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Conveyor belts

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Big size and high capacity

Bearings

Mast Roller for forklifts,

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Roller side

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Technical Characteristics

Technical Characteristics

Working temperature

Load capacity of cylindrical roller bearings

The dimensioning of cylindrical roller bearings is based on their load capacity and lifetime.  About rotating bearings, the dynamic load coefficient must be taken into consideration; for roller bearings that have an occasional rotation, the static load coefficient must be considered. The load coefficients and the calculation procedures refer to DIN ISO 281/1 and ISO 76 regulations. Load capacities for cylindrical roller bearings are adequate to their practical use and performance.


Dynamic load capacity of cylindrical roller bearings

Dynamic coefficient “C” is necessary for the calculation of rotating bearings, that is to say bearings subject to dynamic strain. It indicates the maximum possible load that a bearing can bear (in Kg/N): in theory the lifetime is 1 million rotations.


Static load capacity of cylindrical roller bearings

Static coefficient Co  is used for the calculation of non-revolving bearings (that is to say fixed or subject to slow oscillations) or rotating at very low speed. The static load coefficient Co  is defined as the static load which causes a permanent deformation of the revolving bodies and of the raceways equal to 1/10.000 of the diameter of the revolving bodies, on the most stressed contact point.


Axial load capacity of radial cylindrical roller bearings

C.R. cylindrical roller bearings can bear high axial thrusts and very high radial loads. The axial capacity of radial bearings depends on the dimensions of the edges, in relation to the front surfaces of the rolling bodies. The load capacity of the contact surfaces depends on the shearing speed and on the lubrication. With specific formulas it is possible to obtain axial load values that C.R. bearings can bear: continuous, temporary and alternate loads.


Lubrification

Regular lubrication and maintenance are essential for a long lifetime of revolving bearings. The lubricant has the following functions:


  • It provides a film, which is enough to separate the surfaces of contact.
  • It allows the removal of heat (oil lubrication)
  • It prevents the entry of liquid or solid agents  inside the bearing (grease lubrication).
  • It decreases the noise of the bearing
  • It protects against corrosion.

Revolving bearings can be lubricated – according to a technical choice – with grease or oil, depending on:

  • Form of construction and dimension of the bearing.
  • Type of execution of the housings and of the parts in contact with the bearing.
  • Working condition.


Grease lubrication

The choice of the lubricant grease must be executed according to the specific instruction of lubricant suppliers. Revolving bearings are usually provided with lubricant greases that do not have high density at low temperature. Bearings working at high speed are provided with greases with low dynamic viscosity. In case the bearing is subject to high strain, C.R. recommends the use of EP greases and high viscosity of the oil.


Normally, the bearing should not reach higher temperature than 90° C. In this way, the characteristics of the grease will not be altered. The lifetime of the lubricant is influenced by environmental conditions. According to C.R. experience, the lifetime of the lubricant is guaranteed for three years,  provided that the following conditions are fulfilled:


  • Closed environment (warehouse)
  • Temperature range 0°-40°C
  • Air humidity below 70%
  • Non-contamination by chemical agents.

After 3-year store time, the grease can lose some of its lubricant power. When re-lubrication is not possible, the lifetime of the grease becomes a main point.  For security reason, it is necessary to take into consideration that generally the grease does not have a lifetime of more than three years.

In case the bearing is still functional, it must be cleaned and lubricated with the same quantity of grease used which was used at the beginning. When possible, re-lubrication must be done at working temperature and while the bearing is rotating.

The necessary quantity of grease can vary from 20% to 80% compared to the original one.

It is necessary to verify that the old grease can go out without any problem.

Lubrication range can be exactly calculated only with verifications made during real working conditions. It is possible to establish an indicative value of lubrication range following specific formulas.


Oil lubrication

Oil lubrication guarantees a good distribution of the lubricant and of the bearing surfaces. Oil lubrication is used when the mechanical elements adjacent to the bearing are already lubricated with oil, or in case it is necessary to remove heat from the support. Oils with mineral base or synthesis oils are suitable for oil lubrication.

Mineral oils with additive can be used for continuous working temperatures up to 120° C; synthesis oils up to 210° C.

For working security, C.R. recommends lubricant oils with EP additive.

