Glossary of Spring Terminology
Active Coils - Those coils which are free to deflect under load.
Baking - Heating of electroplated springs to relieve hydrogen embrittlement
Belleville Springs - These are essentially initially coned disk, who may be stacked up to give a variety of load-deflection characteristics.
Buckling - Bowing or lateral deflection of compression springs when compressed, related to the slenderness ratio.
Closed ends - Ends of springs where the pitch of the end coils is reduced so that the end coils touch.
Close-wound - Coiled with adjacent coils touching.
Compressive stress - Is the stress state when the material tends to compact (volume decrease). A simple case of compression is the uniaxial compression induced by the action of opposite, pushing forces. Most materials can carry compressive stress,
Deflection - Motion of the spring ends or arms under the application or removal of an external load.
Ductility - Being capable of sustaining large plastic deformations without fracture. It is characterized by the material flowing under shear stress.
Elastic deformation - Is the spring-like deformation, where a material will return to its original shape - see also Plastic deformation
Elastic limit - Maximum stress to which a material may be subjected without permanent set.
Elastic modulus - See Young's modulus
Endurance limit - Maximum stress at which any given material may operate indefinitely without failure for a given minimum stress.
Fatigue - Is a process by which a material is weakened by cyclic loading. The resulting stress may be below the ultimate tensile stress
Flat Springs - These are made from flat strips and may come in a wide variety of forms.
Fracture - Is the separation of a body into two, or more, pieces under the action of stress.
Free length - The overall length of a spring in the unloaded position.
Ground ends - Ends of springs are ground to provide a flat plane.
Heat setting - Fixturing a spring at elevated temperature to minimize loss of load at operating temperature.
Helical Torsion Springs - Similar to the helical compression springs, these are loaded by a torque about the helix axis. To transmit this torque special ends are normally required.
Hole - This is the minimum diameter of the hole in which spring can work
Hot-wound springs - Having large bar diameters > 16mm and above. They are widely used in automotive and railroad equipment. For smaller bar sizes: 9mm to 16mm can be either hot- or cold-wound
Hydrogen embrittlement - Hydrogen absorbed in electroplating or pickling of carbon steels, tending to make the spring material brittle and susceptible to cracking and failure.
Hysteresis - The mechanical energy loss that always occurs under cyclical loading and unloading of a spring, proportional to the are between the loading and unloading load-deflection curves within the elastic range of a spring.
Initial tension - The force that tends to keep the coils of an extension spring closed and which must be overcome before the coil starts to open.
Leaf springs - These springs consist of flat bars of varying lengths clamped together to obtain greater efficiency and resilience (automotive and railway leaf springs)
Linear load deflection - Deflection is proportional to the load, when load is doubled, the deflection will be doubled e.g. typical compression springs.
Load - The force applied to a spring that causes a deflection
Loops - Coil-like wire shapes at the ends of extension springs that provide for attachment and force application.
Mean coil diameter - Outside wire diameter minus one wire diameter.
Mechanical spring - Elastic body, whose primary function is to deflect or distort or absorb energy under load and which recovers its original shape when released.
Metric system - See SI
Modulus of elasticity - See Young's modulus
Modulus of rigidity - See Shear modulus
Nonlinear load Functions of springs - To absorb energy and mitigate shock, to apply a definite force or torque, to support moving masses or isolate vibration, to indicate or control load or torque
Passivating - Acid treatment of stainless steel to remove contaminants and improve corrosion resistance.
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 load.
Pitch - The distance from center to center of the wire in adjacent active coils.
Plastic deformation - The non-reversible change of shape in response to an applied force
Relaxation - The opposite of stress or tension
Remove set - The process of closing to a solid height a compression spring which has been coiled longer than the desired finished length, so as to increase the elastic limit.
Set - Permanent distortion which occurs when a spring is stressed beyond the elastic limit of the material.
Shaft - This parameter describes the maximum diameter of spring shaft in industrial applications
Shear modulus G - Is defined as the ratio of shear stress to the shear strain.
Shear strain - Is the components of a strain at a point that produce changes in shape of a body (distortion) without a volumetric change
Shear stress - Is caused when a force is applied to produce a sliding failure of a material along a plane that is parallel to the direction of the applied force e.g. when cutting paper with scissors or a steel bolt with a bolt cutter.
Shot peening - A cold-working process in which the material surface is peened to induce compressive stresses and thereby improve fatigue life.
Shot peening - Is a process used to modify mechanical properties of metals, It entails impacting a surface with shot (round metallic particles) with force sufficient to create dimples and with enough shot that those dimples overlap
SI - International System of Units. SI is sometimes referred to as the metric system.
Slenderness ratio - Ratio of spring length to mean coil diameter.
Solid height - Length of a compression spring when under sufficient load to bring all coils into contact with adjacent coils.
Spiral springs - Formed of flat strip wound in the form of a spiral (clock or power springs), such springs are loaded by torque about an axis normal to the plane of the spiral.
Spring index - Ratio of mean coil diameter to wire diameter.
Spring rate (R) - This parameter determines spring's resistance, while it is working. It is measured in 1 DaN/mm = 10 N/mm.
Squared ends = Closed ends.
Squareness of ends - Angular deviation between the axis o a compression spring and a normal to the plane of the other ends.
Static loading - Loading the springs with steady load less then 1000 times. (e.g. gasket pressure)
Stiffness - Is the resistance of an elastic body to deflection by an applied force. Stiffness is typically measured in Newton’s per meter.
Strain - Deformation caused by the action of stress on a solid material. Strain therefore expresses itself as a change in size and/or shape.
Stress - The force that is exerted on a solid material from the outside. The SI unit for stress is the Pascal (symbol Pa); in US Customary units, stress is expressed in pounds per square inch (PSI). See also"
Stress range - The difference in operating stresses at minimum and maximum loads.
Tensile strength (Rm) - Te maximum amount of stretching stress a material can withstand before it tears. Materials rated at a high tensile strength are durable and difficult to tear.
Tensile stress - Is a loading that tends to produce stretching on a material by the application of axially directed pulling forces. Materials can withstand some tensile loading, but if enough force is applied, they will eventually break into two pa
Torque - A twisting action in torsion springs which tends to produce rotation, equal to the load multiplied by the distance (or moment arm) from the load to the axis of the spring body.
Torsion-bar Springs - These are essentially straight bars under torsion, the load usually being applied through splined ends.
Total number of coils - Number of active coils plus the coils forming the ends.
Yield point - See Yield strength
Yield strength - The amount of strain that a material can undergo before moving from elastic deformation into plastic deformation. The stress felt by a material given a certain strain is defined by linear relationship, with a slope defined by the m
Young's modulus - Is a measure of the stiffness of a given material, That is how hard it is to stretch chemical bonds that bind the atoms of a material together.