Seal Type Selection Recommendations

Introduction to Bearing Seals—Preventing Lubricant Leakage

Selection Guide & Application Overview

What are Dust-Proof and Sealed Bearings?

Function of Seals

A bearing "shield" refers to a metal plate that seals the bearing rolling elements together with lubricant, while a "seal" is a similar rubber sealing component. Seals offer the following advantages:

Water, dust, and rust protection, improving rolling element durability
Double-shielded bearings require almost no maintenance
No need for external lubrication

How Seals Work

Shields prevent foreign objects (dust and moisture) from entering from the outside. By preventing foreign matter intrusion, the bearing interior is protected from water, dust, and rust, reducing rotation issues caused by foreign matter and rust, thus improving durability. Bearings with shields and seals contain pre-packed grease and ensure that this lubricant does not leak to the outside.

Bearing Seal Failure Statistics

40-50%

Bearing failures are caused by lubricant leakage and contamination
(Primary failure cause)

10x

Cost of seal failure is approximately 10 times the cost of the seal itself
(Average $5K-$50K per incident)

2-3x

Average lifespan extension with optimal seals compared to improper selection

Types of Dust-Proof and Sealed Bearings

Type	Shielded	Sealed
Contact Type	Non-Contact	Non-Contact	Contact	Low-Torque
Structure	Metal shield, non-contact with inner ring	Rubber seal, non-contact with inner ring	Rubber seal, contact with inner ring	Rubber seal, light contact with inner ring
Friction Torque	Low	Low	High	Medium
Dust & Water Resistance	Poor	Poor	Good	Good
High Speed Performance	Same as open type	Seal heat resistance	Seal heat resistance	Seal heat resistance

Shielded Type (Z/ZZ)

Metal shield, suitable for high-speed operation

Non-Contact Sealed (LB/LLB)

Rubber seal, balances speed and sealing

Contact Sealed (LU/LLU)

Rubber seal, best dust and water resistance

Low-Torque Sealed (LH/LLH)

Rubber seal, balances sealing and torque

Seal Type Comparison Across Manufacturers

Seal Type	NTN	NSK	SKF	NACHI	KOYO
Shielded Single Side	Z	Z	Z	ZE	Z
Shielded Both Sides	ZZ	ZZ	ZZ	ZZE	ZZ
Non-Contact Single Side	LB	V	RZ	NKE	RU
Non-Contact Both Sides	LLB	VV	2RZ	2NKE	2RU
Contact Single Side	LU	DU	RS	NSL,NSE	RS,RK
Contact Both Sides	LLU	DDU	2RS1	2NSL,2NSE	2RS,2RK
Low-Torque Single Side	LH	DW	-	-	RD
Low-Torque Both Sides	LLH	DDW	-	-	2RD

Seal Type Performance Comparison

Shielded Type Best For

Machine tools and precision machinery
High-speed applications
Where high water resistance is not required
Prevention of debris intrusion and oil leakage
Reduced maintenance hours

Sealed Type Best For

Environments with water or dust
Prevention of foreign matter or moisture intrusion
Non-high-speed rotation scenarios
Reduced maintenance hours

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