They must be used in the following cases:


  • Radial cylindrical roller bearings subject to very high loads and axial thrusts.
  • Axial cylindrical roller bearings: before using lubricant oils, it is necessary to verify their compatibility with plastic materials, non-ferrous metals or light alloys.

These are the most popular lubrication systems:

  • Drop oil lubrication: it is used for high speed radial bearings provided with a lubrication hole on the outer ring.
  • Oil bath lubrication, immersion lubrication or oil sump lubrication: it is used for radial bearings.
  • Oil mist lubrication, and oil-air lubrication: they are particularly suitable for radial bearings working at very high speed with low load.
  • Oil recirculation lubrication: it is possible to filter the lubricant and cool it continuously.  It is particularly suitable to remove heat from bearings working at high temperature.


During the run-in of the device, a high contamination of the lubricant can be noticed: in this case, the oil must be changed when the test is over.

According to C.R. experience, it is enough to change the oil once a year, if the bearing temperature is kept below 60° C with a minimum amount of impurities.

In case of unfavourable working condition, C.R. recommends to control the lubricant on regular basis, according to the manufacturer’s instructions.



Assembling, disassembling and washing

C.R. cylindrical roller bearings are precision products.

This is the reason why they need to be treated with very high care, before and during the assembling. Correct functioning mainly depends on good maintenance.



Assembling

The environment where the bearings are assembled must be clean and without dust. Before the assembling, it is useful to have a suitable equipment and a press. If a press is not available, the assembling can be done by strokes on the bushing’s edges. Warning!


During the assembling, no thrusts nor strokes must be transferred on the revolving bodies! Deforming actions on the bearing rings must be avoided.

The assembling of the outer and inner rings can be facilitated  by grooves or radii manufactured for this reason, and by a light lubricating treatment of the different surfaces.

The assembling of the inner rings on the shaft, with interference, is made through their heating with a suitable induction device.

If this device is not available, the heating of the rings can be done in an oil bath or in an oven at a temperature of about 110° C. C.R. recommends the cooling of the housing, before assembling the bearing in it.

It is necessary to make a working test of the bearing, once the assembling is finished.




Disassembling

During design phase, bordering holes or suitable cavities for the extractor should be foreseen in order to allow the bearing to be disassembled. If the bearing is re-used, be careful and avoid strokes and thrusts. After disassembling, the bearing must be cleaned in all its parts.




Washing

The following cleansers can be used to degrease and wash the bearings:

  • Water-based cleansers
  • Organic cleansers

Water-based cleansers can be neutral, acid or alkaline.

Organic cleansers are: petroleum, provided that it is without water or acids, - and gasoline (not the one used for vehicles). After the procedure of washing, the bearings must be immediately dried and treated with a suitable lubricant.



Lifetime calculation

The lifetime of the bearing depends on the applied load and number of rotations, and it is calculated in the following way:

L = (C/P)p            Lh=(16666/n) • (C/P)p


L=106

The lifetime of the bearings depends on the load. Rated duration in million of rotations, which is achieved or overcome by 90% of a representative number of equal bearings, before the material shows signs of wear.


Lh = h

Rated duration in hours of working corresponding to L.


C = N

Dynamic load coefficient. With reference to radial bearings, C corresponds to a load with constant entity and direction. The test on a representative number of bearings proved that the rated duration is one million rotations. With reference to axial bearings, C corresponds to the axial load which operates in central position.


P = N

Equivalent load on the bearings for radial or axial bearings.



P

Lifetime exponent

p=10/3 for needle roller and cylindrical roller bearings

n=min-1

Number of rotations



Basic lubrication range

Basic lubrication range “tf” depends on the GKW speed coefficient and is shown in diagram 02 according to the following formula, considering KL bearing type, the number of rotation n and the medium diameter dM of the bearing.



GKW = KL •  270.000

(n •  dM)

BEARING TYPE


Support rolls and cam followers, with full-complement cage

Support rolls and cam followers, with full-complement rollers

Cylindrical roller bearings

Axial cylindrical roller bearings

KL


0,3

0,15

0,8

0,08

Tab. 01

GKW = Speed coefficient

KL = Tab 01

n = Number of rotation

dM = Medium diameter

PREMISES


Bearing temperature

Load ratio

Number of rotations and load

Load in the main direction

Lubrication grease

Rotation axis

Inner ring

Influence of the external

CONDITIONS


Up to 70°c

Co/p=20

steady

radial on radial bearing – axial on axial bearing

grease with lithium soap

horizontal for radial bearings

revolving

no influence

Premises about lubrication range

DIAGRAM 02

Possibility of

re-lubrication




Re-lubrication

is necessary


a

b

Speed coefficient GKW

Static security coefficient

Static security coefficient defines the security grade against bearing deformations and is calculated with the following formula:







With a static security coefficient So < 8, the bearings are very pressed and with coefficient So•8, the bearings are medium or lightly pressed.



