Spring

There are many factors to consider in spring design. The following is directed specifically toward compression springs although many elements apply to other springs as well.
Spring Diameter: Helical compression springs can be described by three different diametric numbers:
Wire Diameter: ("d") is the diameter of the wire used to manufacture the spring and is a factor used to calculate spring index.

Spring Index: The ratio of the mean coil diameter to wire diameter (D/d). Springs with an index higher than 12 can tangle; springs with an index lower than 4 can be difficult to form. Free Length: "L o "; the overall length of an unloaded ("free") spring.
Number of Coils: Active coils ("N a") are the coils in a compression spring that are free to deflect under load. The greater the number of active coils, the lower the spring rate.
Spring rate is determined by the amount of force, in pounds, required to constrict a spring by one inch. Material size directly impacts spring rate. For example, increasing a wire diameter by 1 percent will result in a 4 percent stronger spring; decreasing diameter by 1 percent will result in a 4 percent weaker spring. Increasing the mean diameter by 1 percent will decrease the spring rate by 1 percent. Important Considerations for Spring Design
Squared (closed) ends ground - squared-end spring finished with a grinding operation to provide a flat plane.
Spring Engineers Tip: Plain ends are best suited for large-index, light-duty applications because they tend to cause the spring to bend, decreasing performance reliability. Squared ends are preferred on springs with wire diameters of .5 mm or less, an index greater than 12, or low spring rates. Spring Engineers Tip: For compression springs, hysteresis is generally low.
Coil Direction: Compression springs can be left- or right-hand coiled.
Spring Engineers Tip: If the spring will be mounted on a bolt, right-hand winding is preferable.
Spring Engineers Tip: For squared-and-ground springs, square-ness is generally specified within a 3-degree tolerance.
Parallelism: Parallelism describes the relationship between a spring's ground ends as the maximum deviation in free length around the spring's circumference.
Deflection: Movement of the spring ends when external loads are applied or removed.
Stress: Stresses are determined by spring dimensions and t he application's load and deflection requirements. Compression springs are stressed in torsion. Maximum stress occurs at the inner surface of the wire; the load varies as the spring is deflected, producing a range of operating stresses that influence the life of the spring.
Spring Engineers Tip: For optimal longevity, higher stress ranges should be used with lower maximum stresses, and high maximum stresses should be used either with lower stress ranges or when the spring will be subjected only to static loading.
Load: Load, the force applied to a spring that causes deflection, can be determined by multiplying the spring rate by deflection. Buckling: Buckling occurs when a spring deforms in a non-axial direction. Typically, buckling deformation accelerates rapidly and the spring fails.
Spring Engineers Tip : Compression springs with free heights greater than 4 times the spring diameter are prone to buckling, and benefit from guidance (either in a tube or over a rod).
Spring Engineers Tip : Presetting, or set removal, increases the load-carrying ability of springs in static applications by increasing the spring's elastic limit. To preset, the spring is coiled longer than its required free length and then compressed to solid, causing the spring to set to its final desired length. This process increases the spring's energy storage capacity to up to 75 percent of the material's tensile strength, and is common for critical springs made from premium materials.
Choice of Operating Stress - Cyclic Conditions: Cyclic applications require a spring to operate repeatedly between specified loads. Spring Engineers Tip : Maximum stress occurs at the wire surface, and any surface defects therefore reduce fatigue life. Garage door springs have been subject to innovation to improve their safety, cycle life, and performance. 1. Galvanized Garage Door Springs
About 20 years ago, galvanized garage door torsion springs broke into the garage door parts market as an alternative to oil-tempered springs. Later, electro-coating on oil-tempered torsion springs augmented the buyer's set of choices.
Most in the garage door service industry, though, ably identify the problem with galvanized springs. Galvanizing weakens the spring. Garage door owners, too, voice objections to galvanized springs because of high maintenance costs. If you seek to remedy this by adding extra spring tension in a "hot" installation, you necessarily decrease the spring cycle life. One proposed solution to the galvanized spring dilemma is the coated spring, intended to cover the oily residue. Galvanized springs need oiling as well. Leading off, Wayne Dalton TorqueMaster springs, which wind with a drill. Because TorqueMaster springs have a smaller mean diameter, they need to be longer to match the lift of a spring. As a result, each spring tends to appear more slinky-like than standard springs.
Spring King: Industrial Spring's Spring King utilizes a drill-winding system for use with standard torsion springs. Clopay/Ideal, maker of the EZ-set spring system, has developed a spring winder device for stretching and installing extension springs. This product addresses the problem of door weight in an extension spring installation. Extension spring safety cables provide peace of mind to many users of extension springs on a sectional door. Considered at least a property-saver, and at best literally a life-saver, safety cables run through the extension spring to contain possibly dangerous airborne extension spring parts in the event of a spring break.
Materials that are worked with include cold drawn and cold rolled low-alloy steel, patent and cold drawn wire, hardenable spring steel, oil tempered spring wire and bainite hardened strip, stainless spring steel, stainless spring steel with extra corrosion properties, stainless spring steel for higher temperatures, stainless non-magnetic steel, alloys, copper alloys, anti-magnetic acid-resistant spring steel, titanium alloys, super-alloys that are heat resistant and highly corrosion resistant spring materials.
Bespoke springs.
Bespoke springs are usually made from alloys of steel. The most common spring steels are music wire, oil tempered wire, chrome silicon, chrome vanadium, and 302 and 17-7 stainless. Other materials can also be formed into springs, depending on the characteristics needed. Chrome Silicon, Chrome Vanadium.010-.500 These are higher quality, higher strength versions of Oil Tempered wire, used in high-temperature applications such as automotive valve springs. Shear strength
Spring design information.
Since spring theory is normally developed on the basis of spring rate (or gradient), the formula for spring rate is the most widely used in spring design.
For extension springs, all coils are active; body length is wire diameter times the total number of coils plus one: d(n + 1). Compression springs.
A compression spring is an open-coil helical spring that offers resistance to a compressive force applied axially. Compression springs are usually coiled as a constant diameter cylinder. Compression springs should be stress-relieved to remove residual bending stresses produced by the coiling operation. The spring manufacturer will usually advise the user of the maximum allowable spring deflection without set whenever springs are specified in this category.
In designing compression springs the space allotted governs the dimensional limits of a spring with regard to allowable solid height and outside and inside diameters.