seminar piston ring 2

8/4/2019 Seminar Piston Ring 2

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[ PISTON RING]

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Rajarambapu Institute of Technology

Rajaramnagar, Sakharale, (415414)

SEMINAR ON: “PISTON RING”

SUBMITTED BY: VIDYASAGR CHAVAN

ROLL NO: 4721

BE MECHANICAL



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ABSTRACT

Advances in modern engine development are becoming more and more

challenging. Piston ring frictionl losses account for approximately 20% of the total

mechanical losess in modern internal combustion engine.A reduction in piston ring

friction would there fore result in nither efficiency,lower fule consumption and reduce

emission.the goal of this study is to develop low friction piston ring design to improve

engine efficiency , without affecting oil consumption,blowby,wear,cost.

To understand the fundamentals of piston ring behavior and in this way the

effects on blow-by and oil consumption, an in this work are the basic functions of the

piston rings, how piston ring manufacture, the design and the materials of the

components, mechanical and thermal loads on the rings, the contact pressure between

ring and liner, the sealing action and type of piston ring.



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INDEX

CHAPTER NO TITLE PAGE NO

1 Introduction 4

2 Function of piston ring 6

3 Ring terminology 9

4 Type of piston ring 14

5 Piston ring material 15

6 High Alloy Steel vs. Ductile Iron 18

7 piston ring forces and moments 19

8 piston ring design 21

9 friction reduction statergies 24



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CHAPTER 1

INTRODUCTION

In the early steam engines no piston rings were used. The temperatures and the

steam .pressures were not as high as the corresponding parameters in today’s internal

combustion engines, and the need for considering thermal expansions and clearances

was smaller. Increasing power demands required higher temperatures, which caused

stronger heat expansion of the piston material. This made it necessary to use a sealant

between the piston and the cylinder liner to allow a decrease in the clearance in cold

conditions, i.e. when the clearances were at their maximum. Keeping the clearance

between the piston and liner wall at a minimum considerably reduces the combustion

gas flow from the combustion chamber past the piston.

The first piston rings used in an engine had the sole task of sealing off the

combustion chamber, thus preventing the combustion gases from trailing down into

the crankcase. This development increased the effective pressure on the piston.

Ramsbottom and Miller were among the pioneers to investigate the behavior of the

piston rings in steam engines. Ramsbottom, in 1854, constructed a single-piece,

metallic piston ring. The free diameter of the ring was 10 per cent larger than the

diameter of the cylinder bore. When

fitted in a groove in a piston, the ring was pressed against the cylinder bore by its own

elasticity. Previous piston rings had consisted of multiple pieces and with springs to

provide an adequate sealing force against the cylinder bore. Miller, in 1862,

introduced a modification to the Ramsbottom ring. This modification consisted of

allowing the steam pressure to act on the backside of the ring, hence providing a

higher sealing force.



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This new solution enabled the use of more flexible rings, which conformed better to

the cylinder bore (Priest and Taylor, 2000). In the early days, the ring pack was

lubricated solely by splash lubrication; i.e. lubrication by the splashing of the rotating

crankshaft into the crankcase oil surface. Subsequently, when the combustion

conditions became even more demanding, i.e. with higher temperatures, pressures and

piston speeds, oil control rings were introduced. A proper lubricant film on the piston,

piston rings and liner wall was required in order to prevent damage. The oil control

rings were, and are, especially designed to appropriately distribute the oil on the

cylinder liner and to scrape off surplus oil to be returned to the crankcase.

But mechanical losses due to friction account for between 4and 15% of the

total energy consumed in modern internal combustion engine 40-50% of those total

mechanical losses occur in the power cylinder and half of the power cylinder friction

losses come from friction generated by the piston ring ,as a result a reduction in piston

ring friction has the potential to improve engine efficiency . lower fuel consumption

and reduction emission these are important objective for today’s engine

manufacturing .who are striving to improve engine performance while trying to meet

increasingly stringent emission standards.



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CHAPTER 2

FUNCTION OF PISTON RING

The selection of piston rings for an engine is fundamentally related to the engine

application. Various vehicles have varying requirements to satisfy which determine

the ring materials and designs. Street engines, competitive racing engines, sport

engines, and specifically fueled engines such as alcohols and nitrous oxides or even

compressed natural gases all may require specific differences in materials and design.

