Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
  • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
  • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0235—Starting from compounds, e.g. oxides

Definitions

• the present invention relates to a method of making ferrous powder of variable bulk density.
• Iron powder is used as raw material for making various components, for example, by compressing such powder in a mold.
• the powder used for that purpose is usually unalloyed, i.e., more or less'pure iron, and such powder is made in accordance with a variety of processes.
• methods of directly reducing iron ore or scale resulting from rolling powder of spongy iron.
• liquidous iron is atomized by air jets or by water jets.
• Direct reduction and atomization processes are combined in a method wherein iron powder, as produced by atomization, and having a relatively high content of carbon, is mixed with oxygen carriers (iron and/or rolling scale) and annealed i.e. malleableized.
• Iron powder as made in accordance with the several known processes differ very little in chemical composition as well as in the size distribution of the particles.
• the geometry of the particles varies significantly with the method of producing them. Consequently, the bulk densities of the different powders differ due to these differences in particle configuration.
• the resulting bulk density is, therefore, to some extent characteristic of the method by which the particular powder was made.
• particles made by directly reducing iron ore or made by air jet atomization have hollow spherical configuration i.e. they are spongy, and in bulk they establish a ,light powder.
• Powder made by waterjet atomization consists of parti cles which are compact with an irregular, spattered surface. Such a powder is relatively heavy. Powder made by the combination process is of medium weight accordingly.
• light powders have bulk density of 2.5 to 2.6 grams per cubic centimeter.
• the heavy powders have bulk density of 3.1 to 3.3 grams per cubic centimeter and the combination method produces powder in the range of 2.7 to 2.9 grams per cubic centi meter.
• Powder press tools and machines are usually constructed so that parts of different weights and different dimensions can be pressed with the same machine.
• the volume of filling the die cavity depends on the cavity dimensions in the die plate proper.
• the position of the lower punch determines the volume of the cavity, and the bulk density of the powder is an additional parameter. Volume metering of the powder is critical for obtaining the predetermined weight or density of the product as resulting from compressing. It is necessary, therefore, to maintain the bulk density of the powder within very close tolerances.
• the construction of the pressing tool generally depends to a considerable extent on the range of the bulk density of the available powder.
• An exchange of powder grades with different apparent densities is hardly possible, at least not for many uses. If the die is operated in fixed steps, such as for pressing sleeves or collars, it is actually impossible tovary the density of the powder used.
• a conventional atomizer for practicing the invention, basically a conventional atomizer can be used, wherein a stream of molten iron or steel pours from a bottom opening of a ladle and passes a nozzle or nozzles directing pressurized jets of water against the down pouring metal stream.
• the metal stream as such disintegrates and multiple droplets coagulate, falling to the bottom while solidifying, at least at their surface before piling on the bottom.
• the atomizing water is provided under pressure to a chamber with a nozzle or nozzles from which the water jets are ejected.
• a raw powder is produced with differently strong an-oxidation at the surface of the individual particles.
• the subsequent reduction converts, so to speak, this oxidation into a spongy coating on and as part of the surface of the particles. That coating is the thicker, the thicker an an-oxidation layer has formed on the particles prior to reduction, and that thickness, in turn, is the greater the more oxygen was added and/or developed.
• the apparent density and bulk density of the final powder decreases with increasing dimension of that spongy coating so that accordingly the bulk density increases with decreasing anoxidation.
• the amount of oxygen added under controlled conditions to the water jet atomizing process controls the resulting bulk density, and variations here permit production of iron powder with bulk density as low as 2.5 g/cm or even lower or as high as 3.2 g/cm".
• the oxygen added under controlled conditions has a higher pressure than the partial pressure of oxygen in water as occurring normally.
• the added oxygen may have a pressure of 2 to 6 atmospheres.
