The process of manufacturing Bearing Steel

 

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Kaiyang_000@yahoo.cn  China Bearings Tires Nominated Supplier in Beijing
     嘉能元国际贸易(北京)有限公司
Beijing JiaNengyuan International Trading Co., Ltd

 

conventional machines and equipment experience is the best guide but

in general the coefficients listed below may be applied to determine

the equivalent load used in the life calculations:

 – 1.2 machinery or mechanisms operating smoothly without repeated

shocks,

                 – 1.3  geared transmissions according to gear quality,

1.4 – 3.0 machinery or equipment operating under repeated shocks or

vibration.

As far as belt drive transmissions are considered, the calculated

tangential load should be multiplied by the following coefficients:

2.0 – 2.5 for v belts,

2.5  – 5.0 for flat belts according to drive tension.

1.6.5.2        Variable loads and speeds

  When the loads and speeds are variable, the life calculation can

only be made by first establishing an assumed constant load and

constant speed equivalent in their effect on the fatigue life of the

radial bearing.

  This type of operating condition is frequently met and the

possible variations although cyclical are numerous. One encounters

this feature in particular, in variable speed drives. 

 1.7 LUBRICATION

Lubrication of the bearing has got such a great importance, as raw material from which from

which they are made. Anticipated life of the bearing largely depends on the quality and quantity

of the lubricant and its method  of application. Rare lubrication and improper lubrication of a

bearing result in the reduced bearing life and its premature failure. It is therefore, very essential

to make a proper choice of lubricant.

The advantages derived from the correct choice of lubricant are:

1.  It protects the bearing from corrosion.

2.  It protects the bearing to a certain extent, from the entrance of foreign matter in to the

bearing.

3.  It minimizes the friction between the races and rolling elements.

4.  It reduces the friction arising due to elastic deformation of rolling elements when under

load.

5.  It facilities the smooth running of bearing by minimizing noise.

6.  It creates the lubricant film on the raceway of the bearing and thereby protects the

raceway from blows of the rolling elements.

7.  It dissipates the heat from the bearing and also helps distribute uniformly the frictional

heat throughout bearing, which is generated during operation. 1. TECHNICAL   INFORMATION

1.1 BEARING HISTORY

Hundred of years ago, when man lacked strength and endurance to carry

loads, such heavy loads to be transported were put on  simple skids and

dragged to the place of destination. The dragging heavy load on dry ground

requires considerable force. These forces can be reduced by using lubricants

between the sledge runners and the ground. This lubricant-probably water –

was poured to reduce the friction and thereby reducing the volume of force.

As the time passed on, these forces were further reduced when man learnt to

insert wooden rollers between the ground and the object. THUS SLIDING

MOTION WAS CONVERTED INTO ROLLING MOTION, which is the

basic principle of bearing. However, things were not much changed for

years, till the concept of BALL was conceived, as the application of rollers

was not practical everywhere. In 17th

 century, stone balls were produced and

were in use for variety of applications to minimize the friction. Since the

stone balls were not suitable for many applications, cast iron balls were also

produced, but that was also not suitable. In 19th

 century, the concept of steel

balls was conceived and steel balls were produced. During this era, on lathe

machines, balls of remarkable accuracy were cut off from a steel rod and the

ends were machined to form a sphere. At the end of 19th

 century, balls

manufactured by this method in England were within the tolerance of 0.025

to 0.050 mm. In the year 1883, Friedric Fischer, instrument maker in

Scheweinfurt – W. Germany, after numerous experiments, developed a

method of grinding wheel balls, turned between the centers on the centre less

principle. For this purpose, he designed ball grinding machine called “BALL

MILL”. In 1898 taper roller bearing unit developed in USA by H. Timken.

During 1913-1914 Roller bearings were put on use.

1.2 GENERAL

The choice of a bearing depends on many factors that need to be examined

in order to obtain the most successful results at the lowest cost.

In most cases the selection should be made when the overall design of the

machine has been decided. Dimensional limits are  then known, as well as

the speeds and loads. At this stage the choice can be made from the many

types of bearings offered from the Galaxy Bearing Ltd. standard ranges and

the notes given in this section will generally permit selection of the most

suitable bearing for each application. When calculating the cost of the assembly, not only should the price of  the bearing be considered, but also

cost for heat treatment, machining and handling and fitting of ancillary items

(snap rings, locking devices, tools etc.) and the eventual quantities required.

