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(11) | EP 0 372 946 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Lubrication of continuous casting moulds |
| (57) A continuous casting mould apparatus is provided which includes a liquid reservoir
(30) for holding lubricating agent, the agent being applied through channels (29)
over the surface of the mould walls (11) by passage from the reservoir (30). The reservoir
(30) is adapted to hold a body of lubricant in a lower region thereof with the lubricant
covering all of a plurality of outlets (29) from the reservoir (30) to the mould
walls (11). A gas cushion is provided above the body of lubricant whereby a uniform
lubricant flow is discharged through all outlets (29), this gas cushion being generated
by feeding lubricant into the reservoir under pressure. |
Field of the invention
[0001] This invention relates to continuous casting moulds, and more particularly to casting moulds having effective lubrication of the mould surface.
[0002] Casting moulds are used to shape molten metal and to extract heat from this metal to form a solid casting or ingot. These moulds have two basic characteristics. The first is to extract heat to effect solidification, and the second is to provide a parting agent or lubricant to prevent adherence between the molten metal and the mould. The distribution of the lubricant over the surface of the inner mould wall has a substantial effect on the surface quality of the ingot.
[0003] For example, in continuous casting in insulated or hot top moulds, it is commonplace to use an insulating head formed of a heat resistant and insulating material, such as a refractory material, which resists contact with the molten metal to be cast. The insulating head is located at a position contiguous with or adjacent to and extending around the periphery of the top portion of the mould wall. The use of an insulating head provides for a relatively constant withdrawal of heat from the molten metal during the casting operation especially when using a short mould wall.
[0004] The lubrication of the walls of moulds with insulating heads has proven to be difficult. Thus, the point of contact between the molten metal and cooled mould wall where the lubricant must be applied is not readily accessible but is covered by the insulating head.
[0005] Lossack et al U.S. Patent 4,057,100, issued November 8, 1977, describes a lubricating system for a continuous casting mould which represents one attempt at overcoming the problems of uniform delivery of lubricant to the mould surface. They have provided a lubricant reservoir within the mould itself, which is arranged such that gravity flow of liquid cannot occur between the reservoir and the mould surface. This design depends upon periodic small pressure changes within the meniscus area between the molten metal and the top of the mould cavity to draw lubricant from the reservoir.
[0006] It is an object of the present invention to provide an improved lubricant delivery system which will more uniformly deliver lubricant to the mould surface under all conditions.
Summary of the Invention
[0007] According to the present invention an apparatus is provided for continuously casting molten metal. This includes a mould for effecting solidification of the molten metal into a formed metal product, means adjacent to an inlet portion of the mould for feeding the molten metal into the mould and means for delivering a lubricating agent to a surface of the mould contacting the molten metal to substantially prevent adhesion of any solidified metal on the surface. A liquid reservoir is provided in the apparatus for holding the lubricating agent, this reservoir having an inlet for lubricating agent and a an outlet or outlets for discharging lubricating agent to the mould surface. This reservoir is adapted to provide a body of lubricant covering all of the outlets and a gas cushion is provided above the body of lubricant whereby a uniform lubricant flow is provided in all outlets. This results in a very uniform delivery of lubricant to the mould surface. The gas cushion is provided by the feeding of the lubricant into the reservoir above or at the top thereof.
[0008] According to a preferred embodiment, the reservoir has converging, sloping side walls in the bottom portion thereof and a plurality of lubricant conduits extend either upwardly or downwardly between the bottom region of the reservoir and oil transfer passages to the mould surface.
[0009] The lubricating agent delivery system may be used with a variety of forming systems, including extrusion, sheeting and insulated or hot top moulds. It is of particular value with a casting device having a mould plate having an inner, axially extending wall defining a mould cavity, and an insulating head member formed of a heat insulating material having a first portion extending transversely over at least a part of the mould cavity and a second portion contiguous with the mould upper surface. The lubricant reservoir may be formed as a cavity within a frame member used to support the insulating head.
[0010] The lubricating agent may be transferred from the reservoir to the mould cavity by way of lateral bores within the mould plate or by way of an oil plate mounted between the mould upper surface and the insulating head member. An annular groove is preferably provided in the mould upper surface adjacent the edge of the oil plate remote from the mould cavity and this annular groove is adapted to transfer lubricant from the lubricant passageways to laterally extending grooves in the bottom face of the oil plate or in the top of the mould plate. When grooves in the top of the mould plate are used, some form of thin plate or barrier is still needed between the grooves and the insulating head to prevent the oil from migrating into the insulation.
[0011] The oil transfer grooves may be replaced by a porous oil plate. Again with the porous plate, some form of barrier must be provided between the top of the porous plate and the insulating head to prevent migration of oil. This barrier must be impervious to oil, and may, for instance, be in the form of a tape or thin plate.
