a permanent magnet with this design.
Here, I would like permission to use some physics and math. Motor output is proportional to the product of the magnetic flux – the strength of the magnetic field at work between the rotor and the stator – and the electrical current. Moreover, magnetic flux is proportional to the product of the strength of the permanent magnet and the gap area.
Gap area is the surface area of the rotor's permanent magnet and the stator's electromagnet that face each other. With the radial-gap motor, it would be the area of the side of the cylindrical rotors. With the axial-gap motor, it is the surface area of the rotor enclosed around the stator.
Maintaining a constant motor dimension, we found that the axial-gap motor had about three times the gap area as the radial-gap motor. In other words, if the motor output is maintained, the permanent magnet could be a third of the strength. Weaker permanent magnets are less expensive. That is, we could create a motor with similar levels of output utilizing the less expensive ferrite magnet.
The quickest way to increase the output of motors is to use a more powerful permanent magnet. For this reason, developing powerful magnets is a very big task in materials engineering. Currently, the most powerful magnet utilized industrially is the neodymium magnet. It is an alloy made of three elements: iron, boron, and neodymium, a rare earth element. Neodymium magnets are used in small, light, and powerful motors that are installed in hard disks, electric cars, etc.
However, neodymium has a low quantity of output and is highly priced. Neodymium magnets are about 20 times the price of ferrite magnets. Moreover, heavy rare-earth elements (Dy, Tb) which enhance the performance of magnets are mostly produced in China, making stable procurement a task in itself.
If weaker permanent magnets could be utilized, we would be able to use ferrite magnets that do not use rare-earth elements such as neodymium. The main components of ferrite magnets are oxides which include iron oxide, zinc oxide, nickel oxide, manganese oxide, etc. While the magnetic force of ferrite magnets is no match compared to neodymium magnets, they are much more affordable.
If amorphous metals are used for the iron core and the axial-gap motor is employed, performance does not decrease with the ferrite magnet and even becomes much more efficient than the conventional motors. With this, we were able to maintain the same size and output. Moreover, the price is less expensive, and we succeeded at developing a high-efficiency motor. Even if all our motors were replaced, we would recoup the expenses within a year with the decrease in electric utility bills alone. However, there are downsides as well. With ferrite magnets, the rotor becomes heavier. For this reason, it would be disadvantageous in fields where speedy responsiveness is required, such as in electric automobiles which often increase and decrease the number of rotations. However, there is no problem seen in industrial motors as most of them maintain a certain rotation speed.
The reason we started employing amorphous metals was not to meet customer needs but was in fact producer-driven. From the start, it had already been decided to use amorphous metals.
The manufacturing method of amorphous foil was developed by AlliedSignal of the U.S., currently known as Honeywell, and this technology was the focus of a department called Metglas. Because that was the only place making amorphous foil, one side of the story is it was not applied widely.
However, in 2003, a Hitachi group company, Hitachi Metals, Ltd., acquired Metglas. This was a major turning point. Because Hitachi Metals, Ltd. wanted to increase their use of amorphous metals, the Chief of Engineers at the time came to us motor developers and requested, "Please conduct research on motors that use amorphous metals." This was why we started the research. With this, we commenced R&D across group companies, involving Hitachi Industrial Equipment Systems Co., Ltd., the motor manufacturing plant.
Traditionally, Hitachi group has often mutually provided technologies and R&D capabilities across group companies and has a culture of creating producer-driven products. Hitachi has also prepared various research schemes to accomplish this. There is a system which allows Hitachi group's business divisions to request research to Hitachi's R&D groups, and Hitachi group has prepared a corporate fund for raising research funds. Even for long-term R&D of about 10 years, funding can be obtained by utilizing these systems.
When the scale becomes larger, funds can also be gathered from outside of Hitachi group. For the development of the amorphous metal motor, we utilized the grant system offered by the New Energy and Industrial Technology Development Organization (NEDO).
The research began with the acquisition of Metglas in 2003, and we first announced tentative accomplishments in 2008. Although all that we had created was a small motor for air conditioners, we emphasized that it was a motor that did not use neodymium magnets or rare-earth elements. The fact that we did not use rare-earth elements led to practical research utilizing NEDO's funds.
Around the mid-2010, China, a major exporter of rare-earth elements, restricted its exports, causing a sudden increase in prices. It was commonly known as the rare-earth (rare-earth elements) crisis. This event motivated us to conduct practical research on industrial motors larger than air conditioners utilizing NEDO's grants. We feel as though our motors were specially selected as even the nation needed to take countermeasures against reliance on rare-earth elements that lie overseas. With the two groups, Hitachi's Research & Development Group and Hitachi Industrial Equipment Systems Co., Ltd., we proposed to NEDO that we would conduct a project that would research, develop, and commercialize industrial motors utilizing amorphous metals, and this is how the project's grants were set in motion.
In productizing the motors, we continuously cut the amorphous foil with a machine that makes a cut called a shear. We needed to verify the productivity and confirm whether it could continuously manufacture properly without encountering trouble. There was also a need to check the reliability of the motor by evaluating the results of the durability tests. For the motor itself, anchoring the iron core into the casing was a major problem. Despite this diverse set of problems, the assistance of experts affiliated with Hitachi's various research labs accelerated our research.
The most difficult development problem that we encountered was cost. Even the best motor in the world could not be commercialized if it was too expensive. The manufacturing cost had to be inexpensive, and we would not rely on special production facilities that required excessive initial investment. There was a need for appropriate initial investment, low cost, and an ability to smoothly manufacture stable, quality products. This was rather difficult to accomplish.
The materials of amorphous metals itself are more expensive than electromagnetic steel at almost two times the price. However, for electromagnetic steel, the iron core is made by punching out shapes. During this process, scrap metal is created. With this manufacturing method, about 40 percent of the material is used while 60 percent becomes scrap metal. In short, 60 percent is wasted. With the amorphous metal iron core that we developed, many sheets of amorphous foil can be manufactured simply by cutting it with a shear. With this method, absolutely no scrap metal is generated. By eliminating waste, we effectively absorbed the price difference between electromagnetic steel and amorphous metals. This is the result of research by the business divisions and the Research & Development Group's production technology research divisions.
Upon graduating a technical high school at the age of 18, I joined Hitachi. I studied at Hitachi's vocational school called Hitachi Keihin Technical College and had the privilege of going to the University of Tokyo as a researcher, compiling experience as a researcher. For a while after joining Hitachi, I was engaged in developing production technology, but as I was involved in the production technology of motors, I was given the responsibility of designing motors. In 2006, I earned my Doctor of Engineering with a thesis titled, "Research on Attaining High-Performance Motors with Split Core Structured Permanent Magnate Synchronous Motors." I also earned qualifications as Professional Engineer.
My work with amorphous metals started with a producer-driven need to use amorphous metal materials, and in the process of productization, various companies in Hitachi group cooperated and provided both manpower and wisdom to launch a new motor. I believe that smooth communication between groups played an important role in our success.
The axial-gap motor that we used for this industrial motor is unique and is not a motor that is commonly used. That is, users will not have the proper knowhow to use it to its fullest. In the future, I hope to expand the number of motors that use amorphous metals.