Magnetically Conductive Plastics?

Did you try googling "Magnetically Conductive Plastic"?

I did, this forum thread was the 4th listing of over 6,000 hits.

Globalspec should have several vendors listed also. You will find a link in small letters in the upper right hand corner of the CR4 page banner.

sorry to dissapoint you but this material already exists. it is used in hospitals in bed wheels so the structure (bed) itself is always electrically grounded. see this link for example: http://www.tente.us/US/cat100/an4886_hospital_bed_casters.html

Don't mix up magnetically conductive with electrically conductive material.

Magnetic conductivity: permanent magnetic or soft magnetic:

Any mixture of plastic with ferrite- or iron-particles is magnetically conductive: permeability much above 1. But be cautious: the quality of the material is much inferior to the original magnetic data as the filling factor (usually below 0.6) is acting squared, so you will get around 30% the quality of the 100% material.

Look at the doors of your refrigerator, very likely the seals have some extruded plastic containing hard magnetic ferrite as filler, magnetised after extrusion.

Electrical conductivity:

Any mixture of a plastic with an electrically conductive material is electrically conductive only if the particles make contacts to the next particle and if the particles stay conductive inside the polymer. Most metals including copper are easily oxidised inside polymers so that initial electrical conductivity vanishes within hours or days or months. Silver is good.

RHABE

hi Rhabe,

So, more ferrite + plastic material is required in order to get the effect of full metal component.

One more thing, I may not be able to get the homogenity of composite and hence my component to component properties will be varying.

This one i am trying for close the magnetic flux path.

Thanks,

Ruban

Hi,

if you use iron (if alternating or constant magnetic field) or steel (if constant magnetic field) and make a wire- or ribbon-wound coil of any shape this will be better than a mixture of particles. This structure can be reinforced by infiltration of epoxi.

As long as the sum of all air-gaps along the field lines is low you will have good (low) magnetic resistance (equivalent to high permeability).

This is best achieved by orienting wires or ribbons along the magnetic field lines. (If geometry allows).

Next would be iron or steel mesh or wool, softened by heat treatment (needs inert gas protection), shaped by pressing to desired shape and then infiltrated. (highest achievable mean density necessary).

A little bit worse will be pre-coating with hot-melting - super-hot curing - epoxi, that can be processed dry and then cured.

If all this would not work I would consider using particle filled epoxi.

RHABE

Here's a subtle point to remember. If you are trying to close the gap of an electromagnet, you should remember that the lowest permeability region of the closed magnetic field loop has the largest amount of magnetic flux. If you saturate this region any added flux will respond to free space permeability. This characteristic is one of the reasons why power cores have an air gap. So when one fills the only air gap with a higher permeability material, the magnet or inductor will become non-linear at lower energies.

You mix up flux and field strength!

The lowest permeability region has the highest field strength!!!

This is equivalent to an electric circuit where the highest resistance region has the highest voltage drop!

In a magnetic circuit (no stray flux assumed) the flux around the loop is constant.

So flux density (Tesla) may vary according to cross-section. If cross section is too low there may be saturation at reaching the maximum flux-density!

This is near 2 T in iron and steel and most iron alloys, 2.3T in certain FeCo-alloys, only 0.7T in some FeNi alloys (known for very good permeability).

"So when one fills the only air gap with a higher permeability material, the magnet or inductor will become non-linear at lower energies."

This statement is ok, as the circuit with nearly no airgap has a much lower "magnetic resistance". Thus a higher flux is existing and related higher flux density. This in turn may reach the limit.

RHABE

You are quite correct, sir. I transposed the terms. But my verbose description did get my concept across. I thank you for confirming the concept.

Try contacting a custom plastic material compounder. Two that come to mind are LNP www.sabic-ip.com and RTP www.rtpcompany.com . They should be able to compound the type of soft magnet material that you need. They take nearly any base plastic resin (ie., Bayer, DuPont, etc.) and mix in whatever fillers, chemicals, etc., that you need to produce a customized plastic for your application. I doubt that you will find a standard material with the requirements you need. Their technicians will be able to recommend a base material and fillers that should best suit your application.