Transcript Lubrication Of Plain Bearings

Lubrication
Of
Plain Bearings
Plain Bearings are the
oldest Types of Bearings
l At first shafts and bushes were
made of wood. Later iron and
bronze were used.
l The lubrication was done with
olive oil or with a mixture of
oil and lime.
Roman building crane with pulley block
and human power drive. (500 B.C.)
Plain Bearings in modern machines
Plain bearings are indispensable in nowadays technology.
A car engine contains more than 90 % plain bearings.
friction value
µ
Friction in Plain Bearings
Stribeck-Kurve
Stribeck
Diagram
l rest position of the shaft,
metal / metal contact
(no lubrication between shaft and bearing)
number of revolutions/sliding speed
l with increasing speed an oil
film between bearing and
shaft is developed.
l it finally results in a total
separation of shaft and bush.
(The friction increases with higher speed (rpm)
in this sector of hydrodynamic friction)
boundary friction
mixed friction
hydrodynamic friction
Plain Bearing
If possible, the bushes, made out of a material with good
sliding abilities, will be put into a housing of cast iron with
good mechanical stability. The bushes remain replaceable.
Comparison of Plain
and Roller Bearings
plain
bearing
roller bearing
minimum diameter
ø 0,1 mm
ø 2,5 mm center
ø 6,0 mm external
maximum diameter
ø 600 mm
+
yes
ø 1250 mm
external
no
seat & bearing surface qualities
-
+
assembly handling
acceptable bearing clearance
true runnig exactness
noise
absorption abilities
effect of dirt
friction
lubrication
+
+
+
+
+
+
+
+
-
mounting dimension
separation possible
Determining Factors
for Plain Bearings
p x v – value
d
p = bearing load
v = sliding speed
D
D
B
Determining Factors
for Plain Bearings
bearing load:
F
pm = ———
DxB
N
[ mm²
]
pm = average surface pressure [N/mm2]
F = active force [N]
D = diameter of bearing [mm]
B = width of bearing [mm]
sliding speed:
D x π.x n
v = ———
100 x 60
[
m
S
]
v = sliding speed [m/s]
D = diameter of bearing [mm]
n = number of revolutions [rpm]
Guide for Plain Bearing materials
Material
bearing material based on tin
(white metal, babbit)
bearing material based on lead
cast bronze
bronze based on phosphate
red bronze / gun - metal
leaded bronze
cast iron
sintered metal
plastics
pm [ N/mm2]
v [ m/s]
5 to 15
10
20
15
30
15
35
1
4 to 10
0,5 to 3
3
5
50
7 to 8
10
1 to 3
7
2
Selection Guide for Lubricants
The viscosity of a lubricating oil
— in a grease the base oil viscosity —
is decisively for the right thickness of the
lubricating film (approx. 3-30µm) under consideration of the type of lubricant supply.
l
low sliding speed
high viscosity
l
high sliding speed
low viscosity
l
high bearing clearance
high viscosity
l
high load (bearing pressure)
higher viscosity
Lubricant supply
Depending on the demands, very
different ways of Lubrication may be used
l permanent oil–circulation lubrication
l interval lubrication
l for-life lubrication
l self-lubrication
Permanent oil circulation with
simultaneous heat dissipation
l car engines
l steam and water turbines
Standard is an oil pressure between 0,5 and 5 bar.
If higher pressure is used it is called forced-oil lubrication.
Interval Lubrication
Lubrication in determined time intervals with oil or grease
For-life Lubrication
(maintenance free)
l sintered bearings
(oil-impregnated)
l lubricant depot
(lubricant grooves/lubricant pockets)
Self Lubrication
Plain bearing materials based on
thermo-plastics with additives like MoS2
base material
typical range of application
polyamide (PA 12)
with graphite (40 to 50 weight %)
or MoS2 (30 weight %)
high heat conductivity,
electrically semi-conductive,
high thermal load capacity
polyamide (PI) with graphite and/or
MoS2
polytetrafluoroethylene (PTFE)
with graphite and/or MoS2
high heat bearing ability for use in
vacuum and aerospace industry
chemically stressed bearings and
higher temperatures
OKS Speciality Lubricants
for Plain Bearings with:
primary requirements
high loads
impact loads
vibrations
low or high number of revolutions
Stop-and-go operations
deepest temperatures
highest temperatures
variation in temperature
influence of moisture
corrosive influence
demand for long life lubrication
OKS Speciality Lubricants
for Plain Bearings with:
secondary requirements
regulations of the food industry
compatibility with plastics
Thank You
for
Your Attention