To design the magnets in a great working status.
(1)The workload point of magnets should be above (BH)max, so as to increase the safety of irreversible demagnetization of magnets at work by sacrificing some magnetic energy product.
(2)To try some bigger magnet design and avoid the magnets with easy magnetization axis less than 1mm. Because the coercive force of NdFeB magnets are decided by nucleation mechanism, which cause the coercive force of magnets and the demagnetization curve squareness are affected by the surface states, specific surface area and L/D ratio of magnets. When the dimension of magnet is less than 1mm, the coercive force of magnets and the demagnetization curve squareness of it is obviously lower than big magnets. The smaller the surface roughness of magnets, the smaller the specific surface area, the larger the L/D ratio, the magnetic properties of magnets will be more stable while working at high temperature.
(3)Using good magnetic circuit ventilate, thermal design.
To use NdFeB magnets with suitable magnetic property.
(1)First of all, we need to make sure when the devices are required to work at a certain temperature, the reversible loss of magnetic flux is smaller or the irreversible loss of magnetic flux is smaller. If the devices require smaller loss of reversible magnetic flux while magnets are working at high temperature, we should choose magnets with small temperature coefficient of Br (for example, magnets which contain Co.). If the devices require smaller loss of irreversible magnetic flux while magnets are working at high temperature, we should choose magnet which have high Hcj such as N35H, N35SH, N35UH and N33EH. If the devices require reversible and irreversible loss of magnetic flux, we should choose magnets which contain Co and high Hcj.
(2)Within an available cost range, we use those magnets with high Hcj.
It is noticeable that the high temperature demagnetization curve and the temperature coefficient of magnets the magnet manufacturers provide to users, are measured by standard size of magnets (such as φ10.0*φ10.0mm). When the magnet products that are used by users have smaller specific surface area, larger L/D ratio than standard samples, the high temperature demagnetization curve and the temperature coefficient of magnets the manufacturers provided can reflect the high temperature operating characteristic of magnets. If the magnets products that are used by users have larger specific surface area, smaller L/D ratio, the actual high temperature operating characteristics of magnets are usually lower than the data manufacturers provided. That is to say, the actual high temperature operating characteristics of sintered NdFeB magnets not only relate to the magnetic properties of magnets themselves, but also the sizes and working status of magnets.
Adopting suitable surface protective layer
In fact, the surface protective layer on the magnets also influences high temperature operating characteristic of magnets. Practice indicates that all the electronic coating will decrease high working temperature characteristic of sintered NdFeB magnets. That is to say, in the case of same magnetic property and dimension, black wafer magnets have a better high temperature operating characteristic than those magnets which have coating. In the existing coating, Ni-Zn coating works best, Zn coating secondly, Nickel plating is the last. But regarding corrosion resistance, Nickel plating is the best, Ni-Zn is the second, Zn coating is the last. Therefore, when users choose the magnet products, in addition to determining the magnetic property and dimension tolerance of magnets, they should also consider about the surface protective layer on magnets, the working environment.
Tags: NdFeB magnets, sintered NdFeB magnets
(1)The workload point of magnets should be above (BH)max, so as to increase the safety of irreversible demagnetization of magnets at work by sacrificing some magnetic energy product.
(2)To try some bigger magnet design and avoid the magnets with easy magnetization axis less than 1mm. Because the coercive force of NdFeB magnets are decided by nucleation mechanism, which cause the coercive force of magnets and the demagnetization curve squareness are affected by the surface states, specific surface area and L/D ratio of magnets. When the dimension of magnet is less than 1mm, the coercive force of magnets and the demagnetization curve squareness of it is obviously lower than big magnets. The smaller the surface roughness of magnets, the smaller the specific surface area, the larger the L/D ratio, the magnetic properties of magnets will be more stable while working at high temperature.
(3)Using good magnetic circuit ventilate, thermal design.
To use NdFeB magnets with suitable magnetic property.
(1)First of all, we need to make sure when the devices are required to work at a certain temperature, the reversible loss of magnetic flux is smaller or the irreversible loss of magnetic flux is smaller. If the devices require smaller loss of reversible magnetic flux while magnets are working at high temperature, we should choose magnets with small temperature coefficient of Br (for example, magnets which contain Co.). If the devices require smaller loss of irreversible magnetic flux while magnets are working at high temperature, we should choose magnet which have high Hcj such as N35H, N35SH, N35UH and N33EH. If the devices require reversible and irreversible loss of magnetic flux, we should choose magnets which contain Co and high Hcj.
(2)Within an available cost range, we use those magnets with high Hcj.
It is noticeable that the high temperature demagnetization curve and the temperature coefficient of magnets the magnet manufacturers provide to users, are measured by standard size of magnets (such as φ10.0*φ10.0mm). When the magnet products that are used by users have smaller specific surface area, larger L/D ratio than standard samples, the high temperature demagnetization curve and the temperature coefficient of magnets the manufacturers provided can reflect the high temperature operating characteristic of magnets. If the magnets products that are used by users have larger specific surface area, smaller L/D ratio, the actual high temperature operating characteristics of magnets are usually lower than the data manufacturers provided. That is to say, the actual high temperature operating characteristics of sintered NdFeB magnets not only relate to the magnetic properties of magnets themselves, but also the sizes and working status of magnets.
Adopting suitable surface protective layer
In fact, the surface protective layer on the magnets also influences high temperature operating characteristic of magnets. Practice indicates that all the electronic coating will decrease high working temperature characteristic of sintered NdFeB magnets. That is to say, in the case of same magnetic property and dimension, black wafer magnets have a better high temperature operating characteristic than those magnets which have coating. In the existing coating, Ni-Zn coating works best, Zn coating secondly, Nickel plating is the last. But regarding corrosion resistance, Nickel plating is the best, Ni-Zn is the second, Zn coating is the last. Therefore, when users choose the magnet products, in addition to determining the magnetic property and dimension tolerance of magnets, they should also consider about the surface protective layer on magnets, the working environment.
Tags: NdFeB magnets, sintered NdFeB magnets
