Spring Material
Music Wire: A common, fairly inexpensive high-carbon steel alloy that’s cold drawn and provides uniform tensile strength.
Stainless Steel: Provides fairly high strength tied with good corrosion resistance for certain applications.
High Carbon Steel: More than .3% displays resistance to abrasion and impact.
Hard Drawn Steel: An inexpensive material with a low working load.
Speciality Metals and Alloys: Can be customized for the application.
Brass: An inexpensive material that can be easily molded, and is corrosion resistant. However, it may not be strong enough for certain applications.
Spring Ends
Open-End: The spring possesses a consistent coil pitch when at free length.
Closed-End: The spring possesses a reduced pitch at the end of the coil, with the last coil resting on the adjacent inner coil.
Open, ground springs: Possesses no reduction in pitch, but the last coil is filed flat to distribute the load more evenly.
Closed, ground springs: A reduce in pitch upon the last coil wrap, and have its ends filed flat to distribute the load more evenly.
Spring Performance
Spring Rate: The amount of force, in pounds, needed to extend the spring one inch. This is affected by wire diameter, material, and coil pitch.
Maximum Load/Deflection: The maximum weight a spring can handle before it disfigures and its mechanical properties are inconsistent.
Free Length: The length of the spring with zero load.
Solid Height: The length of the spring with a maximum load, with each coil resting on the adjacent coil.
Stress: Takes on the form of torsion and governs life expectancy. The higher a spring’s stress range, the lower the maximum stress must be to obtain comparable life.
Pitch: Is the distance between a coil center to the adjoining coil center. In compression springs this may vary widely.
Active Coils: The number of coils that express deflection when under load. In an open, ungrounded spring it will be all of the coils; for a closed, grounded spring, this will be the coils that are not incorporated in the filed base.
Spring Finishes
Cleaned/Oiled: Rely on oil to maintain a friction-free compression.
Phosphated: Springs have additional corrosion resistance, lubrication, and the coating can serve as a base for painting or other further coating.
Powder Coating: Adds abrasion resistance and can also change the exterior color of the spring.
Shot Peening: Uses glass or steel pellets to induce compressive stresses that improve fatigue life.
Additional Terms
Compression Springs can be manufactured in a variety of shapes, such as cylindrical, taper, barrel and hourglass. They are used to return a force when compressed. The force of the compression is determined by factors of the spring such as material, length, diameter and coils. The ends of the compression spring are usually closed, or closed and ground to give a square sitting spring with a larger bearing surface on the mating part. Other end type includes open ends or open and ground ends. Springs can also be made from rectangular, shaped and square wire. Springs of these types can be made with variable pitch, one spring nested inside another, or stacked on top of each other usually separated with a plate.
Extension Springs are used to return a force when extended or pulled tensionally. Usually the ends of the springs have a loop or hook on the spring for it to be attached to a mating part. The end loop can be of various configurations, such as extended loop or hooks, swivel, necked down, threaded bolt end, straight end or no loop ends. Extension springs can also be made cylindrical, taper, barrel shaped and with square, rectangular or shaped wire. Most extension springs are manufactured with initial tension; this initial tension is the force it needs to start separating the coils apart. When more force is applied the spring will continue to extend.
Torsion Springs are used to return a force when applied torsionally. Many configurations for the spring and ends are available for manufacture. Double torsion springs have a clockwise and counter clockwise wind on each end connected in the middle with both legs working in tandem. Double torsion springs can be designed to increase the force over a single torsion spring. Both single and double torsion springs can be manufactured with round, rectangular or square wire.
Garter Springs are usually extension springs with end configurations that connect the spring together to form a circle. There are special applications for garter springs, such as seal ring springs or other applications that would require a circular force. Garter springs can be manufactured to be used for either internal or external type of force.
Flat Metal Springs are specialty designed, in which spring steel is formed to a certain shape to apply a force in a given direction. They can be manufactured out of most material but generally they are made out of strip carbon steel or stainless steel. They can be manufactured with holes, slots, raised areas and clamped to adhere to a mating part.
Wire Forms can be manufactured out of any shape and type of material from soft to hard springs. They are manufactured on a variety of machines that can produce small lots to thousands of parts per day. These wire forms can be anything from handles, shafts, or clamps to stops on a pinball machine.
Coiling is either done by hand (small lots) or by automatic machine. Compression, extension, torsion and garter springs are all manufactured on automatic or semi-automatic machines. Pretempered wire is fed into the machine, and with a qualified operator the springs are produced. There a many variables that can have an effect on the spring being made, extreme care is taken during the coiling process to ensure a quality product is made. When manufacturing a spring, standard tolerances are used, not machining block tolerances.
Stress Relief is a process where springs are placed into an oven at a set temperature for a fixed time to allow the stresses created from coiling to be reduced. Temperature and times are varied for the different material types.
Grinding is where compression springs are passed through a wheel that grinds the ends flat. This produces a spring that will be very perpendicular to allow for the most bearing surface to its mating part.
Secondary Operations are various processes that can be added to the manufacture of springs and wire forms to produce a product to customer specification. Penn-Elkco provides operations such as Presetting, Shot Peening, Heat Setting, Vibratory Finishing, Dueburring Outside and Inside Diameter, Heat Treating, Magnetic Particle Inspection, Demagnetizing, Coining, Threading, Specialty Bends, Welding, assembly and other operations.
Finishing and Packaging: Penn Elkco offers a wide variety of finishing bits in house and subcontracted to other finishing partners. Included are plating, coating, staining, painting, rust preventative protection oil, Ultrasonic Cleaned, Passivating, and other finishes available. Packaging is normally in standard cartons where care is taken during packaging. Finished products can also be packaged using customer specific requirements.
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