Large economies can be made on these  items if the correct bearings are

selected. Something it is more advantageous to choose a bearing of slightly

higher cost, which will however, when all criteria are taken into

consideration, provide the most economic solution. The result obtained from

bearings depends to a large extent on the design and method of assembly,

loading, and alignment between inner  and outer rings. The introduction of

‘Anti-friction’ or ‘Rolling Contact Bearing’ proved far superior to plain

Bearings because of their classic advantages, Such as

™ Low friction – particularly low starting friction.

™ Their ability to support both radial and thrust load and speed.

™ Accurate performance under changing load and speed.

™ High load carrying capacity.

™ Operating ability under extreme conditions of speed and

temperature.

These bearings vary in size, from  ‘tiny pin-head’ to ‘giant sized’

Bearings for Cement/Rolling Mills/Radars etc.

Bearings are so widely used that  today, we find their application in

objects like the charkha, chairs, doors,  filling-cabinets, children’s toys, as

well as in the most sensitive instruments like computers, data processing

machines, rockets and aerospace instruments.

1. 3 BEARING STANDARDS

Galaxy Bearing Ltd standard metric  and Inch bearings conforms to

International standards (ISO) for boundary dimensions, tolerances and

internal clearances. They also comply with the associated DIN, AFBMA

AND British Standards. Galaxy Bearing Ltd has comprehensive

specifications for materials, heat treatment and quality control to ensure high

precision products made from clean bearings steels.

1. 4 MATERIAL

The process of manufacturing Bearing Steel does not start at a Bearing Plant

but at the steel mill. The SAE-52100  standard Bearing Steel contains

varying amount of carbon, iron,  chromium, manganese, phosphorus,

sulphur, silicon, etc. Each of these elements plays a vital role in making the final steel suitable for Bearings.  Chromium and carbon allow deep

hardening. Where as the combination of Carbon, Chromium and Iron helps

to minimize Bearing failures as they increase the surface resistance to

abrasion and wear & tear. A proper combination of all these elements make

the final Bearing Steel tough enough to withstand shocks & heavy loads and

hard enough to resist fatigue.

  Generally Bearings are made from tubes or bars, but nowadays, many

Bearings manufacturers are inclined to make Bearings from forged rings.

Large-sized Bearings are manufactured from forged rings. It is filet that

Forged Bearing Rings have makes them more durable.

         ROLLING ELEMENTS, CAGES SHIELD AND SEALS.

 Moreover, balls characteristically minimize the friction to a greater extent

than any other rolling elements. This is why ‘Ball Bearings’ are more

versatile than any other type of Bearings. Other rolling elements used in

Bearings are Cylindrical Rollers, Taper Rollers, and Spherical Rollers,

Needle rollers, Concave Rollers and a combination of Ball & Needle etc.

         Basically,  every Anti-friction Bearing consists of four basic parts, an

outer ring, rolling element and a cage.

  The cages are made in various designs and out of various materials,

But there are two main types of cages:- 

™ Pressed Steel Cage made from Strip Steel and

™ Turning & Drilling Machine Cage made from Carbon Steel.

The cages keep rolling elements  properly spaced out between two

rings. The cage may be of steel, brass,  etc. depending upon the type and

application of the Bearings.  Rolling  elements can be balls, cylindrical

rollers, spherical rollers or taper rollers. Standard bearings are made using

high quality carbon-chrome through hardening steel of similar composition

of the following specifications:  SAE 52100   OR    100Cr6

1.5 SELECTION OF BEARINGS

1.  After knowing all about bearings the important thing is the proper

selection of bearing for any moving vehicle or machine.

2.  The selection of ball & roller bearings for a given installation depends

upon the following factors.

  The load carrying capacity & the nature of the load.   The type of service under given conditions such as temperature,

humidity, dustiness, acidity, etc.

  The anticipated life of the bearing.

  Magnitude and direction of loads.

  The proportion of thrust to radial load.

3.  Cylindrical Roller Bearings are suitable for those shafts which have   

been allowed to move freely longitudinally within certain limits, and

for far larger and heavily loaded applications.

  Taper Roller Bearings are suitable where radial and thrust loads or

any combination of both are required to be handled and in dealing

with heavy composite loads as in case of automobile parts.

  In very high speed spindles and machines only, bearings with

precision tolerances are used.

