Crankshaft 1

7/31/2019 Crankshaft 1

1/14

CRANKSHAFT

PROJECT BY:

SHWETA NARAYAN

MIT PUNE


2/14


3/14

PERFORMANCEREQUIREMENTS

Crankshafts require the followingcharacteristics:

1. High strength and stiffness to withstand the

high loads in modern engines, and to offeropportunities for downsizing and weightreduction

2. Resistance to fatigue in torsion and bending3. Low vibration

4. Resistance to wear in the bearing areas


4/14

MATERIAL REQUIREMENTS

ensurerepeatability ofmechanical properties

balances theconflicting benefits of low sulphur for fatigue

properties and high sulphur for improvedmachinability

produces consistentresponse to induction hardening

ensure consistent surface hardening throughnitriding

provide good fatigue resistance


5/14


6/14

COMMONLY USED MATERIALS

Sr.

N

o

IS

DESIGNATION

COMPOSITION

C% Mn % Other elements

%

1. 50C4 0.45-0.55 0.3-0.6 -

2. 55C4 0.5-0.6 0.3-0.6 -3. 55C8 0.5-0.6 0.6-0.9 -

4. 60C4 0.55-0.65 0.3-0.6 -

5. 37Mn2 0.32-O.42 1.3-1.7 Si - 0.1-0.35

6. 15Cr3Mo55 0.1-0.2 0.4-0.7 Si - 0.1-0.35

7. 25Cr3Mo55 0.2-0.3 0.4-0.7 Si - 0.1-0.35

Some other materials used for crankshafts are: 35Mn2Mo28, 35Mn2Mo45,

40Cr1Mo28, 40Ni2Cr1Mo28, 20Mn2, 27Mn2, 37Mn2, etc


7/14

The alloying elements typically used in thesemedium carbon steel alloys are:

Manganese

Chromium

Molybdenum

Nickel

Silicon

Cobalt etc

However, Carbon content is the maindeterminant of the ultimate strength andhardness to which the alloy can be heattreated.


8/14

CRANKSHAFT HEATTREATMENT

STEP 1: Transform the structure of the rough-

machined part into the face-centered-cubic

austenite crystalline structure (austenitize) by

heating the part in an oven until the

temperature throughout the part stabilizes in

the neighborhood of 1550F to 1650F.

STEP 2: The part is removed from the

heating oven and rapidly cooled

("quenched") to extract heat from the part

to transform austenitic structure into fine-

grained martensite. The desired martensitic

post-quench crystalline structure is the high-

strength, high-hardness, form of steel.


9/14

STEP 3: Cryogenic treatment, if used, directly follows

quenching. Scientific data from a recent NASA study

confirms that a properly-done cryo process transforms most

of the retained austenite to martensite, relaxes the

crystalline distortions, and produces helpful ("eta")particles at the grain boundaries. The resulting material is

almost fully martensitic, has reduced residual stress, more

homogeneous structure & hence greater fatigue strength.

STEP 4: The part is placed in a tempering oven and soaked

for a specific amount of time at a specific temperature (for

that alloy) in order to reduce the hardness to the desired

level, hence producing the desired strength, ductility,

impact resistance etc.

STEP 5: Nitriding is the process of diffusing elemental

nitrogen into the surface of a steel, producing iron nitrides

(FeNx). The part gains a high-strength, high hardness surface

with high wear resistance, and greatly improved fatigue

performance. These effects occur without the need for

quenching from the nitriding temperature.


10/14


11/14

CRANKSHAFTMANUFACTURING PROCESSES

A] FORGING:

A billet of suitable size is heated to theappropriate forging temperature i.e. 1950-2250F.

Then it is successively pounded or pressed intothe desired shape by squeezing between pairs ofdies under very high pressure.

These die sets have the concave negative form ofthe desired external shape. Complex shapes orextreme deformations often require more thanone set of dies.


12/14

Crankshaft manufactured by forging:


13/14

B] MACHINING:

Billet crankshafts are fully machined from around bar ("billet") of the selected material.

This method provides extreme flexibility of designand allows rapid alterations to a design in searchof optimal performance characteristics.

In addition to the fully-machined surfaces, thebillet process makes it much easier to locate thecounterweights and journal webs exactly wherethe designer wants them to be.

This process involves demanding machiningoperations, i.e. for counterweight shaping andundercutting, rifle-drilling main and rod journals,and drilling lubrication passages.


14/14

Crankshaft manufactured by machining:

Documents

Crankshaft 1