Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D13/00—Centrifugal casting; Casting by using centrifugal force
  • B22D13/08—Centrifugal casting; Casting by using centrifugal force in which a stationary mould is fed from a rotating mass of liquid metal
• • 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
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/115—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces by spraying molten metal, i.e. spray sintering, spray casting
• • 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
• • 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
  • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy

Definitions

• This invention relates to apparatus for centrifugal spraying of molten metal or other material either to effect spray deposition on to a mould or to produce powder.
• Centrifugal spray deposition can be used to atomise liquid metal into droplets and propel them at high velocity to "splat" against a mould surface and build up a solidified metal form.
• the metallic structure of the deposited metal is a homogenous mass, resulting from splatted particles becoming intimately united, of which the density, grain size and other characteristics can be controlled by selection of the operating conditions of temperature, thermal conductivity and thermal capacity of the surfaces contacted by the metal, ambient atmospheric conditions, effective velocity of the centrifuge and the flight path and distribution of the metal droplets.
• centrifugally sprayed atomised metal droplets are allowed to fall freely in a cooling atmosphere with or without impingement against a surface in the path of the spra3 r .
• the present invention Is concerned with apparatus for the spraying of molten material and, according to the invention, the apparatus comprises a closed chamber, means for controlling the atmosphere in the chamber, a spraying rotor mounted on a vertical axis in the chamber and comprising a positive vaned impeller, a wall in the chamber coaxially surrounding the impeller In the path of spray from the Impeller, means for moving the wall relatively to the Impeller, and a tundish mounted above the impeller and arranged to hold and feed molten material to the impeller.
• the tundish preferably has electrical induction heating coils and may be used for maintaining in a molten state metal poured through the tundish, or for melting metal, and controlling Its delivery to the eye of the impeller.
• the positive impeller as compared with a flat dish or shallow bowl as previously proposed, comprises a cup with a refractory lining having an eye in the form of a central well, into which the metal is poured from the tundish, and channels which extend through the refractory lining radially from the central well so that the channel walls form Impeller vanes, which may be straight or curved, for positive impulsion of the molten metal.
• the Impeller is surrounded by a mould wall, having a relatively rough surface for deposition of the sprayed
• L ⁇ metal and means are provided, such as hydraulic or pneumatic jacks, for effecting controlled reciprocation of the wall relatively to the Impeller, and consequently controlled distribution of metal deposited on the mould wall, so as to achieve uniform or varying thickness deposition.
• the reciprocation means preferably support and move the mould wall but reciprocation of the rotor is possible.
• the mould wall may be replaced by a curtain wall having a polished surface to which the droplets do not firmly adhere so that they form powder particles which drop or can be removed from the wall.
• the rotor and mould or curtain wall are enclosed in the chamber provided with means for controlling and monitoring its enclosed atmosphere, usually to ensure an inert or non-oxidising atmosphere for metal spraying, although a reactive atmosphere might be maintained for special purposes.
• the chamber is forme'd by an outer reactor vessel and an inner reactor vessel with Insulated and/or cooled walls to effect thermal control, gas-Injection connections and pressure- release valves for atmospheric control and sealed access openings for the tundish and the jacks or other reciprocation means.
• the outer reactor vessel is provided with positional adjustments, such as by being slidably supported on a base with screw adjusters or other shifting means on intersecting axes, so that the position of the mould, outer vessel and tundish about the rotor axis can be adjusted, usually for centering but possible deliberately eccentric for special purposes, such as variably controlling spray deposition thickne
• Means may be provided for feeding into the eye of the impeller additional materials as additives to be entrained by the sprayed metal.
• Fig. 1 is a vertical axial section through the major part of the whole apparatus
• Fig. 2 is an axial section of the tundish
• Fig. 3 is an axial section, on a larger scale, of the rotor Impeller
• Fig. 4 is an axial section of the chamber vessels showing the atmospheric control connections and positional control means
• Fig. 5 is a fragmentary perspective view of mould wall rotating machanlsm
• Fig. 6 is a fragmentary axial section of an optional feature for introducing an additive to liquid metal to be sprayed.
• Liquid metal can be provided from an induction, resistance or arc furnace and transported to the spray plant using a bottom pouring ladle A.
• the liquid metal can be poured directly from the supply furnace through a separate launder, or melted within the tundish as described in Module 2.
• the liquid metal from the ladle A is discharged into a tundish B which is lined with refractory materials C and surrounded by electrical Induction heating coils D designed to maintain the contents of the tundish within controlled temperature limits during spraying.
