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7. Bearings - general data 7. Bearings - general data

7. Bearings - general data

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7.1 Bearing design data

Besides the suitable type of bearing and the size of it, additional design characteristics that define the bearing in location design have to be defined. The location designed is the one usually responsible for the bearing design. This person has to consider the requirements for accuracy of run, service temperature and lubrication, as well as the assembly and disassembly method.  In order to meet all different requirements for proper run of bearing, bearings are produced in many versions that are characterized with an additional identification of bearings. Thus, bearings with required tolerances, clearances, materials, cage design or sealing can be selected.  Also, accordingly with the identification system, bearings can be specified for certain service conditions that may be characteristic with high revolutions or high temperature, or alternatives of bearings for certain locations can be selected by the knowledge of identification of other bearing manufacturers.

7.2 Main dimensions

Roller bearings are supplied as a final machine part, and the designer has at disposal fixed dimensions that ensure easy exchangeability.  Standardisation applies to outer dimensions important in the assembly point of view. It is convenient for manufacturers and users of bearings for technological and thus also economic reasons. It however does not state inner dimensions, such as the quantity and dimensions of rolling bodies, or designs of cages. Despite that, due to the long-term development and various design and production technology optimisations even the inner design of bearings becomes united to a significant extent. 
The ISO international organization came up with dimension plans for roller bearings of metric dimensions that are defined in the below listed documents:
  • ISO 15:1998 platí pro radiální valivá ložiska metrických rozměrů, s výjimkou kuželíkových ložisek
  • ISO 355:1997 platí pro radiální kuželíková ložiska metrických rozměrů
  • ISO 104:2002 platí pro axiální valivá ložiska metrických rozměrů 
  • ISO 582:1995 uvádí maximální hodnoty sražení montážních hran ložisek

7.2.1 ISO dimension plans

ISO dimension plan allocates to each bearing hole diameter d multiple outer diameters D, and to those different widths B – or – more precisely - T for radial and H for axial bearings. Bearings with the same hole diameter and same outer diameter belong in one diameter row identified by ascending outer diameter with figures 7, 8, 9, 0, 1, 2, 3, 4. Every diameter row contains bearings of different width rows by ascending width: 8, 0, 1, 2, 3, 4, 5, 6 and 7 for radial bearings. Width rows of radial bearings correspond with height rows of axial bearings (height rows by ascending height 7, 9, 1 and 2).
Combining the diameter and width row creates dimension rows that are identified by double figure where the first figure identified the width row, and the second figure identifies the diameter row. This system is clearly indicated in Fig. 7.1.

 

Fig. 7.1

The ISO dimension plan also contains dimensions of bearing ring edge fillet, the so-called installation fillet (Fig. 7.2). The chart section of the catalogue indicates minimum installation fillet values for individual bearing types that you need to know when designing radiuses of transmission of components forming the bearing location.
 

Obr. 7.2

See Chart 7.1 for an overview of the installation fillet complying with the international standard ISO 582.
 
Limit dimensions of installation fillet
  Radial bearings except tapered Tapered bearings Axial bearings
rs min d or D   rs min d or D   rs min rs min
  over to in radial direction in axial direction over to in radial direction in axial direction in radial and axial direction
mm                  
                   
0,15 - - 0,3 0,6 - - - - 0,3
0,2 - - 0,5 0,8 - - - - 0,5
0,3 - 40 0,6 1 - 40 0,7 1,4 0,8
  40 - 0,8 1 40 - 0,9 1,6 0,8
0,6 - 40 1 2 - 40 1,1 1,7 1,5
  40 - 1,3 2 40 - 1,3 2 1,5
1 - 50 1,5 3 - 50 1,6 2,5 2,2
  50 - 1,9 3 50 - 1,9 3 2,2
1,1 - 120 2 3,5 - - - - 2,7
  120 - 2,5 4 - - - - 2,7
1,5 - 120 2,3 4 - 120 2,3 3 3,5
  120 - 3 5 120 250 2,8 3,5 3,5
  - - - - 250 - 3,5 4 3,5
2 - 80 3 4,5 - 120 2,8 4 4
  80 220 3,5 5 120 250 3,5 4,5 4
  220 - 3,8 6 250 - 4 5 4
2,1 - 280 4 6,5 - - - - 4,5
  280 - 4,5 7 - - - - 4,5
2,5 - 100 3,8 6 - 120 3,5 5 -
  100 280 4,5 6 120 250 4 5,5 -
  280 - 5 7 250 - 4,5 6 -
3 - 280 5 8 - 120 4 5,5 5,5
  280 - 5,5 8 120 250 4,5 6,5 5,5
  - - - - 250 400 5 7 5,5
  - - - - 400 - 5,5 7,5 5,5
4 - - 6,5 9 - 120 5 7 6,5
  - - - - 120 250 5,5 7,5 6,5
  - -- -- - 250 400 6 8 6,5
  - - - - 400 - 6,5 8,5 6,5
5 - - 8 10 - 180 6,5 8 8
  - - - - 180 - 7,5 9 8
6 - - 10 13 - 180 7,5 10 10
  - - - - 180 - 9 11 10
7,5 - - 12,5 17 - - - - 12,5
9,5 - - 15 19 - - - - 15
12 - - 18 24 - - - - 18
15 - - 21 30 - - - - 21

7.2.2 Accuracy of bearings

Accuracy of bearings means accuracy of bearing dimensions and run. Bearings are made in the accuracy classes P0, P6, P5, P5A, P4, P4A, P2, SP and UP. The P0 accuracy is general, and is not stated in the bearing identification. Descending number in the identification indicates higher bearing accuracy.
Majority locations can utilise roller bearings of normal accuracy level. Bearings with higher accuracy level are used in locations that require higher running accuracy, such as location of machine tool spindles, and where bearings exceed their limit revolutions. 
The limit dimension and run accuracy values are stated in charts 7.2 to 7.12. These values comply with international standards ISO 492 a ISO 199. The P5A and P4A designation is used for bearings made in relevant accuracy level P5 and P4 but selected parameters feature higher accuracy level than is P5 and P4.

Symbols of quantities and their meaning
d –nominal hole diameter 
d1 –nominal diameter of bigger theoretical tapered hole diameter
d2 –nominal diameter of shaft ring of bidirectional axial bearings 
Δds – deviation of individual hole diameter from nominal dimension
Δdmp – deviation of mean diameter of cylindrical hole in individual radial plane (for tapered hole applies Δdmp for theoretical hole diameter)
Δd1mp – deviation of mean theoretical tapered hole diameter
Δd2mp – deviation of mean shaft ring hole diameter of bidirectional axial bearings in individual radial plane
Vdp – dispersion of individual hole diameter in individual radial plane
Vdmp  – dispersion of mean cylindrical hole diameter 
Vd2p – dispersion of shaft ring hole diameter of bidirectional axial bearings in individual radial plane
D – nominal external diameter 
ΔDs –deviation of individual outer diameter from nominal dimension
ΔDmp – deviation of mean outer cylindrical surface diameter in individual radial plane
VDp – dispersion of individual outer cylindrical surface diameter in individual radial plane
VDmp –dispersion of mean outer cylindrical hole diameter 
B – nominal inner ring width 
T – nominal total width of tapered bearings
T1 – nominal effective width of inner semi-unit 
T2 – nominal effective width of outer semi-unit 
ΔBs – deviation of individual inner ring width 
ΔCs – deviation of individual outer ring width 
ΔTs – deviation of (total) individual bearing width
ΔT1s – deviation of effective width of inner semi-unit 
ΔT2s – deviation of effective width of outer semi-unit 
C – nominal outer ring width 
VBs  – dispersion of individual inner ring width 
VCs  – dispersion of individual outer ring width 
Kia – radial runout of assembled bearing inner ring 
Kea – radial runout of assembled bearing outer ring 
Si – axial runout of shaft ring orbit 
Se – axial runout of body ring orbit 
Sia – axial runout of basic front of assembled bearing inner ring 
Sea – axial runout of basic front of assembled bearing outer ring 
Sd – axial runout of basic front
SD –runout of outer surface against ring front
Ss – runout of inner ring support front against basic front for single row tapered bearings

Limit values of individual parameters for different accuracy levels are stated in the below charts.
 
