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US2872719A - Method of fabricating small spherical pellets - Google Patents

Method of fabricating small spherical pellets Download PDF

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Publication number
US2872719A
US2872719A US686268A US68626857A US2872719A US 2872719 A US2872719 A US 2872719A US 686268 A US686268 A US 686268A US 68626857 A US68626857 A US 68626857A US 2872719 A US2872719 A US 2872719A
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Prior art keywords
spherical pellets
pellets
small spherical
suspension
slip
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US686268A
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Brassfield Henry Clay
Jr Carl T Durham
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01JCHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2/00Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic
    • B01J2/26Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic on endless conveyor belts
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10STECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S264/00Plastic and nonmetallic article shaping or treating: processes
    • Y10S264/37Processes and molds for making capsules
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10STECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S376/00Induced nuclear reactions: processes, systems, and elements
    • Y10S376/90Particular material or material shapes for fission reactors
    • Y10S376/901Fuel
    • Y10S376/903Shapes
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10STECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S425/00Plastic article or earthenware shaping or treating: apparatus
    • Y10S425/101Aggregate and pellet

Definitions

  • This invention deals with a method and apparatus for the fabrication of small spherical shot type pellets, and in particular with a method and apparatus for the formation of spherical pellets from ceramic or refractory materials.
  • spherical pellet formation is affected by several methods, chiefly by dropping from shot towers, by the use of centrifugal force, or by molding.
  • One great disadvantage inherent in all of these above mentioned methods for spherical pellet formation is thefact that it is extremely difiicult to control the size of the pellets with any great degree of exactitude.
  • Another disadvantage is that none of these methods is particularly adapted to the production of very small spherical pellets.
  • the present invention accomplishes spherical pellet formation by a new and radically different method, which method is particularly applicable to the formation of extremely small spherical pellets.
  • An object of this invention is to provide a method and apparatus particularly adapted to effect the production of large quantities of small spherical pellets conveniently and economically.
  • a further object of this invention is to provide a meth- 0d and apparatus particularly adapted to efiect the pro- 1 duction of small spherical pellets, wherein the range of pellet sizes may be easily and automatically controlled thus insuring a consistently uniform product.
  • a container for the slip or suspension which is positioned above and connected to the capillary tube is designated by 2 and 3 designates a conveyor belt which carries the moving bed of water repellent powder 4.
  • the powder hopper 5 and stationary guides 6, provide for the deposition of this moving bed of water repellent powder on the upper surface of the belt.
  • a battery of infra red lamps 7, is positioned over the belt and a screening element, 8,'is located at the end of the conveyor belt, wherein the spherical pellets are separated from the water repellent powder.
  • a voltage supply is designated by 9 and the cable connecting the voltage supply to the slip container as 10.
  • the water repellent powder is loaded into hopper 5, from which it falls in a thin stream onto the. moving belt 3 which is positioned below the hopper..
  • This powder is shaped into a narrow strip by the stationary guides 15.
  • the narrow'bed of water repellent powder is then carried underneath the capillary tip 1, by the mo- 2,872,719 Paftented Feb. 10, 1959 tion of the conveyor belt 3, and as drops of ceramic containing slip form on the tip of the capillary tube 1, they are deposited on the surface of water repellent powder 4.
  • the water repellent properties of the powder cause these small drops to assume spherical shape, and while retaining this spherical shape, the pellets are carried under the battery of infrared drying lamps 7. Here the water is evaporated away from the pellets.
  • the slightly damp ceramic spheres are then carried to the separatory screen 8.
  • the water repellent powder rails through the screen while the pellets are retained upon it.
  • the spherical pellets are then collected and fired to produce the finished product.
  • the capillary-drop apparatus consists of a plastic container, supported above the traveling powder bed, and equipped with a small motor stirrer to maintain uniform dispersion of the suspension of water and ceramic material.
  • the aluminum paddle of the stirrer is electrically insulated from the motor shaft by a plastic coupling, and the shaft is sealed at the container lid by means of a rubber gasket.
  • the size of the drop produced is controlled in three ways.
  • the size is determined principally by the efiective diameter of the capillary tip; however, this dimension having been fixed, variation may be secured by regulation of gas pressure above the liquid and by application of an electrical charge to the slip.
  • the surface of the capillary tip upon which the drop forms should be kept as small as possible. This is accomplished by grinding the tip to a narrow lip. In addition, if the slip is permitted to wet the tip and stem of the capillary, it will creep up the outside wall of the tube and drops will form on a larger surface. Wetting may be prevented by the application of a water-repellent material. No detailed study of the relation of the capillary diameter to drop size has been made, but practice has shown that internal diameters from 0.012 to 0.018-inch yield drops within the desired size range.
  • Gas pressure is applied to the slip container primarily to control the dropping rate, but this in turn affects the drop size.
  • the gas is argon, which is first saturated with water to minimize evaporation of water in the slip and is then led through a pressure regulator to the apparatus. Pressure adjustment is manual, and the normal operating pressure of 0.5 to 2.0 p. s. i. is read on a 0-5 p. s. i. gauge.
  • Ceramic materials are suitable for treatment by this process, specifically alumina (A1 0 beryllia (BeO), uranium dioxide (U0 and molybdenum disilicide (Mosi or mixtures of these materials or other ceramic materials.
  • BeO beryllia
  • U0 uranium dioxide
  • Mosi molybdenum disilicide
  • the ceramic material actually used must be in a very finely divided state.
  • the dried MoSi pellets produced by this method will not sinter to a satisfactorily dense body on firing unless the MoSihas been ground to an'average particle size of 13.0 microns or less.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Compositions Of Oxide Ceramics (AREA)

