ABOUT MAGNETS MEDER electronic Magnets and Their Specifications Magnets are available in multiple specifications on the market. Almost all dimensions and geometries can be realized. To activate the reed switch a magnet (magnet field) is needed. The different magnet materials have either more positive or negative specifications, depending on the dimension and geometries as well as on the environment. Most preferred and used forms are cylinders, rectangles, rings and discs. Depending on the different requirements, magnets can be magnetized in many different ways (see picture # 37). Furthermore each magnet material has a different mag- net force as well as a different flux density. Additionally to dimension and material, other factors exist that define the energy of a magnet. These are mounting position, environment and other magnetic field witch influence the interaction between reed sensor/switch and magnet. In applications were a magnet is used to activate a reed sensor/switch, the environmental temperature needs to be considered (in the application as well as in storage). High temperatures can cause irreversible damage and will have heavy impact on the magnetic force and the long term stability. AlNiCo magnets are best suitable for applications up to 450°C. (Figure #37. An assortment of magnets are shown. Magnets can be formed and made into almost any shape.) www.meder.com 39 ABOUT MAGNETS MEDER electronic General Information to magnet material Magnets have reversible and irreversible demagnetization specifications. Be specially careful with shock, vibration, strong and close external magnetic fields as well as high temperatures. All these factors influence the magnetic force and the long term stability in different intensities. Preferably the magnet is mounted on the moving part of the application. Professional tuning of magnet and reed switch can improve the functionality of the whole sensor-magnet system. LOW HIGH costs Ferrite AlNiCo NdFeB SmCo energy (WxHmax.) Ferrite AlNiCo SmCo NdFeB working temperature NdFeB Ferrite SmCo AlNiCo corrosion - resistant NdFeB SmCo AlNiCo Ferrite opposing field - resistant AlNiCo Ferrite NdFeB SmCo mechanical strength Ferrite SmCo NdFeB AlNiCo temperature coefficient AlNiCo SmCo NdFeB Ferrite AlNiCo - Magnets AINICo Features Standard geometric and magnetization Cylinder Rectangle • working temperature from -250 to 450 oC • low temperature coefficient Raw materials for AlNiCo magnets are aluminium nickel, cobalt, iron and titanium. AlNiCos are produced in a sintering - casting procedure. The hard material needs to be processed by grinding to be cost effective. Due to its specifications, the best dimension is a remarkably longer length than its diameter. In combination with reed sensors / switches we recommend a length / diameter ratio of more than 4. AlNiCo magnets have an excellent temperature stability. Negative are the high raw material prices. Cylindrical AlNiCo magnets can be used with all MEDER reed sensors / switches without any problems. AINiCo Magnetic Values according to DIN 17410 Min. Typ. 35 39.8 kJ/ m3 Remanence 1210 mT Reverse Temperature Coefficients of Br 0.02% %/K Energy Product (B x H) max. Units Coercivity HcB 47.0 51.3 kA/m Coercivity HcJ 48.0 51.7 kA/m - - - %/K 7.4 g/cm3 Reverse Temperature Coefficients of HcJ Density Max. Operating Temperature All details correspond to manufacturers information www.meder.com 40 Max. 450 o C ABOUT MAGNETS MEDER electronic Rare - Earth Magnets SmCo Features Standard geometric and magnetization Disc Rectangle Cylinder • high energy density • small size • working temperature up to 250 oC • best opposing fieldresistance • available plastic bounded NdFeB Features Standard geometric and magnetization Disc Flat Rectangle Ring • high energy density • small size • working temperature up to 180 oC • lower prices compared to SmCo • available plastic bounded Rare - Earth magnets like SmCo and NdFeB have the highest energy density per volume and wight and also • Hartferrit • AlNiCo • SmCo • NdFeB = = = = the best demagnetizations resistance. Following below, we compare other magnets with the same energy: Volumes 6 cm3 Volumes 4 cm3 