Inner race
                                 
d   Δdmp   Vdp     Vdmp Kia ΔBs   VBs Δdmp   Δd1mp dmp V1)dp
        diameter rows                      
        7,8,9 0,1 2,3,4                    
over to max min max max max max max max min max max min max min max
                                 
2,5 10 0 -8 10 8 6 6 10 0 -120 15 - - - - -
10 18 0 -8 10 8 6 6 10 0 -120 20 - - - - -
18 30 0 -10 13 10 8 8 13 0 -120 20 21 0 21 0 13
30 50 0 -12 15 12 9 9 15 0 -120 20 25 0 25 0 15
50 80 0 -15 19 19 11 11 20 0 -150 25 30 0 30 0 19
80 120 0 -20 25 25 15 15 25 0 200 25 35 0 35 0 25
120 180 0 -25 31 31 19 19 30 0 -250 30 40 0 40 0 31
180 250 0 -30 38 38 23 23 40 0 -300 30 46 0 46 0 38
250 315 0 -35 44 44 26 26 50 0 -350 35 52 0 52 0 44
315 400 0 -40 50 50 30 30 60 0 -400 40 57 0 57 0 50
400 500 0 -45 56 56 34 34 65 0 -450 50 63 0 63 0 56
500 630 0 -50 63 63 38 38 70 0 -500 60 - - - - -
630 800 0 -75 - - - - 80 0 -750 70 - - - - -
800 1000 0 -100 - - - - 90 0 -1000 80 - - - - -
1000 1250 0 -125 - - - - 100 0 -1250 100 - - - - -
 
Outer race
D   ΔDmp   VDP       VDmp Kea ΔCs, ΔCs
        Diameter rows          
        7,8,9 0,1 2,3,4 bearings 2)      
              with covers      
over to max min max max max max max max  
mm   µm              
"Corresponds with
ΔBs, VBs
of inner
race
of the same
bearing"
6 18 0 -8 10 8 6 10 6 15
18 30 0 -9 12 9 7 12 7 15
30 50 0 -11 14 11 8 16 8 20
50 80 0 -13 16 13 10 20 10 25
80 120 0 -15 19 19 11 26 11 35
120 150 0 -18 23 23 14 30 14 40
150 180 0 -25 31 31 19 38 19 45
180 250 0 -30 38 38 23 - 23 50
250 315 0 -35 44 44 26 - 26 60
315 400 0 -40 50 50 30 - 30 70
400 500 0 -45 56 56 34 - 34 80
500 630 0 -50 63 63 38 - 38 100
630 800 0 -75 94 94 55 - 55 120
800 1000 0 -100 125 125 75 - 75 140
1000 1250 0 -125 - - - - - 160
1250 1600 0 -160 - - - - - 190
                     
 
  1. Applies in optional radial hole plane
  2. Applies only to bearings of diameter rows 2, 3 and 4
 
Accuracy of dimensions and run of radial bearings (except tapered)
Accuracy level P6
                       
Inner race
d   Δdmp   Vdp     Vdmp Kia ΔBs   VBs
        Diameter rows            
        7,8,9 0,1 2,3,4,          
over to max min max max max max max max min max
mm   µm                  
2,5 10 0 -7 9 7 5 5 6 0 -120 15
10 18 0 -7 9 7 5 5 7 0 -120 20
18 30 0 -8 10 8 6 6 8 0 -120 20
30 50 0 -10 13 10 8 8 10 0 -120 20
50 80 0 -12 15 15 9 9 10 0 -150 25
80 120 0 -15 19 19 11 11 13 0 -200 25
120 180 0 -18 23 23 14 14 18 0 -250 30
180 250 0 -22 28 28 17 17 20 0 -300 30
250 315 0 -25 31 31 19 19 25 0 -350 35
315 400 0 -30 38 38 23 23 30 0 -400 40
400 500 0 -35 44 44 26 26 35 0 -450 45
500 630 0 -40 50 50 30 30 40 0 -500 50
 
Outer race
D   ΔDmp   VDp       VDmp Kea ΔCs VCs
        Diameter rows          
        7,8,9 0,1 2,3,4 bearings 1)      
              with covers      
over to max min max max max max max max  
mm   µm               Corresponds with ΔBs, VBs of the inner race of the same bearing
                   
6 18 0 -7 9 7 5 9 5 8
18 30 0 -8 10 8 6 10 6 9
30 50 0 -9 11 9 7 13 7 10
50 80 0 -11 14 11 8 16 8 13
80 120 0 -13 16 16 10 20 10 18
120 150 0 -15 19 19 11 25 11 20
150 180 0 -18 23 23 14 30 14 23
180 250 0 -20 25 25 15 - 15 25
250 315 0 -25 31 31 19 - 19 30
315 400 0 -28 35 35 21 - 21 35
400 500 0 -33 41 41 25 - 25 40
500 630 0 -38 48 48 29 - 29 50
630 800 0 -45 56 56 34 - 34 60
800 1000 0 -50 75 75 45 - 45 75
 
  1. Applies only to bearings of diameter rows 0, 1, 2, 3 and 4
 
Accuracy of dimensions and run of radial bearings (except tapered)
Accuracy level P5
                         
Inner race
d   Δdmp   Vdp   Vdmp Kia Sd Sia1) ΔBs   VBs
        Diameter rows              
        7,8,9 0,1,2,3,4              
over to max min max max max max max max max min max
mm   µm                    
                         
2,5 10 0 -5 5 4 3 4 7 7 0 -40 5
10 18 0 -5 5 4 3 4 7 7 0 -80 5
18 30 0 -6 6 5 3 4 8 8 0 -120 5
30 50 0 -8 8 6 4 5 8 8 0 -120 5
50 80 0 -9 9 7 5 5 8 8 0 -150 6
80 120 0 -10 10 8 5 6 9 9 0 -200 7
120 180 0 -13 13 10 7 8 10 10 0 -250 8
180 250 0 -15 15 12 8 10 11 13 0 -300 10
250 315 0 -18 18 14 9 13 13 15 0 -350 13
315 400 0 -23 23 18 12 15 15 20 0 -400 15
 
Outer race
D   ΔDmp   Vdp   VDmp Kea SD Sea1) ΔCs VCs
        Diameter rows            
        7,8,9 0,1,2,3,4            
over to max min max max max max max max   max
mm   µm                  
                       
6 18 0 -5 5 4 3 5 8 8 Corresponds with ΔBc of the inner race of the same bearing 5
18 30 0 -6 6 5 3 6 8 8 5
30 50 0 -7 7 5 4 7 8 8 5
50 80 0 -9 9 8 5 8 8 10 6
80 120 0 -10 10 8 5 10 9 11 8
120 150 0 -11 11 8 6 11 10 13 8
150 180 0 -13 13 10 7 13 10 14 8
180 250 0 -15 15 11 8 15 11 15 10
250 315 0 -18 18 14 9 18 13 18 11
315 400 0 -20 20 15 10 20 13 20 13
400 500 0 -23 23 17 12 23 15 23 15
500 630 0 -28 28 21 14 25 18 25 18
630 800 0 -35 35 26 18 30 20 30 20
 
  1. Applies to ball bearings only
  2. Does not apply to covered bearings
 
Accuracy of dimensions and run of radial bearings (except tapered)
Accuracy level P4
                             
Inner race
d   Δdmp   Δds1)   Vdp   Vdmp Kia Sd Sia2) ΔBs   VBs
            Diameter rows              
            7,8,9 0,1,2,3,4              
                             
over to max min max min max max max max max max max min max
mm   µm                        
                             
2,5 10 0 -4 0 -4 4 3 2 2,5 3 3 0 -40 2,5
10 18 0 -4 0 -4 4 3 2 2,5 3 3 0 -80 2,5
18 30 0 -5 0 -5 5 4 2,5 3 4 4 0 -120 2,5
30 50 0 -6 0 -6 6 5 3 4 4 4 0 -120 3
50 80 0 -7 0 -7 7 5 3,5 4 5 5 0 -150 4
80 120 0 -8 0 -8 8 6 4 5 5 5 0 -200 4
120 180 0 -10 0 -10 10 8 5 6 6 7 0 -250 5
180 250 0 -12 0 -12 12 9 6 8 7 8 0 -300 6
 
Outer race
D   ΔDmp   VDs1)   VDp   VDmp Kea SD Sea2) ΔCs VCs
            Diameter rows3)            
            7,8,9 0,1,2,3,4            
over to max min max min max max max max max max   max
mm   µm                      
                       
"Corresponds with
ΔBs of the inner
race
of the same
bearing"
 
6 18 0 -4 0 -4 4 3 2 3 4 5 2,5
18 30 0 -5 0 -5 5 4 2,5 4 4 5 2,5
30 50 0 -6 0 -6 6 5 3 5 4 5 2,5
50 80 0 -7 0 -7 7 5 3,5 5 4 5 3
80 120 0 -8 0 -8 8 6 4 6 5 6 4
120 150 0 -9 0 -9 9 7 5 7 5 7 5
150 180 0 -10 0 -10 10 8 5 8 5 8 5
180 250 0 -11 0 -11 11 8 6 10 7 10 7
250 315 0 -13 0 -13 13 10 7 11 8 10 7
315 400 0 -15 0 -15 15 11 8 13 10 13 8
 
  1. Applies only to bearings of diameter rows 0, 1, 2, 3 and 4
  2. Applies to ball bearings only
  3. Does not apply to covered bearings
 
Accuracy of dimensions and run of roller bearings with tapered hole
Accuracy level SP
                       
Inner race
d   Δdmp   Δd1mp dmp Vdp Kia Sd ΔBs   VBs
over to max min max min max max max max min max
mm   µm                  
                       