Description

Feb. '10, 1959 H. c. BRASSFIELD EI'AL 2,872,719
METHOD OF FABRICATING SMALL SPHERICAL PELLETS Filed Sept. 25, 1957 IN VEN TOR-5. x/i/verz. IAWJJF/flfl BY mez z wax/4w J6 %M a 4M METHOD OF FABRICATING SMALL SPHERICAL PELLETS Henry Clay Brassfield, Fosters, Uhio, and Carl T. Durham, .lr., Roanoke, Va., ass'ignors to the United States of America as represented by the United States Atomic Energy Commission Application September 25, 1957, Serial No. 686,268
13 Claims. (Cl. 25-156) This invention deals with a method and apparatus for the fabrication of small spherical shot type pellets, and in particular with a method and apparatus for the formation of spherical pellets from ceramic or refractory materials.
In the prior art, spherical pellet formation is affected by several methods, chiefly by dropping from shot towers, by the use of centrifugal force, or by molding. One great disadvantage inherent in all of these above mentioned methods for spherical pellet formation is thefact that it is extremely difiicult to control the size of the pellets with any great degree of exactitude. Another disadvantage is that none of these methods is particularly adapted to the production of very small spherical pellets. The present invention accomplishes spherical pellet formation by a new and radically different method, which method is particularly applicable to the formation of extremely small spherical pellets.
An object of this invention is to provide a method and apparatus particularly adapted to effect the production of large quantities of small spherical pellets conveniently and economically.
A further object of this invention is to provide a meth- 0d and apparatus particularly adapted to efiect the pro- 1 duction of small spherical pellets, wherein the range of pellet sizes may be easily and automatically controlled thus insuring a consistently uniform product.
These objects are accomplished by preparing a suspension, or slip, of powdered ceramic material and water with a controlled pH, dropping the suspension through a small capillary into a moving bed of water-repellent pow der, drying the spherical drop on the moving bed, separating the spheres from the bed powder, and firing the spheres at 1500" C.l800 C. to form a dense body.
For a more full and complete understanding of the subject invention, reference is now made to the drawing of an apparatus designed for the practice of this invention.
In Figure l; the capillary tube, at the tip of which the drops of ceramic suspension form, is designated as 1, a container for the slip or suspension which is positioned above and connected to the capillary tube is designated by 2 and 3 designates a conveyor belt which carries the moving bed of water repellent powder 4. The powder hopper 5 and stationary guides 6, provide for the deposition of this moving bed of water repellent powder on the upper surface of the belt. A battery of infra red lamps 7, is positioned over the belt and a screening element, 8,'is located at the end of the conveyor belt, wherein the spherical pellets are separated from the water repellent powder. A voltage supply is designated by 9 and the cable connecting the voltage supply to the slip container as 10.
In operation the water repellent powder is loaded into hopper 5, from which it falls in a thin stream onto the. moving belt 3 which is positioned below the hopper.. This powder is shaped into a narrow strip by the stationary guides 15. The narrow'bed of water repellent powder is then carried underneath the capillary tip 1, by the mo- 2,872,719 Paftented Feb. 10, 1959 tion of the conveyor belt 3, and as drops of ceramic containing slip form on the tip of the capillary tube 1, they are deposited on the surface of water repellent powder 4. The water repellent properties of the powder cause these small drops to assume spherical shape, and while retaining this spherical shape, the pellets are carried under the battery of infrared drying lamps 7. Here the water is evaporated away from the pellets. The slightly damp ceramic spheres are then carried to the separatory screen 8. Here the water repellent powder rails through the screen while the pellets are retained upon it. The spherical pellets are then collected and fired to produce the finished product.