Piston rings serve more than one purpose: to contain and maintain cylinder and

combustion pressure, to prevent oil from getting into the combustion chamber with

the help of the valve guides and seals, and to aid in the control of thermal changes in

the engine.



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Top Ring

The top ring or fire ring is known as the compression ring and is expected to

seal against pressure losses from the combustion process. The compression ring

is also expected to maintain a high build up of pressure as the piston arrives at

the top of the stroke when at a predetermined location the combustible mixture

is ignited building up pressure to force the piston downward. The ability of the

piston ring to maintain this pressure is contingent on a couple of important

items. The ring gap is critical to this event and obviously burning gases do flow

through this gap. The ring gap is also critical to the function of the top ring as it

is related to its stability. In addition to this the fire ring is a barrier and transfers

a large portion of the heat through its contact with the cylinder wall.

Conventional Second Ring or Secondary Compression Ring

The second ring is probably the most misunderstood ring application of all the

rings used on a piston. With a conventional piston ring the ring design is similar

to the top ring. It also has a ring gap which allows hot gases to further penetrate

down the cylinder wall into the crankcase oil. This is known as blow-by and has

deleterious effects on the engine. Blow-by getting into the oil contaminates the oil

with carbon particles from the combustion process, raises the acid level, heats up the

oil and speeds up the oxidation process. This effectively begins the process of slowly

diminishing the lubrication ability of the oil and allows the carbon particles to wear

out all the parts which it is expected to lubricate. The second ring also serves as an oil

scraper ring to help minimize the oil above the second ring and as such compliments

both the compression ring and the oil ring.

Oil Control Rings

Oil control rings are designed along with the piston to effectively permit lubrication

of the rings, pistons, wrist pins and cylinder walls without oil migrating into the



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combustion process. Oil Rings also assist the thermal control of the piston bydirecting oil into the inside of the piston to help cool the piston dome. Total Seal

provides several types of oil rings as may be required including the popular three

piece ring consisting of an expander and two rails. The expander provides the tension

for the rails and are sold in more than one tension depending on the application. When

installing an expander, the expander joint is to be 90 degrees to the wrist pin and the

rails should be 1" apart centered on each side of the wrist pin end.



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CHAPTER 3

Ring Terminology

(A) Ring Land: The part of the piston between the ring grooves and above the top

ring that confines and supports the piston rings.

(B) Heat Dam: A narrow groove in the top land used in some pistons to help control

heat getting to the top ring. It actually fills with carbon in normal operation and limits

heat flow to the ring.

(C) Compression Height: The distance from the pin centerline to the top of the

piston.

(D) Ring Belt: The area on the piston between the top of the pin bore and the top of

the piston where the ring grooves are machined.

(E) Piston Head: The top area of the piston where combustion gas pressure is



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exerted.

(F) Piston Pin: Either press-fit or floating, the pin connects the rod to the piston with

bearing surface.

(G) Skirt: The part of the piston below the ring belt.

(H) Major Thrust Face: The side of the piston carrying the greatest thrust load.

(I) Minor Thrust Face: The side of the piston opposite the major thrust face.

(J) Piston Pin Bushing: If used, the bushing between the piston pin bore and the pin.



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(N) Scuff Band: One or more raised bands of piston material used in some piston

designs to reduce scuffing.

(O) Groove Depth: The distance between the back of the ring groove and the

cylinder wall with the piston centered.

(P) Groove Root Diameter: Piston diameter measured at the back of the groove.

May vary on the same piston between ring grooves.

(Q) Land Diameter: Diameter of a given land .Can sometimes vary by design from

top to bottom.

(R) Land clearance: The difference in diameter between the cylinder bore and the

land diameter. "R" is 1/2 the total.

(S) Skirt Clearance: The difference in diameter between the cylinder bore and skirt

diameter. "S" is 1/2 the total.

(T) Skirt Groove: A ring groove cut below the pin bore to carry an oil ring.

(U) Pin Bore Offset: The distance the pin bore is offset from center.

(V) Groove Spacer: Used on re-grooved pistons to return a ring groove to specs or in

some performance applications to facilitate the use of narrower ring sets than the

grooves were originally cut for.



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Ring Terms And Measurements

(A) Free gap: The ring end clearance when the ring is uncompressed.

