2019-12-24 15:49:36

What are the properties and functions of magnets?

A mineral, magnetite;


Magnet is not invented by people. There is natural magnetite. The first one to discover and use magnet should be Chinese. So the compass is one of the four great inventions of the Chinese people. As for the composition, it is iron, cobalt, nickel, etc. its atomic structure is special, and the atom itself has magnetic moment. Generally, the arrangement of these mineral molecules is disordered. The mutual influence of magnetic areas does not show magnetism.. but under the guidance of external forces (such as magnetic field), the direction of molecular arrangement tends to be the same, which shows magnetism. That is commonly known as magnet. Iron, cobalt, nickel, etc. are the most commonly used magnetic substances. Basically, magnets are divided into permanent magnets and permanent magnets Soft iron permanent magnet is to add strong magnetism to make the spin of magnetic materials and the angular momentum of electrons in a fixed direction. Soft magnetism is to add current (also a method of adding magnetism) and other current to remove soft iron will slowly lose its magnetism. As for the first magnet, who found the oldest record is the guide car of the Yellow Emperor's war with Chiyou in China, it is called one of the four great inventions of China! Before the Western Yuan Dynasty, China The polarization of magnets was known in the first century. In the Warring States period, a natural magnet was used for divination on a calibrated copper plate. In the Northern Song Dynasty, two methods were used to make artificial magnets. One was to place the red hot iron needle in the north-south direction. After rapid cooling, the iron needle was magnetized by the earth's magnetic field; the other was to rub the iron needle with magnet. The existence of magnetic declination is recorded in Mengxi pen tan. It is found that under the influence of magnetic declination, the magnetic needle points to the south, slightly east of the real South. Based on these knowledge, the scientific application of magnet as compass has been developed. Magnet is just a general term, which generally refers to something with magnetism. The actual composition does not necessarily include iron. Pure metal iron has no permanent magnetism. Only near permanent magnet can it induce magnetism. Nantian magnet is specialized in production. General permanent magnet is added with other impurity elements (such as carbon) to stabilize the magnetism, but this will reduce the freedom of electrons and is not easy to conduct electricity. Therefore, when the current passes, the bulb will not light up. Iron is a common magnetic element, but many other elements have stronger magnetism. For example, many powerful magnets are made of rubidium, iron and boron.


Basic knowledge:


Ancient Greeks and Chinese discovered that there was a kind of naturally magnetized stone in the nature, which was called "iron absorption stone". This kind of stone can magically suck up small pieces of iron, and it always points in the same direction after swinging at will. Early mariners used the magnet as their first compass to identify directions at sea.


After thousands of years of development, today magnet has become a powerful material in our life. By synthesizing alloys of different materials, the same effect can be achieved as that of the magnet, and the magnetic force can also be increased. Artificial magnets appeared in the 18th century, but the process of making stronger magnetic materials was very slow until the production of alnico in the 1920s. Subsequently, ferrites were produced in the 1950s, and rare earth magnets (including NdFeB and SmCo) were produced in the 1970s. So far, the magnetic science and technology has been developed rapidly, and the strong magnetic materials also make the components more miniaturized.


What is the magnetization (orientation) direction?


Most magnetic materials can be magnetized to saturation in the same direction, which is called "magnetization direction" (orientation direction). A magnet without orientation (also called an isotropic magnet) is much weaker than an oriented magnet (also called an anisotropic magnet).


What is the standard definition of "north and South Pole" industry?


The definition of "North Pole" is that the north pole of a magnet points to the north pole of the earth after it rotates at will. Likewise, the south pole of the magnet points to the south pole of the earth.


How to distinguish the north pole of magnet without mark?


It's obvious that eyes alone can't tell. You can use a compass to get close to the magnet, and the pointer to the north pole of the earth will point to the south pole of the magnet.


How to handle and store magnets safely?


Always be very careful, because magnets will stick together on their own and may pinch your fingers. It is also possible that the magnets themselves may be damaged by collision when they are adsorbed on each other (collision of corners or cracks).


Keep magnets away from easily magnetized items, such as floppy disks, credit cards, computer monitors, watches, mobile phones, medical devices, etc.


Magnets should be kept away from pacemakers.


For larger size magnet, plastic or hard paper gasket shall be added between each piece to ensure that the magnet can be separated easily.


The magnet should be stored in a dry and constant temperature environment as far as possible.


How to achieve magnetic isolation?


Only the material that can be adsorbed on the magnet can play the role of magnetic field isolation, and the thicker the material, the better the effect of magnetic field isolation.


What is the strongest magnet?


At present, the highest performance magnet is rare earth magnet, and neodymium iron boron is the most powerful magnet. But in the environment above 200 ℃, SmCo is the most powerful magnet.


Types of magnets:

Magnet, should be called magnet, English magnet, magnet is now mainly divided into two categories, one is soft magnetic, one is hard magnetic;


Soft magnet includes silicon steel sheet and soft magnet core; hard magnet includes aluminum nickel cobalt, samarium cobalt, ferrite and neodymium iron boron. Among them, the most expensive is samarium cobalt magnet, the cheapest is ferrite magnet, and the highest performance is neodymium iron boron magnet, but the most stable performance, the best temperature coefficient is aluminum nickel cobalt magnet. Users can choose different hard magnet products according to different needs.


How to define the performance of magnets?


There are three main performance parameters to determine the performance of the magnet:


Remanence br: after the permanent magnet is magnetized to technical saturation and the external magnetic field is removed, the retained BR is called remanent magnetic induction strength.


Coercive force HC: to reduce the B of permanent magnet magnetized to technical saturation to zero, and the intensity of reverse magnetic field to be added is called magnetic coercive force


It's called coercive force

Magnetic energy product BH: represents the magnetic energy density established by the magnet in the air gap space (the space of two magnetic poles of the magnet), that is, the static magnetic energy per unit volume of the air gap. Since this energy is equal to the product of BM and HM of a magnet, it is called the product of magnetic energy.


Magnetic field: the space of magnetic effect on magnetic pole is magnetic field


Surface magnetic field: the magnetic induction intensity of a designated position on the surface of permanent magnet


How to choose magnet?


Before deciding which magnet to choose, it should be clear what role the magnet is required to play?


Main functions: moving objects, fixing objects or lifting objects.


Shape of the magnet required: wafer, torus, square, tile or special shape.


Required magnet dimensions: length, width, height, diameter, tolerance, etc.


Suction force of required magnet, expected price and quantity, etc.