Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2/00—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic
  • B01J2/28—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic using special binding agents
• • 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
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/14—Treatment of metallic powder
  • B22F1/148—Agglomerating
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/10—Alloys containing non-metals

Definitions

• the present invention solves a problem which has existed in the art for seventy years.
• Metal powders produced by the thermal decomposition of metal carbonyls have been available since the days of Ludwig Mond. Such metal powders are valuable metallurgical raw materials because of their high purity.
• the powders have good pressability, provide compacts having high green strength and green compacts made thereof can be sintered to high density at relatively low temperatures as compared to coarser nickel powders produced by other methods.
• the physical nature of these powders is such that they do not flow readily. This lack of flowability prevents utilization of carbonyl metal powders in conventional pressing equipment employed in the powder metallurgy art, despite the other marked advantages of these powders.
• the as-produced powders not only fail to fill dies in automatic pressing equipment, but, also, because of their fineness, quickly cause scoring and seizing of the punch within the die.
• Carbonyl iron and nickel powders have average particle sizes of less than 10 microns and, more usually, less than microns. Carbonyl iron powders generally tend to be spherical in shape and their poor fiowability thus is principally due to the fine particle size thereof. Carbonyl nickel powders tend to be irregular in shape, with spiky projections extending from more or less spherical bodies and, in some grades, with an overall fibrous appearance. These physical attributes further contribute to poor flowability to the extent that a pile of the powder can be parted with a knife and the parted face removed leaving a substantially vertical face.
• Flowable fine metal powders are usually produced industrially by three general techniques: (1) the metal or 3,397,057 Patented Aug. 13, 1968 alloy is produced as a relatively brittle ingot which is then crushed and pulverized; (2) the metal or alloy in nonflowing fine powder form is sintered to a cake which is then crushed; (3) molten metal or alloy is atomized by spraying a liquid stream thereof into a fluid medium. All of these techniques are characterized by commercial objections, including loss of material as unusable fines which must be reprocessed at extra cost, introduction of undesired impurities, including oxides, other compounds, tramp elements, etc., and by the fact that the product does not always have satisfactory flowability. Accordingly, despite many attempts in the art, no commercial method is presently available for increasing the flowability of essentially nonfiowable pure metal powders while still retaining the high purity, good pressability. and good sinterability thereof.
• the present invention is directed to a process for improving the flowability of fine metal powders having high purity and poor flowability comprising balling the metal powder with a liquid such as water, then drying and sintering a bed formed from the resulting agglomerates in a protective atmosphere to a temperature range in which substantial sintering occurs within the agglomerates but below that at which substantial sintering occurs between agglomerates to produce substantially spherical, flowable agglomerates.
• the invention is particularly applicable to the treatment of fine metal powders of high purity having a particle size not exceeding about 10 microns and bulk densi ties of about 0.5 to about 3.5 grams per cubic centimeter (gm./cc.).
• Metal powders such as carbonyl iron, carbonyl nickel and carbonyl cobalt powders are particularly amenable to treatment in accordance with the invention to provide free-flowing particles having a particle size of at least about 20 microns to about 1,000 microns, e.g., about 20 to about microns, while still retaining the high purity and other desirable metallurgical qualities in these materials.
• the wet agglomerates which may contain, for example, about 5% to about 30% water, by weight, have low strength and it is important that they should be transferred immediately, or at least after the lapse of only a short time during which loss of water is prevented, to the sintering and drying operations with only minimal handling.
