What is a Permanent Magnet?
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What is a Permanent Magnet?

Permanent magnets can be natural products, also known as lodestones, or artificially made. A material with a wide hysteresis loop, high coercivity, and high remanence can maintain a constant magnetism once magnetized. Also known as permanent magnetic material, hard magnetic material.
Published: May 19, 2022
What is a Permanent Magnet?

What is a Permanent Magnet?

A permanent magnet refers to a magnet that can retain high remanence for a long time in an open circuit state, which is simply explained as having a magnetic steel rod. Magnets that can maintain their magnetic properties for a long time are called permanent magnets. Such as natural magnets (magnetite) and artificial magnets (AlNiCo alloy). In addition to permanent magnets, some electromagnets need to be energized to be magnetic. Permanent magnets are objects that retain a certain residual magnetization after the external magnetic field is removed. To make the residual magnetization of such an object to be zero and the magnetism to be eliminated, a reverse magnetic field must be added.

The magnitude of the reverse magnetic field required to completely demagnetize the ferromagnetic substance is called the coercive force of the ferromagnetic substance. Both steel and iron are ferromagnetic, but their coercivity is different. Steel has a larger coercivity, while iron has a smaller coercivity. In the process of chain steel, carbon, tungsten, chromium, and other elements are added to the iron to make carbon steel, tungsten steel, chromium steel, etc. The addition of carbon, tungsten, chromium, and other elements causes the steel to have various inhomogeneities at room temperatures, such as inhomogeneous crystal structure, inhomogeneous internal stress, and inhomogeneous magnetic strength. The unevenness of these physical properties increases the straightening force of the steel. And the greater the degree of unevenness within a certain range, the greater the coercivity.

These inhomogeneities are not the best state that the steel has or has achieved in any case. To achieve the best state of the internal inhomogeneity of the steel, proper heat treatment or machining must be carried out. For example, when carbon steel is in the molten state, its magnetic properties are like that of ordinary iron; after it is quenched at high temperature, the unevenness increases rapidly, and becomes a permanent magnet material. If the steel is slowly cooled from a high temperature, or the quenched steel is melted at six or seven hundred degrees Celsius, the internal atoms have sufficient time to arrange into a stable structure, and various inhomogeneities are reduced. So, correction the coercive force is then reduced, and it is no longer a permanent magnet material.

Steel or other materials can become permanent magnets because they are properly treated and processed to have the best internal inhomogeneity and maximum coercivity. The crystal structure of iron, internal stress, and other inhomogeneities are small, and the coercive force is naturally small, so it does not require a strong magnetic field to magnetize or demagnetize it, so it cannot become a permanent magnet. Generally, materials that are easy to magnetize and demagnetize are called soft magnetic materials. Most of the materials used as magnet conductors and electromagnets are soft magnets. The polarity of permanent magnets does not change, whereas the polarity of soft magnets changes with the polarity of the applied magnetic field.

What is a Temporary Magnet?

Temporary magnets are special types of magnets in physics that can change their magnetic properties with changes in external conditions. This means that the magnetic properties of the temporary magnet will not remain the same regardless of external conditions. In the field of physical engineering, permanent magnets are less stable than other types of permanent magnets.

The magnetic domains of temporary magnets are not permanently and continuously aligned with changes in the external magnetic field, and they easily return to their original state. Another name for temporary magnets is soft magnets or electromagnets. The magnetization and demagnetization of magnetic materials completely require an external magnetic field. It is made of different soft, malleable, and ductile materials. The external magnetic field is crucial to its magnetization. Electrical energy is necessary for the magnetization of soft or electromagnetic domains. The poles of an electromagnet can easily be reversed or changed direction. When the applied magnetic field disappears, the electromagnetic behavior disappears immediately.

Soft magnets are usually made of a mixture of soft and malleable materials, giving the magnets special and unique properties, such as soft iron. Temporary magnets have short-range magnetic fields. Soft iron plays a central role in transformers and is used in powerful magnetic tools, such as MRIs with permanent magnets. The performance of a magnet is mainly determined by the hysteresis loop. The smaller the area of the ring, the larger the temporary magnet. The larger the area of the hysteresis loop of the material, the stronger the permanent magnet ability of the magnet.

What is the Difference Between Permanent Magnets and Temporary Magnets?

  • A permanent magnet is a type of magnet that does not require an external magnetic field to remain fully magnetized, while a temporary magnet is a type of magnet that requires an external magnetic field to remain fully magnetized.
  • The properties of a permanent magnet do not change, whereas a temporary magnet is a magnet whose magnetic properties are constantly changing. Permanent magnets are made of hard materials, while temporary magnets are made of soft materials.
  • The magnetic poles of permanent magnets can never be reversed, while the magnetic properties of temporary magnets can be reversed.
  • The magnetic field strength of a permanent magnet is constant, while the strength of a permanent magnet always changes with conditions.
  • Permanent magnets don't need electricity to work like magnets, while temporary magnets always need electricity to work like magnets.
  • Permanent magnets are called bar magnets, while temporary magnets are also called electromagnets.
  • Permanent magnets have a constant magnetic field strength, while temporary magnets have a variable magnetic field strength.
  • Permanent magnets are more stable than temporary magnets, and temporary magnets are less stable than permanent magnets.
  • The magnetic field in the permanent magnet does not disappear with the disappearance of the external magnetic field, while the magnetic field in the permanent magnet disappears when the external magnetic field disappears.
  • The magnetic domains of permanent magnets, once aligned, can never be easily reversed, while the magnetic domains of temporary magnets, once aligned, are easily reversed.
  • In physics, permanent magnets are the type of magnets that are made of a hard permanent ferromagnetic material, while temporary magnets are the type of magnets that are made of some ferromagnetic temporary material.

