THE DESIGNING OF THE BEARINGS CONFIGURATION
Table 12 shows the most typical hardness curve, the required hardness value is the Vickers harness transformed from the related tension value.
The minimum quenching hardness is mainly related with the diameter of the rolling body , the strain of the materials , the core hardness of the materials and the quenching method.
For the case of tray , the its stable load reaches Co (Hertz tension PH=4000N/mm2) , its required quenching hardness will be decided by the following formulas: Surface quenching
Eht0.078.Dw  .............................................( 42)
Flame or induction quenching Rht140.Dw/Rp0.2    ........................................(43)
                 Eht                       mm
              Effective surface quenching hardness depth
                 Rht                       mm
              Quenched hardness penetrating depth (for flame or induction quenching)
                 Dw                        mm
Diameter of the rolling body
Rp0.2                    N/mm2 0.2% of the material central elastic limit tension When the load is less than P=Co or Dw>100mm, experiments show that the quenching hardness depth can be less than the results of formulas (42) or (43).The quenched hardness must not be less than 0.3mm after final abrasion.
The surface precision of the tray
The selection of the surface precision of the tray is depended on the operational condition requirements of the bearings. To fully develop the load capacity of the bearing, the roughness of the tray surface should be Rz1(Ra0.2). For lower requirements, the surface roughness can be lowered down to Rz4(Ra0.8).But for those operation which needs higher stability and low noise , the tray should be ground or super ground so that the minimum ripple surface can be reached.
The dimensional tolerances between the needle and retainer assembly and the punched outer ring tray are shown in the technical remarks before the dimension table of this brochure . the dimensional tolerances of the trays of the needle bearings without inner ring are shown in Table 16. The round tolerances will be no greater than 25% of the associated dimensional tolerances while the parallel tolerances are 50%.
When needle and retainer assembly is used, the width of the tray , after the subtraction of the chamfered sized ( or the radium of the circular angle) , should be enough to ensure that the full width of the retainer will have enough guiding surface .

Working conditions

ISO Tolerance

examples

Bulk bearing seat

The outer ring under rotating load

Heavy impact load

P7

Idle or pulley wheel

Normal load

N7

Idler wheel ,brace organ

Light variable load

M7

Tension wheel

Variable loads

Heavy impact load

M7

Eccentric organ , pump

Normal load

K7

Compressor

Separate bearing seats or bulk bearing seat

Light load

J7

Cam shaft

The outer ring under spot load

Heavy or normal load for bulk needle bearing seats

J7

Engineering machinery, Gear box

Normal load for separate bearing seats of needle bearings or roller bearings

H7

Engineering machinery

Normal load for those roller bearings with lower operational request

H8

Bearing unit with lower requirements

High precession fitting

 

Light load, high speed , small bending deformation

K6

Main shaft of machine tool, fixed central bracket
 

The designing of the tray for the roller bearings

               To reach the rigidity and load capacity the highest possibly while the spaces used can be saved as much
          as possible,  CJSRTL bearings without rings are recommended. The rolling bodies are directly on the shaft or
          rolling in the bearing holes such as the needle and retainer assembly, non-inner needle bearings and punched 
          outer ring needle clutches etc. Special attention should be paid to the followings points:
               Material
               To fully reach the load capacity of the bearing, be sure that its surface hardness should be 670840 HV 
          during the selection of the roll bearing tray materials with enough quenched hard depth .Its purity  requi-
          rements are the same as generally high quality steel. The following steels are specially recommended for the
          rolling body tray materials.
                lThoroughly quenched steel
           In special cases, these rolling bearing steel can be surface quenched.
lSurface quenched steel When selecting the materials, the hardness at the center should be considered besides the quenching hardness. During surface quenching treatment, first selection should be those with fine grain structure and its effective quenched hard depth in compliance with formula (42). lFlame quenched steel or induction quenched steel the flame or induction quenching can be only effected tray position on the machined parts. The pre- condition of selecting material is still the quenchable hardness. Tempering process should be made before quenching hardness treatment.

Quenched hard depth

 The surfaced quenched , flame 
quenched or induction quenched 
trays must get enough quenched 
hard depth Ht beside its surface
hardness of 670-40HV(for surface
quenching, the effective hard
depth is Eht, while the 
quenching hardness penetrate 
depth should be Rht for flame or
induction quenching. The defini-
tion of quenching hard depth is: 
the vertical distance between the
surface and the place where the 
hardness is 550HV.

