STEEN IDAR KJETIL (NO)
NAESS HARALD JR (NO)
STEEN IDAR KJETIL (NO)
| EP0062606A1 | 1982-10-13 | |||
| US2791812A | 1957-05-14 | |||
| US5074353A | 1991-12-24 |
| 1. | Casting equipment for continuous or semicontinuous water casting of metal (DC casting) , in particular casting of billets of aluminium for milling purposes, comprising a casting die (1) which has an open inlet (8) for supplying molten metal and a cavity (9) with an open outlet (11) , where means of supply are provided including a continuous gap or row of holes (3) , which passes along the circumference of the casting die, for supplying water for direct cooling of the molten metal in connection with the formation of a cast billet (2) and means (4) for supplying gas or air to reduce the cooling effect, at least during the start phase of the casting process, c h a r a c t e r i s e d i n t h a t another gap or row of holes (4) is provided within the air gap (3) and predominantly in parallel with the latter, along the circumference of the casting die, for supplying air or gas in order that a skirt of air/gas (15) is formed which is designed to fully or partially deflect the skirt of water (16) and/or form an air cushion between the skirt of water (16) and the cast billet (2) . |
| 2. | Casting equipment in accordance with claim 1, c h a r a c t e r i s e d i n t h a t the air gap (4) is parallel with the cast billet. |
| 3. | Casting equipment in accordance with claim 1, c h a r a c t e r i s e d i n t h a t the air gap forms an angle (13) to the cast billet. |
| 4. | Casting equipment in accordance with claims 13, c h a r a c t e r i s e d i n t h a t the quantities of water and air can be regulated individually. |
The present invention concerns casting equipment for continuous or semi-continuous water casting of metal (DC casting) , in particular casting billets of aluminium for milling purposes, comprising a casting die which has an open inlet for the supply of molten metal and a cavity with an open outlet in which are arranged means for supplying water for direct cooling of the molten metal and means for supplying gas or air to reduce the cooling effect, at least during the start phase of the casting process.
By using various methods, it has been shown that reduced cooling in the start phase of DC cooling of metal gives a positive effect with regard to shrinkage, start cracks and surface quality. It is also probable that it has a positive effect on the formation of so-called "club feet".
In a known method which is disclosed in US patent No. 4.693.298, air is added to the water before it leaves the water gap which passes along the circumference of the casting die opening. The direction of inlet of the air in relation to the water is approximately 90° so that air bubbles are produced in the water flow, i.e. the air is mechanically mixed with the water in the water flow. By replacing some of the volume of water with air as stated here, the intention is to achieve a uniform skirt of water with less water than is normally required to maintain a uniform skirt of water and, by means of the air, to achieve an insulating effect. The addition of air will, however, with otherwise unchanged conditions, increase the speed of the water and thus also the cooling effect of a given quantity of water as the cooling water will pass through the steam phase on the surface of the cast billet more quickly. The reduction in the cooling effect by adding air to the cooling water before it leaves the water gap as stated in the above Norwegian patent application, is therefore
limited. Moreover, the solution as shown in the above patent offers few opportunities for differentiated cooling, i.e. different cooling for one area in relation to another area in the casting die.
In another similar known solution which is described in US patent no. 4.166.495, C0 2 is added to the cooling water instead of air. When the water leaves the water gap in the casting die, very small bubbles of C0 2 will be formed on account of the pressure drop and the increase in temperature. The C0 2 bubbles form a partly insulating layer between the cast billet and the cooling water so that the overall cooling area is reduced. This method produces roughly the same reduction in cooling effect as the first method mentioned but is more expensive to use as C0 2 and not air is used as the additive and as extra pressure regulating equipment and mixing equipment must be used to obtain the pressure conditions which are required to get the process to work. Nor does this method provide any opportunity for differentiated cooling in the casting die or regulation of the cooling effect.
Furthermore, Metal Progress, no. 2 of 1957, pages 70-74, describes a method for reduced or aborted cooling in which air nozzles are used, placed slightly underneath the casting die. When the cooling water flows down over the cast billet and passes the nozzles, the water is blown away from the billet so that the area underneath the air nozzles is not exposed to direct water cooling, only the area above the nozzles. This solution thus does not reduce the cooling in the start phase of the casting process and the positive effect regarding shrinkage and surface quality is small or insignificant.