• This can be readily accomplished, for example, by loading the wet agglomerates directly from the balling operation to a continuous belt communicating with the drying and sintering furnace. Any other means whereby the wet agglomerates are formed into a substantially fixed, quiescent or static bed during drying and sintering may be employed.
• the balling operation may be conducted in a balling disc or drum, a vibrating table, vibrating screen, etc., equipped with a liquid fog or spray feed, or in a rotary twin-cone blender equipped with a rotating liquid spray bar located near the juncture of the cones or in any other convenient type of balling equipment known to those skilled in the art.
• Spray drying may also be employed for agglomerating.
• twin-cone liquid-solids blender having a rotating liquid spray bar adapted to introduce liquid in the form of a spray or fog under substantial velocity and pressure into the tumbling powder.
• Blenders of this general type are described, for example, in US. Patents Nos. 2,890,027 and 2,915,300 and patents mentioned therein.
• Bailing is conducted by tumbling the powder under conditions such that components of rolling and of compression are imparted thereto while the balling liquid is introduced into the tumbling powder. It is advantageous from the control standpoint to introduce the balling liquid in the form of fine droplets as a spray or fog into the dry powder while the powder is in motion in the balling apparatus. Difficulties are encountered in attempting to moisten the metal powder before balling and control of agglomerate size in balling is uncertain, particularly from the standpoint of size uniformity.
• the green strength of the agglomerates can be increased to permit more handling and some motion of the agglomerates during drying and sintering by incorporating a soluble or dispersible organic heat-decomposable binder in the liquid employed for wetting the powder.
• binders such as methyl cellulose, starch, gums, polyacrylamides, dextrines, etc.
• water e.g., demineralized water
• volatile organic solvents including carbon tetrachloride, trichlorethane, ethyl and methyl alcohol, etc.
• solvent-soluble binders such as parafiin, stearic acid, waxes, ethylcellulose, etc.
• demineralized water itself as the liquid medium in the balling operation.
• the water can be removed from the agglomerates during the drying and sintering operations without any detrimental impurities such as carbon, etc., being retained in the final agglomerates.
• the other desirable metallurgical characteristics of the original powder including good pressability, sinterability at low temperatures and purity are retained. It is important that the agglomerates not be disturbed during the interval after drying and before sintering since they then have low strength.
• the sintering operation is conducted in a protective atmosphere which may be, for example, hydrogen, cracked ammonia, partially-combusted natural gas, argon, etc.
• a protective atmosphere which may be, for example, hydrogen, cracked ammonia, partially-combusted natural gas, argon, etc.
• the essential requirement of the atmosphere in the heat hardening or sintering operation is that it prevents oxidation of the metal powder agglomerates being sintered.
• the sintering operation is conducted at a temperature not exceeding about two-thirds of the melting point of the metal as measured in degrees Fahrenheit.
• the initial agglomerates substantially retain their size and shape as a result of the sintering operation but that there is little adhesion between the agglomerates. Any caking or interagglomerate adhesion is readily removed by light mechanical treatment with only minimal loss of material in the form of fine dust. It is found that when sintering of nickel powder agglomerates is conducted at temperatures below about 1000 F., e.g., 800 F., an unduly high proportion of fine material is obtained whereas at a temperature of about 1500 F. only a small amount of fine material resulted.
• a sintering temperature in the range of about 1200 F. to 1300 F. provides sintered agglomerates which do not break down on handling yet have the desired pressability and sinterability for pressing and sintering, direct powder rolling and other powder metallurgical operations.
• pulverizing the sintered agglomerates for example, in a hammer mill, provides a further improvement in fiowability, i.e., reduction in flow time in a fiowmeter, an increase in apparent density and an improved capacity to be directly rolled to strip having higher apparent density.
• fiowability i.e., reduction in flow time in a fiowmeter
• an increase in apparent density and an improved capacity to be directly rolled to strip having higher apparent density As applied to fine carbonyl nickel powders, wateragglomerated balls sintered in hydrogen at temperatures of about 1400 F. to about 1730 F. are particularly suitable for pulverization to improve the flow properties thereof.
