Radial Shaft Seal Catalog  
 

INFLUENCE OF SPEED, TEMPERATURE & LUBRICANT

 

 

 

SEAL FRICTION & LIFE

The choice of lubricants, the environmental temperature, and the application speed are intimately related to the seal’s frictional torque and life. Careful analysis of these variables and their relationship to the choice of seal design and materials allows one to achieve desired durability goals with the most cost effective solution.
 

ROTATING TORQUE
 
 

T =

f  x  Pr  x  r

T = Rotating Torque [N x cm]

f = Coefficient of Friction

Pr = Radial Lip Load [N]

r = Shaft Radius [cm]

f =

Phi (Mu x u x b / Pr) 1/3

Phi = Characteristic Number

Mu = Oil Viscosity [N x S / cm2]

u = Linear Speed [cm / S]

b = Lip Contact Width [cm]
Seal Type: S TYPE
Material: NITRILE
Shaft Dia.: 50 mm
Speed: 1000 RPM

  

 TORQUE VS SHAFT DIAMETER

(SURFACE SPEED CONTROLLED)

   

Seal Type: S TYPE
Material: NITRILE
Lubricant: SAE 30wt Engine Oil
Oil Temp: 80 C (175 F)
Surface Speed: 5 m/s (16.4 ft/s)

 

TORQUE VS SPEED

(OIL TEMP. CONTROLLED)

 
Seal Type: S TYPE / 50 mm Shaft
Material: NITRILE
Lubricant: SAE 90wt Gear Oil
Lube Level: Shaft Center
Oil Temp: 80 C (175 F)

 

TORQUE VS SPEED

(GREASE LUBRICATION)

 
Seal Type: S TYPE / 50 mm Shaft
Material: NITRILE
Lubricant: Grease
Temp: No Heat Added

RECOMMENDED MATERIAL SPEED LIMITATIONS

 

The above curves provide our recommended maximum shaft speeds for each of the common lip seal materials.
 
MINIMUM OIL VOLUME REQUIREMENTS
 

  • The seal lip temperature increases dramatically as the volume of oil reaching the seal lip decreases.

 

ECCENTRICITY
 

 

     

 

 

    

Total eccentricity consists of two components, shaft runout and shaft-to-bore misalignment (offset).  The eccentricity is determined as shown above.  Combine the two results to obtain the maximum eccentricity that the seal must follow as the shaft rotates.  As eccentricity increases or shaft speed increases, it becomes more difficult for the seal lip to follow.
 
 

TOTAL ECCENTRICITY LIMITS
 

  • The total recommended eccentricity (static offset plus dynamic TIR) limits for most oil seals is shown below for different size shafts and speeds.  Note that more extreme eccentricity levels can be met with special designs.

   

RUNOUT INFLUENCE
 

  • A seal's final life is dependent on eccentricity.  A seal will leak when it does not have adequate remaining interference to follow the shaft eccentricities.

  • Minimizing eccentricities maximizes seal life

RUNOUT VS INTERFERENCE

(LEAKAGE LIMIT)

 
Seal Type: S TYPE
Material: NITRILE
Shaft Dia: 35 mm
Lubricant: SAE 90wt Gear Oil
Speed: 2000 RPM
Oil Temp: 80 C (175 F)

SEAL HEAT GENERATION
 

  • A seal will generate heat in excess of the oil sump temperature.  The graph below shows the amount of heat generated versus speed and shaft diameter.

SEAL LIP TEMPERATURE RISE

ABOVE THE OIL SUMP

 
Seal Type: S TYPE
Lubricant: SAE 30 wt Engine Oil
Lube Level: Shaft Center

In order to determine the maximum temperature limitations of any particular material, you must look carefully at the operating conditions.  First, determine the excess lip temperature generated in the application.  Then, add to that the oil sump temperature.  This is the upper temperature limit requirement to be considered for choosing the seal material.
 
 

SEAL LIFE
 

  • The primary factors influencing the durability of a seal are the temperature, fluid, and the seal material.

MATERIAL DEFINITIONS
NBR  = nitrile
ACM  = polyacrylate
VMQ  = silicone
FKM  = fluoroelastomer
 

With the proper choice of seal design and materials seals can often last over 10,000 hours in clean environments.  Even in dirty environments, long life can be achieved if appropriate exclusion devices are applied.