Application of atomization roasting in the preparation of high performance ferrite materials

In recent years, due to the development needs of national defense, scientific research, electronics and other industries, in particular the demand for high-tech products (such as computers, laser, microwave, etc.), the demand for electronic materials ferrite greatly increased, its performance also raised Higher requirements. At present, high-performance ferrite electronic materials belong to the high-tech products of today's world and have broad development prospects. The domestic development and application of this industry is still in its infancy, compared with developed countries such as Europe, America and Japan. Big gap. Research and development of high-performance ferrite materials is of great significance to China's technological progress and economic development, and the consolidation of national defense.
After long-term research and trial and error, an electronic production company has produced a certain type of ferrite electronic material product with the performance of similar products in the world. (The annual demand for this product is about 10,000H, and the world market price is, "10,000 YH As the application range of the product continues to expand, its demand will increase year by year, and the market prospect is broad. However, the scientific and technological achievements produced by the laboratory should be applied to industrial production, to be transformed into productivity and economic benefits, and there are many different places. There are still many work and technical problems to be solved, and the achievement of experimental results is only a key step in the technical process.
The preparation of ferrite can be roughly divided into the following processes: batching - mixing - pre-burning - forming - sintering - heat treatment. In the above process, the ingredients and mixing belong to the company's proprietary technology. After long-term research and experimentation, the process is familiar with it; molding, sintering and heat treatment are several processes, due to the traditional ferrite material preparation process. Basically consistent, only some of the similarities and differences of processing parameters, has been basically mastered; can be used for the process of pre-burning, despite the investment of a lot of manpower and resources, the application of a variety of methods, a variety of attempts, but not explored effective The treatment method is very unsatisfactory—not continuous production, high labor intensity, low labor productivity, difficult production control, large equipment and working surface, and high investment. Because the pre-baking process has a great influence on the quality performance of the product and directly affects the subsequent process, there are many strict requirements for the process. Our hospital conducted a semi-industrial test on the pre-burning process from May to August 2002.
1. Material composition and test requirements 1.1. Material composition The material composition to be processed in this process is as follows:
Resin 27%, powder 28%, water 45% (ultra-pure water), wherein the powder is 90% Fe ₂ O ₃ and a certain proportion of Ni, Zn, etc.; powder particle size < 5 μm; powder bulk density 300 ~400kg/m ³ , density 4000kg/m ³ ; the mixed materials are thick. [next]
1.2 Test requirements Due to the particularity of the quality and performance of the product, strict requirements are imposed on the test:
(1) The material is burned and burned at 600~800 °C, leaving no residual fat and moisture;
(2) Fe ₂ O ₃ and Ni, Zn, etc. in the material after combustion are uniformly mixed, no segregation occurs, the crystal structure is grape-like, complete oxidation, and non-magnetic;
(3) The material should not be contaminated before and after combustion, and the purity of the material after combustion should be 99.99%;
(4) Due to the high price of the product, the recovery rate is required to be 98% or more;
(5) Simple operation and low labor intensity in production;
(6) The equipment has a life expectancy of more than 5 years and the price is moderate.
2, test measures and effects 2.1, the similarities and differences between the new process and the traditional process This product is very demanding, from the ingredients, mixing to pre-burning, and the preparation of traditional ferrite materials is very different, so the pre-burning The process is also fundamentally different, and there is no process and experience to learn from. In the process, uniform mixing of the powder must be obtained by mixing and stirring the powder material, high-purity water, and resin in a storage tank. Conventional mixing, calcined embodiment is generally the material (metal oxide or carbonate) and an appropriate size and number of balls together poured into steel drums, mounted on a ball mill continuously rotated, each steel ball with material Impact, produces uniform mixing and grinding effect. After several hours to several tens of hours, it is taken out and dried, and then heated in a high temperature furnace to promote solid state reaction to form a composite oxide. The preheating temperature is generally 800~1000. °C, holding time 1~4h or more, after the calcination is completed, the ferrite with the desired chemical composition is basically obtained, but the reaction degree is not uniform enough, or there is a small amount of unreacted ingredients, which needs to be in the subsequent process. Process it. The new process adopts a different method from the traditional method. In comparison, the mixing process of the new process is time-saving, simple, and less expensive than the traditional process, regardless of the mixing time or difficulty level. The superiority, but because the mixed product is a viscous liquid, it is difficult to process the mixed product in the next pre-baking process of the mixing process. The conventional pre-baking process can no longer be adapted to handle the mixed product, and the pre-firing temperature is required to be [next] 600 ~ 800 ° C, lower than the traditional pre-burning process temperature to ensure the crystal phase structure of the required materials. The rest of the forming, sintering, and heat treatment processes are not much different from the conventional methods, but differ in processing parameters.
2.2. Test process For the specificity and performance requirements of the materials processed by the pre-burning process, after conducting various investigations, comparisons and detailed demonstration of each pre-burning process, it is decided to use high-temperature clean air as a heat source to avoid materials. Before and after the reaction, it is polluted by the heat source; the material is atomized to make it burn well, and the degreasing and oxidation are complete; the equipment and pipeline are made of stainless steel.
The process flow is shown below:

