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The technology of China sintered Ndfeb magnet is introduced


In recent ten years, China's ndFeb magnet industry has achieved a long and rapid development. At present, the sales volume of sintered NdFeb is equivalent to that of Japan, accounting for about 41% each in the world. It is known as sunrise industry and trans-century industry. In 2000, the global production of sintered Ndfeb magnets was about 15090 tons, with China producing 5550 tons (37%), Japan producing 7700 tons (50%), the US producing 1020 tons (7%) and Europe 820 tons (6%). On this basis, the momentum of production expansion is not reduced, annual output of thousands of tons of large enterprises more and more. Faced with such a strong development momentum, we cannot help but ask: Where is China's Ndfeb compared with the world level? Any other questions? In what direction will it go?

Change of management mode and technology pay equal attention

In the past, we ndFeb enterprise paid more attention to technological progress and regarded performance improvement as the key to enterprise development. In the past, because our performance is far from the performance of foreign countries, so how performance becomes the key to restrict the development of enterprises. Without high performance we would have no orders, so there was nothing wrong with what we did in the past. However, up to now, our Ndfeb backbone enterprises can basically achieve N45, 45M, 42H, 40SH, 35UH, 32EH and so on in terms of performance. Some enterprises can even achieve N50, 48M, 45H, 38UH, 35EH and so on. Only in terms of performance, it is basically the same with the world level or slightly lower, at least to the upper middle level. In fact, N50 and other high performance orders are not too many, most of the orders are in the 45M or below level, so now the key is "stable performance, good internal quality, timely delivery and low price". To achieve the above points, the management of the enterprise will be an important part.

We think China's ndfeb enterprises can be roughly classified into three categories :(1) private enterprises, (2) genuine joint ventures, (3) state-owned and class I state-owned enterprises. The term "true joint venture" is used because some enterprises are nominally joint ventures, but they are actually managed by traditional state-owned enterprises. Such enterprises in the NdFeb industry is not in the minority. Through visiting many peers, we found that private enterprises have the highest management efficiency, and each has its own management and product characteristics. Private enterprise management efficiency is originally in the reasonable, but so high still make us surprised. Just take two representative enterprises for example, their annual output is between 500 and 600 tons, and the equipment maintenance department has only 6 people (3 electricians, 3 mechanics). And general state-owned and similar state-owned enterprises of the same scale, the number of equipment maintenance department between 15 to 25 people. Not only is the number of people, and in the equipment maintenance efficiency of private enterprises far higher than state-owned and state-owned enterprises. If we use 20 people to do the same job for six people, it's easy to see who wins and who loses in the competition. 6 people can do the work of 20 people, because of the following three points :(!) General maintenance is completed by the production team leader himself, equipment maintenance department staff is only responsible for overhaul, equipment maintenance costs and production department linked; (2) Component replacement and maintenance method; (3) In spare time, equipment maintenance department staff shall transform old equipment and manufacture new equipment, and be responsible for the installation of new equipment, etc. The first point makes the operator cherish the equipment more, greatly reduces the equipment damage caused by misoperation, and reduces the frequency and cost of equipment maintenance. The second approach is to replace the damaged parts directly, install the good parts, continue production, and repair the damaged parts. Such maintenance takes up less production time and greatly improves the utilization rate of equipment. The completion of the third point means that the equipment design can be improved according to the use, more suitable for the specific situation of the company, thus reducing maintenance. If part of the equipment is manufactured by the maintenance personnel are very familiar with the condition of the equipment, which is conducive to maintenance. The above is just an example, fundamentally speaking, the key is the change of thought and the change of system. Of course, it is obviously naive and unworkable to let state-owned enterprises or quasi-state-owned enterprises follow the same rules as private enterprises. However, state-owned enterprises or quasi-state-owned enterprises can carry out reform by referring to some methods of private enterprises. We believe that this is not only possible, but also certain to be successful. Remember in Taiyuan, a company manager said such a sentence "now with snacks, to eat fast slow". We believe this is true. It will not be long before that happens if many large enterprises remain the traditional management system of state-owned enterprises. From our point of view, we also want to say: "now we eat with characteristics without characteristics, eat with high efficiency low efficiency, eat with low cost high cost". Ningbo permanent magnetic industry is characterized by high efficiency, high brand products, etc. Ningbo Zhaobao magnetic industry features in product categories, focusing on high coercivity products; Yuxian Jingxiu magnetic Material Co., LTD. Management efficiency, small cylinder product features and low cost is worth learning; Taiyuan Tianhe high-tech Co., Ltd. is characterized by high brand and high price, and there are many lessons to be learned in management. We believe that these companies will have great development in the next 3~5 years.

