Different materials are better suited for different applications and environments. The Material Properties Table provides operating temperature ranges and other useful information.

Stainless Steel becomes magnetic due to cold working in the manufacturing process. Stainless Steel springs are slightly less magnetic than identically sized Carbon Steel counterparts.

Music wire, although its name is derived from the material used for piano wire, is a common high-carbon steel alloy used for spring manufacture. It is cold drawn and offers uniform tensile strength. Music wire springs are not recommended for applications where the temperature exceeds 121 C (250 F). Music wire is highly magnetic.

This is a far more complicated question than it may first seem. In fact, this question raises a series of questions that must be addressed both individually and considered as a whole. The cycle life of a spring depends, in part, on the following variables:

• The design of the part.
• The environment in which the part will be used.
• The temperature range in which the part will operate.
• The material from which the part is made.
• How the part is used in an assembly.

Precision springs are made to tighter load and dimensional tolerances and from higher standards of materials. Generally speaking, Utility springs are better suited for static or low-cycle applications, while Precision springs may be cycled more frequently and have a longer functional life than comparably sized Utility springs.

Springs can fail or break for a variety of reasons, some of the more common of which are:

• Over stressing the part (extending or compressing it beyond design recommendations).
• Excessive cycling.
• Exceeding the recommended temperature for a given material.
• Using a part in a manner inconsistent with its design limitations.
• Exposing the part to a corrosive environment.
• Hydrogen embrittlement (applies to zinc plated extension springs).

Expressed in lbs. per inch (or Newtons per millimeter in metric parts), the Spring Rate is the change in load per unit extension or deflection.

Initial Tension is the amount of force necessary to separate the coils of extension springs. Initial Tension varies from lot to lot and is for reference purposes only. The load at a given extension equals to the Spring Rate added to the Initial Tension.

Relating to “Cut-to-length” compression springs, this figure is used to determine the Spring Rate for a given part. The Spring Rate (in lbs./inch) is calculated by dividing the Spring Constant by the total number of coils used once the spring has been cut to desired length.

This depends on the type of part, as well as the part’s material. For extension and compression springs, Outside Diameter and Wire Diameter are generally considered more critical than free length. Wire Diameter tolerances are listed in supplementary tables. As a “rule of thumb,” extension springs are considered to be within tolerance if they fall within – one wire diameter, although this too varies with the dimension of the parts and the total number of coils.

This is a function of the number of active coils, the ratio of the Outside Diameter to the Wire Diameter, the material and finish, and other variables. Cot Springs, for example, should only be extended a very short distance.

This also depends on the design and material of the part. While many compression springs can safely be compressed to solid height without damaging the part, this is not recommended for those parts with relatively few coils. Material is also a factor. Due to the way in which one coil nests within the other, Conical Compression Springs are designed to be compressed to effectively a solid height of one wire diameter.

Different types of disc springs have different ranges of deflections as do different designs within categories. General deflection ranges, grouped by category, are as follows:

• Belleville Disc Springs: up to 75% of available deflection
• Curved Disc Springs: between 10% – 80% of avail. defl.
• Wave Disc Springs: between 20% – 80% of avail. defl.
• Tri-Dome Disc Springs: up to 75% of available deflection

Yes. Belleville and Tri-Dome Disc Springs can be stacked in either series or parallel to achieve greater loads and/or deflections than possible using a single spring. See supplementary material for more information.