Design and Construction of a

Connecting RodBY

FAISAL BIN FARUK

DEPARTMENT OF MECHANICAL ENGINEERING

KHULNA UNIVERSITY OF ENGINEERING & TECHNOLOGY

KHULNA-9203, BANGLADESH

Outlines Objectives Introduction Manufacturing Process Comparison Design & Construction CAD & Real Models References

Objectives

Study of Connecting Rod To understand the function of the connecting rod CAD Design of Connecting Rod To construct a Connecting Rod using different

operations

Introduction What is a Connecting Rod ?

connecting rod or conrod connects the piston to the crank or crankshaft in a reciprocating piston engine.

What does it do ?

transmits the thrust of the piston to the crank shaft, and as the result the reciprocating motion of the piston is translated into rotational motion of the crank shaft

Introduction (Continued)

It consists of – 1. A pin – end (Small End)2. A shank section (Middle),

and3. An crank end (Big End)

How does it functions ?Connecting rods are

subjected to forces generated by mass and fuel combustion. These two forces results in axial load and bending stresses.

Introduction (Continued)

Capability

A connecting rod must be capable of transmitting axial

tension (Pull), axial compression (Push), and bending stress

caused by the thrust of the piston and by centrifugal force.

Manufacturing Process

Casting: Cast in sand

Small little seam on both sides of the parting edge.

Used in Speed Motor. For example 3.8L Buick engine.

Cap in pin-end is fastened with bolts only.

Maximum rpm 6500. [1]

Fig : Cast Connecting rod

Manufacturing Process (Contd.)

Forging : Thick seam on both sides (Left material)

of the parting edge left from the forging dies in forging process.

Used in speed motors like small-block Chevrolet engine.

I-beam cross section.

Bolt-Nut assembly.

Used in engines of rpm range about 5500-6800 or further. [1]

Fig : Forged Connecting rod

Manufacturing Process (Contd.)

Forged Billet rods: Machined from a solid piece of steel.

No parting edge, 100 % machined.

H-beam cross section.

Bolts are screwed to hold the cap on.

Strongest con-rods. 1200 hp engine [1]

Manufacturing Process (Contd.)

Sintered connecting rods: Powdered metal pressed together and

then put into an oven where it is sintered that means granuals are melted together and forms the rod.

Parting edge where cap and the rod meet is fractured.

Each cap and each rod is unique with itself.

Used in engine of rpm 7000 rpm. [1]

Comparison Oldest Technology :

Cast Con-rods. Used in old engines. Newest Technology :

Sintered Con-rods. Quick acceleration, longer use time. Used in modern engines. Strongest Con-rod :

H-Beam forged connecting rods. Heavy duty engines.

Design & Construction

Fig : Analysis of Buckling Load

For a connecting rod equally strong in Buckling about the both axes,

WB (X axis) = WB (Y axis)

=

Or, Kxx2 = 4 kyy

2

Or, Ixx = 4 Iyy (As, I = Ak2)

In actual practice Ixx is kept slightly lower than 4Iyy

3 < 3.5 WB = ...for calculation WB = Max. gas force × Factor of safety (5~6)

Design & Construction(contd.)Example 32.3: Design a connecting rod for an I.C. engine running at 1800 r.p.m. and developing a maximum pressure of 3.15 N/mm2 . The diameter of the piston is 100 mm ; mass of the reciprocating parts per cylinder 2.25 kg; length of connecting rod 380 mm; stroke of piston 190 mm and compression ratio 6 : 1. Take a factor of safety of 6 for the design. Take length to diameter ratio for big end bearing as 1.3 and small end bearing as 2 and the corresponding bearing pressures as 10 N/mm2 and 15 N/mm2 . The density of material of the rod may be taken as 8000 kg/m3 and the allowable stress in the bolts as 60 N/mm2 and in cap as 80 N/mm2 . The rod is to be of I-section for which you can choose your own proportions. [2]

Fig : Cross Section

Solution :

B = 4tH = 5tA = 2 (4 t × t) + (3t × t) = 11t2 (Figure a)

𝐼 𝑥𝑥=112

[ 4 𝑡 (5 𝑡 )3−3 𝑡 (3 𝑡 )3 ]=𝟒𝟏𝟗𝟏𝟐

𝒕𝟒

Design & Construction(contd.)

𝐼 𝑦𝑦=2×112× 𝑡 (4 𝑡 )3+ 1

12×3 𝑡× 𝑡 3=

𝟏𝟑𝟏𝟏𝟐

𝒕𝟒

As, so the proprtion chosen is satisfactory.

Now, force on connecting rod = maximum gas pressure on piston

Buckling Load,

Length of crank,

Fig : Cross Section

Design & Construction(contd.)

Length of the connecting rod, so, for both ends hinged,

Rankine’s formula ,

148440=320×11𝑡 2

1+17500 ( 3801.78 𝑡 )2 Or, 𝑡 4−42.2𝑡 2−257.3=0

Taking positive value ,

So, thickness of flange is 7mmNow

Width stays constant but depth varies .....at crank end & at pin end

Design & Construction(contd.)

Fig : Right side view and Front View

Fig : Cross section

B = 7 mmH = 11 mmA = 2(2x7) + (7x4) mm2 = 56 mm2

(Middle)

= 95mm dC = 25mm, dP = 8.5 mm tC = 6mm, tP = 4.75mm

Design & Construction(contd.)

Material Aluminium 2014-O Alloy

Property Value Units

Elastic Modulas 72.4-73.1 GPa

Fatigue Strenth 89.6 MPa

Density 2.8 g/cc

Tensile Strength

186 MPa

Brinnel Hardness

45

Machinability 30%

Melting Point 507-638 Degree Celsius

Ingredient Percentage by Weight

Al 90.4-95

Cu 3.9-5

Fe 0.7

Si 0.5-1.2

Mn 0.4-1.2

Cr Max 0.1

Mg 0.2-0.8

[3]

CAD Model

Theoretical

Real Model

Experimental

Referrences

[1] Chen, N., L. Han, W. Zhang and X. Hao, 2006. "Enhancing Mechanical Properties and Avoiding Cracks by Simulation of Quenching Connecting Rod". Material Letters, 61: 3021-3024.

[2] Khurmi R.S., Gupta J.K., “A Textbook of Machine Design”,14th edition 2005, Eurasia Publishing House.

[3] Boyer H.E. and Gall T.L., "Metals Handbook", Eds., American Society for Metals, Materials Park, OH, 1985

Thank You