18 30 10 0 4 0 3 3 8 0 -100 5
30 50 12 0 4 0 4 4 8 0 -120 5
50 80 15 0 5 0 5 4 8 0 -150 6
80 120 20 0 6 0 5 5 9 0 -200 7
120 180 25 0 8 0 7 6 10 0 -250 8
180 250 30 0 10 0 8 8 11 0 -300 10
250 315 35 0 12 0 9 10 13 0 -350 13
315 400 40 0 13 0 12 12 15 0 -400 15
400 500 45 0 15 0 14 12 18 0 -450 25
 
Outer race
D   ΔDmp   VDp Kea SD ΔCs, VCs
over to max min max max max  
mm   µm          
               
50 80 0 -9 5 5 8
"Corresponds with
ΔBs and VBs
of inner
race
of the same
bearing"
80 120 0 -10 5 6 9
120 150 0 -11 6 7 10
150 180 0 -13 7 8 10
180 250 0 -15 8 10 11
250 315 0 -18 9 11 13
315 400 0 -20 10 13 13
400 500 0 -23 12 15 15
500 630 0 -28 14 17 18
630 800 0 -35 18 20 20
 
Accuracy of dimensions and run of roller bearings with tapered hole
Accuracy level UP
Inner race
d   Δdmp   Δd1mp dmp Vdp Kia Sd ΔBs   VBs
over to max min max min max max max max min max
mm   µm                  
                       
18 30 6 0 2 0 3 1,5 3 0 -25 1,5
30 50 7 0 3 0 3 2 3 0 -30 2
50 80 8 0 3 0 4 2 4 0 -40 3
80 120 10 0 4 0 4 3 4 0 -50 3
120 180 12 0 5 0 5 3 5 0 -60 4
180 250 14 0 6 0 6 4 6 0 -75 5
250 315 17 0 8 0 8 5 6 0 -90 6
 
Outer race
D   ΔDmp   VDp Kea SD ΔCs, VCs
over to max min max max max  
mm   µm          
50 80 0 -6 3 3 2
"Corresponds with
ΔBs and VBs
of inner
race
of the same
bearing"
80 120 0 -7 4 3 3
120 150 0 -8 4 4 3
150 180 0 -9 5 4 3
180 250 0 -10 5 5 4
250 315 0 -12 6 6 4
315 400 0 -14 7 7 5
 
Accuracy of dimensions and run of tapered bearings
Accuracy level P0
Inner race and total bearing width
d   Δdmp   Vdp Vdmp Kia ΔBs   ΔTs   ΔT1s   ΔT2s  
over to max min max max max max min max min max min max min
mm   µm                        
10 18 0 -12 12 9 15 0 -120 200 0 100 0 100 0
18 30 0 -12 12 9 18 0 -120 200 0 100 0 100 0
30 50 0 -12 12 9 20 0 -120 200 0 100 0 100 0
50 80 0 -15 15 11 25 0 -150 200 0 100 0 100 0
80 120 0 -20 20 15 30 0 -200 200 -200 100 -100 100 -100
120 180 0 -25 25 19 35 0 -250 350 -250 150 -150 200 -100
180 250 0 -30 30 23 50 0 -300 350 -250 150 -150 200 -100
 
Outer race
D   ΔDmp   VDp VDmp Kea ΔCs  
over to max min max max max max min
mm   µm            
18 30 0 -12 12 9 18 0 -120
30 50 0 -14 14 11 20 0 -120
50 80 0 -16 16 12 25 0 -150
80 120 0 -18 18 14 35 0 -200
120 150 0 -20 20 15 40 0 -250
150 180 0 -25 25 19 45 0 -250
180 250 0 -30 30 23 50 0 -300
250 315 0 -35 35 26 60 0 -350
315 400 0 -40 40 30 70 0 -400
 
Accuracy of dimensions and run of tapered bearings 
Accuracy level P6X
Inner race and total bearing width
d   Δdmp   Vdp Vdmp Kia ΔBs   ΔTs   ΔT1s   ΔT2s  
over to max min max max max max min max min max min max min
mm   µm                        
10 18 0 -12 12 9 15 0 -50 100 0 50 0 50 0
18 30 0 -12 12 9 18 0 -50 100 0 50 0 50 0
30 50 0 -12 12 9 20 0 -50 100 0 50 0 50 0
50 80 0 -15 15 11 25 0 -50 100 0 50 0 50 0
80 120 0 -20 20 15 30 0 -50 100 0 50 0 50 0
120 180 0 -25 25 19 35 0 -50 150 0 50 0 100 0
 
Outer race
D   ΔDmp   VDp VDmp Kea ΔCs  
over to max min max max max max min
mm   µm            
18 30 0 -12 12 9 18 0 -100
30 50 0 -14 14 11 20 0 -100
50 80 0 -16 16 12 25 0 -100
80 120 0 -18 18 14 35 0 -100
120 150 0 -20 20 15 40 0 -100
150 180 0 -25 25 19 45 0 -100
180 250 0 -30 30 23 50 0 -100
250 315 0 -35 35 26 60 0 -100
 
Accuracy of dimensions and run of tapered bearings 
Accuracy level P6
Inner race and total bearing width
d   Δdmp   Kia ΔBs   ΔTs  
over to max min max max min max min
mm   µm            
10 18 0 -7 7 0 -200 200 0
18 30 0 -8 8 0 -200 200 0
30 50 0 -10 10 0 -240 200 0
50 80 0 -12 10 0 -300 200 0
80 120 0 -15 13 0 -400 200 -200
120 180 0 -18 18 0 -500 350 -250
 
Outer race
D   ΔDmp   Kea ΔCs
over to max min max  
mm   µm      
           
18 30 0 -8 9
"Corresponds with ΔBs
of inner
race
of the same
bearing"
30 50 0 -9 10
50 80 0 -11 13
80 120 0 -13 18
120 150 0 -15 20
150 180 0 -18 23
180 250 0 -20 25
250 315 0 -25 30
 
Accuracy of dimensions and run of tapered bearings 
Accuracy level P5
Inner race and total bearing width
d   Δdmp   Vdp Vdmp Kia Sd ΔBs   ΔTs  
over to max min max max max max max min max min
mm   µm                  
10 18 0 -7 5 5 5 7 0 -200 200 -200
18 30 0 -8 6 5 5 8 0 -200 200 -200
30 50 0 -10 8 5 5 8 0 -240 200 -200
50 80 0 -12 9 6 7 8 0 -300 200 -200
80 120 0 -15 11 8 8 9 0 -400 200 -200
120 180 0 -18 14 9 11 10 0 -500 350 -250
 
Outer race
D   ΔDmp   VDp VD Kea SD ΔCs
over to max min max max max max  
mm   µm            
                 
18 30 0 -8 6 5 6 8 Corresponds with ΔBs of the inner
race
of the same
bearing
30 50 0 -9 7 5 7 8
50 80 0 -11 8 6 8 8
80 120 0 -13 10 7 10 9
120 150 0 -15 11 8 11 10
150 180 0 -18 14 9 13 10
180 250 0 -20 15 10 15 11
250 315 0 -25 19 13 18 13
 
Accuracy of dimensions and run of axial bearings 
Accuracy level P0, P6 and P5
Shaft ring
d   Δdmp   Vdp Si   1)
d2   Δd2mp   Vd2p P0 P6 P5
over to max min max max max max
mm   µm          
- 18 0 -8 6 10 5 3
18 30 0 -10 8 10 5 3
30 50 0 -12 9 10 6 3
50 80 0 -15 11 10 7 4
80 120 0 -20 15 15 8 4
120 180 0 -25 19 15 9 5
180 250 0 -30 23 20 10 5
250 315 0 -35 26 25 13 7
315 400 0 -40 30 30 15 7
400 500 0 -45 34 30 18 9
500 630 0 -50 38 35 21 11
630 800 0 -75 - 40 25 13
 
Casing ring
D   ΔDmp   VDp Se 1)
over to max min max    
mm   µm        
             
18 30 0 -13 10 "Corresponds with Si
of shaft
ring of the same
bearing"
30 50 0 -16 12
50 80 0 -19 14
80 120 0 -22 17
120 180 0 -25 19
180 250 0 -30 23
250 315 0 -35 26
315 400 0 -40 30
400 500 0 -45 34
500 630 0 -50 38
630 800 0 -75 55
800 1000 0 -100 75
1000 1250 0 -125 -
1250 1600 0 -160 -
 
  1. Does not apply to axial spherical-roller bearings

7.2.3 Inner clearances of bearings

Clearance in bearing is the value of length of displacement of one assembled bearing ring towards the second ring from one marginal position to another (see Fig. 7.3). The displacement can be in radial direction (radial clearance), or in axial direction (axial clearance).

 

Obr. 7.3

In an in-built bearing we usually detect lower radial clearance than has the same bearing in unassembled state. Reduction of radial clearance is caused by the overlap sizes of bearing rings on the journal and in the body hole, and is therefore dependant on the selected tolerances of location surface diameters for the bearing. Further change of radial clearance, particularly its reduction, takes place during the operation due to temperature induced by the bearing operation itself, and by external sources, and also due to flexible deformations caused by load.  Decisive is for bearing in stabilised service effects. Small prestress between the balls and orbits usually does not have negative effect.

Roller, tapered spherical-roller bearings feature higher rigidity, and therefore they are supposed to have smaller service clearance that is necessary to ensure safe and reliable run, mainly in heavy service conditions. If extremely high rigidity of location is required, e.g. for machine tools, prestressed bearings are mounted.

For normal design bearings the clearance is adjusted so that one of the bearing rings could be located firmly which is sufficient for majority of service ratios in location. Special cases of location with other requirements for radial clearance require bearings with radial clearance designated C1 to C5.

Values of different inner clearance levels according to ISO 5753 standard are for individual design bearing groups stated in charts 7.17 to 7.23 whilst these values apply to non-mounted bearings in zero load during measuring.

 
Radial clearance of single row ball bearings
Hole diameter Radial clearance                 Single row ball bearings separable of E and BO type Radial clearance
                       
d   C2   Normal   C3   C4   C5  
over to min max min max min max min max min max min max
mm   µm                     µm  
2,5 10 0 7 2 13 8 23 14 29 20 37 E10, E12 15 30
10 18 0 9 3 18 11 25 18 33 25 45 E15 15 30
18 24 0 10 5 20 13 28 20 36 28 48 BO17, E17 25 45
24 30 1 11 5 20 13 28 23 41 30 53 E20 20 40
30 40 1 11 6 20 15 33 28 46 40 64      
40 50 1 11 6 23 18 36 30 51 45 73      
50 65 1 15 8 28 23 43 38 61 55 90      
65 80 1 15 10 30 25 51 46 71 65 105      
80 100 1 18 12 36 30 58 53 84 75 120      
100 120 2 20 15 41 36 66 61 97 90 140      
120 140 2 23 18 48 41 81 71 114 105 160      
140 160 2 23 18 53 46 91 81 130 120 180      
160 180 2 25 20 61 53 102 91 147 135 200      
180 200 2 30 25 71 63 117 107 163 150 215      
200 225 2 35 25 85 75 140 125 195 175 265      
225 250 2 40 30 95 85 160 145 225 205 300      
250 280 2 45 35 105 90 170 155 245 225 340      
280 315 2 55 40 115 100 190 175 270 245 370      
315 355 3 60 45 125 110 210 195 300 275 410      
355 400 3 70 55 145 130 240 225 340 315 460      
400 450 3 80 60 170 150 270 250 380 350 520      
450 500 3 90 70 190 170 300 280 420 390 570      
500 560 10 100 80 210 190 330 310 470 440 630      
560 630 10 110 90 230 210 360 340 520 490 700      
630 710 20 130 110 260 240 400 380 570 540 780      
710 800 20 140 120 290 270 450 430 630 600 860      
800 900 20 160 140 320 300 500 480 700 670 960      
900 1000 20 170 150 350 330 550 530 770 740 1040      
1000 1120 20 180 160 380 360 600 580 850 820 1150      
 
Axial clearance of double row angular-contact ball bearings
Hole diameter Axial clearance            
d   C2   normal   C3   C4  
over to min max min max min max min max
mm   µm              
6 10 1 11 5 21 12 28 25 45
10 18 1 12 6 23 13 31 27 47
18 24 2 14 7 25 16 34 28 48
24 30 2 15 8 27 18 37 30 50
30 40 2 16 9 29 21 40 33 54
40 50 2 19 11 33 23 44 36 58
50 65 3 22 13 36 26 48 40 63
65 80 3 24 15 40 30 54 46 71
80 100 3 26 18 46 35 63 - -
100 110 4 30 22 53 42 73 - -
 
Radial clearance of double row tilting ball bearings
Hole diameter Cylindrical hole                 Tapered                  
  Radial clearance                 Radial clearance                
d   C2   normal   C3   C4   C5   C2   normal   C3   C4   C5  
over to min max min max min max min max min max min max min max min max min max min max
mm   μm                   μm                  
2,5 6 1 8 5 15 10 20 15 25 21 33 - - - - - - - - - -
6 10 2 9 6 17 12 25 19 33 27 42 - - - - - - - - - -
10 14 2 10 6 19 13 26 21 35 30 48 - - - - - - - - - -
14 18 3 12 8 21 15 28 23 37 32 50 - - - - - - - - - -
18 24 4 14 10 23 18 30 25 39 34 52 7 17 13 26 20 33 28 42 37 55
24 30 5 16 11 24 19 35 29 46 40 58 9 20 15 28 23 39 33 50 44 62
30 40 6 18 13 29 23 40 34 53 46 66 12 24 19 35 29 46 40 59 52 72
40 50 6 19 14 31 25 44 37 57 50 71 14 27 22 39 33 52 45 65 58 79
50 65 7 21 16 36 30 50 45 69 62 88 18 32 27 47 41 61 56 80 73 99
65 80 8 24 18 40 35 60 54 83 76 108 23 39 35 57 50 75 69 98 91 123
80 100 9 27 22 48 42 70 64 96 89 124 29 47 42 68 62 90 84 116 109 144
100 120 10 31 25 56 50 83 75 114 105 145 35 56 50 81 75 108 100 139 130 170
120 140 10 38 30 68 60 100 90 135 125 175 - - - - - - - - - -
140 160 15 44 35 80 70 120 110 161 150 210 - - - - - - - - - -
 
Radial clearance of single row roller bearings
Hole diameter Radial clearance                
d   C2   normal   C3   C4   C5  
over to min max min max min max min max min max
mm   µm                  
                       
10 24 0 25 20 45 35 60 50 75 65 90
24 30 0 25 20 45 35 60 50 75 70 95
30 40 5 30 25 50 45 70 60 85 80 105
40 50 5 35 30 60 50 80 70 100 95 125
50 65 10 40 40 70 60 90 80 110 110 140
65 80 10 45 40 75 65 100 90 125 130 165
80 100 15 50 50 85 75 110 105 140 155 190
100 120 15 55 50 90 85 125 125 165 180 220
120 140 15 60 60 105 100 145 145 190 200 245
140 160 20 70 70 120 115 165 165 215 225 275
160 180 25 75 75 125 120 170 170 220 250 300
180 200 35 90 90 145 140 195 195 250 275 330
200 225 45 105 105 165 160 220 220 280 305 365
225 250 45 110 110 175 170 235 235 300 330 395
250 280 55 125 125 195 190 260 260 330 370 440
280 315 55 130 130 205 200 275 275 350 410 485
315 355 65 145 145 225 225 305 305 385 455 535
355 400 100 190 190 280 280 370 370 460 510 600
400 450 110 210 210 310 310 410 410 510 565 665
450 500 110 220 220 330 330 440 440 550 625 735
500 560 120 240 240 360 360 480 480 600 695 815
560 630 140 260 260 380 380 500 500 620 780 900
630 710 145 285 285 425 425 565 565 705 870 1010
710 800 150 310 310 470 470 630 630 790 980 1140
800 900 180 350 350 520 520 690 690 860 1100 1270
900 1000 200 390 390 580 580 770 770 960 1220 1410
1000 1120 220 430 430 640 640 850 850 1060 1360 1570
1120 1250 230 470 470 710 710 950 950 1190 1520 1760
 
Radial clearance of double row roller bearings with tapered hole
Bearings with incommutable races designed for work spindles of machine tools 
Hole diameter Radial clearance
d   C1NA   C2NA  
over to min max min max
mm   µm      
24 30 15 25 25 35
30 40 15 25 25 40
40 50 17 30 30 45
50 65 20 35 35 50
65 80 25 40 40 60
80 100 35 55 45 70
100 120 40 60 50 80
120 140 45 70 60 90
140 160 50 75 65 100
160 180 55 85 75 110
180 200 60 90 80 120
200 225 60 95 90 135
225 250 65 100 100 150
250 280 75 110 110 165
280 315 80 120 120 180
315 355 90 135 135 200
355 400 100 150 150 225
400 450 110 170 170 255
450 500 120 190 190 285
500 560 130 210 210 315
560 630 140 230 230 345
630 710 160 260 260 390
710 800 180 290 290 435
800 900 200 320 320 480
900 1000 - - 355 540
 
Radial clearance of single row cageless needle bearings with interchangeable races
Hole diameter Radial clearance
d   normal   C3  
over to min max min max
mm   µm      
10 14 10 50 25 70
14 18 15 55 35 75
18 24 25 65 40 80
24 30 30 65 50 80
30 40 40 75 60 95
40 50 40 85 65 100
50 65 45 90 70 120
65 80 50 110 75 135
80 100 60 115 95 150
100 120 70 125 115 70
120 140 80 155 130 205
140 160 80 160 140 210
 
Radial clearance of double row spherical-roller bearings
Hole diameter Cylindrical hole                
    Radial clearance                
d   C2   normal   C3   C4   C5  
over to min max min max min max min max min max
mm   µm                  
30 40 15 30 30 45 45 60 60 80 80 100
40 50 20 35 35 55 55 75 75 100 100 125
50 65 20 40 40 65 65 90 90 120 120 150
65 80 30 50 50 80 80 110 110 145 145 180
80 100 35 60 60 100 100 135 135 180 180 225
100 120 40 75 75 120 120 160 160 210 210 260
120 140 50 95 95 145 145 190 190 240 240 300
140 160 60 110 110 170 170 220 220 280 280 350
160 180 65 120 120 180 180 240 240 310 310 390
180 200 70 130 130 200 200 260 260 340 340 430
200 225 80 140 140 220 220 290 290 380 380 470
225 250 90 150 150 240 240 320 320 420 420 520
250 280 100 170 170 260 260 350 350 460 460 570
280 315 110 190 190 280 280 370 370 500 500 630
315 355 120 200 200 310 310 410 410 550 550 690
355 400 130 220 220 340 340 450 450 600 600 760
400 450 140 240 240 370 370 500 500 660 660 820
450 500 140 260 260 410 410 550 550 720 720 900
500 560 150 280 280 440 440 600 600 780 780 1000
560 630 170 310 310 480 480 650 650 850 850 1100
630 710 190 350 350 530 530 700 700 920 920 1190
710 800 210 390 390 580 580 770 770 1010 1010 1300
800 900 230 430 430 650 650 860 860 1120 1120 1440
900 1000 260 480 480 710 710 930 930 1220 1220 1570
1000 1120 290 530 530 780 780 1020 1020 1330 1330 1720
 
Radial clearance of double row spherical-roller bearings
Hole diameter Tapered hole                
    Radial clearance                
d   C2   normal   C3   C4   C5  
over to min max min max min max min max min max
mm   µm                  
30 40 25 35 35 50 50 65 65 85 85 105
40 50 30 45 45 60 60 80 80 100 100 130
50 65 40 55 55 75 75 95 95 120 120 160
65 80 50 70 70 95 95 120 120 150 150 200
80 100 55 80 80 110 110 140 140 180 180 230
100 120 65 100 100 135 135 170 170 220 220 280
120 140 80 120 120 160 160 200 200 260 260 330
140 160 90 130 130 180 180 230 230 300 300 380
160 180 100 140 140 200 200 260 260 340 340 430
180 200 110 160 160 220 220 290 290 370 370 470
200 225 120 180 180 250 250 320 320 410 410 520
225 250 140 200 200 270 270 350 350 450 450 570
250 280 150 220 220 300 300 390 390 490 490 620
280 315 170 240 240 330 330 430 430 540 540 680
315 355 190 270 270 360 360 470 470 590 590 740
355 400 210 300 300 400 400 520 520 650 650 820
400 450 230 330 330 440 440 570 570 720 720 910
450 500 260 370 370 490 490 630 630 790 790 1000
500 560 290 410 410 540 540 680 680 870 870 1100
560 630 320 460 460 600 600 760 760 980 980 1230
630 710 350 510 510 670 670 850 850 1090 1090 1360
710 800 390 570 570 750 750 960 960 1220 1220 1500
800 900 440 640 640 840 840 1070 1070 1370 1370 1690
900 1000 490 710 710 930 930 1190 1190 1520 1520 1860
1000 1120 530 770 770 1030 1030 1300 1300 1670 1670 2050

For double row ball bearings with angular contact, axial clearance measured at axial load of 100 N is stated instead of radial clearance.

If different clearance is selected than normal, one needs to process carefully and consider the effect if operating conditions at stabilised state. Radial clearance smaller than normal is selected quite rarely, e.g. in roller bearings for machine tool spindles. More often bearings with radial clearance bigger than normal are needed. This happens mostly in case the limit revolutions are exceeded, or in case of higher temperature gradient between the inner an outer ring and, finally, to increase axial load capacity of single row ball bearings. Axial load capacity of these bearings is increased at the clearance of C3 by approx. 10%, and at clearance C4 by approx. 20% in normal conditions.

It is understandable that not only too small but also too big radial clearance has negative effect on the operation and life service of roller bearing. As we know from experience, roller bearing is more negatively affected by small radial clearance than by big. If the thermal service conditions in the bearing are unclear, it is safer to select quite bigger radial clearance that might in an extreme case reduce the service life of the bearing which is insignificant. 

Single row ball bearings with angular contact and single row tapered bearings are usually mounted in pairs in which radial or axial clearance or prestress are adjusted during the assembly.  With advantage the property of the so-called combined bearings can be utilised in which the final axial clearance is set by the bearing manufacturer.

Dependence of radial and axial clearance in some bearing types is clear from chart 7.24.

 
Dependence of radial clearance Vr and axial clearance Va
Bearing type Va/Vr
Single Row Ball Bearings -
Double Row Angular Contact Ball Bearings, type 32, 33 1,4
Self-Aligning Ball Bearings 1,5/e
Tapered Roller Bearings
Spherical Roller Bearings

Figure 7.4 shows an informative graph of dependence of radial an axial clearance in bearing, applicable to single row roller bearings.
 

Fig. 7.4

7.3 Roller bearings materials

7.3.1 Materials of bearing rings and rolling bodies

In terms of materials used for production of roller bearings, durability and reliability of roller bearings is specifically increased by using more accurate metallurgical technologies based on recent surveys. Previous studies already demonstrated a direct connection between micropurity of the bearing steel used, and the occurrence of subsurface fatigue damage in the rolling contact. With regard to high pressures in the area of the rolling contact, strict requirements for micropurity and uniformity of distribution of carbidic phases are reasonable.   The requirement of continuous durability increase can be satisfied by highly accurate and quality production combined with using materials with low content of oxygen and non-metal intrusions, and technologically correct thermal processing of rings and bearing rolling bodies when specified hardness, microstructure and dimensional stability is achieved. This provides resistance to wear and necessary load capacity of rolling contact.  Chemical composition and maximum contents of undesired elements are defined in the international standard for bearing steels ISO 683-17.
For locations with a risk of damage in the area of rolling contact due to passage of electric current, bearings with ceramic insulation coating of the outer ring can be supplied. 
If there are special requirements for material, design or use of bearings, information is available at the ZKL's technical an consultancy centre.

Semiproducts

Besides economic criteria, a semiproduct for production of roller bearings and rolling bodies has to comply with technological requirements in terms of proper course of fibres and proper distribution of carbidic phases. For the economic reason and also due to convenient passage of fibres, the most convenient is using a tube semiproduct that is cold rolled to final shape prior to thermal processing. In this way, the majority of the bearing assortment with increased basic durability is produced with the identification “NEW FORCE“. 

Through-hardening steels

Majority of standard produced ZKL roller bearings are made of through-hardening steels designed for production of roller bearings. Those are carbon – chromium steels with an approximate content of 1% carbon and 1.5% chromium, complying with the international standard ISO 683-17 “Heat-treated steels, alloy steels and free-cutting steels, Part17:  Steels for rolling bearings”. After thermal treatment, material has the same structure and hardness throughout the component section. After performed martensitic or bainite hardening and subsequent yielding, the hardness of final surfaces is 58 to 65 HRC.
Depending on the type, the highest service temperature of 120°C to 200°C is recommended for standard ZKL roller bearings. The maximum temperature for using the bearings depends on heat treatment of bearing components. For operation at temperatures to 250°C, bearing components can stabilize in a special heat treatment process. In case of thermal stabilization for operation at higher temperatures, the hardness of components reduces significantly, and thus also the dynamic load capacity of the bearings. If long-term operation above 250°C  is required, we recommend bearings from high alloy steels designed for high temperatures.

Case hardening steels

After saturation with carbon and hardening, bearing components feature hard surface and simultaneously also tough core. They are used for production of bearings that are loadable with big strokes, locations with big overlap or alternatively for locations with a possibility of contaminated lubrication.

Corrosion-proof steels

These steels are used for bearings intended for operation in oxidizing environment, for instance for aviation technology or food processing industry.

Steels for high temperatures

These materials are used for bearings operating permanently at temperatures over 250°C whilst maintaining hardness and standard service properties, e.g. in aircraft engines. 

Steels for surface hardening

These steels offer convenient combination of hardened tough orbit with tough section core. They are used mainly in large bearings, or bearings with clamp flanges which are contained in bearing rings.
 

7.3.2 Materials for production of cages

Materials used for production of cages are selected with regard to the service temperature of the bearing, whether the bearing will operate in standard or vibrating environment, alternatively upon the requirements for chemical or corrosion resistance.  
The basic quality of materials used for production of cages is good abrasion resistance and slip properties along with sufficient ductility.  

Pressed steel cages

They are pressed from low carbon steels that ensure accuracy of final cage shape, as well as sufficient ductility. To improve slip properties and abrasion resistance, the surface of pressed cages is chemically and thermally treated. They suit typical temperature regimen of bearing operation up to 300°C.
In smaller bearings sizes, pressed cages are even made of brass sheet.

