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The Non-ferrous Metal Powder Refers To A Group Of Metal Particles Having A Size Of Less Than 1 Mm

 The non-ferrous metal powder refers to a group of metal particles having a size of less than 1 mm. Including a single non-ferrous metal powder, alloy powder and metal properties of some refractory compound powder, powder metallurgy is the main raw material

  Historical traceability

  Non-ferrous Metal Powder The preparation and application of non - ferrous metal powder. Ancient gold, silver, copper, bronze and some of its oxide powder as paint, for pottery, jewelry and other equipment, coloring, decoration. At the beginning of the 20th century, the United States Ku Liji (W.D.Coolidge) with hydrogen reduction tungsten oxide production of tungsten powder to produce tungsten wire, is the beginning of modern non-ferrous metal powder production. Since then, the chemical reduction of copper, cobalt, nickel, iron, tungsten carbide and other kinds of powder, and promote the early powder metallurgy products (oil porous bearings, porous filters, carbide, etc.) development; Carbonyl method to produce iron powder and nickel powder. 30 years first with eddy current grinding method of iron powder, and later with solid carbon reduction method to produce iron powder, the cost is very low. In the early 1930s, molten metal atomization was also present. This method was originally used to produce low melting point metals such as tin, lead, aluminum and other powder, to the early 40s developed into high-pressure air atomization iron powder. 50 years began to use high-pressure water atomization alloy steel and a variety of alloy powder. 60 years to develop a variety of atomization methods to produce high-alloy powder, and promote the development of high-performance powder metallurgy products. Since the 1970s there have been a variety of gas and liquid physical and chemical reaction methods, the preparation of important use of coated powder and ultrafine powder.

  Powder performance

  Non-ferrous metal powder is a loose material, its performance reflects the nature of the metal itself and the individual particles of the traits and particle group characteristics. Generally the performance of non-ferrous metal powder is divided into chemical properties, physical properties and process performance. Chemical properties refer to metal content and impurity content. Physical properties include the average particle size and particle size distribution of the powder, the specific surface and true density of the powder, the shape of the particles, the surface morphology and the internal microstructure. Process performance is a comprehensive performance, including powder flow, bulk density, tap density, compressibility, formability and sintering size changes. In addition, for some special applications also require powder with other chemical and physical properties, such as catalytic performance, electrochemical activity, corrosion resistance, electromagnetic properties, internal friction coefficient. The performance of the non-ferrous metal powder depends to a large extent on the production method of the powder and its preparation process. The basic properties of the powder can be determined by specific standard detection methods. There are many methods for the determination of particle size and its distribution. Generally, the method of sieving (> 44μm), sedimentation analysis (0.5 ~ 100μm), gas permeation method and microscopy method are used. Ultrafine powder (<0.5μm) was measured by electron microscopy and X-ray small angle scattering. Non-ferrous metal powder is often divided into coarse powder, medium powder, fine powder, fine powder and ultra-fine powder five grades.

  Preparation method

  Non-ferrous Metal Powder Usually according to the principle of transformation is divided into mechanical and physical chemistry of two categories, both from the solid, liquid, gaseous metal directly obtained from the fine, but also from its different state of the metal compounds by reduction, pyrolysis, electrolysis and change Preparation. Carbides, nitrides, borides and silicides of refractory metals are generally prepared by direct or reduction-combined processes. Due to the different preparation methods, the same powder shape, structure and particle size and other characteristics are often very different (Figure 2). The method of preparing the powder is as follows, the most widely used is the reduction method, atomization method, electrolysis method.

  Reduction method

  The oxygen in the metal oxide powder is taken with a reducing agent, and the metal is reduced to a powder. The gas reducing agent is hydrogen, ammonia, gas, natural gas and so on. Solid reducing agents are carbon and sodium, calcium, magnesium and other metals. Hydrogen or ammonia reduction, commonly used to produce tungsten, molybdenum, iron, copper, nickel, cobalt and other non-ferrous metal powder. Carbon reduction is often used to produce iron powder. Ni, such as tantalum, niobium, titanium, zirconium, vanadium, beryllium, thorium, uranium and other non-ferrous metal powder (see metal thermal reduction) can be produced with metal strong reducing agent sodium, magnesium and calcium. Nickel, copper, cobalt and its alloys or coated powders (see Hydrometallurgical) can be prepared by reducing the metal salt aqueous solution with high pressure hydrogen. The powder particles made by the reduction method are mostly irregular shapes of the sponge structure. The particle size of the powder depends mainly on the reduction temperature, the time and the particle size of the raw material. The reduction method can produce most of the metal powder, is a widely used method.

  Atomization method

  Non-ferrous Metal Powder The molten metal is atomized into fine droplets and solidified into powder in the cooling medium (Figure 3). Figure 4 widely used two-flow (melt flow and high-speed fluid medium) atomization method is to use high-pressure air, nitrogen, argon and other gas (gas atomization) and high pressure water (water atomization) as a jet medium to crush the metal liquid flow The There are also centrifugal atomization methods using rotary disk pulverization and melt itself (consumable electrodes and crucibles), and other atomization methods such as dissolved hydrogen vacuum atomization, ultrasonic atomization, and the like. Due to the fine droplets and good heat exchange conditions, the droplet condensation rate can generally reach 100 ~ 10000K / s, several times higher than the ingot. So the composition of the alloy uniform, small organization, made of its alloy material without macro segregation, excellent performance. Aerosolized powder is generally spherical, water atomization can be made irregular shape. The properties of the powder, such as particle size, shape and crystal structure, are mainly determined by the properties of the melt (viscosity, surface tension, superheat) and the atomization process parameters (such as melt flow diameter, nozzle structure, injection medium pressure, flow rate, etc.) The Almost all of the metal that can be melted can be produced by atomization, and is particularly suitable for the production of alloy powders. This method produces high efficiency and is easy to expand the industrial scale. It is not only used for mass production of industrial iron, copper, aluminum powder and various alloy powders, but also for the production of high purity alloys (O2 <100ppm), high speed steels, stainless steels and titanium alloys. In addition, the use of chilling technology to produce fast condensing powder (condensation rate> 100,000K / s) increasingly attention. Use it to produce high-performance microcrystalline materials (see fast-frozen microcrystalline alloy).


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