Spring

Springs are mechanical devices of flat wire or round wire that can store potential energy because of its elasticity in a spiral coil used to compress, extend, pull, or rotate using an applied force.  It is a mechanical device or component that is designed to store and release mechanical energy when subjected to external forces or deformations.  Springs are widely used in various applications to provide elasticity, flexibility, and resilience to mechanical systems.

• Tags: Strain and Stress Spring

The primary function of a spring is to return to its original shape or position after being compressed, stretched, or twisted.  This characteristic is commonly referred to as its springiness or resilience.  Springs work based on Hooke's law, which states that the force required to deform an elastic object, like a spring, is directly proportional to the amount of deformation.

Spring Types

• Coil Spring  -
  
  • Helical Spring  -  These are the most common type of coil springs, made by winding a wire around a cylindrical form.
  • Torsion Spring  -  Designed to resist twisting or torsional motion, torsion springs are typically wound in a helix or spiral shape.

• Extension Spring   -  These springs are designed to resist stretching or pulling forces.  They usually have hooks or loops on each end for attachment.
• Compression Spring  -  These springs are designed to resist compressive forces or pushing.  They are often used in applications where space is limited.
• Leaf Spring  -  Typically used in suspension systems for vehicles, leaf springs are made of layers of metal strips (leaves) stacked on top of each other.
• Flat Spring  -  These are made of flat strips of material and can be used for various applications, such as in electrical contacts or switches.
• Belleville Spring  -  Also called conical or disc springs, Belleville springs are conical shaped and are often used as washers to provide high spring force in a small space.
• Wave Spring  -  These springs have a wavy or corrugated shape and are used when a compact design is essential.  They are often used in bearing preload and as alternatives to traditional coil springs.
• Gas Spring  -  Also called gas struts or gas shocks, these springs use compressed gas to provide a controlled and adjustable force.
• Constant Force Spring  -  These springs exert a nearly constant force throughout their deflection range.  They are often used in applications such as retractable cords, window counterbalances, and tape measures.
• Composite Spring  -  These are made by combining different materials, such as metal and plastic, to achieve specific properties like corrosion resistance or weight reduction.
• Disc Spring  -  Also called Belleville washers, these are conical-shaped washers that can be stacked together to create a spring with varying force characteristics.

The choice of spring type depends on factors such as the application requirements, space constraints, load characteristics, and durability considerations.  Each type of spring has its advantages and limitations, and selecting the right type is crucial for the proper functioning of the system in which it is used.

Spring Glossary

A

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• Allow for Set  -  Spring is supplied longer than specified to compensate for length loss when fully compressed in assembly by customer. Usually recommended for large quantity orders to reduce cost.
• Angular Relationship of Ends  -  The relative position of the plane of the hooks or loops of extension springs to each other.

B

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• Baking  -  Heating of electroplated springs to relieve hydrogen embrittlement.
• Blueing  -  A thin blue film of oxide on ferrous alloys, sometimes used to indicate that the material has been stress relieved.
• Buckling  -  Bowing or lateral deflection of compression springs when compressed, related to the slenderness ratio.

C

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• Close Wound  -  Springs in which the wire of the coiled portion is touching, generally tension and torsion springs.
• Closed and Ground Ends  -  Same as with closed ends, except that the end is ground to provide a flat plane.
• Closed Ends  -  Ends of compression springs where pitch of the end coils is reduced so that the end coils touch.
• Coil Wound  -  When some or all of a compression springs coils are touching under compression.
• Cold Coiling  -  Coiling using pre-hardened wire and then stress relieving via heat treatment to remove detrimental stresses introduced via coiling.
• Compression  -  The process of reducing the volume or increasing the density of a substance, typically by applying external forces.  It involves the application of pressure to compress or squeeze a material, resulting in a decrease in its volume.
• Creep  -  A time dependant and permanent deflection increases at a constant load resulting in decreased forces.  With a constant load applied, the spring will compress more over time.

D

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• Deflection  -  Motion of spring ends or arms under the application or removal of an external load.
• Displacement  -  The distance or extent to which a spring has been compressed or stretched from its equilibrium or rest position.  Springs are mechanical components that can store potential energy when deformed from their natural or resting state.
• Duel Rate Pitch  -  A spring with a pitch geometry that allows the transition from the original rate to a higher rate at a defined transition point.

