Failure mode during manufacturing of Neo magnet

[MAC3382]

Hello, All:

We recently received a shipment of Neo magnets that we use in one of our products. We have been using this vendor for many years and they come from China. During a QC inspection, we found some very weak magnets and we have never experineced this before. (Seems like they were partially magnetized.) We sent them out to a Magnetizing equipmnet OEM in Indiana and they remagnetized a small lot of the magnets in question. No help. We were also told that the magnets were indeed "aligned" and anisotropic. (????) okay, but they are still very weak. The OEM suggested a BH curve. We ordered one and the charateristics they deemed important are listed below. Looking at other company's magnet data online the measured values seem very low. (Almost looks like Alnico.)

BR-9,258 Gauss
HC - 760 Oersteds
HCJ - 800 Oersteds
BHMAX - 1.043 MGOE

The OEM sugegsted that there was a manufacturing issue, but they could not offer a particular reason. Would anyone be able to offer a possible explaination for why the suspect Neo magnets would be so weak? The powder blend? Alignment?

I appreciate any commnets you may have to offer.

Thank you,

Mac

 

[IRstuff]

So, what does the material analysis say?

TTFN
faq731-376

 

[EdStainless]

What about their density? Are they full density or are they lighter than good ones?
My first guess is either low density or internal oxidation, but we will see.
First check to see if they are even the right material.

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Plymouth Tube

 

[MagMike]

I don't have an answer for you (yet), but a bunch of questions:
What grade of NdFeB were you expecting? Does your vendor supply a BH curve and chemical composition list? Unless you are getting a special blend, the coercivity (Hc and Hci) should be above 10,000 Oersteds.

Do you know if your supplier is licensed? Currently there are only a handful of Chinese NdFeB companies that can legally sell into the US.

 

[MAC3382]

Thank you for your responses and questions:

1) we do not have a material analysis. This is the leading edge of the investigation. We will send a magnet out for a Chemical Analysis.

2) we do not receive Chem Analysis with BH shipments. Only BH curves. The BH curve that came with the shipment shows something similiar to what we normally receive. I cannot judge the curve, but the listed characteristics are much higher than what we had measured. I am guessing that the C of C information and QC data that was sent to us is "boiler plate" or from some lot of material made around the same time.

3) I did not check the density and that is a great idea. I will do so. What I can say is that the material seems to be sintered. Sintered what, I do not know. It is NOT alnico.

4) No special blend. Grade 35SH. I believe that the vendor is licensed, however we are always told form Chinese vendors that the material is licensed or too old to need to be lincensed.

Let us say that the material is actaully sintered NdfeB. What could go wrong in the mfg process to result in this magnet failure? I have been doing some reading online and it seems to point to the chemistry. I was hoping that this was not normal, but that someone could say: not orienetd, not enough ND and too much FE, Sintered wrong. We are trying to go back to the vendor with a bit of knowledge instead of relying on an answer from them.

Thank you for all of the help,

Mac

 

[IRstuff]

A BH curve would seem to be a design verification test result, since it's unlikely that they would run different magnetizations on every single lot of material shipped, but they clearly need to do something if this happens again.

TTFN
faq731-376

 

[EdStainless]

I doubt that the chemistry is wrong, that is fairly straight forward to control.
I lean toward sintering. Either not fully dense or contaminated.

What fraction of the lot was weak?

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Plymouth Tube

 

[asdad]

If the material is properly aligned, the BH curve should look like a square (not a curve). Since the Hc and Hcj values are close it can be assumed that the material is aligned but you need to look at the actual BH curve to be sure.

Low power usually means low BR value. Check your vendor`s standard about what your BR value should be. Low BR value can be caused from sintering or chemistry problems.

Chemical composition won`t help you because it doesn`t tell you about their phase and crystal structure. Besides, different factories usually have slightly different compositions according to the raw materials used. I think the most possible cause is chemistry problem. A slight shift in the material`s phase and crystal structure can cause big drop in magnetic properties.

Another possibility (unlikely) is that your magnet is not fully magnetized.