The capillary-drop apparatus consists of a plastic container, supported above the traveling powder bed, and equipped with a small motor stirrer to maintain uniform dispersion of the suspension of water and ceramic material. The aluminum paddle of the stirrer is electrically insulated from the motor shaft by a plastic coupling, and the shaft is sealed at the container lid by means of a rubber gasket.
The size of the drop produced is controlled in three ways. The size is determined principally by the efiective diameter of the capillary tip; however, this dimension having been fixed, variation may be secured by regulation of gas pressure above the liquid and by application of an electrical charge to the slip.
The surface of the capillary tip upon which the drop forms should be kept as small as possible. This is accomplished by grinding the tip to a narrow lip. In addition, if the slip is permitted to wet the tip and stem of the capillary, it will creep up the outside wall of the tube and drops will form on a larger surface. Wetting may be prevented by the application of a water-repellent material. No detailed study of the relation of the capillary diameter to drop size has been made, but practice has shown that internal diameters from 0.012 to 0.018-inch yield drops within the desired size range.
Gas pressure is applied to the slip container primarily to control the dropping rate, but this in turn affects the drop size. The gas is argon, which is first saturated with water to minimize evaporation of water in the slip and is then led through a pressure regulator to the apparatus. Pressure adjustment is manual, and the normal operating pressure of 0.5 to 2.0 p. s. i. is read on a 0-5 p. s. i. gauge.
More precise control of drop size is obtained by imposition of a high voltage between the slip and the water repellent powder bed. The voltage is applied to the slip,
which is insulated from the ground, by means of a coaxial and a reduction of the surface tension of the forming.
drops by the accumulation of positive charges on its sur face. To form the drops, potentials between 500 and 4000 volts have sufiiced. 7
Many ceramic materials are suitable for treatment by this process, specifically alumina (A1 0 beryllia (BeO), uranium dioxide (U0 and molybdenum disilicide (Mosi or mixtures of these materials or other ceramic materials. However, the ceramic material actually used must be in a very finely divided state. For example the dried MoSi pellets produced by this method will not sinter to a satisfactorily dense body on firing unless the MoSihas been ground to an'average particle size of 13.0 microns or less.
The creation of a well-formed sphere by the capillary- .drop methoddepends upon the properties of the ,slip 'or- References Cited in the file of this patent UNITED STATES PATENTS Cofiin et a1. Nov. 17, 1925 Buse Aug. 19, 1930 Hermann Nov. 21, 1939 Hood Feb. 24, 1948 Mollring July 24, 1951 Eilbracht et a1. Apr. 30, 1957 Garloni July 16, 1957

Claims (1)

1. A PROCESS FOR PRODUCING SPHERICAL PELLETS OF MATERIAL, WHICH CONSISTS OF POWDERING THE MATERIAL TO BE PELLETIZED, FORMING A SUSPENSION OF THIS POWDERED MATERIAL IN A LIQUID CARRIER OR VEHICLE, CAUSING SMALL DROPS OF THIS SUSPENSION TO REST UPON A SURFACE OF LIQUID REPELLENT POWDER, DRYING THE DROPS OF SUSPENSION, AND COLLECTING AND FIRING THE SPHERICAL PELLETS THUS FORMED.
US686268A 1957-09-25 1957-09-25 Method of fabricating small spherical pellets Expired - Lifetime US2872719A (en)

