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Sintered NdFeB Vacuum Heat Treatment Process
1.Ingredients: According to various product requirements, different formulas are used to accurately measure various materials, among which pure iron needs to remove the oxide layer.
2.Smelting: According to different requirements, there are ordinary smelting furnaces and fast-setting belt smelting furnaces. Melting furnace: In the high vacuum furnace, the medium frequency 2500Hz power supply is used, and the material is heated to about 1650°C by electromagnetic induction, so that the material is completely melted and fully mixed. Rapid casting to shape in corresponding ingot molds with rapid water cooling. After a certain period of time, it will be completely cooled to 50°C, and then it will be released from the furnace; the rapid-setting belt smelting furnace: its working principle is the same as that of the ordinary smelting furnace. The difference lies in the different casting and forming methods. It is poured slowly on the high-speed rotating water-cooled copper roller, and under the action of centrifugal force, a thin sheet of 0.3-0.5 is formed. When the material is cooled to 50°C, it is released. There should be no oxidation on the surface of the baked product, and it will enter the next process after passing the quality control inspection.
3.Crushing: It is divided into mechanical crushing and hydrogen furnace crushing. First use the jaw crusher to break the large steel ingots into small pieces, and then use the medium crusher to pulverize into 0.5mm3 powder under nitrogen protection. The powder is shipped in vacuumed and nitrogen-filled protective barrels for the next step of milling. If it is, the strips can be directly entered into the secondary crusher. The hydrogen broken product can directly enter the next step of milling process.
4.Pulverizing: use the jet mill to pack the powder (0.5mm3) into the middle crusher, and use nitrogen as the medium. According to the principle of particle breaking and collision, the larger particles are crushed by multiple gun jets. Then, a certain particle size powder of 3-6 μm is sorted by a sorting wheel at a certain speed, and then gas-solid separation is carried out through a cyclone separator, and then enters the powder container. After the mixing process of the powder mixing unit, it can enter the next process of pressing.
5.Forming: the process of putting the powder into the mold, and under the action of a certain external magnetic field, using the hydraulic machine to form the required specification and shape. Nitrogen filling protects the powder in the powder container, and in the nitrogen oxygen-exhausting space, the single-mode weighing of the powder required by the process is performed manually or automatically. Take the powder box in bag or under nitrogen protection, put it into the cavity of the molding die, under the action of a strong magnetic field, carry out orientation, pressing, and then demagnetize the corresponding reverse magnetic field, take out the material block, and quickly carry out vacuum packaging. Vacuum packaging generally has 2 layers, the first layer is hand-packed with polyethylene film of about 0.03mm to protect the corners of the material block. Packed into a relatively thick second layer of polyethylene film bags of about 0.08mm. Put it into the vacuum packaging machine, and carry out the process of pumping, exhausting, heat sealing and reclaiming. The block pressed by the above process has a relatively small density and uneven density distribution. In order to increase the density of the block and improve the uniformity of the density distribution, an isostatic press needs to be used for secondary pressing. Put the well-packaged material block into the isostatic press cavity to seal, use hydraulic oil or water as the medium, pressurize to about 20MP, keep it for a certain time (3-8 seconds), release the pressure and take out the material, and place it on the oil filter table superior. Put the intact material block into the sintering material box, put it into the turnover container with the function of air extraction and nitrogen filling, prepare for the furnace, and enter the next process.
6.Vacuum sintering (tempering): In a high vacuum space, high temperature acts on the product, so that the solid particles inside the product are bonded to each other, and the crystal voids (pores) and grain boundaries are gradually reduced. Volume shrinks, density increases, and finally becomes a dense polycrystalline sintered body with a certain microstructure. Place the material box containing the material blocks on the movable furnace frame of the vacuum sintering furnace, arrange them neatly, put a cover on it, push it into the melting chamber, close the furnace door, and gradually start the vacuum unit until the vacuum rises to a certain value (5*10 -2Pa), start the heating sintering program, and complete the entire vacuum sintering process. After completion, fill with argon gas, start the fan, quickly cool to 70°C, and then start the heating and tempering procedure when the vacuum is 5*10-2Pa. After completion, it was filled with argon and rapidly cooled to 70°C for the second aging step. After the whole process is completed, when it is cooled to 50°C, the gas is released, the door is opened, and the furnace is released, and samples are taken by the testing personnel. After passing the test, it can be put into the warehouse for use. So far the whole blank production process is completed. The tempering procedure is the process of stabilizing and increasing the intrinsic coercivity.
Selection of vacuum sintering equipment: The RVS series vacuum sintering furnace produced by SIMUWU is a high-quality product for vacuum heat treatment of tooling and molds. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum sintering process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.
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