Sounds pretty easy to me, provided the electromagnet has a flat face 3 inches in diameter for the electromagnet to hold onto and that the electromagnet bears directly onto the metal (not via half an inch of plastic for example).

I have no idea where you would buy such a thing. In terms of making one, the complexity depends upon how many you want to make and how much effort you want to spend on the design. It also depends on the power source. Is DC ok or must it by 110V 60Hz?

Suppose you just want to make one on DC. A soft iron rod 1 inch in diameter will do. You need to cut the rod into two 6 inch lengths and put the two ends into another soft iron rectangular piece with 1 inch holes in it. Tinned copper wire is then wound on both arms (in the same direction as seen by following the magnetic field path). Put DC current through it from a bench power supply until you get enough field strength for your application.

Do check the type of steel, they are not all the same.

TTFN

Thank you

I am just wondering what sort of lenth of copper wire should i use .

I will use a 12v DC power source.

Mag

If I read you right, you want to:

A  Lift 500 grams of steel 25 cm

B  Hold it for a few seconds

C  Let go

B and C is not a problem. But if you want to lift half i kilogram of steel 25 cm using a fixed magnet, then you will need quite a strong magnet. I do not think that a two or three inch diameter magnet will be able to do it.

Gunnar Englund
www.gke.org

http://www.solenoidcity.com/electromagnet/e-40-300p1.htm
http://www.apwcoinc.com/e-magnet.php
http://scientificsonline.com/product.asp_Q_pn_E_3060435

TTFN

Sanity check Skogs. I have read this posting as

the solenoid touches the target load
the solenoid is then lifted 25cm

This is very easy. If we were trying to lift the load 25cm using a stationary electromagnet then we wouldn't have a hope in hell with a 3 inch electromagnet.

IRstuff's first link above shows some typical holding forces and at 10N per kilogram, we only need 0.5kg= 5N. Easy

Magletrik, the hard thing is working out what size of wire to use. Once you have decided on the core you want as much copper on it as you can wind. This is iterative. Pick a wire guage and it is easy to work out the amount that will fit using elementary maths. But what the required working voltage is as a result is tricky! The easy thing to do is just wind one and see what voltage it likes. Change the wire cross-sectional area to change the operating voltage. Smaller cross-section means higher voltage.

Yes Log,

That's why I excercised some caution.

Smacking a 500 g piece of steel to an electromagnet and then lift it (25 cm or many meters) is a no-brainer.

The fact that the lifting distance is specified makes me read the question as I did.

I think it's time for magletrik to say what he wants to do.

Gunnar Englund
www.gke.org

Well, to move a 500 gram object straight up in the air, you need to counteract the force of gravity.  So, at 25 cM, you would need a magnetic field strong enough to produce a force F of

F = mg = 4.91 Newtons.

Hi

I would like to thank you all for your very helpful assistance.

I would like to have a stationary electromagnet mounted ontop of a plastic pipe which could raise a 500g piece of steel with a blade on the bottom of the mass, and then drop it using a P.L.C to cut my plastic profiles in the correct places.

Maybe i am looking at the wrong technology for the application.

Thank you and i appreciate any continued suggestions.

Thanks

Magletrik

Your choice of technology depends on several things. One is what energy you need to cut the plastic material. I assume that you need less than 1.25 joules since that corresponds to 500 g and .25 m vertical travel.

Another thing is if the plastic material is stationary or moving. If it stationary, a pneumatic cylinder is probably your best choice - or a solenoid with an iron core and a travel that is a wee bit more than the plasich material is thick. If it is moving, you can still use a magnet or a cylinder. But you have to make the movement fast enough so the cutting device doesn't jam.

And, as said before, lifting a 500 g mass 25 cm with a stationary magnet is not possible with a 2 or 3 inch coil. Yes, perhaps if you supercool it. But not with standard technology.

Gunnar Englund
www.gke.org

Well, you should have told us that at the start.  

What you can do is to wind 5 or so different coils along the tube length.  When you energize the first coil, the object rises 5 cM.  Then you turn on the 2nd coild and then turn off the first coil.  The object rises from 5 to 10 cm.  And so on until the last coil is holding the object at the end of the tube.  You then turn off the last coil and the object drops.  A simple microprocessor can time it so it picks up the object, and a interface circuit can have the microprocessor turn on/off the heavy duty pass transistors to handle the coil current.

Why are you not using a hot knife?  

There's little that you've said that indicates that you are controlling the cutting behavior, either in terms of positioning or depth with your approach.  Is that not a concern?

TTFN

Well done skogs. Saved us a lot of time. I nearly started roughing out the design in terms of a starting value for the wire diameter and so forth.

Magletrik, let me revise my response. There is no chance that you can design or buy a 3 inch diameter electromagnetic that can directly lift any significant load by a foot vertically.

I think you can extend the range of an ordinary electromaget by putting on an L-shaped crank so the part at the electromagnet moves say 1 inch and the levered end moves say 4 inches. Nevertheless a foot is a long long way.

I would think a pneumatic solution would be better.

Thank you all

I have got a rough design and will start making a prototype soon.

Thanks a lot

Magletrik