Aerospace springs

...springs push pull and twist.

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Compression springs

Compression springs push, have a wide load and deflection range at either constant or variable rate.

Extension springs pull, have a wide load and deflection range at a constant rate.

Torsion springs twist at a constant rate.

Magazine springs push and drawbar springs pull.

Compression Springs squeeze together to create a load. You will often find these inside switches, automotive suspensions, and jack-in-the-boxes.

Extension springs

Extension Springs stretch apart to create load. They often have little loops on the ends to attach to things. In domestic environments, you may find these on the screen door hinge, garage door etc

Torsion springs

Torsion Springs rotate around an axis to create load. They release their load in an arc around the axis. They are commonly found in mouse traps and rocker switches.

Constant force springs

Constant Force Springs, also called "clock springs", because it is often found in clockworks. This spring is made of a band of steel wrapped around itself a number of times to create a geometric spiral. The idea is to create a rotational force that releases a constant amount of load, instead of a quick burst of power. Besides clocks, they are found in all sorts of wind-up toys. Be careful when removing these from a mechanism. They tend to unravel with a dynamic flair and much excitement. They are great for things that need to rotate many times and still have a reasonable amount of force to apply and release.

Constant Force Springs type 2

This type of clock spring is used when more power is required. It has many fewer rotations and a much thicker band of steel. They are used in seat recliners and other heavy duty applications

Belleville springs

Belleville Springs (aka Belleville Washers) are coned disk springs typically containing a hole in the center for non-permanent fasteners (or bolts). Bolt pretensioning is a typical use for a Belleville washer. Belleville springs can be nested (making springs in parallel) making more spring deflection for the same amount of load OR allowing higher loads with the same deflection - depending on their orientation. While useful, nesting Belleville springs can be unstable. With proper design (selection), Belleville springs can be used for a "snap-acting" mechanism. Likewise, with proper design/selection, the spring can have constant force over a large deflection. This type of design maintains bolt pretension when a dynamic load is present or in situation where thermal expansion/contraction is significant.

Spring Clips

This category includes snap rings and hose clamps. The spring is a portion of a circle and the force is applied radially concentric to the centre point of the circle.

The history of springs

Like most other fundamental mechanisms, metal springs have existed since the Bronze Age. Even before metals, wood was used as a flexible structural member in archery bows and military catapults. Precision springs first became a necessity during the Renaissance with the advent of accurate timepieces. The fourteenth century saw the development of precise clocks which revolutionized celestial navigation. World exploration and conquest by the European colonial powers continued to provide an impetus to the clockmakers' science and art. Firearms were another area that pushed spring development.

The eighteenth century dawn of the industrial revolution raised the need for large, accurate, and inexpensive springs. Whereas clockmakers' springs were often hand-made, now springs needed to be mass-produced from music wire and the like. Manufacturing methodologies were developed so that today springs are ubiquitous. Computer-controlled wire and sheet metal bending machines now allow custom springs to be tooled within weeks, although the throughput is not as high as that for dedicated machinery.

Glossary of spring terminology:

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 or the legs of a torsion spring to each other.

Baking

Heating of electroplated springs to relieve hydrogen embrittlement.

Buckling

Bowing or lateral deflection of compression springs when compressed, related to the slenderness ratio (Free Length/Mean Coil Diameter).

Closed ends and squared

Ends of compression springs where pitch of the end coils is reduced so that the end coils touch and are square with the spring axis.

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.

Compression Spring

Helical compression springs have applications to resist applied compression forces or in the push mode, store energy to provide the "push". Different forms of compression springs are produced. There are conical, barrel, hourglass, or straight conical compression springs. These compression springs can be made with or without variable spacing between coils. Round wire springs can store more energy than rectangular wire compression springs.

Deflection

Motion of spring ends or legs under the application or removal of an external load.

Elastic limit

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

Endurance limit

Maximum stress at which any given material will operate for a determined number of cycles without failure for a given minimum stress.

Extension Spring

Extension Springs exert a pulling force or energy. They are usually close wound with initial tension and are mostly made from round wire. The design of the extension springs' ends are limitless. Hooks, loops, bends, crossbars, etc.

Free angle

Angle between the legs of a torsion spring which is not under load.

Free length

The overall length of a spring which is not under load.

Gradient

See Rate

Heat setting

Fixturing a spring at elevated temperature to minimize loss of load at operating temperature.

Helix

The spiral form (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. Proper baking is required to relieve the hydrogen.

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 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 coils start to open.

Load

The force applied to a spring that causes a deflection.

Loops

Formed wire shapes at the ends of extension springs that provide for attachment and force application.

Mean coil diameter

Outside spring diameter minus one wire diameter.

Modulus in shear or torsion

Coefficient of stiffness for extension and compression springs. (Modulus of Rigidity)

Modulus in tension or bending

Coefficient of stiffness used for torsion and flat 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. See Torque.

Open ends, not ground

End of a compression spring with a constant pitch for each coil and the last coils not touching adjacent coils.

Open ends ground

"Open ends, not ground" followed by an end grinding operation.

Passivating

Acid treatment to remove contaminants and improve corrosion resistance of stainless steel.

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 has taken a "permanent set."

Pitch

The distance from center to center of the wire in adjacent active coils (recommended practice is to specify number of active coils rather than pitch).

Plain Ends

End coils of a compression spring having a constant pitch and not squared.

Poisson's Ratio

The ratio of the strain in the transverse direction to the strain in the longitudinal direction.

Preset

See Remove set.

Rate

Change in load per unit deflection, generally given in pounds per inch.

Remove set

The process of closing to solid height a compression spring which has been coiled longer than the desired finished length, so as to increase the apparent elastic limit.

Residual stress

Stresses mechanically induced by set removal, shot peening, cold working, forming or other means. These stresses may or may not be beneficial, depending on the application of the spring.

Set

Permanent distortion in length, height, or positon which occurs when a spring is stressed beyond the elastic limit of the material.

Shot peening

Blasting the surfaces of the spring with pellets to induce compressive stresses and thereby improve fatigue life.

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; no additional deflection is possible.

Spring index

Ratio of mean coil diameter to wire diameter.

Squared and ground ends

See Closed and ground ends.

Squared ends

See Closed ends.

Stress range

The difference in operating stresses at minimum and maximum loads.

Stress relieve

To subject springs to low-temperature heat treatment so as to relieve residual stresses.

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. 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. Usually expressed in oz./in., lb./in., lb./ft., or in. N/mm.

Torsion Spring

A torsion spring provides rotational energy or torque. You can have a single bodied or double bodied torsion spring. You must have three points of support and the body usually sits on a shaft or arbor. Again, the design of the ends or legs of a torsion spring are limitless. The stress in a torsion spring is bending. Round wire is still the preferred material due to the cost of rectangular wire, even though rectangular is more efficient in bending.

Total number of coils

Number of active coils. For compression springs, active coils plus the number of dead coils forming the ends.

Wahl Factor

A factor to correct stress in helical springs effects of curvature and direct shear.