E

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• Elastic Limit  -  Maximum stress to which a material may be subjected without producing permanent set.
• Elastic Modulus  -  A measure of a material's stiffness or ability to resist deformation under an applied force.
• Endurance Limit  -  Maximum stress at which any given material will operate indefinitely without failure for a given minimum stress.
• Equilibrium   -  The net external forces that act upon an object are balanced.  This does not mean all the forces are equal to each other.  If the net force is zero, then the net external forces in any direction is zero.

F

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• Free Angle  -  Angle between the arms of a torsion spring when the spring is not loaded.
• Free Length  -  The overall length of a spring in the unloaded position.
• Frequency  -  The number of cycles per second a spring operates.

G

• Bround Ends  -  The finishing of the ends of spring by grinding to create a flat load-bearing surface.  Usually, 270° of the end coil is ground flat.

H

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• Heat Setting  -  Fixturing a spring at elevated temperature to minimize loss of load at operating temperature.
• Heat Treatment  -  Process in which to change the properties of a spring material or relieve detrimental stresses.
• Hooke's Law  -  It describes the relationship between the force applied to a spring and the resulting displacement or deformation of the spring.  It states that the force required to stretch or compress a spring is directly proportional to the displacement or change in length of the spring, as long as the elastic limit of the spring is not exceeded.
• Hooks  -  Open loops or ends of extension springs that are generally longer than a standard loops.
• Hot Coiling  -  The process of heating wire to approximately 900 degrees celsius, coiling, then quenching in oil and tempering, allowing extremely large diameter spring material to be coiled and tight index coiling to be achieved.
• Hydrogeh Embrittlement  -  Hydrogen absorbed in electroplating or pickling of carbon steels, tending to make the spring material brittle and susceptible to cracking and failure, particularly under sustained loads.
• Hysteresis  -  The mechanical energy loss that always occurs under cyclic loading and unloading of a spring, proportional to the area between the loading and unloading load deflection curves within the elastic range to a spring.

I

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• Imnitial Tension  -  The force that keeps the coils of an extension spring closed and which must be overcome before the coils start to open.

J

K

L

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• Linear Spring Shear Stress  -  The stress experienced by a material or a structure due to the application of a shear force, specifically in the context of linear springs.
• Load  -   The force or load applied to a spring, causing it to deform or compress.  Springs are mechanical components designed to store and release mechanical energy when subjected to a force or load.
• Loops  -  Coil like wire shapes at the end of extension springs that provide for attachment and force application.

M

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• Mean Coil Diameter  -  Outside spring diameter (O.D.) minus one wire diameter.

N

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• Number of Active Coils  -  The open wound coils exerting energy while under a load of compression, extending, or deflection.  A coil is formed when it is wound one complete 360 degree helix starting with the second coil and count to the second coil on the other end.  The number of active coils should be 3 or more to stabilize spring charactacteistics.

O

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• Open Ends, Not Ground  -  End of a compression spring with a constant pitch for each coil.
• Open and Ground Ends  -  Open ends, not ground, followed by an end grinding operation.

P

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• Passivating  -  Acid treatment of stainless steel to remove contaminates and improve corrosion resistance.
• Patenting  -  A process of heating carbon steel above its critical temperature and then cooling slowly, resulting in a fine pearlitic microstructure with good ductility and conducive to drawing.
• Permanent Set  -  A material that is deflected so far that its elastic properties have been exceeded and it does not return to its original condition upon release of the load.
• Pig Tail  -  Compression spring with the end coils reduced in diameter to the centre of the body.
• Pitch  -  The distance between successive coils or turns in a helical spring.  The spring pitch is measured along the axis of the spring and is the axial distance between two adjacent points on the wire that forms the coil.
• Potential Energy  -  The energy stored within a stretched or compressed spring.  When a spring is deformed from its equilibrium position, it possesses the ability to restore its original shape or position by exerting a restoring force.
• Preset  -  Removal of set by deflecting a spring to a high stress condition and releasing.
• Pre-stress  -  When a compression spring is compressed to a solid length to intentionally take the material past, it’s the elastic limit and introduces plastic deformation.  This aligns the beneficial stresses in the material to actually help the spring achieve a longer fatigue life.  Pre-setting also reduces the amount of loss of length in service.
• Progressive Rate  -  A rate that increases in proportion to increased deflection of a compression spring.

