Steam Turbine Bearings

8/22/2019 Steam Turbine Bearings

1/44

IMT 161/121Drive Systems

Chapter 2


2/44

Journals are the parts of a shaft that is

supported by bearings.

Journals are always machined smooth and

true.

2


3/44

3


4/44

4

Bearing support block


5/44

Guides and supports a rotating shaft.

Confines radial motion of a shaft.

Formed in a cylindrical shape or a portion

of a cylinder.

Can be anti-friction or plain bearings.

Can be made of many different materials.

5


6/44

Advantages compared to anti-friction bearings;

1. Less radial space required.

2. Quiet operation.

3. Less likely to be damaged by contamination. 4. Better resistance to overloading and shock

loads.

5. Lower original cost (generally).

6


7/44

Can be stored indefinitely without

deteriorating.

Require good lubrication practices.

7


8/448


9/44

When the shaft is rotating, a thin film of

lube prevents metal to metal contact

between the bearing surface and the shaft

surface.

Full film lubrication is when there is NO

metal to metal contact.

9


10/44

When the shaft is not turning, there will be

metal to metal contact.

As the shaft starts to turn, boundary

lubrication is achieved.

Boundary lubrication means there is some

separation of metal surfaces but metal to

metal contact occurs at high spots.

10


11/4411


12/44

Two types of lubricants are used with PJB.

1. Oil--the measure of an oils ability to flow

is viscosity. Slow flowing oils have a high

(thick) viscosity.

12


13/44

2. Grease--used where oil leakage may be

a problem. The hardness (or softness) of

a grease is expressed by the term

consistency.

13


14/44

Thick (hard) grease may not properly coat

a bearing surface, leaving bare spots.

Thin (soft) grease may run off a bearing

surface leaving no lubricant film.

14


15/44

Improper lubrication means: too much, not

enough or the wrong kind of lubricant.

Good lubrication means: the right amount

of the right type in the right place at the

right time.

15


16/44

Check the manufacturers specifications

for the right type and amount of lubricant.

16


17/44

17


18/44

PJB often have lubrication grooves on the

inside surfaces.

Grooves are not generally positioned in the

lower 1/3 of the bearing. This would

disrupt the full film lube.

Grooves are generally located in the areas

of least resistance.

18


19/44

Depth of oil grooves is generally 1/3 the

wall thickness.

Width of oil grooves is generally twice the

depth.

19


20/44

Grease grooves are usually wider and

deeper than oil grooves.

Edges of grooves are beveled to aid in

lube dispersion.

20


21/44

The simplest of groove patterns are axial

and circumferential.

Some grooves are variations/combinations

of axial and circumferential grooves.

21


22/44

22


23/44

23

Shaft

Bearing

inserts


24/44

24


25/44

Prevent contamination from entering the

bearing area.

Prevent lubrication leakage.

Not all bearings are sealed.

Can be made of felt or synthetic rubber.

Many styles, materials and designs.

25


26/44

26


27/44

27


28/44

28


29/44

Solid --one piece, can be called bushings

or sleeve bearings.

Bushings are generally thin walled & are

pressed into place.Sleeve bearings are usually thick walled.

Split--generally two equal sized pieces.

Multi-part--generally, 4 pieces.Partial--generally a half-bearing.

29


30/44

Matching halves--Must be used in pairs,

saw cut from a solid bearing.

Precision halves--are interchangeable

because they are made to close tolerances

30


31/44

31


32/44

32


33/44

Bronze. Hard drawn bronze.

Cast bronze.

The solid bronze sleeve bearing is

considered to be the most reliable of all

types of bearings available.

33


34/44

34


35/44

Split bearings are often made by liningsteel, cast iron or bronze shells with a lowfriction material.

Babbitt. Bimetal construction.

Precision inserts fit into accuratelymachined shells.

Tri-metal construction.

35


36/44

36

Drive

box

Molten

babbitt

Fire

Babbitt

No

Glasses


37/44

37


38/44

Crush and spread.

38


39/44

Crush is the extra amount of lining material

that makes each insert half slightly larger

than a half circle. Helps clamp the insert

into the bearing seat.Spread is the slight increase in diameter

of the insert across the open-end width,

requires the insert to be lightly forced intoplace.

39


40/44

40

Insert


41/44

Each type of bearing has advantages and

not all bearings are good for all

applications.

Criteria for choosing a bearing:1. Load.

2. Clearance.

3. How the bearing can be installed.4. Alignment stability.

41


42/44

5. Shaft size and speed

6. Lubrication method and type

7. Environment of equipment

8. Operating temperature9. Maintenance practices

10. Duty cycle

42


43/44

43


44/44

Steam Turbine Bearings

Documents

Transcript of Steam Turbine Bearings