4.  The capacity of the bearings decreases as the speed increases. If a 

bearing operates continuously, its life expectancy measured in hours

will obviously be shorter than if operated intermittently. Some types

of bearings can carry only radial  loads or thrust loads while some

types of bearings can carry both radial as well as thrust loads. So if a

bearing which can carry only thrust loads is put under radial loads, it

will either break or damage the machine into which it is fitted. So, a

proper selection is necessary. One  major cause for bearing failure

depends on selection of bearings.

  In short the proper selection of bearings is most essential and

will ensure the longer life of the bearings as well as the life of the

machine in which it is used.

  If the bearing loads with its directions of the ratio of radial and

thrust capacity and speed is accurately determined, its life span can

also be established. The necessary bearings size can also be

determined. However the selection is so complex that general rules

can hardly be drawn up.

1.6 CALCULATION FOR RADIAL ROLLING BEARINGS

The calculations for radial rolling  bearings must take account of the

following principal factors:

™  Actual supported loads and possible shock loads

™  Speed of rotation

™  Operating temperature

™  Hardness of the bearing raceways Other features such as lubrication, sealing and alignment do not enter

directly into life calculations but they must be considered in order to avoid

introducing unfavorable factors.

  The life calculation of a radial  bearing or a thrust bearing under

rotation is established from the dynamic capacity C indicated in the tables of

dimensions. The static capacity Co enables one to determine the maximum

load under certain conditions.

1.6.1 DYNAMIC CAPACITY C

The dynamic capacity of a bearing is the constant radial load

which it can support during 1 000 000 revolutions before the first

signs of fatigue appear on a bearing race or rolling element. 

1.6.2 NOMINAL LIFE

The life of a radial bearing is the number of revolutions (or the

number of hours at constant speed)  that it will maintain before

showing the first signs of material fatigue.

The relationship between the life is millions of revolutions L10,

the dynamic capacity C and the supported load P, is given by the

formula:

L10 =   ( C/P )

p

In which :

L10   –  Basic rating life (106

Revolutions)

C  –  Basic dynamic load rating (Newton)

P  –  Equivalent dynamic load (Newton)

P  –  is equal to 10/3 for needle or roller bearings and 3

for ball bearings. 

The formula above is independent of speed of rotation, which

must not exceed the recommended limit in respect of the radial

bearing or the thrust bearing used and the method of lubrication.

If the speed of rotation n (rpm) is constant, the life is given in

hours by the function:

L10 h = (L10 x 106

)/60 n      hours

The life in hours is then inversely proportional to the speed.

The above formulae will ensure that 90% of the bearings

operating under the same conditions will attain at least the calculated

L10  life, known as the nominal life (the figure being the percentage of bearings which may not attain this life). The formulae are based on the

use of standard quality bearing steel and assume a satisfactory method

of lubrication.

1.6.3 MODIFIEDL LIFE  Lna

In various conditions modified life can be determined (in

millions of revolutions) following the general formula:

Lna  = a1 a2 a3 L10

Lna = adjusted rating life, millions of revolutions

In which a1, a2 and a3 are  correction factors linked to

reliability, material and lubrication respectively.

           1.6.4 Reliability correction factor a1

    A reliability factor in excess of 90% may be required in

certain industries, such as aviation, for reasons of security and to reduce the

risk of very costly immobilization.

    The table below indicates the values of the correction

factor a1 as a function of reliability:

Reliability %  Factor a1  Corrected  Life

Lna1

90

95

96

97

98

99

1

0.62

0.53

0.44

0.33

0.21

L10

L5

L4

L3

L2

L1

  In order to select as an example a bearing of L4  life

(reliability 96%) it is necessary to consider a theoretical L10  life

(reliability 90%), equal to L4/0.53 applied in the formula L10 = (C/P)

p

using the dynamic capacity C given in this catalogue.

1.6.5   EQUIVALENT LOAD AND SPEEDS

1.6.5.1    Overload factors

The load on a radial or thrust bearing is established from the

characteristics of the machine together with the working loads

prevailing. However, account should also be taken as far as possible

of the supplementary loads which  arises due to imperfections in

transmission, etc. or due to overloads, shocks and vibration. For 8.  Power losses can be saved, as internal friction can be prevented.

9.  It also helps the bearing to attain the required speed.

    10. It helps to attain the anticipated life of the bearing.

There are TWO types of lubricants used for bearing lubrication. OIL and 

 GREASE

 1.7.1 OIL

Oil lubrication is considered to be the most  efficient than Grease, provided proper sealing

methods are employed to prevent the leakage. Only highly refined OIL should be used as bearing

lubricant.

