English
French
German
6308 Deep Groove Ball Bearing 40x90x23mm
The 6308 bearing sits at the 90mm OD mark where a single-row deep groove bearing can replace a paired angular-contact arrangement in moderate combined-load applications. At 40mm bore and 23mm width, it delivers 42.3 kN dynamic load without the assembly complexity of two matched bearings.
Key Specifications
- Sealing: Open, ZZ (metal shields), 2RS (NBR rubber contact seals). ZZ retains full rated speed.
- Speed and Load: 42.3 kN dynamic (Cr), 24.5 kN static (Cor). 7,000 RPM open/ZZ; 4,000 RPM with 2RS seals.
- Axial Load: Supports 15-20% of radial rating in CN clearance. Approximately 6.3-8.5 kN sustained.
- Temperature: -40 to 120 C with standard grease. Fluorinated grease options extend to 200 C.
- Material and Precision: GCr15 bearing steel (AISI 52100 equivalent). ABEC-3 standard; ABEC-5 available.
For any inquiries, please contact with our Supporting Team at sales@yuanhecd.com.
| Model | 6308 |
| Bore (d) | 40 mm |
| OD (D) | 90 mm |
| Width (B) | 23 mm |
| Type | Open / Shielded / Sealed |
| ABEC | ABEC-3 |
| Material | GCr15 bearing steel (AISI 52100) |
| Dynamic Load Cr | 42.3 kN |
| Static Load Cor | 24.5 kN |
| Max Speed | 7,000 RPM (open/ZZ) 4,000 RPM (2RS) |
| Temperature | -40 to 120 C |
Bore x OD x Width
40 x 90 x 23 mm
Dynamic Load Cr
42.3 kN
Static Load Cor
24.5 kN
Max Speed
7,000 RPM
Sealing
Open / ZZ / 2RS
Precision
ABEC-3
Shielding and Lubrication
The 6308 ZZ bearing uses non-contact SPCC steel shields pressed into the outer ring. At 90mm OD and 7,000 RPM, the shield surface velocity reaches 33 m/s at the outer edge. The factory-set labyrinth clearance is calibrated for this velocity, maintaining separation without contact across the full speed range. Each bearing ships at 25-35% fill with lithium soap grease. For motors above 20 hp, the initial grease fill covers the break-in period; establish a regreasing schedule based on operating hours and temperature.
The 6308 2RS bearing variant uses nitrile contact seals on the inner ring shoulder. At 23mm width, the grease volume is approximately 40% greater than a 6208 bearing, supporting longer service intervals in pump and fan applications where bearing access requires partial machine disassembly. The 2RS seal limits sustained speed to 4,000 RPM due to contact friction and temperature rise at the seal lip.
Performance
At 42.3 kN dynamic and 24.5 kN static, the 6308 bearing delivers 45% more capacity than the 6208 bearing (40x80x18mm, 29.1 kN Cr). The 10mm larger OD and 5mm extra width over the 62-series accommodate significantly larger balls in a deeper groove. A 6008 bearing (40x68x15mm, 17.8 kN) saves 22mm OD and 8mm width for lightweight designs but carries less than half the dynamic load. Select the 6308 bearing when radial load governs the design and the housing bore can accept 90mm. If OD is constrained to 80mm or below, specify a 6208 or 6008 bearing instead.
C3 radial clearance is standard for the 6308 bearing in induction motors from 20 to 50 hp. At this bearing size, the thermal expansion differential between shaft and housing at steady-state consumes 15-25 microns of the initial clearance. C3 provides 23-43 microns of radial play, maintaining a positive running clearance. For coupled motor-pump assemblies where axial thrust from the impeller adds to rotor weight, the combined load mode shifts the contact angle. The deep groove ball bearing handles this shift without requiring a separate angular-contact bearing at the non-drive end.
OEM and Customization
Yuanhe manufactures the 6308 bearing to customer specifications. Common OEM customizations include C3 and C4 internal clearance for motors and pumps from 20 to 50 hp, fluorinated grease rated to 200 C for steel mill runout tables and kiln car applications, and stainless steel (AISI 440C) rings for food processing and chemical washdown. Cage options include stamped steel, glass-reinforced PA66, and machined brass for sustained operation above 5,000 RPM. Standard lead time is 7 to 15 days. Submit drawings or existing part numbers for a quote, or contact Yuanhe directly.
Applications
Electric motors (20 to 60 hp)
Industrial gearboxes and transmission assemblies
Centrifugal and mixed-flow pumps
Conveyor head pulleys and drive drums
HVAC fan shafts and large air handlers
Agricultural combine and baler drivelines
Steel mill runout table rollers
Mining conveyor and crusher idlers
Paper mill drying cylinder rolls
Frequently Asked Questions
Can a single 6308 bearing replace a paired angular-contact arrangement on a pump shaft? +
In many cases, yes. A paired angular-contact set requires matched mounting, accurate axial preload, and two bearing positions. The 6308 bearing (42.3 kN Cr) handles up to 8.5 kN axial load in C3 clearance. For pump applications where impeller thrust stays below this value and radial load from coupling misalignment is moderate, a single 6308 bearing at each shaft end eliminates the paired angular-contact arrangement. For thrust above 8.5 kN, retain the angular-contact set or add a separate thrust bearing.
What is the correct running clearance for a 6308 bearing in a 30 hp motor? +
C3 radial clearance (23-43 microns) is standard. At 30 hp, the 40mm shaft journal reaches operating temperature 15-25 C above the housing, consuming 15-25 microns of initial radial play. C3 ensures residual clearance stays at 3-18 microns in operation, preventing preload while minimizing ball skidding at light load. For D-flange motors where the housing bolts to a large thermal mass and runs cooler than the shaft, C4 clearance (36-56 microns) compensates for the larger thermal differential.
At what operating temperature does the 6308 bearing require special grease? +
Standard lithium soap grease with mineral base oil is rated to 120 C bearing ring temperature. Above 120 C, the base oil oxidizes rapidly. For 120-160 C, polyurea grease with synthetic ester base oil maintains film strength. For 160-200 C, fluorinated grease (PTFE-thickened perfluoropolyether) is required. Above 200 C, GCr15 steel begins to lose hardness; specify AISI M50 tool steel or silicon nitride (Si3N4) ceramic hybrid bearings for these temperatures.
Does the 6308 bearing need a regreasing schedule, or is it sealed for life? +
The 6308 ZZ bearing is not sealed for life at full load. The initial 25-35% grease fill provides approximately 2,000-4,000 operating hours at moderate load and speed. For longer intervals, specify a housing with regreasing provisions (nipple and relief port). Regrease at 40% of free volume with lithium soap or polyurea grease of NLGI 2 consistency. The 2RS sealed variant is maintenance-free within its design life at loads below 20% of Cr and speeds below 3,000 RPM. Above these thresholds, specify ZZ with external regreasing.
