A solenoid is an electromagnet, also called an actuator, that performs a linear stroke movement. When energized, the armature plunger is attracted and thus executes the desired movement. Typically, strokes of up to 45mm can be realized.
Solenoids, like all other electromagnets, are based on the principle of electromagnetism. Electric current flows through a coil of copper wire, generating an electromagnetic field that is guided through iron components so that the armature — a movable iron core — is attracted. This movement (also called a stroke) moves a connected armature rod, which transfers the armature's movement outward and can be used to operate valves or mechanical devices.
Generally, the force of an electromagnet is determined by the current flowing through the coil. It should be noted that the flowing current causes electron vibrations that generate heat and thus increase resistance. When increasing the current, care must be taken not to overheat or damage the device.
By using a control unit and a coil optimized for the application, the holding current can be reduced when the armature is in the end position and increased again for the magnet's movement. It is also possible to work with short-term higher voltages to generate more power at critical points.
Please contact us to find an optimal solution for your application.
Solenoids are available in the following designs:
Simple solenoids can be pulling or pushing but act only in one direction. Simple solenoids do not perform return movements. Such movements must be realized by external forces (spring, gravity, weight, etc.).
Reversible solenoids move the armature in two directions using two coils that generate opposite movements. The direction depends on which coil is energized.
Monostable reversible solenoids operate with one coil and move the armature in two directions. Integrated permanent magnets hold the armature in the desired position without power. Springs can provide a second power-free position. Only a new current pulse moves the armature, making these electromagnets suitable for energy-saving pulse operation.
Bistable reversible solenoids work with two coils and move the armature in two directions. Integrated permanent magnets hold the armature in position without power. Only a new current pulse moves the armature, also suitable for energy-saving pulse operation.
When solenoids are mounted on a valve, they are called valve magnets.
A locking unit usually consists of a solenoid whose specially designed armature rod serves as a locking bolt. Depending on requirements and functionality, simple solenoids or mono- or bistable solenoids can be used in locking units. Usually, the armature's return is realized by a spring, enabling energy-saving pulse operation.
Special attention must be paid to the armature's bearing in locking units, as relevant lateral forces typically act there. It is also possible to query the locking unit's position via additional electronics. Depending on the application, pulling (locked without power) or pushing (unlocked without power) versions can be used.
Please contact us to select the appropriate locking unit together.
Rotary solenoids are reset to the end position by a return spring.
The reset force of the rotary solenoid can be adjusted by modifying the return spring.
Holding magnets can only achieve very small strokes and are used where magnetizable workpieces or doors need to be held. By using magnetizable fasteners, non-magnetizable workpieces can also be attracted.
Holding magnets are often combined with permanent magnets to ensure high safety, for example, when the removal of workpieces is only possible when energized. In such cases, the housing contains a permanent magnet in addition to the coil, which constantly attracts ferromagnetic parts. Energizing the electromagnet then reduces the permanent magnet's magnetic field.
The standard program from indEAS includes holding magnets with diameters from 20 to 70mm. Custom applications can also be designed. Standard holding forces go up to 1,500N but can be significantly higher in custom applications.
In practice, even minimal air gaps, rough surfaces, contamination, etc. can greatly reduce the magnet's performance.
indEAS holding magnets come standard with a threaded hole on the back. Many other mounting solutions are possible on customer request.
The black ring consists of casting resin that fixes the coil inside the magnet housing. To prevent the casting resin from protruding beyond the pole face and creating an unwanted air gap, it is recessed slightly.
An air gap refers to the distance between the magnet's holding surface and the attracted surface of the workpiece. Surface texture, contamination, coating, etc., play an important role because they interrupt the magnetic flux.
Due to the low magnetic permeability, the air gap is a critical factor for magnetic flux.
indEAS actuation magnets generate movements and are available in three types: pushing, pulling, and pushing + pulling.
The armature movement inside electromagnets is always the same: the armature is pulled into the housing by the magnetic field generated in the coil. By guiding the armature rod outward, this identical movement can create a pulling movement on one side of the magnet and a pushing movement on the other.
Duty cycle is the time between switching the current on and off. The off-time is the time between switching the current off and on again. The sum of duty cycle and off-time results in the cycle time. The maximum cycle time depends on the degree of overexcitation and the size of the magnet.
The relative duty cycle is the ratio of duty cycle to cycle time.
For a cycle time of 30 seconds, the maximum permissible duty cycle is:
1.5 s at 5% duty cycle
4.5 s at 15% duty cycle
7.5 s at 25% duty cycle
12 s at 40% duty cycle
100% duty cycle means continuous operation.
When magnetizing a ferromagnetic component, part of the magnetization remains in the material after the excitation or energizing ends. Due to this remanence or residual magnetism, magnetizable materials behave like weak permanent magnets. The residual holding force caused by remanence largely disappears when the workpiece is separated from the holding surface.
To prevent unwanted remanence, an air gap can be included in the design. The larger the air gap, the lower the expected remanence.
A voice coil actuator is based on the Lorentz force principle, which states that in a permanent magnetic field, the force on a current-carrying conductor is proportional to the magnetic field strength and the current. By reversing the current direction, the force direction changes, allowing bidirectional drives. The actuator behaves identically in both directions.
What are the advantages of a voice coil actuator compared to an electromagnet?
Good controllability in both directions
Force and speed proportional to current supply
Can be supplemented with position sensing
High acceleration
Low noise
High efficiency