In fact, all ndfeb enterprises have a lot in common, there should be many general rules in management, here we put forward a few points for your reference.

1.1 Implementation of the "co-production contract system" in each production process: The co-production contract system is not a new method. In fact, it has been popularized in rural areas of China since 1978. 20 over the years, this way in the countryside proved to be successful, and in many private enterprise in the industry of ndfeb is successfully implement this way, so in the state-owned or state-owned enterprises and joint ventures, the approach to improve the work efficiency, ensure the production quality, reduce cost, etc should be effective. The reason is simple, because the performance of work and income tied together, really embodies the principle of "more work, more gain". It can be contracted by smelting, powder making (including medium breaking, air grinding, etc.), molding, sintering, quality inspection, post-processing, packaging and other groups.

1.2 Improve the "self-inspection and other-inspection of each process" : If we want to adopt the co-production contract system, we must strengthen the self-inspection and other-inspection, otherwise we will only emphasize the quantity but neglect the quality. Each process must have the self-inspection quality and quantity report, at the same time must obtain the other inspection approval of the next process to enter the next process, the quality inspection department as the arbitration unit will play an increasing role in ensuring the quality.

1.3 Daily maintenance of production equipment shall be disconnected from the equipment department: the basic daily maintenance of equipment shall be completed by the contractor himself. If the contractor is not able to complete, the contractor should adopt the way of joint contracting with maintenance workers or daily maintenance personnel must be affiliated to the production workshop, and not full-time maintenance workers. The equipment department of a larger company should have 2 to 3 full-time personnel, who are responsible for equipment transformation, overhaul, installation and commissioning of new equipment and manufacturing of new equipment, etc. in cooperation with r&d and production.

We emphasize the importance of management because if management cannot keep up, even the best technology and product performance still cannot guarantee us to win in the fierce market competition. We can say that today is the time to emphasize management! But that doesn't mean our technology is perfect. We still have a lot of work to do in terms of technology.

2. Direction of technology development

For neodymium iron boron, only from the point of view of knowledge, The Chinese than the Japanese, americans, Europeans and so on are not bad, in fact, the so-called technological progress in today at least 90% is equipment progress. As we can see from the following statement, we have a lot of work to do.

2.1 smelting


Strip casting process is also called quick-setting thin section process. The process was first adopted and patented by Japan's Famichi Metal (which provides only quick-setting thin bands but does not produce magnets) and Sumitomo Metal. The strip casting process is characterized by the effective elimination of -Fe, uniform distribution of neodymium rich phase and refinement of grain, easy to obtain products with high magnetic remanence and high coerciveness. The NdFeb magnet manufacturer in China began to know this information and started research work around 1997. After more than 5 years of efforts, Chinese equipment manufacturers have made great progress in this regard. Now there are not only 25kg belt flasher, but also 50kg and 100kg belt flasher have been marketized. But in terms of the consistency of the belt, there is still a considerable gap compared with the three DE metal, free surface uneven phenomenon is very serious. At the beginning, the main problem was the thickness of the tape. At that time, it was very difficult to dump the tape thickness to more than 0.2mm. There were a lot of amorphous materials, which made it difficult to sintered NdFeb. Now the belt thickness of several major manufacturers can achieve more than 0.3mm, some can even to 0.5mm, in addition to the belt consistency is not good, adhesion problem is also an important issue affecting the quality. FIG. 1 shows the product of a manufacturer (with adhesion phenomenon) (cross-sectional metallography), a large number of -Fe precipitation can be seen. Figure 2 shows the metallography of the tape from another manufacturer. The thickness of the tape is 0.3~0.5mm. The columnar grain size is wide. But the distribution of neodymium - rich phase is not uniform. FIG. 3 shows the rapidly condensing thin band of Sande metal from Japan. Most of the columnar crystals are around 3 in width, without -Fe precipitation, and the neodymium rich phase is evenly distributed. The current gap can be clearly seen from the three metallographic photographs.