[0012] The invention also relates to a process for producing metal ingot by a continuous casting process. Such process typically comprises the steps of:
(a) providing means for supplying molten metal to a mould adjacent an inlet portion of the mould,
(b) feeding molten metal into the mould,
(c) at least partially solidifying the molten metal within the mould and
(d) withdrawing the at least partially solidified molten metal from the mould.
[0013] The improvement according to this invention comprises a method of delivering lubricating oil to the mould surface in an exceptionally uniform manner. This is achieved by feeding the oil from a reservoir having a gas cushion above the body of oil in the reservoir; the gas cushion serving to maintain a constant pressure on the oil.
[0014] According to a preferred feature, the improved lubricant delivery system of this invention is used with a direct chill casting process comprising the steps of:
(a) pouring molten metal into an open-ended thermally insulated annular top section having a flat bottom surface;
(b) allowing the molten metal to descend from the hot top section into a lower chilled annular mould section axially aligned with the hot top section and bring the molten metal into contact with the chilled mould section to produce a solidified peripheral layer or skin; and
(c) withdrawing the metal continuously from the chilled mould section at a predetermined casting rate and applying streams of liquid coolant directly to the surface of the solidified peripheral layer of metal emerging from the chilled mould section.
Brief description of the drawings
[0015] The invention will be more fully understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:
Figure 1 is a perspective view of a mould assembly according to invention;
Figure 2 is a sectional view of a mould assembly according to the invention;
Figure 3 is an enlarged sectional view of the lubricant delivery system;
Figure 4 is an enlarged sectional view of an alternative form of the lubricant delivery system;
Figure 5 is an enlarged sectional view of a further alternative lubricant delivery system;
Figure 6 is an enlarged sectional view of a mould incorporating a lubricant reservoir; and
Figure 7 is an enlarged sectional view of a mould showing a further embodiment of the reservoir of Figure 6.
Description of the Preferred Embodiments
[0016] It will be seen from Figures 1 and 2 that the mould assembly has an open-ended rectangular body configuration. The mould plate 10 has a short vertical mould face 11, a top face 12 and a bottom face 13. This plate is conveniently manufactured from aluminum and includes a coolant channel 15 in the form of a slot or series of laterally spaced bores each with plug 44 at the outer end and with a plurality of laterally spaced dispersal channels 16 communicating between coolant channel or channels 15 and the bottom of the mould plate 10.
[0017] The coolant channel or channels 15 are flow connected by way of a plurality of holes 17 to a coolant manifold 18 mounted on the bottom face 13 of mould plate 10. The coolant manifold 18 is manufactured with heavy side walls 19 and a bottom wall 20. The heavy side walls 19 of the coolant manifold serve a significant structural purpose in that they provide rigidity to the mould plate 10. The coolant manifold 18 is mounted to the bottom of the mould plate 10 by means of studs or bolts 23 which also extend through frame members 27. The faces between the manifold and mould plate are sealed by O-rings.
[0018] With this system, water flows under pressure into manifold reservoir 40 through inlet 21 and from here flows through screen 41 and upwardly through hole 42 in a coolant regulating plate 14. This regulating plate serves to direct the flow of coolant upwardly through holes 17 in a uniform manner. The coolant then flows along the channel or channels 15 extending parallel to the top face 12 of the mould plate 10. Preferably a series of laterally spaced bores are used for the channels, e.g. bores having a diameter of about 4 mm and spaced from each other by a distance of about 6 mm.
[0019] It is also possible to replace the coolant chamber by a chamber or chambers separated from the mould. With this arrangement, communication between individual chambers permits the coolant flow.
[0020] The inlet portion of the mould assembly includes an insulating head 33 which generally conforms to the shape of the mould with which it is associated. This insulating head is formed of a heat resistant and insulating material, such a refractory material, which will not deteriorate when in contact with the molten metal to be cast. This head 33 is located at a position continguous with or adjacent to and extending around the periphery of the top portion of the mould wall face 11. The use of such insulating head provides for relatively constant withdrawal of heat from the molten metal during the casting operation when using a short mould wall. The insulating material 33 is held in place by frame members 27 and top plates 35. These may be made from aluminum and are preferably compressed against the mould plate 10 by means of stud 23. Each frame member 27 includes recesses 28 which hold O-rings to provide a seal against the top face of the mould plate.
[0021] For casting an ingot, molten aluminum 37 is fed into the insulating head 33 and is chilled while passing moulding plate wall face 11 sufficiently to form an outer skin. This is further cooled by a water spray from coolant dispersal passages 16 to form an ingot 36. The water spray is directed by means of baffle 38 operated by an actuator mechanism 39. The baffle is pivotally mounted and is spring biased by spring mechanism 43 in a direction to move away from the ingot 36.