Massive brass cages

They are made in routing from roughened or spun semiproducts. Service temperature should not exceed 250°C.

Massive steel cages

In justified cases they are an alternative to brass massive cages. Service temperature may range up to 300°C. The surface of the cage can be chemically and thermally treated.

7.3.3 Other materials

Polymers

Polymers, usually of polyamide 66 reinforced with glass fibres, are used mainly for production of cages and cage guide rings of double row spherical roller bearings of CJ design. Service operation of these components should not exceed 120°C in the long term with the use of common lubricants, 150°C in the short term (within 10 hours), and 170°C in peaks (within 20 minutes). Usefulness of bearings with polyamide components at lower temperatures is, with regard to polyamide elasticity loss, up to the temperatures of -40°C.

Ceramic materials

Are used mostly to prevent bearings from damage by passage of electric current, either in form of thermally layered coats on the surface of the outer or inner ring, alternatively by using rolling ceramic bodies. Use of rolling bodies from ceramic material is justified even in special high-revolution bearings.

Other

Materials of contact seals are selected so as their thermal and degradation resistance suited the selected use.

7.4 Cages

Cage has the below functions in a roller bearing:  Distributes rolling bodies uniformly around the circumference and prevents their mutual contact which reduced friction in the bearing. It prevents slippage of rolling bodies in the bearing and falling rolling bodies out of separable bearings during their assembly. 

In terms of design and materials, cages are divided in pressed (Fig. 7.5) and massive (Fig. 7.6).  
Pressed cages are made mostly by pressing from steel or brass sheet, and usually are used in dimensionally smaller up to medium bearings. Comparing to massive cages, their advantage is lower weight. 

Massive cages are made of steel, brass, bronze, light metals or plastics in various designs. Metal cage materials are used whenever increased requirements are imposed on the rigidity of the cage, and the bearing is designed for higher service temperatures. Cages in bearing run radially on rolling bodies which is the most common way, or on collar of one of the bearing rings (Fig. 7.7).

 

Fig. 7.5

Fig. 7.6

Fig. 7.7

Massive polymer cages are made in injection moulding. The injection moulding technology allows to production such cage shapes that enable designing bearings with high load capacity. Elasticity and low polyamide weight applies positively in shock stress of bearings, high acceleration and deceleration.  Polyamide cages feature good slip properties. During lubrication of bearings with oil, the additives contained in the oil may affect negatively the service life of the cage.

Cages made of phenological resin are light but not suitable to high temperatures. They however feature good resistance to centrifugal forces. They are typically use in accurate ball bearings with angular contact.

  Journal cages are made of steel; the condition is use of holy rolling bodies (Fig. 7.8). Journal cages are used mainly in large bearings

Fig. 7.8

Cageless bearings, i.e. with full number of rolling bodies, are used rarely - only in some types of bearings, e.g. single row roller bearings.

In texts to individual design bearing groups the section dedicated to cages always states an overview of cages made in the general design, and delivery option of bearings with cages in different designs. 

7.5 Covers and seals

Bearings with covers on one or both sides are made with cover sheets (Z, 2Z, ZR, 2ZR – Fig. 7.9), or with contact seal ((RS, 2RS, RSR, 2RSR – Fig. 7.10). Cover sheets create contact-free sealing. In Z or 2Z version, the fitting for cover sheet is on the inner ring; ZR or 2ZR variants have cover sheet adhered to the smooth collar of the inner bearing ring.

 

Fig. 7.9

Fig. 7.10

The seal consists of sealing rings of nitrile rubber vulcanized on metal reinforcements that form an efficient contact seal in a design with rounded fitting on the inner ring (RS, 2RS), or in a design with contact on the smooth collar of the inner ring (RSR, 2RSR).

Covers and sealing rings are fastened in the outer ring recess, and are not detachable.
Bearings in basic design are filled with a quality plastic lubricant with temperature range between -30°C and + 100°C, in the short term even up to + 120°C. Filler of plastic lubricant usually ensures greasing throughout the service life in normal service conditions.  Bearings in this design cannot be additionally greased. 

7.6 Identification of roller bearings

Bearing is designated by basic identification and extension expressing the difference between this bearing and the standard version bearing. Identification of bearings contains numerical and literal characters that determine the type, size and design of the bearing. Overview of symbols and their order is based on the scheme shown in figure 7.11.

 

Fig. 7.11

7.6.1 General bearing version

In standard version, bearings are identified with basic designation consisting of the identification of the type and size of the bearing. The designation usually consists of a symbol expressing the design of the bearing (position 3 of the scheme), and a symbol for the dimensional group or diameter row (positions 4 and 5), e.g. type 223, 302, NJ22, 511, 62, 12 and so on. Designation of the bearing size contains characters for nominal bearing hole diameter d (position 6).

Bearings with hole diameter d < 10 mm:

Figures separate with fraction line or the last digit states directly the nominal hole dimension in mm, e.g. 619/2, 624.

Bearings with hole diameter d = 10 up to 17 mm:

double issue     00 identifies the hole     d = 10 mm, e.g.: 6200
        01         d = 12 mm, např. 51101
        02         d = 15 mm, např. 3202
        03         d = 17 mm, např. 6303
Exception in designation are single row ball bearings of separable type E and BO where the double issue states directly the hole diameter in mm, e.g.: E17.

Bearings with hole diameter d = 20 mm up to 480 mm

Hole diameter is quintuple of the last double issue, e.g. bearing 1320 features hole diameter d = 20 x 5 = 100 mm.
Exceptions are bearings with hole diameter d = 22, 28 a 32 mm where the double issue separated with fraction line stated directly the diameter of hole in mm, e.g. a320/32AX, and some bearing types, such as e.g. separable single row ball bearings of E type, and single row ball bearings of NG type where the double or triple issue states directly the hole diameter in mm, e.g.: E20, NG160.

Bearings with hole diameter d > 500 mm:
The last double issue or triple digit separated with fraction line states directly the hole dimension in mm, e.g. 230/530M, NU29/1060.

7.6.2 Full identification of bearings

Bearing produced in designs different from the standard are identified by the so-called designation, as is shown in the scheme in Fig. 7.11. It consists of the basic identification and supplementary characters that express the difference from the basic version.

Meaning of supplementary characters

The following part states, in accordance with full designation, an overview and meaning of supplementary characters used. The digit in the bracket stated with individual groups corresponds with the position number in the scheme. The scheme also states positions in full naming of the bearing that us separated with a gap. Other characters are written together without a gap. Characters for extension of designation that mean a digit are separated with a dash from the basic designation, e.g.  6305-2Z.
The meaning of supplementary characters for design variances of different bearing types is described in relevant chapters of the chart section of the catalogue.

Supplementary characters before basic designation

Other material than common steel for roller bearings (1)

C    –    rolling bodies from ceramics – e.g. C B7006CTA
HAA – high speed steel, e.g.: HSS 6215
X    –    corrosion resistant steel, e.g.: X 623
T    –    case hardening steel, e.g.: T 32240


Bearing incompleteness (2)

L     –     separate detachable ring of separable bearing, e.g. L NU206, in axial ball bearings without a shaft ring, e.g. L 51215
R     –     Separable bearing without detachable ring, e.g. R NU206 nebo R N310
E     –     separate shaft ring or axial ball bearing, e.g. E 51314
W     – separate body ring of axial ball bearing, e.g. W 51414
K     –     cage with rolling bodies e.g.: K NU320

Supplementary characters behind the basic designation

Difference in inner design (7)

A    –    single row angular-contact ball bearings with contact angle α = 25°, e.g. B7205ATB P5
    –    single row tapered bearings with higher load capacity and higher limit revolution frequency, e.g. 30206A
    –    axial ball bearings with higher limit revolution frequency, e.g. 51,105A
AA    - single row angular-contact ball bearings with contact angle α = 26°, e.g. B7210AATB P5
B    –    single row angular-contact ball bearings with contact angle α = 40°, e.g. 7304B
    –     single row tapered bearings with contact angle α = 17°, e.g. 32315B
BE    - single row angular-contact ball bearings with contact angle α = 40°, in new design, e.g. 7310BETNG
C    –    single row angular-contact ball bearings with contact angle α = 15°, e.g. 7220CTB P4
    –    double row spherical roller bearings in new design, e.g. 22216C
CA    –    single row angular-contact ball bearings with contact angle α = 12°, e.g. B7202CATB P5
CB    –    single row angular-contact ball bearings with contact angle α = 10°, e.g. B7206CBTB P4
D    –    single row ball bearing of type 160 with higher load capacity, e.g. 16004D
E    –    single row ball bearings with higher load capacity, e.g. NU209E
    –     double row spherical roller bearings with higher load capacity, e.g. 22215E
    –     Axial spherical roller bearings with higher load capacity, e.g. 29416E

Difference in main dimensions (8)

X    –    Change in main dimensions, established by new international standards, e.g. 32028AX

Covers (9)

