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Discuss how to ensure the quality of NdFeB permanent magnet materials in the production of “four defenses” work

Posted by: steel world 2021-10-15 Comments Off on Discuss how to ensure the quality of NdFeB permanent magnet materials in the production of “four defenses” work

The sintered NdFeB permanent magnet material is manufactured by powder metallurgy. The process flow is as follows: raw material processing → batching → smelting → powder making → magnetic field orientation and pressing → sintering compaction → tempering aging → machining and surface treatment → inspection . It can be seen from the technological process that the entire technological process is a systematic engineering, especially the high-performance NdFeB permanent magnet material. Every technological link of the production process has the “decision right” and the “right to deny” the performance of the product. “. In order to produce high-performance NdFeB permanent magnet materials, enterprise organizations and managers should pay attention to every link of the production process and guide employees to pay attention to every detail in the process. This is to require employees to do the most basic “anti-oxidation” , Anti-aliasing, anti-impurity, anti-moisture “four-proof” work. To lay a solid foundation for the production of high-quality neodymium iron boron permanent magnet materials.
In order to ensure the quality of sintered NdFeB permanent magnet materials, our daily basic work should be carried out around the “four preventions”, that is, anti-oxidation, anti-aliasing, anti-impurity and anti-moisture.
1. Anti-oxidation
NdFeB is a kind of rare earth permanent magnet material, and the formula contains a large proportion of rare earth elements. The characteristics of rare earth elements are that they are very active in chemical properties and easily react with oxygen in the air to form rare earth oxides. For example, neodymium reacts with oxygen to form neodymium oxide. After the rare earth is oxidized, the magnetic properties of the product will be greatly reduced. Therefore, in the production process of our NdFeB materials, how to do “anti-oxidation” work is a very important quality link.
First of all, when we purchase raw materials, we must ensure the purity of rare earth metals and reduce the oxygen content. When materials are stored, they should be sealed with plastic bags and put in the barrel to avoid contact with air. When the ingredients are finished, the materials with higher quality requirements should be filled with nitrogen for protection and the bag mouth should be wrapped. When mixing small pieces of metal neodymium and other rare earth materials, try not to cut too much for use. It will oxidize after a longer time. For example, the fracture of neodymium metal will become red, and metal praseodymium will become white.
Secondly, we must ensure the atmosphere of the furnace during the smelting process. New molds, new furnaces or furnaces with more repaired furnaces must be dried before they can be officially put into production; the sealing of the valves and connecting parts of the smelting furnace must be ensured to be normal. The vacuum pumps (mechanical pumps, Roots pumps, diffusion pumps) must play a good role without air leakage, water leakage, and oil leakage. If the pump is unable to pump air, it should be repaired and maintained in time. Vacuum hygiene should be cleaned regularly in accordance with the process regulations. In order to ensure the vacuum in the furnace, good products can be made.
The coarse crushing, medium crushing, jet milling, and stirring of the powder making process must be protected by nitrogen filling according to the process. Check and replenish the nitrogen pressure of the stainless steel drum (plastic bag) at any time. Check the stainless steel drum valve or plastic bag for air leakage before use. If it is found in use, it should be replaced in time or covered with a new bag. When the powder is found to be hot during processing, cooling measures such as nitrogen filling should be taken to prevent oxidation.
During the molding process, pay close attention to the oxygen content of the powder box and the nitrogen protection box to ensure that it is lower than the value specified in the process to prevent oxidation of the magnetic powder. In the process of stripping the oil and entering the furnace, the time is required to be tight. Especially high-performance products are particularly important, and must be operated in a nitrogen protective box according to process requirements. Prevent oxidation of water chestnuts and corners of the product.
In addition, we should always pay attention to the purity of the argon used, and deal with it in time if it is found to be abnormal. Always observe the temperature of the cooling water and determine the cooling time. The temperature of the product after the furnace is lower than 80 ℃ to avoid high temperature from the furnace, which will cause the product to oxidize.
Therefore, the “anti-oxidation” work is an indispensable part of our work to grasp the quality of NdFeB permanent magnet materials. We must start from the actual work bit by bit, steadfastly, and constantly work hard.
