Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: ciniva on 20/09/2017 20:55:04

Title: How is magnet size and shape calculated to provide a given magnetic field?
Post by: ciniva on 20/09/2017 20:55:04
Please experts on the science of magnetism if they can help me.

I need to calculate the dimensions of the magnets in relation to its weight and the magnitude of the magnetic field.

In the image below you note that I want to raise a magnet 'C' for 45 degrees up.

I'm interested in how to find the optimal characteristics of magnets (dimensions, volume, weight, size). The thickness of the magnet must be 30mm.
Topic related to this topic https://www.thenakedscientists.com/forum/index.php?topic=71383.0

The process flow in the picture below would be the following:
By bringing the magnets 'A' to the magnet B, the magnetic field the magnet must be rejected 'B' in a circular arc so that the magnet is lifted 'C' for 45 degrees.

All magnets must be of the same dimensions, weight and volume.
How to calculate the strength (grade), the volume and dimensions of the magnet, so that the power of rejection of 'A' and 'B' magnets, he could lift up the 'C' magnet by lever.

My apologies to the bad English. I hope that you will understand my problem.
Thanks in advance for possible help


* magnetup.png (13.95 kB . 739x707 - viewed 6148 times)
Title: Re: How is magnet size and shape calculated to provide a given magnetic field?
Post by: Kryptid on 20/09/2017 21:47:16
This web calculator might be of some help to you: https://www.kjmagnetics.com/calculator.asp (https://www.kjmagnetics.com/calculator.asp)
Title: Re: How is magnet size and shape calculated to provide a given magnetic field?
Post by: ciniva on 21/09/2017 20:35:38
Hi Kryptid
Thank you for the link.
Helps, but not completely.
Title: Re: How is magnet size and shape calculated to provide a given magnetic field?
Post by: Kryptid on 21/09/2017 23:36:46
Just out of curiosity, are you trying to design a perpetual motion machine with magnets?
Title: Re: How is magnet size and shape calculated to provide a given magnetic field?
Post by: ciniva on 22/09/2017 14:29:34
I want to find out what kind of magnet 'A' and 'B' I have to use to raise the magnet 'C'.
I want to calculate dimensions, strength, 'A' magnets to raise the weight of the 'C' magnets.
I want to find the strongest option if all the magnets have the same characteristics.
Title: Re: How is magnet size and shape calculated to provide a given magnetic field?
Post by: evan_au on 22/09/2017 20:35:43
You get the greatest force of attraction when they are in direct contact.
But it also requires the greatest amount of energy to separate them again (in fact, slightly more energy than was released when they first came into contact).

To some extent, you can concentrate magnetic fields where you want them by using high-permeability ferromagnetic materials like iron or nickel which "conduct" magnetic fields more easily than air.

See: https://simple.wikipedia.org/wiki/Permeability_(electromagnetism)

Title: Re: How is magnet size and shape calculated to provide a given magnetic field?
Post by: ciniva on 23/09/2017 07:01:14
Everything is OK. But, I'm a total ignorant of the science of magnetism.
I need a concrete answer.
(I did not buy magnets yet. I want to first calculate the dimensions, and then buy the magnets.)
What size should be (dimensional, volume and weight) of magnets of the same characteristics to raise up the weight of the 'C' magnet.

Can the magnet of these characteristics lift up its weight (see the construction in the first post)

Example 1
Neodymium magnet grade = N52 (or N35 or N48 or N50M)
L = 21mm
W = 21mm
T = 30mm
Weight = ?

Example 2
Neodymium magnet grade = N52 (or N35 or N48 or N50M)
L = 26.93mm
W = 12.53mm
T = 30mm
Weight = ?

Does anyone know the answer to this question?
My respect to all the scientists.
Title: Re: How is magnet size and shape calculated to provide a given magnetic field?
Post by: evan_au on 23/09/2017 09:35:08
You could use a datasheet like this one (http://e-magnetsuk.com/neodymium_magnets/characteristics.aspx) to calculate some of these factors.

Density= 7.5g/cc
Use the dimensions to work out the mass of each magnet
Title: Re: How is magnet size and shape calculated to provide a given magnetic field?
Post by: ciniva on 23/09/2017 13:38:05
Quote
You could use a datasheet like this one to calculate some of these factors.
Thanks for the link. I'll try to calculate.
Title: Re: How is magnet size and shape calculated to provide a given magnetic field?
Post by: Kryptid on 26/09/2017 14:47:49
Nice try but as some mod removed by posts  from this thread, here's mine:

I was asking ciniva specifically, as the diagram he posted strongly reminded me of a "perpetual motion machine" that I designed when I was a child. I know now that it would not have worked.
Title: Re: How is magnet size and shape calculated to provide a given magnetic field?
Post by: ciniva on 27/09/2017 07:51:33
My inventions over the last 5 years:
Very impressive and captivating. Your knowledge is astounding. (I hope I have written well English)
Can you answer, to my questions on this forum.

I designed when I was a child. I know now that it would not have worked.
All is OK, but probably this was many years ago.
Today is: new time, new materials, new knowledge, new technology, etc.
This is the key to possible solutions that I want.
link: https://www.thenakedscientists.com/forum/index.php?topic=71465.0
Title: Re: How is magnet size and shape calculated to provide a given magnetic field?
Post by: Colin2B on 27/09/2017 14:03:20
Can you answer, to my questions on this forum.
I very much doubt that he has the skills you seek.

This is the key to possible solutions that I want.
link: https://www.thenakedscientists.com/forum/index.php?topic=71465.0
Looking at that link I see a comment:
I am admittedly curious as to what would happen if you constructed a shielded magnet like the type shown in post number 6. Would the magnetic field stop working altogether?
I think Kryptid is right. The magnetic field lines will flow through the shielding material from the enclosed pole and at the open end the field lines will try to take the shortest route to the open pole - the surrounding shielding will act as the opposite pole. You will have made something similar to a horseshoe magnet where one pole (the outer pole) surrounds the inner one, this means the field will not extend out as far as an unshielded pole. However, I think you will need to leave an air gap between the poles otherwise the field extent will be minimal.

Title: Re: How is magnet size and shape calculated to provide a given magnetic field?
Post by: ciniva on 28/09/2017 11:25:53
I think you will need to leave an air gap between the poles otherwise the field extent will be minimal.
I have taken into consideration the air gap. At the moment I have purchased a metal sheet of stainless steel, also known as INOX steel.
I'll try to make several layers separated by plastic material.