(B) Compressed gap: Also known as ring gap, it is the end gap measured when the

ring is installed.

(C) Radial Wall Thickness: the distance between the inside and outside faces of the

ring wall

(D) Ring Diameter: Measured with the ring installed.

(E) Inside Diameter: Measured with the ring installed.

(F) Ring Sides: The top and bottom surfaces of the ring.

(G) Ring Face: The part of the ring in contact with the cylinder wall.

(H) Side Clearance: Clearance between the ring groove and the ring.

(J) Torsion Twist: A built-in imbalance between the way the upper and lower sides

compress that causes a twist in the ring when compressed. Used to sea both the ring in



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the groove and the ring to the cylinder wall.

(K) Back Clearance: Distance between the inside diameter of the ring and the

bottom of the ring groove with the ring installed

\\



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CHAPTER 4

TYPE OF PISTON RING



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CHAPTER 5

PISTON RING MATERIALS

Phosphate

Piston ring materials and coatings

A piston ring material is chosen to meet the demands set by the running

conditions.

Furthermore, the material should be resistant against damage even in emergency

conditions. Elasticity and corrosion resistance of the ring material is required. The

ring coating, if applied, needs to work well together with both the ring and the linermaterials, as well as with the lubricant. As one task of the rings is to conduct heat to

the liner wall, good thermal conductivity is required. Grey cast iron is used as the

main material for piston rings (Federal Mogul, 1998). From a tribological point of



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view, the 14 grey cast iron is beneficial, as a dry lubrication effect of the graphite

phase of the material can occur under conditions of oil starvation. Furthermore, the

graphite phase

can act as an oil reservoir that supplies oil at dry starts or similar conditions of oil

starvation (Glaeser, 1992). Coatings for rings are widely used. One example of such a

coating is chromium, which is used in abrasive and corrosive conditions where

running conditions are severe. Hard chrome plating is particularly relevant for the

compression ring. Piston ring surfaces are, in addition to chromium plating, thermally

(plasma) sprayed with molybdenum, metal composites, metal-ceramic composites or

ceramic composites, as a uniform coating or an inlay coating material (Mollenhauer,

1997).



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Experimental work with new powder compositions for thermal spraying has included

molybdenum-nickel-chromium alloys, chromium oxide (Cr2O3) with metallic

chromium binder, alumina-titania (Al2O3-TiO2), tungsten carbide (WC) with

metallic cobalt binder, MoSi2, CrC-NiCr (Dufrane, 1989, Radil, 2001). Hard

chromium layers can be improved by plasma spraying chromium ceramic on the ring

face, thus increasing the thermal load capacity. A dense chromium carbide coating,

produced by HVOF coating was found promising for piston ring applications in the

work by Rastegar and Richardson (Rastegar and Richardson, 1997).

Thin, hard coatings produced by PVD or CVD include coating compositions like

titanium nitride (TiN), chromium nitride (CrN); however coatings of this type are

currently used exclusively for small series production for competition engines and

selected production engines (Federal Mogul, 1998, Broszeit et al., 1999). Multilayer

Ti- TiN coatings have been experimentally deposited onto cast-iron piston rings, and

the coating is claimed to be more wear resistant than a chromium plated or phosphate

surface, particularly when the number of layers is high (Zhuo et al., 2000).

Haselkorn and Kelley have investigated coatings for use in low-heat rejection

engines. They conclude that high carbon iron-molybdenum blend and chrome-silica

composite applied by plasma spray, and further chrome nitride applied by low-

temperature arc vapour are coatings with properties that meet the demands in low-

heat rejection engines (Haselkorn and Kelley, 1992).

Surface coatings/treatments for the entire piston ring surface are based on phosphorus,

nitrides, ferro-oxides, copper and tin.



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CHAPTER 6

Alloy steel compression rings provide strength that last

Piston rings made of ductile or gray cast iron have been the material of choice

for years. Today, more engine builders than ever prefer steel over cast iron

compression rings. The reason is MAHLE Original steel ring technology.

