Conical Outer Spherical Ball Bearing With Retaining Ring

Set screw mounted insert ball bearings are the most widely used sub-category in the insert ball bearing family. As a special structural form of ball bearings, they feature the core design highlights of "set screw fixing + spherical compensation". They perform exceptionally well in medium-low speed scenarios with low installation precision requirements and complex working conditions, serving as key components for stable shafting operation in fields such as general machinery, agricultural equipment, and mining machinery, while offering the dual advantages of convenience and fault tolerance.​

1. Product Definition and Core Positioning​

Set screw mounted insert ball bearings are ball bearings that use precision steel balls as rolling elements. They achieve quick fixing with the shaft through set screws on the inner ring, and their outer ring has a convex spherical structure that can match the concave spherical surface of the supporting pillow block. Their core positioning is to "adapt to low-precision installation and simplify maintenance procedures". They mainly bear radial loads and can also withstand bidirectional axial loads not exceeding 10% of the radial load. Suitable for medium-low speed, medium-load working conditions with a maximum speed of ≤3000r/min and a basic dynamic load rating of 5-50kN, they effectively solve bearing damage issues caused by shaft misalignment during installation, base deformation, or shafting deflection. Compared with ordinary deep groove ball bearings, their installation efficiency is increased by over 60%, and maintenance costs are reduced by 30%-40%.​

2. In-depth Structural Analysis: Synergy Between Set Screw Design and Spherical Matching​

Set screw mounted insert ball bearings consist of five core components, and the design details of each component directly determine their performance and application scenarios. The specific analysis is as follows:​

(1) Core Functional Components​

Inner Ring​

The inner ring is made of high-carbon chromium bearing steel (GCr15), undergoing integral quenching (hardness HRC58-62) and precision grinding. The inner hole surface roughness is Ra ≤ 0.4μm to ensure good fit with the shaft. The key design lies in the set screw hole structure:​

Number of set screws: Conventional models are equipped with 1-2 set screw holes. Small-sized models (inner diameter ≤ 30mm) mostly have 1 hole, while medium and large-sized models (inner diameter > 30mm) have 2 holes, symmetrically distributed on the side or end face of the inner ring to avoid inner ring deformation caused by single set screw force.​

Set screw specifications: Set screws are mostly hexagon socket head cap screws, made of high-strength alloy steel (e.g., 45# steel, hardness HRC35-40) with a thread precision of 6g. After tightening, fixation is achieved through friction between the set screw end face and the shaft. Some set screw end faces are provided with anti-slip serrations, increasing the friction coefficient by 20% to prevent loosening.​

Fit tolerance: The fit between the inner ring and the shaft is a H7/h6 transition fit, with a clearance controlled between 0.005-0.02mm. This avoids inner ring deformation due to interference fit and prevents set screw slippage caused by excessive clearance.​

Outer Ring with Convex Spherical Surface​

The outer ring is also made of GCr15 steel, with its outer circle processed into a convex spherical structure. The spherical radius is consistent with that of the concave spherical surface of the supporting pillow block, and the sphericity error is ≤ 0.01mm to ensure tight fitting.​

Raceway design: The inner raceway of the outer ring is a deep groove type, forming point contact with the steel balls. The raceway radius of curvature is 52%-54% of the steel ball diameter, optimizing contact stress distribution and extending fatigue life.​

Spherical compensation angle: The matching between the convex spherical surface and the concave spherical surface of the pillow block allows an angular deviation compensation of ±2°-±5° (the specific angle varies with the pillow block type: vertical pillow blocks allow ±3°, square pillow blocks allow ±5°). This can offset additional torque caused by installation misalignment, base vibration, or shafting bending, avoiding local stress concentration on the bearing.​

Outer ring marking: The outer surface of the outer ring is usually laser-marked with the model, inner diameter size, and manufacturer's logo. Some large-sized models are provided with positioning grooves to facilitate installation and positioning with the pillow block.​

Precision Steel Balls​

The rolling elements are high-purity bearing steel balls (GCr15SiMn) with a diameter tolerance grade of G10 (tolerance range ±0.002mm), a roundness error of ≤ 0.001mm, and a surface roughness of Ra ≤ 0.025μm. The number of steel balls is designed based on the bearing inner diameter: 6-8 balls for inner diameters of 10-20mm, and 8-12 balls for inner diameters of 20-50mm. Uniform distribution ensures balanced load transmission and reduces operating vibration. Some high-end models use ceramic balls (silicon nitride material), which are 40% lighter than steel balls and have a 15% lower friction coefficient, suitable for corrosion-resistant and high-speed (close to 3000r/min) working conditions.​

Cage​

Cages are made of two types of materials to adapt to different working conditions:​

Stamped steel plate cage: Made of high-quality 08F steel plate through stamping and phosphating for rust prevention. Suitable for medium-load scenarios with temperatures ≤ 120℃ (e.g., fans, water pumps), it is cost-effective, lightweight, and can withstand slight impacts.​

