Product structure:

The 684 ZZ is a miniature deep groove ball bearing with standard dimensions: 4mm bore, 9mm outer diameter, and 4mm width. It consists of inner and outer rings made of high-carbon chromium bearing steel (GCr15), a set of precision steel balls, and a stamped steel cage (or engineering plastic cage). The suffix “ZZ” indicates that the bearing is equipped with non-contact (or slight-contact) metal shields (dust covers) on both sides. These shields are stamped from thin steel plates, forming a minimal gap with the inner ring, providing basic dust protection while generating very little frictional resistance, which is conducive to high-speed operation.

Key performance features:

• Compact and Lightweight: Its small footprint and 2.5mm thickness allow for efficient rotational support in confined spaces, contributing to equipment miniaturization.
• Excellent High-Speed Performance: Thanks to the non-contact metal shields and precise internal structure, this bearing features low frictional torque and a high limiting speed, suitable for the high-speed operation demands of micro motors.
• Basic Sealing Protection: The double-sided metal shields effectively prevent larger particles such as dust and debris from entering the bearing interior, extending service life in clean to moderately contaminated environments.
• Smooth and Quiet Operation: High-precision raceway machining and quality steel balls ensure low vibration and low noise operation, meeting the requirements of precision instruments and quiet equipment.
• Ready-to-Install and Long Life: Pre-lubricated with high-performance grease at the factory, it can achieve maintenance-free operation under correct working conditions, providing durable and reliable performance.

Main application scenarios:

This bearing is primarily used to support and guide various small, high-speed rotating shafts. Typical applications include: shafts of small DC/AC motors (e.g., drone flight control motors, small cooling fan motors); paper feed rollers and optical component scanning shafts in office equipment; rotary encoders and flow meter rotors in precision instruments; mixer shafts and electric toothbrush motors in household appliances; gearboxes and axles in model toys; and small sensors and guide rollers in industrial automation. In these scenarios, it plays a key role in reducing friction, ensuring rotational accuracy, and transmitting power.

Technical Specifications and Requirements

• Dimensions and Tolerances: Conforms to the 688 series dimensions in the ISO 15:2011 standard. Tolerance grades for bore, outer diameter, and width are typically Normal class (P0, corresponding to ABEC-1). Higher precision grades (e.g., P6/ABEC-3) can be provided upon request.
• Material and Heat Treatment: Rings and balls are made of high-purity bearing steel (e.g., GCr15/52100) and undergo quenching and tempering heat treatment to achieve a hardness of HRC 58-64, ensuring wear resistance and contact fatigue strength. Shields are made of anti-rust steel.
• Lubrication: Filled with special high-speed miniature bearing grease, such as synthetic hydrocarbon or ester-based grease, according to the expected speed and temperature range, ensuring lubrication effectiveness across a wide temperature range and at high speeds.
• Performance Indicators: Dynamic load rating (C) and static load rating (Co) comply with ISO 281 standards. Users must verify and select based on actual load, speed, and life requirements.
• Installation and Operating Environment: Installation must ensure the concentricity and perpendicularity of the shaft and housing bore to avoid improper installation stress. It is recommended for use in clean, dry environments, avoiding extreme high temperatures, strong corrosion, or heavy contamination. Metal shields are not suitable for underwater applications or situations requiring pressure sealing.

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