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3139465A (en) * 1959-05-29 1964-06-30 Dow Chemical Co Pelleting method
US3141852A (en) * 1957-11-18 1964-07-21 Saint Gobain Nuclear fuels
US3228749A (en) * 1962-02-23 1966-01-11 Mitsubishi Metal Mining Co Ltd Production of spherical uranium nuclear fuel substances
US3287472A (en) * 1964-04-13 1966-11-22 Wolfen Filmfab Veb Method of making molecular sieves
US3549341A (en) * 1968-08-05 1970-12-22 Minnesota Mining & Mfg Method for producing pyramidal shaped tumbling media
US3875271A (en) * 1973-07-30 1975-04-01 Coors Porcelain Co Hollow pellets and method for making same
USRE30569E (en) * 1972-07-13 1981-04-07 The Standard Oil Company (Ohio) Process for preparing aggregates
US4407967A (en) * 1979-08-16 1983-10-04 Frenchtown American Corp. Method for producing spheroidal ceramics
US20040208811A1 (en) * 2001-05-23 2004-10-21 Kjell Anflo Method of preparing granules

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1561971A (en) * 1923-10-16 1925-11-17 Naugatuck Chem Co Method for treating pulverulent material and product
US1773257A (en) * 1928-02-13 1930-08-19 Grasselli Chemical Co Production of granular substances
US2180757A (en) * 1937-07-26 1939-11-21 Earnest T Hermann Method of forming lightweight fluid pervious ceramic bodies
US2436771A (en) * 1943-07-19 1948-02-24 Monsanto Chemicals Method of making pellets
US2562149A (en) * 1947-04-17 1951-07-24 Gilman B Mollring Asphalt pelletizer
US2790201A (en) * 1954-06-19 1957-04-30 Basf Ag Apparatus for manufacturing pellets from fusible materials
US2799074A (en) * 1957-07-16 qarloni

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2799074A (en) * 1957-07-16 qarloni
US1561971A (en) * 1923-10-16 1925-11-17 Naugatuck Chem Co Method for treating pulverulent material and product
US1773257A (en) * 1928-02-13 1930-08-19 Grasselli Chemical Co Production of granular substances
US2180757A (en) * 1937-07-26 1939-11-21 Earnest T Hermann Method of forming lightweight fluid pervious ceramic bodies
US2436771A (en) * 1943-07-19 1948-02-24 Monsanto Chemicals Method of making pellets
US2562149A (en) * 1947-04-17 1951-07-24 Gilman B Mollring Asphalt pelletizer
US2790201A (en) * 1954-06-19 1957-04-30 Basf Ag Apparatus for manufacturing pellets from fusible materials

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3141852A (en) * 1957-11-18 1964-07-21 Saint Gobain Nuclear fuels
US3139465A (en) * 1959-05-29 1964-06-30 Dow Chemical Co Pelleting method
US3228749A (en) * 1962-02-23 1966-01-11 Mitsubishi Metal Mining Co Ltd Production of spherical uranium nuclear fuel substances
US3287472A (en) * 1964-04-13 1966-11-22 Wolfen Filmfab Veb Method of making molecular sieves
US3549341A (en) * 1968-08-05 1970-12-22 Minnesota Mining & Mfg Method for producing pyramidal shaped tumbling media
USRE30569E (en) * 1972-07-13 1981-04-07 The Standard Oil Company (Ohio) Process for preparing aggregates
US3875271A (en) * 1973-07-30 1975-04-01 Coors Porcelain Co Hollow pellets and method for making same
US4407967A (en) * 1979-08-16 1983-10-04 Frenchtown American Corp. Method for producing spheroidal ceramics
US20040208811A1 (en) * 2001-05-23 2004-10-21 Kjell Anflo Method of preparing granules
US7211233B2 (en) * 2001-05-23 2007-05-01 Svenska Rymdaktiebolaget Method of preparing granules

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