MOLD FOR CONTINUOUS CASTING OF METAL STRANDS

Abstract

A mold for semi-continuous casting of metal strands from liquid metal, comprising a mold body provided with at least one mold cavity. The at least one mold cavity comprises a liquid metal inlet defined by a nozzle plate; an insert defining a perimeter wall intended to be in contact with the metal leaving said liquid metal inlet; a mold outlet; a plurality of spray nozzles for spraying cooling fluid onto the metal strand, the spray nozzles being preferably provided in the insert. The mold body is provided with a channel for cooling fluid. The insert is removable and is made from a metallic material. The mold is useful for casting aluminium strands.

Claims

1-20. (canceled)

21. A mold for semi-continuous casting of metal strands from liquid metal, the mold comprising: a mold body having a channel for cooling fluid and at least one mold cavity that includes: a liquid metal inlet defined by a nozzle plate, a removable insert defining a perimeter wall for contact with the liquid metal leaving the liquid metal inlet, the removable insert being formed of a metallic material selected from the group formed by aluminium, aluminium alloys, copper, and copper alloys, a mold outlet, and a plurality of spray nozzles provided in the removable insert for spraying cooling fluid onto the metal strands.

22. The mold of claim 21, wherein the mold body further has a removable front plate.

23. The mold of claim 22, wherein the channel is arranged in the mold body or is adjacent to the mold body.

24. The mold of claim 23, wherein the mold body, the removable insert, and the front plate define a waterbox that forms the channel.

25. The mold of claim 24, wherein the channel is arranged: in the mold body, or between the mold body and the removable insert, or between the mold body, the removable insert, and the removable front plate.

26. The mold of claim 25, further comprising a removable insert clamping plate fixed onto the front plate to clamp the removable insert against the nozzle plate.

27. The mold of claim 26, wherein the removable insert is clamped between the nozzle plate using a nozzle clamping plate, and the mold body using an insert clamping plate.

28. The mold of claim 27, wherein the nozzle plate is formed from a non-metallic inorganic material.

29. The mold of claim 28, further comprising at least one conduit provided in the removable insert, the at least one conduit being in fluid connection with a connection interface for a lubricant fluid.

30. The mold of claim 29, wherein the at least one conduit is operable to admit the lubricant fluid between the removable insert and the nozzle plate.

31. The mold of claim 30, wherein the at least one mold cavity comprises a plurality of mold cavities.

32. The mold of claim 31, wherein the waterbox extends substantially over the entire mold.

33. The mold of claim 32, wherein each mold cavity is provided with means for oil pressure adjustment and/or oil throughput.

34. Use of the mold of claim 21 for casting of metal strands with a non-circular cross-section, the metal strands being formed as foundry ingots.

35. The use of claim 34, further comprising a plurality of mold cavities arranged in a row, for horizontal casting of the metal strands.

36. The use of claim 35, wherein the metal strands are cast in aluminium or aluminum alloys.

37. The use of claim 35, wherein during casting: cooling fluid is circulated in the cooling channels and/or the waterbox, and/or cooling fluid is sprayed onto the metal strand emerging from the mold outlet using the spray nozzles, and/or lubricant fluid is admitted through the conduits on the surface of the metal strand.

38. A method of maintaining or repairing the mold of claim 21, the method comprising: removing the insert clamping plate to remove the removable insert for maintenance, repair, or replacement; installing a new removable insert or a renovated removable insert; and reinstalling and fastening the insert clamping plate.

39. The method of claim 38, further comprising: before removing the insert clamping plate, unlocking fixation means of the insert clamping plate; after removing the insert clamping plate, cleaning accessible surfaces of the mold cavity; wherein installing the new removable insert or the renovated removable insert comprises installing the new removable insert or the renovated removable insert and an O-ring; wherein reinstalling and fastening the insert clamping plate comprises reinstalling the insert clamping plate and then fastening the fixation means to fix the insert clamping plate in position.

40. A method for changing the nozzle plate of the mold of claim 21, the method comprising: unlocking fixation means of the nozzle clamping plate; removing the nozzle clamping plate; removing the nozzle plate; installing a new nozzle plate or a renovated nozzle plate; reinstalling the nozzle clamping plate; and fixing the nozzle clamping plate in position by fastening the fixation means.

Description

DRAWINGS

[0045] FIGS. 1 to 5 represent various aspects and embodiments of the invention. They are given for illustration only and are not meant to limit the scope of the invention.

