A brief introduction of tribo-systems definition. The relevant variables play a role on system variables like friction, wear and lubricity are listed. Examples on the most common tribo-systems are exposed.

1. Tribo-Systems Introduction
The slides are available at my profile page in
F. Xavier Borras
16th May 2016

2. 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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3. Tribological System
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B) Interacting Components
a. Geometry
b. Material proprieties
c. Dependencies
d. Surface roughness
e. Surface hardness
C) Lubricant
a. Material proprieties
b. Dependencies
c. Availability
d. Debris and contaminants
A) Mechanism
a. Relative motion
b. Relative velocity
c. Load
d. Environment

4. 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 .

5. 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.

6. 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.

7. Tribological System
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8. Static Seal
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Components geometry
Material Proprieties
- Housing
- Static seal
- Lubricant
- Sealed gases
Pressure difference Pa-Pb
Operating temperatures Ta , Tb , Tr , Ts
Surface Roughness Ss , Sr , Sh

9. 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 geometry
Material Proprieties
- Shaft
- Housing
- Lubricant

10. 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 geometry
Material Proprieties
- Collar
- Pad
- Babbitt
- Pad support
- Lubricant

11. 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 geometry
Material Proprieties
- Piston head
- Piston rings
- Piston rings energizers
- Cylinder
- Lubricant

12. 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 geometry
Material Proprieties
- Shaft
- Seal
- Reinforcement
- Garter spring
- Housing
- Lubricant

13. 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 geometry
Material Proprieties
- Shaft
- Bush
- Housing
- Lubricant

14. 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 geometry
Material Proprieties
- Follower
- Cam shaft
- Lubricant
- Housing

15. Reciprocating Shaft Seal
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Components geometry
Material 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

16. Conclusions
• System variables such as friction, wear and lubricity
need 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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