• Carbonyl nickel powder agglomerates sintered at temperatures above 1730 F. cannot readily be pulverized.
• Example I About 2,000 grams of nickel powder produced by the decomposition of nickel carbonyl and having an average particle size in the range of about 3 to 5 microns with an apparent density in the range of about 1.6 to 2.1 gm./ cc. were water agglomerated in a liquid-solids blender of the twin-cone type equipped with a high speed liquid spray feed bar. About 350 milliliters of water were employed in the operation and the powders were simultaneously tumbled and blended during the wetting to achieve agglomeration. Portions of the wetted agglomerates were placed in a metal boat and were dried and sintered at 1150 F., 1200 F. and 1250 F. in a furnace having a hydrogen atmosphere for about 5 minutes.
• Example II Two types of carbonyl iron powder having, respectively, an average particle size of about 5 microns and about 6 microns and an apparent density of about 3 gm./cc. and about 3 gm./ cc. were agglomerated with water in the manner described in conjunction with Example I and were sintered in hydrogen at a temperature of about 1250 F. for about 5 minutes.
• the fiow rate of the resulting material was about 46.9 seconds whereas the initial powder would not pass through the fiowmeter.
• the apparent density of the resulting material was about 2.12 gm./ cc.
• Example III An electrodeposited copper powder having an average particle size of about 8 microns and an apparent density of about 2.3 gm./cc. was agglomerated with water in the manner described in Example I using about 230 milliliters of Water for a charge weight of 1,370 grams of powder. Portions of the resulting agglomerated powder were sintered at 895 F. and 1300 F. for about 10 minutes. The sintered agglomerates had a flow rate of 48.9 seconds whereas the initial powder would not pass through the flowmeter.
• the invention also contemplates agglomerated metal powders, especially carbonyl nickel, cobalt and iron powders and mixtures and alloys thereof, having a particle size of at least about 20 microns and up to about 1,000 microns, having good flowability, e.g., a flow rate of about 25 to about 50 seconds in the standard Hall Flowmeter described in A.S.T.M. Standard B-213, and having an apparent density of about 1.5 to about 3 or 4 grams per cubic centimeter.
• agglomerates having an apparent density in the range of about 1.7 to about 2.7 grams per cubic centimeter are readily provided.
• a further characteristic of the agglomerates is that they are compactible and may readily be hot or cold roll-compacted directly to strip without lamination of the strip.
• the agglomerates have an irregular particle outline.
• portions of the same carbonyl nickel powder described in conjunction with Example I were sintered in hydrogen to form cakes.
• a temperature in the range of 1700 F. to 2000 F. was required to produce sintered cakes from the loosely packed powder.
• the cakes were quite tough and ductile.
• the cakes were mechanically crushed it was found that the resulting crushed powder aggregates were irregularly shaped and they exhibited poor flow characteristics.
• carbonyl nickel powder of the same type as that described in conjunction with Example I is sintered in hydrogen without agglomeration at a temperature of about 1200 F. and the resulting sintered material is crushed, the powder obtained has a size distribution similar to that of the initial powder and is not improved in flow rate.
• material processed with agglomeration in accordance with the invention and sintered at 1200 F. is a free-flowing agglomerated powder.
• the foregoing confirms that the invention alfords a method for producing free-flowing metal powder starting with materials such as fine carbony l nickel powder having a poor flow characteristic wherein only a low energy input is required. This feature provides economy in carrying out the process of the invention.
• powders of a single metal be agglomerated in accordance with the invention to provide free-flowing powder agglomerates but that also carbonyl codeposited iron-nickel powders, alloyed powders, coated powders and mixtures of initial single metal powders can be treated so as to produce powder agglomerates containing controlled proportions of the initial metals.
• agglomerates containing nickel and iron; nickel and cobalt; nickel, iron and cobalt; nickel and copper, etc. can readily be produced in accordance with the invention and these materials can be employed directly to produce alloy articles by pressing and sintering in accordance with conventional powder metallurgy techniques.
