Patent Application
20080283212
The present invention relates to a gas and lubricant delivery apparatus and more particularly to a lubricant delivery element, in particular for direct chill continuous casting hot top moulds.
One known method of casting metal ingots is that of direct chill continuous casting using a hot top mould. In this method, a bath of molten metal is located directly above or next to the mould cavity, through which the molten metal is either drawn horizontally or flows vertically under gravity. The mould body is continuously cooled using a coolant in a chamber around the mould, thus chilling the molten metal to form the ingots. The mould body also acts as an outlet for the direct chill water spray.
A lubricant is introduced into the mould cavity to improve the surface quality of the ingots by preventing the sticking of the metal to the inside wall of the mould.
In U.S. Pat. No. 4,157,728 it was found that the surface quality of non-ferrous metal ingots cast using this method is known to be improved by the introduction of gas into the mould cavity just below the hot top containing the molten metal bath. This was done using an array of small holes which delivered oil to the molten metal entry end of the mould cavity (ie. the top in the vertical case), with radial slots used to deliver the air.
Subsequently, various means of delivering the lubricant and gas into the mould cavity have been disclosed. In one version, disclosed in U.S. Pat. No. 4,598,763, air and oil are introduced into the mould cavity through a porous graphite ring whose primary function is to act as a mould liner to form the casting surface. This arrangement involves the introduction of the air and oil in contact with the molten metal at the point where the molten metal solidifies in the mould. This results in one significant problem, being that tar-like deposits build up within the graphite due to the vaporisation of the oil, thus restricting the flow of both air and oil. A further problem with this arrangement is that high delivery pressures are required to force the oil through the graphite ring, increasing the manufacturing and operating costs of the hot top mould.
In another version, disclosed in U.S. Pat. No. 5,320,159, oil and air are introduced into the mould cavity via grooves in the top and bottom of a distribution plate. Circumferential channels in the mould body are provided to deliver oil and air to the radial grooves in the distribution plate. However, the grooves in the distribution plate may suffer from molten metal entry. After entering the grooves the metal solidifies, resulting in tearing of the billet surface and damage to the distribution plate. This problem may be minimised by reducing the diameter of the grooves (to as little as 100-200 micron), however, the manufacturing required is costly and ultimately it is not sufficient to completely prevent metal entry should the gas pressure in the mould cavity be insufficient.
A further problem with using a distribution plate, is that because oil is introduced to the distribution plate at one point from the circumferential channel, this results in a region of low oil flow directly opposite the feed point and hence an uneven distribution of oil occurs in the mould cavity. Similar problems may also occur with the air distribution.
According to a first aspect of the present invention there is provided a lubricant delivery element for delivering lubricant into a cavity, the lubricant distribution element comprising a thin element of porous material for delivering lubricant into the cavity through the element.
Preferably, the lubricant distribution element has a thickness of less than approximately 5 mm.
Preferably, the lubricant distribution element has a thickness of 0.1 to 5 mm, more preferably, 1-5 mm, more preferably 2-3 mm.
Preferably, the lubricant distribution element has a thickness of approximately 1.5 mm.
The lubricant distribution element may however, have a thickness of less than 0.1 mm.
The lubricant distribution element may have at least one groove formed in the surface of the element. When present, the groove may assist in the circumferential distribution of lubricant through the element for even flow of lubricant from the circumference or sides of the distribution element.
Preferably, the groove extends substantially around the circumference or the sides of the element.
Preferably, the groove is approximately 0.5 mm deep.
Preferably, the porous material comprises an agglomerate of particles.
Preferably, the particles have an average diameter of less than approximately 0.25 mm.
Preferably, the particles have an average diameter of 10 to 100 micron.
More preferably, the particles have an average diameter of 40 to 70 micron.
The average diameter of the particles may be less than 10 microns.
Preferably, the average diameter of the pores in the porous material is less than the size of the particles.
Preferably, the porous material has a porosity of 10 to 70%, more preferably 20 to 40%.
