Description
Structure of oil seals and workings of each part
The following figure and table show the structure of oil seals and workings of each part, respectively.
Structure of oil seals and workings of each part
Name
Workings of each part
Lip
Lip tip
The lip tip has a wedge-shaped cross section and the function of sealing the fluid as it is pressed against the shaft surface.
Seal lip
The seal lip is made of a flexible elastomer, and designed to maintain stable sealing performance against vibration of machinery and pressure change of the sealed fluid. The spring maintains the force of the seal lip pressed against the shaft for a long time.
Dust lip
The dust lip is a supplemental lip without spring, and has the function of preventing the entry of dust.
Fitting portion
The fitting portion has the function of fixing the oil seal in the housing hole and preventing the leakage of the fluid from the contact surface between the outer circumferential surface of the oil seal and the inner circumferential surface of the housing or the entry of dust. The metallic ring has the function of securing the fitting force to fix the oil seal on the housing.
Main types, characteristics and related standards of oil seals
Shape
Type
Applications/characteristics
JIS B2402
JASO F401
ISO 6194
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 shows main rubber materials, springs and metallic ring materials used for oil seals.
Main rubber material
Main material
Characteristics of rubber material
Operating temperature
(heat resistance)
Material cost
Nitrile rubber (NBR)
・ Material costs are low.
・ Offers versatility and most commonly used.
・ The operating temperature (heat resistance) is limited.
~100℃
Acrylic rubber (ACM)
・ Superior in heat resistance to nitrile rubber.
・ Resistance to brake fluid and fuel oil is inferior.
~130℃
Silicone rubber (VMQ)
・ Superior in heat resistance to acrylic rubber.
・ Has best cold resistance.(-60℃~)
・ Inferior in resistance to alkali and water.
~150℃
Fluororubber (FKM)
・ Has best heat resistance.
・ Most widely suitable for lubricating oils and fuel oils.
~180℃
Spring and metallic ring material
Fluid to be sealed\
Spring and metallic ring material
Spring
Metallic ring
Standard material
Dedicated material
Standard material
Dedicated material
JIS G3521 SW
Dedicated material
JIS G3522 SWP
(Piano wire)
JIS G4309 SUS
(Stainless steel wire)
JIS G3141 SPCC
(Cold-rolled steel sheets
and steel strips)
JIS G3131 SPHC
(Hot-rolled steel sheets
and steel strips)
JIS G4305 SUS
(Cold-rolled stainless steel sheets)
JIS G4307 SUS
(Cold-rolled stainless steel strips)
304
316
304
316
Lubricating oil/grease
○
○
○
○
○
○
Water
×
○
○
×
○
○
Vapor
×
○
○
×
○
○
Seawater
×
×
○
×
×
○
Acid
×
×
○
×
×
○
Alkali
×
○
○
×
○
○
○: Usable ×: Not usable
Method of selecting oil seals
To make full use of the function of oil seals, selecting the most suitable shape and material for the use conditions is necessary. Generally, the following steps are followed:
Since NOK offers a wide range of lineup that meets various requirements, please see our catalogs or contact the sales office nearest you.
Design of oil seal mounted portion
Since the shaft, housing shape, roughness, etc. influence the performance of oil seals, key points for general shaft and housing design are described below.
Key points for shaft and housing design
Mounted portion
Design key points and recommended values
Remarks (precautions)
Shaft
Material
Use of carbon steel pipes for mechanical structures is recommended.
Use of cast iron should be avoided as much as possible since pinholes may be generated.
Hardness
30 HRC min.
Roughness and machining method
・ 0.32—0.1 μmRa and 2.5—0.8 μmRz are recommended.
・ Finish with a grinder or emery paper is recommended.
If shaft machining marks have orientation, leakage may be caused.
Chamfering
Chamfer the shaft ends.
Housing
Material
Steel or cast iron is recommended.
Use of light metal or resign should be avoided as much as possible since they are thermally expanded significantly.
Inner circumferential surface roughness
Outer metal: 3.2—0.4 μmRa, 12.5—1.6 μmRz Outer rubber: 3.2—1.6 μmRa, 12.5—6.3 μmRz
When the inner circumferential surface roughness is large, a gap is created between the contact faces, causing leakage.