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2.3. Test Measures There are several difficult technical problems in the above process:
(1) Acquisition of high temperature clean air. To produce high temperature air of 600~700 °C, there are high requirements for the material and processing of heat exchangers;
(2) Delivery and atomization of the slurry. Because the prepared slurry has high viscosity and poor fluidity, it is difficult to transport and atomize in the pipeline, and is easy to agglomerate when heated, blocking the pipeline and the nozzle;
(3) Dynamic control of the combustion reaction process. In the process, the supplied hot air temperature is 600~700 °C, the resin releases heat when the slurry is burned, the water evaporates and absorbs heat, and the high temperature combustion chamber has heat loss to the surrounding environment, so that the slurry is 600~800 °C, lower combustion, so the combustion process must be strictly controlled, is a dynamic control process, to maintain its relative thermal balance to ensure that the temperature of the atomizing combustion chamber is within the required range; in addition, to burn fully, without leaving residual fat and For moisture, ensure sufficient reaction time and ample air.
(4) Contradiction between equipment and investment control. Due to the high requirements on material purity and equipment service life, the equipment cost is necessarily relatively high. Therefore, it is necessary to effectively reduce costs while ensuring that the requirements are met.
After detailed calculation and careful design, the above problems have been better solved. First of all, the acquisition of high-temperature clean air, after comparison of economic benefits and environmental sanitation, decided to use heavy oil as fuel, using high-efficiency adjustable burner as combustion equipment, burning high-temperature flue gas into the heat exchanger, and filtering clean The cold air is heated to 600~700 °C, and then enters the combustion chamber. For the heat exchanger, the requirement of 600~700 °C high temperature air is required. In order to improve the heat exchange efficiency and effectively reduce the cost, the heat exchanger is divided into high temperature heat exchanger. Two low-temperature heat exchangers, the low-temperature heat exchanger preheats the cold air to not more than 500 ° C, and the high-temperature heat exchanger finally heats it to the required temperature; because of the large proportion of the low-temperature heat exchanger, The requirements for materials and processing are relatively low, which greatly reduces the cost of the heat exchanger. The use of high and low temperature heat exchangers not only improves the heat exchange efficiency, meets the heat transfer requirements, but also effectively controls the cost. [next]
Secondly, the transportation and atomization of the slurry is poor in fluidity due to its viscosity. In the design of the solution, it is considered to minimize the length of the conveying pipe and reduce the number of elbows to reduce the flow resistance; raise the position of the storage bin to raise the height of the storage bin. There is a reasonable height difference with the nozzle, which can generate self-flow; for the nozzle, after investigation and comparison, the high-speed centrifugal atomizer is a good choice. The technical parameters are: spray disc diameter 120mm; rotation speed 18000r/min; maximum evaporation of water 50kg /h.
The production practice of many production enterprises shows that the nozzle has excellent atomization effect on viscous materials, and due to its high-speed rotation, negative pressure is generated, which makes the pipes and nozzles difficult to block.
Third, for the control of the combustion reaction process, after detailed calculation, the heat generated by the combustion of the resin in the slurry basically offsets the heat absorbed by the vaporization of the water vaporization, so it is necessary to ensure that the slurry burns at 600~800 °C, as long as it is burning The room is well insulated to minimize heat loss and to ensure the supply of heat. In addition, on the basis of theoretical calculation of the required gas volume, the supply of gas volume is appropriately increased, and the gas flow rate is strictly controlled to ensure sufficient combustion, no residual fat, and sufficient reaction time.
Fourth, in order to effectively reduce costs, the pre-burning process has been compared and selected, and each device has been carefully designed to meet the requirements of different temperature ranges in the entire process. Under the use of different steel materials and processing requirements. Practice has proved that this is an effective method of investment control.
3, test effect test and test results show that the program fully meets the requirements of pre-burning process, the process is simple, compact, the production process can be automatically controlled, simple operation, low labor intensity, continuous production, complete combustion, no Residual fat, uniform material mixing, no segregation, no magnetic, no pollution, and because the product is fine powder, thus eliminating the next process in the original process - the crushing and grinding process, also avoiding the material in It is polluted during the crushing and grinding process to ensure the purity of the material, thus effectively ensuring the high performance requirements of the ferrite material.

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