Engineering Data of Mounted Units - Part Two

3.3 Pressed Steel Housings

• 3.3.1 Tolerances for Pressed Steel Pillow Block Type Housings

Tolerances for pressed steel pillow block type housings are shown in Table 23.

Table 23.   (mm)

• 3.3.2 Tolerances for Pressed Round and Oval Flange Type Housings.

Tolerances for pressed steel round and oval flange type housings are shown in Table 24.

Table 24.    (mm)

4. Selection of Ball Bearing Units

The bearing size is usually selected according to the required bearing life and reliability under a specified type of load charged on the bearing.

The load applied to the bearing operating under a static or slow oscillating and rotating (n-10r/min)condition is defined as static load,while the load applied to the bearing operating under a speedy rotating(n>10r/min) condition is defined as dynamic load.

The  load  capacity  of  the  bearing  is  expressed  by  the  basic  dynamic  load  rating  and  basic  static  load rating which is shown in the bearing table. (B120~B141)

Usually, the important factor of the selection of a rolling bearing is life calculation,which refers to fatigue life of the bearing.When bearing is under proper usage,appropriate load  capacity,correct installation,good lubrication, the fatigue flake of rolling surface caused by alternating contact stress is the main element of bearing failure and this damage to the bearing can not be avoided completely.

Due to different application of each machinery and different requirement of the bearing,bearing could only be required to keep a certain kind of performance level during a specified period.After some time of working,factors like increased noise &vibration,declined precision caused by wear,grease aging will result in bearing failure or cannot satisfy the requirement of the machine.These type of life before bearing failure are called noise life,wear life and grease life.

Besides life,bearing failure may occur for the reason of burning,breakage,crack,seal failure etc which should be regarded as bearing malfunction.Bearing malfunction occurs because of improper selection of bearing, poor design of machinery,improper installation & usage and maintenance mistake which should be distinguished from bearing life.

4.1 Basic Load Rating and Life

Basic  dynamic  load  rating:The  basic  dynamic  load  rating  is  defined  as  the  constant  load  applied  to  a bearings with stationary outer rings that the inner rings can endure for a rating life of one million revolutions (106 rev.).

Life: The  life  of  a  rolling  bearing  is  defined  as  the  total  number  of  revolutions  which  the  bearing  is capable  of  enduring  before  the  first  evidence  of  fatigue  flaking  develops  on  any  one  of  the  rings  or rolling  elements.

Reliability: The reliability is the percentage of the bearing of a group of apparently identical bearings operating under identical conditions which can expect to attain or exceed a certain defined life.The reliability of an individual bearing is the probability of the bearing to attain or exceed a defined life.

Basic rating life L10: For a group of apparently identical rolling bearings operating under identical conditions, the basic rating life is defined as the total number of revolutions that 90%of the bearings can be expected to complete or exceed.

The basic rating life L10 estimation for ball bearings with different speeds and ratios is shown in page A27~A28.

4.2   Bearings Selection According to Basic Dynamic Load Rating

• 4.2.1   Basic Rating Life

The fatigue rating of deep groove ball bearings is calculated by following formula:

Where  L₁₀=basic rating life  (10⁶r)

Cr =basic dynamic load rating (N)

Pr =equivalent dynamic bearing load (N)

The basic dynamic load rating C is a hypothetical constant load with a fixed direction under which the bearing can attain basic rating life of one million revolutions.For radial bearing,the load refers to the radial load.

The equivalent dynamic bearing load P is a constant load with a fixed direction under which the bearing life is Identical to that of the bearing operating under actual load.

For a bearing operating with a constant rotation speed,the basic rating life can be expressed in terms of operating hours:

Where  L10h=basic  rating  life (h)

n=bearing operating speed of rotation (r/min)

For easier calculation,500 hours as base of rating life is taken, And the speed factor fn and the life factor fn is introduced

In this way, the formula is simplified to

The values of fn and fn can be found in Fig.1 by referring to the operation speed n and the anticipated bearing service life L10h.Then,with the radial load (or the equivalent dynamic bearing load ), the basic dynamic load rating can be determined.By this way,the bearing size can be determined according to the basic dynamic load rating value in the bearings Table.(B120~B141)

If the bearing operates under indeterminate loads and rotation speed,the following formula should be applied when calculating the bearing life:

Where Pm =mean equivalent dynamic bearing load (N)

P=equivalent dynamic bearing load (N)

N =total revolution numbers within one load changing cycle (r)

• 4.2.2   Anticipated Bearing Service Life

When selecting a bearing,one should usually predetermine an appropriate service life according to the relevant machine type,operating conditions and reliability requirement.Generally speaking,the anticipated bearing

service life can be determined by referring to the maintenance period of a machine.