1, flame or induction quenching
2, surface quenching
3 required hardness

Figure 12 quenched hard depth Eht and Rht

 

The effect of temperature on the dimension stability

                The organizational structure inside the commonly standard bearing materials will change with the
           operational temperature exceeds + 120℃ which will cause the variation of the bearing size. Therefore, 
           to ensure the normal operation of the bearings  under high temperature , the bearings must go through
           dimensional stability treatment . In  this case , we  must also consider the decrease of the material
           hardness caused thence. For small bearings,the dimensional stability requirements usually are not very
           high . But to guarantee the  stability combination  and the initial radical clearance of the big scale
           bearings, at least the inner rings should be dimensional stabilization treated. This can be expressed
           with different additional codes as per the different operational temperature requirements.
 

The radical positioning of the rolling beaeings

            The following factors must be considered in the positioning to the rolling bearings:
                l        ROTATION STATE
                 The rotation state means the movements of the bush rings in relation with the load directions..
Rotation load: bearing bush ring rotates while load remains standstill or vise ad versa . Both of these cases belong to rotating load states . Under the rotating loads , if the combination to the shaft or bearing seats is too loose , deviation will occur on the bearing bush ring position .The- refore more compacted combination must be ensured to avoid such position deviation. The heavier the load is , the greater of the bush ring dimension should be and the more compacted combination should be chosen.
Spot load : when bearing bush ring load are still , or when the bearing bush ring and load are rotating with the same speed, the two cases are regarded still loads. In this case , comparatively looser combination can be selected because at this time , no position deviation will change on the bearing bush ring.
Variable load direction: the irregularly changing load , the rocking load or impact and vibrating load are all called variable load direction, more compacted combination of the two bush rings must be selected.
l   LOAD TYPE AND NATURE For the bush ring of the rotating load or the variable load, the greater the load is, the more       compacted combination should be.          l THE BEARING TYPE AND SIZE Table 14 only shows the bearing seat hole tolerances only used for steel or cast iron bearing seats while Table 15 shows the shaft tolerances for the solid shaft. More compacted combination should be used in the cases of bearing seats made of light metal or the hollow shaft . The shaft tolerances for the needle bearings without inner rings are listed in Table 16.
From the factors mentioned above,it is clear that it is impossible to find a selective principle that contains all the combination tolerances for all combinations under all factors. Therefore , allthe figures listed in the tables will be regarded as reference values only.

Table 15the selective principles for the shaft tolerance limit for inner

ring needle bearings and roller bearings

Working condition

 

Shaft diameter

mm

ISO Tolerance

examples

Roller bearings

Cylindrical roller bearings

Inner ring under spot load

Easy to fit

All kinds of bearing diameters

g6

g6

The rolling wheels , adjusting pole , on the still seated shaft or the inner wheel , pulley and rolling wheel , tension wheel
 

General purpose

h6

h6

High precision and stable operation

h5

--

Inner ring under rotating load or variable load

Light load and variable load

 

 

 

To  50

j5

j6

Gearing box, electric motor, the main shaft of grinding machine, pump , machine tool , general purpose engineering machinery.

Over  50

To  100

k5

k6

Over 100

To  200

m61)

m61)

Over 200

 

n62)

n62)

Normal load

 

 

 

 

To  50

k53)

k6

Over  50

To  100

m5,m61)

m61)

Over 150

To  200

n62)

n62)

Over 200

To  500

p62)

p62)

Under very critical condition or impact and heavy load

 

To  150

n62)

n62)

Over150

 

p62)

p62)

        After the tolerance limited of the shaft and the bearing seat is chosen, the  working clearance must be rechecked.
        Greater radical clearance is needed for tolerances of n6 and p6.
        Combination should be no greater than k5 for needle angular contact bearings.