If the current situation of the sling in China is a conclusion, it is: usable, but not very satisfactory. We believe that in addition to solving the uniformity, consistency, but also to solve the problem of productivity and efficiency. In the next 3~5 years, the equipment manufacturer should be able to provide 500~1000kg of sling furnace. Now the height of the furnace is not enough, at least 10~15m high to be able to have enough space and thin belt cooling time. If the quick-setting thin strip is qualified, the strip casting process should be one of the simplest processes (the formula is single, the medium crushing and air grinding efficiency is high, and the rest have no obvious difference with the traditional process), so it is most likely to be promoted in China.

2.1.2. Double alloy process or similar double alloy process

In addition to the work of the quick-setting thin strip, most manufacturers in China focus on reducing the thickness of the ingot and improving the cooling efficiency. In terms of reducing the thickness of ingot, the double-sided water-cooled ingot with a thickness of 10mm has been widely adopted, and there are also manufacturers with a 100kg turntable one-side cold pouring process with a thickness of 15mm or so. Some manufacturers adopt the method of melting furnace ingot mold with brine freezing liquid. All of these methods have made positive contributions to improving the performance of our magnets. But we should also see that there is hardly much room for development of this line of thought (the gate cannot be narrower, the ingot mould cannot be larger; The thickness of rotating disk ingot is uneven, and the surface is hard to polish. The double alloy method should be a feasible way. It is a pity that in the past few years, most of the NdFeb manufacturers in China have not paid enough attention to the dual alloy process. We've known for a long time that the double alloy method is nothing, and its advantages are obvious. If we adopt the double alloy method, we will not need to refine dozens of spindles with different formulations, but only have a few main phase alloys and a few neodymium-rich phase alloys to get all the properties of magnets. VAC from Germany and Hitachi metal from Japan used this method to get sintered NdFeb magnets with excellent performance, and the performance of their products is no worse than sumitomo's products with casting method. The common practice now is to make the spindle thin. The double-alloy method does not care much about the thickness of the spindle. On the contrary, because the spindle needs to be homogenized, excessively thin spindles are prone to oxidation (because the thinner the spindle is, the larger the surface area of the spindle is). We think it is advisable to use 200~500kg melting furnace to make this spindle in China at present, otherwise its advantages (uniformity, consistency is better than 25kg furnace, high efficiency) are difficult to show. Homogenization is the key step of the double alloy method. In fact, the spindle after homogenization can also be used in the single alloy method, which is called "quasi-double alloy method" here. This method has been used by many domestic manufacturers to produce high performance products. However, we believe that the potential of this method is not fully realized if the melting furnace of 25kg is still used. In short, for smelting we should develop towards two poles: either thinner or thicker.

2.1.3 Centrifugal casting method

The method is to hold the alloy melting pot in a rotating metal cylinder, when the alloy melting fall, due to centrifugal effect, the liquid paste on the metal cylinder wall quickly condensation. This is a kind of method between the sling method and the traditional ingot casting method. The thickness of the product is less than 10mm, the performance is excellent, the efficiency is high, and the development potential is very great.

