Ferrite Noise-cancelling Magnetic Head Core Vacuum Sintering

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Ferrite silencing magnetic head core is one of the magnetic core materials for making AC silencing magnetic head at home and abroad. Because of its small size, hard and brittle texture, high shape accuracy, and unique electromagnetic performance requirements, there is no designated factory in China so far. The magnetic head core is prepared by machining such as cutting, slotting and grinding. Due to the poor consistency of appearance and performance indicators, low yield and high production cost, it is difficult to mass produce. The ferrite AC noise-absorbing magnetic head core made by the new process of “vacuum sintering of forming magnetic core” is more advanced and practical than the former, which is prepared by machining method. The process greatly simplifies the production process, has a high pass rate, and greatly reduces the production cost of the magnetic head. Compared with the DC noise-cancelling magnetic head, the recording and playback noise of the whole machine can be reduced from 18% to 3%, the signal-to-noise ratio of the whole channel is increased from 35dB to 64dB, and the frequency response is increased from 6300Hz to 9000Hz, which makes the factory level of the recording equipment one step higher.

The process flow is as follows: raw material selection – preparation of powder – mixing – pre-burning – crushing – forming – drying – sintering – post-processing – testing – packaging.

Material selection: According to the practical experience in the past few years, it is very important to choose raw materials with high purity and good activity. Especially for ferric oxide, in addition to the high enough purity requirements, its particle size and shape should also be considered. Therefore, selecting raw materials and adjusting the formula is a very meticulous work. In addition, the factors of doping (adding traces of mineralizers, fluxes and admixtures) are considered. In short, when determining the formula, in addition to ensuring that the magnetic core has the best physical properties, it is more important to find a formula area that is convenient for production control. Within this formula area, the single-phase solid solution area is wide, so the process operation is more flexible. , the quality of the magnetic core can be more stable, which is also one of the effective measures to ensure the consistency of product performance.

Forming: The forming of the magnetic core is a very critical process. Because the magnetic core used for assembling the magnetic head has a very high requirement on the accuracy of its external dimensions, for the formed magnetic core, the powder fineness, granulation method, forming pressure, product density, sintering shrinkage, deformation state and forming must also be comprehensively considered. It is affected by many complex factors such as equipment and mold accuracy.

When the molding pressure is 0.5t~1.5t/cm3, the molding density is 2.6~3.2g/cm3. When the compression ratio of the powder is 1:3.1, the technical problems such as green body spallation, elastic expansion and uneven density distribution can be better solved, so that the external dimensions of the product are guaranteed, and the sintering deformation is also greatly improved. .

Sintering: The choice of sintering temperature is one of the most important factors that determine the microstructure and electromagnetic properties of the magnetic core. When the final firing temperature changes, the magnetic permeability also changes accordingly. It can be seen that the final firing temperature affects the magnetic permeability. is very obvious.

Cooling: After the magnetic core is sintered in the furnace, it can generally be cooled slowly in the air, rapidly cooled, slowly cooled in an inert gas, and controlled cooling in a vacuum. We believe that cooling the material in air is not advisable, as the core is severely oxidized, resulting in a significant drop in performance, while slow cooling in a vacuum can achieve higher performance.

Equipment selection: The RVS vacuum sintering furnace provided by SIMUWU is an excellent product for processing this kind of process. It has the characteristics of good temperature uniformity and high temperature control accuracy. SIMUWU provides a professional team of engineers who can solve various problems encountered in the production process and are committed to giving customers the most convenient and efficient experience.