轴承配置的设计english

        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
            Eht≥0.078.Dw  .............................................( 42)    
               Flame or induction quenching
             Rht≥140.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 670�840 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
Working condition		Shaft diameter mm		Roller bearings	Cylindrical roller bearings	examples
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)
	Under　very　critical condition or impact and heavy load	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

Less than normal value

Normal value

Greater than normal value

160

180

200

250

315

160

180

200

250

315

400