Single Row Deep Groove Ball Bearing Without Inner Ring

Inner ring-free spiral roller bearings are innovative heavy-duty radial bearings featuring a core design that eliminates the traditional inner ring and uses the shaft journal directly as the raceway. This design enables direct line-contact load-bearing between the spiral rollers and the shaft journal. While retaining the inherent advantages of spiral rollers-such as impact resistance and heavy-load tolerance-these bearings address installation challenges and cost pressures associated with inner ring-equipped bearings in large shaft diameter applications. Specifically engineered for equipment with qualified shaft journal precision (meeting requirements for surface hardness, roughness, and roundness) that requires long-term heavy-load operation, they are widely used in industrial fields including mining, metallurgy, and heavy machinery, serving as key supporting components for balancing "performance, cost, and space" in heavy-load transmission systems.​

1. Core Structure and Design Innovation​

The structural design of inner ring-free spiral roller bearings centers on "using the shaft journal as a replacement for the inner ring," with all components optimized for "direct contact load-bearing." Detailed structural components and design highlights are as follows:​

(1) Technical Details of Key Components​

Spiral Roller Assembly: Core Load-Bearing Element​

Spiral Rollers: Two main materials are used: spring steel (60Si2MnA) for high-frequency impact conditions (e.g., mining crushing equipment) and bearing steel (GCr15SiMn) for high-wear-resistance scenarios (e.g., metallurgical rolls). The manufacturing process involves three critical steps: cold-rolled spiral forming (pitch tolerance ≤ 0.1mm), integral quenching (hardness HRC58-62), and ultra-precision grinding (surface roughness Ra ≤ 0.4μm), ensuring roller surface smoothness and dimensional accuracy. The rollers feature a hollow spiral structure with a controlled radial elastic deformation of 0.01-0.03mm, capable of cushioning short-term impacts of 1.5-2 times the rated load. Additionally, the hollow design facilitates lubricating oil penetration, enhancing lubrication uniformity.​

Cages: Available in two types: stamped steel (SPCC material, suitable for medium-to-low load scenarios with lower cost) and brass (H62 material, suitable for heavy-load, high-temperature environments with strong wear resistance). Structurally, they adopt either a "comb-shaped integrated forming" or "split assembly" design. The number of pockets is 10% higher than that of inner ring-equipped models (e.g., 18-22 pockets for models with a 150mm shaft diameter), ensuring uniform roller distribution and preventing localized stress concentration. Both ends of the cage are equipped with 2-3mm high flanges to effectively prevent axial movement of the rollers, adapting to the relative linear motion between the shaft journal and the outer ring.​

Outer Ring: Positioning and Auxiliary Load-Bearing​

Material and Raceway Processing: The outer ring is made of high-carbon chromium bearing steel (GCr15), undergoing integral quenching (hardness HRC60-62), arc-shaped raceway machining on the inner bore (curvature radius 1.05-1.1 times the roller radius), and ultra-precision grinding (surface roughness Ra ≤ 0.4μm). The arc-shaped raceway design increases the contact area with the rollers (15%-20% larger than cylindrical raceways), reducing load per unit area and extending service life.​

Adaptability Optimization: The outer ring outer diameter adopts a loose tolerance of grade h8, and a clearance fit of H9/h8 is used when mating with the bearing housing, eliminating the need for strict coaxiality calibration (allowing a deviation of ±0.05mm) and simplifying the installation process. Large-sized models (bearing width ≥ 50mm) are uniformly drilled with 2-4 oil holes (3-6mm in diameter) along the circumference, which connect to the raceway surface. These oil holes allow direct injection of lubricating oil into the contact area between the rollers and the shaft journal, addressing lubrication blind spots in traditional bearings. Some models feature 3-5mm wide positioning grooves machined on both end faces of the outer ring, which can be used with retaining rings to prevent axial movement of the outer ring during equipment operation.​

Sealing and Protection System (Optional Configuration)​

Seals are available in two types: nitrile rubber (NBR) seals (suitable for temperatures ranging from -30℃ to 120℃, IP54 dustproof rating, ideal for humid, dusty environments such as underground mines) and fluororubber (FKM) seals (suitable for high-temperature environments from -20℃ to 200℃, IP54 dustproof rating, designed for high-temperature metallurgical equipment). The interference between the seal lip and the shaft journal surface is controlled at 0.05-0.1mm, ensuring effective sealing while avoiding excessive frictional heat generation due to overly large interference.​

Dust covers are made of 0.3-0.5mm thick stamped steel plates (SPCC), galvanized on the surface, and connected to the outer ring via snaps. They are suitable for dry, low-dust environments (e.g., heavy machinery spindles) and effectively prevent foreign objects from entering the contact area between the rollers and the shaft journal.​

