Lubrication Of Plain Bearings

Plain Bearings are the oldest Types of Bearings Roman building crane with pulley block and human power drive. (500 B.C.) 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.

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 l rest position of the shaft, metal / metal contact (no lubrication between shaft and bearing) 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) Stribeck-Kurve number of revolutions/sliding speed Stribeck Diagram friction value µ 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

Determining Factors for Plain Bearings p = bearing load v = sliding speed p x v – value d D B D

Determining Factors for Plain Bearings bearing load: p m = ——— F D x B p m = average surface pressure [N/mm 2 ] F = active force [N] D = diameter of bearing [mm] B = width of bearing [mm] N mm² [ ] sliding speed: v = ——— D x x n 100 x 60 π.π. v = sliding speed [m/s] D = diameter of bearing [mm] n = number of revolutions [rpm] [ ] mSmS

Guide for Plain Bearing materials

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. 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 MoS 2

OKS Speciality Lubricants for 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 Lubricants for Plain Bearings with: compatibility with plastics regulations of the food industry secondary requirements

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