• the provision of the induction heating coils also provides the capability to melt small charges of metal within the tundish itself.
• Liquid metal flow out of the tundish is controlled by the head E of liquid metal in the tundish and the diameter of the tundish nozzle F subject to the opening of a stopper indicated in broken lines.
• the nozzle F is constructed from refractory material, preferably of low thermal mass, and is mounted within a refractory casing G.
• the liquid metal emerges from the tundish nozzle F as a small stream and enters the eye of a rapidly rotating impeller H.
• the impeller H consists of a steel cup 1, which may be circular or polygonal in plan, and a fitting refractory lining 2 having a central well 3 at the centre of the bottom of which there is a rounded boss 4 on to which the stream of liquid metal Impinges so as to spread smoothly outwards. Rotation of the impeller will cause the liquid metal to move radially outwards so that the boss 4 is substantially exposed to the impinging stream.
• the lining 2 has a regular array of radial channels 5 which extend radially outward, in straight or curved paths, to open through ports 6 in the peripheral wall of the cup 1.
• a refractory ring 7 forms an overhanging rim to stop spash-back- of liquid metal from the well.
• the base of the cup 1 has a socket 8 for mounting the impeller on the polygonal head of a driving shaft 9 of an electric motor 10 (Fig. 1).
• liquid metal poured Into the well 3 is spun outwards to enter the channels 5 of which the walls act as impeller vanes ejecting the liquid metal through the ports 6 as an atomised spray of liquid metal droplets.
• th _ rate of pour from the tundish and the speed of the motor 10 the spray can be controlled in quantity and droplet size.
• Liquid metal droplets leaving the Impeller H are projected within an atmosphere of inert gas such as nitrogen, argon or helium, to impact against a mould wall I.
• inert gas such as nitrogen, argon or helium
• the inert atmosphere is maintained in a chamber J between two drum-shaped concentric thermally Insulated and water cooled vessels K and L and the purity is monitored prior to and during operation.
• the rapid increase in inert gas temper ⁇ ature and the consequent increase in gas pressure which accompanies the start of liquid metal spraying is regulated by a combination of water cooling, gas injection through connections M and the inclusion of pressure release valves N at various points on the vessels K and L.
• Fig. 4 MODULE 5 - Wall Movement. Figs. 1, 4 and 5
• Liquid droplets colliding with the mould wall I flatten or "splat" and solidify rapidly. Movement of the wall relative to the droplet spray exposes relatively cool areas of the wall, or of deposited metal, for further splat deposition. Reciprocation of the wall by hydraulic or pneumatic jacks 0 through the droplet flight path promotes overlapping of deposits and allows a thick homogenous solidified form to be prepared.
• the heat flux is substantially normal to the wall surface.
• the droplets For the achievement of a high density within the deposited form, the droplets must remain in a liquid state up to the point of impact on the mould wall.
• the movement of the mould wall can be programmed to provide periods of dwell and rapid acceleration.
• the mould itself can be machined to provide a complex pattern for splat casting.
• the outer vessel L which carries the tundish B in a central recess in its closed top, is movable by screwed radial adjusters, at right angles, of which one Is shown at S.
• the vessel L has a broad base flange slidable on a supporting sealing ring 11.
• the mould wall may be rotated about the rotor axis. This can be done, as shown in Fig. 5, by providing the mould wall I with a ring gear base flange 12 which rests, by ball bearings 13, on a support ring 14 carried by the jacks 0.
• the support ring 14 also carries a bracket 15 on which Is mounted a reversible electric motor 16 driving a pinion 17 In mesh with the ring gear of the flange 12.
• the mould wall I can be rotated as required In either direction about the axis of the rotor.
• the impeller is an efficient mixer the delivery of metal or non-metal additions to the impeller eye In combination with a liquid metal stream from the tundish can result in the manufacture of alloys which are difficult or impossible to produce by other methods.
• metal or non-metal powders can be dispersed within a metal matrix.
• (c) dual phase alloys can be prepared by simultan ⁇ eously spraying two dissimilar liquid metals or a solid in combination with a liquid.
• FIG. 6 A typical arrangement is indicated in Fig. 6 in which particles of an additive entrained in a low pressure gas stream are fed to the eye of the impeller H through a pipe P and a ring distributor R through the open centre of which the stream of liquid metal passes.
• Deliberate variation of the liquid metal composition passing through the tundish nozzle during a spraying cycle can provide conditions necessary to prepare layered or composite structures.
• the ability to combine alternate layers of different " metals or alloys provides the potential of producing for example, corrosion resistant, heat resistant or wear resistant coatings.
• a composite structure can be prepared by spray deposit of a thin coating of a second component on to the rough as-splatted surface of a previous deposit.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)

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• 1982
  • 1982-05-04 EP EP19820901301 patent/EP0078272A1/de not_active Withdrawn
  • 1982-05-04 WO PCT/GB1982/000135 patent/WO1982003809A1/en unknown

Non-Patent Citations (1)

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