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Guardian Solenoids
Guardian is leading the industry
in solenoid manufacturing providing simple and complex design
applications in AC solenoids and DC solenoids. With simple
custom modifications or complex design structures, we can
provide the type, force, power consumption and solenoid design
to suit your specific requirements. Our DC solenoids are available
in frame, latching push type, tubular and long-life models.
Our AC frame solenoids can be laminated, push-type or a combination
design. Both solenoid types can be either intermittent or
continuous cycles.
If our standard solenoid models
do not meet your design specifications, Guardian's Engineering
Team will custom design the solenoid that best fits your application,
taking into consideration your voltage requirements, duty
cycle, force curves, power input configurations and plunger
configurations.
Solenoid
Operation
Solenoids are electro-magnetic
devices which act as electric to mechanical energy converters
by converting an electrical signal into linear motion. A solenoid
is a long cylinder with a coil of wire wrapped around it.
As an electrical signal passes through the solenoid coil a
magnetic field is produced. The coil is made of magnetic copper
wire. If the coil has many turns of wire, the magnetic current
produced increases, creating a stronger solenoid.
As electrical current
is applied to the solenoid coil, the plunger which is located
within its iron core, moves in reaction to the magnetic field
created by the copper coil. The amount of electrical current
flowing through the coil is known as the flux. The plunger,
also known as armature, is made of ferrous metal to increase
magnetism or permeability. As electric current is applied
the plunger, it is completely pulled into the solenoid coil
allowing the magnetic force to flow throughout the solenoid.
At this point, the solenoid is considered closed and is at
its strongest.
The solenoid is enclosed
with a steel housing which is part of the magnetic circuit.
The solenoid body also provides structural integrity as well
as a mounting means.
Solenoid
Force
The force of a solenoid
is determined by the number of turns of the coil(N), the electrical
current (I) flowing through the solenoid coil, and the magnetic
character of the steel for maximum magnetic efficiency. The
force produced is affected by two major variables:
1. Manufacturing Tolerances:
The manufacturing variations in solenoid designs are in the
total number of turns in the solenoid coil and coil resistance.
Other variations have no effect on the force produced.
2. Coil Temperature: Since
coil resistance, coil current and NI are affected by temperature,
the force developed is also affected. To determine the force
developed, the total coil temperature due to both ambient
temperature and self-heating must be taken into consideration.
As electrical current
is increased, the solenoid plunger is cycled faster, creating
heat. If the rise in temperature is not dissipated, the solenoid
magnetism will be reduced, decreasing the overall force of
the solenoid.
Solenoid Stroke
The stroke is the space
between the solenoid plunger end and the plug in the de-energized
position, which is commonly referred to as the air gap. An
inverse relationship exists between the solenoid stroke and
force. As the stroke increases, the solenoid force decreases.
When selecting solenoids, the shortest stroke should be chosen
to maximize force and improve efficiency.
Plug and Plunger
Solenoid Geometries
There are 4 basic plug
and plunger geometries available for solenoids: flat face,
60 degree conical, 90 degree conical and stepped conical.
The flat faced configuration is best for short strokes and
high holding solenoid force, whereas the 60 degree conical
is best for longer stroke applications. The 90 degree conical
and stepped conicals are better for medium stroke applications.
Guardian's Enhanced Engineering Support Team will custom
design a solenoid with unusual force/stroke solenoid requirements.
Solenoid Temperature
As solenoid coil temperature
increases, the force developed decreases. The variation in
solenoid force due to temperature cannot be addressed with
a predetermined value since it is dependent upon the user's
ambient temperature, magnitude of input wattage and the relationship
of on-time to off-time, or duty cycle. Heat rise curves can
be used to estimate the effect of self heating and increased
ambient temperature. The temperature taken from heat rise
curves, added to the user's ambient temperature, produces
the final operating temperature.
Solenoid Duty
Cycle
Solenoid duty cycle is
the ratio of amount of time the solenoid is considered on
to the total time of the solenoid cycle operation. It is expressed
in percent. When specifying the duty cycle of an operation,
either the on-time or the off-time, or both must be specifically
stated. Stated alone, a 10% duty cycle could be .1 seconds
on-time or .9 seconds off-time, or could be 1 year on-time
and 9 years off-time. Continuous duty cycle is a 100% duty
cycle. One cycle of operation is the time from the beginning
of one on-time to the beginning of the next on-time. If a
solenoid is energized for 100 seconds and de-energized for
300 seconds, the duty cycle is 25%.
Solenoid Selection
The solenoid selected
for a particular application must be one which produces the
force required throughout its entire stroke and operating
temperature range. The load must never exceed the force developed
at the stroke and NI value. If the load is too great, the
plunger will not pull in or seat. On the other hand, a highly
overrated solenoid which develops substantially more force
than required by the load should not be used unless speed
of operation is the determining factor. Excessive energy imparted
to the solenoid must be dissipated by some other means. If
it is not dissipated, the plunger and field piece assembly
must absorb energy of impact causing premature failure.
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