China permanent magnet manufacturer:

How to buy bar magnets

What is a bar magnet?

Bar magnet is a kind of permanent magnetic strip object which is composed of alnico permanent magnet alloy, Fe Cr co permanent magnet alloy, permanent ferrite, rare earth permanent magnet material or composite permanent magnet material. It has two magnetic poles, a North Pole and a South Pole, so that when the magnet is free to float, the magnet will automatically align, so that the north pole points to the magnetic north pole of the earth.

Types of bar magnets

There are two types of bar magnets:

  • Cylindrical bar magnet: cylindrical bar, also known as rod magnet, is thicker than its diameter and has high magnetism. These bar magnets can be used for educational, experimental and research purposes.
  • Rectangular bar magnet: rectangular bar, also known as block magnet. Rectangular magnets are widely used in manufacturing and engineering industries because their magnetic field strength and magnetic field are larger than other magnets.

Characteristics of bar magnet

Bar magnet refers to the magnet with bar shape and magnetic pole at both ends. In order to judge this characteristic, we can use the two ends and the middle part to attract other magnetic materials.

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Moving the bar magnet close to the three iron balls, we can find that the two ends of the bar magnet have a greater effect on the iron ball, and the middle has a smaller effect on the iron ball. We can judge the characteristics of the bar magnet that the two ends are strong and the middle is weak.

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Moving the bar magnet from the spring scale with iron blocks to the right, we will find that the effect of both ends of the bar magnet on the iron block is greater than the effect of the middle on the iron block. We can judge that the magnetic properties of the bar magnet are strong at both ends and weak in the middle.

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Lift the bar magnet placed on a pile of pins, and you will find that both ends of the bar magnet attract more pins than the middle. You can judge the characteristics of the bar magnet, which is strong at both ends and weak in the middle.

The magnetic field generated outside the bar magnet is smaller than that generated inside the bar magnet (the magnetic field in the middle part is the strongest):

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  • 1. The magnetic induction line around the magnet is from the N pole of magnet to the S pole;
  • 2. Magnetic induction lines will not cross;
  • 3. The local magnetic field with dense magnetic induction line is strong and sparse, and the local magnetic field is weak;
  • 4. Magnetic induction line is a closed curve;
  • 5. Magnetic induction line is not really exist is the human imagination, magnetic field is real.

Magnetic Field of a Cylindrical Bar Magnet

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A bar magnet is often approximated simply as a magnetic dipole with north and south magnetic poles separated by a distance L. This is not accurate when the magnet has a significant size, so that magnetic lines of force also emanate from the central portion of the magnet. In this Demonstration, we consider a cylindrical bar magnet of length L, radius a, and magnetization M—the magnetic moment per unit volume, which is characteristic of the ferromagnetic material. The magnetization is assumed to be uniform throughout the volume of the magnet, which neglects slight inhomogeneities and possible deviations from the assumed relation dB/dH=constant.
The magnetic induction outside the magnet can conveniently be expressed as the negative gradient of a magnetostatic potential:
B(r)=Φm(r). For a point magnetic dipole m,Φm(r)=μ04πm·r/r3. This is integrated over the volume of the magnet. It is most convenient to work in cylindrical coordinates: R,Φ,for the source and ρ,ϕ,z for the field point (ϕ can arbitrarily be set equal to 0, in view of the anticipated cylindrical symmetry). The detailed computation is given in Details below. A simplifying feature is that integration over Z shows that the problem can be reduced to two magnetic monopolar disks separated by the distance L.

For ease of visualization, only the field lines in the medial plane of the magnet are shown. The three-dimensional field can easily be pictured by virtue of the cylindrical symmetry about the Z axis. The lines of force originate from the north pole on the right and terminate on the south pole on the left. Magnetic-induction magnitudes are not emphasized in this Demonstration, only the geometry of field lines.

Material of bar magnet

1. NdFeB magnet
It is the highest commercial performance magnet, known as magneto, with extremely high magnetic properties, and its maximum magnetic energy product (BHmax) is more than 10 times higher than that of ferrite. Its machining performance is also quite good. The working temperature can reach up to 200 ℃. And its hard texture, stable performance, has a good cost performance, so it is widely used. But because of its strong chemical activity, its surface must be coated. (such as Zn, Ni plating, electrophoresis, passivation, etc.).
2. Ferrite magnet
It is made by ceramic technology. It is hard and brittle. Because of its good temperature resistance, low price and moderate performance, ferrite magnet has become the most widely used permanent magnet.
3. Alnico magnet
It is an alloy composed of aluminum, nickel, cobalt, iron and other trace metal elements. The casting process can be processed into different sizes and shapes with good machinability. The cast alnico permanent magnet has the lowest reversible temperature coefficient, and its working temperature can be as high as 600 ℃. Alnico permanent magnet products are widely used in various instruments and other application fields.

