Naked Science Forum

Non Life Sciences => Technology => Topic started by: Slartibartfast on 30/09/2014 05:10:49

Title: How do Permanent Magnetic Lifters Work?
Post by: Slartibartfast on 30/09/2014 05:10:49

I've only heard about these recently but many workshops use these lifting magnets that have an activation leaver.  You place the device on the item to be lifted, throw the leaver to activate the magnet then lift the item via the magnet.  Once you have moved the item to where you want it you simply throw the leaver back to deactivate the magnet and remove it.

Since hearing about them I have been searching all over to try and find an explanation of how they work but can't seem to find much that is useful.  The one thing I am clear on is they are not electro-magnets.

Could any one explain or point me to a source that explains how they work?
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.activelifting.com.au%2Fimages%2FLiftingEquipment%2Fmagnets%2FBML%2Fmagneticlifter-1.jpg&hash=91c89c8eed256d331d4aa2fdba92a14a)
Image is one of the first images found when searching for "permanent magnet lifter" on Google.


Thanks,
Slarti.

Title: Re: How do Permanent Magnetic Lifters Work?
Post by: alancalverd on 30/09/2014 09:25:53

The usual trick is to have several magnets arranged with alternating polarity. This concentrates the convergent field close to their surface. The lever simply moves the asssembly of magnets up and down a millimeter or so. In contact with a smooth steel surface, this provides huge "suction" but a very small shift will release it.   

Title: Re: How do Permanent Magnetic Lifters Work?
Post by: Slartibartfast on 30/09/2014 09:28:48

Hmm, fascinating.

Are you able to point me to a diagram explaining it?
I'm finding it hard to envisage.

Title: Re: How do Permanent Magnetic Lifters Work?
Post by: evan_au on 30/09/2014 10:53:14

It doesn't make the object any lighter to lift - in fact, it makes it heavier, because you must lift the lifters too!

What it does is to temporarily attach a couple of convenient handles to the object that lets you lift it by hand, or attach it to a crane hook. The lever lets you gently attach or detach the lifter.

It will only work with ferromagnetic materials, so it won't work on plastic or glass.
I've seen similar devices that can lift flat sheets of glass or plastic, using "suction cups".

Title: Re: How do Permanent Magnetic Lifters Work?
Post by: mtgaunce on 27/10/2014 14:24:31

Hello,

First post here. I design these type of magnets. Our company actually has a great post about how these work. It's not as simple as the user above said.

You will find this very helpful I think: Switchable Magnets Explained (http://www.docmagnet.com/learning-center/switchable-magnets-exchanged/)

Basically, when you turn the lever you turn a rotor inside the body of the assembly. When the rotor is in the 'On' position, there is a magnetic circuit that creates a loop through the thing being picked up. When the rotor is in the 'Off' position, the magnetic circuit is redirected and contained entirely inside of the assembly.

Hope this helps,
Michael

Title: Re: How do Permanent Magnetic Lifters Work?
Post by: tib on 20/11/2014 07:35:45

What kind of material do you use for such a good magnetic shielding?

Title: Re: How do Permanent Magnetic Lifters Work?
Post by: CliffordK on 22/11/2014 06:32:05

Those devices are commonly used for work stands for either scientific use, or perhaps holding measuring instruments in a machine shop.

I don't believe they need any "shielding", but rather are made of steel.  Interesting "horse-shoe" design either conducting or not conducting the magnetic force.

Title: Re: How do Permanent Magnetic Lifters Work?
Post by: wolfekeeper on 02/01/2015 18:23:00

There's more than one way to do this. The iron backing plate has already been mentioned. And by the look of it, that's how the device displayed works.

However, you can also do it with Halbach arrays:

https://en.wikipedia.org/wiki/Halbach_array#Variable_flat_arrays