Toshiba America Electronic Components, (TAEC) Inc., Advanced Materials Division (AMD) is the largest supplier of silicon nitride ball blanks to the North American and European precision ball finishing industry. The Toshiba TSN-03NH grade silicon nitride is considered by the bearing industry to be an industry standard due to its high level of performance and quality.
Toshiba silicon nitride combines strength, hardness, toughness, corrosion resistance, high-temperature capability, and reduced weight. These attributes make it useful for many applications involving high contact stress sliding or rolling contact, corrosive chemicals, or high temperatures. Several successful high-production-volume applications utilizing these unique characteristics have been developed.
Silicon nitride is used by the largest bearing companies in the world, including FAG, Barden, SKF and JTKEKT. It was the only material to be approved for use in ball and roller bearings in the NASA space shuttle's main engine high pressure liquid oxygen and liquid hydrogen turbopumps - one of the most severe applications ever developed for rolling element bearings. It also helped the Thrust SSC car achieve its record-breaking Mach 1+ land speed run by allowing the wheel bearings to operate reliably at over 480,000 dN. Silicon nitride balls have also been used extensively as check balls in high pressure or corrosive fluid systems. Most major diesel fuel systems manufacturers are using silicon nitride check balls today.
The material is lightweight, reduces adhesive wear, and is corrosion resistant resulting in less wear of both the ball and the check-valve seat, thereby reducing leakage. Other applications include machine tool spindles, wind turbines, turbomolecular vacuum pumps, high-performance bicycles and in-line skates, as well as aircraft APUs and starter motor/generators and food processing equipment. TAEC-AMD can supply ball blanks from 1 mm to 2-1/4 inches in diameter, roller blanks and bearing race blanks, as well as custom manufactured components. If your application involves high rolling or sliding contact stresses, this material can handle the load.
Toshiba TSN-03NH is certified to meet ASTM F2094 Class I requirements, the highest industry classification for silicon nitride bearing materials.
Toshiba America Electronic Components, Inc.
Advanced Materials Division
290 Donald Lynch Blvd.
Marlborough, MA 01752
In 1986, Cummins Inc. introduced the Step Timing Control (STC™) fuel system to provide improved exhaust emissions to meet tightened emissions regulations. A by-product of these changes was an increased level of abrasive soot particles generated during the combustion process and collecting in the lubricating oil.
The mechanically actuated unit injector as originally designed incorporated a tool steel link that transferred a load of 2000 lbs (900 kg) from the overhead to the injector plunger. The high contact stresses, boundary lubrication conditions, and higher concentration of abrasive soot particles combined to produce unacceptably high wear. As a result, the injectors had to be reset periodically to maintain engine performance and compliance with emissions regulations, a significant inconvenience for customers.
The incorporation of the silicon nitride link dramatically reduced wear to an acceptable level without requiring additional design changes to the injector. The increased hardness of the link and the lack of asperity welding with the steel socket resulted in a reduction in abrasive and adhesive wear mechanisms. The silicon nitride link has the same geometry as the steel link it replaced. The spherical ends are precision ground to within 15 micrometers of the nominal profile.
Production of the link began in 1989 and more than 3 million have been put into service. This was the first use of silicon nitride as a structural component in production diesel engines. There has not been a single reported failure of a link in service and links are typically reused when injectors are rebuilt, thereby amortizing the higher initial cost over several injector lifetimes.
Summary: This application proved that silicon nitride is a viable engineering material that can dramatically reduce wear in a degraded lubrication environment.
The amount of wear reduction that silicon nitride can provide is clearly demonstrated in the Cummins C-Brake™ engine compression brake used on the N14 model heavy-duty diesel engine. Silicon nitride was incorporated into the master piston in the form of a wear pad. The master piston contacts a bearing steel adjusting screw head with a force of 2200 lbs while relying on splash lubrication to prevent wear. The previous master piston material, D4 tool steel, could not provide the required wear performance under the higher loads and increased durability requirements of newer engines.
The novel design was critical to meeting the tight cost target. The design comprises a lower cost steel body, a simple retaining ring attachment, and a relaxed tolerance ceramic pad which requires no post-sinter machining.
Toshiba's experience in designing cost effectively with ceramic resulted in a component with dramatically improved wear characteristics with a cost that was comparable to the tool steel master piston.
Summary: Silicon nitride in lubricated sliding contact with steel can significantly reduce total wear, especially under degraded lubrication conditions. Toshiba has the proven capability to develop cost effective design solutions incorporating ceramic elements. More information regarding this application can be found in SAE paper 930159.
Ceramic Advantage: Reduced Wear and Friction
In FALEX 1 Block-on-Ring rig testing, silicon nitride-on-steel material combinations exhibit reduced sliding wear and friction compared to steel-on-steel, especially in degraded lubrication conditions.
Test Conditions: 120°C Oil Temperature, 700 MPa Contact Stress, 0 . 55 m/s Sliding Speed, Fresh and Engine-Tested CD/SF 15W40 Oil.
Results: Silicon nitride-on-steel exhibited dramatically less total wear and reduced friction compared with steel-on-steel, even in used diesel engine oil containing abrasive soot particles. Similar results have been documented with steels other than 52100 and confirmed in actual engine tests.
Benefit Summary: Silicon nitride can significantly reduce total wear when in lubricated-sample sliding contact with steel, especially in degraded lubrication conditions. Reduced friction can reduce parasitic power and energy losses in engines and other industrial machinery applications.