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
  • B22F9/10—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 using centrifugal force

Definitions

• the present invention relates to a method and apparatus for melt spin casting of materials, and more specifically, a method and apparatus for continuous, economical melt spin casting of homogenous materials.
• BACKGROUND OF THE INVENTION A number of techniques are known for the production of homogeneous materials. In the field of producing powdered materials, for example those materials used as electrode material for rechargeable electrochemical cells, property requirements include size, homogenous chemistry, and homogenous crystalline structure. In the field of battery production, a hydrogen storage alloy is commonly formed as a bulk ingot from a melt. One method of producing a hydrogen storage alloy is disclosed in commonly assigned U.S. Pat. No. 4,948,423 to Fetcenko, Sumner, and LaRocca for ALLOY PREPARATION OF HYDROGEN STORAGE MATERIALS, incorporated herein by reference.
• Hydrogen storage negative electrodes utilizing the aforementioned alloys are of relatively high hardness. Indeed, these alloys can typically exhibit
• the alloy in order to attain the high surface areas per unit volume and per unit mass necessary for high capacity electrochemical performance, the alloy must be in the form of fine particles.
• the hydrogen storage alloy powder must pass through a 200 U.S. mesh screen, thus being smaller than 75 microns in size (200 U.S. mesh screen has interstices of about 75 microns). Therefore, the resulting hydrogen storage alloy material is comminuted, e.g., crushed, ground, milled or the like, before the hydrogen storage material is fabricated into electrode form.
• Rapid solidification refers to a technique for rapidly quenching material from a liquid, or molten, state into a solid state at a rate sufficient to freeze the position of atoms.
• One rapid solidification technique is a spin cast technique where the molten material into is formed into ribbons.
• Spin casting is a method of dispersing molten material on a rotating wheel, also commonly known as melt spin casting.
• the rotating wheel made of a highly conductive metal, typically copper, is positioned proximal to a reservoir of molten material.
• the reservoir typically has an orifice or nozzle to direct molten material onto the rotating wheel.
• the molten material is rapidly solidified because of the mass of the wheel and the significant difference in temperature between the wheel and the molten material.
• the wheel need not be cooled in order to provide a sufficiently cold moving surface relative to the molten material, however, the wheel may be cooled to achieve higher quench rate if so desired.
• a wheel is typically between 6" and 10" (15.24 and 25.40 centimeters) in diameter and is rotated at a rotational velocity of between 1 ,000 and 5,000 rpm thereby to obtain a linear velocity, at the point of contact at the material with the cylindrical periphery of the wheel, of 32.81 to 65.62 feet per second (1 ,000 - 2,000 centimeters per second).
• Materials produced by melt spin casting techniques of the prior art exhibit material property variations due to a number of factors. Variations such as flow rate, stream diameter and material temperature, and compositional variations including chemistry and impurities within the melt stream contribute to inhomogeneity of the solidified material. Changes in the diameter and flow rate of the molten material stream result in different cooling rates of the material. As explained above, different cooling rates will effect the material's crystalline structure. Inhomogeneity is the main drawback of the melt spin processes of the prior art. Increased homogeneity requirements of materials make an improved technique especially important.
• melt spin casting is an attractive method for producing ribbons of material because of the lack of complexity involved. This technique may be employed to form ribbons of material such as metals, metal alloys, or thermoplastics.
• One method of producing materials by melt spin casting is disclosed in commonly assigned U.S. Pat. No. 4,637,967 to Keem et al for ELECTRODES MADE WITH DISORDERED ACTIVE MATERIAL AND METHODS OF MAKING THE SAME, the disclosure of which is incorporated herein by reference.
• the '967 patent discloses a heated crucible that is equipped with means for pressurizing the crucible to extrude molten material through a nozzle onto the surface of a chill wheel.
• a hydrostatic system may be employed to provide the necessary force to extrude the molten material from the crucible.
• a hydrostatic system may be employed to provide the necessary force to extrude the molten material from the crucible.
• Such a device is disclosed in U.S. Pat. No. 4,485,839 to Ward for RAPIDLY CAST ALLOY STRIP HAVING DISSIMILAR PORTIONS.
• the '839 patent discloses a planar flow casting technique for drawing thin ribbons. Although this technique includes a hydrostatic system for delivering the molten material, there are shortcomings associated with this invention.
• the device disclosed is not capable of providing a true, continuous melt casting operation.
