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