Pioneered for heavy duty applications by the former Perfect Circle group, steel

compression rings now have a proven record of success in all types of vehicle

engines. Today’s engines put greater demand on piston rings than ever before:

operating temperatures, compression, stress and restrictive emission standards are

higher. All these factors created the need for a ring that is stronger, harder, seals better

and resists breakage and wear under load. The answer is steel - SAE-9254 high alloysteel. It’s another evolution in engine design and rebuilding.

High Alloy Steel vs. Ductile Iron

Physical Advantages:

„ Higher Tensile Strength

„ Higher Yield Strength

„ Greater Fatigue Resistance

„ Greater Hardness

„ Lower Ring Mass

Performance Benefits:

„ Better Stress Resistance

„ Reduced Groove Poundout

„ Less Side Wear

„ Superior Oil Economy

„ Superior Blow-by Control

„ Lower Friction

„ Longer Service Life

„ Better cylinder wall conformability

The use of steel in the design of a piston ring allows a reduction in the radial wall

thickness which will provide several benefits: First, the lighter ring will seal against

the bottom of the ring groove more effectively. Secondly, the smaller cross section,

permitted by the greater strength, improves the ability of the ring to conform better to

less than perfect cylinders. Both features mean that oil consumption is reduced.



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CHAPTER 7

Piston ring forces and moments

The piston ring secondary motions can be divided into piston ring motion in

the transverse direction, piston ring rotation, ring lift, and ring twist. These types of

motion result from different loads acting on the ring. Loads of this kind are inertia

loads arising from the piston acceleration and deceleration, oil film damping loads,

loads owing to the pressure difference across the ring, and friction loads from the

sliding contact between the ring and cylinder liner. The gas pressure above, below

and behind the ring produces resultant forces on the ring section . The inertia forces

acting on the piston rings, as well as those acting on the other reciprocating crank

mechanism components, change proportionally to the square of the engine speed .

The side loading of the piston against the cylinder wall is a result of the articulated

joint of the connecting rod . The effect of the clearance between the cylinder liner and

the piston on the piston and piston ring motion and to the ring forces is presented in

Section 5.1,. The shearing of the lubricating film, the sliding friction forces and the

contact pressure between the ring and the liner cause normal and tangential forces on

the ring face. The elastic distortion of the piston and liner can affect the effective

geometry of the ring face and cylinder liner contact, which causes a non-uniform

distribution of the contact pressure between the cylinder liner and the piston ring face

and can thus lead to increased blow-by and oil consumption .



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The piston pin is often offset from the piston centreline. This arrangement is

applied in order to avoid piston-generated noise or to reduce the thermal load on the

ring grooves . Haddad and Tjan have used a computer program to investigate the

influence of the offset of a piston pin, centre of gravity, and crank offset from the bore

centreline, on the mechanical efficiency and engine noise. The results presented

predict that, generally, the kinetic energy loss decreases when the piston pin offset is

set to the thrust side of the piston and the mechanical efficiency increases when the

piston pin offset is set to the minor thrust side of the piston. In the conclusions of their

work, the authors state that the piston pin offset is the most sensitive parameter

producing considerable variations in kinetic energy loss and mechanical efficiency.

Furthermore, the kinetic energy loss can be reduced, and the mechanical efficiency

can be increased by setting the piston pin offset to the thrust side of the piston centre .

Chittenden and Priest have presented the same kind of results. According to their

predictions, the contact situation will be worse and the friction losses will increase if

the piston pin offset is positioned towards the minor thrust side of the piston .



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CHAPTER 8

piston ring design

Number of piston ring:

There are no strict rules for deciding the number

of compression ring .the number of compression rings in automobile and aircraft

engines usually between 3to 4. In stationary diesel engine , 5to 7compresion ring are

used .in that number of oil ring 1 to 3.

Dimension of cross section : compression ring have rectangular cross

section as show in fig .

The radial width of the ring is give by

b=D√

where,

b=radial width of ring (mm)



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Pw=allowable radial pressure on cylinder wall(N/mm2)

t=permissible tensile stress for ring material (N/mm2)

Note

The radial wall pressure is usually taken from 0.025to 0.042 Mpa.

