Bantalan (Bearing)

Dedison Gasni, Ph.D

Bearings are broadly categorized into

two types

1. Fluid Film Bearings :

a. Sliding contact type

b. Journal bearing

c. Thrust bearingc. Thrust bearing

d. Slider bearing

2. Rolling Contact Bearings :

a. Ball Bearing

b. Roller Bearings

Comparison of bearing frictions

Journal Bearing

Stribeck Curve

Rolling contact bearing

Rolling contact bearings are also called anti-friction bearing due to its low friction characteristics.

These bearings are used for radial load, thrust load and

combination of thrust and radial load.

These bearings are extensively used due to its relatively lower price, being almost maintenance free and for its operational

ease.

However, friction increases at high speeds for rolling contact bearings and it may be noisy while running.

Ball bearing

A typical arrangement

Single row-radial ball bearing : Four

Series

• Extra light (100 Series)

• Light (200 Series)

• Medium (300 Series)

• Heavy (400 Series)• Heavy (400 Series)

307 : Medium series 35 mm bore

Roller Bearings

Rolling contact bearing selection

• Rating life:

Rating life is defined as the life of a group of

apparently identical ball or roller bearings, in apparently identical ball or roller bearings, in

number of revolutions or hours, rotating at a

given speed, so that 90% of the bearings will

complete or exceed before any indication of

failure occur.

Definition of life of rolling contact

bearing

Bearing load

If two groups of identical bearings are tested

under loads P1 and P2 for respective lives of L1

and L2 , then,

n = speed, rpm and L = life, hours

Basic load rating

It is that load which a group of apparently

identical bearings can withstand for a rating

life of one million revolutions.

Equivalent radial load

The load rating of a bearing is given for radial

loads only. Therefore, if a bearing is subjected

to both axial and radial load, then an quivalent

radial load is estimated as,radial load is estimated as,

Nilai untuk X dan Y

Fa/izD2 X Y

25 0.56 2.30

50 1.99

100 1.71

150 1.55

200 1.45

300 1.31

500 1.15

750 1.04

1.000 1.00

Shock and Impact Factors

Type of Load C1

Constant or steady 1.0

Light Shocks 1.5

Moderate Shocks 2.0

Heavy Shocks 3.0 and up

Example #1

For the 207 bearing (C = 4,440 lb) , find the

radial load P for a rating life of 500 hr, at 1,500

rpm.

Solution: 106C3=N P 3Solution: 106C3=N1P13

Example #2

Suppose the bearing in example 1 carries a

combined load of 400 lb radially and 300 lb

axially at 1,200 rpm. The outer ring rotates,

and the bearing is subjected to moderate and the bearing is subjected to moderate

shock. Find the rating life of this bearing in

hours.

Example #3

What change in the loading of ball bearing will

cause the expected life to be doubled?

Design for Variable Loading

Ball bearings frequently operate under conditions of variableload and speed.

Suppose P1, P2,….. are loads on the bearing for successiveintervals of the work cycle.

Let N be the life of the bearing, revolution, if operatedLet N1 be the life of the bearing, revolution, if operatedexclusively at the constant load P1.

Let there be N1’ applications of load P1.

Then N1’/N1 represents the proportion of the life consumed inthis portion of cycle.

The sum of these proportions represents the

total life of the bearing or unity. Then

Let Ne be the life of the bearing under the

combined loading. Let N ’=α N where ααααcombined loading. Let N1’=α1Ne where αααα1

represents the proportion of the total life,

consumed under load P1.

from

Example #1

A ball bearing is to operate on the following

work cycle.

Radial load of 1,400 lb at 200 rpm for 25% of the time

Radial load of 2,000 lb at 500 rpm for 20% of the timeRadial load of 2,000 lb at 500 rpm for 20% of the time

Radial load of 800 lb at 400 rpm for 55% of the time

The inner ring rotates ; loads are steady. Find the minimum value

of the basic rating load C for a suitable bearing for this

application if the required life is 7 years at 4 hr per day.

Solution : The equation will be applied on the basis of a work

cycle of 1 min.Interval,min rpm Interval,rev

P1 = 1,400 lb 0.25 200 50

P2 = 2,000 lb 0.20 500 100

P3 = 800 lb 0.55 400 220

1.00 370 rpm

A working year is assumed to consist of 250 days

Ne = 7 x 250 x 4 x 60 x 370 = 155,400,000

Example #2

A 306 radial ball bearing with inner ring rotation

has a 10-sec work cycle as follows.

For 2 sec For 8 sec

F = 800 lb F = 600 lb

Find the rating life of this bearing in hours and in

years of 250 working days of 2 hr each.

Fr = 800 lb Fr = 600 lb

Fa = 400 lb Fa = 0

n = 900 rpm n = 1,200 rpm

Light shock Steady load

Solution : the work cycle of 10 sec.

306, Z = 8, D = 0.5 in, and C = 5,120 lb

Y = 1.45

Pe = 1.5(0.56 x 1 x 800 + 1.45 x 400)

= 1,540 lb, equivalent radial load

No. of revolutions = 2 x 900/60 = 30, in 2 sec

For 8 sec: Pe = Fr = 600 lb

No. of revolutions = 8 x 1,200/60 = 160, in 8 sec

For 10 sec:

No. of revolutions = 30 + 160 = 190

Then: Then: