CHARTS: Density’s Effect on Powdered Soft Magnetic Iron.

Posted by Horizon Technology - June 15, 2018

In powder metal parts manufacturing, soft magnetic iron performance is affected by post-pressing processing and your part’s density. It’s that second part engineers and developers seem to forget when requesting a magnetic component.

The unique properties of soft magnetic iron can do amazing things for your design -- a more compact, 3-D, complex part suddenly becomes possible. Here are some charts and other helpful information to get you started on the right track for your next project.

Why Does Density Matter to Soft Magnetic Iron Components?

Magnetic performance is a function of the:

  • Alloy system used
  • Sintering temperature
  • Carbon and nitrogen contents after sintering
  • Final part density, which influences permeability and saturation induction

Heated die compaction is often used to promote higher density. A high-pressure, highly compressible powder, in turn, improves magnetism.

A denser part is a more magnetic part.

Effect of Density on Magnetic Properties using Fe +.45% Phos

Here’s some eye-opening density data for sintered soft magnetic composites. You’ll see that as density increases, permeability and magnetic induction also increase.

(Note for advanced folks: The applied field in this table is 15 oersted [measurement of magnetic field intensity], or ~1200 amp/meter)

soft magnetic iron

[T] represents a measurement in Tesla, while [G] is the same density in gauss.

Relative to magnetic induction, this is often expressed:

  1. As induction at a predetermined applied field
  2. As if you have a relatively unlimited applied field or current

In the table above, induction is measured at 15 oersteds, or 1200 A/m. One property not listed in this table is the maximum magnetic saturation (Bsat). This is defined as the maximum magnetic field that can be imparted to a material when all magnetic domains are in the same direction.

For conventional wrought steel, this Bsat value is assumed to be 21,500 G or 2.15 T.  However, in PM soft magnetic materials, you also have the added variable of part density. The magnetic saturation for powder metal materials depends on the density of the component, expressed as:

  • Bsat = (part density / 7.85) * 2.15 T

The saturation flux density (Bsat) value essentially measures the max amount of magnetic flux that can be stored in your iron.

So, What Does This All Actually Mean?

To put all this in more simple terms? There’s a linear relationship between maximum magnetic induction and your part’s density.

A smaller density number might tell a designer, “Wait ... I have to increase the wall thickness of this part.” But if you have a higher density, that designer might realize, “OK, this material fits in more nicely with my design.”

Note that your material has the same Bsat level whether its sintered or a soft magnetic composite. Maximum magnetic induction depends solely on the iron’s density. How much current it takes to get there will be different based on the process.

Density -- and Cost -- in Parts Made With 1P, 3P, & 5P SMCs

Permeability is also density-dependent, but is also a function how your parts are processed. SMCs can be processed by either the 1P, 3P, or 5P material processes. The graph below shows the permeability response for each processing option in relation to part density.

soft magnetic iron 1p 3p 5p

Higher density will give you higher performance levels. This graphics shows how quickly your component can store energy with the applied current.

As you move forward on that chart density-wise, you will potentially encounter higher cost. This applies to both sintered and SMC parts to a certain extent. If you can live with slightly lower density, some of those cost implications will matter less.

Head Hurt? Let Us Help

Density is hugely important to the magnetic performance of your product. Powder metal parts made from iron-based sintered or SMCs can help achieve ideal magnetic properties.

Since not all companies and engineers have wizened up to the abilities of soft magnetics yet, your head may be spinning from all these unfamiliar numbers and equations. If you need help understanding how sintered materials or soft magnetic composites can improve your electric-based design, get in touch by clicking the button below.

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Topics: Magnetics, Materials

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