Norma S.r.l.  

norma.srl@virgilio.it
  control panels   |   magnets   |   heatsinks   |   diodes and rectifiers  


 

MAGNETS
MAGNETS
 

The NORMA Company, born in 1949 on initiative of a group of friends, is gone from the very beginning towards the industrial application of the electricity.
The production of ceramic permanent magnets started in 1963 in order to obtain components with high uniformity and stability, characteristics almost too difficult to find in the market at that time.
As a matter of fact the first NORMA magnets were used initially on a new device designed and produced by the company: the magnetic switch. Soon after, due to the increase of the productive capacity it was decided to put on the market cylindrical and square magnets where the overall dimensions correspond to a geometric series.
The possibility to find out, quickly and at lower price, ceramic permanet magnets has helped the performance of these components. For that reason their industrial applications have been greatly increased.
Today permanet magnets are used in many fields such as electric motors, generators, telephone appliances, automatic machinery, level transducers, antitheft devices, arcing contacts, filters, conveyors, watermeters, couplings, magnet closures, etc.

SOME HISTORY OVER MAGNETISM

The presence of magnetism is well known to the man, in his most simple appearance, since about 2000 years. The word “magnet” probably comes down from the thessalic town of Magnesia where at first was found and digged out a material, the magnetite, with peculiar characteristics.
The Chinese, around the second century A.D., utilized an instrument, based on magnetism, which could be compared to a very primitive compass.
In Europe the first experiments over magnetism were taken around the thirteenth century A.D. Well known in Italy is Flavio Gioia, who probably discovered the terrestrial magnetism and to follow invented to the compass.
In the year 1600 Gilbert published the first systematic work which can be regarded as a proper and genuine treatise of experimental physics.
Finally in the year 1820, thanks to the Danish scientist Oersted, the teoric foundations of magnetism were laid down giving incontrovertible proof of its links with the electricity.

MATERIALS AND THEIR MAGNETIC PROPERTIES

Materials can be classified also according to their behaviour in a magnetic field, and divided consequently between non-magnetic and ferromagnetic.
To the non-magnetic materials (diamagnetic and paramagnetic) belong the gases, liquids, organic matter and some metals. They don’t have any tendency to be magnetized and the magnetic flux goes through them without any resistance thus not modifiyng their physical condition. These non-magnetic materials cannot be used as magnetic shields or insulators. They are normally used as supports or containers for the magnets.
Ferromagnetic materials come under two categories: SOFT and HARD.
Between the SOFT ferromagnetic materials we may recall:

  • the soft Iron, pure, without Carbon
  • the Nichel-Cobalt alloys
  • the Iron-Cobalt alloys
  • some stainless steels
  • the soft Ferrites

These materials are easily saturated even by magnetic fields very weak. But disappearing these external actions they lose almost completely the magnetic characteristics. Soft ferromagnetic materials are used normally as preferential circuits for the magnetic flux lines (cores, armatures, polar expansions).
HARD ferromagnetic materials are the most suitable for the production of permanent magnets. Among these compounds we may recall:

  • the Iron-Nichel-Aluminium-Cobalt alloys
  • the Hard Ferrites (Barium and Strontium Ferrites)
  • the Platinum-Cobalt alloys
  • the Rare Earth alloys, like Samarium-Cobalt and the Iron-Cobalt Neodimium alloys.
These materials are, due to their magnetic properties, very stable in the long time as well outside magnetic fields.