Lubrication System
[0022] The oil delivery system of the invention is illustrated in Figures 3-5 and is intended to provide a uniform distribution of oil on the mould face under all moulding conditions. In the embodiment of Figure 3, an oil plate 31 is sandwiched between frame member 27 and insulating member 33 on the one side and the mould plate 10 on the other side. This oil plate 31 flow connects at the inner edge thereof by way of oil channels 29 to an oil reservoir or cavity 30 formed within the frame member 27. Oil is supplied to the reservoir 30 under pressure through the oil inlet connector 32, preferably through a valve assembly connected to the inlet connector.
[0023] The reservoir 30 preferably has inwardly and downwardly tapering side walls 45 and 46 in a bottom region. The bottom end 47 of reservoir 30 contains a plurality of outlet openings connected to a plurality of downwardly sloping lubricant passageways 29. An annular groove 50 is preferably provided in the top face of mould 11 adjacent the edge of the oil plate 31 which is remote from the mould surface 11. This permits oil to accumulate from the passageways 29 and to be transferred into and through the grooves (of known type) formed in the bottom face of the oil plate 31.
[0024] In the embodiment of Figure 4, grooves 48 are formed on the top face 12 of mould plate 10 and the oil plate 31 is formed without grooves. With this arrangement, the plate simply serves as a barrier between the grooves and the insulation.
[0025] An alternative arrangement for oil delivery to the mould face is shown in Figure 5. It includes an oil reservoir 30 with outlet oil channels 29. The oil channels 29 are connected via an annular groove 62 to lateral oil bores 60. These oil bores 60 have a diameter of about 2 mm at a lateral spacing of about 25 mm. One end of each bore 60 is closed by a closure plug 61 while the other end connects to an outlet passage 63 having a diameter of about 0.9 mm. This directs oil at spaced locations into the corner between mould face 11 and the bottom of insulating head 33.
[0026] There are a number of advantages in arranging the reservoir 30 with the inclined lower walls 45 and 46 and the plurality of passageways 29 extending from or near the bottom of the reservoir. Thus, when lubricant is fed into the reservoir under pressure, it quickly distributes to the bottom part between the inclined walls. As soon as the last outlet hole in the bottom 47 is covered by the lubricant, a uniform pressure is realized within the reservoir 30 which yields uniform lubricant flow. The pumping of additional fluid into the reservoir compresses the low viscosity air above the fluid in the reservoir, forming an air cushion, so that the pressure distribution is uniform in all outlet channels.
[0027] It is also possible to replace the oil reservoir 30 within frame member 27 by an external reservoir which functions in a manner similar to reservoir 30.
[0028] Figures 6 and 7 show standard casting moulds incorporating the present invention. These moulds each include a top portion 65, an edge portion 66 with a mould face 11 and a bottom portion 67, with a bottom coolant outlet 16. In the embodiment of Figure 6, a lubricant reservoir 30 is incorporated in the mould wall with a lubricant outlet channel 29 extending in an upward direction between a bottom region of reservoir 30 and mould face 11. Figure 7 shows a separate plate 68 mounted on the top portion 65 of the mould with the reservoir 30 formed within plate 68. The lubricant outlet channel 29 extends downwardly from a bottom region of reservoir 30 to the interface of the top edge of mould face 11 and plate 68. In Figures 6 and 7 lubricant is fed under pressure into reservoir 30 through inlet connector 32.
(a) a mould for effecting solidification of the molten metal into a formed metal product;
(b) means adjacent to an inlet portion of said mould for feeding said molten metal into the mould;
(c) means for delivering a lubricating agent to a surface of said mould contacting the molten metal to substantially prevent adhesion of any solidified metal on said surface, and
(d) a reservoir for holding liquid lubricating agent, said reservoir having an inlet for lubricating agent and outlets for discharging lubricating agent to the delivery means and said reservoir being adapted to provide a body of lubricant covering said outlets and a gas cushion above the body of lubricant whereby a uniform lubricant flow is provided in all outlets.
(a) a mould plate having a longitudinal axis, an inner, axially extending wall defining a mould chamber, and an upper surface;
(b) an insulating head member formed of a heat insulating material having a first portion extending transversely over at least a part of said mould chamber and a second portion contiguous with the mould upper surface;
(c) oil delivery means adapted to transfer lubricant laterally to the mould chamber, and
(d) a reservoir for holding liquid lubricating agent, said reservoir having an inlet for lubricating agent and outlets for discharging lubricating agent to the delivery means and said reservoir being adapted to provide a body of lubricant covering said outlets and a gas cushion above the body of lubricant whereby a uniform lubricant flow is provided in all outlets.
(a) providing means for supplying molten metal to a mould adjacent an inlet portion of the mould,
(b) feeding molten metal into the mould,
(c) at least partially solidifying the molten metal within the mould and
(d) withdrawing the at least partially solidified molten metal from the mould,
the improvement which comprises providing a reservoir holding liquid lubricating agent
with a gas cushion above the body of lubricant in the reservoir and transferring lubricating
agent from said reservoir to a mould surface contacting the molten metal in a uniform
manner under the action of the gas cushion.