General Notes on Springs

More details on Spring design are to be found in the links below the table.

INTRODUCTION

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

Spring Rate

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.

k_a = T / θ

T = Torque (Nm)
θ = Angular displacement (Radians)

Spring Class

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:

Spring State

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.

Links to Spring Design

Mitcalc ...A excel based software package -very convenient to use

Machine_Parts_Index
Spring Index