Permanent Magnet Application:

Permanent magnets are widely used in various fields such as electronic, electrical, mechanical, transportation, medical and daily necessities. Such as speakers, permanent magnets of telephone receivers, magnetic systems of magnetoelectric meters, generators, and magnetic poles in permanent magnet motors. Permanent magnet devices used in machine manufacturing (such as permanent magnet chucks of surface grinders, etc.), as well as magnetic suspension systems, magnetic bearings, magnetic separation systems, magnetic mineral separation, magnetic water purification systems, magnetrons, magnetic systems of proton accelerators, etc.

Permanent Magnet Material:

Permanent magnet materials refer to materials with wide hysteresis loops, high coercivity, and high remanence, which can maintain constant magnetism once magnetized, also known as hard magnetic materials. The former is an intermetallic compound formed by rare earth elements cerium, strontium, lanthanum, neodymium, etc., and cobalt. Its magnetic energy product can reach 150 times that of carbon steel, 3 to 5 times that of AlNiCo permanent magnet materials, and 8 to 8 times that of permanent ferrite 10 times, low-temperature coefficient, stable magnetic, coercive force up to 800 kA/m. Rubber Magnet is one of the series of ferrite magnetic materials. It is made of bonded ferrite powder and synthetic rubber through extrusion, calendering, injection molding, and other processes. It has softness, elasticity, and twist ability. magnet.

What Are the Commonly Used Permanent Magnet Materials?

  1. AlNiCo permanent magnet alloy:
    It is mainly composed of iron, nickel, and aluminum elements, and contains copper, cobalt, titanium, and other elements. With high remanence and low-temperature coefficient, magnetic stability. There are two types of casting alloys and powder sintering alloys. Now it is mostly used in the manufacture of magnetoelectric instruments, flow meters, micro motors, relays, etc. in the instrument industry.
  2. Iron-chromium-cobalt permanent magnet alloy:
    It is mainly composed of iron, chromium, and cobalt elements, and contains molybdenum and a small amount of titanium and silicon elements. Its processing performance is good, it can be cold thermoplastically deformed, its magnetic properties are like that of AlNiCo permanent magnet alloys, and its magnetic properties can be improved by plastic deformation and heat treatment. It is used to manufacture various small magnet components with small cross-sections and complex shapes.
  3. Permanent magnet:
    There are mainly barium ferrite and strontium ferrite, which have high resistivity and large coercivity and can be effectively applied in the magnetic circuit of large air gaps, especially suitable for permanent magnets of small generators and motors. Permanent magnet ferrite does not contain precious metals nickel, cobalt, etc., and has rich raw material sources, simple process, and low cost. It can replace AlNiCo permanent magnets to manufacture magnetic separators, magnetic thrust bearings, speakers, microwave devices, etc. However, its maximum magnetic energy product is low, its temperature stability is poor, its texture is brittle and fragile, and it is not resistant to shock and vibration, so it is not suitable for measuring instruments and magnet devices with precise requirements.
  4. Rare earth permanent magnet material:
    Mainly rare earth cobalt permanent magnet materials and NdFeB permanent magnet materials. The former is an intermetallic compound formed by rare earth elements cerium, strontium, lanthanum, neodymium, etc., and cobalt. Its magnetic energy product can reach 150 times that of carbon steel, 3 to 5 times that of AlNiCo permanent magnet materials, and 8 to 8 times that of permanent ferrite. 10 times, low-temperature coefficient, stable magnetic, coercive force up to 800 kA/m. Mainly used for magnetic systems of low-speed torque motors, starter motors, sensors, magnetic thrust bearings, etc. NdFeB permanent magnet material is the third generation of rare earth permanent magnet material. Its remanence, coercive force and maximum magnetic energy product are higher than the former, it is not fragile, it has good mechanical properties, and the alloy density is low, which is conducive to the lightweight of magnetic components. miniaturization, thinning, miniaturization, and ultra-miniaturization. But its high magnetic temperature coefficient limits its application.
  5. Composite permanent magnet material:
    It is composed of permanent magnetic material powder and plastic material as a binder. Since it contains a certain proportion of binder, its magnetic properties are significantly lower than the corresponding magnetic material without binder. In addition to metal composite permanent magnet materials, other composite permanent magnet materials are limited by the heat resistance of the binder, and the operating temperature is low, generally not exceeding 150 ℃. However, the composite permanent magnet material has high dimensional accuracy, good mechanical properties, good performance uniformity of each part of the magnet, and is easy to perform radial orientation of the magnet and multi-pole magnetization. Mainly used in the manufacture of instrumentation, communication equipment, rotating machinery, magnetic therapy equipment, and sporting goods.
Published by May 19, 2022 Source :easyatm, Source :tl80

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