Wave Springs

Definition:
Wave springs are precise flat wire compression springs that fit into assemblies in which other springs cannot. The overall length and operating height of wave springs are significantly less than that of standard compression springs, thus they will reduce the size of an assembly by as much as 50%. This also reduces the part weight and raw material cost of every spring produced. Load and spring rates are more accurate, more predictable, and may have higher tolerances when using wave springs. There are many types of wave springs available. The first is the gap and overlap type. This particular type of wave spring is used for short deflections and low-medium forces and will function with precision and dependability.

The second type of wave spring is the crest-to-crest wave spring. This spring is pre-stacked in series, decreasing the spring rate proportionality to the number of turns. The key advantage to this type of spring is the design eliminates the need to keep the wave crests aligned so it holds it's configuration. This type is also available with shim ends which allow a 360 degree contact surface. The third type of wave spring is the nested wave spring. Nest springs are pre-stacked in parallel from one continuous filament of flat wire. These springs can exert a tremendous amount of force, yet maintain the precision of a circular-grain wave spring. The last major category in wave springs are linear expanders. Linear expanders are a continuous wave form wire length produced from spring tempered material. They act as a load bearing device having approximately the same load/deflection characteristics as a wave spring.

Applications:
Wave springs can be used in a variety of industrial applications. For example in a pressure release valve a wave spring is used in order to maintain an exact load applied to the top sealing plate. Wave springs are also used in clutch drives. The most common application for wave springs is a bearing preload arrangement. Using the wave spring within the bearing lowers operating temperature, reduces vibration, minimizes wear, and provided for a quieter and smoother performance. Wave springs can also be found in very common household products. Sprinkler valves contain wave springs in order to maintain constant pressure on the pop-up-head, firmly holding it closed. The water pressure will overcome the springs force and the water will be released, after the water pressure decreases the force of the spring will regain statute and the pop-up-head is resealed. One of the last major applications of wave springs are the ones found within the gear box drive. The wave spring greatly reduces the vibration within the gear box. Also, the spring takes up tolerances that accumulate in the plastic components of the box.

Design Considerations:
As seen above wave springs are used in a variety of applications however there are distinct rules for defining spring requirements.

1. Working Cavity: In order to design a wave spring you must first know the amount of space that can be allocated to the spring movement. The working cavity usually consists of a bore the spring operates in and/or the shaft the spring has to clear. The spring stays in position by piloting the bore and/or shaft. The axial working cavity or the work height of the spring is defined by the distance between the loading surfaces.

2. Load Requirement: When installed at its work height a spring must produce a certain amount of axial force which is defined as the load requirement. Load requirement is important because it defines the amount of tolerance that is allowed for the load. Some applications have two or more operating heights that are critical and must be considered in the design.

3. Operating Environment: When considering the design of the spring it is crucial to take into consideration the operating environment. This encompasses all aspect of the surroundings such as temperature, fatigue, corrosive media, or other unusual conditions.

4. Diameter Expansion: When taking into consideration the maximum outer diameter you need to consider diameter expansion. In order to do this it is necessary to address certain categories. These categories are wave radius, number of waves, angle (degrees), radial wall, wave frequency, and mean free height.

5. Stress: Stress is one of the major factors that causes a spring to deteriorate. There are many different types of stress such as operating stress, maximum design stress, residual stress, and fatigue. Operating stress is the compression of a spring that creates bending stress similar to the bending of a beam. Maximum design stress is finding the approximate yield strength due to the minimal elongation of hardened flat wire. Residual stress is compressing the spring beyond its yield point or presetting and increasing the load capacity. Since preset springs are manufactured to a higher than needed free height and load, by reducing the free height and load the material surfaces now exhibit residual stress, which enhances spring performance. The amount of fatigue allocated to a spring will determine the estimated life cycle of the spring.

6. Material Cross-Section: Material cross-section plays an important role in wave spring design because it can make a spring more economical and can determine the life span of any given spring.

Materials:
Selecting the proper material for a wave spring is a crucial element in spring design. The type of material will determine the cost and can prevent future failures in operation. The most commonly used materials for wave springs are carbon steel and stainless steel. Carbon steel is the most cost effective method, however using stainless steel provides are far superior corrosion resistance and has a higher temperature operating limits. There are two types of carbon steel commonly used to make wave springs. The first is old tempered and the second is hard drawn. In either temper, carbon steel is best suited in applications that have a protected environment since this material corrodes if not properly lubricated.

There are three commonly used types of stainless steel. The first is 302 stainless steel, which is a widely used material because of its combination of corrosion resistance and physical properties. The second type of stainless steel is 316. This material is very similar to 302 however it provides and additional corrosion resistance and is commonly used in food, chemical, and sea water applications. The last type of stainless steel commonly used it 17-7. In fatigue and high stress applications 17-7 outperforms even the finest grade of carbon steel. This is used almost exclusively for wave springs. Some of the other materials used seldom to make wave springs are the alloys such as Inconel X-750, A286 Alloy, and Elgiloy and coppers such as Beryllium copper alloy # 25 and Phosphor Bronze (Grade A).

Plating and Coating:
Some of the material finishes used for wave springs are black oxide, cadmium plating, oil dip, passivation (optional cleaning operation for stainless steel), zinc phosphate, vapor degrease (standard cleaning finish for all stainless steels) and vibratory deburr (used to remove all sharp edges and corners).