The porosity of the material may change across the width of the lubricant distribution element.
Preferably, the porous material is of the kind commonly used in powder metallurgy applications.
Preferably, the porous material is aluminium, iron, copper or sintered bronze, more preferably, sintered bronze. In this embodiment, the thin element of porous material is manufactured by sintering bronze powder in a steel die at high temperature.
The porous material may be a porous ceramic.
The porous material may also be graphite. However, if the porous material is graphite, then the lubricant distribution element is preferably provided with a strengthening means. The strengthening means may be, for example, a thin element of metal laminated to the graphite.
The porous material may be a porous plastic, such as polytetrafluoroethylene.
Preferably, the lubricant distribution element is shaped so that in use, it extends around the perimeter of the cavity.
Typically, the lubricant distribution element is in the shape of an annular disc. The annulus of the annular disc may be round or non-round in shape.
The lubricant distribution element may comprise a single element or a number of parts which, in use, abut one another to form the lubricant distribution element.
Preferably, the lubricant delivery element further comprises a sealant for sealing the lubricant distribution element.
Preferably, the sealant seals at least portions of the horizontal surfaces of the element. This forces the lubricant to flow through the element as opposed to over the surface.
Preferably, the sealant seals at least a portion of the surface of the lubricant distribution element which is not arranged to be exposed to the cavity.
Preferably, the sealant comprises a layer of varnish on at least a portion of the surface of the lubricant distribution element.
Alternatively, the sealant may comprise a layer of impermeable foil on at least a portion of the surface of the lubricant distribution element.
Alternatively, the sealant may comprise a layer of settable rubber. The settable rubber is applied as a paste which sets after application.
The sealant may comprise a combination of layers of any two or more of varnish, impermeable foil and a settable rubber.
Alternatively, the sealant comprises a fibre gasket(s).
Alternatively, the sealant comprises an O-ring.
Alternatively, the sealant comprises a flat surface.
Preferably, the flat surface is provided by a metal plate. The flat surface may, alternatively, be provided by the top of the mould body.
According to a second aspect of the present invention there is provided a gas delivery element for delivering gas into a cavity, the element comprising a thin element of porous material for delivering gas into the cavity through the element.
Preferably, the gas distribution element has one or more of the features of the lubricant distribution element according to the first aspect.
According to a third aspect of the present invention there is provided a gas and lubricant delivery apparatus for delivering gas and lubricant into a cavity, the apparatus comprising a lubricant distribution element according to the first aspect of the present invention, and a gas distribution element for delivering gas into the cavity.
Preferably, the gas distribution element is substantially similar to the lubricant distribution element. In this embodiment gas is delivered into the cavity through the gas distribution element.
The gas distribution element may be integrally formed with the lubricant distribution element.
In this embodiment, the gas distribution element preferably comprises radial grooves and at least one circumferential groove formed in the upper surface of the lubricant distribution element.
Alternatively, the gas distribution element may take the form of a distribution plate, which may be part of the top of the cavity wall or be a separate plate.
In this embodiment, preferably, the distribution plate has a first set of grooves formed in the top surface of the plate for delivery of gas into the cavity.
Preferably, the distribution plate also has a second set of grooves formed in the top surface to connect the first set of grooves to one another for distribution of the gas to all the grooves in the first set.
Preferably, the distribution plate is manufactured from a metal, such as, for example steel or aluminium.
Alternatively, the distribution plate is manufactured from a ceramic.
Alternatively, the distribution plate is manufactured from a plastic, such as polytetrafluoro-ethylene.
Preferably, the gas distribution element is shaped to extend around the perimeter of the cavity.
Preferably, the gas distribution element is of a similar shape to the lubricant distribution element.
Typically, the gas distribution element is in the shape of an annular disc. The annulus of the annular disc may be round or non-round in shape.
Preferably, the gas distribution element is arranged, in use, to be located above the lubricant distribution element.