Engineering plastic cage: Mostly made of nylon 66 (PA66 + glass fiber reinforcement) with a temperature resistance range of -40℃-120℃. It has a low friction coefficient (25% lower than that of steel plate cages) and no metal friction noise, making it suitable for environments with high noise reduction requirements and humidity (e.g., food machinery, agricultural irrigation equipment). Some models are added with flame retardants to meet explosion-proof scenario requirements.​

Seals​

Most models are pre-equipped with double-sided seals for dust and water protection. Common types include:​

Rubber seal rings (2RS): Made of nitrile rubber (NBR) or fluororubber (FKM). NBR is suitable for ordinary working conditions with temperatures of -30℃-100℃, while FKM is suitable for oil mist or corrosive environments with temperatures of -20℃-200℃. The seal ring forms an interference fit (interference 0.1-0.2mm) with the inner ring seal groove, creating an effective seal to prevent dust and moisture from entering, while retaining the long-life lithium-based grease pre-filled inside the bearing.​

Dust covers (ZZ): Made of cold-rolled steel plate through stamping, with galvanized surfaces for rust prevention. Suitable for dry, low-dust scenarios (e.g., machine tool guide rollers), they have 10% lower friction resistance than 2RS seals but weaker water resistance, requiring regular grease replenishment.​

(2) Supporting Pillow Blocks: Important Support for Spherical Matching​

Set screw mounted insert ball bearings need to be used with dedicated pillow blocks, and the structure of the pillow block determines the installation method and deviation compensation capability. Common types and their characteristics are as follows:​

3. Core Performance Advantages​

Installation Convenience: No Complex Shaft Machining​

The set screw fixing design eliminates the need for keyway milling, shaft shoulder setting, or thread machining on the shaft. Only the shaft diameter tolerance needs to meet the h6 requirement, and on-site tightening of set screws can be completed using a hexagon socket wrench. The installation time for a single bearing can be shortened to 5-10 minutes (compared to 20-30 minutes for ordinary bearings), making it particularly suitable for quick replacement during equipment maintenance and reducing downtime.​

Deviation Fault Tolerance: Adaptation to Harsh Installation Environments​

The matching between the convex spherical outer ring and the pillow block can compensate for angular deviations of ±2°-±5°. When the equipment base deforms due to vibration, the shafting is misaligned due to uneven bolt tightening during installation, or the shaft bends due to force during operation, the bearing can automatically adjust the contact position between the steel balls and the raceway, avoiding local stress concentration. This extends the bearing life by 50%-80% compared to ordinary deep groove ball bearings, providing significant advantages in scenarios with low installation precision such as agricultural machinery and mining equipment.​

Maintenance Economy: Seal + Pre-lubrication Design​

The pre-installed 2RS seals or ZZ dust covers effectively prevent dust, moisture, and impurities from entering. The interior is pre-filled with long-life lithium-based grease (e.g., Grade 2 lithium-based grease), with a filling amount of 1/3-1/2 of the internal bearing space, eliminating the need for initial lubrication. Under conventional working conditions, the maintenance cycle can be as long as 3000-5000 hours (compared to 1000-2000 hours for ordinary open bearings requiring grease replenishment). If the fit clearance between the inner ring and the shaft increases due to wear, the clearance can be fine-tuned by re-tightening the set screws without replacing the entire bearing, reducing the maintenance cost of a single bearing by more than 30%.​

Load Adaptability: Balancing Load and Working Conditions​

Adopting a point-contact rolling structure, it has stable radial load-carrying capacity. The basic dynamic load rating ranges from 5-50kN, which can meet the needs of most medium-load scenarios such as fans (radial load 2-5kN), agricultural machinery (radial load 3-8kN), and mining equipment (radial load 8-15kN). At the same time, it can withstand small bidirectional axial loads, avoiding abnormal noise caused by slight shafting runout and adapting to transmission systems with slight axial forces.​

4. Application Scenarios 

General Machinery Field: Suitable for fan and water pump shaft ends. Set screw fixing simplifies shaft machining; ±3° deviation compensation offsets base settlement; 2RS seals (IP54) resist outdoor humidity. Typical models: UCP205 (inner diameter 25mm), UCP206 (inner diameter 30mm).​

Agricultural Machinery Field: Used for harvester drum shafts and tractor drive wheels. 2RS seals prevent soil and straw ingress; double set screws resist loosening due to vibration; square pillow blocks (UCF type) fit narrow spaces. Typical models: UCF207 (inner diameter 35mm), UCF208 (inner diameter 40mm).​

Mining Equipment Field: Suitable for vibrating screen drive parts and feeder shaft ends. Cast steel flange pillow blocks (UCFL type) are impact-resistant; ±5° deviation compensation adapts to uneven bases; steel plate cages withstand frequent start-stops. Typical models: UCFL209 (inner diameter 45mm), UCFL210 (inner diameter 50mm).​

Light Industry Equipment Field: Used for printing machine guide rollers and packaging machine conveyor shafts. Nylon cages achieve low noise (≤60dB); diamond pillow blocks (UCL type) enable compact installation; reference speed of 2000r/min adapts to working conditions. Typical models: UCL204 (inner diameter 20mm), UCL205 (inner diameter 25mm).

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