electromagnet / solenoid - bigger rings equal bigger area of effect?

[potatodude]

I'm building a magnet, doesn't have to be very powerful in terms of its pulling force, but I'd like it to cover a large area, at least 30cm diameter. Is it a simple case of using more wire to make bigger rings?

I understand a solenoid is just a ring, whereas if it has a ferous core then it is an electromagnet. Please correct me if I am wrong about that.

Thanks

 

[rjenkinsgb]

A solenoid typically has a moving core inside the coil, often also with a ferrous shell and possibly partial fixed core.
It can also mean other variations using a combination of an electromagnet and moving core in a single assembly to produce a mechanical effect; "Rotary solenoids" such as Ledex actuators come to mind.

http://www.ermec.com/catalogos/2017/saia/Rotary%20DC%20Solenoids%20mm.pdf

Large electromagnets are often made in segments, with an array, concentric circles or grid of coils, each with its own polepiece and arranged to give alternate magnetic polarities at the magnet surface, so a stronger field circulates through the external object.

See the photos in this link:

Magnetic chuck repair, chuck repair, electromagnetic chuck repair, permanent chuck repair repair any make of electromagnetic or permanent magnetic chuck - Newman Tools

Supplying High Quality Tools and Supplies for Machine Shops, Plant Engineering and Maintenance since 1955

www.newmantools.com

The rectangular one will likely have all the coils the same polarity, as the "alternate poles" come from the back of the coils.
The circular ones are probably alternating to the circular polepieces between them alternate north-south.

More examples below, both variations again: The round ones have almost all the metalwork (polepieces) through them, so likely alternating polarity on each coil, to get similar areas of north and south poles to the face of the magnet. The rectangular one has a lot of metal around the magnet coils, so probably all the same polarity.

If you can find some old transformers with identical size cores, you could strip them and use the "E" part of the core and coilformer to make good electromagnets.

 

[potatodude]

thanks thats really interesting and helpful. I'm going to give it some more thought.