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Alnicos ;are a group of heat-treated Fe–Co–Ni–Al–Cu alloys that can be divided into two main subgroups: isotropic alloys containing 0–20 wt.% Co (alnicos 1–4) and anisotropic alloys with 22–24 wt.% Co and titanium content of 5–8 wt.% (alnicos 5–9). The anisotropy in the case of alnicos 5–9 is produced by controlled cooling or isothermal heat treatment in a saturating magnetic field. The main source of anisotropy is the shape anisotropy associated with elongated Fe–Co particles in a Ni-Al matrix aligned parallel to the magnetic field during spinodal decomposition of the alloy. Alnicos are widely used as permanent magnets. The most important applications are loudspeakers, watt-hour meters, electric motors, generators, and alternators.
Samarium–cobalt magnet
A samarium–cobalt (SmCo) magnet, a type of rare-earth magnet, is a strong permanent magnet made of two basic elements: samarium and cobalt.
They were developed in the early 1960s based on work done by Karl Strnat at Wright-Patterson Air Force Base and Alden Ray at the University of Dayton. In particular, Strnat and Ray developed the first formulation of SmCo5.
Samarium–cobalt magnets are generally ranked similarly in strength to neodymium magnets, but have higher temperature ratings and higher coercivity.
Attributes
Extremely resistant to demagnetization
Good temperature stability (maximum use temperatures between 250 °C (523 K) and 550 °C (823 K); Curie temperatures from 700 °C (973 K) to 800 °C (1,070 K)
Expensive and subject to price fluctuations (cobalt is market price sensitive)
Samarium–cobalt magnets have a strong resistance to corrosion and oxidation resistance, usually do not need to be coated, and can be widely used in high temperatures and poor working conditions.[4]
They are brittle and prone to cracking and chipping. Samarium–cobalt magnets have maximum energy products (BHmax) that range from 14 megagauss-oersteds (MG·Oe) to 33 MG·Oe, which is approx. 112 kJ/m3 to 264 kJ/m3; their theoretical limit is 34 MG·Oe, about 272 kJ/m3.
Sintered Samarium–Cobalt magnets exhibit magnetic anisotropy, meaning they can only be magnetized in the axis of their magnetic orientation. This is done by aligning the crystal structure of the material during the manufacturing process.
FeCrCo & Crovac
Descriptions of products
FeCrCo/Crovac ;as a new type of magnet has come into the world in the 1970s. It is widely used in space, aviation, shipping instrument, automobile instrument, magnetic motor, compasses, computer embroider machines and signal systems, etc.
FeCrCo/Crovac has good plasticity, ductility, and machining ability. And can be drilled, planned, stamped, and other machining operations. The minimum diameter can be 0.05 mm and the thickness of the strip can be 0.1 mm, especially suited for tinny elements with accurate dimensions and complicated shapes, such as strip, wire, bar, tube, etc.
FeCrCo/Crovac has excellent temperature stability, good corrosion resistance, and a high Curie temperature(around 680℃). The maximum working temperature is 400℃.
Neodymium magnet
A neodymium magnet (also known as NdFeB, NIB, or Neo magnet) is the most widely used] type of rare-earth magnet. It is a permanent magnet made from an alloy of neodymium, iron, and boron to form the Nd2Fe14B tetragonal crystalline structure. Developed independently in 1984 by General Motors and Sumitomo Special Metals, neodymium magnets are the strongest type of permanent magnet available commercially.
NdFeB ;magnets can be classified as sintered or bonded, depending on the manufacturing process used. They have replaced other types of magnets in many applications in modern products that require strong permanent magnets, such as electric motors in cordless tools, hard disk drives, and magnetic fasteners.
New applications
The strength and magnetic field homogeneity on neodymium magnets has also opened new applications in the medical field with the introduction of open magnetic resonance imaging (MRI) scanners used to image the body in radiology departments as an alternative to superconducting magnets that use a coil of superconducting wire to produce the magnetic field.
