EP0293349B1

EP0293349B1 - A device for manufacture of a metal granulate in the form of small "needles"

Info

Publication number: EP0293349B1
Application number: EP88850143A
Authority: EP
Inventors: Tor Osteng
Original assignee: Raufoss Ammunisjonsfabrikker AS
Current assignee: Raufoss Ammunisjonsfabrikker AS
Priority date: 1987-04-27
Filing date: 1988-04-26
Publication date: 1992-12-09
Also published as: DE3876499D1; NO164341C; NO871736L; DE3876499T2; NO871736D0; EP0293349A1; NO164341B

Description

The present invention relates to a device for manufacture of a metal granulate in the form of "needles" by rapid solidification, comprising a rotatable, cylindrical crucible having a vertical axis of rotation and small apertures in the wall and a supply tube for the melt provided vertically above the crucible, a sleeve surrounding the supply tube and defining a space around the tube, said sleeve being journalled for rotation together with the crucible, driven by a motor. A granulate in form of "needles" is well suited inter alia for pressing and extrusion. An advantage relatively to the use of a bolt as the basis material is that the manufacture of a bolt of suitable dimensions is avoided, and the manufactured products become more homogene than by use of a bolt. The "needles" of an aluminium alloy are used, and without the mentioning it as any limitation in this connection the "needles" may for instance have a length of some mm and a maximum thickness of some tenths of a mm. In particular the "needles" may, in addition to aluminium, contain one or more of the metals Zr, Mg, Si, Ag, Ni and Cu.
It is known to produce such needles by supplying a melt to a rotating, cylindrical crucible having small apertures in the wall, whereby the melt is forced through the apertures and are slung out of the crucible, whereby the particles take the shape of needles and solidify prior to falling down on a base. Experience shows that the needles obtain a very thin oxide layer. The cooling velocity is high, and is supposed to be in the range of 100 to 1000° C per sec. The base onto which the needles fall may conveniently have the form of a hopper, whereby the collecting of the needles is facilitated. The hopper may have a diameter of several meters.
A problem of the production of the "needles" is that the melt may oxidize before it arrives at the crucible. This is undesirable because the "needles" should comprise as little oxide as possible in addition to the outer thin layer. Oxidation of the melt also involves the danger of making "needles" which more or less consist of oxide. This may to a considerable extent reduce the quality of the products manufactured with the "needles" as the basis material.
An example of a previously known device for the manufacture of a metal granulate is given in DE-A1-2654956 wherein cooling gas is introduced outside of the shaft of the crucible. The aim of this document is to propose a possibility of quick de-mounting of the device so that solidified metal can be removed. There is however no teaching in this document of how to avoid feeding of oxidized melt to the crucible.
The object of the present invention is to achieve a device which brings about the avoidance of supplying oxidized melt to the rotating crucible.
This is achieved with the device wherein a non-rotating end closure is sealingly provided at the top of the sleeve, said end closure comprising an aperture for the supply tube and at least one passageway extending through said end closure for supply of an inert gas into the space surrounding the supply tube.
The device can be connected to a furnace either in such a manner that the supply tube is mounted in the bottom of the furnace or in that a gutter leads the melt from the furnace to the supply tube. When using a gutter, which preferably is thermally insulated, the supply tube can be fastened in a hole in the bottom of the gutter, and the end of the gutter is closed.
The invention will be explained more detailed in the following, with reference to the accompanying drawing showing a device in accordance with the invention in combination with a gutter which leads melt from a furnace.
The device comprises a crucible 1 with small apertures in the wall for slinging out small particles of melt metal when the crucible is rotating about its vertical axis. The crucible is fastened to a sleeve 5 through an end closure 7 on the sleeve 5. The sleeve 5 has internal thermal insulation 6. In the embodiment shown the sleeve 5 is journalled in a frame 17, and bearings 14 situated in a cylinder 15 on the frame 17 guides the sleeve 5 and transmits the load to the frame 17.
In the example the sleeve 5 is made integrally with a driving wheel 10 which can be driven by a belt 8 by means of a motor 9 equipped with a drive pulley 22. The belt shown is a V belt, but other belts, chains or toothed wheels can of course be used.
In the example shown the sleeve 5 having the drive wheel 10 provides support both of an upper end closure 11 and a gutter 3 for supply of melt. A bearing 13 allows rotation of the sleeve 5 while the end closure 11 is stationary, resting on the bearing 13. The end closure 11 does not need to be fastened, whereby it can be adapted to be lifted and removed from the sleeve 5 together with the gutter 3. Two bearings 16 mounted on respective shafts 12, 20 on the end closure 11 provide support for the gutter 3, through support plates 21, whereby the sloping direction of the gutter from the not shown furnace can be adjusted. The gutter 3 has external insulation 4, and during use the gutter can be covered by one or more covers, in order to reduce the heat emission from the flowing melt in the gutter 3.
Also the supply tube 2, which in the example shown depends from the gutter 3, is preferably made of a thermally insulating material, for instance a ceramic material, of which also the gutter 3 may consist. The lower end closure 7 and the internal insulation 6 in the sleeve 5 may also consist of such a material.
The shaft 12 on the end closure 11 is hollow, and the cavity continues downwardly through the end closure 11, whereby an inert gas can be supplied to the cavity in the sleeve 5 and prevent admission of air.
In the example the frame 17 is hinged to a base 19, whereby, when the gutter 3 with the tube 2 and the end closure 11 are removed from the sleeve 5, the sleeve 5 and the crucible 1 can be swung up together with the motor 9. Thereby the crucible 1 in a simple manner becomes accessible for cleaning or replacement. This is of particular importance when a hopper of large dimensions is used for collecting the "needles" coming out of the crucible 1, in which case the distance from the bottom of the hopper up to the crucible 1 can be several meters. In the example the upper end of the crucible 1 has been screwed up into the end closure 7.
When melt from a furnace flows in the gutter 3 oxide will be formed at the top of the melt. The oxide layer will, however, be lying stationary while the melt flows below the oxide layer, and melt free from oxide will flow down through the tube 2 and down into the crucible 3 without coming into contact with air.
The journalling of the end closure 11 and the gutter 3 on the sleeve 5 also brings about the advantage that the gutter 3 can be pivoted about the journalling, whereby the other end of the gutter can be moved between two or more furnaces situated along a circular arc.
The longitudinal aperture through the tube 2 is sized in such a manner that the melt from the gutter 3 flows with a rate which is adapted to the amount of "needles" being formed per unit of time.
If the melt is drained directly through the bottom of a furnace the gutter 3 is of course omitted. In such a case the tube 2 can depend from the bottom of the furnace.
Because an inert gas is supplied to the cavity in the sleeve 5 under a certain excess pressure no particularly good sealing is needed at the bearing 13, and it may be sufficient that the end closure 11 has a planar annular surface lying against the upper ring of the bearing 13.

Claims

A device for manufacture of a metal granulate in the form of "needles" by rapid solidification, comprising a rotatable, cylindrical crucible having a vertical axis of rotation and small apertures in the wall and a supply tube (2) for the melt provided vertically above the crucible (1), a sleeve (5) surrounding the supply tube and defining a space around the tube, said sleeve being journalled for rotation together with the crucible, driven by a motor, characterized in that a non-rotating end closure (11) is sealingly provided at the top of the sleeve (5), said end closure (11) comprising an aperture for the supply tube (2) and at least one passageway extending through said end closure (11) for supply of an inert gas into the space surrounding the supply tube (2).
A device according to claim 1, characterized in that the passageway extends through a hollow shaft (12) on the end closure (11), said shaft forming a support for a gutter (3) for supply of melt from a furnace.