US3830281A

US3830281A - Method of continuously casting aluminum for simultaneous production of plural ingots

Info

Publication number: US3830281A
Application number: US00315500A
Authority: US
Inventors: J Snider
Original assignee: Alcan Research and Development Ltd
Current assignee: Alcan Research and Development Ltd
Priority date: 1971-12-17
Filing date: 1972-12-15
Publication date: 1974-08-20
Anticipated expiration: 1991-08-20
Also published as: DE2261879A1; GB1401766A; DE2261879C3; NO136397B; DE2261879B2; NO136397C; CA965927A

Abstract

In the continuous casting of aluminium a series of moulds are supplied with molten metal through individual dip tubes from a common trough system. To approximately synchronise entry of metal to the moulds, the mouth of each dip tube is initially closed by means of a buoyant plug to prevent entry of metal to the dip tube, until a predetermined depth of metal has been established in the trough system.

Description

United States Patent Snider Aug. 20, 1974 [54] METHOD OF CONTINUOUSLY CASTING 3,224,460 12/1965 Cann 137 399 ALUMINUM FDR SIMULTANEOUS 3,332,474 7/1967 Sickbert 164/64 X PRODUCTION OF PLURAL INGOTS Inventor:

[75] James Roy Snider, Kingston,

Ontario, Canada [73] Assignee: Alcan Research and Development Limited, Montreal, Quebec, Canada Filed: Dec. 15, 1972 App]. No.: 315,500

References Cited UNITED STATES PATENTS 10/1940 Junghans 164/281 FOREIGN PATENTS OR APPLICATIONS 72,085 5/1947 Norway ..164/281 448,396 3/1968 Switzerland 164/281 Primary Examiner-R. Spencer Annear Attorney, Agent, or Firm-Dunham, Cooper, Clark, Griffin & Moran [57] ABSTRACT In the continuous casting of aluminium a series of moulds are supplied with molten metal through individual dip tubes from a common trough system. To approximately synchronise entry of metal to the moulds, the mouth of each dip tube is initially closed by means of a buoyant plug to prevent entry of metal to the dip tube, until a predetermined depth of metal has been established in the trough system.

5 Claims, 2 Drawing Figures PATENIEDAUBZOIHH I The present invention relates to the continuous casting of aluminum (including aluminium alloys). In the continuous casting of aluminium it is conventional to cast a number of ingots in a single operation. It is common practice to cast as many as 48 ingots simultaneously. The metal is distributed from a holding furnace to the individual moulds via a trough system, from which it enters the moulds through dip tubes. The lower ends of the moulds are initially closed by means of stools, which are mounted on a common table. The table is supported by a hydraulic ram to permit it to be lowered at a controlled rate. Each dip tube is provided with a float, which closes the bottom end of the dip tube when the level of metal in the mould rises above a predetermined value.

At the beginning of the casting operation it is inevitable that the metal poured into the trough system will reach and enter the mouth of some of the dip tubes in advance of reaching the remainder of the dip tubes and this presents certain difficulties in controlling the pouring of the ingots. Since the lowering of the table cannot be commenced until a pool of metal of a predetermined depth has been established in each of the moulds, solidification will have proceeded to differing extents in the moulds if the metal commences to enter some dip tubes before others. i

It is an object of the present invention to overcome this difficulty by preventing the entry of metal into a dip tube until there is a predetermined depth of metal in the trough at the dip tube locality. Although this does not result in exact synchronisation of entry of metal into all the dip tubes it is found in fact to overcome previously experienced difficulties.

In order to achieve this result according to the present invention each of the dip tubes is provided with a buoyant plug of a material which is substantially unaffected by molten aluminum. Each of these plugs has a stem, which fits loosely within the mouth of the dip tube and an enlarged head. It will be appreciated that the stem of the plug must be of sufficient size to prevent displacement of the plug by the stream of metal poured into the trough system. The enlarged head of the plug must provide sufficient buoyancy in molten aluminium to lift the total weight of the plug, formed by the head and stem since initially the stem will be out of contact with the aluminium. Preferably the stem, although fitting loosely into the mouth of the dip tube, is a sufficiently close fit to prevent any substantial flow of metal into the dip tube until the lower end of the stem has been lifted out of the tube by reason of the rise of the metal level in the trough'system. The stem and head may be so dimensioned in respect to each other that, after being lifted out of the mouth of the dip tube, the plug turns on its side, thus precluding the possibility of reentering the mouth of a dip tube and closing it off before the trough system has emptied itself. It will be seen that the plug must be formed of a material which has a substantially lower specific gravity than molten aluminum since the head must provide the buoyancy to lift both itself and the stem at the beginning of the operation. In general it may be said that the specific gravity of the plug should not exceed three quarters of the specific gravity of molten aluminium and more preferably does not exceed one quarter of such specific gravity.

In the accompanying drawings:

FIG. 1 illustrates a typical trough system to which the present invention may be applied, and

FIG. 2 is a detail of a plug in the mouth of a dip tube.

