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Plastics


Over the last years have the rapid advancement in the manufacturing of plastics simultaneously lead to new opportunities in the usage of plastics in rolling bearing cages. More and more is the use of traditional steel- or brass cages abolished. Partially are technological milling processes or spraying methods used for manufacturing very complex geometries.

 

Through the use of a variety of additives become base-polymers complex polymeric structures. These are than used in amorphous or semi- crystalline plastics. They can not be used as cage material since almost all amorphous plastics lead to stress cracking caused by environmental circumstances.

 

Besides being of good mechanical strength, having high toughness, and friction resistance do the following characteristics qualify plastic as cage material.

 

High temperature stability
Chemical consistency opposite lubricants and environmental media
Good tribological characteristics
Greatest deformation possible in operating state (Pull- and bending strength)
Absorption of impact load (impact strength)
Limited water absorption capacity

 

The table below lists the material characteristics used for plastic of selected rolling bearing cages. Furthermore, special conditions apply for a variety of high- performance plastics.

 

 




Material characteristics    PEEK PA66 PTFE PCTFE PI 
Density  ρ g/cm³ 1,32 1,14 2,3 2,1 1,6 
Elasticity modulus MPa 4100 2830 500 1400  
Pulling strength  MPa 97  30-35 32-40  
Bending strength  MPa 170     
Water absorption  0,5 8,5 0,005 0,23 
Shore-Hardness   50-60 76-80    
Melting point  °C 340 255 335 214  
Heat expansion
coefficient  
α 10-5/K 4,7 (<143°C)
10,8 (>143°C) 
10 (<100°C) 5,5 (<70°C)
25 (<150°C) 
2,9 
Heat conductivity λ W/m•K 0,25 0,23 0,26 0,135  
Temperature limit
 
 °C 280 100 250 150 260 
Chemical
consistency  
  ++ ++ ++ 



 
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