Lecture 24 som 16.04.2021

BIBIN CHIDAMBARANATHAN
TORSION
OF
SPRINGS
4/16
1 BIBIN.C / ASSOCIATE PROFESSOR / MECHANICAL ENGINEERING / RMK COLLEGE OF ENGINEERING AND TECHNOLOGY 4/16

Definition of spring
• A spring is an elastic object used to exert a force or a torque and, at the same
time, to store mechanical energy. Springs are elastic bodies (generally of metals)
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.
• The energy expended in deforming the spring is stored in it and can be
recovered when the spring returns to its original shape.
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Definition of spring
• Generally, the amount of the shape change is directly related to the amount of force
exerted.
• However, if too large a force is applied, then the spring will permanently deform
and never return to its original shape.
• The force can be a linear push or pull, or it can be radial, acting similarly to a
rubber band around a roll of drawings.
• The torque can be used to cause a rotation, for example, to provide a
counterbalance force for a machine element pivoting on a hinge.
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Objectives of spring
• The objectives of a spring when used as a machine member are as follows.
• Cushioning, absorbing, or controlling of energy due to shock and vibration.
Examples are car springs, railway buffers, vibration dampers etc.
• Control of motion – A spring control the motion by maintaining contact between
two elements.
• In a cam and a follower arrangement, widely used in numerous applications, a
spring maintains contact between the two elements in this way primarily controls
the motion.
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• Creation of the necessary pressure in a friction device (a brake or a clutch).
• For example, in a car a brake or a clutch is used for controlling the car motion.
• A spring system keep the brake in disengaged position until applied to stop the car.
• The clutch has also got a spring system (single springs or multiple springs) which
engages and disengages the engine with the transmission system.
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• Restoration of a machine part to its normal position when the applied force is
withdrawn.
• A typical example is a governor for turbine speed control.
• A governor system uses a spring controlled valve to regulate flow of fluid through
the turbine, thereby controlling the turbine speed.
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• Storing of energy
• An example of storing of energy by springs is winding clocks.
• The clock has spiral type of spring which is wound to coil and then the stored
energy helps gradual recoil of the spring when in operation.
• Measuring forces
• Examples are spring balances, and gauges etc.
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Classification of springs
There are several methods used for the classification of the springs.
• Springs can be classified depending on how the load force is applied to them. As per
this classification method there are the following types of springs.
• Tension/extension springs
• These springs are designed to operate with a tension load and hence the spring
stretches as the load is applied to it.
• Compression springs
• These springs are designed to operate with a compression load and hence the
spring becomes shorter as the load is applied to it.
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• Torsion spring
• As compared to the tension and compression springs where the applied load is an
axial force, the load applied to a torsion spring is a torque or twisting force, and the
end of the spring rotates through an angle as the load is applied.
• Constant spring
• In this type of spring, the supported load remains the same throughout deflection
cycle.
• Variable spring
• In this type of spring the resistance of the coil to load varies during the
compression.
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• The springs can also be classified according to their shape. As per this
classification method the springs are of the following type.
• Coil springs - A coil spring is made of a coil or helix of wire.
• Flat springs - A flat spring is made of a flat or conical shaped piece of metal.
• Machined springs - This type of spring is produced by machining a steel
bar with a lathe and/or milling operation rather than coiling wire. Since it is
machined, the spring may incorporate features in addition to the elastic
element. Machined springs can be made in the typical load cases of
compression/extension, torsion, etc.
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• The most common types of spring are as follows.
• Cantilever spring – This is a type of spring which is fixed only at one end.
• Hairspring or balance spring – It is a delicate spiral torsion spring used in
watches and galvanometers, and places where electricity is to be carried to
partially rotating devices such as steering wheels without hindering the rotation.
• Leaf spring – It is a flat spring used in vehicle suspensions, electrical switches, and
bows.
• V spring – V springs are used in antique firearm mechanisms such as the wheel
lock, flint lock, and percussion cap locks.
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• Coil spring – It is also known as helical spring. It is made by winding a wire around a
cylinder or a cone. In case wire is wound on a cone then the spring is called a conical
spring. Coil springs are usually of two types. The first type consists of a compression
spring which is designed to become shorter when loaded. Their turns (loops) are not
touching in the unloaded position, and they need no attachment points. A volute spring is
also a compression spring in the form of a cone, designed so that under compression the
coils are not forced against each other, thus permitting longer travel. The second type
consists of tension or extension springs which are designed to become longer under load.
Their turns (loops) are normally touching in the unloaded position, and they have a hook,
eye or some other means of attachment at each end.
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• The other types of springs which are commonly used are as given below.
• Belleville washer or Belleville spring – It is a disc shaped spring normally used
to apply tension to a bolt. It is used in the initiation mechanism of pressure
activated landmines.
• Constant force spring – It consists of a tightly rolled ribbon which exerts a nearly
constant force as it is unrolled.
