• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The invention relates to the production of refractory materials, in particular tungsten carbide. The purpose of the invention is to improve the quality of the material and ensure the continuity of the process. For this, the mixture of powdered material and binder dissolved in water is compacted by extrusion to form a solid rod 11. Insert the rod 11 into the cold crucible 1 and melt it by magnetic induction. The molten material flows through the bottom hole 7 of the crucible. 2 sec. f-ly, 4 zp f-ly, 1 ill. 77 G Y VI S Yu
    公开号:SU1722221A3
    申请号:SU874202128
    申请日:1987-03-12
    公开日:1992-03-23
    发明作者:Брюне Пьер；Эсно Фортуна；Мэйбон Ги；Перрье Де Ля Бати Рене
    申请人:Текножениа С.А. (Фирма)；
    IPC主号:
    专利说明:

    This invention relates to refractory materials that could not be melted without affecting or melting the container containing them. These are metals such as tungsten (TPl 3400 ° C), molybdenum (mp 2600 ° C), or refractory oxides and products of synthesis (silicides, carbides),
    Solid synthesized refractory materials (in a non-powder state) are obtained by sintering or melting in a consumable crucible. Sintering consists in pressing the powder, heating the pressed parts to create sintered bonds between the particles of the material. In the case of metals, they can then be forged, rolled hot, until solid parts having a theoretical metal density are obtained. This technology is used to produce parts made of tungsten or molybdenum,
    Sintering in the liquid phase is used for the production of cermet, this technology is used for the manufacture of tungsten carbide parts. Powdered refractory, carbides (CW, TIC, TAC) are mixed with cobalt powder. The mixtures are depressed. They are heated to the melting point of cobalt. After cooling, the carbides are bound by a viscous and strong cobalt film.
    The production of molten tungsten carbide in a hot crucible is carried out as follows: inject a powdered mixture of carbon and tungsten into a graphite crucible. The walls of this crucible are heated by induction, exposing it to a high-frequency magnetic field, or by another method of heating. Thus, the crucible itself is at a high temperature, and its walls increase the temperature of the powder mixture by heat conduction. The mixture of powders is reached by conduction melting point. This temperature is close to 2750 ° C, which requires a good external insulation of the crucible, the walls of which must have an even higher temperature.
    This method has several disadvantages:
    the amount of carbon in the resulting alloy is poorly controlled, as part of the graphite crucible goes into the alloy, and because of this, the crucible gradually wears out; it is difficult to foresee continuous production due to the type of heating and due to the heating of the crucible itself.
    Melting a material such as tungsten carbide in a hot crucible requires a very rapid discharge of the material from the crucible after melting in order to obtain a satisfactory structure. It is incompatible
    with a continuous process, as the exposure of the liquid mass of tungsten carbide melted in a graphite crucible for a sufficient time leads to a gradual increase in the carbon content of tungsten carbide and an increase in the melting point.
    Known heating technology by induction in a cold crucible, in which a solid component is heated directly, exposing it to an alternating magnetic field. By cold crucible is meant a crucible in which the walls are made to transmit and concentrate a magnetic field without their significant heating by induced currents,
    However, it is difficult to heat and melt directly the powdered refractory mixtures in a similar cold crucible. For a granulometry of several tenths of a millimeter, for example, for a tungsten powder, it is necessary to use a magnetic field frequency of more than 1 MHz, which is difficult to obtain in industry.
    The aim of the invention is to improve the quality of the material and ensure the continuity of the process.
    This melting is carried out in a cold crucible in such a way that the crucible material, being at a relatively low temperature, is not miscible, even in small proportion, with the materials forming the meltable mixture. Thus, the composition and proportions of the resulting alloy are fully controlled. A continuous melting process is carried out and individual round shaped articles are obtained.
    The method includes a stage during which the refractory material in a compacted form is introduced into a cold crucible, which has an appropriate self-supporting form and adhesion sufficient for loading and unloading, as well as an appropriate electrical resistance, and is heated by induction directly to a temperature higher than its temperature. melting. By compaction is meant the agglomeration of material grains by extrusion, which makes it possible to obtain a self-supporting form and sufficient electrical conductivity, precisely by bringing the grains closer together.
    Powder material refers to a refractory metal powder to produce a pure metal element or a mixture of powders of various refractory materials to effect the synthesis of an alloy or composition. The term self-supporting means that an element of compacted material does not tend to scatter when it is
    carrying, for example, you can lift an element in the form of a piece or bar at one end and transport it without causing it to collapse.
