Springs are mechanical components designed to store mechanical energy, working on
the principle of flexible deformation of material. Springs belong to
the most loaded machine components. Applications for springs include:
- Storing energy as in clock and watch springs
- Energy absorbers for drives and reciprocating devices
- Applying set forces as used in relief valves
- Maintaining the position of a linked mechanical item such as a brake panel or door
- Shock absorbers in anti-vibration protection
- Indicating /controlling a load in a scale or instrument.
- Lifting devices-Used to reduce effort in manual hoists
An important initial factor in spring design is the Spring Rate
When considering linear motion the spring rate is the load divided by the elastic deflection.
k = P / δ
P = Force (N)
δ = deflection (mm or m)
When considering angular (rotary) motion the spring rate is the Torque divided by the elastic angular deflection.
ka = T / θ
T = Torque (Nm)
θ = Angular displacement (Radians)
Metal springs are generally fall into one of three classes of duty;
- High Duty..Springs subject to rapidly reciprocating loads e.g. engine valve springs
- General Duty..Springs that work infrequently for limited periods
- Static Load Springs..Springs that are used to apply a fixed load throughout their life
Spring Energy Storage
Based on the deformation pattern, springs can be divided into the following three types:
- springs with linear characteristics
- springs with degressive characteristics
- springs with progressive characteristics
The W area under the spring characteristic curve represents
the deformation work (energy) of a spring performed by the spring during its loading.
Deformation energy of springs subjected to compression, tension or bending is
specified by the formula:
For springs subjected to torsion the deformation energy is:
At any point in a springs operating life it can be in one of a number of states
- Free- The spring is unloaded
- Preloaded - The spring is loaded as and initial operating state
- Loaded - The spring is loaded to under some operating condition
- Fully Loaded - The spring is subject to the maximum design operational loading
- Limiting Loaded - The spring is exposed to the limit load as defined by the strength or design condition
A limiting load as defined by strength may be considered as at the limit of elasticity or at yield.
A limiting load as defined by design limitations is exampled by a compression spring with all coils in contact.