• Gas spring – The spring action is provided by a volume of gas which is
compressed.
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• Ideal spring – In reality this spring does not exist. It is the notional spring used in
physics and it has no weight, mass, or damping losses.
• Negator spring – It is a thin metal band slightly concave in cross-section. When
coiled it adopts a flat cross-section but when unrolled it returns to its former curve,
thus producing a constant force throughout the displacement and negating any
tendency to re-wind. The most common application is the retracting steel tape
rule.
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• Progressive rate coil spring – It is a coil spring with a variable rate, usually
achieved by having unequal pitch so that when the spring is compressed one or
more coils rests against its neighbour.
• Rubber band – It is a tension spring where energy is stored by stretching the
material.
• Spring washer – It is used to apply a constant tensile force along the axis of a
fastener.
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• Torsion spring – it is a spring which is designed to be twisted rather than
compressed or extended. This spring is used in torsion bar vehicle
suspension systems.
• Wave spring – It is a thin spring washer into which waves have been pressed.
• Mainspring – it is a spiral ribbon shaped spring used as a power source in
watches, clocks, music boxes, wind-up toys, and mechanically powered flash
lights.
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What is Mechanical Spring?
• A Mechanical Spring is a device that can also be defined as an elastic or
resilient member, whose main function is to deflect under the action of load
and recovers it’s original shape when the load is removed. It also used for
storing energy.
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Types of Mechanical Springs
• Helical Spring
• Conical and volute Spring
• Torsion Spring
• Laminated or leaf Spring
• Disc or Belleville Spring
• Special Purpose Spring
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Helical Spring
• Helical spring is one type of torsion spring which is made of wire coiled, form as a helix shape. It is
one of the most used mechanical spring.
• The cross-section of the wire by which Helical Spring is made can be circular, rectangle or square in
shape.
• In this type of spring, the spring can store the energy when it is pressed and released the store
energy later on, as well as it can withstand the pulling force between two objects. This type of
spring can also resist or absorb sudden jerk or impact.
• In practice, if you see the suspension of a motorcycle or a high-end railway coach, there you can see
helical springs are used. Other than this, helical springs are used for carrying, pulling or
compressing of any loads.
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Properties of Helical Springs
• It is durable.
• Higher dimension stability
• High tensile strength
• Corrosion-resistant.
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Types of Helical Spring
• Closed Coil Helical Spring
• Open Coil Helical Spring
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Open Coil Helical Spring
• As the name denotes open coil, that means the distance
between two consecutive turns is more (Helix angle is
greater than 10 degree). These springs are used to resist
compression.
• Generally, open-coil helical springs are used in Automobile,
Motorcycles and even V/Vs assembly of IC Engine.
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Closed Coil Helical Spring
• In closed coil helical spring, the distance between each turn or coil is pretty less, or
you can say the pitch distance is too small. The angle of the helix of closed coil
helical spring is less than 10 degree.
• This type of spring is used to resist the elongation or twisting. The stiffness of
closed coil helical spring is generally higher than any other spring, for this reason,
it is used in heavy-duty applications.
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Conical and Volute Spring
• This is generally one type of compression spring, conical in
shape. When the compression load applies to the spring,
then the coils are slide over each other, make it short length
and compact in shape than other helical springs.
• This type of springs is used in electrical or electronics
equipment, garden secateurs etc. In practical life, you can see
this type of spring in the remote or clock’s battery section.
• This type of spring is also known as tapered spring.
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Torsion Springs
• Torsion spring is one kind of close coil helical
spring. In this type of spring, when twisting occurs
then the spring stored the energy inside it, and
when the twisting force lifted it push back to its
actual position. When it is twisted than a torque
generated at the opposite direction of the twisting
force, which helps the spring to back its actual
shape.
• Torsion springs are widely used in the garage door,
clips, mouse catcher, torsion bar suspension, etc.
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Leaf springs
• It is an arc-shaped spring, made of metal strips one after another and held
together by using nut and bolt or clamp.
• It is widely used as a suspension system of commercial vehicle such as bus, truck,
etc.
• This spring is capable to withstand large forces in small areas.
• It is generally made of Steel, Graphite epoxy, Carbon epoxy.
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Disc Springs
• Disc or Belleville spring is a conical shape washers held
together by bolt or tube which has the characteristic of
spring.
• It is non-flat, conical shell spring which generally loads
axially.
• This type of spring can exert constant pressure throughout
the object and also provides a high load in small areas.
• It can be used where thermal expansion or contraction
happens rapidly.
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Special Purpose Springs
• Air spring, gas spring, extension Spring, grater spring, etc. falls under the category of
Special Purpose Springs. As the name denotes “Special Purpose” that means these
springs are not widely used, but still in some cases like, vice-grip pliers, carburetors,
trampolines, washing devices, even in toys we use extension spring.
