Alnico magnets are those magnets produced by combining, aluminum, nickel and cobalt and certain other metals such as iron, copper and titanium. In fact the term 'alnico' is derived from the abbreviations of the three main metals, namely aluminum, cobalt and nickel. By varying the combination of metals, the magnetic properties of this magnet can be tailored to need, so as to suit various applications. Thus, alnico magnet is an alloy of several metals and is characterized by superb temperature stability (resistant to elevated temperatures), comparatively high energies and high residual induction.
Properties of Alnico Magnets
Alnico magnets are strong permanent magnets producing strong magnetic fields that are 3000 times the strength of the Earth's magnetic field. They exhibit exceptionally tiny changes in magnetic properties to temperature effects. They have strong corrosion resistance ability and low coercive force. Since they have a low coercive force, they have to be handled carefully. Subjecting the magnets to adverse repelling fields can result in their partial demagnetization.
Since these magnets are brittle, coarse and crack easily, the regular machines cannot be used to treat them. Machining and drilling cannot be carried out by ordinary techniques, so the foundry is where the holes are cored. They get easily demagnetized and therefore have to be handled carefully. If handled properly, these magnets can turn out to be the most stable magnets. The maximum working temperature of this magnet can be as high as 450-5500 C. Alnico magnets require no coating to protect their surface.
Types of Alnico Magnets
Alnico magnets are divided into two types, based on their manufacturing processes.
- Cast alnico
- Sintered alnico
How are Alnico Magnets Manufactured?
They can be manufactured by two processes: casting or sintering. The casting process involves pouring the metal alloy into a mold, then solidifying, grinding roughly and cooling after treating with heat. Once the heat treatment is done, the magnet is cooled, ground to specific tolerances and magnetized. A dark gray magnet with a rough surface is the outcome of this process; however, when machined, it has a shiny surface. Cast magnets are always complex shaped, for example, horse-shoe shaped. This is not possible with other magnet types.
The sintering process involves the process of compacting the alnico powder with the help of a press. Further, the compacted powder is sintered into a strong alnico magnet. This is also known as powder metallurgy process, wherein the magnets are prepared under controlled atmosphere and high temperatures. Sintered alnico magnets feature better mechanical characteristics as compared to cast magnets. However, cast magnets offer somewhat higher magnetic properties as compared to sintered magnets.
Applications of Alnico Magnets
Alnico magnets exhibit exceptional linear temperature, high magnetic flux and good corrosion resistance, which is why they are greatly desired as materials for industrial purposes. They are mostly used in applications requiring stable temperature properties, such as meters and instruments. The common applications of these magnets are in vending machines, volt-amp meters, medical instruments, generators, electronic ignition systems, hand tools, magnetic reed switches and cow magnets.
They are also used in lighters and odometers of automobiles in the automobile industry. Further, their applications are also seen in high stability arenas such as space flights, military technology and aviation. Moreover, these magnets are also used in polarized relays, temperature and pressure controllers, and in a wide range of magnetic sensors. Sintered alnico magnets find their application in mini speakers, hearing aids and buzzers of mobile phones. In the cast alnico category, cast alnico 5 is the most commonly used cast alnico. Its common applications are in holding applications, sensing devices, rotating machinery, etc.
Alnico magnets were developed in the 1940s, and since then have been and still are the most widely used and economical magnets for industrial purposes. Recently, in certain applications, these magnets have been replaced by injection molded magnets or sintered neodymium.