With the present invention, DC casting equipment of the type mentioned in the introduction has been invented which is at least as simple as or more simple than the known solutions but which provides considerably greater flexibility with regard to regulation of the cooling effect and increased opportunity for reducing the cooling effect in the start phase of the casting
process. Furthermore, a solution has been arrived at which makes it possible to differentiate the cooling in the casting die by means of sectional control of the cooling speed so that optimal cooling conditions can be obtained, for example in the corners and on the short sides where most problems arise in the start phase of the casting process.
The present invention is characterised in that, within the water gap and predominantly in parallel with it along the circumference of the casting die, a further gap, row of holes or similar is provided to supply air or gas so that a skirt of air/gas is formed which is designed to deflect the skirt of water and/or form an air cushion between the skirt of water and the cast billet.
The dependent claims 2-4 define advantageous features of the present invention.
The present invention will be described in the following in further detail by means of examples and with reference to the drawings, of which:
Fig. 1 shows a cross-section in accordance with the present invention, Fig. 2 shows an enlarged part of the casting die shown in Fig.
1 with an illustration of the way in which the present invention works, Fig. 3 shows the same as in Fig. 2 but in accordance with an alternative design in which the air and water have a different outlet angle.
As stated, Fig. 1 shows casting equipment 10 in accordance with the present invention, comprising an inlet part with an inlet 8 for molten metal, a cavity 9 and an outlet 11 for a finished cast billet 2. The cavity is enclosed by a casting die 1 which is preferably made of metal . A support 1 , which can be moved vertically, seals the outlet at the start of the casting process and supports the cast billet as it is formed by means of
controlled downward movement. The cast metal 2, which can be a billet, ingot or similar, is cast with this equipment in defined lengths and the equipment is therefore defined as being semi- continuous.
The casting die 1 is provided with a water chamber and supply ducts for water which emerge in a gap 3, a row of holes or similar. The gap 3 passes along the full circumference of the cavity on the lower side of the casting die 1 and can be divided up into sections (not shown in detail) to enable the quantity of water to be regulated. I.e. the cooling around the circumference can be differentiated, which is particularly desirable in connection with casting billets to obtain optimum cooling conditions in the start phase of the casting process. As the water gap 3 passes all the way around the cavity, a coherent skirt of water 16 is formed around the whole billet 2 during the casting process.
The casting itself takes place by the molten metal being supplied via inlet 8 and as the support 14 is lowered the metal will gradually harden on its way down in the cavity 9, firstly in an external "shell" in the cavity during the primary cooling process and then further inside the metal billet when it passes out of the cavity outlet 11 and is cooled by water during the secondary cooling process.
The special aspect of the present invention is that supply ducts and a further gap, row of holes or similar 4 are provided within the water gap 3, on the underside of the casting die 1, to supply air or another gas. The purpose of this air gap, which preferably also passes along the full circumference of the cavity, is to procure a skirt of air 15 which can deflect the skirt of water 16 and/or form an air/gas cushion between the metal billet and the skirt of water 16.
Fig. 2 shows an enlarged part of the casting die shown in Fig. 1, more precisely the lower, left part of the casting die which illustrates the method of operation of the invention. The water
gap 3 forms an angle in relation to the longitudinal axis of the cast billet in such a way that the skirt of water 16 is in a diagonal downward direction in towards the cast billet. The air gap is arranged parallel with the cast billet; the air supplied will deflect the skirt of water (at 6) so that the water meets the ) Cast billet at a point 7 lower down. The deflection can be increased and reduced by increasing or reducing the quantity of air and/or the quantity of water. It should be noted here that the quantity of air, in similar fashion to the water, can be controlled in sections along the circumference in order to further be able to optimise cooling during the casting process.
Studies of the flow of water show that the air which deflects the skirt of water penetrates and forms bubbles in the water so that, in addition to the reduced cooling which is achieved by lowering the point at which the water meets the cast billet, further reduced cooling is achieved on account of the insulating effect of these bubbles and that parts of the water in the flow of water are blown away from'the cast billet.
Fig. '3 shows an alternative solution in accordance with the present invention in which the air gap 4 forms an angle 13 to the cast billet. This causes the skirt of air 15 to meet the cast billet just above the point at which the skirt of water 16 meets the billet so that an air cushion is formed between the cast billet and the water.
It should be noted that the present invention as defined in the claims is not limited to the angles of the water gap and the air gap in the figures. Nor are there any restrictions with regard to how much air or water can be supplied or the ratio between the quantities of these two media. Thus the present invention as defined in the claims can be varied with regard to the quantity of air and the quantity of water and the angles so that optimal, differentiated cooling with full or partial deflection of the skirt of water is achieved. This also means that both the air and the water can be supplied intermittently, i.e. in pulses.