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Magnets

Magnets are metallic composites, usually ferrous metal composites, which produce a “magnetic field”; the magnetic field causes other magnetic objects to be attracted to the magnet while other magnets are either attracted or repelled. There are many different types of magnets all with different magnetic strength, heat resistance, corrosion tolerance and permanence.

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Industry Information

The Many Types of Magnets

Magnets are objects or pieces of material that generate a magnetic field that is either natural or forced. A magnetic field is moving electrical charges that repel or attract one another. Size, strength, shape, and materials all differ in the make up of magnets, making each one unique to serve an exact purpose. Magnets are used in the industrial, medical, dental, and many other industries as well as in the home and workplace. There are four basic types of magnets, permanent, temporary, electromagnets, and superconductors.

Permanent magnets are the most commonly used magnets around. These can be found on refrigerators, white boards to hold notes, in speakers, compasses and more, and are usually made out of neodymium iron boron, samarium cobalt, alnico, ceramic or ferrite.

Temporary magnets are objects that perform like permanent magnets, but only when they are in range of a powerful magnetic field. Objects that are temporary magnets include paper clips, bobby pins, nails and screws, and needles. When these magnets are removed from the magnetic field, their magnetism is gone. Temporary magnets can be found in electric motors and telephones.

Electromagnets work by the flow of electric current producing the magnetic fields and are made up of tightly wound coil of wire. To maintain the magnetic field there must be a continuous supply of electrical energy, but the supply can easily be turned off and on as needed. Magnets of this type can be found in use in items like televisions, radios, and computers.

Superconductors are also composed of wire coils of special metal alloys without a metal core. When cooled below a critical temperature, the metal alloys become superconductors. This process is conducted through Magnetic Resonance Imaging machines, mass separation processes and more. Out of all magnets, superconductors are the strongest. 

Magnets  

Magnets can largely be broken up into two categories: non-permanent and permanent; non-permanent magnets are electromagnets which require an external source of power and are triggered electrically to be magnetic. Electromagnets have many industrial applications such as solenoid valves, AC and DC motors, biomagnetic separation, transformers and so on. Permanent magnets include ceramic magnets (also known as ferrite magnets), alnico magnets and rare earth magnets. For instance, ceramic magnets have lower magnetic power and are more brittle and easily breakable than some other magnets, but they are much more cost-effective and are used in non-structural applications in motors, magnetic chucks and magnetic tools. Rare earth magnets, on the other hand, are less cost-effective to manufacture but are far more powerful and retain their magnetism better than ferrite magnets; they are used as industrial magnets for holding and lifting, motors, speakers and sensors, testing and MRIs.

Magnetic assemblies are tools or systems which use electromagnets, ceramic magnets, alnico magnets, rare earth magnets or a combination to do specific kinds of lifting, holding or separating of metallic materials. Combinations of different magnets in assemblies can increase the overall magnetic force of the tool. Most magnetic assemblies used in industrial and metal manufacturing use permanent industrial magnets to do various kinds of physical work, including metal parts and sheet metal lifting, mounting and holding, separating and water treatment. Permanent and nonpermanent (electromagnetic) magnet assemblies are used in automotive, aerospace, electronics and biomedical fields in beam control, film and software disk programming and erasing, Magnetic Resonance Imaging (MRI), sound speakers, sensors, TV monitors, welding equipment, power meters, ignition timing systems, linear actuators, blood testing and separating, electric motor activation and more. Many types of magnets are specifically used for certain industries and applications. For example, sheet magnets are a flexible ferrite-plastic composite which is extruded into magnetic sheets and used in automotive and consumer industries, and can be cut into magnetic strips of rubber material. Bar magnets are the most common type of magnet used today, and are made from a ferrite metal material.

The most important properties magnet manufacturers consider during fabrication are porosity, ease of fabrication, magnetic retention under heat and corrosion, magnetic strength and cost. There is not one magical type of magnet that will have all of these characteristics, and different types of permanent magnets are made from various composites and therefore have very different properties and applications. Ceramic magnets are sintered powder composites of ceramic powder, iron oxide and either strontium or barium. Ceramic magnets can be compressed, extruded or sintered into a variety of shapes. The finished material is a cost-efficient, brittle, porous charcoal gray ceramic which is often sintered into arcs for motors, discs and blocks for lifting and holding. In addition, because ceramic magnets are porous they are highly susceptible to corrosion and lose their magnetism under high temperatures. Slightly more expensive alnico magnets are composites of aluminum, nickel, cobalt and iron and are similar to ferrite ceramic magnets but are less brittle, more easily fabricated into shapes, and have higher magnetic resistance.

Rare earth magnets include neodymium magnets and samarium cobalt magnets and are far more powerful than ferrite ceramics or alnico magnets. Rare earth lanthanide elements neodymium and samarium have partially filled outer f-electron shells which are the source of their exceptionally powerful magnetic fields. Neodymium magnets are neodymium, iron and boron composites with more powerful magnetic pull than any other type of magnet. Although they have high magnetic force, neodymium magnets have low heat and corrosion resistance and lose magnetism under 200 degrees Celsius or more. Samarium cobalt magnets are composed of samarium and cobalt and are much more resistant to demagnetization and corrosion than neodymium magnets, with a thermal stability of up to 550 degrees Celsius. Samarium cobalt is therefore used most in high heat applications such as motors and medical tools. Neodymium magnets are harder than ceramic magnets but are still brittle and are therefore most often nickel-coated for protection. Due to the scarcity of rare earth materials and the long process of rare earth extraction from lanthanide ores, rare earth magnets are significantly more costly than non rare earth magnets.