• 4.2.3  Calculation Method of Equivalent Dynamic Bearing Load P

The basic equivalent dynamic bearing load is determined under a hypothetical condition.When calculating the

Bearing life,the actual load has to be converted into equivalent dynamic bearing load which is in conformity with

the load condition determining the equivalent dynamic load rating.

General equation for calculating the equivalent dynamic bearing load:

P=X F_r+Y F_a

Where P=equivalent dynamic bearing load (N)

Fr = actual radial load (N)

Fa = actual axial load (N)

X  = radial factor

Y  = axial factor

The values of X and Y are determined by the ratio between the applied axial load Fa and the basic static load rating C0. The axial load which the spherical outside surface bearings can carry is determined by the mounting method of the bearing on the shafts.

For the setscrews locking type or eccentric locking collar type bearings,if flexible shafts are applied and the setscrews are tightened enough(See Table 38 on page A25 for reference torque),the axial load Fa which the bearing can carry must not surpass 20% of the radial load Fr.

For the adapter sleeve locking type bearing, if the nuts are properly tightened, the axial load Fa can be maximum 15% to 20%of the  radial  load.

The values of radial and axial factors X and Y for spherical outside surface ball bearings can be obtained from the following table:

Table 25

When twist load is applied to the bearings,the equivalent dynamic bearing load is calculated by:

P_m=f_m·P

Where P_m=equivalent dynamic bearing load when considering twist load

F_m = twist load factor,which is defined as follows:

when the twist  load  is  small: fm=1.5

when the twist load is big: fm =2

When shocking load is applied to the bearings,the equivalent dynamic bearing load can be calculated by the following equation:

P_d=f_d·P

Where Pd=equivalent dynamic bearing load when considering shocking load

fd=shocking load factor,which is defined as follows:

When no shocking load or minor shocking load is applied:

fd=1~1.2

When adequate shocking load is applied;

fd=1.2~1.8

• 4.3   Example of bearing size selection

One ball bearing is to operate at a rotation speed of 1000 r/min under only a radial load of Fr=3000 N,with a basic rating life of at least 20000 hours,select the bearing size.

From the required rotation speed,it can be found that:

fn=0.322(Fig  1.shows  about  0.32)

From the required basic rating life (anticipated service life), at least 20000 hours,it can be found that:

fn=3.42(Fig    1.shows    about0.34)

Under only a radial load,i.e.,

P=Fr=3000(N)

Therefore,

A simplified way to calculate the bearing life can be applied by using Fig 2.

Life calculation chart

By connecting n(1000r/min)and the required basic rating life L10h(20000 hours)with a straight line,it can be

found that C/P value 10.6, As known,P=Fr=3000(N),thus the required basic dynamic load rating is:

C=10.6P

=10.6×3000=31800(N)

In this way, we can select the bearing from the bearing table (Please refer to page B120-B141)

4.4   Adjusted Rating Life Equation

The basic rating life L10 calculated with the bearing life calculation formula can be applied to calculate the rating life of bearing made of ordinary bearings steel (i.e.,bearing life with reliability of 90%.)

Due to more and more of machinery products demanding higher reliability and better quality steel,GB/T6391-1995(equaling to ISO281:1990)suggested an adjusted rating life calculation equation,i.e.,

L_na=a₁·a₂·a₃·L₁₀

For the deep groove ball bearings:

Where L_na=under specified material and lubricating conditions,bearing life with (100-n)% no breaking probability (i.e.reliability)

a₁=life adjustment factor for reliability(Table 26.)

a₂=life adjustment factor for materials (Table 27.)

a₃=life adjustment factor for operating conditions (Table 28.)