Two, anti-aliasing
Sintered NdFeB is distinguished by different grades according to different performance requirements, such as residual magnetic induction, coercivity, maximum magnetic energy product, etc. At present, our company mainly uses seven series of N, M, H, SH, UH, EH, AH. The coercivity gradually increases from N to AH. In each series, different numbers are used to distinguish the magnetic energy product. For example, the N series include N30, N35, N38, N42, N45, N50, N52, etc. The larger the number, the higher the magnetic energy product.
According to differences in climate, material, formula, etc., we use “-1”, “-2” and other distinctions after the brand to indicate, such as N35-1, N35-2, etc.
For products with special performance requirements, add character descriptions at the end of the grade.
From the above, it can be seen that the English letters and numbers are different, the brand, formula, process, and meaning are also different. We use different grades and processes to produce according to customers’ various orders to meet customer needs.
Therefore, we must pay attention to the “anti-aliasing” work during the batching and smelting operations. Don’t get the grades wrong, calculate the weight of the ingredients according to the formula sheet, and put the correct identification plate in time after weighing. The smelting operator should follow Grades accurately record original data records and smelting tracking sheets. When the spindles are released into the warehouse, the identification plate and tracking list of each spindle must be sent to the warehouse accurately and timely for verification. At the same time, the workshop should check and supervise the above situation at any time. Finally, check the spindle carefully when weighing, fill in the certificate after weighing, and put it in the bucket after checking. When sending the material, check whether the label on the outside of the barrel is consistent with the certificate of conformity inside the barrel, and make sure that it does not match.
When smelting, avoid mixing different grades of raw materials, alloy liquid in the crucible, and ingots after the furnace. The raw material warehouse and batching group must pay attention to strengthen the proofreading and inspection of materials of various origins, properties, specifications, contents or numbers in time to prevent errors.
In the pulverizing process, the “smelting tracking list” must be followed when the spindle is coarsely broken or medium broken, and if any abnormality of the spindle is found, it will be reported back to the smelting workshop for tracing. All equipment being processed must be marked with a brand name, and all products “to be processed” and “processed” must be marked with a brand name. The processing equipment and the discharging barrel must be cleaned to prevent mixing with other brands of powder.
During the molding process, the powder material used must be carefully checked whether the identification sheet of the powder material is consistent with the grade requirements of the construction sheet before the powder is formed and weighed. It is said that each batch of powder in the powder box must be cleaned up to prevent mixing of different batches of powder. The molded product must be clearly marked before it can be circulated. In the process of stripping the oil and entering the furnace, it must be checked according to the furnace entry list and product identification sheet, and the operation can only be performed after correctness. After the sintered product is released, it must be marked according to the furnace entry list, which is clear and clear to prevent product confusion.
If the concept is vague and careless, resulting in brand confusion, and the performance of the product cannot meet customer requirements after sintering, it will cause great losses to the company. I hope that all of our employees must put the “anti-confusion” work in a very important position.
3. Anti-impurity
Sintered neodymium iron boron permanent magnet material, it is through the organic combination of rare earth, iron, boron and other raw materials in the optimal ratio to form the main phase of Nd2Fe14B and other basic phases. After a series of processes of smelting, powdering, molding, and sintering, Finally, a magnet with certain magnetic properties, density and specifications is obtained. Only qualified magnets can ensure the internal and external quality of post-processed slices and electroplated products.
From the performance point of view, we must prevent the entry of harmful elements to prevent the basic composition of the magnet; for this reason, we must prevent the inclusion of impurity elements to avoid different melting points and shrinkage during sintering of the product, foaming, shrinkage, or shrinkage of the magnet. Spots, peeling, etc. will occur after electroplating and pickling, which will affect product quality. Therefore, impurities are the enemy of our sintered NdFeB. Market competition is largely reflected in product quality competition. If we want to stand firm in such a fierce market competition, we must strictly control product quality.
In the process of raw material processing, the raw materials must be cleaned, and the oxides covering the surface of the neodymium, iron and other raw materials must be cleaned up before the ingredients, so that the oxides are not used and can only be used after being removed. Pour out all empty barrels and cans before ingredients.