Preferably, the gas distribution element has a cut away portion in its lower surface into which the lubricant distribution element is adapted to fit snugly.
The gas distribution element may comprise a single element or a number of parts which, in use, abut one another to form the gas distribution element.
Preferably, the apparatus for delivering gas and lubricant further comprises a sealant for sealing the lubricant distribution element and the gas distribution element.
Preferably, the sealant seals the gas distribution element from the lubricant distribution element.
Preferably, the sealant seals at least a portion of the surface of the gas and lubricant distribution elements.
Preferably, the sealant comprises a layer of varnish and/or impermeable foil and/or settable rubber and/or a fibre gasket(s) on at least some of the surface of the gas and lubricant elements.
Alternatively, the sealant may comprise an O-ring.
Alternatively, the sealant may comprise a flat surface.
Preferably, the sealant further comprises a sealing plate overlaying the gas distribution element for sealing the top of the gas distribution element.
According to a fourth aspect of the present invention, there is provided a hot top mould for direct chill continuous casting of metal ingots comprising a mould having a mould body and a cavity defined in the mould body and a gas and lubricant delivery apparatus for delivering gas and lubricant to the mould cavity according to any one or more features of the third aspect of the invention.
Preferably, the gas and lubricant delivery apparatus is located proximate the molten metal entry end of the mould.
Preferably, the gas and lubricant delivery apparatus is located above the level of the mould body at which the molten metal solidifies.
Preferably, the gas and lubricant delivery apparatus is located on top of the mould body.
Preferably, the mould body has a space therein for the flow of coolant through the mould body.
Preferably, the space for the flow of coolant is shaped to flow the coolant close to the gas and lubricant delivery apparatus.
Preferably, the hot top mould further comprises a supply mechanism for supplying gas and lubricant to the gas and lubricant delivery apparatus.
Preferably, the supply mechanism comprises gas and lubricant supply channels formed separately in the top of the mould, the supply channels being in fluid connection with the gas and lubricant delivery apparatus.
Alternatively, the supply mechanism may comprise pipe fittings through the mould body and connected directly to the gas and lubricant delivery apparatus.
Preferably, the hot top mould further comprises a molten metal bath for feeding molten metal to the mould cavity.
Preferably, the hot top mould further comprises an orifice plate, which spaces the molten metal bath from the mould.
The mould body may or may not have a graphite insert located just below the gas and lubricant delivery apparatus.
Preferably, the metal is a non-ferrous metal such as aluminium, magnesium, copper or zinc and their alloys.
According to a fifth aspect of the present invention, there is provided a hot top mould for direct chill continuous casting of metal ingots-comprising a mould having a mould body and a cavity defined in the mould body, and a lubricant delivery element for delivering lubricant to the mould cavity according to the first aspect of the present invention.
A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Referring firstly to
The hot top mould 10 also comprises a gas and lubricant delivery apparatus 13 according to preferred embodiments of the present invention located at the top of the mould body 14 (ie. proximate the molten metal entry end of the mould 12 and above the level of the mould body 14 at which the molten metal contacts the mould body 14) for the delivery of gas (typically air) and lubricant (typically oil) to the mould cavity 15.
The mould body 14 in use is cooled using a coolant (typically water) flowing through a space 17 in the mould body 14 in order to solidify the molten metal. The mould body 14 preferably, but not necessarily, has an insert 27 manufactured of graphite.
The gas and lubricant delivery apparatus 13 comprises a lubricant distribution element 20 and a gas distribution element 21. The lubricant distribution element 20 is an annular disc of porous material through which lubricant is delivered to the mould cavity 15. Although the annulus of the annular disc is shown as being round, it may be non-round. Furthermore, the lubricant distribution element 20 may comprise a single element or a number of parts which, in use, abut one another to form the lubricant distribution element 20. The porous annular disc is thin, having a thickness of approximately 1 to 5 mm. This range represents a balance between the disc being as thin as practical to fit into the hot top mould 10 and the pressure required to force the oil through the disc into the mould cavity 15. However, it may be possible to use a much thinner disc of, for example, less than 0.1 mm. In an alternative embodiment (not shown here) the disc has a thickness of at least approximately 1.5 mm with a 0.5 mm groove formed in the top surface of the disc to further improve the distribution of oil around the circumference of the disc for even circumferential flow of lubricant and gas from the apparatus 13.