• the disclosed operation relies on heating a crucible to prevent the nozzles from clogging, which is ineffective since it is commonly known that slags and other impurities are present within the crucible. Also, because of the tolerances associated with this device, less than 0J20" (3.05 mm), the surface of the chill wheel must be constantly maintained.
• the present invention disclosed herein is an apparatus for continuous melt spin casting of materials.
• the apparatus comprises a supply crucible and a casting crucible disposed a chamber.
• the supply crucible provides molten material to the casting crucible for ejecting at least two streams of molten material upon a chill wheel for solidification. Each stream is ejected through one of at least two orifices in the casting crucible.
• Monitoring means determine the level of molten material in the casting crucible.
• the apparatus of the present invention includes a selectively actuated flow control valve for controlling the flow of molten material from the supply crucible to the casting crucible to maintain the level of molten material in the casting crucible within a range.
• Valve control means actuate the flow control valve as a function of material level in the casting crucible as sensed by the monitoring means.
• the present invention includes means for filtering the molten material prior to casting and thermal control means for controlling the temperature of material within said casting crucible.
• the means for filtering is one or more removable filter elements disposed in a movable support assembly.
• Each orifice is at an equal distance from a point of contact on the chill wheel.
• Equal length streams of material at a uniform temperature and flow rate are rapidly solidified form homogenous ribbons by the chill wheel.
• the apparatus further comprises a melting crucible to providing the supply crucible with molten material.
• the melting crucible may be disposed within the chamber or be located external to the chamber.
• Conveyor means to supply the melting crucible with ingot material is also disclosed.
• Means for removing accumulated material from an external surface of said orifices is also disclosed, the means may be the chill wheel or an attachment such as a diamond wheel. Also disclosed herein is a method for continuous melt spin casting of materials.
• the novel method comprises the steps of providing a material supply crucible and a casting crucible disposed within a chamber, where the material supply crucible is provided to receive molten material to be supplied to the casting crucible; monitoring the level of molten material in the casting crucible; releasing molten material from the supply crucible through a flow control valve; filtering the molten material released from the material supply crucible prior to solidification; maintaining the molten material level in the casting crucible, whereby the molten material flow rate through the orifices is controlled by the static pressure of the molten material in the casting crucible to provide a constant material flow rate; maintaining the temperature of the molten material in the casting crucible to provide material for casting at a consistent temperature; ejecting at least two streams of molten material from the casting crucible, each stream ejected through one of at least two orifices in the casting crucible; and rapidly solidifying the molten material by ejecting equal length and diameter streams of
• the molten material may be filtered through a filter element that is removable during continuous casting.
• a movable support assembly such as a turntable is provided wherein one or more filter elements may be disposed in a movable support assembly.
• At least two nozzles may be provided, each nozzle in communication with one of at least two orifices, accumulated material deposits are removed from the orifices or nozzles by means including a shearing device, the chill wheel or a diamond wheel.
• Conveyor means may be provided to supply the melting crucible with ingot material.
• Figure 1 is a cross sectional view of one embodiment of the present invention taken through a chamber to reveal the operative elements therein.
• Figure 2 is a cross sectional view showing one operating position of one embodiment of a casting crucible in relation to a chill wheel.
• Figure 3 is a sectional view of the casting crucible and chill wheel taken along section A-A of Figure 2.
• the apparatus 10 of the present invention includes a chamber 20 containing a supply crucible 30 and casting crucible 40.
• the supply crucible 30 is provided to receive molten material and has a selectively actuated flow control valve 70 for releasing molten material into the casting crucible 40.
• the casting crucible 40 has at least two orifices 50, each orifice 50 for ejecting a stream of molten material upon a chill wheel 110 having a horizontal axis of rotation.
• a melting crucible 120 is disposed within the chamber 20 to provide molten material to the supply crucible 30.
• melting crucible 120 may be located external to the chamber 20.
• Conveyor means (not shown) may be employed to supply the apparatus 10 with material for casting-
• a loading vessel 130 in communication with the chamber 20 provides material to the melting crucible 120 without exposing the materials within the chamber 20 to contaminants by incorporating a flap valve 135.
• flap valve is used to seal the chamber 20, any suitable means known in the art may be substituted for a flap valve.
• An induction heater 240 is employed to heat material within the melting crucible 120.
• the melting crucible 120 has a flow control valve 250 that is selectively actuated by valve control means 260 for releasing material to the supply crucible 40. Upon melting, the material within the melting crucible 120 is stirred electrodynamically, by agitation, or any other suitable means known in the art.
