This presentation contains a simplified explanation of tribology in Piston-Cylinder System. Description of working conditions, material requirement and wear types are provided.

1. TRIBOLOGICAL STUDY OF
PISTON
CR4102 – TRIBOLOGY OF MATERIALS
TA - ASSIGNMENT

2. INDEX
• Introduction
• Requirements for Piston
System
• Piston Rings
• Piston Ring Materials and
Coatings
• Cylinder Liner
• Types of Motion
• Function and Conditions of
Lubrication
• Wear Process of Piston-
Cylinder

3. INTRODUCTION
 Pistons have been used since the inception of
steam engines.
 After modifications and development, pistons are
used in various internal combustion engines.
 In modern ICE, pistons are the main components
which do the conversion of energy from fuel to
mechanical energy.
 Tribological study of piston includes the study of
interaction of surface of the piston rings and
cylinder lining.
 The engine oil that we most commonly know act as
lubricant in this tribological system.
 In this presentation, tribological analysis of piston
ring and cylinder lining and the effect of lubrication
is described .
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4. REQUIREMENTS FOR PISTON
SYSTEM
 Low friction
 Low wear of ring
 Low wear of cylinder liner
 Limiting flow of engine oil into combustion chamber
 Good sealing capability
 Resistance against mechanical and thermal fatigue,
chemical attacks and hot erosion
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5. PISTON RINGS
 A ring pack consists of 2-5 rings.
 2-4 compression rings.
 Compression rings act as gas seal between
piston and liner wall.
 Prevents combustion gases from going to
the crankcase.
 0-3 oil control rings.
 Distributes oil evenly onto the cylinder liner.
 Has groves to redirect scraped oil and apply
an even layer on cylinder liner and transport
back extra to the crankcase.
 Scraper rings can also be used to scrap off
the oil from the cylinder liner wall.
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6. PISTON RING MATERIALS AND COATINGS
 Grey cast iron
 Dry lubrication effect of graphite phase of the material if oil is less.
 Graphite phase acts as oil reservoir to provide oil at dry starts.
 Coatings
 Chromium
 Plasma sprayed molybdenum
 Metal composites
 Metal-ceramic composites
 PVD/CVD coated TiN and CrN (for high performance engines)
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7. CYLINDER LINER
 Piston and piston rings move in the cylinder, it is the
sliding surface against them.
 Can be made of cast iron containing phosphorus,
manganese, chromium, molybdenum, vanadium and
titanium as alloying elements, or steel and aluminium.
 Larger engines prefer cast iron cylinders.
 Liner surface can be coated with a chromium layer to
improve wear resistance.
 Grey cast iron gives the same benefits in the cylinder
as it does for piston rings.
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8. TYPES OF MOTION
Primary
Motion
Reciprocating
piston motion
Velocity and
acceleration
influences the
phenomenon
of ring lift.
Secondar
Motion
Sideways and
orientation
changes
Clearance between
the piston and
cylinder liner allows
this movement
according to forces
and moments acting
on it
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9. FRICTION AND CONDITIONS OF
LUBRICATION
Three types of friction can occur
 Dry friction
 Without lubrication
 Direct contact between the surfaces
 Shear occurs at points of contact, develops heat.
 Undesirable, not sustainable.
 Semi-dry or semi-liquid friction
 Occurs in the boundary lubrication
 Lubricant located in the recesses, layer is less than height of surface roughness.
 Liquid friction
 Proper lubrication
 Surfaces are completely separated by a layer of liquid lubricant
 Lubricant layer thickness should be higher than the roughness of sliding surfaces
 Hydrodynamic lubrication is achieved 9

10. WEAR PROCESS OF PISTON-CYLINDER
 System consists of cylinder liners, piston rings,
piston and structural clearance between the piston
and liner containing lubricating oil.
 The piston rings wear most, since it is a working
surface always in contact with the wall.
 Maximum cylinder liner wear occurs around the
area where it changes direction of movement.
 Wear of piston is much less than the wear of
piston rings and cylinder.
Wear of cylinder
Wear of piston
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11. WEAR PROCESS OF PISTON-CYLINDER
 Conditions affecting wear
 Gap between piston and cylinder casing
 Oil film thickness
 Working temperature
 Working conditions
 Properties of material contact surfaces
 There is expansion of metals as the temperature increases and hence the
working gap decreases, which increases pressure on the wall causing
higher wear.
 Abrasion due to lack of oil can occur when gap is more than optimum,
causing rapid wear.
Wear due to corroded materials
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12. THANK YOU
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