(2) Core Design Principles and Advantages​

The core principle of the inner ring-free structure is "using the shaft journal to replace the inner ring," achieving performance breakthroughs through three key design aspects:​

Load Transmission Optimization: Spiral rollers make direct contact with the shaft journal, eliminating the inner ring transmission link and avoiding stress losses caused by the fit gap between the inner ring and the shaft. This increases the radial rated dynamic load by 5%-10% compared to inner ring-equipped models of the same size (e.g., for a 120mm shaft diameter, inner ring-equipped models have a rated dynamic load of 420-520kN, while inner ring-free models can reach 450-550kN).​

Space and Cost Optimization: By omitting the inner ring, the radial dimension of the bearing is reduced by 15%-25% compared to inner ring-equipped models (e.g., for a 150mm shaft diameter, inner ring-equipped models have a radial width ≥ 50mm, while inner ring-free models are ≤ 40mm), making them suitable for equipment with limited radial space in the bearing housing. Additionally, this design reduces raw material consumption and processing steps for the inner ring, lowering manufacturing costs by 20%-30%-with even more significant cost advantages for large shaft diameter models (≥ 200mm).​

Shaft Journal Adaptation Requirements: The shaft journal must meet strict technical indicators: surface hardness ≥ HRC58 (large shaft journals use surface induction hardening with a hardened layer depth ≥ 2mm to prevent crushing by spiral rollers), surface roughness Ra ≤ 0.8μm (Ra ≤ 0.4μm for precision transmission scenarios to reduce roller wear), and roundness error ≤ 0.01mm (to ensure uniform contact). If the shaft journal precision is substandard, surface chrome plating or grinding repair is required; otherwise, premature failure of the bearing and shaft journal will occur.​

2. Core Performance Indicators and Advantages​

Leveraging structural design innovations, inner ring-free spiral roller bearings excel in heavy-load capacity, impact resistance, and adaptability. Key performance indicators and advantages are as follows:​

(1) Key Performance Parameters (for Mainstream Models)

(2) Core Performance Advantages​

Dual Excellence in Heavy-Load and Impact Resistance: The radial rated dynamic load is 5%-10% higher than that of inner ring-equipped models, enabling long-term bearing of 300-800kN heavy loads (e.g., for drum shafts of mining belt conveyors). The impact load capacity reaches 2-2.5 times the rated load, with an impact absorption capacity ≥ 8J-15% higher than inner ring-equipped models-making them suitable for high-frequency impact scenarios such as steel billet collisions and material crushing.​

Significant Structural Simplification and Cost Advantages: Omitting the inner ring reduces the number of components by 25% and simplifies assembly steps by 40% (e.g., for a 200mm shaft diameter model, inner ring-equipped versions require 3 assembly steps, while inner ring-free versions only need 2). Manufacturing costs are reduced by 20%-30%, and cost savings can reach up to 40% for large shaft diameter models (≥ 300mm), significantly lowering the overall procurement cost of equipment.​

Strong Adaptability to Large Shaft Diameters: Eliminating the need for custom large inner rings, these bearings can directly adapt to ultra-large shaft systems with diameters ranging from 100mm to 1000mm (e.g., hollow shafts of large mining ball mills with diameters up to 800-1000mm). This solves challenges such as high manufacturing difficulty, inconvenient transportation, and difficult installation precision control for large inner rings in inner ring-equipped models.​

High Maintenance Flexibility: If the shaft journal experiences localized wear (depth ≤ 0.05mm), it can be restored through grinding (recovering surface roughness Ra ≤ 0.8μm and roundness error ≤ 0.01mm) for continued use, eliminating the need to replace the entire bearing. Compared to inner ring-equipped models, this avoids the need to replace both the inner ring and rollers when the inner ring is worn, reducing maintenance costs by 30%-50% and shortening maintenance cycles by 40%.​

3. Shaft Journal Technical Requirements (Prerequisite for Adaptation)​

The performance of inner ring-free spiral roller bearings fully depends on the quality of the shaft journal. The shaft journal must meet the following four core technical indicators; otherwise, premature failure of the bearing and shaft journal will occur (service life reduced by more than 50%):​

Surface Hardness: The shaft journal surface must undergo quenching. Medium-to-small shaft journals (diameter ≤ 200mm) use integral quenching with hardness ≥ HRC58; large shaft journals (diameter ＞ 200mm) use surface induction hardening with a hardened layer depth ≥ 2mm (measured from the surface) and surface hardness ≥ HRC58. This ensures sufficient wear resistance and deformation resistance of the shaft journal to prevent crushing by spiral rollers.​