Approximate values of static security coefficient










Influence of temperature on the bearing

Temperature influences the bearing by decreasing the dynamic load capacity “C”; such output is calculated according to this correction formula:







The reduction of hardness due to the increase of temperature does not affect the static load capacity “Co”, therefore it can be overlooked for temperatures up to +300° C.


S0 = C0  / F0

S0 =

C0 =

F0 =

static security coefficient

static load coefficient

maximum load of the bearing


(N)

(N)



Silent working with few vibrations and normal working with minimum need for quietness:
bearing with minimum rotation.

Normal working with more need for quietness.

Working with high impact loads.

Supports with high demand for precision of rotation and quietness.


Application Case

SO


≥1


≥2

≥3

≥4


CT = fT  . C

CT =

fT =

C =

effective dynamic load coefficient for high temperatures

temperature factor according to graph 03

dynamic load coefficient

Bearing clearance and working clearance


The good functioning of revolving bearings depends on a correct working.

This depends on radial clearance and on the change of radial clearance as a consequence of the assembling interference and of working temperature.


Working clearance

The radial moving of the shaft with regard to the outer ring of the bearing determines the working clearance.

The working clearance depends on the reduction of the radial clearance, as a consequence of the assembling interference and the temperature.

The reduction of the radial clearance of the assembled bearing – due to the couplings – is the result of the inner ring expansion and the contraction of the outer ring.

The difference of temperature between inner ring and outer ring can cause a reduction or an increase of working clearance



Radial clearance of the bearing

The radial clearance of the disassembled revolving bearing is expressed through the value of the radial shifting from edge to edge of the inner ring towards the outer ring.

The bearing radial clearance is divided into four groups (see table 04).

C.R. bearings manufactured with normal CN clearance guarantee a correct working clearance in normal working conditions, considering the suitable tolerances for shaft and housing. C3 and C4 radial clearances are taken into consideration for bearings having big dimensions, subject to high loads; in case of assembling interference and big difference of temperature between the inner ring and outer ring.

Bearings with C2 radial clearance are to be employed only in special cases (for example, in case of high combined alternate loads with swinging movements or a limited number of rotations).

In these particular cases it is highly recommended to check the bearings during the functioning, since they are subject to heating.

The values of C2, CN, C3 and C4 radial clearances are listed in table 05.

The customer must specify the bearing clearance, except for CN clearance.


MEANING


Bearing radial clearance lower than CN

Normal bearing radial clearance

Bearing radial clearance higher than CN

Bearing radial clearance higher than C3

FIELD


C2

CN

C3

C4

Tab. 04

More than

-

24

30

40

50

65

80

100

120

140

160

180

200

225

250

280

315

355

400

450

Tab. 05

Up to

24

30

40

50

65

80

100

120

140

160

180

200

225

250

280

315

355

400

450

500

min.

0

0

5

5

10

10

15

15

15

20

25

35

45

45

55

55

65

100

110

110

max.

25

25

30

35

40

45

50

55

60

70

75

90

105

110

125

130

145

190

210

220

min.

20

20

25

30

40

40

50

50

60

70

75

90

105

110

125

130

145

190

210

220

max.

45

45

50

60

70

75

85

90

105

120

125

145

165

175

195

205

225

280

310

330

min.

35

35

45

50

60

65

75

85

100

115

120

140

160

170

190

200

225

280

310

330

max.

60

60

70

80

90

100

110

125

145

165

170

195

220

235

260

275

305

370

410

440

min.

35

35

45

50

60

65

75

85

100

115

120

140

160

170

190

200

225

280

310

330

max.

75

75

85

100

110

125

140

165

190

215

220

250

280

300

330

350

385

460

510

550

d

C2

CN

C3

C4

Rated Ø of the

holes in mm.

Bearing radial clearance in µm.