OIL is preferred when…

1.  Bearing speed is very high.

2.  Operating temperature is consistently high.

3.  Sealing methods can be easily employed.

4.  Bearing application demands that Grease is not suitable.

Then during operational condition, most of the lubricant will be forced out of the bearing which

can never come back into the bearing, and such lubricant is not suitable for reuse.

1.7.2   GREASE

For many applications, grease is considered to  be more convenient than oil. Grease used as

lubricant should be of smooth texture and non-fibrous. It must  be free from chemically or

mechanically active ingredients. For bearing lubricants, general-purpose sodium-soap petroleum

grease is preferred. It is suitable for variety of speed and temperature conditions and has rust

preventive character under humid conditions.

For specific working conditions and operational requirements special type of Greases are used

which are…

1.  Lithium soap petroleum oil grease.

2.  Lithium soap di-ester grease.

3.  Lithium soap silicon grease.

4.  Special quality grease to withstand temperature conditions from minus 200

to 3000

 F.

Generally Grease lubrication is preferred when…

1.  Temperature is not excessive (Not over 200 F).

2.  Speeds are moderate.

3.  Extra protection from Dirt, Fumes, and other foreign matter is required.

4.  Long time operations without maintenance are the requirement.

1.7.3 SELECTION OF LUBRICANT

1.  For small size bearing operating at high speed, low viscosity oil is used.

2.  Large bearings carrying heavy loads, lubricant with higher viscosity and additional adhesive

properties may be used. 3.  For any application, the  lubricant must have sufficient lubricating capacity  at prevailing

temperature.

4.  It must from a load sustaining lubricating film for prevailing load conditions.

5.  It must have the capacity to absorb water  to a certain extent, without affecting the

lubricating capacity, wherever the application demands.

Thus one should ascertain the correct type of lubricant, which is suitable for operating

conditions. When the lubricant quantity is inadequate, it results in the cage failure, and

inadequate lubrication may heat up cage, may breakdown the ball pocket, and progressively

break the whole cage. Even non-metallic cage also becomes brittle, dry and crack apart under

heat and stress. Due to break  down of the lubricating film  on raceway and rolling element

surfaces, they may also develop scoring marks,  gradually resulting in bearing failure. This

condition may also result in the deformation of parts, and when the bearing with deformed parts

rotate under load, it will have sliding motion instead of rolling motion, and it ends up in bearing

failure. Normally a medium size bearing running at the speed of 2000-6000 RPM can be

sufficient lubricated with only few drops of oil per hour. 

   1.8 BEARING TOLERANCES

   1.8.1   SYMBOLS

  GBL tolerances for bearings conform to values for normal class bearings to ISO

Standards. Bearings of other tolerance classes (closer tolerances) can be supplied at extra

cost provided the quantity is sufficient.

d  =  bearing bore diameter, nominal

d1  =  basic diameter at the theoretical large end of a basically tapered bore

Δds  =  deviation of a single bore diameter

Δdmp  =  single plane mean bore diameter deviation

Δd1mp   =  mean bore diameter deviations at the theoretical large end of a basically

tapered bore

Vdp  =  bore diameter variation in a single radial plane

Vdmp  =  mean bore diameter variation 

D  =  bearing outside diameter, nominal

D1  =  outside diameter of outer ring flange

ΔDs  =  deviation of a single outside diameter

ΔD1s  =  deviation of a single outside diameter of outer ring flange.

ΔDmp  =  single plane mean outside diameter deviation

VDP  =  outside diameter variation in a single radial plane

VDMP  =  mean outside diameter variation

B  =  Inner ring width, nominal

ΔBs  =  deviation of a single width of inner ring

VBS  =  Inner ring width variation

C  =  outer ring width, nominal

C1  =  outer ring flange width

ΔCs  =  deviation of a single width of outer ring

ΔC1s  =  deviation of a single width of outer ring flange

VCS  =  outer ring width variation VC1S  = variation of outer ring flange width

Kia  =  radial run out of assembled bearing inner ring

Kea  =  radial run out of assembled bearing outer ring

Sd  =  runout of inner ring reference face (back face, where applicable) with 

  respect to the bore

SD  =  variation of outer ring outside surface generatrix inclination with   

  respect to the outer ring reference face (back face)