2.2 the broken

2.2.1 Hydrogen blasting technology (HD)

It's not new, and in the exact sense, it shouldn't be called a process by itself, it's just a step in our production. It can be used either for strip casting, for ordinary ingot casting, or for double alloy casting. We are familiar with its process. The HD method has been delayed for at least 3 years for mass production mainly due to equipment. Now the prototype of the hydrogen explosion equipment has been completed. It is expected that at least half of the production of Ndfeb sintered in China will use HD process in the next three years. The good news is that we know of at least three companies that are mass-producing HD. By adopting HD, the air flow grinding efficiency (50-80 kg/h) can be improved, the microstructure of the magnet can be improved, and the corrosion resistance can be greatly improved (for example, the weight loss of a certain product is only 8mg/cm2 after 168h in the PCT experimental box at 120℃ and 0.2mpa). Figure 4 shows a metallographic image of the HD process with a grain size of about 10 m.

2.2.2 Improved hammer-like grinding equipment

Now most companies have adopted the two-step crushing method, namely alligator break or rough hammer break + hammer mill. In this way, we get rid of the equipment such as roller, ball grinding and cone grinding, saving time and improving efficiency. Generally, one equipment can handle about 200kg of spindle per hour, and the granularity of coarse powder can be between 50~100 mesh. The efficiency of this equipment is improved, but there are two problems as follows: first, the granularity distribution is too wide, too much fine powder; Second, the failure rate is too high. The first problem exists in both types of equipment, and the second problem is mainly in the hammer mill. The problem of sticking machine in the grinding chamber often occurs, and the whole grinding chamber needs to be removed for maintenance, which is very inconvenient. These problems should be solved in the next two years.

2.3 jet mill

Our country's air flow mill is basically imitating the design of German Hosokawa Alphas. Although some manufacturers think that the air flow mill has been improved, and in the homemade air flow mill, but most of the improvements are without theoretical basis, and the effect is not good. Of course, some manufacturers have been successful in this regard. We believe that there are three problems in the current air flow mill in China :(1) too much ultrafine powder and too wide particle size distribution; (2) Pipe wall adhesive phenomenon is serious; (3) Slow discharging speed. If there are many ultrafine powder, magnetic powder is easy to catch fire. If the tube wall adhesive is serious, it is easy to appear large particles; The discharging speed should reach 60~80kg/h to reduce the total amount of rare earth and prevent oxidation. The solution to these problems has been found in some manufacturers, and it is estimated that it will be implemented in the whole country in about 3 years.

2.4 the molding

2.4.1 Both semi-automatic press molding and hand molding

We found in the investigation that the ningbo area semi-automatic press molding far more than taiyuan area, Taiyuan area is basically holding the mold (manual mold, hand gridding mold) molding. Of course, it depends on the scale of production. The larger the production scale, the larger the order, the more conducive to the use of semi-automatic press. The problem we found here is that some fairly large enterprises actually do not have semi-automatic presses, while some larger enterprises have basically abandoned the hand mold. What we want to see is a balance between the two. The semi-automatic press has high efficiency, but the product is easy to crack, the mold production cost is high, the time is long; Holding the mold production is easy, for pressing 3~ 10mm column and special products (such as ring, cylinder, etc.) have unique.

2.4.2 Parallel press

In fact, when the neodymium iron boron was first produced, it used a parallel press, but later in China, it was basically changed to vertical pressure. Parallel pressure product Br low, from parallel pressure to vertical pressure is undoubtedly an improvement. In general, for the same material, the vertical residual magnetism should be increased by 0.03~ 0.05t (300~500G), and the magnetic energy product by 24~40kJ/m3 (3~5MGOe). But now the situation is different, we can easily achieve around 1.35t remanence, and in many cases we do not need such a high remanence. Considering the advantages of parallel press in cylindrical (very round outside, low grinding) and special-shaped (example VCM) products, we predict that there will be a great development of parallel press in recent years.

2.4.3 Radial orientation suppression

Our current vertical press is very suitable for radial orientation cylinder or ring products, for large size products, of course, there is no problem; However, the efficiency is too low if the multi-hole mould is not used for small size products. The mold making itself is not a problem, the problem is how to evenly fill multiple parallel holes. One solution is to use hand molds, which can only partially solve the problem; The other is an automatic feeding system.

