Because with magnetics you can "do work" on an object without even touching it! That's why!

Magnetism has, due to such special abilities, found many applications over the years. From medicine (magneto-therapy) to transportation (magneto-levitated-vehicles). The common VCR and tape-deck also use principles of magnetics to record and playback movies, music, speech and data. If we were to discuss all of these applications we would need more pages than are available in this entire book. However, since this is a directory specifically made for Manufacturers and users of Material Handling Equipment we will try to cover most of the common applications of Magnetics for that purpose.

In the Material Handling Industry magnets are usually used to hold, convey, elevate, control, or separate magnetic (ferrous) material. Today magnets are made out of either Ferrite magnetic powder (Barium or Strontium phosphate) or by winding coils around a ferrous core (Electromagnets). Other material like Samarium- Cobalt, Neodymium-Iron-Cobalt, rubberised ferrite materials, etc. are also used but these have very specialised applications (wiper and disk drive motors, gaskets of household appliances, etc.).

Magnets made out of Ferrite (or older Aluminum-Nickel-Cobalt -- AL- Ni-Co) magnetic powder are called Permanent magnets since they retain magnetism after the magnetising current is switched off. Magnets which require a constant source of electricity are called Electromagnets. Certain designs also incorporate hybrids of these two magnetic forms - they are called electro-permanent magnets.

Electromagnets and permanent magnets have a number of inherent advantages over mechanical or pneumatic equipment to perform the same function. Foremost among these advantages is the ability of magnetic equipment to produce a force and do work without direct contact. Magnets can operate efficiently through walls of tanks, pipes, chutes or conveyor belts.

Magnetic equipment also have a long life and constant strength. Permanent magnets for example loose only about 0.5% of their strength every 100 years provided they are not abused by hammering, banging, excessive heating etc.. Electromagnets also have a very long life - most failures in properly designed electromagnets can be traced to operator misuse or gross abuse.

Either type of magnet can produce relatively uniform, widely distributed and consistently repeatable forces. Magnets can also be designed to produce intense fields in small places. In contrast to most other mechanical devices the force produced by a magnet can readily be controlled and/or limited. This feature of magnets can often be used to provide for safety releases - if the force opposing the magnet exceeds the magnet's holding power it will "let go" without any physical failure or any changes in it's ability to perform the same task again.

Magnetic equipment may be subjected to temperatures as high as 600 degree Centigrade without loss of strength or mechanical properties and can hold ferrous material of different sizes and shapes. It is therefore excellent for lifting and transporting magnetic material, and separating and sorting magnetic material from non- magnetic material.

The principles of magnetism are used by manufacturers of Material Handling Equipment, Steel Plants, Power Plants, Cement Factories, Foundries, Food and Fertiliser Plants, Iron Ore Mines, Crane Manufacturers, Glass and Abrasives Manufacturers, Machine Tool Manufacturers and other related industries.

Applications of magnetic principles are so vast that they are practically limited only by one's imagination. However to understand how and when to apply these principles one must know the advantages and disadvantages of magnetism. Magnetism, for example, only works on ferrous material (in general - exceptions include eddy current based separators for non-ferrous metals); can only create as much "force" as the object is able to absorb, and is very inefficient and expensive when working over large distances.
Both permanent magnets and electromagnets have advantages and disadvantages. Some of these are listed below.

• High efficiency - no operating cost
• No power required hence not affected by power failure
• No electrical connections required
• Can be used for liquids easily
• Usable up to 150 degree Centigrade (350 degree Centigrade for Al-Ni-Co magnets)
• Hardly any maintenance
• Can be used in hazardous atmospheres
• Unaffected by shock or vibrations (not banging or hammering)

DISADVANTAGES OF PERMANENT MAGNETS

• Not easy to control the power (force)
• Limited working depth (field depth)
• Cannot be switched off and forced to release load (except in very specialised applications)

• Strength readily Controllable
• Excellent depth of field
• Can carry much higher loads than Permanent magnets
• Can be made to work with loads having temperatures up to 600 degree Centigrade
• Can be switched off and forced to release load

DISADVANTAGES OF ELECTROMAGNETS

• Requires D.C. power
• Limited in operational parameters (not readily water-resistant, heat-resistant, shock-resistant etc.)
• Power failure can cause damage/injury
• Eventual Burnout

Magnets can only "work" on ferrous objects. A magnet performs a function on a ferrous object because it can "induce" a "field" in that object. The intensity of the "field" is directly related to the potential ability to do "work". The "field" generated by a magnet is also be called "MAGNETIC FLUX". MAGNETIC FLUX is bi- directional (POLARISED). The directions of MAGNETIC FLUX are called NORTH and SOUTH. The magnetic field (FLUX) can be thought of as entering the ferrous object through the SOUTH POLE of the object and leave the object through the NORTH POLE. Only "unlike" POLES attract. That means that only the NORTH and SOUTH poles of two magnets will attract - "like" poles will repel!

Many countries have used this feature of magnetism to create contact-less transportation in the form of trains that are levitated by a magnetic system. A levitated train has virtually no friction and requires very little energy to move!

The strength of the magnetic poles is dependent on the amount of iron in the object it's shape, and the external magnetising force produced by the magnet (the strength of the magnet). Hence both parts of the magnetic system must be considered.

When a magnet produces a magnetic field in a ferrous object the work done can be calculated as the force of the field multiplied by the distance through which the object moves (Work = Force x Distance). If the object does not move towards the magnet the magnet will continue to exert it's force but the magnet does no work.

In selecting magnetic equipment one must know the function one wants to perform. As mentioned earlier, magnets can hold, separate, convey, control and elevate material. A magnet can de designed to perform any combination of these tasks. The user must then select equipment whose fundamental design and performance characteristics are properly related to the function.

Some performance characteristics (design parameters) are: Holding or Pulling Power, Flux Gradient, and Flux Distribution. The user can then decide whether an Electromagnet or Permanent magnet will be most suited for the application and the size and shape of the magnetic assembly.

Each parameter of the magnetic assembly can be tested. However due to the number of variables involved the user may find that the magnet does not perform up to expectations. For example, in the case of Scrap Handling Magnets (a Lifting Magnet designed to lift scrap ferrous material) the bulk density of the scrap plays a crucial role in determining the amount of scrap that will be lifted; or in the case of a Magnetic Separator (a magnet designed to separate magnetic material from non-magnetic material) if the magnetic material is too small or buried deep under the burden of other material, (on a conveyor) it may not be separated.

Magnetic equipment can be tested. Unfortunately these tests are usually perfomred under controlled conditions. These conditions may not be replicated in actual industrial applications. Hence it is advantageous for the user to know as much about the material (density, size, shape, oxidation level etc.) and it's surroundings (temperature, humidity, etc.) as possible.

It may not be possible to determine the exact performance of magnetic equipment under all variations and combinations of materials and surroundings but one can now make a good "guess- timate" of the performance. For example in the case of a lifting magent, if the bulk denisty of the material is 20% less than the "test density" one can assume than the lifting magnet will lift approximately 20% less load per lift.

If one is more interested in the various testing procedures, one can study the testing procedures for various magnetic equipment of the British Standards (BS), German Standards (VDE), and American Standards (UL).