How to buy disc magnets
What is a disc magnet?
Table of Contents
- What is a disc magnet?
- Types of disc powerful magnets
- Which is more expensive, NdFeB square magnet or disc magnet?
- Two processing methods of NdFeB magnets
- Calculation formula of disc magnet weight: (density is calculated according to 7.5)
- Writing format of circular magnet
- Application fields of Disc Magnets
- How is the NdFeb disc magnet made?
- Where are the poles of a disc magnet located?
- What are the precautions for the storage and transportation of disc magnets?
- Where to buy disc magnets?
- The price of disc magnets
Disc magnet is thin flat circular magnet where the thickness does not exceed the diameter. Disc magnets are a type of magnet that is shaped like a disc. With around and thin shape that is smooth throughout the entire circumference of the object, disc magnets are used for a variety of purposes in everyday life.
Types of disc powerful magnets
1). There are many kinds of magnets, which are generally divided into permanent magnet and soft magnet
The first category is: metal alloy magnets, including NdFeB magnets, SmCo magnets and AlNiCo magnets.
The second category is ferrite permanent magnet materials
- 1. Ferrite magnet: the main raw materials of ferrite include BaFe12O19 and SrFe12O19. 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.
- 2. NdFeB magnet: NdFeB is the most commercialized magnet found at present, which is called magneto. It has extremely high magnetic properties, and its maximum 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.).
- 3. SmCo magnets can be divided into SmCo5 and Sm2Co17 according to their composition. Due to the high price of SmCo, its development is limited. As a rare earth permanent magnet, SmCo not only has high magnetic energy product (14-28mgoe), reliable coercivity and good temperature characteristics. Compared with NdFeB magnet, SmCo magnet is more suitable for working in high temperature environment.
- 4. Alnico magnet: alnico 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.
2). The order of magnetic force is: NdFeB magnet, SmCo magnet, alnico magnet and ferrite magnet.
Characteristics of NdFeB: NdFeB permanent magnetic material is based on the intermetallic compound Nd2Fe14B. Nd-Fe-B permanent magnet material has been widely used in modern industry and electronic technology because of its high magnetic energy product and coercive force and high energy density, which makes it possible to miniaturize, lighten and thin instruments, electro acoustic motors, magnetic separation and magnetization equipment.
Neodymium iron boron material features: neodymium iron boron has the advantages of high cost performance and good mechanical properties; the disadvantages are low Curie temperature point, poor temperature characteristics, and easy to powdering corrosion. It must be improved by adjusting its chemical composition and adopting surface treatment methods to meet the requirements of practical application.
Manufacturing process of NdFeB circular magnet: powder metallurgy process is adopted for NdFeB manufacturing.
The technological process of Nd-Fe-B circular magnet is as follows: proportioning → smelting ingot → pulverizing → pressing → sintering and tempering → magnetic detection → grinding → pin cutting → electroplating → 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.
- Ferrite disc magnet
Features of ferrite disc magnet: its main raw materials include BaFe12O19 and SrFe12O19. 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.
Characteristics of ferrite disc magnet: higher magnetic properties, better time stability and lower temperature coefficient.
Applications of ferrite disc magnets: widely used in electric meters, instruments, motors, automatic control, microwave devices, radar and medical devices.
Magnetization direction of ferrite disc magnet: axial, radial or as required.
- Alnico disc magnet
Features of alnico circular magnet: it is an alloy composed of Al, Ni, Co, Fe 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.
Classification of alnico circular magnets: it can be divided into cast alnico and sintered alnico.
It is mainly used in aerospace instruments, such as aluminum, cobalt, aluminum, aluminum, cobalt, etc. Sintered al Ni Co is produced by powder metallurgy. It is suitable for producing complex, light, thin and small products. It is widely used in instrument, communication, magnetoelectric switch and various sensors.
- Samarium cobalt disc magnet
Samarium cobalt magnet is also called samarium cobalt magnetic steel, samarium cobalt permanent magnet, samarium cobalt permanent magnet, samarium cobalt strong magnet, rare earth cobalt permanent magnet, etc. It is a kind of magnetic material made from samarium, cobalt and other metal rare earth materials by mixing, melting and smelting, crushing, pressing and sintering. It has high magnetic energy product and extremely low temperature coefficient. The maximum working temperature can reach 350 ℃ and the negative temperature is unlimited. When the working temperature is above 180 ℃, its maximum magnetic energy product, temperature stability and chemical stability are better than those of NdFeB permanent magnetic material. It has strong corrosion resistance and oxidation resistance, so it is widely used in aerospace, national defense, military industry, microwave devices, communication, medical equipment, instruments, various magnetic transmission devices, sensors, magnetic processors, motors, magnetic cranes, etc.
The production process of SmCo circular magnet is as follows: proportioning → smelting ingot → pulverizing → pressing → sintering and tempering → magnetic detection → grinding → pin cutting → finished product
Which is more expensive, NdFeB square magnet or disc magnet?
There are no more than two kinds of magnets in great demand. One is the circular magnet, and the other is the square magnet. Because it is more conventional and common, most manufacturers can produce them, and the price is not enough. Especially for those who have no requirements for magnets, what they care about is just a price. Whoever has a low price will do it for them.
In addition to the price, one of the factors affecting the transaction is the delivery time. Many customers ask you how long the delivery time of square magnets will take?
It takes about 10-12 days for the magnet to be formed by cutting three times. If you want to catch up, you can mention it. However, for overtime work, you still have to pay for some urgent expenses.
Why is NdFeB square magnet more expensive than disc magnet?
Square magnets are relatively expensive. Is it more expensive? Yes, the square magnet is more expensive than the circular magnet, which depends on the processing technology.
When the magnet is not processed, it is the raw material blank. The blank of the square magnet is the square type, and the blank of the circular magnet is the cylindrical type. From this, we can see that my circular disc is formed when I use the slicer to cut one knife, and there is no waste. The number of knives for the square magnet is 3, and the waste is more.
Two processing methods of NdFeB magnets
There are basically two kinds of processing of NdFeB: one is slicing machine cutting, and the other is cutting by wire cutting.
The slicer is a diamond inner hole cutter with a thickness of about 0.3mm, which cuts the magnet to the required size according to the requirements. But this method is only suitable for simple square magnet shape, circular magnet shape and cylinder shape.
Another method is wire cutting. Generally used for cutting NdFeB tiles, special-shaped magnets, and large-size products.
The dimensional accuracy of NdFeB products is generally about (+ / -) 0.05mm. In fact, the existing processing methods can achieve the accuracy of (+ / -) 0.01, and the cost will increase a lot if finishing is needed. For the size that needs strict tolerance, should we consider whether such strict tolerance is needed.
Calculation formula of disc magnet weight: (density is calculated according to 7.5)
For example, the specification is Φ 20.5 * 8.9
The calculation formula is: area × thickness × density △ 1000 = weight (g), i.e
- 7.5 * 3.14 * 20.5 M2 * 8.9/4000 = 22.02g or 7.5 * 3.14 * 10.. 25 m2 * 8.9/1000 = 22.02g
Writing format of circular magnet
The English word for diameter is diameter, so the diameter is represented by D, and so is the magnet industry. In addition, the diameter can also be represented by Φ. For example, a circular magnet with a diameter of 10 mm and a thickness of 5 mm can be written as D10 * 5 mm.
Dia diameter * H thickness:
Φ 10 * 5 (represents thickness magnetization)
Φ 10 * 5 (represents radial magnetization)
Application fields of Disc Magnets
It is also widely used in medical equipment, permanent magnet drive system, magnetic disc, magnetic instrument, magnetic transmission system and so on.
1. Raw material preparation and pretreatment:
Process introduction: raw materials are pretreated by weighing, crushing, breaking and derusting.
Process equipment: steel cutting machine, roller polishing machine, etc
The production process of NdFeB circular magnet is as follows:
Process Description: raw materials such as praseodymium and neodymium, pure iron, ferroboron, etc. after pretreatment are proportioned and added into the vacuum melting furnace. After high temperature melting under the protection of argon, the strip is thrown. The results show that the product has uniform composition, high crystallinity orientation, good structure consistency, and avoids the formation of α – Fe.
Process equipment: vacuum melting furnace.
3. Hydrogen explosion:
Process Description: hydrogen explosion (hd) process is to use the hydrogen absorption characteristics of rare earth intermetallic compounds to place the NdFeB alloy in hydrogen environment. Hydrogen enters into the alloy along the thin layer of neodymium rich phase to make it expand, burst and break, and crack along the layer of neodymium rich phase, so as to ensure the integrity of the main phase grains and the boundary phase between the neodymium rich grains. HD process makes the casting of NdFeB very loose, improves the pulverizing efficiency and reduces the production cost.
Process introduction: jet milling is to crush the material by high-speed collision of the material itself, which has no wear on the inner wall of the grinding chamber, so the powder can be prepared efficiently.
Process equipment: jet mill.
5. Forming orientation:
Process introduction: the function of orientation is to make the easy magnetization direction c axis of disorderly oriented powder particles turn to the same direction, so as to obtain remanence. The main purpose of pressing is to crush the powder into shape and size, while keeping the grain orientation obtained in the magnetic field orientation as much as possible. We design to use the forming magnetic field press and isostatic press for secondary forming. For the special-shaped magnet, we use special mold tooling to directly form. The sintered magnet can be put into use with only a little surface treatment, which greatly saves the material and subsequent processing costs.
Process equipment: magnetic press, isostatic press.
Process introduction: sintering is a simple and cheap way to change the microstructure of materials to improve the magnetic properties of materials. Sintering is a post forming process of materials, which has a great influence on the density and microstructure of magnets.
Process equipment: vacuum sintering furnace.
Process introduction: the NdFeB magnets obtained after sintering are all blank, which need further machining to obtain products of various sizes, sizes and shapes. Because of its brittleness and poor mechanical properties, NdFeB magnets can only be processed by grinding and cutting.
Process equipment: surface grinder, double face grinder, chamfering machine, slicer.
The blank should be polished first. Why? Because the surface of purchased blank is very smooth, for rough and uneven blank, glue is only needed after polishing. Glue links are very important. It is necessary to attach the magnet blank to the asbestos sheet and then attach the asbestos sheet to the fixture. After gluing, install the fixture on the slicer and adjust it before cutting.
8. Surface treatment:
Process Description: surface treatment of various shapes of rare earth permanent magnets, such as electrophoresis, zinc plating, nickel, nickel copper nickel and phosphating, is carried out to ensure the appearance and corrosion resistance of the products.
9. Finished product inspection and packaging:
Process Description: the magnetic properties, corrosion resistance, high temperature performance of the products are tested, and then packaged to meet the various needs of customers.
The above is NdFeB circular magnet production process steps.
Where are the poles of a disc magnet located?
The disc magnet made of hard magnetic material has no magnetism before magnetization. The position and number of magnetic poles depend on the way of magnetization. In fact, you can see all kinds of disc magnets.
Pole position of a disc magnet:
Some have one or more pairs of magnetic poles in the outer ring of the ring; some have one or more pairs of magnetic poles in the inner ring of the ring; some have two annular end faces (one n, one s) in the upper and lower ring; some have one or more pairs of magnetic poles in one annular end face.
What are the precautions for the storage and transportation of disc magnets?
As a special product, how is the disc magnet transported? What should be paid attention to in transportation?
First of all, the storage of disc magnets, how do disc magnets store?
Pay attention to the humidity in the room. It must be maintained at a dry level.