SD1  =  variation of outer ring outside surface generatrix inclination with   

  respect to the outer ring flange back face

Sia  =  runout of inner ring face (back face) with respect to the raceway of 

 assembled bearing

Sea  =  runout of outer ring face (back face) with respect to the raceway of 

 assembled bearing

Sea1  =  runout of outer ring flange back face with respect to the raceway of 

 assembled bearing

‘α  =  taper angle (half the cone angle) of inner ring bore

1.8.2  ADDITIONAL SYMBOLS FOR TAPERED ROLLER BEARINGS

T =  bearing width

ΔTs  =  deviation of the actual bearing width

T1  =  effective inner subunit width

ΔT1s  =  deviation of the actual effective inner subunit width

T2  =  effective outer subunit width

ΔT2s  =  deviation of the actual bearing width 

        1.8.3  NORMAL TOLERANCE CLASS

(Radial bearings except tapered roller bearings)

Bore diameter tolerances given in the table apply basically to cylindrical bores.

          1.8.5  TOLERANCES FOR TAPERED ROLLER BEARINGS (INCH SERIES):

Tolerance values in microns

Inner Ring

Tolerances

for inner

ring width

(ΔBs)

Tolerances

for outer

ring width

(ΔCs)

Assembled

bearings

Outer Ring

Tolerances for bore dia. and running

accuracy  Tolerances

for actual

bearing

width

(ΔTs)

Tolerances for OD and running

accuracy

Nominal bore

diameter d (mm)

Δdmp

Radial

runout

(Kie)

Nominal

outside

diameter D

(mm)

Normal

class

(ΔDmp)

Radial

runout

(Kea)

over  Incl.  high  low  Max.  high  low  high  low  high  low  over  incl  high  low  Max.

–  76.200  +13  0  51  +76  -254  +51  -254  +203  0  –  304.800  +25  0  51 76.200  266.700  +25  0  51          +356  -254           

1.8.6   TAPERED BORE TOLERANCES – NORMAL TOLERANCE CLASS

Basically tapered bores, tapers 1:12 and 1:30

a)  For taper 1:12

  The taper angle (half the cone angle) is α = 2° 23’ 9.4” = 2.385 94° = 0.041 643

rad 

  The diameter at the theoretical large end of the bore is d1 = d + (1/12) B

b)  For taper 1:30

  The taper angle (half the cone angle) is α = 0° 57’ 17.4” = 0.954 84° = 0.016 665

rad

  The diameter at the theoretical large end of the bore is d1 = d + (1/30) B

The tolerances for a tapered bore comprise:

o  A mean diameter tolerance, given by limits for the mean diameter

deviation at the theoretical small end of the bore Δdmp ;

o  A taper tolerance, given by limits for the difference between the mean

diameter deviations at the two ends of the bore, Δd1mp – Δdmp ;

o  A tolerance for the diameter variation, Vdp,  given by a maximum value

applying in any radial plane of the bore.

Tapered bore, taper 1:12  Tolerance values in micrometers

d

mm

Δdmp

Vdp

Δd1mp – Δdmp

over  Incl  High  low  max  high  low

18

30

50

80

30

50

80

120

+21

+25

+30

+35

0

0

0

0

13

15

19

25

+21

+25

+30

+35

0

0

0

0 120  180  +40  0  31  +40  0

Tapered bore, taper 1:30  Tolerance values in micrometers

d

mm

Δdmp

Vdp

Δd1mp – Δdmp

over  Incl  High  low  max  high  low

80

120

180

120

180

250

+20

+25

+30

0

0

0

25

31

38

+40

+50

+55

0

0

0

1.9   CHAMFER DIMENSION LIMITS

Limit dimensions of chamfar

Symbol

r1, r3    Chamfar in radial direction

r2, r4    Chamfar in axial direction

rsmin   General symbol for the minimum

chamfar r1smin,r2smin,r3smin,r4smin

r1smax, r3smax    maximum chamfar in radi

                     direction

r2smax, r4smax    maximum chamfar in axia

                     direction

al

l

 rs2max

r2

rsmin

r1smax

r1

rsmin

D

d

r1smax

r1

rsmin

r2smax

r2

rsmin

r4max

r4

rsmin

r3smax

r3

rsmin

r1smax

r1

rsmin

r2smax

r2

rsmin

D

d

r2smax

r2

rsmin

r1smax

r1

rsmin

r2smax

r2

rsmin

Dg

Dw

 Cham far  of  radial  bearings

rsm in

Dim ension in m m

0,1 0,15 0,2 0,3 0,6 1 1,1 1,5 2 2,1 2,5 3 4 5 6 7,5 9,5 12 15

Nom inal     over

diam eter   to 40

40

40 50 120 120 80 220 280 280

40 50 120 120 80 100

100

280 280 220

280

280

r1m ax  0.2  0.3  0.5  0.6  0.8  1  1.3  1.5  1.9  2  2.5  2.3  3  3.5  3.8  4  4.5  3.8  4.5  5  5  5.5  6.5  8  10 12.5  15  18  21  25

r1m ax  0.4  0.6  0.8  1  1  2  2  3  3  3.5  4  4  5  4.5  5  6  6.5  7  6  6  7  8  8  9  10  13  17  19  24  30

