lubrication of plain bearings. plain bearings are the oldest types of bearings roman building crane...
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Lubrication
Of
Plain Bearings
Plain Bearings are theoldest Types of Bearings
Roman building crane with pulley block and human power drive. (500 B.C.)
At first shafts and bushes were made of wood. Later iron and bronze were used.
The lubrication was done with olive oil or with a mixture of oil and lime.
Plain Bearings in modern machines
Plain bearings are indispensable in nowadays technology.
A car engine contains more than 90 % plain bearings.
Friction in Plain Bearings
rest position of the shaft, metal / metal contact (no lubrication between shaft and bearing)
with increasing speed an oil film between bearing and shaft is developed.
it finally results in a total separation of shaft and bush.
(The friction increases with higher speed (rpm) in this sector of hydrodynamic friction)
Stribeck-Kurve
number of revolutions/sliding speed
Stribeck Diagram
fric
tion
valu
eµ
boundary friction mixed friction hydrodynamic friction
Plain Bearing
If possible, the bushes, made out of a material with goodsliding abilities, will be put into a housing of cast iron with
good mechanical stability. The bushes remain replaceable.
Comparison of Plainand Roller Bearings
plain bearing
roller bearing
minimum diameter ø 0,1 mmø 2,5 mm center
ø 6,0 mm external
maximum diameter ø 600 mmø 1250 mm
externalmounting dimension + -separation possible yes no
seat & bearing surface qualities - +
assembly handling + -acceptable bearing clearance + -true runnig exactness + -noise + -absorption abilities + -effect of dirt + -friction - +lubrication + -
Determining Factorsfor Plain Bearings
p = bearing loadv = sliding speed
p x v – value
d D
BD
Determining Factorsfor Plain Bearings
bearing load: pm = ———FD x B
pm = average surface pressure [N/mm2]F = active force [N]D = diameter of bearing [mm]B = width of bearing [mm]
Nmm²[ ]
sliding speed: v = ———D x x n100 x 60
π.
v = sliding speed [m/s]D = diameter of bearing [mm]n = number of revolutions [rpm]
[ ]mS
Guide for Plain Bearing materials
Material pm [ N/mm2] v [ m/s]
bearing material based on tin (white metal, babbit)
5 to 15 10
bearing material based on lead 20 3cast bronze 15 5bronze based on phosphate 30 50red bronze / gun - metal 15 7 to 8leaded bronze 35 10cast iron 1 1 to 3sintered metal 4 to 10 7plastics 0,5 to 3 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 con-
sideration of the type of lubricant supply.
low sliding speed high viscosity
high sliding speed low viscosity
high bearing clearance high viscosity
high load (bearing pressure) higher viscosity
Lubricant supply
Depending on the demands, very different ways of Lubrication may be used
permanent oil–circulation lubrication
interval lubrication
for-life lubrication
self-lubrication
Permanent oil circulation withsimultaneous heat dissipation
car engines
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)
sintered bearings (oil-impregnated)
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
high heat bearing ability for use in vacuum and aerospace industry
polytetrafluoroethylene (PTFE) with graphite and/or MoS2
chemically stressed bearings and higher temperatures
OKS Speciality Lubricantsfor Plain Bearings with:
primary requirements
highest temperatures
deepest temperatures
low or high number of revolutions
high loads
influence of moisture
corrosive influence
demand for long life lubrication
Stop-and-go operations
impact loads
vibrations
variation in temperature
OKS Speciality Lubricantsfor Plain Bearings with:
compatibility with plastics
regulations of the food industry
secondary requirements
Thank You
for
Your Attention
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