    The method can be made continuous by using a specially shaped cold crucible containing a bottom with a hole through which a constant molten metal leak is possible. The melting material is introduced through the upper crucible orifice, which is gradually heated by induction as it moves from top to bottom. The continuous nature of the process greatly facilitates and accelerates melting due to the fact that part of the molten material is in contact with the not yet molten part, while the molten material is more susceptible to magnetic energy and tends to accelerate by induction the heating of the adjacent, not yet molten part of the material.
    The continuous nature of the process allows the flow of molten material to be separated from the crucible and affect the shape of the particles obtained. Depending on the physical characteristics of the materials to be melted, sealing should be provided by various methods.
    In the case of materials that easily form agglomerates by pressing, for example, for a powder of pure and very fine tungsten, the material is compacted by compressing in a cold state under a pressure of 100-150 bar to give it the desired dense and self-supporting shape. However, this method of compaction by simple cold compression is not suitable for a mixture of carbon and tungsten. Then, a subsequent sintering operation can be applied by placing the compacted mixture at a higher temperature, slightly lower than the melting point of the mixture, for example, 800-1000 ° C.
    When compaction of the material only by compression is insufficient, compaction is carried out by applying pressure to the mixture of melted materials with the binder, and the binder is usually dissolved in a solvent. After compaction with a solvent, this solvent is partially removed by drying.
    Compaction is carried out by forming under pressure a mixture of material with a binder dissolved in a solvent, and also by extrusion with a core thread or without it a mixture of material with a binder dissolved in a solvent. The core yarn material is selected such that
    to eliminate incompatibility with the extrudable mixture.
    The proposed apparatus is applicable to the production of molten tungsten carbide from carbon and tungsten powders. The powdered state of carbon and tungsten favors a homogeneous mixture and gives a very high reactivity. Both powders are mixed with an organic binder and a solvent, such as water. The amount of binder should be sufficient to extrude the mixture (0.5-2.5 wt.% Of the mixture). The amount of water is also regulated depending on the properties required for extrusion, and is three to four times the weight of the binder.
    The nature of the binder directly affects the electrical conductivity of the compacted product. The binder also affects the process of bringing the grains together and making the mixture. Binders used for agglomeration before sintering are not suitable for melting by induction. Advantageously, a binder capable of decomposing at a high temperature, for example by pyrolysis, is used.
    Good results have been obtained with polysaccharides as binders, such as galactomannose, hydroxymethylcellulose, carboxymethylcellulose, such as carbohexamethylcellulose, or alginate. Extrusion is carried out, for example, under a pressure of 200 bar with a known extruder, and at the exit from the extruder the product has the form of dense and self-supporting rods. After several hours of drying, most of the water is removed, the rods become stiff and can be transported.
    The rods are then preheated to remove residual water and most of the organic binder. The treatment is carried out at a temperature close to 800 ° C. To avoid the oxidation of the carbon / tungsten mixture, this treatment is carried out in a sealed inert gas circulating furnace. The carbon resulting from the decomposition of the binder is in a very small part of the mixture and is practically negligible. After this heat treatment, the electrical conductivity of the mixture increases substantially, and the rod can be directly heated by electromagnetic induction.
    The drawing shows a cold crucible.
    The crucible 1 contains a copper cylinder 2 with a vertical axis, divided into sections by radial planes and surrounded by an electrical conductor 3 in the form of a coaxial coil connected to a high-frequency current generator (not shown). The sectors of the copper cylinder are cooled by circulating a fluid, such as water, in the conduits 4. A crucible having a dozen sectors can be used. The crucible is open on top and has a large central top window 5 for introducing molten material. The bottom 6 of the crucible is rounded. The bottom 6 of the crucible contains the lower central opening 7, which communicates the inner space of the crucible with the external one and ensures the outflow of the molten material.
    At the exit under the crucible there is a massive copper cylinder 9, which is driven into rotation around the horizontal axis by driving means and along the periphery of which the molten material flows. The cylinder 9 divides the flow in order to obtain individual pieces of material with the desired dimensions and shape. Pieces 10 or rods 11 of molten compacted material are used, the cross section of which is larger than the cross section of the lower hole 7 and smaller than the cross section of the upper window 5. The rotation speed of the cylinder is 3000 rpm. The device allows the separation of molten tungsten carbide without damaging the cylinder, although the temperature of the molten tungsten carbide will be much higher than the melting point of copper.