The space 17 in the mould body 14 for the coolant is shaped to flow the coolant close to the gas and lubricant delivery apparatus 13. Because the lubricant distribution element 20 is so thin it is readily cooled by the coolant cooling the mould body 14. This substantially prevents the lubricant, while it is inside the distribution element 20, from reaching a temperature where it will vaporise and decompose into tar-like deposits and thus restrict its flow through the lubricant distribution element 20.
The lubricant distribution element 20 in the form of a porous annular disc may be manufactured from any materials commonly used in powder metallurgy applications; such as aluminium, iron, copper or sintered bronze. Sintered bronze is a preferable material as it provides the required strength and flexibility and is readily and cost effectively manufactured into any shape, including thin annular discs by sintering bronze powder in a steel die at high temperatures. In addition, sintered bronze allows for good control over the porosity and pore size, particularly compared to graphite. Use of porous ceramic materials to form the disc may also be possible. Another alternative material which could be used is a porous plastic such as polytetrafluoroethylene. Furthermore, it may also be possible to form the thin disc of graphite of adequate porosity. In this case, the graphite would need to be strengthened by, for example, lamination to a thin metal support disc as of itself, graphite would not have the required strength.
In forming the disc, it has been found that as the particle size of the material forming the porous disc increases, the uniformity of circumferential oil distribution throughout the disc, in use, decreases. The diameter of the particles used to form the disc is therefore less than approximately 0.25 mm. Particles smaller than approximately 10-20 micron in diameter may be used to form a disc, however, at smaller particle sizes, the pressure required to force the oil through the porous disc may become too high for effective operation of the lubricant and gas delivery apparatus 13. The diameter of the pores is generally approximately 20-40 micron. However, for discs manufactured of smaller particles, this diameter may be reduced. The porosity of the thin disc is 10 to 70%, preferably, 20 to 40%. In an alternative embodiment, the disc has a gradient of changing porosity across its width.
Because the diameter of the pores/porosity is so small the surface tension of the molten metal acts to prevent it from entering the pores and damaging the lubricant distribution element 20.
Referring now also to
In an alternative embodiment (not shown), the gas distribution element 21 is integrally formed with the lubricant distribution element 20 by forming radial grooves and at least one circumferential groove on the upper surface of the lubricant distribution element 20 which is in the form of an annular disc of porous material.
Referring more specifically again to
Thus, the gas and lubricant delivery apparatus 13 is arranged so that it is highly unlikely to be contacted by molten metal. Instead, the molten metal meniscus will contact the graphite liner 27 which is below the gas and lubricant delivery apparatus 13. This means that the apparatus 13 is not directly heated by the molten metal and hence the likelihood of lubricant vaporisation is further reduced. In use, the lubricant is allowed to enter the mould cavity 15 as a liquid and flow down a part of the mould body 15 before reaching the solidifying molten metal.
The supply of gas and lubricant to the gas and lubricant delivery apparatus 13 is provided by gas and lubricant supply channels 30,31 respectively formed in the top of the mould body 14. Alternatively, pipe fittings through the mould body 14 may be used to supply lubricant and/or gas directly to the gas and lubricant delivery apparatus 13. A first O-ring 32 seals the lubricant and gas supply channels 30,31 from one another. A second O-ring 33 seals the entire gas and lubricant delivery apparatus 13 at the boundary between the locking plate 26 and the top of the mould body 14.
