Sphere is a symbol of perfection. 

For Tsubaki Nakashima, a global company well known today all over the world, the sphere is something more than a symbol: it represents the growth of its company, providing a core business and continuous research through the years to serve customers at its best. 

Development 

Back in 1913, in Ann Arbor, MI., Leander J. Hoover founded the Hoover Steel Ball Company. In 1990, Tsubaki Nakashima company of Japan acquired the US ball manufacturing company and is currently the biggest manufacturer and supplier of precision balls in the world. Its first markets were the growing automotive and precision bearing industries. More than a century later, the electric vehicles (EV) market is becoming more and more relevant, though the combustible auto industry continues to grow. Its market for high-quality precision products has extended to medical, aerospace, military defense, and critical applications. After the great age of steel, a new era opened wide spaces for more extreme materials which paved the way for ceramics. 

Tsubaki Nakashima has nineteen locations globally, among which ceramic specialty division factories are located in the United States, Thailand and Japan.  Setting “quality” as the watchword to obtain excellent products for customers, the company constantly improves its know-how and its production processes, updating standards and parameters annually, with strict attention to help ensure quality, starting from suppliers and raw materials. 

Silicon Nitride Balls 

Ceramic Balls can be considered the new frontier in product developments suitable for bearing and high-performance applications. Above all, they are a specialty product line of the company which are commonly used for: hybrid bearings, machine tools, electric motors, fuel injection systems, wind energy and valves. 

Ceramic balls are made with Aluminum Oxide, Zirconium Oxide and Silicon Nitride. These components allow great efficiency and high performance. Among ceramic balls, Silicon Nitride balls (Si3N4) have proved to be an ideal solution in many applications because of their advanced characteristics. Silicon Nitride ball production specifically helped Tsubaki Nakashima to be well known and present in major EV platforms. The company produces silicon nitride balls in its plants in the United States, in Japan and in Thailand, with a large variety of dimensions suitable for every use (from 0.5 to 86 mm) and with a focused attention to the origin and the quality of its blank materials and to the production process. This is fundamental to offer the best performances to customers.

The production process 

Ball blanks are sintered ceramic balls. The material is prepared by special processes at very high temperature, pressure on inert atmosphere for reaching highest properties. The result is a spherical shape which is the ball blank. The grinding operation removes the slight belt and small protrusions left on the surface faces, by rolling them between two hard alloy plates under high pressure. The next step is the lapping operation. Flashed balls are rolled between two cast iron plates. One plate is fixed while the other is rotated at a very low speed. The real secret of the extreme quality of precision balls happens here. At this stage the sphericity and size have been established and are carefully inspected according to ASTM F2094 standard and customer requirements. The final production operation is polishing which adds the shiny luster to the finished ball. The balls are inspected visually and/or mechanically.

Top quality materials and best production techniques 

An excellent performance of Silicon Nitride balls comes from excellent materials used to make them. Tsubaki Nakashima selects the highest quality rare earth minerals available in the world. The better the rare earth is the better the density of the ball. The higher density generates higher hardness and increases rupture strength which is required to be classified as CLASS 1 per ASTM 2094 standards. Hardness and rupture strength decreases when using a lesser quality rare earth mineral.  These are important parameters for customers to evaluate quality, performance, and durability of the balls.

The ball blanks, used at the beginning of the production process, are manufactured utilizing Hot Isostatic Press (HIP) and Cold Isostatic Press (CIP) process. These processes allow the highest quality balls over a large range of sizes. Referring to Tsubaki Nakashima, the company has developed the most innovated automated method for inspection of Silicon Nitride balls. This equipment is unique, and it is the result of over 10 years of research and updating to reach the best solution. The new machines automate the inspection process, which reduces overhead, manual human errors and increases output.

Main properties and comparisons with other materials 

Silicon Nitride ceramic balls are remarkable for their ability to perform in extreme conditions. 

They show the following several outstanding properties.

• Resistance to wear and abrasion
 This makes them ideal for demanding applications.

• Excellent corrosion resistance
 Withstands attack from harsh chemicals and demanding environmental conditions.

• Lightweight

Silicon Nitride weighs 60% less than steel: this benefit reduces centrifugal force, skidding and wear under high speed and acceleration.

• Anti-magnetic and electrically insulating

Prevents passage of electric current and arcing.

• High resistance with low friction

Silicon nitride balls mark a low coefficient of friction that enhances wear resistance to enable the bearing to run cooler even under poor lubrication conditions. This means better lubrication, less noise, and lower operating temperatures. That is particularly suitable considering their application in bearings and especially in industries like aerospace, military defense, and hybrid bearings. 

• Temperature hardness and range

They can work in high temperatures, retaining their strength and hardness, up to +1400 °C and function at extreme low temperatures. This is due mainly to their hardness and above all to their lower coefficient of thermal expansion, that is only 29% of similar steel rolling elements. This means they can be less sensitive to temperature gradients for more accurate preload.

• Superior surface finish

Ra 0.17-0.25 micro-inches may extend L-10 life to as much as 10 times that of steel bearings.

• Low density, flexural strength, and fracture toughness

Silicon Nitride is further characterized by its low density of 3.2 g/cc, high flexural strength of 1.0 Gpa, and fracture toughness of 6 Mpa/M2.  This means higher speeds, less weight, lower inertia, and more rapid starts and stops. Basically, in this way, the bearings can run faster and cooler.

• Higher modulus of elasticity

Elasticity’s modulus is 50% higher in ceramic rolling elements than in steel ones: this helps increased bearing stiffness and reduced deflection under load to promote reliable performance.

Main applications

Typical applications include bearings for EV engines and transmissions, electrical vehicle battery, fuel injectors and regulators, high performance racing, space mechanism, critical aircraft parts, high speed instruments, food processing, machine tools, measurement instruments, pumps, and other industries that demand high precision and performance.

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