User:Renard/Spring

From Wikipedia, the free encyclopedia

1 Springs
2 Types of Springs
- 2.1 Terminology
3 Compression Springs
4 Extension Springs

[edit] Springs

A spring is an elastic mechanical component which, after having been deformed (deflected) by the application of a load, will revert to its original shape when that load is removed.

Springs are very efficient energy storage devices. The energy that is applied to deflect the spring initially will be held in storage for very long periods of time. When the load is released, the spring snaps back instantly releasing all the stored energy.

A good example of this is the common mouse trap. Cocking the trap stores energy which may be held for several years. When the trigger is tripped the stored energy is instantly released, killing the mouse.

Most springs are made from music wire. Stainless steel springs are also available but they will have slightly less load capacity.

Care must be taken to avoid overstressing springs. The tables list maximum recommended deflection. (Deflection stands for the amount that (a) compression springs are compressed (b) that extension springs are stretched and (c) torsion springs are twisted.) If these limits are exceeded, the springs may take a permanent "set" and the life of the spring will be reduced. The life is expressed as how many times the springs can be deflected before they break. Typically the life is expressed in millions of cycles. Although this may seem as a very long life, this requirement is not unusual in manufacturing applications such as stamping tools.

[edit] Types of Springs

Assorted Coil Springs

Springs come in a wide variety of shapes and sizes, the most common type being the coil springs as seen in the accompanying photo.

- Compression springs (left in photo) are designed to be squeezed (deflected) axially. Consequently the coils are wound with space between them as seen here.

- Extension springs (center) are designed to be stretched. These springs are wound with the coils tightly together, and some form of hook or loop at either end.

- Torsion springs (right) are also wound with the coils tightly together, but these are designed to be twisted about their axis. They are usually made with some extension at either end which can be attached to the mechanism to be actuated.

[edit] Terminology

The internet provides access to catalogs of major spring manufacturers. The following section will introduce you to the terminology used in these catalogs.

- Deflection This is the amount that a spring is deformed under load.

- Outside Diameter (OD) This is self explanatory, simply the outer diameter of the coil.

- Wire Diameter This is the size of the wire used to form the coil.

- Free Length The length of the spring without any load applied.

- Load Length The length of the spring under maximum loading.
  - In the case of compression springs, this would be the minimum recommended compressed length.
  - For extension springs, this would be the maximum recommended stretched length.

[edit] Compression Springs

Compression Springs

Compression springs are designed to be deflected axially. If the spring is compressed to its maximum, all the coils will be pushed tightly one against the other. The resulting length is referred to as its solid height. It is not good practice to deflect a spring to this extent since it is now effectively a solid tube without any of the resilience that springs are selected for in the first place. Further, springs deflected to their solid height may be stressed beyond their safe limits and will be prone to premature failure.

Compression springs with a length to diameter ratio of 2 or more are prone to buckling if not guided properly. There are two common ways to do this. The photo of the ball point pen shows how the spring may be slipped over a mandrel of some sort. Alternatively, the springs may be inserted into a hole slightly larger than their outside diameter.

Compression spring in a ball point pen

Note that all of the springs in the photographs have the coils at either end deformed to present a flat surface perpendicular to their axis. This also helps to control buckling. In very large, heavy duty springs, the end coils are ground flat rather than deformed.