Four-point Contact Ball

I. Product Overview​

Four-Point Contact Ball Bearings (abbreviated as FPCB) are a specialized category within the ball bearing family, designed for scenarios requiring space efficiency, single-bearing bidirectional axial positioning, and radial load-bearing capabilities. Their core competitiveness lies in the triple characteristics of "single-bearing bidirectional axial load capacity + compact structure + high rigidity" - through a unique "double-arc combination" design of the inner and outer ring raceways, steel balls form four contact points with the raceways (two on each side of the raceway) simultaneously. This breaks the limitation of standard angular contact ball bearings, which "can only bear unidirectional axial loads with a single bearing". A single FPCB can simultaneously bear radial loads and bidirectional axial loads (with axial load capacity increased by over 80% compared to single-row angular contact ball bearings of the same size). Adopting an integrated compact structure, it eliminates the need for paired installation of standard angular contact ball bearings, saving 30%-50% of installation space and completely solving the industry pain points of "complex axial positioning structures and insufficient installation space" for space-constrained equipment.​

The outer diameter of these bearings ranges from 20mm to 500mm, with an inner diameter spanning 10mm to 250mm. The basic dynamic load rating is 5kN-250kN, and the basic static load rating is 3kN-150kN. The limiting speed under grease lubrication is 8,000-30,000 r/min (high-speed models can reach 40,000 r/min), and precision grades are mainly P6-P4 (P2 grade is optional for precision scenarios). Structurally, they are divided into separable types (outer ring separable, suffix MB) and non-separable types (integral structure, no suffix). They are suitable for precision transmission systems with space constraints and bidirectional axial positioning requirements, such as machine tool spindles, robot joints, aerospace equipment, and medical devices. The complexity of the equipment transmission structure is reduced by 40%, and space utilization is increased by more than 30%.​

Compared with standard angular contact ball bearings, FPCBs do not require "back-to-back/face-to-face" paired installation to achieve bidirectional load-bearing; a single bearing can complete bidirectional axial positioning, greatly simplifying transmission design. The optimized double-arc raceway design ensures more uniform contact stress, extending service life by over 50% compared to paired standard angular contact ball bearings under the same load conditions. With a coverage rate of over 60% in the space-constrained precision transmission field, FPCBs are core transmission components that balance "space saving, function integration, and reliable performance".​

II. Core Structure and Design Features​

1. Precision Structural Composition​

The four core components of FPCBs are deeply optimized to meet the requirements of "bidirectional load-bearing, compact integration, and stable force transmission", ensuring reliable operation under space-constrained conditions:​

Inner and Outer Rings: Adopt a double-arc raceway structure. Both inner and outer ring raceways consist of two symmetrical arc segments (the radius of curvature of the arcs is slightly larger than that of the steel balls, with a curvature coefficient f=0.52-0.55). The transition between the two arc segments is smooth, allowing steel balls to form stable contact points with the raceways on both sides when bearing bidirectional axial loads (contact points on one side of the raceway bear force under positive axial loads, and contact points on the other side bear force under reverse axial loads). The material used is SUJ2 high-carbon chromium bearing steel (20CrNiMo alloy carburized steel is optional for high-speed/heavy-load scenarios), which undergoes "vacuum quenching + ultra-precision grinding" processes. The surface hardness reaches HRC 62-66, the raceway surface roughness is Ra ≤ 0.03μm, and the roundness error is ≤ 1μm, ensuring uniform contact between steel balls and raceways and avoiding local stress concentration.​

Rolling Elements (Steel Balls): High-purity large-diameter steel balls are used, with a diameter 10%-15% larger than that of single-row angular contact ball bearings of the same size (e.g., for the QJ206 model with an inner diameter of 30mm, the steel ball diameter increases from 7.938mm to 9.525mm). The quantity is 2-4 more than that of single-row angular contact ball bearings. Bidirectional axial load capacity is enhanced by increasing the contact area and quantity of rolling elements. The material is GCr15SiMn ultra-high-toughness bearing steel, processed through "vacuum melting + multi-stage precision grinding + nano-level polishing". The impact toughness αk ≥ 25J/cm², the roundness error is ≤ 0.15μm, the surface roughness is Ra ≤ 0.01μm, and wear resistance is improved by 40% compared to ordinary steel balls. For high-speed scenarios (e.g., machine tool spindles), silicon nitride ceramic balls are optional, reducing weight by 40% and achieving a friction coefficient as low as 0.0015.​

Cage: Lightweight and high-strength cages are used. Mainstream models adopt PA66 + 30% glass fiber reinforced nylon cages (for medium-low speed scenarios), which are lightweight and have a low friction coefficient (0.002-0.003), suitable for rotational speeds ≤ 20,000 r/min. For high-speed scenarios (rotational speed 20,000-30,000 r/min), HPb59-1 brass cages are used, featuring good heat dissipation and strong deformation resistance. For ultra-high-speed scenarios (rotational speed ＞ 30,000 r/min), titanium alloy cages (TC4 material) are used, with high strength and fatigue resistance. The cage pockets adopt a "double-arc adaptive design", with the clearance between pockets and steel balls controlled at 0.1-0.2mm to prevent steel ball movement during bidirectional load switching, ensuring an operating noise of ≤ 50dB.​