Q

R

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• Rate  -  Is not the same as spring load.  The spring rate is based on the spring's working load.  Spring rate is the rate of force or weight required to travel one unit of measurement.
• Relaxation  -  Influenced by temperature/design stress/time, relaxation is the gradual decrease of force from a spring with no appreciable change in spring rate.
• Remove Set  -  Full compression of a spring to solid state by manufacturer when needed to prevent length loss in operation.
• Residual Stress  -  Stresses induced by set removal, shot peening, cold working, forming and other means.  These stresses may or may not be beneficial, depending on the application.

S

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• Set  -  Length loss in operation due to the high stress condition of the spring.
• Set Permanent  -  Change of length, height or position after a spring is stressed beyond material’s elastic limit.
• Set Point  -  Stress at which some arbitrarily chosen amount of set (usually 2%) occurs.  Set percentage is the set divided by the deflection which produced it.
• Shear Modulus  -  A material property that describes its resistance to shear deformation when a shearing force is applied.  Shearing force involves forces that act parallel to each other but in opposite directions, causing adjacent layers of a material to slide past each other.
• Shear Stress  -  A type of stress that occurs when a force is applied parallel to the surface of an object or material.  It is a measure of the internal resistance to the sliding or deformation of adjacent layers of a material when subjected to the applied force.
• Shot Peened  -  A cold working process in which the material surface is peened to induce compressive stresses and thereby improve fatigue life.
• Slendering Ratio  -  Ratio of length to mean diameter.
• Solid Coil Height  -  The total compressed height of the spring when all the coils are pressed together such that there is no space between them.  At this point, the spring can no longer be compressed further.
• Spring Constant  -  The stiffness or elasticity of a spring.  It is a measure of how much force is required to stretch or compress a spring by a certain amount.   Hooke's law states that the force exerted by a spring is directly proportional to the amount it is stretched or compressed from its equilibrium position, with the spring constant determining the proportionality constant. 
• Spring Diameter  -  The outer diameter of a helical or coiled spring, which is a mechanical component often used to store and release mechanical energy.
• Spring Index  -  The ratio between the spring and wire diameter for a helical spring.  This number tells how tight the springs coils are.  All wire sizes have a limit to the coil diameter being formed, too small there can be damage to the material.
• Squareness of Ends  -  Angular deviation between the axis of a compression spring and a normal to the plane of the ends.
• Squareness Under Load  -  Same as Squareness of Ends, except with the spring under load.
• Stress Range  -  The difference in operating stress at minimum and maximum loads.
• Stress Relieve  -  To subject springs to low-temperature heat treatment so as to relieve residual stresses.

T

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• Tensile Strength  -  The maximum stress a material can resist before it starts to elongate.  Ultimate tensile strength is a mechanical property that represents the maximum stress a material can withstand before it fractures or breaks under tensile loading. 
• Torque  -  A type of force that is applied to an object that results in the object rotating around an axis.  It is a measure of how much twisting is applied to an object.
• Torsion  -  The twisting or rotational deformation of an object when subjected to a torque or twisting force.  This force causes the object to twist about its longitudinal axis.
• Travel  -  The amount of available deflection from a compression spring.

U

V

W

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• Wahl Correction Factor  -  A measure of the degree to which external stress is amplified at the curvature of the spring coil.  It is used in stress analysis and engineering to account for the stress concentration effect caused by changes in the cross-sectional shape or discontinuities in a structural member.
• Wire Length  -  The wire used to make a coil spring and is based on the number of coils, the mean coil diameter, and the pitch of the coils. 
• Wire Stress  -  The internal forces and resulting deformations that occur within a coiled spring when it is subjected to an external load or force.  Springs are mechanical devices designed to store and release energy by deforming elastically when subjected to a force and returning to their original shape when the force is removed.

X

Y

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• Yield Strength  -  The minimum stress that leads to permanent deformation of the material.   It is important to note that the yield strength of a material is not a fixed value, but rather depends on various factors such as the composition, processing, and testing conditions of the material.

Z