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Frequently Asked Questions/Technical Information

 

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Q: What material should I choose when selecting a spring?
A: Different materials are better suited for different applications and environments. The Material Properties Table provides operating temperature ranges and other useful information.

Q: Why are Stainless Steel springs magnetic?
A: 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.

Q: What is Music Wire, and why is it used to make springs?
A: 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.

Q: How often can I cycle a part?
A: 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:

a) The design of the part.
b) The environment in which the part will be used.
c) The temperature range in which the part will operate.
d) The material from which the part is made.
e) How the part is used in an assembly.

Q: What is the difference between Utility and Precision springs?
A: 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.

Q: Why did my spring(s) break or fail?
A: Springs can fail or break for a variety of reasons, some of the more common of which are:

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

Q: What is Spring Rate?
A: 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.

Q: What is Initial Tension?
A: 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.

Q: What is the Spring Constant?
A: 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.

Q: How can I tell if my spring is within physical tolerances?
A: 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.

Q: How can I tell if my spring is within load/rate tolerances?
A: This also depends on the type of material of the part. Precision Extension and Precision Compression springs have tighter load/rate tolerances than Utility springs. Disc spring load tolerances vary based on the type of disc spring, the material, and the design of the part.

Q: How far can I safely extend an extension spring?
A: 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.

Q: How far can I safely compress a compression spring?
A: 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.

Q: How far can I safely compress a Disc Spring?
A: 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:

a) Belleville Disc Springs: up to 75% of available deflection
b) Curved Disc Springs: between 10% - 80% of avail. defl.
c) Wave Disc Springs: between 20% - 80% of avail. defl.
d) Tri-Dome Disc Springs: up to 75% of available deflection

Q: Can Disc Springs be Stacked?
A: 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.