Table  26.    Life adjustment factors for reliability a1

Table  27.   Life  adjustment  factors  for  materials  a₂

Table  28.  Life  adjustment  factors  for  operating  conditions  a₃

5. Lubrication and Operating Temperature

5.1 Lubricants

The industry lithium based N0.2 lubricating grease defined in GB7324 "Lithium based lubricant grease"is

filled the spherical outside surface ball bearings during manufacturing. Its physical and chemical properties

are shown in table 29.

Table 29.

5.2 Operating Temperature.

The bearings usually operate below the temperature of 120℃(the measuring temperature of the outer ring is  100  ℃).Grease  life  reduction  has  to  be  taken  into  account  when  the  bearings  continue  to  operate  at  a temperature above 70 ℃.The lowest operating temperature should not be lower than -20 ℃ .

For higher or lower temperature application, please consult us for further information.

5.3 Relubricate Period

Under normal operating condition,the grease should conform to the life of the bearings. Relubricatable type bearing units must be periodically greased to assure long life.

The greasing interval is dependent on the bearing running speed,operating temperatures and ambient conditions.

The following table shows the standard relubrication period.

Table 30.

5.4 Grease Fittings

The grease nipples supplied by LDK bearing units are classified as A type(straight),B type(type 45°)and C type  (type 90°)made of brass,A3 steel.Grease nipple types for LDK standard bearing units are given in table 31.The  availability of the grease nipple dimensions and designation to each type are M6xl,M8x1,M10x1,1/14-28UNF, NPT1/8 and G1/8, as given in table 32. If any other grease fitting is required,the customers are required to specify  dimensions and designations.

Table 31.   Grease nipple types for LDK standard bearing units

Table 32.   Grease nipple dimensions and designations of applicable bearing units

6. Limiting Speed

The limiting speed of the ball bearing units are mainly determined by the fit between the bearings and the shafts.Under normal conditions,the fit for the setscrews type and eccentric locking collar type bearing unit is h7.h8 or h9 fit is applied when with light load and slow speed,while tighter fit j7 is applied when with heavy load and high speed.The shaft applied to the adapter sleeve bearing is h9 class,with IT5 class tolerances.

The speed ratings for ball bearing UD200(-2RS)series are the same as deep groove ball bearings which are shown in Table 33.

The limiting speeds for the ball bearing units with different fits are shown in Table 33.

Table 33.    Limiting Speed  (r/min)

Note: The h9/IT5 column fit for adapter sleeve type ball bearing units,and the rest j7~h9 column fit for the setscrews type and eccentric locking collar type ball bearing units.

7. Shaft Design

The ball bearing units are provided with two hexagonal setscrews 120° apart on one side of the inner rings. Under normal operating conditions, the inner rings are mounted on shafts by means of a loose fit to ensure convenience of installation.In this case, the dimensional accuracy of the shafts is shown in Table 34.

Table 34.  Dimensional accuracy of the shafts to be used in the cylindrical bore bearings(Loose fit)     (μm)

When the ball bearing units are used at a high speed or under heavy load,the inner rings of the ball bearings

should be mounted to the shafts by means of a tight fit.As shown in Table 35.

Table 35.   Dimensional accuracy of the shafts to be used in the cylindrical bore bearings(Tight fit)      (μm)

Some  bearings  can  be  installed  to  the  shafts  by  means  of adapter  sleeves. In  this  method, the  bearing bore is made of 1:12 taper and the corresponding tapered adapter sleeves are applied. This is a convenient method that can be used as the intermediate bearings of a long shaft. In this case,the dimensional accuracy of shafts is shown in Table 36.

Table 36.   Dimensional accuracy of shafts to be used in tapered bore bearings   (μm)

Most industrial fans operate at high speeds.The inner ring of the ball bearing units should be mounted to

the shafts by means of h5 or j5 fit, As shown in table 37.

Table 37.  Dimensional  accuracy  of  shafts for  HVAC  industry      (μm)

8.Mounting of Bearings on Shafts

8.1 Setscrews Locking Type Bearings

There are two setscrews  located  at two  places  on one side of the wide  inner  ring  120° apart with which the bearings can be mounted to the shafts.When mounting the bearings to the shafts,the torque shown in the table 38 is recommended to tighten the setscrews to shafts.