Volumes 1 cm3 Volumes 0.5 cm3 www.meder.com 41 MEDER electronic ABOUT MAGNETS Both magnets are produced by sintering and can only be processed by grinding, due to the strength and brittle of the material. The temperature range goes up to + 250 °C. Very small magnets can be produced. Disadvantages are the high raw material prices and the lim- SmCo5 Magnetic Values according to DIN 17410 Energy Product Remanence ited availability of special alloys. The supply of different geometry, size and magnetization allow many creative combination of reed sensor / switch and magnet and help to find the best functionality of the sensor - magnet system for each application. Min. Typ. (B x H) max. 160 170 Br 900 Reverse Temperature Coefficients of Br Max. Units kJ/ m3 925 mT -0.042 %/K Coercivity HcB 680 2000 kA/m Coercivity HcJ 1750 -0.25 kA/m %/K Reverse Temperature Coefficients of HcJ Density g/cm3 8.3 Max. Operating Temperature 250 o C All details correspond to manufacturers information NdFeB Magnetic Values according to DIN 17410 Energy Product Remanence Min. Typ. (B x H) max. 205 295 kJ/ m3 Br 1180 1240 mT Units -0.1 %/K Coercivity HcB 680 920 kA/m Coercivity HcJ 1750 1900 kA/m Reverse Temperature Coefficients of Br Reverse Temperature Coefficients of HcJ -0.6 %/K Density 7.6 g/cm3 Max. Operating Temperature All details correspond to manufacturers information www.meder.com 42 Max. 160 o C ABOUT MAGNETS MEDER electronic Hard ferrite - Magnets Ferrit Features Standard geometric and magnetization Disc Cylinder Rectangle Ring • cheapest magnet material • working temperature up to 300 oC • many options in form and magnetiuation • available plastic bounded Hard ferrite magnets are produced with iron oxide and barium or strontium oxide. The raw materials are mixed together and normally pre sintered, to generate the magnetic phase. The pre sintered mixture then gets crushed. The resulting powder gets pressed together (wet or dry) either in a magnetic field (an - isotropic) or without a magnetic field (isotropic) and in the end sintered. Proceedings are only possible by grinding. Due to the low cost of the raw material, hard ferrite magnets are the cheapest magnet type out of the actual sup- Ferrit 28/26 Magnetic Values according to DIN 17410 Energy Product Remanence ply of magnets. Ferrites have a very good electrical isolation effect and are hard to demagnetize even in strong external magnetic fields. Corrosion tendency is low. Preferred shapes are long and thin but also round forms are easy to produce. Disadvantages are the high breakability and the low tensile strength. The strength and brittleness of hard ferrites are similar to ceramics. Furthermore the temperature resistance is limited and they have only a low energy to volume ratio. Min. Typ. Max. Units (B x H) max. 28 30 kJ/ m3 Br 385 395 mT -0.2 %/K Coercivity HcB 250 265 kA/m Coercivity HcJ 260 275 kA/m Reverse Temperature Coefficients of Br Reverse Temperature Coefficients of HcJ 0.3 %/K Density 4.85 g/cm3 Max. Operating Temperature 250 o C All details correspond to manufacturers information www.meder.com 43 ABOUT MAGNETS MEDER electronic Handling information for magnets The strong magnetic forces of attraction can cause skin bruises. Sufficient security distances need to be kept between each magnet and all other ferromagnetic elements! A crash of magnets with high energy can produce splinters. Therefore always wear protection gloves and glasses! Grinding dust of Rear – Earth Magnets is spontaneously inflammable. Always process with water! Crashes of magnets can cause sparks. Handling and processing in EX – environment is therefore strictly prohibited! Strong magnetic fields can influence electronic and electrical devices as well as data mediums. Don’t bring magnets close to peace makers, navigation instruments, diskettes, plug-in boards etc. For air cargo a special declaration maybe possible. Radioactivity as well as joining together equal poles can reduce the magnetic force. The highest defined working temperature must not be passed. For all questions concerning magnets and, of course, reed products, please consult your nearest MEDER sales office. www.meder.com 44