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Tuesday 14 May, 2013 |

How to Manufacturing the magnet?

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Just as the materials are different for different kinds of magnets, the manufacturing processes are also different. Many electromagnets are cast using standard metal casting techniques. Flexible permanent magnets are formed in a plastic extrusion process in which the materials are mixed, heated, and forced through a shaped opening under pressure.

Some ndfeb magnets are formed using a modified powdered metallurgy process in which finely powdered metal is subjected to pressure, heat, and magnetic forces to form the final magnet. Here is a typical powdered metallurgy process used to produce powerful neodymium-iron-boron permanent magnets with cross-sectional areas of about 3-10 square inches (20-65 sq cm):
Preparing the powdered metal

1. The appropriate amounts of neodymium, iron, and boron are heated to melting in a vacuum. The vacuum prevents any chemical reaction between air and the melting materials that might contaminate the final metal alloy.

2. Once the metal has cooled and solidified, it is broken up and crushed into small pieces. The small pieces are then ground into a fine powder in a ball mill.

Pressing
3. The powdered metal is placed in a mold, called a die, that is the same length and width (or diameter, for round magnets) as the finished magnet. A magnetic force is applied to the powdered material to line up the powder particles. While the magnetic force is being applied, the powder is pressed from the top and bottom with hydraulic or mechanical rams to compress it to within about 0.125 inches (0.32 cm) of its final intended thickness. Typical pressures are about 10,000 psi to 15,000 psi (70 MPa to 100 MPa). Some shapes are made by placing the powdered material in a flexible, air-tight, evacuated container and pressing it into shape with liquid or gas pressure. This is known as isostatic compaction.

Heating
4. The compressed “slug” of powdered metal is removed from the die and placed in an oven. The process of heating compressed powdered metals to transform them into fused, solid metal pieces is called sintering. The process usually consists of three stages. In the first stage, the compressed material is heated at a low temperature to slowly drive off any moisture or other contaminants that may have become entrapped during the pressing process. In the second stage, the temperature is raised to about 70-90% of the melting point of the metal alloy and held there for a period of several hours or several days to allow the small particles to fuse together. Finally, the material is cooled down slowly in controlled, step-by-step temperature increments.

Annealing
5. The sintered material then undergoes a second controlled heating and cooling process known as annealing. This process removes any residual stresses within the material and strengthens it.

Finishing
6. The annealed material is very close to the finished shape and dimensions desired. This condition is known as “nearnet” shape. A final machining process removes any excess material and produces a smooth surface where needed. The material is then given a protective coating to seal the surfaces.

Magnetizing
7. Up to this point, the material is just a piece of compressed and fused metal. Even though it was subjected to a magnetic force during pressing, that force didn’t magnetize the material, it simply lined up the loose powder particles. To turn it into a magnet, the piece is placed between the poles of a very powerful electromagnet and oriented in the desired direction of magnetization. The electromagnet is then energized for a period of time. The magnetic force aligns the groups of atoms, or magnetic domains, within the material to make the piece into a strong permanent magnet.

Quality Control
Each step of the manufacturing process is monitored and controlled. The sintering and annealing processes are especially critical to the final mechanical and magnetic properties of the magnet, and the variables of time and temperature must be closely controlled.

Introduce Five types Permanent Magnet

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Permanent magnet materials currently on the market, as well as due to the production process of the original or cost reasons, not the wide range of applications and eliminated, such as CuNiFe Magnet The FeCoMo Magnet The, FeCoV Magnet The MnBi Magnet The AlMnC Magnet The.

1.NdFeB Magnet
according to the production process is divided into the following three

a. Sintered NdFeB Magnet
(Sintered NdFeB permanent magnets after grinding the powder after the airflow smelting, high values of coercive force, and has high magnetic properties, the maximum energy product (BHmax) higher than 10 times higher than the ferrite (the Ferrite) its own mechanical properties is also very good, cutting different shapes and drilling. high-performance products of the highest operating temperature of up to 200 degrees Celsius. easily lead to corrosion due to its material content, according to different requirements must be on the surface different coatings (such as plating of Zn, Ni, Au, Epoxy, etc.) very hard and brittle, highly resistant to retreat magnetic, high cost / performance ratio does not apply to the high operating temperature);

b. Bonded NdFeB Magnet
Bonded NdFeB NdFeB powder and resin, plastic or low melting point metal binder uniformly mixed, and then use compression, extrusion or injection molding methods such as composite made of NdFeB. Forming, no secondary processing, can be made into complex shapes. All directions of the bonded NdFeB magnetic, can be processed into NdFeB compression molds and injection molds. High precision and excellent magnetic properties, good corrosion resistance, good temperature stability.

c. Zhusu NdFeB Magnet
High accuracy, easily made from the anisotropic shape of complex thin-walled rings or thin magnet

2. Sintered the Ferrite Magnet
The main raw material, including BaFe12O19 and SrFe12O19, and divided into isotropic and anisotropic magnet according to the orientation of the magnetic crystal. Due to its low price and moderate magnetic energy to become the most widely used as a magnet. The annual production of 300 tons or more. Ferrite magnet is made of ceramic technology, the texture is relatively hard, but also in the case of brittle materials, has become the most widely used permanent magnets, ferrite magnets have good temperature and low prices.

3.Rubber Magnet
Is a series of Ferrite Magnets, bonded ferrite material powder and synthetic rubber compound by extrusion, calendering, injection molding process and made of soft, flexible, and can distort the magnet . Can be processed into strips, rolls, sheet, and a variety of complex shapes. Rubber magnet by the magnetic particle (SrO6Fe2O3), the composition of the polyethylene (CPE) and other additives (EBSO DOP), by extrusion, calendering made. Rubber Magnets can be homosexual or heterosexual, it is made of ferrite powder, CPE and certain trace elements can bend, twist, scroll up. It does not require more machining can be used, you can also trim shape of the desired size, the complex of PVC rubber magnet according to customer requirements, gum, on the UV oil. Its energy product between 0.60 to 1.50 MGOe. Rubber Magnets areas of application: refrigerator, messages, notices rack, advertising and other objects fixed on the metal body to be used as fasteners, for toys, teaching instruments, switches and sensors disk. Mainly used in micro motors, refrigerator, disinfection cabinet, kitchen cabinet, toys, stationery, advertising and other industries.

4.AlNiCo Magnet
The earliest development of a permanent magnetic material is an alloy of aluminum, nickel, cobalt, iron and other trace metals. According to the different production processes into Sintered Alnico Sintered of AlNiCo Cast Alnico Cast of AlNiCo. The product shape is round and square. Casting process can be processed production into different sizes and shapes; compared with the casting process and sintered products is limited to the small size of its production out of the rough size tolerance rough better than casting products, magnetic properties to be slightly lower than the casting products, but can be processed is better. The cast aluminum nickel and cobalt permanent magnet permanent magnet materials, the lowest reversible temperature coefficient, operating temperature up to 600 degrees Celsius. Alnico permanent magnet products are widely used in various instruments and other applications.

5.SmCo Magnet
Based on the composition of the different divided into SmCo5 and of Sm2Co17, respectively, for the undertaking of generation and the undertaking of the second generation rare earth permanent magnet materials. Its development because of its raw material is very scarce, expensive and restricted. Samarium cobalt (SmCo) as second-generation rare earth permanent magnet, not only has a high energy product (14-28MGOe) and reliable coercive force, but in the rare earth permanent magnet series showed good temperature characteristics. Compared with NdFeB, samarium cobalt is more suitable for work in high temperature environment.

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