RS    –    seal on one side, e.g. 6304RS
-2RS    –    seal on both sides, e.g. 6204-2RS
RSN    –    seal on one side and snap ring groove on the outer ring on the opposite side than the seal, e.g. 6306RSN
RSNB    - seal on one side and snap ring groove on the outer ring on the same side as the seal, e.g. 6210RSNB
-2RSN    - seal on both sides and snap ring groove on the outer ring, e.g. 6310-2RSN
RSR    –    seal on one side, adhering to the smooth inner ring collar, e.g. 624RSR
-2RSR    –těsnění na obou stranách přiléhající na hladký nákružek vnitřního kroužku, 
např. 608-2RSR
Z    –    Cover sheet on one side, e.g. 6206Z
-2Z    –    Cover sheet on both sides, e.g. 6304-2Z
ZN    –    seal on one side and snap ring groove on the outer ring on the opposite side than the cover sheet, e.g. 6208ZN
ZNB    –    cover sheet on one side and snap ring groove on the outer ring on the same side as the cover sheet, e.g. 6306ZNB
-2ZN    –    cover sheets on both sides and snap ring groove on the outer ring, e.g. 6208-2ZN
ZR    –    cover sheet on one side, adhering to the smooth inner ring collar, e.g. 608ZR
-2ZR    –    cover sheets on both sides, adhering to the smooth inner ring collars, e.g. 608-2ZR


Design change of bearing rings (10)

K    –    Tapered hole, taper ratio 1:12, e.g. 1207K
K30    –    Tapered hole, taper ratio 01:30:00, e.g. 24064K30M
N    –    snap ring groove on the outer ring, e.g. 6308N
NR    –    snap ring groove on the outer ring, and inserted snap ring, e.g. 6310NR
NX    –    snap ring groove on the outer ring, dimensions of which do not comply with ČSN 02 4605, e.g. 6210NX
D    –    split inner ring, e.g. 3309D
W33    –    groove and lubrication holes on the outer ring circumference, e.g. 23148W33M
O    –    lubrication slots on outer ring fillet of the bearing , e.g. NU1014O


Cage (11)

Material of cages for standard design bearings is usually not specified.
J    –    cage pressed from steel plate, guided on rolling bodies e.g.: 6034J
J2    –    cage pressed from steel plate, guided on rolling bodies. New design of single row tapered bearings, e.g. 30206AJ2
Y    –    cage pressed from brass sheet, guided on rolling bodies e.g.: 6001Y
F    –    massive steel cage, guided on rolling bodies e.g.: 6418F
L    –    massive light metal cage, guided on rolling bodies e.g.: NG180L C3S0
M    –    massive brass or bronze cage, guided on rolling bodies e.g.: NU330M
T    –    massive textite cage, guided on rolling bodies e.g.: 6005T
TN    –    massive cage of polyamide or similar plastic, guided on rolling bodies e.g.: 6207TN
TNG    - massive cage of polyamide or similar plastic, stiffened by glass fibres, guided on rolling bodies e.g.: 2305TNG

Cage design (stated characters are always used in combination with cage material characters).
A    –     cage guided on outer ring, e.g. NU226MA
B     –     cage guided on inner ring, e.g. B7204CATB P5
P     –     massive window cage, e.g.: NU1060MAP
H     –     open single-piece cage, e.g.: 629TNH
S     –     cage with lubrication slots, e.g.: NJ418MAS
R     –     silver-plated cage, e.g.: 6210MAR
V     –     bearing without cage with full number of rolling bodies, e.g. NU209V


Accuracy level (12)

P0    –    normal accuracy level (is not designated), e.g. 6204
P6    –    higher accuracy level than normal, e.g. 6322 P6
P5    –    higher accuracy level than P6, e.g. 6201 P5
P5A    –    higher accuracy level than P5 in some parameters, e.g. 6006TB P5A
P4    –    higher accuracy level than P5, e.g. B7204CBTB P4
P4A    –    higher accuracy level than P4 in some parameters, e.g. B7205CATB P4A
P2    –    higher accuracy level than P4, e.g. B7200CBTB P2
P6E    –    higher accuracy level for rotary electrical machines, e.g. 6204 P6E
P6X    –    higher accuracy level for single row tapered bearings, e.g. 30210A P6X
SP    –    higher accuracy level for roller bearings with tapered hole, e.g. NN3022K SPC2NA
UP    –    higher accuracy level such as SP for roller bearings with tapered hole, e.g. N1016K UPC1NA


Clearance (13)

C2    –    smaller clearance than normal, e.g. 608 C2
    –    normal clearance (is not designated), e.g. 6204
C3    –    bigger clearance than normal, e.g. 6310 C3
C4    –    bigger clearance than C3, e.g. NU320M C4
C5    –    bigger clearance than C4, e.g. 22330M C5
NA    –    radial clearance in bearings with incommutable rings (is indicated always behind the radial clearance group), e.g. NU215 P63NA
R...    –    radial clearance in non-standardised range (range in µm) , e.g. 6210 R10-20
A...    –    axial clearance in non-standardised range (range in µm) , e.g. 3210 A20-30


Noise level (14)

C6    –     reduced noise level lower than normal (is not designated), e.g. 6304 C6
C06    - reduced noise level lower than C6, e.g. 6205 C06
C66    - reduced noise level lower than C06, e.g. 6205 C66
Specific values for C06 and C66 are determined based on an agreement between customer and supplier.
Note: Bearings in accuracy level P5 and higher feature noise level within C6.


Increased operational safety (15)

C7, C8, C9 – bearings with increased operational safety designed mainly for use in aviation industry, e.g. 6008MB P68


Combining characters (12-15)

Characters/symbols of accuracy level, clearance in bearing, noise levels and increased operational safety are combined with simultaneous omission of C character and following special property of bearings, e.g.
P6 + C3 = P63     e.g. 6211 P63
P6 + C8 = P68     e.g. 16002 P68
C3 + C6 = C36     e.g. 6303-2RS C36
P5 + C3 + C9 = P539     e.g. 6205MA P539
P6 + C2NA + C6 = P626NA     e.g. NU1038 P626NA


Bearing association (16)

Designation of associated pair, triplet or quaternion of bearings consists of characters expressing arrangement of bearings and of characters defining the inner clearance or prestress of associated bearings. 

 

Fig. 7.12

Apart from characters stated in the chart the U character is used to identify that relevant bearings can be associate universally, example of designation B7003CTA P4UL.

Inner clearance or prestress

Stated characters are always used in combination with association characters.
A    –    Association of bearings with clearances, e.g. 7305OA
O    –    Association of bearings without clearances, e.g. 7305 P6XO
L    –    Association of bearings with small prestress, e.g. B7205CATB P4UL
M    –    Association of bearings with medium prestress, e.g. B7204CATB P5XM
S    –    Association of bearings with big prestress, e.g. B7304AATB P4OS


Stabilisation for operation at higher temperature (17)

Both rings have stabilised dimensions for operation at higher temperature.
S0 – for service temperature     up to 150 °C
S1     up to 200 °C
S2     up to 250 °C
S3     up to 300 °C
S4     up to 350 °C
S5     up to 400 °C
Example of designation NG160LB C4S3


Friction torque (18)

JU    –    reduced friction torque, e.g. 619/2 JU
JUA    –    bearings with defined friction torque at start-up 632 JUA
JUB    –    bearings with defined friction torque at after-running, e.g. 623 JUB
 

Plastic lubricant (19)

For bearings with cover or seal on both sides, the plastic lubrication other than common is designated by means additional characters. The first two characters define the range of service temperature, and the third character (letter) defines the name or type of lubricant according to the manufacturer's specification, or another character (digit) defines the amount of plastic lubricant that fills the covered space of the bearing.
TL    –    lubricant for low service temperatures from -60 °C to +100 °C
        example of designation 6302 2RSTL
TM    –    lubricant for medium service temperatures from -35 °C to +140 °C
        example of designation 6204 2ZRTM
TH    –    lubricant for high service temperatures from -30 °C to +200 °C
        example of designation 6202 2ZTH
TW    –    lubricant for both low and high service temperatures from -40 °C to +150 °C
        example of designation 6310 2ZC4TW
Note: The TM marking need not be stated on bearings and containers.
 

Bearings by special technical conditions

Single purpose bearings dimensions of which comply with the dimensional plan but the list of all characters of extension expressing their technical characteristics would cause confusion of marking, can be upon agreement between manufacturer and customer replaced with basic designation, attaching the TPF or TPFK marking and a two- or three-digit number behind the basic designation of the bearing, which defines the number of the agreed technical specification determining all technical parameters of bearings.
TPF    –    bearings made by special technical conditions agreed with customer, e.g. bearing 6205MA P66 by technical terms TPF 11142-71 is designated as follows: 6205MA P66 TPF 142.
TPFK    -     bearings by special technical terms agreed with customer which have high number of characters stating changes against the basic version. In this case, basic characters are replaced with designation TPFK containing relevant number of technical terms, e.g. bearing NU1015 made by technical terms. TPFK 11137-70 is designated as NU1015 TPFK137.