19

 38

 3Cup

rsmin

Dimension in mm

0,3 0,6  2 2,5  4  6

Nominal     over

outside diameter D

50

50 120 120 120 400

120 250 120 250 120 400

250

250

r3max  0.7  0.9  1.1  1.3  1.6  1.9  2.3  2.8  3.5  2.8  3.5  4  3.5  4  4.5  4  4.5  5  5.5  5  5.5  6  6.5  6.5  7.5  7.5  9

r4max  1.4  1.6  1.7  2  2.5  3  3  3.5  4  4  4.5  5  5  5.5  6  5.5  6.5  7  7.5  7  7.5  8  8.5  8  9  10  11

 11,5  3  5

40

40

40

40

250 250

250

120 250

120

120

120

400

400

250

250

180

180

180

180

2. BEARING MOUNTINGS

Bearing is a precision machine member and is very sensitive to improper treatment.

Therefore, while mounting the bearing, utmost care is necessary:

1.  Mounting of a bearing should be done in clean, dry, dust free room.

2.  While mounting, never remove the preservative coating of thee bearing.

3.  If the bearing becomes DIRTY, then clean it with suitable solvents.

4.  Never wash NEW bearing with kerosene etc. before mounting.

5.  Never remove bearing from its packing, till it is ready for mounting.

6.  Bearing seating and other components should be thoroughly cleaned.

7.  Check thoroughly dimensional and form accuracy of seating and shaft.

8.  Prescribed FITS must be maintained on the shaft and housing.

9.  While mounting the smaller bearing onto the shaft, transmit the force thru inner ring only

and NOT thru outer ring or thru cage.

10. While mounting the bearing in the housing, force must be transmitted through outer ring

only and not thru inner ring or the cage.

11. Never blow hammer directly on thee bearing.  Instead, use a suitable size of mounting

bush thru which uniform force can be transmitted over the entire ring surface. 12. For mounting the large size bearing it is preferable to heat the bearing up to 800

 to 1000

C.

While heating the bearing, make sure that  accurate temperature control is maintained,

because excessive heat may cause the reduction in the hardness of the bearing.

Oil bath, Hot plate, Temperature controlled electric oven etc. are suitable means to heat the

bearing. At last see that mounting of the bearing is done by a skilled person, who has through

knowledge of the job procedures, tools, knowledge of the force to be applied etc. Any ignorance

of these factors may result in damage of the bearing and reduced service life. Experience shows

that the amount of shrinkage required for easy fitting is barely depending upon the interference

fit tolerance.

As a general rule, the following temperature value can be used.

               Bore                                        Temperature

    Below 100 mm                                    900

 C (1950

 F)

    From 100 mm to 150 mm                  1200

 C (2500

 F)

    Above 150 mm                                   1300

 C (2650

 F)

2.1 HOW TO PREPARE ROLLING BEARING FOR MOUNTING

2.1.1 Working Planning 

Know in advance what you are going to do so that the mounting work can proceed in a

straightforward manner. Study the shop drawing to acquaint you with the design details

of the application and the assembly sequence. Phase the individual operations and get

reliable information on heating temperatures, mounting forces and the type and the

amount of greases to be packed into the bearing. Whenever the installation and removal

of rolling bearing necessitates special measures the fitter should be provided with

comprehensive instructions on mounting details, including topics such as the means of

transport for the bearing, the mounting equipment, measuring devices, heating facilities

and type and quantity of lubricant.  

2.1.2    Before starting mounting

Before starting mounting the fitter should satisfy himself that bearing number stamped on

the package agrees with the designation given on the drawing and in part list. He should

therefore be familiar with the bearing numbering and identification system.

2.1.3        Handling of rolling bearings before mounting:

Before being packed, the bearings are coated with preservative oil, which prevents corrosion.

The oil does not need to be washed out when mounting the bearing. In service, the oil

combines with the bearing lubricant. Do not perform any modifications on the bearings.