Dimensional and tolerance symbols

d

Ddmp

Vdp

Vdmp

D

DDmp

VDp

VDmp

DBs

VBs

DCs

VCs

Kia

Kea

Sd

SD

Rated hole diameter

Tolerance of the medium diameter of the hole in a plan

Variation of hole diameter in a single radial plan

Variation of the medium diameter of the hole

Rated outer diameter

Tolerance of medium outer diameter in a single radial plan

Variation of medium outer diameter in a single radial plan

Variation of medium outer diameter

Tolerance of one single size of inner ring width

Variation of inner ring width

Tolerance of one single width of outer ring

Variation of outer ring width

Radial defect of inner ring rotation, to be measured on the assembled bearing

Radial defect of outer ring rotation, to be measured on the assembled bearing

Defect of quadrature of the surfaces with regard to the hole

Variation of outer cylindrical surface inclination related to lateral surfaces



circularity

parallelism



circularity

parallelism


parallelism


parallelism

concentricity

concentricity

flatness

flatness

Symbol

d

C4

Radial bearing tolerances


The tolerances of cylindrical roller bearings are according to DIN 620 part 2 and 3. Generally C.R. bearings correspond to PN class; in case of need of higher precision bearings, the tolerances can be reduced to the values of classes P6 and P5.


More than

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Tab. 06 - inner rings

Up to

-8

-8

-8

-10

-12

-15

-20

-25

-30

-35

-40

-45

-50

-75

-100

-125

-160

-200

max

10

10

10

13

15

19

25

31

38

44

50

56

63

-

-

-

-

-

max

8

8

8

10

12

19

25

31

38

44

50

56

63

-

-

-

-

-

max

6

6

6

8

9

11

15

19

23

26

30

34

38

-

-

-

-

-

max.

6

6

6

8

9

11

15

19

23

26

30

34

38

-

-

-

-

-

max

10

10

10

13

15

20

25

30

40

50

60

65

70

80

90

100

120

140

sup.

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

max

12

15

20

20

20

25

25

30

30

35

40

50

60

70

80

100

120

140


dmp

Vdp

Vdmp

VBs

More than

0,6 (*)

2,5

10

18

30

50

80

120

180

250

315

400

500

630

800

1000

1250

1600

Up to

2,5

10

18

30

50

80

120

180

250

315

400

500

630

800

1000

1250

1600

2000

inf.

-40

-120

-120

-120

-120

-150

-200

-250

-300

-350

-400

-450

-500

-750

-1000

-1250

-1600

-2000

d

8,9

0

2,3

mm

mm

Kia

Bs

Tolerance

Range of diameters

Tolerance

(*) This diameter is included

Tolerance values in µm

More than

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Tab. 06.1 - outer rings

Up to

-8

-8

-9

-11

-13

-15

-18

-25

-30

-35

-40

-45

-50

-75

-100

-125

-160

-200

-250

max

10

10

12

14

16

19

23

31

38

44

50

56

63

94

125

-

-

-

-

max

8

8

9

11

13

19

23

31

38

44

50

56

63

94

125

-

-

-

-

max

6

6

7

8

10

11

14

19

23

26

30

34

38

55

75

-

-

-

-

max.

6

6

7

8

10

11

14

19

23

26

30

34

38

55

75

-

-

-

-

max

15

15

15

20

25

35

40

45

50

60

70

80

100

120

140

160

190

220

250

Identical to Bs and VBs for inner ring of same bearing

(see tab. 06)




dmp

Vdp (**)

VDmp

VCs

More than

2,5 (*)

6

18

30

50

80

120

150

180

250

315

400

500

630

800

1000

1250

1600

2000

Up to

6

18

30

50

80

120

150

180

250

315

400

500

630

800

1000

1250

1600

2000

2500

D

8,9

0

2,3

mm

mm

Kea

Cs

Tolerance

Range of diameters

Tolerance

(*) This diameter is included

(**) Valid before the assembling of the bearing and/or after disassembling the outer and inner spring rings.

Tolerance values in µm

More than

0

0

0

0

0

0

0

0

0

0

0

0

0


Tab. 07 - inner rings

Up to

-7

-7

-7

-8

-10

-12

-15

-18

-22

-25

-30

-35

-40

max

9

9

9

10

13

15

19

23

28

31

38

44

50

max

7

7

7

8

10

15

19

23

28

31

38

44

50

max

5

5

5

6

8

9

11

14

17

19

23

26

30

max.