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Images Provided by Master Magnetics, Inc.



Magnet Types

  • Alnico magnets are sintered from a compound of aluminum, nickel and cobalt and have higher magnetic permanence and strength than all other non-rare earth magnets.
  • Bar magnets are narrow, rectangular pieces of ferromagnetic material or composite that generate a magnetic field.
  • Bipolar assemblies are advantageous during part transference, welding alignments and part holding applications. Bipolar magnetic assemblies maintain high heat resistance and wide magnetic reach.
  • Ceramic assemblies maintain resistance to demagnetization, can withstand exposure to electrical fields and vibration and are economical. Their demagnetization resistance is beneficial in the welding and construction industries, as well as other environments subject to vibration and electricity, but they do have low heat resistance.
  • Ceramic magnets made of strontium carbonate and iron oxide.
  • Custom magnets are sheet, alnico, neodymium, rare earth or ceramic magnets which are fabricated to specialized sizes, magnetic strengths or densities to fit certain applications.
  • Electromagnets require an electric current for the production of a magnetic field.
  • Industrial magnets are heavy-duty magnets used for industrial applications.
  • Magnetic assemblies are tools and systems that use large amounts of magnets to lift, separate and hold metallic materials.
  • Magnetic strips are thin pieces of flexible magnetic rubber material that usually have an adhesive on one side and can conform to irregular or uneven surfaces.
  • Neodymium magnets are composed of a combination of neodymium, iron, and boron.
  • Permanent magnets retain magnetism without a magnetic field. Permanent magnets do not generate electricity or heat.
  • Rare earth assemblies maintain the highest holding ability of all magnetic assemblies in a compact design but generally possess low heat resistance. Rare earth magnets consist of neodymium magnets and samarium cobalt magnets, referred to as rare earth magnets because of their location in the periodic table.
  • Rare earth magnets are composed of elements found in the "Rare Earth" part of the Periodic Table.
  • Sheet magnets are large, flat magnets that can cover a large area.



Magnet Terms

Alnico (Aluminum-Nickel-Cobalt) - A shorthand reference to magnets made from an aluminum nickel cobalt compound; these types of magnets have medium to high magnetic strength and have excellent magnetic resistance to heat.

Anisotropic - Magnetic characteristic whereby magnetic orientation exists toward a specific direction as a result of the application of a magnetic field to the magnet during production.
 
Badge Magnet - Encased magnet used to hold identification badges to clothing without causing damage.
 
Bipole Electromagnet - An electromagnet design in which the magnetic coil is located between two steel plates parallel to each other, which act as the north and south poles.
 
Ceramic Magnet - Magnet assemblies composed of strontium carbonate and iron oxide that are charcoal in color and typically appear in the forms of discs, rings, blocks, cylinders and even arcs for motors.
 
Curie Temperature - The temperature at which point the magnetic properties of a magnet begin to decrease upon exposure.
 
Demagnetizer - A device that can eliminate magnetism in magnetic assemblies by using an alternating electrical current.
 
Demagnetizing Force - Forces like temperature, shock, vibration or electrical or magnetic currents that completely or partially demagnetize magnetic material.
 
Ferrite Magnet - A commonly used, low-cost magnet that is very brittle though relatively hard and has good resistance to demagnetization, good temperature stability and excellent corrosion resistance.
 
Ferrous Material - A material containing iron, making it inherently magnetically attracted.

Flexible Magnet - A magnet made by combining a mixture of ferrite powder and rubber polymer resin, forming it by extrusion or rollers, then magnetizing and laminating it with vinyl or adhesive. Flexible magnets are the most pliable permanent magnet and are the least expensive by volume.

Flux - The measure of strength of the total size of a given magnetic field found in magnetic assemblies.

Gauss - Unit of measurement indicating magnetic induction.

Industrial Magnet - A magnet that is optimal for any big projects in which large metal products without brackets need to be lifted. Industrial magnets are adaptable enough to give companies the flexibility to customize them in order to make them better and more efficient for specific applications.

Isotropic - Magnetic characteristic whereby magnetic orientation toward a specific direction does not exist. Isotropic, or non-oriented, magnets can be magnetized in all directions.
 
Lifting Magnet - A magnet that is part of a lifting device used to move a variety of ferrous metals, ranging from small bundles of rod or scrap to large, heavy blocks.
 
Magnetic Field - An area characterized by the movement of an electric charge. Magnetic fields remain most intense at opposite ends of magnets, known as the North and South poles.
 
Magnetic Flux - The strength of the magnetic field of a magnet exemplified by the rate of movement of magnetic energy.
 
Magnetic Induction - The initial magnetization of an object created by forces emanating from a magnetic field.
 
Magnetic Orientation - The direction toward which a magnet is predisposed as a result of exposure to a magnetic field during production.  
 
Magnetic Pole - Area of magnetic flux concentration where magnetic fields are strongest. The North and South Poles are magnetic poles.
 
Magnetic Separators - Devices that remove ferrous metals from various materials, while protecting machinery.
 
Maxwell - Unit of measurement indicating magnetic flux.
 
Neodymium Magnet - A magnet made of a rare earth element that is smaller, stronger and cheaper than most other magnets.
 
Oersted (Oe) - Unit of measurement indicating the strength of a magnetic field.
 
Permanent Magnet - A magnet that after having been removed from a magnetic field still retains its magnetism.  
 
Rotary Magnetic Sweeper - A device that picks up all metal debris when rolled over spills. A release lever drops everything the rotary magnetic sweeper picks up, eliminating the need to handle potentially hazardous metal pieces.




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