2.4.4 Multipole directional press

The application of multipole directional products is more and more, so in the next few years, the multipole directional press will have certain problems.

2.4.5 monolithic pressure

Neodymium iron boron enterprises in China are basically the first to get sintered blank, and then slice or wire cut to the finished product, while in foreign countries single slice has been a very mature process. For example, VCM magnets can be pressed in a single chip, and only the upper and lower sides can be ground, thus saving material, high efficiency and low cost. Generally, single sheet pressing is parallel pressing and adopts one-way press and automatic feeding. After parallel pressure pass, it is estimated that monolithic pressure will soon become a reality.

2.4.6 Injection molding

Injection molding, originally a conventional method of making bonded magnets, has been transplanted into sintered magnets. Some people call it "sintered magnets of near net size with no post-processing in a single molding". The process route is as follows: magnetic powder + binder and mixing → injection molding (in the magnetic field) → debinding → sintering + aging. It has the advantage of requiring no post-processing and is especially advantageous for products with complex shapes. As for this work, the current research in China is mainly in universities, and it will take at least 4-5 years for production.

2.4.7 Rubber die isostatic pressure Technology (RIP)

RIP (Rubber Isostatic Pressing) has been around for five or six years, but to be honest, it was just a conceptual experimental device. The basic steps are as follows: filling the rubber mold with magnetic powder → pulse magnetic field orientation → quasi-isostatic pressing → taking out the pressed blank. Over the past few years, there have been advances in understanding, as well as improvements in equipment. We have been able to mass produce NdFeb permanent magnet in this way. One press can press 200~300kg of magnetic powder per day. Due to the high pulse oriented magnetic field, the orientation of magnetic powder is high. In general, the residual magnetism can be improved by 0.03~ 0.04t (300~400G) compared with the mold pressing. At present, domestic manufacturers can provide this press, but not fully automatic, but manual. From the operation, the manual press is not less efficient than the automatic press. The price of Japan's RIP press is too high, in recent years it is impossible to promote in most enterprises in China, but the domestic manual RIP press is likely to be promoted.

2.4.8 Automatic feeding system

At present, there is no automatic press in Our country, the main problem is that there is no automatic feeding system. If there is no automatic feeding system, it is very difficult to apply multi-hole cylinder in parallel pressure, multi-hole radial direction in vertical pressure and single-chip pressure. Matching with the automatic feeding system is the automatic removal and pressing of blank and code plate technology, it is best to use the two technologies simultaneously. The main difficulty encountered in the past has been the poor fluidity of magnetic particles, which makes automatic feeding by volumetric method difficult. Today, most manufacturers have adopted lubricant technology, the fluidity of magnetic powder has been significantly improved, the time is ripe for the use of automatic feeding. In addition, our understanding of weight loss is not what it used to be, so automatic feeding presses should be available within the next two to three years.

2.5 the sintering

2.5.1 Three-point temperature control sintering furnace

About a decade ago we imported ABAR and VES furnaces, and then many manufacturers copied them. At that time, these two kinds of furnaces were only general heat treatment furnaces, not specially made for NdFeb. Their biggest disadvantage is a point of temperature control, so sintering furnace temperature uniformity is difficult to adjust. After more than ten years of development, China's sintering furnace manufacturers have fully mastered the special sintered ndFeb manufacturing technology, and now are three point temperature control. It is safe to say that there is no difference between our homemade sintering furnace and foreign ones, and since special for ndFeb manufacturers are still using the former one-point temperature-controlled sintering furnace, it is expected that most of the one-point temperature-controlled sintering furnace will be eliminated in the recent three years, replaced by three-point temperature-controlled sintering furnace.

2.5.2 Partial pressure sintering furnace

Now we are basically using vacuum sintering furnace, sintering process in the vacuum. Many foreign manufacturers adopt partial pressure sintering, that is to say, a small amount of argon is filled in the sintering process, but the negative pressure is still maintained. Theoretically, because of partial pressure sintering

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