Introduction to Smco Magnets

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Courtesy of Stanford Magnets

Samarium (Sm) magnets are rare earth magnets manufactured into two series. The first series is sometimes referred to as SmCo5 (Co means cobalt), which is usually a high energy product of about 18 to 22 MGOe. The second is the most commonly known as Sm2Co17, which is a higher energy product of about 22 to 30 MGOe. It combines 2 Sm atoms and Co atoms between 13 and 17. It is basically an alloy of 35% Sm and 60% Co. Other elements in these magnets include iron, copper, and transitional metal (rare earth).

Although these magnets may not be as strong as neodymium (NdFeB) magnets, they possess highly magnetic properties. Some of their properties are thermal stability and excellent corrosion resistance. They can operate on higher temperatures with much better temperature coefficient. They are also ideal for application in very low temperatures. They can tolerate temperatures of almost Absolute Zero. Compared to NdFeB magnets, their high operating temperatures of up to 350? or 662? gives them a distinctive advantage. They easily outperform the neodymium magnets at 150 to 180?.

The alloys undergo drilling, machining or grinding in an un-magnetized state. Diamond tip drills or grind wheels are used in a process that requires sufficient coolant. Because its grinding dust is very volatile, care should be exercised when handling it. Ignition can easily occur from small sparks created from static electricity or from collision with hard tools. These can easily set the SmCo dust or powder ablaze. The ensuing fires are usually super-hot and are extremely difficult to extinguish or bring under control.


Applications

Due to their good temperature, stability and high de-magnetization resistance, these magnets are suitable for various technological applications. These include bias magnets, actuators, AC servo-motors, Watches, computer hard drives, automobiles, printers, ultrasonic transducers, electronic instrumentations, travelling wave tubes, high performance and high input motors, etc.
They are available in diverse shapes like blocks, arcs, disc rods and other customized shapes. Because they contain minimal free iron, no coat is usually added to the magnets. In special instances like when the magnets are soldered to printed circuit boards, nickel plating can be added.
Coupling in magnets involves the employment of magnetic and objective forces in the transmission of thrusting or rotating forces. These forces are transmitted from the driving side to the side that is driven without establishing contact. Both sides become completely isolated upon installation of a bulkhead between the driving and the driven side.

Care and handling

1. Should be kept out of reach of small children. They can cause asphyxiation if swallowed or lodged in children's throat.
2. Their brittle nature makes them unsuitable as structural or mechanical components.
3. Their strong attractive power makes them prone to chipping shattering or cracking especially when mishandled. It is vital to always have eye protection when working with them.
4. These magnets are still considered acceptable if they possess minor imperfections. IMA standards allow for chirped edges as long as the surface that is missing is less the 10%. Cracks that extend for less than 50% of the pole surface are also accepted.

Advantages of SmCo magnets

SmCo magnets have recorded stable prices for an extended period. While other magnets like NdFeB have been recording higher prices, SmCo magnets are now much cheaper.
SmCo performs much better than other magnets in high temperatures. It can operate in temperatures of up to 300? with much better temperature coefficient. Therefore this magnet is also ideal in low temperatures.
These magnets also possess stable magnetic property, their anticorrosion property is excellent. Even without coating, it does not get corroded. This quality makes it capable of working in special environments. It can reach more accurate dimension tolerance even without coating.

Manufacturing methods

1. Sintered method
In this process, the fine SmCo powder is first compacted in a die before being sintered. This fuses the powder into a solid piece. The powder is then pressed. Pressing can be accomplished in two forms, the first form is called die pressing. Here the powder is placed in a hard die before getting pressed. The second form is called isostatic pressing. The powder is first placed in a rubber die then equal force is applied onto it from all directions. While the isostatically pressed magnet possess enhanced magnetic properties, the die pressed magnet has a higher uniformity of characteristic. To achieve final tolerances, sintered pieces usually require extra finish machining.

2. Compression bonded
In this technique, a plastic carrier material is blended with a special kind of SmCo powder. It is then pressed before being heated. Pieces manufactured using this method can come in a variety of complex shapes. They usually have close tolerances. No further machining is usually necessary. They are basically lower energy products compared to sintered materials.

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