Table 38.   Proper tightening torque of setscrews

In  case  of  either  the  vibration  is  caused  to  the  bearing: or  1)the  alternating  movement  takes  place, 2)the  load applied to the  bearings  is  large, 3)The  shafts  rotation speed  is  rapid, it  is  desired  to  provide  with the filed seat or concave section at the part where the setscrews contact with the shafts. As shown in Fig.3.

Fig.3

• 8.2 Adapter Sleeves Locking Type Bearings

The  inner  ring  bore  of this type of bearings  has  a taper of  1:12.The  sleeves are  installed to  an arbitrary position.After the shake proof washers are inserted,the correct nuts tightening condition can be obtained if they are tightened enough by hand and then rotated by 2/5 to 3/5 revolution with a spanner.

After tightening the nuts,bend the shake proof washers within the slots. Otherwise,the nuts may loosen and creep may happen between the shaft and sleeves.

• 8.3 Eccentric Locking Collar Type Bearings

The eccentric part of the collars mates with the inner rings of the bearings which is made eccentric with the collars.When locked to the shafts by hand in direction of the shafts rotation,the eccentric locking collars tighten automatically to the shafts by force of working radial loads.Then,lock the setscrews provided on the collar to fix the eccentric collars to the shafts.

• 8.4 Mounting Method of Housings

The desired installation order is:first install the housing,then the shaft and bearing.The bearing units can be easily installed,in principle,at any place.However,in order to have a long

service life,it is desired that the mounting base is flat and rigid.

Fig.4.

The pillow block type and flange type housings are desired that the angle between the surface on which the housing is mounted and the shaft be maintained to a tolerance of±2°(Fig.5).

When there are shields or seals on the bearing housing,the slanted angle which is the angle between the central line of bearing bore and the central line of bearing housing bore is required within±1°

Fig.5.

• 8.5 Mounting Method of Take-up Units

The Take-up units are mounted on two parallel slides, bearing centers to be adjusted by adjustable bolts. The relevant parts dimensions are shown as Fig.6. Mounting tolerances are shown in Table 39 and Table 40.

Fig.6

Table   39.    (mm)

Table 40.   (mm)

9. Bearing Inserts-Life Estimation for Different Speeds and Cr/Pr Ratios

Table 41.

Life estimation for UC212 insert bearing with steady radial load Fr=3250 N at a speed of 1500 r/min.

The dynamic load rating Cr of the inset bearing UC212 from page B120 is 47680 N.

Since the bearing  is  not subject to axial load,the equivalent load  Pr = Fr x fd  = 3250N x1.2=3900  N  (When no shocking load or minor shocking load,shocking load factor fd =1~1.2)

Using the  load  ratio  tables, an approximate  life  can  be  obtained  by  locating  the  nearest  Cr/Pr value  in  the appropriate r/min column.

Under the n=1500 r/min column,the nearest Cr/Pr value is 12.2 with give an approximate life of 20000 hours.

10.WARRANTY  &  DISCLAIMER

10.1 Warranty

LDK warrants that the products well be free from defects in material and workmanship for one year from date of sale.LDK makes no other warranty of any kind,express or implied.LDK shall have no obligation under the foregoing warranty where the defect is the result of improper or abnormal use,negligence,vehicle accident,improper or incorrect installation or maintenance,nor when the product has been repaired or altered in anyway so as (in our judgment)to affect its performance. LDK's liability in the case of defective products subjects to the foregoing warranty shall be limited to the repair or replacement, at LDK's option,of the defective products.Except expressly provide herein,LDK shall have no liability (on account negligence or otherwise)for,or in connection with,defects or deficiencies in the products and in no event shall LDK be liable for any incidental,special or consequential damages or commercial loss (including loss revenue or profits)of buyer or any other person,arising out of the use,or inability to use the goods,or the failure or ineffectiveness of the goods.

10.2 DISCLAIMER

LDK reserves the right to substitute equal or stronger materials at their discretion.LDK reserves the right to change specifications and other information included in this catalog without notice.All information,data and dimension tables in this catalog have been carefully complied and thoroughly checked.However,no responsibility for errors or omissions can be assumed.

WARNING

Since the manufacturer is unable to determine all applications in which a part may be placed, it's the user's responsibility to determine the suitability of the part of its intended use.This is especially true where safety is a factor.Incorrect application or installation may result in property damage,bodily injury,or death.For technical assistance,please check with us.