Sealing/Dust-Proof Structure (Optional): Equipped with thin contact seals (suffix 2RS) or non-contact dust covers (suffix 2Z). The 2RS seals are made of nitrile rubber (NBR) with a seal lip thickness of 0.5-0.8mm, achieving an IP54 dust and water resistance rating, suitable for humid, low-dust scenarios (e.g., robot joints, medical devices). The 2Z dust covers are made of 0.2-0.3mm thick cold-rolled steel plates, fixed by laser welding, providing good dust resistance without affecting rotational speed or precision, suitable for dry, dusty scenarios (e.g., machine tool spindles, fans). All sealing structures adopt a compact design, without additional installation space for the bearing.​

2. Key Design Characteristics​

Single-Bearing Bidirectional Axial Load Capacity: Relying on the double-arc raceway design, a single bearing can simultaneously bear radial loads and bidirectional axial loads. The axial rated dynamic load is increased by over 80% compared to single-row angular contact ball bearings of the same size (e.g., the axial rated dynamic load of the QJ206 model reaches 18kN, while that of the same-sized 7206AC model is only 10kN). There is no need for paired installation of standard angular contact ball bearings, completely simplifying the axial positioning structure, especially suitable for space-constrained transmission systems.​

Compact Structure for Space Saving: The integrated design ensures that the radial dimension of the bearing is basically the same as that of a single-row angular contact ball bearing of the same size (width only increases by 10%-15%), but it can replace the combined structure of "2 standard angular contact ball bearings + spacer". Installation space is saved by 30%-50% (e.g., at the machine tool spindle end, where paired bearings originally required 100mm of installation length, FPCBs only require 60mm), greatly improving equipment space utilization.​

High Rigidity and Stable Force Transmission: The four-point contact design between the double-arc raceways and steel balls ensures more uniform contact stress (contact stress ≤ 2,800MPa, 20% lower than that of paired standard angular contact ball bearings), and radial rigidity is increased by over 30% compared to single-row angular contact ball bearings of the same size. During bidirectional axial load switching (e.g., forward and reverse rotation of robot joints), the bearing does not experience "clearance impact", ensuring more stable force transmission and improving equipment operation accuracy by 0.01-0.02mm.​

Adaptability to Multiple Working Conditions: By optimizing the raceway arc radius and contact angle (contact angle is usually 35°-40°, and can be customized to 25°-45° according to requirements), it can adapt to scenarios with different load ratios - models with large contact angles (40°-45°) focus on axial load-bearing (e.g., axial positioning of machine tool spindles), while models with small contact angles (25°-30°) focus on radial load-bearing (e.g., radial support of robot joints). At the same time, it supports grease lubrication and oil mist lubrication, adapting to multiple working conditions such as low-speed heavy-load (3,000-8,000 r/min) and high-speed light-load (20,000-30,000 r/min).​

III. Main Product Models and Classification​

1. Classification by Structural Type

2. Classification by Precision Grade​

Grade P6: Dimensional tolerance ±8μm, geometric tolerance ±5μm. Suitable for general precision scenarios (e.g., standard robot joints, fans), with moderate cost and high cost-effectiveness, accounting for over 60% of the market share.​

Grade P5: Dimensional tolerance ±5μm, geometric tolerance ±3μm. Suitable for medium-precision scenarios (e.g., precision machine tool spindles, medical devices), capable of meeting micron-level transmission requirements, accounting for approximately 30% of the market share.​

Grade P4: Dimensional tolerance ±3μm, geometric tolerance ±2μm. Suitable for high-precision scenarios (e.g., aerospace equipment, semiconductor processing equipment), requiring ultra-precision grinding and strict testing, accounting for approximately 10% of the market share.​

Grade P2: Dimensional tolerance ±1μm, geometric tolerance ±0.5μm. Suitable for ultra-precision scenarios (e.g., laser measuring instruments, high-end CNC machine tools), with a high price, only used in fields with extremely high precision requirements.​

3. Classification by Sealing/Lubrication Method​

Open Four-Point Contact Ball Bearings (No Suffix): No sealing/dust-proof structure, with the smallest rotational resistance. Suitable for dry, clean scenarios with independent lubrication systems (e.g., high-precision machine tool spindles with oil mist lubrication).​

Four-Point Contact Ball Bearings with Dust Covers (Suffix 2Z): Double-sided thin steel dust covers, providing good dust resistance without affecting rotational speed or precision. Suitable for dry, dusty scenarios (e.g., robot joints, fans).​