The permissible tensile stress for cast iron ring is taken from 85 to 110 N/mm2

The axial thickness of piston ring is given by,

h= (0.7*b) to b

where

h is axial thickness of the piston ring in (mm)

there is a limit on the minimum axial thickness .

it is given by

h min = (D/10z)

z=number of ring

it is preferred to provided more number of thin piston ring than a small number of

thick ring . it has the following advantage:

a) Thin ring s reduce frictional loss and wear of the surface .

b) More number of thin ring have better scaling action than a few thick ring .

c) Thin ring occupy less piston length.

d) More number of thin ring provide better heat transfer from the piston top to

the cylinder .

Gap between free ends : the diameter of a piston ring is slightly more than the

cylinder bore (d). a part of the ring is slightly cut diagonally as shown in fig.

during the assembly , the ring is compression diagonally and pass into the line

The gap G between the free ends of the ring is as following.

G= 3.5 b to 4b (before assembly )

G= 0.002dD to 0.004 D (after assembly in cylinder )



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Width of top land and ring land .:

The distance from the top of the piston to the first ring groove (h1) is called

top land . it is given by ,

h1= (th) to(1.2 th)

the distance between two consecutive ring grooves (h2) is called the width of

the ring groove and is given by.

h2=0.75h to h.



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CHAPTER 9

FRICTION REDUCTION STATEGIES

High pressure generated by a top ring along the liner in the region near TDC

of compression , the pressure term typical exceeds ring load due to tension by

at least an order of magnitude. therefore , design to reduce friction should be

focus on reduction contribution from the pressure difference acting on the

lower part of the top ring .since the pressure difference is controlled by

compression and combustion process. but most effective way to reduce top

ring friction in this region is by reducing the area exposed to high pressure

difference (B2).

At this point ,it should be noted that this design strategy is develop by

assuming there is no oil in the dry region .

Skewed barrel profile

The top ring can be manufactured in such a way that the physical

length of the region below the minimum point is reduces .this is generally

referred to as a skewed barrel profile design. Such a design clearly reduction

the area over which the high pressure difference act , which reduces the

friction generated between the top ring and the liner in this region .



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Top ring groove upward tilt

The high pressure generated in the cylinder due to compression and

combustion force the top ring to conform well to the lower groove flank

around TDC of compression , as the result , if upward groove tilt angle were

introduce in top ring groove , the point on the ring that is the closest to the

linear (minimum point ) would move down along the profile if the top ring

were conform to the upward tilt groove around TDC of compression .as would

be a case of skewed barrel profile design , this design would result in

reduction of area over which the high radial pressure act and reduction in

friction.



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Reduce top ring high :

One other method to reduce area over which the high radial pressure

difference act around the TDC compression would be to reduce the over all

axial height of top ring . this reduce the both B1&B2 and since the high



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pressure difference act over B2 , the friction could be reduced using this

design

Adverse effect of reduced friction designs

1. Reduce ring life .

2. Increase top ring groove wear :when the cylinder pressure rise sufficiently to

push the top ring downward to conform to groove , concentrated contact is fist

made at the outer diameter corner of the lower groove flak because of the

upward tilt angle .3. Increase oil consumption .

SUMMARY :

The piston ring is the largest single contribution to friction power loss in modern

internal combustion engine .in this study reduce friction forces , design of piston

ring ,material for piston ring and function of piston ring .



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Conclusion;

The primary role Piston ring pack is to maintain an effective gas seal betweenthe combustion chamber and the crankcase. The rings of the piston ring pack,

which together effectively form a labyrinth seal, achieve this by closely

conforming to their grooves in the piston and to the cylinder wall.

But mechanical losses due to friction account for between 4and 15% of the

total energy consumed in modern internal combustion engine 40-50% of those

total mechanical losses occur in the power cylinder and half of the power

cylinder friction losses come from friction generated by the piston ring ,

most effective way to reduce top ring friction in this region is by reducing the

area exposed to high pressure difference



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REFERENCES:

1.DESIGN OF MACHINE ELEMENTS BY V B BHANDARI (DESIGN OF IC ENGINE

COMPONENT)

2 .http://ezinearticles.com/?Piston-Ring-Failure---Causes-and-Prevention& id=2217996.

3.ISSN 1455 – 0865 (URL: http://www.inf.vtt.fi/pdf/ )

4. www.vtt.fi/inf/pdf/tiedotteet/2002/T2178.pdf

http://ezinearticles.com/?Piston-Ring-Failure---Causes-and-Prevention&%20id=2217996



http://www.inf.vtt.fi/pdf/





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