Since March 1, 2010 our headquarter is located in Essen.
From 26.-30. October 2010 ThyssenKrupp Magnettechnik is represented at the world's largest sheet metal working exhibition.
Please visit our stand E22 in exhibition hall 16!
Viewed historically, this
system type was the first electrically switchable permanent
magnet system and is today of hardly any importance any longer
because of its high pulse power when switching from the „magnetic“
state to the „neutral“ state. Nevertheless, it
may be practical to use it wherever a low switching frequency
is guaranteed and the „magnetically neutral“ state
must be on over longer periods. The switching time of this
type of magnet is usually markedly higher than that of the
monostable systems. There are 2 types of switchover systems
here also, Type 1 representing a „rapid-switching“
version and Type 2a version which is specially suitable for
load-elevating applications.
The functional principle
It is designed with 2 poles and has two kinds of magnets;
this makes the system very interesting from the point of view
of the technology of magnets. It is designed as presented
in Fig. 2.
Due to the field strength of the coil the AlNiCo-magnet will be magnetized in the one or the other direction. Herewith the HF-magnets are strengthened or diminuished in their strength.
The advantage of this system is that both switching states
(„magnetic“ and „neutral“) are stable
and that electrical energy is required only for switching
over the states. However, a high level of switching current
is necessary, putting a heavy load on the mains supply; this
involves a development of heat which then allows a switching
frequency of only approx. 60 switches per minute.
Fig. 2: Bistable magnetic system of type 1 with two magnetic
materials
This system also is open at the top, making it impermissible
for ferromagnetic material to be located directly over the
magnet system (similarly to that of the displacement system
of Type 2A).
There is an additional problem in minimizing the residual adhesive power, because the AlNiCo magnet must compensate exactly the magnetic field of the two ferrite magnets, i.e. it must have the same magnetic flux. Since the magnetic values, however, are subject to scatter, there is always a certain residual adhesive power remaining. This system is interesting because the very different demagnetization curves of the two magnet types have been ideally combined. The high remanence of the AlNiCo 500 cast is necessary so as to make available the necessary flux in as small a space as possible in the highly enclosed system; the coil diameter may thus be kept small, since the full hysteresis curve of the magnet traverses the coil field. In addition, it is also important that the AlNiCo magnet has a low coercivity so as to facilitate remagnetizing by means of the coil.
On the other hand, the high coercivity of the ferrite magnet is used, because this magnet must not be affected by the coil field. Everywhere that it is unavoidable to maintain both magnetic states over longer periods, there is no alternative to these systems, unless electric systems are used, which, however, involve a safety risk in the „magnetic“ state if the electricity fails.
Today the ferrit magnet is often displaced through the rare earth material NdFeB which reduces the own weight.