In the system of FIG. 1 metal is distributed from a holding furnace to a plurality of conventional continuous casting moulds 1 through a trough system 2, the entry to. each mould from the trough system being through dip tubes 3. In FIG. 1 for convenience a single casting mould 1 is indicated diagrammatically. A float 4 is provided in each mould l to control the flow of metal through the dip tube 3 during the casting operation. The bottom end of each dip tube is initially open, the float 4 being supported by a pair of support wires 5, which rest on the top of the mould. In FIG. 1 the top of each dip tube 3 is indicated at 6. It will however be understood that the number of dip tubes will commonly be far in excess of the number indicated in FIG. 1. Each dip tube is provided with a plug 16. In operation the metal from a holding furnace enters the trough system through a launder 12 so that normally the metal reaches and commences to enter some dip tubes in advance of others.

In FIG. 2 the normal operating level of metal in the trough during the pouring of the ingots is indicated by the chain line 15. It is desired to retard the entry of metal into the dip tubes 3 until the metal level in the trough 2 is approaching this level.

The plug 16 illustrated in FIG. 2 is made of marinite, a refractory having a specific gravity of about 0.6, as compared with the specific gravity of 2.7 of molten aluminium. The plug 16 has a head 17 which may be frusto-conical, as illustrated, or which may be cylindrical or other shape, as desired. The head 17 has a flat undersurface 18 to seal off the mouth of the dip tube 3 although it is unnecessary for such a seal to exist in order for the apparatus to function effectively. The stem 19 of the plug has a diameter of about 0.040 inches (about 1 mm.) less than the internal diameter of the dip tube 14, so that it can rise freely in the dip tube, and so that it can move freely therein without permitting entry of molten metal until the stem is fully withdrawn from the dip tube. However a greater clearance than this may be employed since surface effects will retard the entry of the molten metal into the narrow gap between the stem 19 and the wall of the dip tube. The length of the stem 19 controls the level to which the metal must rise in the trough before the dip tube is opened to the entry of metal. In FIG. 2 the stem 19 is not fully withdrawn until the metal level reaches the line 25. Thus the mouth of each dip tube is maintained in a closed condition until a substantial depth of metal has been established in the trough 2 in its locality. This expedient is found to result in adequate, although not exact, synchronisation of the entry of metal to the different dip tubes of a multimould casting apparatus. It will be understood that the dimensions of the head 17 must be such as to provide sufficient buoyancy for the whole plug. Thus it may be necessary to increase the dimensions of the head if the length of the stem is increased. As already stated, there is no difficulty in designing the plugs so that they turn to a substantially horizontal position.

An advantage of the use of the dip tube plugs of the present invention is that dross on the surface of the to the individual moulds characterised by the steps of introducing molten aluminum into said trough with each dip tube being fitted with a buoyant plug member for preventing flow of metal through the dip tube until the local metal level has attained a predetermined value, each of said plugs being formed of a material substantially unaffected by molten aluminium and each of said plugs having a substantially lower specific gravity than molten aluminum and comprising a head of greater width than the mouth of the dip tube and a stern having a diameter slightly less than the internal diameter of the dip tube to permit movement freely therein without permitting access of molten aluminium, the size of the head of the plug being sufiicient to provide buoyancy for the whole plug and continuing to supply molten metal to the trough with the plugs floating free of the dip tubes.

2. A method according to claim 1 in which the plugs have a specific gravity less than one quarter of the specific gravity of molten aluminium.

3. A method according to claim 1 wherein the specific gravity of each said plug is not greater than three quarters of the specific gravity of molten aluminum.

4. A method according to claim 1 wherein each said plug is shaped to turn through a substantial angle upon floating free of the dip tube mouth for preventing reentry of the plug into the dip tube mouth.

5. A method according to claim 1 wherein the head of each said plug has a flat under surface for sealably closing the mouth of a dip tube when the plug is fitted in the dip tube mouth.

Claims

1. A method of continuously casting aluminium to produce a plurality of ingots simultaneously by supplying metal to a plurality of casting moulds by means of a trough system fitted with individual dip tubes leading to the individual moulds characterised by the steps of introducing molten aluminum into said trough with each dip tube being fitted with a buoyant plug member for preventing flow of metal through the dip tube until the local metal level has attained a predetermined value, each of said plugs being formed of a material substantially unaffected by molten aluminium and each of said plugs having a substantially lower specific gravity than molten aluminum and comprising a head of greater width than the mouth of the dip tube and a stem having a diameter slightly less than the internal diameter of the dip tube to permit movement freely therein without permitting access of molten aluminium, the size of the head of the plug being sufficient to provide buoyancy for the whole plug and continuing to supply molten metal to the trough with the plugs floating free of the dip tubes.

4. A method according to claim 1 wherein each said plug is shaped to turn through a substantial angle upon floating free of the dip tube mouth for preventing re-entry of the plug into the dip tube mouth.