LINEAR AND ROTARY SOLENOIDS – FUNCTIONAL SCOPE

The basic principle of solenoids is the conversion of electrical energy into force and movement.

When the actuation process for automating a machine involves linear or rotary motion, be it simple on-off operation or more complex sequencing, solenoid are the best choice in terms of size, cost, simplified installation and ease of use.

There are other device to converting electrical energy into linear motion, such as electric motor or a pneumatic cylinder. Compared to solenoids, these devices are not very competitive economically and are more suitable for long runs or where the use of the electromagnet is not possible.

How solenoid works and construction

When an electric current passes through a coil, a magnetic field is created around the winding. As the number of windings (turns) of the wire of which the coil is made increases, the magnetic field will be stronger.

By adding an iron or steel containing structure around the coil, the magnetic field will flow much more easily and will concentrate where we want it. If we also add a movable iron core called “plunger” to the center of the coil, the magnetism will become even more concentrated. In this way we have made the basic electromagnet.

A solenoid is essentially constituted by a coil, an iron shell or case and and a movable plunger or pole and is designed to operate in continuous or alternating current.

A major objective in the design of a solenoid is to provide an iron path capable of transmitting maximum magnetic flux density with a minimum energy input.

The magnetic flux density in the work area can be increased by increasing the electrical input to the coil. However, as the electrical energy increases, the coil temperature increases and the work force is reduced. The maximum value with which the input current can be increased depends on the duty cycle and the maximum permissible coil temperature.

The maximum temperature is defined by the insulation class of the material used in the construction.

DUTY CYCLE

The Duty Cycle can be defined as the time in which the electromagnet can be energized without overheating. The formula for calculating the duty cycle is:

RELATIVE DUTY CYCLE % = (ON TIME / (ON + OFF TIME) x 100

Continuous operation should not be confused with continuous duty cycle

The continuous duty cycle (100% rating) means that the solenoid can be left energised for an indefinite period of time at its rated voltage without overheating.

In continuous operation, on the other hand, it is possible to alternate between actuation states (ON) and deactivation (OFF), as long as the relative% of the permitted work cycle is not exceeded. Some duty cycles have been developed to allow solenoids to produce greater forces where they are not continuously energized.

Linear or rotary solenoid?

Although solenoids basically function in much the same way, the resulting direction of movement can be different. It is determined by the type of mechanical assembly in which the electromagnetic circuit is housed.

Linear solenoids provide a mechanical pulling or pushing force or motion dependent on the mechanical configuration of the unit, which can be unidirectional or bidirectional. Since the operation of linear solenoids is simpler than rotary, making them more cost effective.

Usually classified as pull, where the electromagnetic path pulls a plunger into the solenoid body. Or push type where the plunger / shaft is extended through the base of the solenoid to provide a push action.

Many varieties and configurations, including: Tubular Solenoids, Open Frame Solenoids, Low Profile Solenoids e Magnetic Latching Solenoids.

Example linear applications include door locks, control valves, pinch valves, interlocks, printers and diverters.

Our range of  rotary solenoids  employs 3 inclined ball races to convert linear motion to rotary and  e offer high-speed operation and strokes of up to 95 degrees of rotation. Their compact design provide higher starting force / torque than linear solenoids and can be unidirectional or bidirectional depending on the needs of the application

Example rotary applications include  lasers, shutters, processing machinery, medical equipment, industrial sewing machines and diverter.

Our solenoids are manufactured by NSF Controls, part of the Comestero Sistemi Group since 1997

If you are looking for a new electromagnet or are looking for advice, contact us by clicking here, our technicians will recommend the best product for your needs.

Choice of the electromagnet

To achieve optimal operation and long life from an electromagnet, attention must be paid to the choice and use. The best electromagnet for a particular application is generally the smallest that will provide sufficient traction and will not burn out.

Below are the various points that must be taken into consideration for the choice:

• Solenoid strength
• Usage voltage
• Operating and ambient temperature
• Mounting specifications
• Stroke
• Direction of traction
• Connect to the application
• Operating time
• Working cycle

In the event that a competitor’s product needs to be replaced, although it is useful to have a sample in use, it is much better to have the data requested above. The solenoid identified will, in all likelihood, be the standard closest to the competitor.

VDC and VAC solenoids

VDC electromagnets generally have an iron structure for the frame and plunger that works in a brass or plastic tube, while VAC electromagnets are of laminated construction. Laminate construction is essential to prevent excessive losses due to eddy currents.

The force characteristics of an VDC solenoid can be varied considerably by changing the shape of the mobile core (see figure on the side). In this way, the force / stroke characteristic can be varied to suit the application requirements.

The VDC solenoid is characterized by the high input voltage which makes it difficult to position the mobile core. With an electromagnet in VAC the inductance decreases as the movable core exits the electromagnet, the current and voltage along the stroke increase. This condition is the root cause of most problems in applying a VAC electromagnet resulting in rapid overheating.

To prevent the burn-out of the coils, it is possible to add a thermal protector with automatic intervention on the winding. This device will open the coil circuit before dangerous temperatures are reached.

If you are looking for a new electromagnet or are looking for advice, contact us by clicking here, our technicians will recommend the best product for your needs.

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