• the process provided in accordance with the invention can be employed to provide coated powders.
• nickel coatings can be produced upon other powders such as chromium, graphite and copper by agglomerating and sintering in accordance with the invention.
• the particles to be coated may be of major particle sizes, e.g., about 15 to about microns, and these can be coated with fine particle size powders by wet agglomeration and sintering as described hereinbefore.
• the invention is also applicable to the production of free-flowing material for use in dispersionhardening systems.
• the 'agglomerating liquid may contain therein a salt which is heat-decomposable to a stable oxide such as thoria, alumina, etc., to provide thorough wetting of the initial powder with a salt such as, for example, thorium nitrate.
• a salt such as, for example, thorium nitrate.
• the salt decomposes to provide finely dispersed material intimately mixed throughout the hardened agglomerates. Oxides, carbides, nitrides, silicides and other dispersants can be introduced into nickel and other metal powders in this manner by wet agglomeration with a solution of an appropriate decomposable salt.
• the process for producing free-flowing metal powder agglomerates from a fine metal powder having an average particle size not exceeding about 10 microns and having poor flow properties which comprises tumbling said powder while spraying a balling liquid thereon to form separate ball agglomerates to said powder containing up to about 30% by weight of said liquid, quiescently drying said agglomerates to remove said liquid and thereafter sintering the resultant agglomerates in a protective atmosphere at a temperature at which sintering occurs within said agglomerates but below that at which substantial sintering occurs between agglomerates to produce freeflowing metal powder agglomerates having an average particle size of about 20 to 1,000 microns.
• the metal powder is a fine metal powder from the group consisting of nickel, cobalt, iron, copper, tungsten and molybdenum, and alloys and mixtures thereof.
• the metal pow-der is a codeposited nickel-iron carbonyl powder
• the sintering temperature is of the order of 1700 F.
• the sintered agglomerates are pulverized to improve the flow rate thereof.
• the sintered agglomerates are pulverized to improve the flow rate thereof.
• the process for producing free-flowing metal powder agglomerates from a fine metal pow-der from the group consisting of nickel, cobalt, iron, copper, tungsten and molybdenum and alloys or mixtures thereof having an average particle size not exceeding about 10 microns and having poor flow properties which comprises tumbling said powder while spraying a balling liquid consisting essentially of water thereon to form separate ball agglomerates of said powder containing about 5% to about 30% by weight of water, quiescently drying said agglomerates and thereafter sintering the resultant agglomerates in contact with each other in a protective atmosphere at a temperature not exceeding about two-thirds of the melting point of said metal in degrees Fahrenheit to produce free flowing metal powder agglomerates having an average particle size of about 20 to about 1,000 microns.
• the metal powder is carbonyl nickel powder
• the balling liquid is demineralized water
• the sintering temperature is about 1000 F. to about 1730 F.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Powder Metallurgy (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Closing And Opening Devices For Wings, And Checks For Wings (AREA)
• Glanulating (AREA)

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Cited By (15)

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Citations (8)

• 1966
  • 1966-09-26 US US581768A patent/US3397057A/en not_active Expired - Lifetime
• 1967
  • 1967-09-15 GB GB42112/67A patent/GB1158620A/en not_active Expired
  • 1967-09-18 NO NO169772A patent/NO119756B/no unknown
  • 1967-09-22 GR GR670134468A patent/GR34468B/el unknown
  • 1967-09-22 FI FI672536A patent/FI46596C/fi active
  • 1967-09-23 DE DE1583742A patent/DE1583742C3/de not_active Expired
  • 1967-09-25 NL NL6713041A patent/NL6713041A/xx unknown
  • 1967-09-25 ES ES345430A patent/ES345430A1/es not_active Expired
  • 1967-09-25 AT AT867767A patent/AT285964B/de active
  • 1967-09-26 CH CH1342767A patent/CH475053A/fr not_active IP Right Cessation
  • 1967-09-26 DO DO1967001388A patent/DOP1967001388A/es unknown
  • 1967-09-26 BE BE704310D patent/BE704310A/xx unknown
  • 1967-09-26 SE SE13195/67A patent/SE323178B/xx unknown

Patent Citations (8)

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