Sealed Four-Point Contact Ball Bearings (Suffix 2RS): Double-sided nitrile rubber seals, achieving an IP54 dust and water resistance rating. Suitable for humid, low-dust scenarios (e.g., medical devices, outdoor precision equipment), with rotational resistance slightly higher than that of 2Z models (increased by 5%-10%).​

Four-Point Contact Ball Bearings with Lubrication Grooves (Suffix /W33): Equipped with annular lubrication grooves and oil holes on the outer ring, facilitating regular grease replenishment. Suitable for long-term continuous operation scenarios (e.g., large fans, conveyor equipment).​

IV. Applicable Industries and Typical Applications​

With core advantages of "single-bearing bidirectional load-bearing and compact structure", FPCBs are widely used in precision industrial fields with space constraints and bidirectional axial positioning requirements. Typical applications include:​

Machine Tool Industry: CNC machine tool spindles (suitable for Model QJ212P5, non-separable type, 35° contact angle, single-bearing achieving bidirectional axial positioning of the spindle, accuracy ±0.005mm at 15,000 r/min), machining center turrets (suitable for Model QJ208MBP6, separable type, facilitating turret disassembly and maintenance, bearing bidirectional axial force of the tool holder), and lathe spindle ends (suitable for Model QJ210P4, high rigidity, ensuring radial and axial stability during turning).​

Robot and Automation Industry: Industrial robot joints (suitable for Model QJ206P5/2Z, compact structure saving joint space, bidirectional load-bearing adapting to forward and reverse rotation loads of joints, noise ≤ 48dB at 8,000 r/min), collaborative robot wrists (suitable for Model QJ205P6/2RS, IP54 seal adapting to humid workshop environments, single-bearing simplifying the wrist transmission structure), and drive shafts of automated conveyor equipment (suitable for Model QJ215P6, bearing bidirectional axial movement of conveyor rollers, stable operation for long periods).​

Aerospace Industry: Auxiliary shafts of small aircraft engines (suitable for Model QJ207P4, high precision, adapting to high-altitude low-pressure environments, single-bearing achieving bidirectional axial positioning), satellite attitude adjustment mechanisms (suitable for Model QJ204P2, ultra-precision, ensuring attitude adjustment error ≤ 0.1°, lightweight design reducing satellite load), and UAV gimbals (suitable for Model QJ203P5, compact structure, bidirectional load-bearing adapting to forward and reverse rotation of gimbals, ensuring stable shooting).​

Medical Device Industry: CT scanner rotating frames (suitable for Model QJ214MBP5/2RS, separable type facilitating maintenance, IP54 seal resisting moisture inside CT scanners, vibration ≤ 1.5m/s² at 10,000 r/min), MRI equipment (suitable for Model QJ209P5, non-magnetic material options available to avoid affecting magnetic field environments, single-bearing simplifying the rotating component structure), and precision surgical robots (suitable for Model QJ206P4, high rigidity, ensuring surgical movement accuracy ±0.01mm).​

General Precision Machinery Industry: Robot arms for semiconductor wafer handling (suitable for Model QJ208P4, high precision, avoiding position deviation during wafer handling), adjustment shafts of laser cutting equipment mirrors (suitable for Model QJ205P3, ultra-precision, ensuring mirror angle adjustment accuracy), and drum shafts of large printers (suitable for Model QJ216P6/2Z, dust-proof structure, bearing bidirectional axial movement of drums, ensuring printing accuracy).

V. Product Advantages Summary
Single set for bidirectional bearing capacity, simplifies transmission design: Breaks through the limitation of single-direction bearing capacity of ordinary angular contact ball bearings, a single set can achieve combined radial + bidirectional axial bearing capacity without the need for paired installation. The complexity of the transmission structure is reduced by 40%, and the equipment design and manufacturing costs are decreased.
Compact structure, saves installation space: Integrated design replaces the "two bearings + spacer sleeve" combination, saving 30%-50% of installation space. Especially suitable for scenarios with limited space such as robot joints and machine tool spindles, improving equipment integration and miniaturization level.
High rigidity for stable force transmission, better precision: Four-point contact design makes the contact stress more uniform, the radial rigidity is over 30% higher than that of single-row angular contact ball bearings; bidirectional load switching without gap impact, the equipment operation accuracy is improved by 0.01-0.02mm, suitable for precise transmission requirements.
Multi-condition compatibility, strong versatility: Supports customization of different contact angles, multiple sealing / lubrication methods, suitable for various working conditions such as low-speed heavy load, high-speed light load, and humid dusty conditions; separable / non-separable structures are available to meet different requirements such as frequent disassembly and fixed installation.
Longer service life, lower operation and maintenance costs: Uniform contact stress and high toughness material design, under the same working conditions, the service life is extended by more than 50% compared to paired ordinary angular contact ball bearings; the sealing structure reduces grease consumption, the maintenance cycle is extended by 2-3 times, and the equipment operation and maintenance costs are reduced by 30%.

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