- The temperature should not exceed room temperature;
- Black block or blank state of the product can be properly oiled (general oil can be);
- Electroplating products should be vacuum sealed or isolated from air storage, to ensure the corrosion resistance of the coating; Magnetized products should be sucked together and stored in boxes, so as not to suck up other metal bodies;
The magnetized products shall be stored away from magnetic discs, magnetic cards, magnetic tapes, computer monitors, watches and other objects sensitive to magnetic fields.
How are the disc magnets transported? What should I pay attention to?
There are two main problems in disc magnet transportation, one is how to protect the disc magnet, the other is how to prevent the damage of disc magnet magnetic field to the surrounding environment and personnel.
First of all, we must ensure that the environment in which the disc magnets are stored during transportation is dry. If the humidity is relatively high, it is easy to cause the disc magnets to rust. You can also use some anti rust oil on the surface of the disc magnet, which can prevent the disc magnet from rusting. For the disc magnet with electroplated coating, it should be transported in vacuum to prevent corrosion of electroplated coating.
In addition, the temperature of transportation must not be too high. Generally, demagnetization will occur when the disc magnet exceeds 80 degrees. Therefore, during transportation, try to keep it at room temperature. Secondly, in order to prevent collision between disc magnets during transportation, which may cause damage, it is better to separate magnets with wooden board. In the process of transportation, we must prevent the fierce collision. In the process of transportation, the operator should handle it with care.
Next, it is to solve the impact of magnetic field on the environment. First of all, try not to transport disc magnets together with computers, watches and other items sensitive to magnetic field. For the problem of how to shield the magnetic field, the simplest way is to wrap the magnet with iron sheet or carbon steel plate, and then arrange the magnetism of the magnet to form a good magnetic circuit inside. When choosing the means of transportation, maglev train and air transportation are good choices. However, the price will be higher. Moreover, if air transportation is carried out, the shielding of magnetic field will be more strict.
Often see netizens in the major forum post bar asked how to take a strong magnet on the plane, what measures need to be done? What are the requirements for packaging?
As the weak stray magnetic field interferes with the navigation system and control signal of the aircraft, the International Air Transport Association (IATA) lists magnetic goods as category 9 dangerous goods, which must be restricted during the collection and transportation. So now some of the air cargo with magnetic materials need magnetic detection, in order to ensure the normal flight of the aircraft. Magnetic materials, audio materials and other instruments containing magnetic accessories should be tested for magnetism.
Magnet air transport standard
According to the relevant provisions of IATA902: if the maximum magnetic field intensity measured at 2.1m away from the measured object does not exceed 0.159a/m (200nt, i.e. 2mgs = 0.002gs), the article is not restricted as a magnetic material and can be treated as a general cargo.
If the maximum magnetic field intensity measured at 2.1m away from the object is more than 0.159a/m, but any magnetic field intensity measured at 4.6m away from the surface of the object is less than 0.418a/m, the goods can be collected and transported as dangerous goods.
If the magnetic field intensity at 4.6m away from the surface of the object is greater than 0.418a/m, then the object is not allowed to be transported by air.
How to meet the air transportation standard?
In order to meet the above requirements of air transportation, it is necessary to demagnetize the magnets for air transportation. Although it is called demagnetization, it is not demagnetization of the magnets, but through special shielding packaging, so that the magnetism displayed on the package can meet the requirements of aviation safety transportation. Shielding packaging usually uses high magnetic conductivity materials, such as cold rolled sheet, galvanized sheet, etc. if the amount of magnetic materials is large, several layers should be packed. According to the principle of Faraday cage, after packaging, the magnetic field mainly circulates in the box, and there is little leakage. Outside the shielding package, the magnetic field is packed in cartons or wooden cases.
The packing of disc magnet in air transportation:
- 1. The opposite magnetic poles of magnetron, illuminometer and other instruments and devices must be placed relatively.
- 2. Permanent magnet materials must be equipped with magnetic armature or shielding to prevent compass instrument deviation caused by magnetic field.
