The 4 most common questions about magnetization and demagnetization
We field all kinds of questions about magnetization and demagnetization. Our customers like to be informed, and we like to help in any way we can.
Here you’ll find answers to the 4 questions we hear more than any other.
Does it take a lot of energy to magnetize each magnet?
Magnets are exposed to magnetic fields measured in Oersteds.
- Alnico magnets require around 3,000 Oersteds to magnetize.
- Sm-Co magnets require at least 20,000 Oersteds, sometimes as mhcn as 40,000 or more.
- Nd-Fe-B materials require 30,000 or more Oersteds, occasionally surpassing 40,000
How does the magnetizing process work?
High energy materials are often magnetized by discharging a bank of capacitors into an air core solenoid surrounding the part, or a stack of parts. The current pulse supplies energy to overcome the self demagnetizing effect and the energy required to align magnetic domains.
During this process, a magnetic field develops around the solenoid windings before expanding and degrading with time. To be effective, the pulse reaching the center of the magnet must have sufficient amplitude to align domains there. When magnetizing parts with low resistivity and/or a large area normal to the direction of orientation, eddy currents slow propagation of the magnetizing field into the part, so pulse width is an important consideration.
Pulse width is determined by the reactance of the magnetizing system, including the capacitor bank, and the resistance and inductance of the solenoid. A wide pulse insures all domains are exposed to an adequate magnetizing field strength. However, a pulse wider than necessary results in losses due to heat, so production magnetizing systems must be well planned.
Do magnets knock down as soon as they are repelled?
Magnetic flux lines cannot cross each other, so magnets in repulsion develop radial vectors that increase in intensity as the magnets approach each other. To the extent that the amplitude of the radial component of flux density exceeds coercivity of magnetic domains, there will be changes to the properties of the magnet. These changes are due to reorientation of these domains.
Materials such as Nd-Fe-B, Sm-Co, Ceramic, and bonded Nd-Fe-B will see insignificant permanent changes, if any. This will be noticeable as a change in the external flux density, and the total flux available to the magnetic circuit. Magnets with a 'knee' in their second quadrant normal curve, such as Alnico 5 or true Ceramic 5, can demagnetize significantly.
How can I remove magnets after they are shipped in rows?
Each row should be separated from every adjacent row. Do this by pulling each row directly away, outward. To isolate individual magnets, the magnet should be pulled straight away from the next.
The main rule is breaking vs sliding. It is better to break the magnets away from each other than to slide them.
If you have any other magnetization or demagnetization questions, our expert team is ready to help. Give us a call today and place your order.