• the apparatus 10 may also include at least two nozzles 55, each nozzle in communication with one of the orifices 50 in the casting crucible 40.
• the flow control valve 70 is selectively actuated by valve control means 80 to provide the molten material to the casting crucible 40.
• the valve control means 80 may be manually operated or automatically controlled by a controller (not shown).
• the valve control means 80 are actuated as a function of the material level in the casting crucible 40.
• the molten material is ejected from the casting crucible 40 onto the chill wheel 110.
• the molten material level within the casting crucible 40 provides hydrostatic pressure at the orifices 50 to eject molten material upon the chill wheel 110.
• the material level in the casting crucible 40 is maintained in order to maintain a uniform flow rate.
• the chill wheel 110 is preferably formed of a material having a high thermal conductivity such as copper.
• the temperature of the chill wheel 110 may be controlled by any suitable cooling means (not shown) known in the art, including a cooling medium such as a water and ethylene glycol mixture.
• the chill wheel 110 has a passage to allow the cooling medium to pass through and draw heat away from the casting wheel 110.
• the supply crucible 30 is heated by thermal control means 100; in the preferred embodiment, the thermal control means is an induction heater 180.
• the molten material within the supply crucible 30 may be mixed by any suitable means known in the art to maintain homogeneity.
• the casting crucible 40 is heated by thermal controls means 105, and in the exemplary embodiment, the thermal control means is an induction heater 190 as well.
• the casting crucible 40 may be stirred by any suitable means known in the art.
• the atmosphere in the chamber 20 may consist of an insert gas or may be pumped down to a vacuum to prevent contamination.
• heat is provided by the induction heater 180 to maintain viscosity.
• the material within the supply crucible 30 is mixed to maintain homogeneity.
• the frequency of the induction heater 180 the material may be electrodynamically mixed.
• the induction heaters 180 and 190 are reduced below 1000 Hz, resulting in excellent mixing results. It should be noted that other mixing operations may be substituted for electrodynamic mixing, such as agitation.
• the chill wheel 110 is shown in one of many potential locations.
• the chill wheel 110 is movable in the X, Y, and Z-axis, providing many advantages to the present invention.
• By adjusting the position of the chill wheel 110 along the Z-axis the length of the streams is changed, changing the exposure time to ambient conditions and ultimately, temperature. Therefore, fine temperature adjustments of the molten material prior to contacting the chill wheel 110 may be made by adjusting the position of the chill wheel 110 along the Z-axis.
• the form of the ribbons produced by apparatus 10 of the present invention may be altered by moving the chill wheel 110 along the X-axis, which will change the angle of incidence of the material streams on the chill wheel 110.
• the chill wheel 110 may be positioned by any combination of orthogonal coordinate changes and then translated along the Y-axis to remove material which has accumulated upon the orifices 50 by shearing the accumulated material with the chill wheel 110.
• Any other suitable means for removing accumulated material 160 including shearing or grinding means may otherwise be adapted to remove accumulated material from the orifices 50 or nozzles 55 to avoid contact with the chill wheel 110, for example a diamond wheel.
• the orifices 50 or nozzles 55 may be heated to reduce material accumulation.
• a thermal screen 220 may also be disposed below the supply crucible 40 to stabilize the flow rate of the molten material exiting the supply crucible 40.
• the thermal screen 220 is heated whereby the material temperature is preserved as the material exits the supply crucible 40.
• Means for filtering 90 the molten material prior to casting are provided.
• the means 90 may be a filter element 230, such as a ceramic filter capable of high temperature filtering of molten materials for the removal of slags, oxides or other impurities.
• a common occurrence experienced when melting is pieces of the crucible break away due to thermal cycling, and become inclusions in the melt.
• the means for filtering 90 molten material include a removable filter element 140 disposed in a movable support assembly 150.
• the filter element 140 may comprise a fine filter component and coarse filter component to improve filter element 140 viability.
• the filter element 140 and support assembly 150 are disposed between the casting crucible 40 and the supply crucible 30.
• the movable support assembly 150 is cycled while the supply crucible 30 is not providing material to the casting crucible 40.
• each contaminated filter element 140 may be replaced with a new filter element 140.
• a seal 155 isolates the chamber 20, preventing contamination of the casting material when exchanging filter elements 140.
• the temperature of the material within the casting crucible 40 is maintained by the induction heater 190 and stirred to maintain homogeneity.
