Tribo-Systems Introduction

The slides are available at my profile page in

F. Xavier Borras16th May 2016

Tribological System

• What is the Coefficient of Friction of Stainless Steel?

– The question makes no sense since friction is a system variable. Friction is not a material propriety.

– The whole tribological system needs to be approached to address friction, wear or lubricity.

• How to define a tribology system? Which variables are involved?

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Tribological System

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B) Interacting Components

a. Geometry b. Material proprietiesc. Dependenciesd. Surface roughnesse. Surface hardness

C) Lubricant

a. Material proprietiesb. Dependenciesc. Availabilityd. Debris and contaminants

A) Mechanism

a. Relative motionb. Relative velocityc. Loadd. Environment

Tribological System

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Tribology generally works on the µm and MPa range.

It is advisable to start with a kinematic and loading analysis of the mechanism .

Tribological System

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A material can perform in an absolutely different way when running under different operating conditions. Thoroughly defining the operating range for the application is a must.

Tribological System

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The viscosity of a lubricant highly decreases with temperature. Over speeding a mechanism, for example, can cause the thinning of the oil layer leading to the destruction of the components.

Tribological System

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Static Seal

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Components geometryMaterial Proprieties- Housing- Static seal- Lubricant- Sealed gases

Pressure difference Pa-Pb

Operating temperatures Ta , Tb , Tr , Ts

Surface Roughness Ss , Sr , Sh

Journal Bearing

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Shaft Rotational Speed v

Hydrostatic pressure Pa

Shaft-bush clearance ε

Operating temperatures Ta , Th , Ts

Shaft load Fshaft

Surface roughness Ss , Sh

Contaminants/Debris

Components geometryMaterial Proprieties- Shaft- Housing- Lubricant

Thrust Bearing

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Shaft Rotational Speed n

Shaft load Fshaft

Number of pads

Pivot point/line/springs location

Hydrostatic pressure Pa

Operating temperatures Ta, Tb , Th , Ts

Surface roughness Ss , Sr , Sh

Contaminants/Debris

Components geometryMaterial Proprieties- Collar- Pad- Babbitt- Pad support- Lubricant

Piston Rings

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Piston stroke

Number of piston rings

Reciprocating speed v

Pressure difference Pa-Pb

Shaft clearance ε

Operating temperatures Ta, Tb, Th, Ts

Rings energizers Fspring

Surface Roughness Ss, Sr, Sh

Contaminants/Debris

Components geometryMaterial Proprieties- Piston head- Piston rings- Piston rings energizers- Cylinder- Lubricant

Rotary Lip Seal

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Rotary peripheral speed nDπ/60

Pressure difference Pa-Pb

Garter spring force Fspring

Shaft eccentricity ε

Operating temperatures Ta , Tb , Th , Ts

Surface Roughness Ss , Sr , Sh

Contaminants/Debris

Components geometryMaterial Proprieties- Shaft- Seal- Reinforcement- Garter spring- Housing- Lubricant

Ball Bearing

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Shaft Rotational Speed v

Hydrostatic pressure Pa

Shaft-bush clearance ε

Shaft load Fshaft

Operating temperatures Ta , Th , Ts, Tb

Surface roughness Ss , Sr , Sh , Sb

Contaminants/Debris

Components geometryMaterial Proprieties- Shaft- Bush- Housing- Lubricant

Cam Follower

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Rotary peripheral speed

Spring force Fspring

Cam-Follower profile ε

Hydrostatic pressure Pa

Operating temperatures Ta , Th , Ts

Surface Roughness Ss , Sh

Contaminants/Debris

Components geometryMaterial Proprieties- Follower- Cam shaft- Lubricant- Housing

Reciprocating Shaft Seal

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Components geometryMaterial Proprieties- Housing- Shaft- Lubricant

Piston stroke

Reciprocating speed v

Pressure difference Pa-Pb

Spring force Fspring

Shaft clearance ε

Operating temperatures Ta , Tb , Th , Ts

Surface Roughness Ss , Sr , Sh

Conclusions

• System variables such as friction, wear and lubricityneed the study of the whole tribo-system for its correct assessment.

• There is a high dependency between the material proprieties and the running conditions which generally does not allow to independently study particular aspects of the tribo-system.

• Novel measurement techniques and computational models are nowadays developed allowing to predict the overall performance.

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