Bearing Seal Codes Z and V Explained and Selection Guide for 3000 rpm Conditions

Title: Bearing Seal Codes Z and V Explained and Selection Guide for 3000 rpm Conditions

1. Meaning of Bearing Seal Codes
The following seal/shield codes are common in bearing suffix designations:

Code Chinese Name English Name Structural Characteristics
Z Single-side metal shield Single metal shield Non-contact steel plate shield on one side
ZZ Double-side metal shield Double metal shield Non-contact steel plate shields on both sides
V Single-side non-contact rubber seal Single non-contact rubber seal Non-contact rubber seal on one side (common in some brands such as NSK)
VV Double-side non-contact rubber seal Double non-contact rubber seal Non-contact rubber seals on both sides
2RS Double-side contact rubber seal Double contact rubber seal Contact rubber seals on both sides, commonly referred to as V-type seals
RS Single-side contact rubber seal Single contact rubber seal Contact rubber seal on one side
Note: Different brands have slightly different codes. For example, SKF uses 2Z for double metal shields and 2RS1 for double rubber seals; NSK uses VV for non-contact rubber seals and DDU for contact rubber seals. In the general industry, "Z" typically refers to a non-contact metal shield, while "V" or "2RS" refers to a contact rubber seal.

2. In-depth Analysis of Z-type Seals (Metal Shields)
2.1 Structure and Principle
Z-type seals are made of stamped steel plates 0.3-0.5mm thick, fixed into a groove on the bearing outer ring by pressure. An annular gap of 0.1-0.3mm is maintained between the inner edge of the shield and the inner ring, with no contact. This design allows the shield to block larger solid contaminants (such as dust and debris) from entering the bearing, while allowing air and lubricant vapor to pass through without generating additional friction.

2.2 Suitable Operating Conditions
Dry environment with no liquid water

Coarse dust particles (larger than the gap)

Bearing speed approaching or reaching the limiting speed

Low friction and low energy consumption required

Equipment not frequently washed

2.3 Advantages and Disadvantages
Advantages Disadvantages
Highest speed capability (100%) Not waterproof or moisture-proof
Extremely low friction torque Does not block fine dust
Low cost Possible grease leakage (vertical shaft mounting)
Wide operating temperature range No protection against corrosive gases
3. In-depth Analysis of V-type Seals (Rubber Seals)
3.1 Structure and Principle
V-type seals are molded from synthetic rubber (NBR, FKM, VMQ, etc.) with a metal insert to maintain shape. The sealing lip tightly contacts the chamfer or rib surface of the bearing inner ring, forming a contact seal. They effectively block moisture, dust, and grease leakage under both static and dynamic conditions. The sealing lip is often designed with a spring (like a single-lip oil seal) or relies on the rubber's own elasticity to generate a holding force.

3.2 Rubber Material Comparison
Material Code Temperature Range Oil Resistance Water Resistance Chemical Resistance Cost
Nitrile rubber NBR -40~120°C Excellent Good Moderate Low
Fluoroelastomer FKM/Viton -20~200°C Excellent Excellent Excellent High
Silicone rubber VMQ -60~200°C Poor Good Moderate Medium
3.3 Suitable Operating Conditions
Humid environment with condensation or wash water

Fine dust present (e.g., textile fibers, food powder)

Equipment requiring frequent washing (food processing, pharmaceutical)

Vertical shaft mounting requiring prevention of grease leakage

Strict noise requirements (rubber absorbs sound)

3.4 Advantages and Disadvantages
Advantages Disadvantages
Excellent water and dust protection Speed capability reduced by 15-20%
Prevents grease leakage Higher friction torque, more energy consumption
High-temperature material options (FKM) Higher cost
Reduced operating noise Lip wear and aging after long operation
4. Technical Requirements for Bearings at 3000 rpm
When a bearing needs to operate stably at 3000 rpm (the common synchronous speed for 2-pole motors at 50Hz), the following technical requirements must be met:

4.1 Speed Limit Verification
Different bearing models and sizes have vastly different speed limits. Examples:

Bearing Model Bore (mm) Grease-lubricated Speed Limit (rpm) Is 3000 rpm safe?
6200 10 approx. 24,000 Yes
6204 20 approx. 14,000 Yes
6208 40 approx. 8,000 Yes
6215 75 approx. 4,000 Yes (needs C3 clearance)
6218 90 approx. 3,200 Marginal (enhance lubrication)
6222 110 approx. 2,400 No (requires special design)
Conclusion: For common bearings with bore ≤75mm, 3000 rpm is well below their speed limit; no special treatment needed. For bore 80-100mm, they are near the limit, requiring C3 clearance and high-quality grease. For bore >100mm, special design is required.

4.2 Precision Grade Selection
【Table 6: Recommended Precision Grades at 3000 rpm】

Bearing Type Normal (P0) Medium (P6) High (P5/P4) Notes
Deep groove ball bearing (general motor) ★Recommended Optional Unnecessary 3000 rpm is normal speed
Deep groove ball bearing (precision equipment) Not recommended ★Recommended Optional e.g., machine tool cooling pump
Angular contact ball bearing (spindle) Not applicable Not recommended ★Recommended (P5) Requires preload, high rigidity
Cylindrical roller bearing ★Recommended Optional Unnecessary Mainly radial load
4.3 Clearance Grade Selection
At 3000 rpm with some temperature rise, clearance selection recommendations:

CN clearance: Suitable for temperature rise <40°C and normal fit tolerance

C3 clearance: Recommended for temperature rise 40-70°C or tight fits (e.g., k6 shaft diameter)

C4 clearance: Only for extremely high temperature or very tight fits; generally not needed at 3000 rpm

Rule of thumb: If the outer ring temperature feels noticeably hot (>70°C) or if the equipment makes abnormal noise during initial operation (which disappears after thermal expansion), choose C3 clearance.

4.4 Grease Selection
【Table 7: Recommended Grease Types at 3000 rpm】

Grease Type Base Oil Viscosity Temperature Range Recommended Applications
Lithium grease No.2 (general) 100-150 cSt@40°C -20~120°C General motors, fans, pumps
Extreme pressure lithium grease No.2 150-200 cSt@40°C -20~120°C Heavy loads, impact conditions
Polyurea grease 80-120 cSt@40°C -40~180°C High-temperature, high-speed motors
Synthetic oil-based grease (PAO) 60-100 cSt@40°C -50~150°C Low-temperature start-up, high speed
Grease fill quantity: 1/3 to 1/2 of the bearing free space; for high-speed, take 1/3.

4.5 Seal Type Selection (Z vs V) Decision at 3000 rpm
Operating Condition Seal Selection Speed Verification
Indoor dry dust-free motor Z/ZZ Safe, no speed reduction needed
Outdoor motor (weather-protected) V/2RS Need to verify bearing speed limit ≥3500 rpm
Food processing equipment (frequent washdown) V/2RS (FKM seal) Need to verify seal temperature resistance ≥120°C
High-speed fan (3000 rpm) Z/ZZ Preferred, avoid rubber heat generation
Water pump V/2RS (contact) Must be waterproof; accept speed reduction
5. Maintenance and Life of Z vs V Sealed Bearings
Z-type sealed bearings: Largely maintenance-free. However, when operating in dusty environments for long periods, dust may enter through the gap, shortening life. Periodic cleaning of external dust is recommended.

V-type sealed bearings: The seal is a wear part. In high-temperature or chemical environments, rubber will age and harden, leading to seal failure. It is recommended to inspect the seal lip condition every 2000-4000 operating hours, and replace if cracks or hardening are found.