5

5

5

6

8

9

11

14

17

19

23

26

30

max

5

6

7

8

10

10

13

18

20

25

30

35

40

sup.

0

0

0

0

0

0

0

0

0

0

0

0

0

max

12

15

20

20

20

25

25

30

30

35

40

45

50

dmp

Vdp

Vdmp

VBs

More than

0,6 (*)

2,5

10

18

30

50

80

120

180

250

315

400

500

Up to

2,5

10

18

30

50

80

120

180

250

315

400

500

630


inf.

-40

-120

-120

-120

-120

-150

-200

-250

-300

-350

-400

-450

-500

d

8,9

0

2,3

mm

mm

Kia

Bs

Tolerance

Range of diameters

Tolerance

(*) This diameter is included

Tolerance values in µm

More than

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Tab. 07.1 - outer rings

Up to

-7

-7

-8

-9

-11

-13

-15

-18

-20

-25

-28

-33

-38

-45

-60

max

9

9

10

11

14

16

19

23

25

31

35

41

48

56

75

max

7

7

8

9

11

16

19

23

25

31

35

41

48

56

75

max

5

5

6

7

8

10

11

14

15

19

21

25

29

34

45

max.

5

5

6

7

8

10

11

14

15

19

21

25

29

34

45

max

8

8

9

10

13

18

20

23

25

30

35

40

50

60

75

Identical to Bs and VBs for inner ring of same bearing

(see tab. 07)





dmp

Vdp (**)

VDmp

VCs

More than

2,5 (*)

6

18

30

50

80

120

150

180

250

315

400

500

630

800

Up to

6

18

30

50

80

120

150

180

250

315

400

500

630

800

1000

D

8,9

0

2,3

mm

mm

Kea

Cs

Tolerance

Range of diameters

Tolerance

(*) This diameter is included

(**) Valid before the assembling of the bearing and/or after disassembling the outer and inner spring rings.

Tolerance values in µm

Class of Tolerance  P6

Class of Tolerance PN (normal tolerance)

More than

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Tab. 08.1 - outer rings

Up to

-5

-5

-6

-7

-9

-10

-11

-13

-15

-18

-20

-23

-28

-35

max

5

5

6

7

9

10

11

13

15

18

20

23

28

35

max

4

4

5

5

7

8

8

10

11

14

15

17

21

26

max.

3

3

3

4

5

5

6

7

8

9

10

12

14

18

max

5

5

6

7

8

10

11

13

15

18

20

23

25

30

dmp

Vdp (**)

VDmp

VCs

More than

2,5 (*)

6

18

30

50

80

120

150

180

250

315

400

500

630

Up to

6

18

30

50

80

120

150

180

250

315

400

500

630

800

D

8,9

2,3

mm

mm

Kea

Cs

Tolerance

Range of diameters

Tolerance

Tolerance values in µm

Class of Tolerance P5

More than

0

0

0

0

0

0

0

0

0

0

0

Tab. 08 - innner rings

Up to

-5

-5

-5

-6

-8

-9

-10

-13

-15

-18

-23

max

5

5

5

6

8

9

10

13

15

18

23

max

4

4

4

5

6

7

8

10

12

14

18

max.

3

3

3

3

4

5

5

7

8

9

12

max

4

4

4

4

5

5

6

8

10

13

15

sup.

0

0

0

0

0

0

0

0

0

0

0


max

5

5

5

5

5

6

7

8

10

13

15

dmp

Vdp

Vdmp

VBs

More than

0,6 (*)

2,5

10

18

30

50

80

120

180

250

315

Up to

2,5

10

18

30

50

80

120

180

250

315

400

inf.

-40

-40

-80

-120

-120

-150

-200

-250

-300

-350

-400

d

8,9

2,3

mm

mm

Kia

Bs

Tolerance

Range of diameters

Tolerance

Tolerance values in µm

(*) This diameter is included

Identical to Bs and VBs for inner ring of same bearing

(see tab. 08)

max

5

5

5

5

6

8

8

8

10

11

13

15

18

20

(*) This diameter is included

(**) Valid before the assembling of the bearing and/or after disassembling the outer and inner spring rings.

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