A solenoid is a long wire, wound with a helical pattern, usually surrounded by a steel frame, having a steel core inside the winding.
When carrying a current "i ", the solenoid becomes an electro-mechanical device, in which electrical energy is converted into mechanical work.
The core of a solenoid is
usually made of two sections, a movable actuator, or plunger, and a fixed
end core or back stop.
The efficiency of a solenoid is a factor of mechanical geometry,
electrical configuration and magnetic permeability of core, plunger and
housing.
The plunger is free to travel in the center of winding in a linear
direction. When the coil is energized by the electric current "i
", a magnetic force is created between plunger and end core, causing
the plunger to travel. The higher the permeability of steel used, the
better the performance.
It is essential for a solenoid to lose its magnetic force when input
electrical power is removed. This is to allow the plunger to resume its
original position. Any remaining magnetic field is called residual
magnetism.
Material of the central guide and plating of plunger must be chosen to
introduce minimum friction and low wear. Glass filled nylon and brass for
the guide and electro-less nickel plating or other low friction coatings
for the plunger are often good candidates.
Design and selection of a solenoid requires basic knowledge of mechanical
and electrical interrelationships. In many cases it is essential to make
tradeoffs among a variety of mechanical, electrical, thermal, acoustical,
and physical properties.
Information provided by: http://www.solenoidcity.com