Subsequent drilling of lubricating holes, machining of grooves, flats and the like will disturb the stress distributions in the ring resulting in premature bearing failure. There is also the risk

of chips or grit entering the bearing.

2.1.4     Cleanliness in mounting

An absolute “must” for the proper fitting of roller bearings is working in clean

surroundings. The tools to be used should be free  from dirt & fillings.  In the room where the

fittings of the bearings are carried out it is absolutely essential to avoid machining with metal

cutting tools. If, despite these precautions, bearings get dirty by improper handling, they must not

be rotated because even the smallest particles penetrating into the bearing will damage the races

and in this way the service life of the bearing will be considerably reduced.

Attention should also be given to the cleanliness of shaft, housing and any other mating

parts. Castings must be free from sand. After cleaning the housing bore should receive a

protective coating. Bearing seats on the shaft and in housing bore should be carefully cleaned

from antirust components and residual paint. Turned parts must be free from burr and sharp

edges.

2.1.5    Surrounding parts

All surrounding parts should be carefully  checked for dimensional and geometrical

accuracy before starting mounting. Non-observance of the tolerances for shaft and housing seat

diameters, out of roundness of these parts, out  of square of abutment  shoulders etc. impair

bearing performances and lead to premature failure is not always easy to establish and much time

can be lost in looking for the cause of failure.

2.2    Fits

          Good bearing performance  is  largely depending on adherence to the fits specified for the

two rings in the drawing. No one can give a straight answer to the questions of the “right” fit.

Indeed the selection of fits is determined by  the operating conditions of the machines and the

design characteristics of the bearing mounting. 

           Basically,  both  rings  should  be well supported over their seating areas and should

therefore be tight fits. This, however, can not be used in all cases, since other factors, such as

axial freedom of the floating bearing or easy mounting must also be taken into consideration.

The interference produced by tight fits expends  the inner ring and contracts the outer ring

resulting in a reduction of redial clearance. Hence the radial clearance should be adapted to the

fits. The shaft and housing tolerances should be checked. A too loose fit causes the ring to creep

on the shaft, which tends to damage both ring and shaft. It also affects the working accuracy of

the machine or causes premature raceway fatigue from poor support. On the other hand, to tight a

fit leads to a reduction in radial clearance, which might result in detrimental preload and hot

running of the bearing. The seating areas must, moreover, be checked for out of round in

addition to diameter. As the walls of the rolling bearings are relatively thin, possible poor

geometry of shaft or housing is transmitted to the raceways. Out of  round and deviation from

true parallelism and taper should not exceed half the specified diameter tolerance.        For Radial bearings with cylindrical bore of normal precision class.          (Tapered &

Cylindrical Bearings)

  Several factors like the type and magnitude of bearing load, temperature difference,

method of bearing mounting and dismounting should be taking into consideration while

selecting the proper fit.

  The recommended tolerances for shaft and housing for common applications are given

below as general guide lines:

Operating

Condition

Type of rotation  Load

Conditions

Type of fitting

Inner Ring  Outer Ring  Inner Ring  Outer Ring

  Rotation  Stationary  Rotating  inner

ring load

Stationary outer

ring load

Tight Fit  Loose Fit

  Stationary  Rotation

  Stationary  Rotation  Rotating  inner

ring load

Stationary outer

ring load

Tight Fit  Loose Fit

  Rotation  Stationary

Direct of

load

indeterminate

due to

variation of

direction

Rotating or

Stationary

Rotating or

Stationary

Direction of

load

indeterminate

Tight Fit  Tight Fit

TABLE – RECOMMENDED SEATING FITS FOR SHAFTS*

Load Conditions  Examples

Shaft Diameter (mm)

Shaft Tolerances  Cylindrical Roller & Taper

Roller Bearings

Rotating

Outer Ring

Load

Easy axial

displacement

of inner ring

on shaft

desirable

Wheels on Stationary

Axles

All Shaft Diameters

‘g6

Easy axial

displacement

of inner ring

on shaft 

unnecessary

Tension Pulleys and Rope

Sheaves

‘h6 Rotating

inner Ring

Load or

Direction of

Load

Indetermina

te

Light Load

(<0.06 C

(1)

)

Variable

Load

Electrical Appliances,

Pumps, Blowers,

Transport Vehicles,

Precision Machinery,

Machine Tools

< 40  ‘js6 (j6)

40 ~ 140  ‘k6

140 ~ 200  ‘m6

Normal

Loads (0.06

to 0.13 C(1)

)