Neodymium magnets are used as a surgically placed anti-reflux system which is a band of magnets surgically implanted around the lower esophageal sphincter to treat gastroesophageal reflux disease (GERD). They have also been implanted in the fingertips in order to provide the sensory perception of magnetic fields, though this is an experimental procedure only popular among biohackers and grinders
Alnico Magnets Info
Cast Alnico ;was first developed in the 1930s and uses Aluminum, Nickel, and Cobalt from the lowest levels of Alnico Bonded up to Alnico 10 which is a hot mold exothermic material. This requires great foundry and heat-treating expertise. It is still widely used in watt-hour meters, instruments, and some holding devices such as pot magnets and medical devices. ;
Cast Alnico 5 is the most commonly used of all the cast Alnicos. This material is used extensively in rotating machinery, meters, instruments, sensing devices, and holding applications, to name a few.
Excellent temperature stability, high residual induction, and relatively high energies characterize Alnico materials, composed primarily of alloys of Aluminum, Nickel, and Cobalt. They are manufactured through either a casting or sintering process. Cast magnets may be manufactured in complex shapes, such as horseshoes, not possible with other magnet materials. Sintered Alnicos offer slightly lower magnetic properties but better mechanical characteristics than cast Alnicos.
Alnico is hard and brittle. Machining or drilling cannot, therefore, be accomplished by ordinary methods. Holes are usually cored in at the foundry, and magnets are cast close to final size and then finish machined to closer tolerances.
Alnico has a low coercive force and is easily demagnetized if not handled with care. For optimum performance of Alnico 5, the magnetic length should be approximately 5 times the pole diameter or equivalent diameter. For example, a 0.250" diameter magnet should be about 1.250" long.
Because of its higher coercivity, Alnico 8 may be used in shorter lengths and in disc shapes.
Advantages and Applications of Sintered AlNiCo Magnets
Advantages of Sintered AlNiCo Magnets
1. The use temperature of the Sintered AlNiCo ;magnets can be as high as 450-500 degrees Celsius. Besides, they come with a small magnetic output change and temperature change among the permanent magnets.
2. Although the magnetic properties of sintered AlNiCo magnets are slightly lower than those of the cast AlNiCo magnets, their mechanical properties are much better.
3. The size and dimensional tolerances of Sintered AlNiCo Magnets are relatively smaller than those of cast magnets and do not require much further processing.
4. Sintered AlNiCo Magnets are suitable for mass production.
5. Sintered AlNiCo Magnets have excellent corrosion resistance.
Applications of Sintered AlNiCo Magnets
Alnico permanent magnets are mainly composed of aluminum, nickel, cobalt, iron, copper, titanium, and other materials.
Newly developed application areas of AlNiCo magnets: Hall components for temperature sensors and electronic sensors for automobiles.
Traditional applications of Alnico Magnets include magnetrons, TWT amplifiers, regulators, motors, and meters. ;
Rare earth permanent magnets have replaced Alnico magnets in many application fields.
Sintered NdFeB Magnets
Sintered NdFeB ;magnets, i.e. sintered neodymium iron boron magnets, are those permanent magnetic materials based on an Nd-Fe-B tetragonal crystal structure. Sintered NdFeB magnets were invented by M. Sagawa’s team in the early 1980s, they are manufactured through a powder metallurgy process.
Sintered NdFeB magnets contain three basic elements neodymium, iron, and boron. The neodymium element can be substituted by a portion of other rare earth elements including praseodymium, dysprosium, terbium, cerium, etc. The iron element can be substituted by a portion of cobalt element to increase the magnets’ Curie temperature Tc, thermal stability, and corrosion resistance. In order to control the microstructure and the microchemistry so as to meet the required performance, it also adds some doping elements including aluminum, copper, niobium, gallium, etc. For custom NdFeB magnets sintered, controlling the formula is the basic method to obtain the required magnet grades.
Due to their outstanding magnetic properties (high remanence Br 1.1-1.5 T, middle high coercivity Hcj 800-3000 kA/m^3 and high maximum energy product (BH)max 220-430 kJ/m^3) together with competitive cost, sintered NdFeB magnets are widely applied in DC motors, servo motors, stepper/stepping motors, synchronous motors, linear motors, voice coil motors (VCMs), wind turbines and generators, magnetic resonance imaging (MRI), electric power steering (EPS), magnetic separation, etc. |
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