Good spring design depends upon many factors in addition to dimensional and load requirements. One factor is environment. How hot or cold will it be? Will the spring be exposed to corrosion? Another is required life. How long must the spring survive without breaking or experiencing excessive permanent set? After considering all the factors that could affect performance, we can design a spring that will give the greatest possible value to the spring user.
Often insufficient space is allowed for springs in newly designed equipment. This can force the use of costly, high stressed, close tolerance springs, which increase the risk of early failure. We can save you time and money by helping you design a spring before you are committed to a final design.
As with most components, no matter how much time and effort is spent to ensure long life, it is practically impossible to guarantee that there will be no failures in a given production lot of springs. In addition to breakage, loss of load and distortion may also be failures.
Predicting spring life is not an exact science. Nevertheless, spring life can be extended by careful design and selection of material, as well as quality control of both material and production.
One of the most neglected factors that can adversely affect spring performance is corrosion. Often microscopic corrosion is the origin of spring failure, but its presence goes undetected, and the cause of failure is attributed to something else.
Springs made of uncoated steel must be given some kind of corrosion protection, even during manufacturing, shipping, and storage. The degree of protection required after installation is another matter and depends upon the nature of the application. We can help you with this problem if we know the environment in which the spring will be operating.
Since it is an economic consideration, specified tolerances should be generous enough to permit the fabrication of acceptable springs by ordinary production methods.
Also, it,s smart to apply tolerances only on functional requirements and dimensions. This gives us an opportunity to compensate for variations in the size and mechanical properties of all spring materials.
If your standard drawing forms have tolerance boxes for machined dimensions, they are almost sure to be impractical for springs. We suggest you delete them and apply realistic tolerances to spring requirements.
Some draftsmen include a note on all drawings reading, "Remove all burrs." This can result in additional cost without adding value to the part. Burrs are produced, to some degree or other, by many of the operations used in manufacturing springs.
Burrs created in the cutting-off operation are often harmless and it would be unwise to pay for their removal. Burrs arising from other operations may sometimes be controlled within limits as to size, shape, and location. If we can agree upon such limits, they may be a chance for significant savings.
Whenever a carbon steel is pickled in preparation for plating or during some electroplating processes, hydrogen can become absorbed into the material. While cracks can develop in the pickling or plating bath, more often then they appear when the plated springs are in service.
The hazard of hydrogen embrittlement becomes more acute when there is (1) high stress concentration, (2) high Rockwell hardness, or (3) high carbon content. Tempered materials are particularly susceptible.
To relieve embrittlement, the springs must be baked immediately after plating to drive the hydrogen out of the material.