Welcome to the world of steel balls!

LESSON2 Here they are, rotating

I think I have a basic idea of what steel balls are now…but you don’t usually see them at all, do you? Where are they used?
Professor Amatsuji
Kyusuke, that’s an excellent question! Well then, let’s take a look next at steel balls hard at work around us in our daily lives?
  • Here they are, rotating「Vehicles」

     Vehicles are gold mines for steel balls. They’re used in the engine, motor, dynamo, hubs connecting the axels and the wheels, constant-velocity joints, transmission (gearbox) for shifting gears, wipers, and many other places. The number of steel balls used in an electric vehicle (EV) is approximately 300, and in a gasoline-powered vehicle is approximately 500 to as many as 1,000. It is imperative for a vehicle to run safely that all of these balls continue to rotate without breaking.


    That’s an amazing number!
    What would happen if there weren’t any balls?

    Professor Amatsuji

    Hmmm, let’s look at the motor, for example. If there were no bearings or steel balls, immense friction would occur. This would generate heat and rattling, and the vehicle would quickly break down. Using steel balls reduces friction and enables power to be conveyed efficiently. Fuel consumption improves and carbon dioxide emissions decrease, which is kind to both household budgets and the environment.

  • Here they are, rotating「Aircraft」

     We can now easily go on overseas trips because airplanes were invented. The engines and wheels of airplanes also contain steel balls. Inside jet engines in particular, steel balls must endure high-speed revolutions in high-temperature, high-pressure air, and so these balls need to have especially high heat resistance and durability.


    Gee, they’re OK even in an environment like that?!
    What materials are they made of?

    Professor Amatsuji

    These steel balls are made of a material known as “M50”, which is a special heat-resistant steel developed for use in jet engines. However, M50 needs to undergo extremely complex heat processing for it to function fully. That is, it is a material that cannot simply be rounded into balls but can only be handled by steel ball manufacturers using advanced processing technology.

  • Here they are, rotating「Household appliances」

     Air conditioners and other household appliances contain fan motors for cooling. A major factor for household appliances is the extent to which the noise of the rotating fan motor can be reduced. The reason that appliances have become more and more quiet in recent years is that the steel balls used in them have become more and more spherical. Amongst the factors that steel balls contribute, this quietness is an especially important property.

    Household appliances

    Now that you mention it, washing machines and refrigerators have become quieter and quieter, haven’t they?
    When did this start happening?

    Professor Amatsuji

    Well, we need to go back to the 1950s, when the three status symbols (electric washing machine, electric refrigerator, and black-and-white television) appeared in Japan. At that time, Western bearings were the mainstream, and quietness was of secondary importance. That’s right, it was actually Japanese manufacturers who focused their attention on noise. Today, in a world overflowing with household appliances, high-quality and high-precision Japanese bearings and steel balls are used around the globe.

  • Here they are, rotating「Industrial machinery」

     Metal cutting machine tools that produce machinery parts, production robots used on factory production lines, and construction equipment such as huge cranes used in the construction of super-high-rise buildings and gigantic excavators used to dig tunnels…industrial machines are front-and-foremost in the manufacturing workplace. Balls are also used in the rotating and moving parts of these machines.

    Industrial machinery

    Wow, balls are also rotating inside robots and cranes.
    How fast do they rotate?

    Professor Amatsuji

    Well, for example, a spindle motor for a metal cutting machine tool rotates at more than 100,000 revolutions per minute.


    Really? 100,000 revolutions? I’m getting dizzy just imagining it!

    Professor Amatsuji

    To enable them to endure such ultra high-speed revolutions, the specific gravity of the balls must be very light, and so silicone nitride balls—which are lighter than ordinary steel balls—are used. Of course, they can’t just be light; the balls also need to be sufficiently precise and durable.

  • Here they are, rotating「Satellites」

     Satellites enrich our lives from space, providing weather forecasts, satellite broadcasting, car navigator positional information, and other information. Steel balls are also used in satellites. Since the space environment is very different from the environment on Earth— microgravity, high-vacuum, cosmic radiation, wide temperature range—the properties balls require vastly differ from those on the Earth.


    That’s amazing! There are even balls rotating in space!

    Professor Amatsuji

    That right. They are used in the attitude control wheels of satellites. In the vacuum of space, these balls must continue rotating stably for lengthy periods of between 10 and 15 years with only a tiny amount of lubricant. Rotation causes vibrations, but since this must not interfere with the satellite’s observational functioning, the vibrations need to be minimized as far as possible. The steel balls also have to withstand vibrations and a blast environment when the satellite is launched, as well as temperatures changes while in orbit…they therefore need to be of especially high quality.