• Nowadays we use air spring, where the air is used to pump the bladder which helps
us to absorb the shock and vibration completely. So these types of springs are falls
under the category of special-purpose springs
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The Function of Spring
The Function of Springs are:
• To absorb the shock or vibration as in-car springs, railway buffers, etc.
• To measure the forces in a spring balance.
• Apply forces in brakes and clutches to stop the vehicles.
• Spring is also used to store the energy as in clocks, toys, etc.
• Spring can control the motion of cams and followers by maintaining contact
between two elements.
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Commonly used spring materials
• Hard-drawn wire – Cold drawn steel wires are the cheapest materials used for the
making of springs. Springs made from cold steel wires are generally used for low
stress and static loads. This material is not suitable for springs to be used at sub-
zero temperatures and at temperatures above 120 deg C.
• High carbon blue tempered and polished spring steel- It is a standard material
for conventional springs. It is a low cost material and best suited for applications
that have a protected environment, as carbon steel corrodes if not lubricated or
atmospherically sealed.
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• Oil tempered wire – Oil tempered wires are cold drawn, quenched, and tempered.
These spring steel wires are used for general purpose springs. Springs made from
these wires are not suitable for fatigue or sudden loads as well as at sub-zero
temperatures and at temperatures above 180 deg C.
• Alloy steels containing chromium and vanadium – Springs made from alloy
steels containing chromium and vanadium are used for high stress conditions and
at high temperature up to 220 deg C. These springs are good for fatigue resistance
and long endurance for shock and impact loads.
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• Alloy steels containing chromium and silicon – This material can be used for
making of highly stressed springs. The material is suitable for springs requiring for
long life and shock loading. Springs made from these alloy steels are suitable for
temperature up to 250 deg C.
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• Piano wire – Piano wire is also known music wire and is made from tempered
high carbon steel. Piano wire is normally the most widely used material for
springs. This spring material is generally used for small springs. Springs made
from this material are the toughest and have highest tensile strength. These
springs can withstand repeated loading at high stresses. However, springs made
from piano wires cannot be used at sub-zero temperatures as well as
temperatures above 120 deg C.
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• Stainless steel – These are alloy steels containing at least 10 % chromium and
offer much improved corrosion resistance over plain or alloy steels. Springs made
from stainless steels stain and corrode very slowly in severe environments such as
seawater. These springs have improved resistance to high temperature and can be
used for temperatures up to 288 deg C. Springs made from stainless steels of 18-8
composition can be used for sub-zero temperatures.
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• Spring materials other than steels – Usually phosphor bronze and brass are used
as spring materials. Springs made from these materials have good corrosion
resistance and electrical conductivity. They are normally used for contacts in
electrical switches. Springs made from brass can be used at sub-zero temperatures.
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• Hard drawn wire: These are general purpose spring, where we need low-
temperature resistance and low stress we can use these types of spring material.
• Stainless Steel: Nowadays stainless steel is widely used in making of spring.
• Phosphor Bronze: These types of spring are used in Electrical industry due to the
material have good electrical conductivity and good resistance to corrosion.
• Chrome Silicon: This type of spring can be used in high temperature up to 250-
degree celsius.
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• Chrome Vanadium: These types of spring have good thermal conductivity up to
220-degree Celsius and also has good fatigue resistance.
• Graphite epoxy: It is used in high strength spring such as leaf spring.
• Carbon epoxy: It is made of carbon fibre, and have the ability to bear a high
load, this material is also used in high strength applications like automobile, and
locomotive.
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Applications of Spring
Springs are used in the following areas:
• Automobile suspension system.
• In cam-follower assembly, we use spring too.
• Spring is used in railway boogies.
• We used spring in the clutch, brake, and valve assembly to exert force on these
objects.
• Springs are used in garage doors, gardening equipment, door lock, and many other
household accessories.
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Advantages of Spring
These are the following advantages of spring:
• Produce a good cushioning effect.
• Spring has a good shock-absorbing ability.
• It has high durability.
• Spring has the ability of stored energy inside it.
• It is easy to design and cheaper to produce.
• Spring is a maintenance-free device.
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Disadvantages of Spring
A Spring has this following disadvantage
• Day by day its loose it shape and stability.
• Sometimes when the axial load of the spring is increased, it produce the buckling
phenomena.
• If spring is broken then it is hard to repair.
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MAXIMUM BENDING
STRESS DEVELOPED
IN THE PLATE OF
LEAF SPRING
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CENTRAL
DEFLECTION
OF
LEAF SPRING
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PROBLEM
ON
LEAF SPRING
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MAXIMUM SHEAR
STRESS INDUCED IN
A WIRE
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EXPRESSION FOR
STIFFNESS
OF
SPRING
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DEFLECTION OF A
CLOSELY COILED
HELICAL SPRING
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EXPRESSION FOR
STIFFNESS OF
SPRING
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Thank You
4/16

Lecture 24 som 16.04.2021

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Lecture 24 som 16.04.2021