Bearings by special drawing documentation PLC

Bearings which by some of their dimension do not comply with the dimensional plan or are in line with the next development are marked with PLC by their manufacturer, as well as with other numerical characters. Usually they are single purpose bearings for one customer or a certain application method.

PLC ABC-DE.F (designation structure until 2012)

PLC    –    identification of special roller bearing
A    –    design assembly 
0    –     single row ball bearings
1    –    double row ball bearings:
2    –    axial ball bearings
3    –    Not completed.
4    –    single row roller, spherical-roller and needle bearings
5    –    double and multirow roller, spherical-roller and needle bearings
6    –    single row, double row and four row tapered bearings
7    –    special double row bearings
8    –    assembly units and separate parts
9    –    axial roller, spherical-roller, tapered and needle bearings
BC    –    dimensional assembly – two digit characters
DE    –    ordinal number within dimensional assembly – two digit characters
F    –    difference in design - one digit or combination of numerical character and letter

Due to extending the assortment of special bearings, it was decided in 2013 to change the structure of designating special bearings: Upon the establishing of a new system, the designation on already produced bearings will not be changed.
 
PLC AB-CD-EF.G (designation structure since 2013)

PLC    –    identification of special roller bearing
A    –    design assembly 
1    –    ball bearings
2    –    axial ball bearings
3    –    roller bearings
4    –    axial roller bearings
5    –    needle bearings
6    –    spherical-roller bearings
7    –    axial spherical-roller bearings
8    –    tapered bearings
9    –    axial tapered bearings
0 – other bearings and mounting assemblies
B    –    number of rolling units or bearings in mounting assemblies
CD     –    dimensional assembly – two digit characters
EF – ordinal number within dimensional assembly – two digit characters
G    –    difference in design - one digit or combination of numerical character and letter

7.7 NEW FORCE bearings

In order to satisfy the needs of technically advanced customers, ZKL pays particular attention to technical development of products and investments in new technologies. The outcome of one of the recent key innovations is initiation of successive start up of production of ZKL bearings with higher quality standard with designation NEW FORCE.

The NEW FORCE bearings represent a new generation of ZKL bearings. Launching of bearings brings customers higher durability of bearings, enhanced operational safety, prolonged maintenance intervals and thus substantial reduction of operating costs. NEW FORCE bearings are designed for extreme locations of transmissions, railway vehicles, presses, rolling mills, paper machines, pumps, machine tools, power engineering plants, polygraphic machines, etc.
As the first integrated new generation bearings, the radial spherical-roller bearings were launched on the market, double row tilting ball bearings, double row angular-contact ball bearings and axial ball bearings. The next phase of launching bearings of this standard was the production assortment of bearings with outer diameter over 400 mm.

The achieved parameters of NEW FORCE bearings are the result of ZKL development in the following areas:
  • Material of roller bearing components
  • Technology of bearing ring flaring
  • Optimisation of inner construction
  • Surface treatments of bearing components

The achieved results allowed ZKL to offer NEW FORCE roller bearings with high utility properties to their customers:
  • high dynamic load capacity 
  • low friction
  • reliability in the extreme operating conditions

High durability of bearings

Increase of dynamic load capacity by 8% to 25% brings increase of durability of bearings by 30% up to 110%, comparing to the up-to-now designs. 

 

Fig. 7.13

Increase of dynamic load capacity allows customer to design construction with smaller dimensions to transfer the same load. Thus ZKL brings to their customer an opportunity to reduce total price of the equipment, and achieve power savings during operation. 

Use of quality bearing material

Steels for production of bearings meet the parameters of international standards defined by ISO 683- 17. Production of bearing rings and rolling bodies utilised high quality material of selected smelting houses. Long-term cooperation with suppliers ensures continuous process of improving parameters of input material. 

Key quality parameters of steel and its processing affect the service properties of bearing, i.e. resistance to fatigue damage, abrasion resistance and dimensional stability. These are:
  • chemical composition and heat treatment
    Selection of the type of bearing steel and optimisation of heat treatment conditions is conducted by the dimension of the component. The heat treatment processing technology of NEW FORCE bearings ensures stabile hardness values of bearing components in the entire section. Spherical-roller bearing components are heat treated to ideal material structure and hardness that enable using of the bearings at service temperatures to 200 °C. The final material structure ensures dimensional stability of bearing components throughout their service life.
  • Content of non-metal intrusions - micropurity
    Reduction of content of non-metal intrusions is the key quality parameter in the bearing steel metallurgy development. In production of bearings, ZKL utilises bearing steel with minimum oxygen content.
  • Type of semiproduct
    The quality of bearing and production economics are affected also by selection of the semiproduct type. The level of forming and positive angle of forming fibre contact towards the orbit are the parameters that positively increase resistance of the NEW FORCE bearings against fatigue damage.

Technology of bearing ring flaring

Základní výzkum prokázal vliv směru vláken materiálu vzhledem ke kontaktní ploše na trvanlivost ložiska. Nejvýhodnější je takové uspořádání vláken, kdy jejich směr je rovnoběžný s kontaktní plochou. Se zvětšujícím se úhlem směru vláken ke kontaktní ploše se trvanlivost snižuje. Technologie rozválcování za studena nebo poloohřevu přinesla ložiskům NEW FORCE optimální strukturu materiálu pro dosahování vyšší trvanlivosti ložisek.
 

Fig. 7.15
 

Optimised design and inner geometry

Advanced design and calculation programs, together with new bearing production technologies, enabled optimisation of inner construction of bearings and improved accuracy of functional areas. Thus the NEW FORCE version bearings achieved better quality of functional surfaces and improved course of discharge voltages in bearing component sections, comparing to the standard bearing designs. 

This brings reduced noise level and higher accuracy of bearing run, as well as extended durability of bearings.

Special surface treatment

Within innovation programs, a new design of sheet cages for radial and axial spherical-roller bearings was launched in the production. Cages are made of steel plate with surface treatment in order to improve slip properties and reduce wear of cages. The design of cages allows achieving better lubrication and extended service life of bearings.  Surface treatments of bearing components represent a well tested way of improving bearing properties for certain locations.  The benefit of surface layers lies in better keeping the lubricant in the rolling contact, reduced friction and enhanced resistance to wear and corrosion. We recommend that suitability of surface treatment for special operating condition is discussed with the technical and consultancy services of ZKL.

Bearings NEW FORCE +

ZKL bearings with NEW FORCE+ marking represent a brand new generation of ZKL bearings which is characterised by an innovated modification of the bearing inner structure geometry towards optimum voltage course in the area of rolling contact. This ZKL bearings' innovation is associated with further enhancement of accuracy, comparing to the standardly produced bearing assortment, including the NEW FORCE bearings. 
Optimisation of the shape of rolling surfaces brings improved dynamic load capacity of bearings and thus also significant extension of bearings' durability.  Development of the NEW FORCE+ generation is associated with the introduction of new calculation methods in the structure of bearings based on MKP and production upgrade by introducing numerically controlled machines that enable achieving final shapes of functional surfaces with modified geometry. 
With regard to the fact that the entire design optimisation and production process of modified parts is unique for every bearing application, the NEW FORCE+ bearing generation is not designed to be launched in the standard production program of ZKL. The bearings will be manufactured upon request for extreme locations for selected OEM customers.

7.8 Technical support

ZKL operates as bearing manufacturer and supplier already since 1947. Since the beginning, the company has been cooperating with their customers worldwide. This allows continuous expansion of the ZKL roller bearing production assortment offered in maximum quality at reasonable price. Experience in operation of bearings obtained in cooperation with customers, along with continuous education of their employees allows ongoing development of technical support to ZKL customers and extension of services for ZKL bearing users.

Proposal verification

The ZKL bearings' structure and their basic parameters are designed by the ZKL's own well tested methodologies that adhere to the international ISO standards.  Designing new bearings utilises most sophisticated design and calculation CAD systems. Designs of new bearings are optimised and their rigidity checked by means of MKP based numerical calculations. When creating designs, information obtained in achieved test results and experiences from production and operation of ZKL bearings are utilised.

Verification of quality parameters of ZKL bearings

Parameters of ZKL roller bearings are verified in tests within development, as well as in periodical quality assessment during series production. Tests are conducted according to the company's own methods in the test stations of the bearing test room. Bearing and input material tests results are analysed and serve as the basis for new design, technological and investment solutions.

Technical support for ZKL bearing users

Customer needs are solved by fully available workers of ZKL technical and consultancy services. Expert workers are ready to solve operatively requests and questions of ZKL bearing users in the area of selection of bearings, design of rolling location and assembly procedures. ZKL technical support provides users with information in the area of roller bearings, accessories and tribology.  Upon user's request it also provides professional supervision over assembly and disassembly of bearings directly at customer, and organizes professional training course of user employees. It cooperates with manufacturers in development of rolling location. It draws up expert opinions on broken bearings. It determines causes of accidents and proposes measures to prevent them.