Oil seals | General-purpose seal technology

Dec. 09, 2024

Description

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Structure of oil seals and workings of each part

The diagram and accompanying table illustrate the construction of oil seals and the functions of each component.

Structure of oil seals and workings of each part

Name	Workings of each part
Lip	Lip tip: The lip tip features a wedge-shaped cross-section designed to seal fluids effectively as it makes contact with the shaft's surface.
Seal lip	The seal lip is constructed from a flexible elastomer, engineered to deliver consistent sealing performance in response to machinery vibrations and changes in the fluid's pressure. A spring applies pressure to keep the seal lip firmly against the shaft over time.
Dust lip	The dust lip serves as an auxiliary lip that does not employ a spring, tasked with preventing the ingress of dust and other contaminants.
Fitting portion	The fitting portion secures the oil seal within the housing and shields against fluid leakage where the outer surface of the oil seal meets the inner surface of the housing. Additionally, a metallic ring ensures that the seal is firmly fixed in place.

Main types, characteristics and related standards of oil seals

Shape	Type	Applications/Characteristics	JIS B	JASO F401	ISO
SC SB	For oil, no dust lip	Type 1 Type 2	S SM	TYPE1 TYPE2	-
TC TB	For oil, with dust lip	Type 4 Type 5	D DM	TYPE3 TYPE4	-
VC VB	For grease, no dust lip	(G) (GM)	G GM	-	-
KC KB	For grease, with dust lip	-	P PM	-	-

Materials used for oil seals

The following table outlines the primary rubber materials, spring types, and metallic ring materials utilized in manufacturing oil seals.

Main rubber material

Main material	Characteristics of rubber material	Operating temperature (heat resistance)	Material cost
Nitrile rubber (NBR)	Cost-effective, versatile, mostly utilized, but with limited heat resistance.	100°C	Low
Acrylic rubber (ACM)	Better heat resistance compared to NBR, but inferior resistance to brake fluid and fuel oil.	130°C	Medium
Silicone rubber (VMQ)	Superior heat and cold resistance, yet weaker against alkalis and water.	150°C	High
Fluororubber (FKM)	Best heat resistance, suitable for lubricating and fuel oils.	180°C	High

Spring and metallic ring material

Fluid to be sealed Spring and metallic ring material	Spring	Metallic ring
Standard material	Dedicated material	Standard material
JIS G SW Dedicated material JIS G SWP Piano wire	JIS G SUS (Stainless steel wire)	JIS G SPCC (Cold-rolled steel sheets and steel strips) JIS G SPHC (Hot-rolled steel sheets and steel strips)

Method of selecting oil seals

To optimize the functionality of oil seals, it is critical to choose the right shape and material for the specific conditions of use. The general selection process includes:

Select the shape.
Select the lip material.
Select the metallic material.
Select the dimensions.

Given that NOK has an extensive range of products meeting various requirements, kindly refer to our catalogs or reach out to your nearest sales office.

Design of oil seal mounted portion

The performance of oil seals can be affected by the shaft, housing shape, and roughness, thus below are important considerations for general shaft and housing design.

Key points for shaft and housing design

Mounted portion	Design key points and recommended values	Remarks (precautions)
Shaft	Use of carbon steel pipes for mechanical structures is advisable.	Avoid cast iron as it may generate pinholes.
Hardness	Minimum of 30 HRC.	-
Roughness and machining method	0.32 to 0.1 μmRa and 2.5 to 0.8 μmRz are recommended. Use grinders or emery paper for finishing.	Be cautious; if machining marks have orientation, leakage may occur.
Chamfering	Chamfer the ends of the shaft.	-
Housing	Steel or cast iron is preferred.	Avoid using lightweight metals or resins as they can thermally expand significantly.
Inner circumferential surface roughness	Recommended values are as follows: Outer metal: 3.2 to 0.4 μmRa, 12.5 to 1.6 μmRz and Outer rubber: 3.2 to 1.6 μmRa, 12.5 to 6.3 μmRz.	Excessive roughness can create gaps between contact surfaces, leading to leakage.