- 3. Each package of magnetic material must be correctly marked and labeled in accordance with Chapter 7 of IATA Dangerous Goods rules.
- 4. Ensure that the magnetic field strength measured at 4.6 m (15 ft) from the surface of the package does not exceed 0.418 A / M (0.00525 Gauss) before shipment.
- 5. It is suggested to pack large pieces in wooden cases.
The carrier of magnetic materials airlines or logistics companies will require customers to do magnetic testing, issued “air transport conditions identification report”, in order to ensure the normal flight of the aircraft. Generally, the air transportation appraisal can only be issued by a qualified professional appraisal company recognized by the Civil Aviation Administration of the country, and generally, samples need to be sent to the appraisal company for professional testing, and then the appraisal report needs to be issued. If it is not convenient to send samples, the professional personnel of the appraisal company shall conduct on-site testing, and then issue the appraisal report. The validity period of the appraisal report is generally used in this year, and it should be redone after the year.
In magnetic testing, customers need to pack the goods according to the requirements of air transportation, and the testing will not damage the packaging of the goods. In principle, the testing does not open the box of the goods, but only tests the stray magnetic field on six sides of each goods. If the magnetic inspection of the goods is unqualified, special attention should be paid. First, with the consent of the customer, the magnetic inspection staff will be entrusted to open the box to check the goods, and then put forward relevant reasonable suggestions according to the specific situation. If the shielding can meet the requirements of air transportation, the goods shall be screened according to the client’s entrustment, and relevant fees shall be charged.
Understanding the magnetic field
In order to confirm the accuracy of the above contents, our company dialled the major mainstream logistics companies in the name of sending NdFeB high-intensity magnet, and obtained the following conclusions:
Send to China: mainstream logistics companies such as Shunfeng and Shentong do not accept air waybill for magnetic materials, they can only transport them by land; EMS, if the customer can issue “identification report of air transport conditions”, the express collector will determine whether they can receive them according to the situation.
Send abroad: EMS and SF will not accept the waybill of magnetic materials sent abroad (including Hong Kong, Macao and Taiwan), and will not accept the waybill no matter by land or air. DHL or UPS can be used overseas, but customers are required to do magnetic testing. Express companies can apply for testing business on behalf of DGM (different delivery places and testing institutions), and the cost is paid by customers.
Where to buy disc magnets?
1. Trade Fair
One of the best places to find high quality rare earth disc magnet manufacturers from China is trade fair. You will have a chance to see what kind of rare earth disc magnets they can build and check process closely. At the same time, you can collect valuable information from face-to-face conversations with sales representatives, gain in-depth understanding of rare earth disc magnet company, and be able to compare various competitors immediately. According to where you are, I recommend some rare earth disc magnet exhibitions.
- Shenzhen (China) International Small Motor, Electric Machinery & Magnetic Materials Exhibition
- Global Summit and Expo on Magnetism and Magnetic Materials
Of course, the budget of the trade show may be a headache.
2. Internet search
Most suppliers of rare earth disc magnets in China have a good website (for example: www.rizinia.com), which is easy to find. Go to Google or social media, like LinkedIn, Facebook, etc. Checking their posts will give you a lot of information. Online forums are another place to exchange stories, ideas and experiences.
Others in the permanent magnet industry may be willing to lead you to a leading supplier of rare earth disc magnets. Ask them to share their recommended manufacturers. Or you can tell people on the Internet what you’re looking for. You will contact several manufacturers of rare earth disc magnets, both offshore and overseas.
The price of disc magnets
The price of disc magnet is related to size, tolerance precision and machining difficulty: the larger the size of disc magnet, the more precise the tolerance, the more difficult the machining, and the more expensive the price of rare earth permanent magnet.
In addition, the price of rare earth permanent disc magnets is also related to the required quantity, performance grade, temperature resistance, surface treatment, etc.
Source: China Permanent Magnet Manufacturer www.rizinia.com