Table 16 the reference values for the selective shaft tolerance limits of the needle bearings without inner rings

Inscribed ring (tolerance with F6)

Fw    mm

Operational clearance

Exceed

to

Less than normal value

Normal value

Greater than normal value

--

65

80

160

180

200

250

315

65

80

160

180

200

250

315

400

k5

k5

k5

k5

j5

j5

h5

g5

h5

h5

g5

g5

g5

f6

f6

f6

g6

f6

f6

e6

e6

e6

e6

d6

                   1)The tolerance suitable to the bearing seat is up to K7,for the bearing seat tolerance
                above K7 , the clearance must be got through calculation or measuring.
                Mounting  tolerance
                   Bearing bush rings has perfect radical positioning while the bush rings are evenly supported
            on their circular surfaces and widths. These will decisively effect the normal operation and a longer 
            life of the bearing. Therefor the mounting tolerances must be selected very carefully.
                Thedesigning of  the bearing bush ring supporting surface
                   For normal function of the rolling bearings,the surfaces in combination with the bearings(shaft
            and bearing seat holes) must be made as per the appropriate bearing precision grade.
The surface dimensional tolerance of the recommended geometric precision value associated with the bearings are listed in Table 17.
The contacting surfaces of the divided bearing seats must be de-burred and chamfered.. Table 17 the surface dimensional tolerance and geometric precision associated with the bearings

Precision grade

Bearing combination surface

Diameter tolerance

Circular tolerance

Parallel tolerance

Side swing

P0

Shaft

IT6(IT5)

Rotating loadIT4/2

IT4

IT4

Spot loadIT5/2

IT5

Bearing seat

IT7(IT6)

Rotating loadIT5/2

IT5

IT5

Spot loadIT6/2

IT6

P6

Shaft

IT5

Rotating loadIT3/2

IT3

IT3

Spot loadIT4/2

IT4

Bearing seat

IT6

Rotating loadIT4/2

IT4

IT4

Spot loadIT5/2

IT5

P5

Shaft

IT5

Rotating loadIT2/2

IT2

IT2

Spot loadIT3/2

IT3

Bearing seat

IT6

Rotating loadIT3/2

IT3

IT3

Spot loadIT4/2

IT4

 

The axial directional positioning of the rolling bearings

            To prevent the side slip of the needle bearings or the cylindrical roller bearings, the bearings must 
         be positioned in axle direction and be clamped. No axle clamping device are permitted if the combination
         tolerance is compact enough. (see figure 12a which shows the needle bearing of punched outer ring)
The needle and retainer assembly must have axial directional guide. (see figure 13 and fig 14)
The designing of the guiding surface
The side directional guiding surface of the needle and retainer assembly must me machined very care- fully to ensure on burr existing . The neighboring faces must be quenched and ground for high speed operation. There should be a washer added before the stopping ring. (see fig 14) The axial directional positioning of the bearing bush ring
The bearing bush ring is always positioned by the shaft or the retaining shoulder. The retaining shoulder must have enough altitude and be vertical to the axle line of the bearing. Also they must be produced in the same machining of the surface combined with the bearing bush ring.
The circular angle and the cutter exit groove must be in compliance with the regulation in the transit parts between the retaining shoulder and the surface combined with the bearing.
The circular angle or the cutter exit groove will ensure the whole face of the bearing bush ring be supported by the retaining shoulder , so attention must be paid to the minimum value of he chamfered angle ?s given in the dimension list.
If the bearing is used as the fixed end support and bears the axial direction load, the both ends of the bush ring must be fixed tightly (see figure 16,17 18), especially for the case of the inner ring of the separation inner ring (Nk1b , see fig 16 and SL04 , fig 24) and the cylindrical roller bearing divided outer ring series SL01(Figure 17 or 18) , series SL11 and SL12. In these cases, the two ends must be closed clamped.
Fir the single directional positioned bearing ( Figure 19 and 20 ) , it will be enough to have the one end of the retaining edge supported where the axial directional load is effected on the bearing bush ring.
The support height of the retaining edge of the cylindrical roller bearings under the axial direction load should be increased to the size of d1 or D1 (see dimension list)

Figure 12a

Figure13

Figure14

Figure15

Figure16

Figure17

Figure18

Figure19

Figure20

 