• Monitoring means 60 such as a sight glass for measuring height or a balance for determining material mass, is provided to evaluate the material level in the casting crucible 40.
• the flow rate of the material from the casting crucible 40 is governed by hydrostatic pressure.
• the material level in the casting crucible 40 will determine the rate material is ejected from the casting crucible 40.
• the material level must be maintained within a range in order to provide a uniform flow rate of the molten material stream.
• the size and the form of the ribbons can be modified by changing the rotational speed and diameter of the chill wheel 110.
• By increasing the speed of the chill wheel thin ribbons are formed and the material dwell time is reduced.
• the surface of the casting wheel 40 is polished to provide sufficient mechanical and thermal contact with the melt streams.
• process throughput is increased.
• the orifices 50 are positioned at a uniform distance from a contact point of the material stream upon the chill wheel 110. Flow rate, temperature, material purity, and homogeneity must be simultaneously maintained in order to obtain uniform material properties such as crystallite size and homogeneity of the solidified material.
• the present invention discloses an economical solution to melt spin casting concerns found in the state of the art.
• the present invention has improved throughput without a need for a mechanical device to provide additional pressure within the casting crucible 40, such as a piston. Also, an uninterrupted stream of material with excellent homogeneity and purity for rapid solidification upon the chill wheel 110 is provided.
• the chamber 20 is hermetically sealed and operated in a vacuum to prevent oxidizing of the melt, thereby achieving higher purity.
• An ingot of negative electrode material for a rechargeable electrochemical storage cell is provided to the melting crucible 120 within chamber 20 by the loading vessel 130 and heated to 1550°C. After melting, the melt it is mixed electrodynamically to increase homogeneity.
• flow control means 260 open the flow control valve 250 to released the molten material into the supply crucible 30.
• Thermal control means 100 sustain the material temperature until the material is released into casting crucible 40.
• the molten material within the supply crucible 30 is electrodynamically mixed. By lowering the frequency of the induction heater to below 1000 Hz frequency, more efficient mixing is achieved.
• the molten material in the supply crucible 30 is released to the casting crucible 40 by actuating the valve control means 80 to open the flow control valve 70.
• the material released by the control valve 70 passes through the thermal screen 220 where the material temperature is stabilized to avoid cooling.
• the material then passes through the filter element 140 and into the casting crucible 40.
• the material temperature in the casting crucible 40 is stabilized by an induction heater 190.
• valve control means 80 close the supply crucible flow control valve 70.
• the material level in the casting crucible 40 is evaluated by a sight glass disposed within chamber 20 to assure a material height of 200 mm is maintained.
• ten streams of molten material each stream formed by one of ten calibrated orifices 50, are ejected onto the rotating chill wheel 110.
• Each orifice 50 being uniform in diameter and equidistant from the chill wheel
• melt stream 110 forms a melt stream that is equal in length and diameter.
• the orifices are disposed about 150 mm from the contact point on chill wheel
• a cooling medium is flowed through a passage in the chill wheel 110.
• ribbons are formed having a constant width and thickness.
• the ribbons produced by this technique exhibit high homogeneity of properties and uniform crystallite size while increasing the productivity of the process.
• the temperature of the casting crucible is regulated to about 1500°C and the level of the melt bath to about 200 mm.
• the casting crucible 40 flow rate is between about 0J5 to 0.32 L/min (1 to 2.5 kg/min).
• the ten streams have an equal length, less than about 150 mm in the present example, and a diameter between about 1.0 to 2.5 mm.
• the chill wheel 110 rotates with a linear speed of between about 5 to 25 m/sec.
• the apparatus and method of the present can be used to produce threads, films, ribbons and any variant thereof.
• metallic materials and alloys have been specifically referenced, it should become apparent to those skilled in the art that a variety of material, including non metallic materials, such as plastics, may be formed by employing the teachings set forth herein.

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• 2000
  • 2000-01-11 CA CA002362434A patent/CA2362434A1/en not_active Abandoned
  • 2000-01-11 WO PCT/US2000/000685 patent/WO2000047351A1/en not_active Application Discontinuation
  • 2000-01-11 EP EP00931889A patent/EP1165273A4/en not_active Withdrawn
  • 2000-01-11 JP JP2000598297A patent/JP2002536185A/ja active Pending
  • 2000-01-11 AU AU49699/00A patent/AU4969900A/en not_active Abandoned

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