Further sealing of the lubricant and gas distribution elements 20,21 may be provided. In
Referring now to
In the embodiment shown in
Rear surfaces 136 of both the lubricant and gas distribution elements 120,121 are sealed selectively using an impermeable foil, varnish layer, or a thin fibre gasket. The lower surface 132 of the lubricant distribution element 120 is similarly sealed. Notably, the lower surface 137 is not sealed where it is located above the lubricant supply channel 132 so that lubricant can be fed to the lubricant distribution element 120 from the channel 132.
Referring now to
In this embodiment of the gas and lubricant delivery apparatus 213, the gas and lubricant distribution elements 220,221 are shown extending beyond the mould body 214 defined by the graphite liner 227 into the mould cavity 215. Furthermore, the gas distribution element 221 overhangs the lubricant distribution element 220. This assists in directing the flow of gas perpendicular to the mould bodies 214. The gas distribution element 221 in
Referring now to
The delivery apparatus 313 comprises lubricant and gas distribution elements 320 and 321, respectively. The top and bottom surfaces of the lubricant distribution element 320 are sealed by thin fibre gaskets 355, 356.
The gas distribution element 321 is different from previously described embodiments in that the radial and circumferential grooves 340, 342 for delivering the gas to the mould cavity 315 are formed in the lower surface 344 of the gas distribution element 321 as opposed to the top surface. As shown specifically in
The delivery apparatus 313 is also shown comprising a locating pin 357 for correctly positioning the gas and lubricant distribution elements 320, 321 within the hot top mould 310.
A hot top mould 10 according to preferred embodiments of the invention was used to cast a billet of aluminium alloy 6063. The lubricant distribution element 20 in the form of an annular disc was formed from particles of sintered bronze of between 45 and 63 micron in diameter. The resulting disc had a porosity of 45-50%. The disc had a thickness of approximately 1.5 mm. The gas distribution element 21 comprised a metal disc having radial grooves machined on one surface. Air was used as the gas and oil as the lubricant.
A single billet with a diameter of 152 mm was cast under the following conditions:
Casting Speed: 150 mm/min
Coolant Water Flowrate: 75 L/min
Metal Head: 75 mm
Air Pressure: 2.5 kPa
Melt Temperature: 670-710° C.
Oil Flowrate: 5 mL/min
The resulting casting had a surface which was free of any defects as shown in
A test mould was set up in the lab to test a gas and lubricant delivery apparatus 13 according to embodiments of the present invention, in which the lubricant distribution element 20 and the gas distribution element 21 are formed of a porous plastic material, specifically polytetrafluoroethylene (“PTFE”).
A very uniform circumferential distribution of gas was obtained at a flow rate of 2.0 litres per minute. The gas pressure required to achieve this flow was low, approximately 20-30 mbar, High gas flows did not change the distribution which remained uniform around the circumference of the mould.
On initial connection of the lubricant supplied to the mould, gas was found to be bubbling back through the lubricant supply. This was traced to the gas supply and was due to a portion of the surface of the gas distribution element 21 not being coated with silicon. This portion of the surface was subsequently coated and as a result no bypass of gas to the oil supply line occurred. At a head height of 1000 mm, a flow rate of 1 ml/min of lubricant to the lubricant distribution element 21 was obtained. Even circumferential flow was obtained after about 10 minutes.
A hot top mould 10 according to a preferred embodiment of the invention was used to cast a billet of magnesium alloy AZ80. The mould diameter was 203 mm. The nominal composition for AZ80 is 8.5% Aluminium and 0.5% Zinc, with the balance magnesium. Table 1 below provides details of the operating conditions usd for the casting of the AZ80 billet.
The alloy was successfully cast to a length of approximately 1380 mm.
In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, ie. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.
It is to be clearly understood that although prior art publications are referred to herein, this reference does not constitute an admission that any of these documents forms part of the common general knowledge in the art in Australia or in any other country.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005906692 | Nov 2005 | AU | national |
| PCT/AU2006/001820 | Nov 2006 | AU | national |