Surface Precision: The surface roughness must reach Ra ≤ 0.8μm (Ra ≤ 0.4μm for precision transmission scenarios such as port crane wheel shafts); the roundness error ≤ 0.01mm and cylindricity error ≤ 0.02mm/m. This prevents uneven contact between the rollers and the shaft journal, which would cause localized stress concentration and premature wear.​

Dimensional Tolerance: The shaft journal diameter tolerance must match the inner diameter of the bearing roller set, typically using grade h7 or g6 tolerances (e.g., for a bearing roller set adapted to a 150mm shaft diameter, the shaft journal diameter tolerance is φ150h7, i.e., a diameter range of 150-150.027mm). This ensures the interference between the rollers and the shaft journal is controlled at 0.01-0.03mm-too little interference causes looseness, while too much increases frictional resistance and leads to excessive temperature rise.​

Surface Condition: The shaft journal surface must be free of scratches (depth ≤ 0.02mm), rust (rusted area ≤ 5%), burrs, and dents. Before assembly, the surface must be cleaned of oil and impurities using gasoline or alcohol. After drying, a thin layer of anti-rust lubricating grease (e.g., lithium-based grease) is applied to prevent surface scratches during assembly.​

4. Typical Application Scenarios and Practical Cases​

Inner ring-free spiral roller bearings are suitable for applications that simultaneously meet three conditions: "large shaft diameter (≥ 100mm), heavy load (≥ 150kN), and qualified shaft journal precision." Below are typical application cases in four core fields:​

(1) Mining Machinery: Drum Shafts of Belt Conveyors​

Operating Conditions: Shaft diameter 200-500mm, radial load 300-800kN, material impact during operation (short-term load peak up to 1.8 times the rated value), high dust concentration (≥ 100mg/m³), required bearing service life ≥ 8000h.​

Suitable Model: RNA6004 (adapted to 200mm shaft diameter, 50mm bearing width, 480kN radial rated dynamic load, with NBR seal).​

Application Results: After a large mining company adopted this model, compared to the previously used inner ring-equipped bearings, the radial installation space was reduced by 20% (from 55mm to 44mm) and manufacturing costs by 25%. The dustproof design of the seal reduced dust intrusion into the bearing by 90%, achieving a continuous operation life of 12,000h with only 0.03mm of shaft journal wear. The maintenance cycle was extended from 6 months to 12 months.​

(2) Metallurgical Equipment: Roller Shafts of Continuous Casters​

Operating Conditions: Shaft diameter 150-300mm, radial load 200-600kN, operating temperature 80-120℃, continuous operation (annual operating time ≥ 7000h), required shaft journal roughness Ra ≤ 0.4μm.​

Suitable Model: RNAO50 (adapted to 250mm shaft diameter, 60mm bearing width, 550kN radial rated dynamic load, with FKM dust cover and high-temperature grease).​

Application Results: After a steel mill adopted this model for its continuous caster, the FKM dust cover withstood 120℃ high temperatures, and the high-temperature grease (withstanding 150℃) ensured effective lubrication. The bearing operated continuously for 10,000h without failure, with no significant shaft journal wear. Compared to inner ring-equipped bearings, installation time was reduced by 50% (from 4 hours to 2 hours) and maintenance costs by 35%.​

(3) Heavy General Machinery: Wheel Shafts of Port Cranes​

Operating Conditions: Shaft diameter 120-400mm, radial load 150-500kN, intermittent impact during start-up/braking (load peak up to 2 times the rated value), required shaft journal cylindricity error ≤ 0.02mm/m.​

Suitable Model: RN324 (adapted to 120mm shaft diameter, 50mm bearing width, 320kN radial rated dynamic load, no seal, used with the equipment's integral sealing system).​

Application Results: After a port adopted this model for its crane wheel shafts, the shaft journals were quenched (HRC58) and used with the equipment's integral sealing system. The bearing operated continuously for 15,000h under intermittent impact conditions with wear ≤ 0.04mm. During maintenance, only surface grinding of the shaft journal was required (costing approximately 200 yuan), eliminating the need for bearing replacement-reducing maintenance costs by 40% compared to inner ring-equipped models.​

(4) Construction Machinery: Drum Shafts of Large Winches​

Operating Conditions: Shaft diameter 180-350mm, radial load 250-600kN, low operating speed (≤ 500r/min), humid environment (humidity ≥ 85%RH).​

Suitable Model: RNA6006 (adapted to 300mm shaft diameter, 70mm bearing width, 680kN radial rated dynamic load, with NBR seal).​

Application Results: After a construction company adopted this model for its winch, the NBR seal effectively prevented the intrusion of humid air and impurities. The bearing operated continuously for 9,000h in a humid environment without rust. Compared to inner ring-equipped bearings, procurement costs were reduced by 30%, installation space by 22%, and it was well-adapted to the compact drum structure of the winch.

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