A magnetic particle clutch is a special type of

electromagnetic clutch Electromagnetic clutches operate electrically but transmit torque mechanically. This is why they used to be referred to as electro-mechanical clutches. Over the years, EM became known as electromagnetic versus electro-mechanical, referring more a ...

which does not use friction plates. Instead, it uses a fine powder of magnetically susceptible material (typically

stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...

) to mechanically link an otherwise free-wheeling disc attached to one shaft, to a rotor attached to the other shaft. This clutch is a form of a powder clutch.

Torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...

is transmitted mechanically, through a metal powder filling. In the magnetically controlled version, an applied magnetic field is used to lock the particles in place. Unlike a pure

magnetic Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particle ...

coupling though, this field takes no part in transmitting torque magnetically. When a

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

is applied by a coil to the powder, it forms chains connecting the disc and rotor. The strength of the chains depends on the strength of the magnetic field. If there is not a magnetic field being applied to the powder, then powder is free floating. In this state the clutch is able to spin freely without any engagement of the input shaft to the output shaft. Magnetic particle clutches have made equipment control easier while also prolonging life of machine components.

Components

* Electrical coil – produces the magnetic field for the particles to react to. * Input shaft – the end of the main shaft that is attached to the driving force. * Output shaft – the shaft that is on the other side of the clutch. This shaft is the one affected by the amount the clutch is being engaged. * Bearings – allow the input and output shaft to spin freely without binding. * Magnetic particles – the powdered magnetic material inside the clutch.

Applications

In the late 1970s and early '80s, these were used in high-speed

line printer A line printer prints one entire line of text before advancing to another line. Most early line printers were impact printers. Line printers are mostly associated with unit record equipment and the early days of digital computing, but the ...

s to stop a spinning drum stamped with 96 or more columns, and 40 or more rows containing the

alphabet An alphabet is a standardized set of basic written graphemes (called letters) that represent the phonemes of certain spoken languages. Not all writing systems represent language in this way; in a syllabary, each character represents a syll ...

. The drum was stopped momentarily by the clutch while hammers struck ink and paper in the appropriate column. Each revolution of the drum, produced a full line of text and symbols. These drums spun at 300 to 1200

RPM Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...

. Factories have also used them to regulate the speed in which a spool of material is unwound. A real-world example of this can be found in

paper mill A paper mill is a factory devoted to making paper from vegetable fibres such as wood pulp, old rags, and other ingredients. Prior to the invention and adoption of the Fourdrinier machine and other types of paper machine that use an endless belt, ...

s. Paper mills require material to be fed into their rollers at a constant rate. These clutches allow the material to be fed into the rollers at the right speed while also maintaining tension on the material. Magnetic particle clutches are also used in cycle controls. They allow cycles to have a constant amount of torque while the cycle is being completed. A great example of this is a machine that puts caps on bottles. Magnetic particle clutches can also be found in gym equipment. They are used in

treadmill A treadmill is a device generally used for walking, running, or climbing while staying in the same place. Treadmills were introduced before the development of powered machines to harness the power of animals or humans to do work, often a type of ...

s to control the speed of the belt smoothly. It is also used to protect the electric motor of the machine from being overloaded when people with different weights use it.

Advantages

Advantages over a friction plate clutch include: * it doesn't exhibit

stick-slip phenomenon The stick–slip phenomenon, also known as the slip–stick phenomenon or simply stick–slip, is the spontaneous jerking motion that can occur while two objects are sliding over each other. Cause Below is a simple, heuristic description of stick ...

* the

torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...

may be easily and quickly controlled * it is more resistant to wear * it may be used for continuous slip applications * it has a very fast response time * Over load protection. * Works great for soft start applications

Disadvantages

* Can be more expensive than a conventional clutch system * Requires a power source to control the

References

{{Reflist, refs= {{Cite web , url=https://ogura-clutch.com/electromagnetic-particle-clutch.php , title=Electromagnetic Particle Clutch , website=ogura-clutch.com , access-date=2019-02-14 {{Cite web , url=https://placidindustries.com/engineering-resources/magnetic-particle-clutches-work/ , title=How Magnetic Particle Clutches Work , website=Placid Industries , language=en-US , access-date=2019-02-14 Clutches Automotive transmission technologies Electromagnetic brakes and clutches