Hello Mr. Budhram,

The traditional methods for iron removal involve the use of hanging overhead electro-magnets (either static or self cleaning) or magnetized discharge pulleys with a separate collection chute for the tramp metal. If you have, or suspect that, other sources of magnetism that are interfering with the process you can remove those sources or increase the effectiveness of your removal magnets.

I suggest that you (1) scan your equipment to determine if you do, in fact, have errant sources of magnetism; (2) determine if your magnet is placed properly for metal removal purposes; and contact supplier/manufacturer companies, such as Eriez to discuss what is best suited for your process. Since the manufacturers will want details on your system, you should have the information available before contacting them.

Regards, ■

You indicated that recently the magnet's effectiveness was questioned. Were they effective previously? If so then something may have changed, such as the conveyor speed, the size of material or a capacity increase which may have increased material depth and made the magnets less effective or the magnets may have been raised decreasing their effectiveness.

A magnet should not be placed directly over a steel idler roll because it inductively magnetizes it and causes tramp iron to adhere to it, rather than migrating to the magnet. Any chute which is adjacent to the magnet should be made of non-magnetic material.

Can you describe the position of the magnet? Is it a self-cleaning type, is it mounted over the trajectory of the material or parallel over the belt? Look forward to your response.

Don Morgan

Walker Magnetics

mormag@execpc.com ■

Dear Shri Dinesh,

Firstly, please check that the tramp irons (miner pikes) are magnetic in nature. Sometimes manganese steel is non-magnetic in nature and if the pikes are made of such material than magnetic separation will not be effective.

If the magnetic separator is unable to remove the tramp iron, there are three possibilities A, B or C as below :

A) Magnetic separator flux density and flux gradient are not of adequate strength and thereby they are unable to remove the tramp iron in the available time.

B) The belt conveyor speed is very high and consequently time available for the separation is not adequate for physical extraction of the tramp iron.

C) The magnetic separator operating height is excessive. The effectiveness of the magnetic separator is highly sensitive to operating height. If possible, make it bare minimum. This could be approximately material burden depth of regular profile + half the lump size + 100 mm clearance.

Also check that the magnetic separator orientation is proper, for maximum effect.

If you have exhausted the possibilities A, B and C, then one solution is as below :

For effective removal, the solution is to have one small length conveyor of wider belt width in combination with cross belt magnetic separator and magnetic pulley. This should have speed less or somewhere around 1.0 m/s (60 m/min or 200 FPM). This solution is comparatively expensive, but if designed properly it can positively remove the tramp irons.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyor.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916 ■

We experienced a problem where increase in production caused the inability of our magnet to lift the metal through the product on the belt. Increasing the size of our magnet solved the problem.

We also utilize a Ramsey metal detector (see link below) downstream of the magnet. If the magnet does not pick up the metal then the detector will shutdown the belt and alarm the operator. This may not be a possibility for you but if the cost of the equipment damage is greater than the short shutdown period to remove the metal manually. This could also trigger a material deflector to knock product and metal off the belt for a short duration. (again this may or may not suit your application)

Hope this helps,

Gary

http://www.thermo.com/eThermo/CDA/Pr...-13963,00.html ■

Can you clarify the position, type and orientation of the magnet.

A cross belt magnet will not be as efficient as a magnet mounted over the head discharge pulley. This is the typical location for heavy metal removal. The world's strongest conveyor belt magnets are mounted over the head pulley. The flow stream is opened and the magnet can be placed close to the stream.

The belt velocity and head discharge arrangement may allow an efficient design. However, belts operating over 4 m/s will have less efficiency. Eventually, higher tonnage will require an slower speed, wide inspection belt with a magnet before and metal detector after (manganese steels, et al) the loading point.

Chute and pulley design may have to be modified for the discharge magnet.

Lawrence Nordell

Conveyor Dynamics, Inc. ■

Dear Mr.Dinesh,

To answar you, I want to assume the following:

-You have matel dectector in connection with magnet.

-You have placed the magnet at such a distance so that magnet can get 15 sec. time to energish itself after detection by metal detector.

-Condition of magnet is healthy.

- You have provided two metal dectector with marker.

If all the above are incorporated , I think there would not be any problem.

Regards.

A.Banerjee ■

The paper below has some interesting comments on magnets.

http://www.saimh.co.za/beltcon/beltcon7/paper715.html ■