General Bearing

Applications, Medium &

Large Motors, Turbines,

Pumps, Engine Main

Bearings, Gears,

Woodworking Machines

< 40  ‘k5~6

40 ~ 100  ‘m5~6

100 ~ 140  ‘m6

140 ~ 200  ‘n6

200 ~ 400  ‘p6

Heavy Loads

( >0.13 C(1)

)

Shock Loads

Railway Axle boxes,

Industrial Vehicles,

Traction Motors,

Construction Equipment,

Crushers

50 ~ 140  ‘n6

140 ~ 200  ‘p6

Over 200  ‘r6

Axial Loads Only    All Shaft Diameters  ‘js6(j6)

Note

(1)

  C represents the basic dynamic capacity of the bearing

*   Applicable only to solid steel shafts

TABLE – RECOMMENDED SEATING FITS FOR HOUSING*

Load Conditions  Examples

Housing

bore

Tolerance

s

Axial

Displaceme

nt of Outer

Ring

Solid

Housing

Rotating

Outer Ring

Load

Heavy Loads on

Bearing in Thin-

Walled Housing

Heavy Shock

Loads

Automotive Wheel

Hubs (Roller

Bearings) Crane

Travelling Wheels

P7

Impossible  Normal and Heavy

loads

Automotive Wheel

Hubs (Ball

Bearings) Vibrating

Screens

N7

Light and variable

load

Conveyor Rollers,

Rope Sheaves,

Tension Pulleys

M7

Direction

of Load

indetermin

te  a

Heavy shock loads  Traction Motors

Normal and Heavy

Loads

Pumps, Crankshaft

Main Bearings

Medium Large

Motors

K7

Generally

Impossible

Solid or

Split

Housings

Normal and Light

loads

JS7 (J7)  Possible

Rotating

Inner Ring

Load

Loads of all kinds

General Bearing

Application,

Railway Axle boxes

H7

Easy

Displaceme

nt Normal and Light

Loads

Plummer Blocks  H8

High temperature

rise of inner Ring

Through Shaft

Papers Dryers  G7

Solid

Housing

Accurate Running

Desirable under

Normal and Light

Loads

Grinding Spindle

Rear Ball Bearings,

High Speed

Centrifugal

Compressor Fixed

Bearings

JS6(J6)  Possible

Direction

of Load

indetermin

ate

Grinding Spindle

Front Ball Bearings,

High Speed

centrifugal

compressor fixed

Bearings

K6

Generally

Impossible

Rotating

Ringing

Load

Accurate Running

and High rigidity

Desirable under

Normal and Light

Loads

Cylindrical Roller

Bearings for

Machine Tool Main

Spindle

M6 / N6  Impossible

Minimum Noise is

required

Electrical Home

appliances

H6

Easily

Possible

* Applicable for cast iron and steel housings. For housings made of light alloy, the

interference should be tighter than those in this table.

3. BEARING HANDLING

 When handling bearings…….

DO  DON’T

1. Remove all outside dirt from housing

before exposing bearing

1. Don’t work in dirty surrounding.

2. Treat a used bearing as carefully as you

would a new one.

2. Don’t use dirty, brittle or chipped tools.

3. Work with clean tools in clean

surroundings.

3. Don’t use wooden mallets or work on

wooden bench tops.

4. Handle with clean, dry hands, or better,  4. Don’t handle with dirty, moist hands. clean canvas gloves.

5. Use clean solvents and flushing oils.  5. Don’t use gasoline containing

tetraethyl lead, as they may be injurious

to health.

6. Lay bearings out on clean newspaper.  6. Don’t spin uncleaned bearings.

7. Protect disassembled bearings from

rust and dirt.

7. Don’t spin bearings with compressed

air.

8. Use clean rags to wipe bearings.  8. Don’t use cotton waste or dirty cloth to

wipe bearings.

9. Keep bearings wrapped in oil proof

paper when not in use.

9. Don’t expose bearings to rust or dirt.

10. Clean inside of housing before

replacing bearing.

10. Don’t nick or scratch bearing

surfaces.

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About bearings007

i am a handsome boy living in Beijing Beijing JiaNengyuan International Trading Co., Ltd http://www.jnyzc.com .We supply bearings FAG NSK TIMKEN Bearings NTN KOYO INA and all kinds of tires including wind ,wind power, TBR, LTR, PCR, OTR etc. We have our brand "FEN RIVER" well developed and exported for years contact: kaiyang_000(at)yahoo.cn
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