Modi, Well done!!!
Double C - CORE VS E-I CORE !!!
Basic (very) domain theory tells us that magnetic steels function by two main processes, domain growth and domain rotation.
Under low magnetization, the field domains, which are oriented in the direction of the applied field, grow at the expense of their non-oriented and anti-parallel neighbors, this low field domain growth is generally reversible if the field is removed.
Under a medium applied field again domain growth is the predominant factor. However there will be some non-reversible growth of the domains, and a reverse field is required to return them to their original state.
Under a large magnetization field those domains, which were not oriented in the direction of the applied field start to rotate towards that direction. Eventually all of the domains are pointing in the direction of the applied field and saturation is reached.
This neatly explains the familiar shape of the B-H curve and hysteresis loop.
Essentially iron crystallizes in a body cubic form and the domains are oriented parallel to the edges of the crystal, therefore an iron crystal will be easier to magnetize if the applied field is parallel to an edge, and will be most difficult to magnetize in a diagonal direction across the cube.
In a non-oriented material the crystals and the domains are oriented randomly, therefore it will magnetize much the same in any direction. However no direction is aligned with the preferred direction of all of the crystals, and a lot of the crystals will be oriented in the worst direction.
Therefore permeability is low and losses are high. The hysteresis loop will be wide and rounded. In a singly oriented steel (M4 etc, there are cubic oriented types which we use as well) the crystals are oriented so that two of the faces are perpendicular to the strip rolling direction, two of the edges are parallel to it and the other edges are at 45 degrees to the strip surface. In other words the plane of the strip cuts the diagonal of the faces, which are perpendicular to it. This means that the material is very easy to magnetize by a field parallel to the strip rolling direction as the domains are facing in that direction.
This makes for a material with a high permeability, low losses and a narrow rectangular hysteresis loop when the field is in the strip direction. But it also means that a field in any other direction in the plane of the strip will be trying to magnetize the crystal in it's worst possible mode. The highest losses always occur at approximately 45 degrees to the rolling direction, in the plane of the strip. |