Active Coils – Coils that are free to deflect under load.
Angular Relationship of Ends – Relative position of hooks or loops of an extension spring (or ends of a torsion spring) to each other.
Baking – Heating of electroplated springs to relieve hydrogen embrittlement.
Block – Length of a compression spring when deflected under sufficient load to bring all adjacent coils into contact.
Buckling – Bowing or lateral displacement of a compression spring. This effect is related to slenderness ratio L/D.
Close Wound – Adjacent coils are touching.
Closed and Ground Ends – Same as Closed Ends, except the first and last coils are ground to provide a flat bearing surface.
Closed Ends – Compression spring ends with coil pitch angle reduced so they are square with the spring axis and touch the adjacent coils.
Closed Length – Length of a compression spring when deflected under sufficient load to bring all adjacent coils into contact.
Coils Per Inch – Distance from center to center of wire in adjacent coils in an open-wound spring.
Deflection – Motion imparted to a spring by application or removal of an external load.
Elastic Limit – Maximum stress to which a material may be subjected without permanent set.
Endurance Limit – Maximum stress, at a given stress ratio, at which material will operate in a given environment for a stated number of cycles without failure.
Fixture Tempering – Restraining parts during tempering to improve dimensional control.
Free Angle – Angular relationship between arms of a helical torsion spring which is not under load.
Free Length – Overall length of a spring that is not under load.
Gradient – Spring gradient, or change in load per unit of deflection.
Heat Setting – A process to pre-relax a spring in order to improve stress relaxation resistance in service.
Helical Springs – Springs made of bar stock or wire coiled into a helical form. This category includes compression, extension and torsion springs.
Hooks – Open loops or ends of extension springs.
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 – 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 (Modulus of Rigidity G) – Coefficient of stiffness used for compression and extension springs.
Moment – 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 – 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 final pearlitic microstructure.
Pitch – 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 square.
Plain Ends, Ground – Same as Plain Ends, except wire ends are ground square with the axis.
Rate – 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 material’s elastic limit.
Set Point – Stress at which some arbitrary chosen amount of set (usually 2%) occurs. Set percentage is the set divided by the deflection that produced it.
Set Removal – An operation that causes a permanent loss 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 – Length of a compression spring when deflected under sufficient load to bring all adjacent coils into contact.
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 – Ratio of mean diameter to wire diameter.
Squared and Ground Ends – Same as Closed Ends, except the first and last coils are ground to provide a flat bearing surface.
Squared Ends – Compression spring ends with coil pitch angle reduced so they are square with the spring axis and touch the adjacent coils.
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 – A product of the distance from the spring axis to the point of load application, and the force component normal to the distance line.
Total Number of Coils – The sum of the number of active and inactive coils in a spring body.
Bibliographical References
- Johnson, Leonard, G., The Statistical Treatment of Fatigue Experiments. New York: Elsevier Publishing Co., 1965
- Little, R.E. and E. H. Jebe., Statistical Design of Fatigue Experiments. New York: John Wiley & Sons, 1975.
- Wahl, A. M., Mechanical Springs, 2nd Edition, New York: McGraw-Hill, 1963.
- Berry, W. R., Spring Design: A Practical Treatment. London: Emmot & Co., 1961.
- Almen, J. O. and A. Laszlo., “The Uniform Section Disc Spring,” A.S.M.E. Transactions, vol. 58, no. 4, (May 1936)
- Blake, A., Design of Curved Members for Machines. New York: Industrial Press, 1966.
- Bisshopp, K. E. and D. C. Drucker., “Large Deflection of Cantilever Beams,” Quarterly of Applied Mathematics, vol. 3, no. 3 (1945), p. 272.
- Maker, J. H., “Steel Springs,” Metal Handbook. 9th edition. Metal Park: ASM, vol. 1, (1978), pp. 283-313.
- Design and Manufacture of Volute Springs. New York: SAE, 1945.
- Peterson, R. E., Stress Concentration Factors. New York: John Wiley & Sons, (1974), p. 231.
- Maier, Karl W., “Dynamic Loading of Compression Springs,” Product Engineering, (January 1954), pp. 162-167. “Dynamic Loading of Compression Springs,” (March 1955), pp. 162-172. “Surge Waves in Compression Springs,” (August 1957), pp. 167-174.
