Engine materials for camshaft and crankshaft

Materials and technology for automotive engine

Catania, 06/07/2012, A.Manicone

Material and technology for Automotive engine:

brief overview

o The camshaft

o The crankshaft


The camshaft


The camshaft - 1

The valve operating mechanism transforms

rotation of thecrankshaft into reciprocating

motion in the valves.

The valves protrude intothe combustion chamber and

are pushed back by the reactive force of the valve

spring.

Ωcamshaft= Ωcrankshaft/2 - Ωcamshaft high: contact pressure is reduced by the inertia of the valve lifter (oil is providing hydrodynamic lubrication);- Ωcamshaft low: contact pressure is highest and lubrication most challenging.



Machining, dimension accuracy, clearance, roughness Friction condition

1. Lubrication2. Contact3. Foreign objectLubricating oil

condition

Wear of sliding portion1. Rugged surface due to wear2. Adhesive wear3. Fatigue wear4. Corrosive wear

Flaking (scagliatura)

Pitting (corrosione per vaiolatura)

The camshaft - 2

• It is very important to choose an appropriate combination of materials.

• The torque from the crankshaft drives the camshaft: it must have high torsional rigidity.



The camshaft - 3

Chill hardening cannot be used where the gap between the cam lobes is narrow because of the difficulty in using the chiller, so forged camshafts are used.

Tough martensite is more resistant to pitting than the chill microstructure.



The camshaft - 4

• Finishing – boring and grinding

• E.g.: Hydroforming

• ASSEMBLING



The crankshaft



The crankshaft - 1

The crankshaft converts reciprocative motion to rotational motion.

Two types: • the monolithic type• the assembled type



The crankshaft - 2

Carbon steel

Alloyed steel

Micro Alloyed steel

Typical materials • nodular cast iron: for high-volume,

low-load production.

• forged steel: for fuel-efficient engines requiring a high power-to-displacement ratio.

Note: Included lead or MnS particles significantly function as a chip breaker and a solid lubricant and increase machinability.

• less expensive

• lower rigidity: abnormal vibrations (resonance)

• more expensive

• increases in rigidity of more than 10%• reduces noise levels and harshness• makes possible a careful design



The crankshaft - 3


• Static: combustion pressure, inertial forces of the piston and con-rod, bearing load and drive torque.

• Dynamic: The vibration causes dynamic stress. If it occurs at the resonating frequency, the deformation will be very high and will instantly rupture the crankshaft.

STRESS on Crankshaft

Fatigue fracture of a carbon steel S50C crankshaft

HIGH STATIC AND DYNAMIC RIGIDITY:

- increasing the crankpin diameter (increasing weight)

- using forged steel

- Surface-hardening methods



Cicli alla rottura, Nf

105104 106 107

σa

σL

Tipici acciai

Leghe di alluminio

Principi (macro)

Fatigue behaviour: principles and survey

Wöhler [1860]

* Legge di Basquin: σa = σf’ (2Nf)b

Ampiezza tensione applicata

*

Dipende da:

•Tipo di materiale • Concentrazione di tensioni

• Contenuto di inclusioni e impurezze

• Trattamento termico superficiale

• Tensione media e tipo di sollecitazione

Curva tipica per acciai

Vita infinita

Vita finita


The crankshaft - 4


HOT FORGING PROCESS (for a four-stroke crankshaft)

• The coarse structure is broke down and is replaced, as recrystallisation proceeds, by one which is of relatively fine grain

• Impuritires are redistribuited in a fibrous form

• Introduction of compressive residual stresses


The crankshaft - 5


SURFACE HARDENING (carburizing, nitring, carbonitring and nitrocarburizing):• CARBURIZING

Pitting observed at a crankpin surface

O: origins

S: a few beachmarks

B: arrest lines

R: ratchet marks


The crankshaft - 6


SURFACE HARDENING (carburizing, nitring, carbonitring and nitrocarburizing):• CARBURIZING

Compressive residual stress generated by carburizing


Fe

C

Cr

Mn

Siti di adsorbimento

Acetilene

H2

Steel

A. Manicone

The crankshaft - 7


Modern carburizing technology: Acetylene Vacuum Carburizing- AvaC


Avac - Adsorbimento (T>Taustenitizzazione)

Fe

C

Cr

Mn


Acetilene

H2

A. Manicone

The crankshaft - 7


Steel


Avac - Decomposizione in radicali

Fe

C

Cr

Mn


Acetilene

H2

A. Manicone

The crankshaft - 7


Steel


Fe

C

Cr

Mn


Acetilene

H2

Avac - Inizio cementazione (T>Taustenitizzazione)

A. Manicone

The crankshaft - 7


Steel



Fe

C

Cr

Mn


Acetilene

H2

A. Manicone

The crankshaft - 7


Steel



Fe

C

Cr

Mn


Acetilene

H2

Steel

A. Manicone

The crankshaft - 7



Fe

C

Cr

Mn


Acetilene

H2

Diffusione nell‘acciaio (T>Taustenitizzazione)

A. Manicone

The crankshaft - 7


Steel


Saturazione

Fe

C

Cr

Mn


Acetilene

H2

A. Manicone

The crankshaft - 7


Steel


The crankshaft - 7


SURFACE HARDENING (carburizing, nitring, carbonitring and nitrocarburizing):

• NITRING: NH3

decomposes at the steel surface to catalytically generate elemental nitrogen, which diffuses into the material. The nitrogen expands the iron lattice and also forms hard compounds (the nitrides Fe4N and Fe3N) with iron atoms.

Nitridable steel reaches the necessary hardness by forming stable nitrides (Al, Cr, V…)

• NITROCARBURIZING, CARBONITRURING

• higher hardness surface, • but lower toughness

• INDUCTION HARDENING


The crankshaft - 8


RECENT TRENDS: Micro alloyed steel, via plasma ion nitring

Precipitation hardening is the main method for increasing strength at thecooling stage after hot forging.

Micro-alloyed steel contains a small amount of V, which dissolves in the matrix during hot forging above 1,200 °C. During air cooling, the dissolved V combines with carbon and nitrogen to precipitate as vanadium carbide and nitride at around 900 °C.

the vanadiumcarbide and nitride will be more finely dispersed.


The crankshaft - 9


Manufacturing process

• Trade-off: machinability-fatigue resistance

• Surface roughness

For low and medium loaded bearings: Ra = 15 microinch max. Rz = 60 microinch max.

For highly loaded bearings: Ra = 10 microinch max. Rz = 30 microinch max.


The crankshaft - 10


Conclusions: Methods to strengthen crankshafts



Thanks for attention

Material and technology for Automotive engine:

brief overview


Engine materials for camshaft and crankshaft

Automotive

crankshaft materials

automotive engine catania

automotive enginecatania

automotive enginea

stroke crankshaft

s50c crankshaft

modern carburizing technology

expensive materials