Casting wheel

Details Casting wheel Casting wheel

1999-08-23

2001-08-21

Lin, Kuang Y. (Department: 1722)

Metal founding

Means to shape metallic material

Including ladle or crucible type melt receptacle

C164S136000, C222S591000

Reexamination Certificate

active

06276435

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to casting wheels for use in filling ingot moulds in automatic metal ingot moulding lines, and to a wheel member for such a casting wheel.
BACKGROUND TO THE INVENTION
Casting wheels (or rotating launders) are commonly used in the aluminium industry. Casting wheels have also occasionally been used for the casting of ingots of other metals.
The general construction of a casting wheel includes a number of spouts (sometimes referred to as buckets) positioned on the perimeter of a wheel which is designed to rotate about its axis. The casting wheel is usually indexed to a substantially flat conveyor which includes a number of ingot moulds. The number and positioning of the spouts on the casting wheel is indexed such that each spout corresponds to one mould and allows for the filling of the mould with molten metal from the spout.
The general objective of all casting wheels is to provide an apparatus to prepare ingots of substantially equal size and weight which are free from scum and dross.
Problems associated with known casting wheels include the formation of blockages in the pouring spouts; poor design of the spouts such that the molten metal experiences excessive turbulence when poured into the mould and results in excessive dross; complex construction; and difficulty of cleaning and maintenance.
Consistent ingot weight is only achieved if spout blockages do not occur. Such blockages occur due to either oxide or dross formation. Dross formation would appear to be worse in the case of metals such as magnesium than for aluminium, although some inconsistency in operation does occur with current aluminium casting wheels.
The turbulence issue is a function of the casting wheel design, the way metal is added into the casting wheel and the location of the spout tips in relation to the height of metal in the ingot mould. Most aluminium casting wheels are of a squat cylindrical design and run with a pool of metal in an open main trough or launder. When this pool encounters a spout, metal flows into the spout and then into the mould, hopefully in such a way as the top surface skin of the metal in the pool is not disturbed. In practice, this usually means pouring more than one mould at a time. This can cause metal to flow into the mould when the spout tip is 5-10 cm above the mould bottom, causing splash and drossing.
In addition, the method of construction of the casting wheel needs to be addressed. They are usually cast from steel or iron or are fabricated from heavy gauge steel and are provided with some form of mould wash or coating. If the thermal mass of the casting wheel is too large, extensive heating of it is required to prevent freezing of the metal in the casting wheel. Known cast wheels need to have thick sections to enable them to be cast successfully. Cast wheels are normally limited production items of complex design and so the casting costs are usually high.
Further problems are observed if casting wheels are used for casting metals such as magnesium where the metal is cast under an inert or protective gas as gas heating cannot be used.
At least in preferred forms, the present invention is concerned with casting wheels, and wheel members for such wheels, which are suitable for casting magnesium or magnesium alloys.
SUMMARY OF THE INVENTION
In a first aspect, the present invention provides a wheel member, for a casting wheel for use in filling ingot moulds of an ingot mould line, the wheel member comprising:
a hub by which the wheel member is arranged to be mounted for rotation on an axis of rotation and which defines a central region; and
a plurality of spouts formed from sheet metal which are integral with the hub and extend outwardly from the central region in an angularly spaced array, each spout having an inlet end adjacent the central region and an outlet end remote from the hub.
Preferably, the wheel member is formed from metal components which are secured together to provide an integral rigid structure. This enables the wheel member to be readily designed for a specific installation. Preferably, the metal components are welded together. The spouts are formed from sheet metal and, to enhance rigidity, the hub is typically formed from relatively thin metal plate, for example, in the order of 10 mm thick plate. The sheet metal from which the spouts are formed can be of relatively thin thickness, such as from about 1.5 mm to 4 mm thick, for example, about 2 mm thick. The sheet metal is preferably of low thermal mass. For example, the spouts may be formed from steel, titanium or a titanium alloy such as palladium stabilised titanium. The wheel member may therefore have a low thermal mass which obviates the need for heating other than by molten metal being cast in order to prevent freezing of the molten metal. Additionally, the inside of the spouts may be coated with a heat insulating material to reduce heat transfer to the spouts from molten metal flowing through the spouts. For example, the inside of the spouts may be plasma sprayed with alumina.
The wheel member may be of either of two distinct forms. In a first of these forms, the spouts are of open channel form in which molten metal flowing from the inlet to the outlet of successive spouts, in turn, is fully exposed to the surrounding atmosphere which, depending upon the metal being cast, may be an inert or protective atmosphere. In the other distinct form, each spout is of closed channel form between its inlet and outlet ends and, in that case, the outlet end typically is submerged in molten metal of a mould being filled.
In a first preferred embodiment, the wheel member principally is intended to be mounted for rotation about a substantially horizontal axis of rotation, and is rotatable so that each spout in turn moves to a melt pouring position in which it projects downwardly and forwardly from the hub. The spouts diverge outwardly and forwardly from the hub in a frusto-conical array, at a half cone-angle which is such as to ensure that each spout, when in the pouring position, is inclined downwardly and forwardly at an angle providing required, controlled flow of the melt.
In a second preferred embodiment, the axis of rotation preferably is inclined to the horizontal at an acute angle with the spouts generally perpendicular to that axis, such that each spout is inclined downwardly and forwardly when in the pouring position at an angle providing controlled flow of the melt.
It is to be understood that the first and second embodiments are opposite extremes. Thus, in a third preferred embodiment, each spout may be at a required angle providing controlled flow of the melt as a consequence of the spouts diverging at a greater half cone-angle than for the first embodiment, but with the axis of rotation being at a lesser angle to the horizontal than in the second case embodiment.
In each of the first, second and third embodiments, the arrangement preferably is such that each spout has a longitudinal centre-line which is in a respective radial plane of the wheel member which contains the axis of rotation. For a spout in the pouring position, such plane most preferably is substantially vertical. The inclination of the axis of rotation and of the spouts preferably is such that a spout, when in the pouring position, is inclined downwardly and forwardly from the hub at an angle of from about 25° to about 45° to the vertical, such as at an angle of about 30° to the vertical.
The spouts of the first, second and third embodiments may be of open, channel form. A variety of cross-sectional configurations are suitable for this, for example, V-section. In any event, it is desirable that, in cross-section, opposite side walls of each spout are inclined downwardly and inwardly towards each other. Most preferably the outer end of each spout has a transverse end wall over which molten metal issues as a thin curtain when the spout is in its pouring position. Such end wall, when its spout is in that position, most preferably is inclined downwardly and forwardly at a relatively shallow an

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