I. Basic Science: Definition and Characteristics of Three Sealing Types
1. Open Deep Groove Ball Bearings
Structural Features: No sealing cover is installed on the end faces of the inner and outer rings, and the internal rolling elements (steel balls) and cages are directly exposed to the external environment. Manufactured from high-carbon chromium bearing steel GCr15, these bearings cover precision grades from P0 (standard) to P6 (precision) and feature the lowest processing cost among the three types.
Core Characteristics: Without additional sealing components, the bearing retains sufficient internal space for refilling with any grade of lubricating grease independently. It is applicable to clean working conditions with no sealing requirements.
2. Shielded Deep Groove Ball Bearings
Structural Features: Single or double-sided low-carbon steel shields with a thickness of 0.8-1.2 mm are adopted for non-contact sealing, with a 0.1-0.2 mm gap reserved between the shield and the outer ring end face. The shields are cold-stamped and require no additional machining, resulting in light weight and simple structure.
Core Characteristics: The bearings can block dust particles of 5μm and above from entering the interior, making them suitable for lightly dusty environments. Their maximum rotational speed reaches 15,000 rpm, 20% higher than that of sealed bearings. Lubricating grease can be replenished through dedicated grease filling holes.
3. Sealed Deep Groove Ball Bearings
Structural Features: Adopting contact sealing with a combined structure of a steel frame and rubber lip, the nitrile rubber (NBR) lip (standard temperature resistance: -30℃ to 120℃) fits closely against the inner ring end face to achieve full sealing. The manufacturing process requires high coaxiality precision for the rubber lip, with processing costs 15%-20% higher than that of shielded bearings.
Core Characteristics: The bearings can completely block dust, moisture and prevent lubricant leakage, adapting to humid working conditions with medium splashing. The maximum rotational speed is 8,000 rpm. They are maintenance-free internally and need overall replacement once the sealing lip wears out.
II. Differences in Working Condition Adaptation
1. Open Deep Groove Ball Bearings
Applicable Scenarios: Ultra-clean industrial environments, including spindles of semiconductor packaging equipment, high-precision experimental instruments, and internal transmission ends of food packaging machines. Regular maintenance is required: replenish lubricating grease every 2 to 3 months, with the filling volume accounting for 2/3 of the bearing’s internal space.
2. Shielded Deep Groove Ball Bearings
Applicable Scenarios: General-load equipment operating in lightly dusty conditions, such as ventilation fans in textile mills, roller conveyor lines, and ordinary water pumps. Applicable dust concentration ≤ 10 mg/m³. No internal grease replenishment is required, and the equipment overhaul cycle can be extended to 1 year.
3. Sealed Deep Groove Ball Bearings
Applicable Scenarios: Harsh working conditions with humidity or medium contact, such as transmission ends of mine crushers, conveying lines for soy sauce production, and chemical pumps. For water and weak acid corrosion resistance, fluororubber lips are preferred, with the temperature resistance range upgraded to -40℃ to 180℃. This type of bearing is not suitable for high-speed operation; line speeds exceeding 10 m/s will accelerate lip wear.
III. Key Points for Model Selection and Maintenance
1. Core Parameter Matching
- Sealing Type: Select sealed bearings for dust concentration ≥ 15 mg/m³, shielded bearings for 5-10 mg/m³, and open bearings for ≤ 5 mg/m³;
- Line Speed: Maximum applicable line speed: shielded bearings ≤ 15 m/s, sealed bearings ≤ 12 m/s; open bearings are required for ultra-high speed conditions;
- Internal Clearance: C2 clearance (pre-tightened) for open bearings; C0 clearance (standard) for sealed bearings.
2. Installation Precautions to Avoid Errors
- The sealing lip of sealed bearings must face the load side to prevent medium intrusion from the non-load side;
- During installation, align the shield of shielded bearings with the outer ring positioning groove; do not force-fit to avoid deformation;
- Remove internal burrs before greasing after installing open bearings.
3. Maintenance Cost Comparison
-Open Bearings: Grease replenishment every 3 months, annual maintenance cost: approximately 12 RMB per unit;
- Shielded Bearings: No internal maintenance required, annual maintenance cost: approximately 2 RMB per unit;
- Sealed Bearings: Overall replacement every 1 to 2 years, annual maintenance cost: approximately 25 RMB per unit.
4. Purchase Guidelines to Avoid Pitfalls
- Do not apply non-contact shields (code: Z/ZZ) to waterproof scenarios such as water pump shaft ends; contact seals (code: 2RS/RS) are mandatory;
- Avoid non-standard bearings without marked sealing codes; verify the sealing type via product manuals (e.g., 6205-Z denotes shielded type, 6205-2RS denotes sealed type);
- Sealed bearings are prohibited for high-speed working conditions (rotational speed ＞ 10,000 rpm), as lip wear will cause premature bearing failure.