During the smelting process, be sure to pay attention to the use of the crucible and the sprue cup. If corundum or refractory mud is found to fall off during use, it must be treated before use, and replaced in time if necessary. When cleaning the vacuum sanitation, cover the melting mold in time to prevent dust from entering and sticking to the mold wall and affecting the surface quality of the spindle. The spindles are not allowed to be placed randomly after they are out of the oven. They should be placed in a stainless steel basin for picking up impurities. After careful inspection, they should be placed in a clean empty bucket, marked and covered in time to prevent dust and other impurities from entering. It is strictly forbidden to expose the spindle in the dusty space, and proper measures must be taken.
During the coarse and medium crushing of the powder, the fracture should be opened frequently for observation. If there is any impurities, deal with it in time and feed back to the previous process. All kinds of processing equipment must be cleaned up before use, especially for equipment that has not been used for a long time, the internal cavity of the equipment must be cleaned with nitrogen before use to prevent the mixing of impurities caused by the oxidation of the original remaining powder. The inlet and outlet of the alloy ingot and the equipment used should be covered in time. Dust in the workshop is strictly prohibited, and proper dust prevention measures must be taken if necessary. In the fine powder mixing process, pay attention to the cleanliness of the stainless steel bottle to prevent leftovers and impurities in the barrel, which may cause impurities or oxidation spots in the final product.
During the molding process, pay attention to clean up the leftover powder in the powder box every time to prevent the oxidized leftover powder from mixing in, causing product impurities or oxidation spots.
At first glance, impurities are very small things, but once they are mixed into the product, they become a black sheep, affecting the quality of the product and causing great losses to the company. Therefore, we must not underestimate the impurities. The consequences caused by small losses are very serious. We must attach great importance to “preventing impurities”.
Fourth, prevent moisture
The NdFeB rare earth permanent magnet material formula contains a relatively large proportion of rare earth elements. The characteristic of rare earth elements is that they are very active in chemical properties and easily react with oxygen in the air to produce rare earth oxides, which will greatly reduce the magnetic properties of the product. When damp raw materials or equipment, tooling and fixtures used contain high moisture, in the high temperature process of processing, water molecules are easily decomposed into oxygen and hydrogen elements and chemically react with rare earth elements such as neodymium. Therefore, in the production process of our NdFeB materials, how to do a good job of “anti-moisture” is a key quality assurance link.
During the processing of NdFeB permanent magnet materials, the “moisture-proof” work in the melting process includes: if the raw materials are not smelted in time after the raw materials are processed or batched, the necessary moisture-proof measures must be placed in a special plastic bag or iron bucket to prevent moisture . The ingots out of the furnace must be put into the barrel and covered in time; the empty furnace equipment must be vacuumed and protected in time. The above measures are to prevent raw materials, products and equipment from adsorbing moisture in the air and becoming damp.
The “anti-moisture” tasks in the flour milling process include: controlling the indoor temperature and humidity, turning on the dehumidifier and air conditioner if necessary. For the processed powder, it is strictly forbidden to use damp barrels. The water content of aviation gasoline used for mixing is controlled, because gasoline can easily absorb water in the air.
The “anti-moisture” work in the sintering process includes: closing the furnace door in time to vacuum protection after the furnace is out, to prevent the equipment from adsorbing moisture in the air and becoming damp. The sintering pot must be kept dry by drying and other measures to ensure that the sintering pot is dry before use to prevent the product from being damp during the sintering process.
The daily production process seems to be a trivial matter for the “anti-moisture” work. It is a relatively simple task, but it plays a vital role in the quality assurance of the product. Therefore, we will also focus on the daily “anti-moisture” work.
In short, as the processing of sintered NdFeB permanent magnet materials, each process link in the production process has a “right to decide” and “right to deny” the performance of the product, which determines whether the product is qualified or not. Therefore, attention should be paid to every link in the production process. Daily production management should start from the most basic details, that is to say, from the “four preventions” of “anti-oxidation, anti-aliasing, anti-impurity, and anti-moisture” Start the work to ensure the quality of our products and improve the quality of our products.

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