ME 1001 – BASIC MECHANICAL ENGINEERING. CONTENTS 1.Unit I: Machine elements I (springs and cams)...
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Transcript of ME 1001 – BASIC MECHANICAL ENGINEERING. CONTENTS 1.Unit I: Machine elements I (springs and cams)...
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ME 1001 – BASIC MECHANICAL ENGINEERING
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CONTENTS
1. Unit I: Machine elements I (springs and cams)
2. Unit II: Machine elements II ( Gears, Belt drives, chain drives,
simple problems)
3. Unit III: Energy (Renewable and non Renewable, Power
generation, EC & IC engines, simple problems)
4. Unit IV: Manufacturing process I (sheet metal work, welding,
soldering and brazing)
5. Unit V: Manufacturing process II (Lathe practices, drilling,
simple problems)
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TEXTBOOKS & REFERENCES
Prabhu.T.J, Jai Ganesh. V, and Jebaraj. S, "Basic
Mechanical Engineering", SciTech Publications Chennai,
2000.
Nag.P.K, "Power Plant Engineering", Tata McGraw-Hill,
New Delhi, 2008.
Rattan.S.S, "Theory of Machines", Tata McGraw-Hill, New
Delhi, 2010.
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OBJECTIVE & INSTRUCTIONAL OBJECTIVES
OBJECTIVE:
To familiarize with the basics of Mechanical Engineering.
INSTRUCTIONAL OBJECTIVES :
1. To familiarize with the basic machine elements
2. To familiarize with the sources of Energy and Power generation
3. To familiarize with the various manufacturing processes
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MACHINE ELEMENTS - ISprings:• Springs are elastic bodies (generally metal) that can be twisted,
pulled, or stretched by some force. They can return to their original
shape when the force is released.
• In other words it is also termed as a resilient member.
• Spring act as a flexible joint in between two parts or bodies.
Objectives of spring:
1. Cushioning , absorbing , or controlling of energy due to
shock and vibration.
2. Control of motion.
3. Measuring forces.
4. Storing of energy.
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SPRING MATERIALS
1) Hard drawn high carbon steel. 9) Chrome vanadium.
2) Oil tempered high carbon steel. 10) Chrome silicon.
3) Stainless steel
4) Copper or nickel based alloys.
5) Phosphor bronze.
6) Inconel.
7) Monel
8) Titanium.
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SPRING MATERIALS
Limited number of materials and alloys are suitable for use as springs.
Ideal spring material would have high ultimate strength, high yield
point, and low modulus of elasticity in order to provide maximum
energy storage (area under elastic portion of stress-strain curve).
For dynamically loaded springs, fatigue strength properties of material
are of primary importance.
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CLASSIFICATION OF SPRINGS
1) Helical springs:
a) Tension helical spring
b) Compression helical spring
c) Torsion spring
d) Spiral spring
2) Leaf springs or laminated or semi elliptical springs
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HELICAL SPRING CLASSIFICATION
1) Open coil helical spring
2) Closed coil helical spring
3) Torsion spring
4) Spiral spring
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HELICAL SPRINGS
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TORQUE IN COMPRESSION SPRINGS
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SPRING RATE
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SHEAR STRESS IN SPRING
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WAHL STRESS FACTOR K
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Number of coils
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TORSION SPRING1. It is also a form of helical spring but it rotates about an axis to
create load.
2. It releases the load in an arc around the axis.
3. Mainly used for torque transmission
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SPIRAL SPRING
1. It is made of a band of steel wrapped around itself a number of
times to create a geometric shape.
2. It releases power when it unwinds.
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τ=shear stress, andI = Polar moment of inertia = π d⁴ 32It may be noted that each section of the coil is under torsion but there are small bending and shearing stress which being small are usually neglected.Shear stress τ:From torsion equation, T = Cθ = τ ; T = τ I l r I rOr, T= τI = τ×πd⁴×2 = τ. π d³ r 32 d 16
P
PP
P
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τ = 16T πd³τ = 16WR (T=WR) πd³Deflection, δ:Again, T = Cθ IP l θ= Tl = WR×2πRn×32 = 64WR²n CIP C ×πd⁴ Cd⁴ δ = R×θ δ = 64WR³n Cd⁴
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Energy stored, U:U= 1 . T . Θ = 1 . W.R.δ = 1 . W.δ (δ=Rθ) 2 2 R 2 i.e. U= 1 Wδ 2
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LEAF OR LAMINATED SPRING OR SEMI ELLIPTICAL SPRING
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LEAF SPRING (CONTD..)
Also called as a semi-elliptical spring, as it takes the form of
a slender arc shaped length of spring steel of rectangular
cross section.
In Heavy vehicles, leaves are stacked one upon the other to
ensure rigidity and strength.
It provides dampness and springing function.
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NIPPING IN LEAF SPRING?
Because of the difference in the leaf length,
different stress will be there at each leaf. To
compensate the stress level, prestressing is to
be done.
Prestressing is achieved by bending the leaves
to different radius of curvature before they are
assembled with the center clip.
The radius of curvature decreases with shorter
leaves.
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NIPPING IN LEAF SPRING (CONTD..)
The extra intail gap found between the extra full length leaf and
graduated length leaf is called as nip. Such prestressing achieved
by a difference in the radius of curvature is known as nipping.
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NOMENCLATURE OF COMPRESSION HELICAL SPRING
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TERMINOLOGIES OF A SPRING
1) Free length
2) Pitch
3) Endurance limit
4) Active coils
5) Solid length
6) Pitch angle
7) Initial tension
8) Spring index
9) Spring rate
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COMPRESSION SPRING - TERMINOLOGIES
SOLID LENGTH:
When the compression spring is compressed until the
coils come in contact with each other the spring is said
to be solid. The solid length of a spring is the product
of total number of coils and the diameter of the wire.
• LS=n’*d• n’- total number of coils d- diameter of the wire
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COMPRESSION SPRING - TERMINOLOGIES
FREE LENGTH:
It is the length of the spring in the free or unloaded
condition. It is equal to the solid length plus the
maximum deflection or compression of the spring
and the clearance between the adjacent coils.
• LF=n’*d+δmax+0.15 δmax
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COMPRESSION SPRING - TERMINOLOGIES
PITCH LENGTH:
The pitch of the coil is defined as the axial
distance between adjacent coil in uncompressed
state.
Pitch length=free length/(n’-1)
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SPRINGS IN SERIES
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SPRINGS IN PARALLEL
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COMBINED SYSTEM(BOTH SERIES AND PARALLEL)
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WHEN SPRINGS ARE IN PARALLEL
[UNSYMMETRICAL DISPLACEMENT(Δ1≠Δ2)]
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APPLICATIONS OF SPRINGS
Brakes Clutches Watches and Toys Vehicle and machine foundation Railway carriages, motor cars, scooters, motorcycles