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Question about a Hysteresis Brake

Question about a Hysteresis Brake

Question about a Hysteresis Brake

Hi All

I’m new here so bear with me!
I have a question regarding a Hysteresis Brake or Clutch??
Does anyone know what material the disc is made from, or can be made from??


RE: Question about a Hysteresis Brake

Aluminum works well.  It is light, corrosion resistance and electricly conductive.  The last one is the key, that is how the Eddy Currents are generated.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

RE: Question about a Hysteresis Brake

As I recall, hysteresis brakes rely on the ability to move portions of the ring material through the various quadrants of the magnetic hysteresis curve for that material.  A common material used for this is circumfrentially oriented Alnico 5 - i.e. the grains of the material are aligned perpendicular to the radii of the ring.

Gareth P. Hatch, Ph.D.
Director of Technology
Dexter Magnetic Technologies

RE: Question about a Hysteresis Brake

Thank you for the help.

RE: Question about a Hysteresis Brake

A lot depends on if the disc itself forms a part of the magnetic circuit. While an aluminium disc would work very well between two pole pieces, the disc will make the air gap larger than it might otherwise be.

In something pretty large like an eddy current engine dynamometer, it is more usual to make the disc from iron or steel. The disc itself then bridges the pole pieces and becomes a part of the magnetic circuit, as well as the eddy current circuit.

If the power level is quite high, the disc might need to be an inch or more thick, and have internal cooling fins. An aluminium disc would mean the magnetic air-gap would also have to be one inch, plus mechanical clearance, and clearly that would not work.

On the other hand a very thin aluminium disc may be more efficient if the dimensions and power level are very low.

RE: Question about a Hysteresis Brake

That would be for eddy current brakes, not hysteresis brakes - right?

Gareth P. Hatch, Ph.D.
Director of Technology
Dexter Magnetic Technologies

RE: Question about a Hysteresis Brake

Only "magnetic" materials have significant hysteresis, so Aluminium would be useless. Note that an eddy current brake has to slip, whereas a hysteresis brake does not. If an iron brake is slipping then there will be both eddy current and hysteresis braking occurring.

RE: Question about a Hysteresis Brake

There seems to be some confusion here about types of magnetic couplings, clutches, and brakes. There are three different types of magnetic interactions that can be used.

1. Synchronous- The pole pieces attract one another and torque is transmitted in synch with one another. There is no relative motion between the driver and driven (other than static rotation relative to the pole pieces due to torque). When the torque rating of this coupling/clutch is exceeded, the two parts slip and very little torque is transmitted.

2. Hysteresis- A strongly magnetic driver is attracted to a "weak" magnetic material (like AlNiCo). Torque is transmitted up to a point where the weak material slips. When this happens, the torque transmitted is constant as the weak material is magnetized and demagnetized, and the two parts move realtive to one another. During this process substantial heat may be generated. The slip torque may be adjusted by changing the realative position of opposing strong magnets on either side of the weak magnetic material.

3. Eddy Current- Here the properties of conductors in a magnetic field are exploited. A series of rotating magnets is in close proximity to a highly conductive material (aluminum, copper, etc). The rotating magnetic field sets up opposing eddy currents in the conductive disc causing then to "drag" a magnetic field. Eventually, the conductive disk will nearly catchup with the driving magnets (there will always be slippage unless a lockup clutch is used). This type can also be made variable torque by adjusting the phase or air gap of the magnets.
We manufacture all three types, for more info see our website www.magnetictech.com

Howard Schwerdlin
Coupling Product Manager
Magnetic Technologies Ltd.  

RE: Question about a Hysteresis Brake

A lot of excellent comments on this query

RE: Question about a Hysteresis Brake

I am certainly glad that I didn't answer this thread! What I thought was the one and only truth turned out to be at least three truths - and one of them is entirely new to me...

Thanks for the education!

RE: Question about a Hysteresis Brake

Nice summary, Howard1954!

Gareth P. Hatch, Ph.D.
Director of Technology
Dexter Magnetic Technologies

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