The sealing of the rolling bearing

                The operational reliability and the life time of the bearing mainly depends on the effective protection of its sealing unit against the
                      entering of the dirt and vapor and the leakage of the lubrications. The applicable conditions should be taken into account when selecting 
                     the sealing type.
                              Non contacting sealing is mainly used in the following cases: the place where sealing friction must be avoided in high speed circular
                    movement, the sealing friction is hoped to be avoided under hgih temperature. Gap sealing will get good sealing result for lubricating grease .
                   The gap sealing back flow design (the groove, centrifugal ring , spiral groove etc) will help this sealing to be used in the case of lubrication oils.
The slit of the simple gap sealing is 0.1-0.2mm. the slit in the permissive space range can be as long as possible. Those with ring-- shape groove (fig 21) will help to improve the sealing effect.
Labyrinth sealing (fig 23) has better effect. To avoid pump absorption phenomenon, the slit of the radical expansion can not be very narrow . A better result will be got with grease in the slit . Generally speaking , the lubrication grease should be the same as that used in the bearing , or at least the densification agents for the lubrication grease must be the same . If the above mentioned requirements can not be satisfied due to the sealing medium, special sealing grease should be used. In this case, separating space should be provided so tha the sealing grease will not enter into the bearing.

Fig 21 gap sealing

Fig 22 centrifugal ring sealing

Fig 23 labyrinth sealing

              Contacting sealing
                  Contacting sealing is usually better than the non contacting sealing. In contacting sealing,the 
          sealed surfaces contact is kept by pre-tension. Therefore, the friction heat thus caused will limit the 
          permissive circular speed . In operation , a bigger initial friction surface will decrease drastically . 
          The sealed combination surfaces should be lubricated as well, or abrasion loss will occur.
                  Seal lip sealing (Fig 24-Fig 27). This kind of sealing is applicable to the oil lubrication and 
          grease lubrication  with the circular speed of  12m/s . If the purpose of the sealing is to prevent the 
          sealing lubricant leakage from the bearing seat,the seallip should be fitted inward while if the purpose 
          is only to prevent the dirt from entering into the bearing unit, leas lip should be fitted outward.
Rotating shaft sealing: As per DIN3760 (Fig 27) this is a king of seal lip sealing which are very effective for many kinds of bearing units.
 

Fig24 seal lip sealing , series pp

lRTL sealed needle and cylindrical roller bearings

    (Fig 24) is seal lip sealed bearing (suffixed "RS"or "P" , no additional sealing space is required 
in this structure . This kind of bulk sealing is applicable to the sealing unit without pressure need . 
In general operational condition, it can prevent dirt from entering the bearing and the leakage of lu-
bricating grease. In re-lubrication, the used grease can be drained out from here.

Fig25 seal lip sealing , series G

 

Fig26 seal lip sealing , series SD

Fig27 rotating shaft sealing,DIN3760

            Felt  lubrication
This lubrication is used in the case of a circular speed less than 4m/s. Felt sealing ring and the ring groove are all standardized in DIN5419. Felt sealing unit must be dipped into the hot oil (about + 80℃) before mounting. There must be no scratches or scores on the combination face. If there is no spiral trails after surface grinding, better sealing result will achieved. The recommended roughness is Rz1-Rz4 or Ra0.2-Ra0.8. the surface hardness must be no less than 450HV. When the circular speed exceed 4m/s, the minimum should reach 600HV. There must be guiding chamfered angle at the ends of contacting sealing combination surfaces so that seal lips will not be turned over in mounting.
The lubricating grease should be coated onto the seal lips and the combination surfaces before fitting to avoid the dry friction in the first rotation of the shaft. If double lip sealing or several sealed units are mounted, the lubricating grease should be filled into the gaps in between.
If the sealing purpose is mainly to prevent the lubricant leakage from the bearing, the seal lip should be fitted inward while the outward fitted lips will help preventing the dirt outside from entering . also, the used lubricants can be drained out when lubricate again.
When the sealing unit is to be pressed into the bearing seat hole, pressing pole should be used to ensure alignment of the center and vertical to the axle. In case there is a sharp angle at the surface top end of the sealing unit combination, associated auxiliary sleeve should be used. The diameter of the assembling sleeve should be a little bigger than the diameter of the sealing unit combination surface with a long guiding chamfering angle.(about 15℃)
The roughness of the RTL inner (IR series) ring tray is very small and its surface is suitable for the combination path of the lubrication seal lip. When it is used for oil lubricating sealing, to get better sealing effect, the inner ring should be machine without spiral scores (IR...EGS), and a chamfered angle to prevent the seal lip from being scraped.