• the atomizer employed may be an annular nozzle such as shown, e.g. in U.S. Pat. No. 2,892,215, or patent applications of common assignee Ser. No. 251,839, filed May 9, 1972 or Ser. No. 227,044, filed Feb. 17, 1972.
• Molten steel pours through a central opening of such a nozzle chamber which directs jets of pressurized water against the stream from all sides.
• the molten steel was composed of iron with 0.1% C, 0.10% Si and 0.20% Mn. Assuming first a conventional process, just water was applied under pressure of about 50 atmospheres, for atomizing the steel and forming particles of not more than 0.4 mm diameter.
• the process was supplemented by supplying oxygen to the nozzle chamber.
• the water was supplied under pressure of 50 atmosphere.
• the additional oxygen was applied at a pressure of a few atmospheres.
• air was sucked into the nozzle so that a water and oxygen-enriched-air-mixture provided the atomization.
• the basic atomizing agent was, of course, water, but the added oxygen controlled the resulting powder density.
• the addition of oxygen can be controlled either through pressure control or by adjusting the effective cross section of the flow path for the oxygen.
• bulk density can be controlled by adding hydrogen peroxide to the atomizing water.
• hydrogen peroxide 0.1 to 20% to cover more than the stated range.
• 0.2% to 4% peroxide is added to the atomizing water for purposes of density control.
• the oxygen is developed at the area of steel-atomizing agent interaction.
• a method for atomizing molten iron or steel by means of pressurized water atomizing a pouring stream of the liquidous iron or steel to obtain a ferrous powder which is subsequently annealed for reducing the oxygen and carbon content and which is to be used for press-forming of parts by pressing such powder into a mold
• the improvement comprising, adding pure oxygen or oxygen enriched air at an oxygen pressure from 2 to 6 atmospheres to the water to enrich the relative oxygen content in the water, so that the partial pressure of the oxygen is larger than normal; and using the oxygen-enriched water for the atomization so as to increase the oxidation layer on the powder particles as produced by the atomization beyond the layer thickness as resulting from mere use of water as atomizing agent, so that the surface of the individual powder particles are spongy as resulting from removal of the oxygen during subsequent annealing to obtain a reduction in the bulk density of the powder.
• a method for atomizing molten iron or steel by means of pressurized water atomizing a pouring stream of the liquidous iron or steel to obtain a ferrous powder which is subsequently annealed for reducing the oxygen and carbon content and which is to be used for press-forming of parts by pressing such powder into a mold
• the improvement comprising, adding about 0.1 to 20 hydrogen peroxide to the water to enrich the relative oxygen content inthe water, the content being the higher, the lower a bulk density of the powder to be made is desired; and using the oxygen-enriched water for the atomization so as to increase the oxidation layer on the powder particles as produced by the atomization beyond the layer thickness as resulting from mere use of water as atomizing agent, so that the surface of the individual powder particles are spongy as resulting from removal of the oxygen during subsequent annealing to obtain a reduction in the bulk density of the powder.
• the amount of hydrogen peroxide added is about 0.2 to 4 5.
• the improvement comprising, using water for atomization which is enriched with gasesous oxygen at a partial pressure in excess of the partial pressure of oxygen in regular water, so as to increase the oxidation layer on the powder particles as produced by the atomization beyond the layer thickness as resulting from mere use of water as atomizing agent, so that the surface of the individual powder particles are spongy as resulting from removal of the oxygen during subsequent annealing to obtain a reduction in the bulk density of the powder.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)
• Powder Metallurgy (AREA)

Applications Claiming Priority (1)

Publications (1)

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ID=5849647

Family Applications (1)

Country Status (7)

Cited By (7)

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Citations (5)

• 1972
  • 1972-06-29 DE DE2232760A patent/DE2232760C2/de not_active Expired
• 1973
  • 1973-05-17 GB GB2366173A patent/GB1425195A/en not_active Expired
  • 1973-05-18 FR FR7318143A patent/FR2190554B1/fr not_active Expired
  • 1973-05-29 SE SE7307631*A patent/SE380458B/sv unknown
  • 1973-05-30 JP JP6074273A patent/JPS572761B2/ja not_active Expired
  • 1973-06-27 US US374100A patent/US3909239A/en not_active Expired - Lifetime
  • 1973-06-29 CA CA172,729A patent/CA991890A/en not_active Expired

Patent Citations (5)

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