    In operation, the rod 11 of molten compacted material is introduced into the crucible through the upper window 5 and freely placed on the bottom 6 of the crucible. By feeding the conductor 3 with electric energy, the rod is gradually heated, and its lower part melts and flows out through the opening 7. Advantageously, rods whose length is greater than the depth of the crucible can be used in order not to load the rods too often, and also several rods can be gathered one after the other. to ensure a continuous process or compacted pieces, simply poured into a crucible,
    PRI me R 1. You can get a continuous smelting of a mixture of tungsten carbide type WC-W2C, that is, containing about 4 wt.% Carbon. After extrusion, about 800 ° C is preheated. The crucible used for melting contains a bottom 6 and an outlet 7 about 10 millimeters in diameter. The frequency needed to achieve
    melting under good conditions is about 250-400 KHz. Material consumption is close to four hundred grams per minute for a power of 600 kW.
    Example 2. You can use the method
    to melt pure tungsten. Mix tungsten powder with 2% organic binder, add 6% water. By extrusion at 200 bar, a tungsten rod with a diameter of 20 mm is obtained. The rods are preheated for several minutes at 1000 ° C in a furnace in an argon atmosphere to completely eliminate the binder. The rods are then brought to Tm in cold
    crucible. The frequency used can be lower, for example, good results can be obtained with a frequency of 30 KHz.
    In all examples, a seal should be provided that is sufficient to
    so that the core or pieces of material introduced into the crucible have a corresponding electrical resistivity. In fact, the resistivity should be such that electrical currents,
    induced by a magnetic field in a rod or piece, were sufficiently intense to ensure heating and melting of the rod or piece. Thus, the resistivity of the compacted material should
    be below a given maximum value of P. This given maximum value of P depends on a number of parameters. It can be calculated from Maxwell's equations, which lead to a formula that gives the crust thickness depending on the resistivity of the material and the frequency of the magnetic field. When maximum resistivity P is reached, the thickness of the crust in the material is equal to half the radius R d
    rod in the form of a cylinder of rotation,
    The formula allowing to calculate the given maximum value of P, in this case, will be:
    where R is the maximum resistivity in ohm; 500 magnetic permeability,
    F is the frequency in Hz applied for heating by induction;
    权利要求:
    Claims (6)
    [1]
    1. A method of producing a powder of a refractory material, comprising introducing the starting material into a crucible, heating it by induction of an alternating magnetic field above the melting point,
    melt flow through the crucible bottom hole and dividing it into droplets, characterized in that, in order to improve the quality of the material and ensure the continuity of the process, the starting material is introduced into the crucible in the form of a compacted powder, while the powder is compacted to obtain an electrical resistivity the piece is below the specified maximum resistivity, provided that the maximum resistivity of the compacted powder corresponds to the thickness of the crust in the material, equal to half the average radius of the pieces nennogo powder and heating are invariant under the action of induction directly on the compacted powder, the separation of the melt into droplets is performed by dropping it onto a rotating copper cylinder.
    [2]
    2. A method according to claim 1, characterized in that the raw material in powder form is compacted by extrusion before it is introduced into the crucible.
    [3]
    3. The method according to PP, 1 and 2, that is, that the pressed powder is sintered.
    [4]
    4. The method according to PP, 1, 3 and 4, of which is impregnated with the fact that the compacted powder is introduced into the crucible in the form of pieces or rods with a cross section larger than the bottom opening of the crucible.
    [5]
    5. Method according to claims 1, 3 and 4, characterized in that the pieces or rods of compacted material are freely placed on the bottom of the crucible.
    [6]
    6. A device for producing a powder of a refractory material containing a crucible with a bottom hole and a melt separation unit into droplets, characterized in that, in order to improve the quality of the material and ensure the continuity of the process, the crucible is made in the form of a copper cylinder divided into sectors along radial planes, refrigerant pipelines and an upper window for introducing the source material, and the melt separation unit into droplets is made in the form of a massive copper cylinder with a rotating drive, and is installed under the crucible perpendicular cool angles to the axis of the crucible.
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    同族专利:
    公开号 | 公开日
    FR2595716A1|1987-09-18|
    HUT43169A|1987-09-28|
    EP0238425A1|1987-09-23|
    AT66171T|1991-08-15|
    HU202641B|1991-03-28|
    EP0238425B1|1991-08-14|
    FR2595716B1|1992-07-10|
    GR3002836T3|1993-01-25|
    US4723996A|1988-02-09|
    ES2025196B3|1992-03-16|
    JPS62213682A|1987-09-19|
    DE3772075D1|1991-09-19|
    JP2682823B2|1997-11-26|
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    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    FR8604119A|FR2595716B1|1986-03-13|1986-03-13|PROCESS AND DEVICE FOR THE ELABORATION OF REFRACTORY MATERIALS BY INDUCTION|
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