Manufacturing technology of bar magnet

Raw material
The main raw materials of NdFeB magnets are: rare earth metal neodymium, rare earth metal praseodymium, pure iron, aluminum, ferroboron alloy and other rare earth raw materials
Machining tools
There are special slicer, wire cutting machine, flat mill, double-sided machine, drilling machine, chamfering machine, electroplating equipment.
Technological process of bar magnet
The manufacturing process of NdFeB magnet, SmCo magnet, alnico magnet and ferrite magnet is also different. In terms of technology, there are sintered NdFeB magnets and bonded NdFeB magnets. We mainly talk about sintered NdFeB magnets.
Proportioning → smelting ingot → pulverizing → pressing → sintering and tempering → magnetic detection → grinding → pin cutting → electroplating → magnetization → finished product. Among them, batching is the basis, sintering and tempering is the key. The production tools of NdFeB magnets include melting furnace, crushing machine, ball mill, air flow mill, pressing machine, vacuum packaging machine, isostatic press, sintering furnace, heat treatment vacuum furnace, magnetic property tester and Gauss meter.

Differentiate between bar magnet and electromagnet

The basic difference between them is that a bar magnet is a permanent magnet whereas an electromagnet is a temporary magnet. An electromagnet is formed when an electric current is passed through wires wound around soft metalcore. An electromagnet loses its magnetism once the current flow is stopped.

Complete Step by step solution

Following are the differences between a bar magnet and an electromagnet:

A bar magnet is a permanent magnet. An electromagnet is a temporary magnet.
The magnetism is caused by electron spins. These electrons spin in a particular orientation around the nucleus of ferromagnetic material and cause magnetism. The magnetism is caused by passing electricity through a conductor and winding it around a core, to align the electrons in a proper orientation.
The strength of the magnetic field produced by a bar magnet is constant. The strength of the magnetic field produced by an electromagnetic can be varied, depending on the current that passes through the winding or the number of turns.
The polarity of a bar magnet cannot be changed. The polarity of an electromagnet can be changed by reversing the direction of the current or the winding.
Magnetically hard iron/steel is used to manufacture a bar magnet because once magnetized, it can retain the magnetic property by itself. This property is called ‘remanence’. A soft iron core is used in the electromagnets, ‘soft’ means that this material gets magnetized and demagnetized easily, which allows the electromagnet to be turned on and off easily.
Examples of permanent magnets include bar magnets, horseshoe magnets, disc magnets, etc. Examples of electromagnets include solenoid and toroid.

Note: a ferromagnetic material can be converted into a permanent magnet if it is kept under a constant magnetic field for a long period. Thus, if instead of a soft iron core, we used a magnetically hardcore (ferromagnetic material), the magnetic properties are retained even after the current flow is stopped.

Application of bar magnet

  • The bar magnet is used as a stirrer for magnetic experiment in the laboratory.
  • They also found applications in medical procedures.
  • Electronic devices (such as telephones, radios and televisions) use magnets.
  • Many industries use bar magnets to collect loose metal and retain the magnetism of other magnets.

How to choose high quality bar magnets?

After the magnet manufacturers have processed magnets in the previous series of production processes, the packaging process is also the top priority. In the process of packaging bar magnets, the test is the magnet manufacturers’ requirements for the quality of bar magnets. Today, I would like to share with you how to select high-quality bar magnets in the packaging process.
First of all, what you can see is a lot of bar magnets filled with magnets in our factory. These bar magnets are very messy. We need to put them on our workbench, and the packing staff should arrange them and clean them up. Only when we look at them can we pick out the unqualified products.
We will be missing corners, cracks, abnormal thickness and other unqualified bar magnets selected and placed in the defective box, neatly arranged, our packaging staff can pack into the carton, paste the product label, indicate the basic information of the product, waiting for warehousing and shipment.

How to buy bar magnets?

  • 1. Provide accurate material, performance, specification and dimensional tolerance of bar magnet.
  • 2. The customer provides the drawing / sample of the bar magnet.
  • 3. Our company provides the quotation of bar magnet (proofing fee, proofing time, unit price, delivery time)
  • 4. Customers confirm quotation, sign purchase contract and pay advance payment.
  • 5. In strict accordance with customer demand for bar magnet proofing.
  • 6. The customer confirms the sample of the bar magnet, and then makes the bulk of the bar magnet after OK.
  • 7. The company provides a large sample of bar magnets, packaged and ready to go pictures.
  • 8. The customer confirms to pay the balance and issue the invoice for delivery.

SourceChina Permanent Magnet Manufacturer




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