Glossary of Spring Terms

Active coils: Those coils which are free to deflect under load.

Angular relationship of ends: The relative position of the plane of the hooks or loops of extension springs to each other.

Baking: Heating of electroplated springs to relieve hydrogen embrittlement.

Buckling: Bowing or lateral deflection of compression springs when compressed, related to slenderness ratio (L/D).

Closed ends: Ends of compression springs where pitch of the end coils is reduced so that the end coils touch.

Closed and ground ends: As with closed ends, except that the end is ground to provide a flat plane.

Closed length: see Solid height

Close-wound: Coiled with adjacent coils touching.

Coils per inch: see Pitch

Deflection (F): Motion of spring ends or arms under the application or removal of an external load (P).

Elastic limit: Maximum stress to which a material may be subjected without permanent set.

Endurance limit: Maximum stress at which any given material will operate indefinitely without failure for a given minimum stress.

Free angle: Angle between the arms of a torsion spring when the spring is not loaded.

Free length (L): The overall length of a spring in the unloaded position.

Frequency (natural): The lowest inherent rate of free vibration of a spring itself (usually in cycle per second) with ends restrained.

Gradient: see Rate (R)

Heat setting: Fixturing a spring atelevated temperature to minimize loss of load at operating temperature.

Helix: The spiral for (open or closed) of compression, extension, and torsion springs.

Hooke’s Law: Load is proportional to displacement.

Hooks: Open loops or ends of extension springs.

Hot pressing: see Heat setting

Hydrogen 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: Mechanical energy loss occurring during loading and unloading of a spring within the elastic range. It is illustrated by the area between load deflection curves.

Initial Tension: A force that tends to keep coils of a close-wound extension spring closed and which must be overcome before the coils start to open.

Loops: Formed ends with minimal gaps at the ends of extension springs.

Mean Diameter (D): The average diameter of the mass of spring material, equal to one-half the sum of the outside and inside diameters. In a helical spring, this is the equivalent to the outside diameter minus one wire diameter.

Modulus in Shear or Torsion (G): (Modulus of Rigidity G) Coefficient of stiffness used for compression and extension springs.

Modulus in Tension or Bending (E): (Young Modulus E) Coefficient or stiffness used for torsion or flat springs.

Moment (M): A product of the distance from the spring axis to the point of load application, and the force component normal to the distance line.

Natural Frequency (n): Lowest inherent rate of free vibration of a spring vibrating between its own ends.

Patenting: The process of heating carbon steel above its critical temperature and cooling at a controlled rate to achieve a fine pearlitic microstructure.

Pitch (p): Distance from center to center of wire in adjacent coils in an open-wound spring.

Plain Ends: End coils of a helical spring having a constant pitch and ends not squared.

Plain Ends, Ground: Same as Plain Ends, except wire ends are ground square with the axis.

Rate (R): Spring gradient, or change in load per unit of deflection.
Residual Stress: Stress mechanically induced by such means as set removal, shot-peening, cold working, or forming. It may be beneficial or not, depending on the spring application.

Set: Permanent change of length, height, or position after a spring is stressed beyond the 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.

Set Removal: An operation which causes a permanent loss of length or height due to spring deflection.

Shot-Peening: Blasting the surfaces of spring material with steel or glass pellets to induce compressive stresses that improve fatigue life.

Slenderness Ratio: Ratio of spring length to mean diameter L/D in helical springs.

Solid Height (LS): Length of a compression spring when deflected under sufficient load to bring all adjacent coils into contact – no additional deflection is possible.

Spiral Springs: Springs formed from flat strip or wire wound in the form of a spiral, loaded by torque about an axis normal to the plane of the spiral.

Spring Index (C): Ratio of mean diameter to wire diameter.

Squared and Ground Ends: See Closed and Ground Ends.

Squared Ends: See Closed Ends.

Squareness: Angular deviation, between the axis of a compression spring in a free state and a line normal to the end planes.

Stress Range: Difference in operating stresses at minimum and maximum loads.

Stress Ratio: Minimum stress divided by maximum stress.

Stress Relief: A low temperature heat treatment given springs to relieve residual stresses produced by prior cold forming.

Torque (M): See Moment.

Total Number of Coils (N): The sum of the number of active and inactive coils in a spring body.

Compression Springs

The most common form of compression spring is a straight cylindrical coil spring with the ends squared (closed), and a common example is a ball point pen spring. Listed are a few variations of the standard compression spring.

Compression springs are often installed over a rod or inside a hole to reduce buckling

Extension Springs

Extension springs are helical springs designed to resist a pulling force. Spring rates are typically expressed in lbs./inch plus the initial tension. With wire diameters ranging from .010” to .625” coiled to virtually any outside diameter. Initial tensions from zero all the way up to the maximum allowable by index of coil (wire diameter to mean diameter ratio). End configuration options are endless with the most common being machine hooks.

Torsion Springs

Torsion springs are typically used to counterbalance mechanical loads. Proper design considerations must be taken to size the spring(s) to perform the work at hand. Leg configuration options are endless from straight legs to multiple bends. Wire diameters of .010”-.625” coiled to specification. Torsion spring loads are typically expressed in inch pounds, similar to a torque wrench. Most torsion springs have a few degrees of pre-load to stabilize assemblies such as simple levers. A particular torsion spring known as a double torsion spring is popular because of its ability to make two parts into one which makes installation time twice as fast. Western Spring manufacturers a wide variety of torsion springs for product and industry.

Wire Forms

The designs of wire forms are entirely up to one’s imagination. Wire forms consist of material bent into a configuration that may have some properties of compression, extension or torsion springs. Wire forms typically require non-traditional spring machinery or processes to manufacture. Western Spring uses fully automated CNC wire forming equipment to manufacture parts as efficiently as possible. Check out our link to YouTube.com to see our equipment in action.

Flat Springs

Flat springs are usually made out of strip material that is formed as annealed stock then heat treated to a spring temper. The material and size options are endless. Pre-tempered material is also an option for simple flat springs. Prototypes to production quantities can be sourced at Western Spring. We can work with you to design a product that works for your application.

Medical Springs

As a medical device spring manufacturer not only do we supply custom springs (including custom coil springs, small compression springs, miniature springs, cable guides, catheter springs, extension springs, torsion springs, medical coils, wire forms, magazine springs, micro springs, small coil springs etc.) but we also provide spring design assistance from our experienced development team. We look forward to helping make your project a success so feel free to contact us at any time.

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