[0046] FIG. 1 shows a perspective front view of a multiple-strand mold for ingots with substantially rectangular cross section according to the invention, capable of producing up to ten cast bars.

[0047] FIG. 2 shows an exploded and enlarged perspective front view of the multiple-strand mold of FIG. 1.

[0048] FIG. 3 shows a perspective rear view of the mold of FIG. 1.

[0049] FIG. 4 shows an exploded and enlarged perspective rear view of the mold of FIG. 1.

[0050] FIG. 5 shows a cross section of the mold according to FIG. 1.

DESCRIPTION

[0051] The term aluminium as used herein includes aluminium alloys, and the term copper as used herein includes copper alloys.

[0052] Typical molds according to the invention will be described here in relation with FIGS. 1 to 5.

[0053] The mold 1 shown on FIG. 1 in a perspective front view comprises ten mold cavities 2 arranged in a row. FIG. 3 shows the corresponding perspective rear view. In this embodiment the mold cavities 2 are identical, and in particular have an identical cross section, but in other embodiments they can have different cross sections and/or sizes. Each mold cavity 2 has a liquid metal inlet 3 (visible on FIG. 3) and a mold outlet 4. During the continuous casting process, liquid metal will be introduced into the mould cavity 2 through its inlet 3, and a solidified metal strand (not shown on the figures) will emerge from said mold outlet 4.

[0054] The mold 1 comprises several parts, namely a front plate 28 and a back plate 29, arranged parallel to each other, and each manufactured from a single piece. Said front plate 28 and back plate 29 are pressed against a body 8, held together by appropriate means 9 for fastening or assembling, such as bolts. The back plate 29 comprises the liquid metal inlet 3, whereas the front plate 28 comprises the mold outlet 4. Said body 8, front plate 28 and back plate 29 are typically made from metallic materials having a good thermal conductivity. As an example, the following metals and their alloys can be used: aluminium, copper, titanium, as well as stainless steel. As an example, if the mold 1 is intended to be used for casting aluminium or aluminium alloys, the back plate 29 is typically made from steel, and the front plate 28 is typically made from copper or aluminium, whereas the body 8 is advangeously made from copper.

[0055] The inner surface (called here contact surface) of a mold is in contact with liquid metal and solid metal and is subject to friction and wear. According to the invention, at least part of the contact surface is the inner surface of a sleeve which can be replaced if needed. This sleeve takes the form of an insert 20, which protects at least part of the mold cavity. In particular, said insert forms the perimeter wall 32 of the mold cavity 2, the inner, flat surface 5 of said perimeter wall being in contact with the molten metal during the casting operation.

[0056] Said insert 20 is substantially rectangular in cross section; its edges may be rounded. The insert 20 is fixed with an insert clamping plate 24 against the front plate 28 using fixing means such as bolts 22. This can be seen from FIG. 1, as well as from FIG. 2 which shows an enlarged exploded perspective front view of the mold of FIG. 1. As can be seen, the insert 20 can be removed by unlocking said fixing means 22 and removing the clamping plate 24.

[0057] According to the invention, any direct contact between the inner surface of the mold body 8 and the liquid metal is avoided. Instead, it is the inner surface 5 of the perimeter wall of the protective insert 20 that will be in contact with the liquid metal. Said protective insert 20 is in thermal contact with a cooling fluid. Said protective insert 20 being subject to wear, it can be replaced if necessary. Protective inserts 20 with a cross section that is substantially rectangular are shown in FIGS. 1 to 5 for a first embodiment; protective inserts having a cross section that is substantially circular can be used for billet casting (not shown of the figures).

[0058] On the rear of the mold 1, the insert 20 is completed by a nozzle plate 25. This can be seen from FIG. 3 which shows a perspective rear view of the mold of FIG. 1. The liquid metal enters the liquid metal inlet 3 through the nozzle plate 25 having a substantially circular perimeter wall 27. The nozzle plate 25 is fixed against the back plate 29 of the mold body 8 by nozzle clamping plate 26 using a fixation means 22 such as bolts. Said nozzle clamping plate 26 advantageously has the same height as the mold boldly 8. Said nozzle plate 25 and said nozzle clamping plate 26 are typically arranged parallel to each other, and parallel with respect to the front plate 28 and the back plate 29. As can be seen from FIG. 4, nozzle plate 25 can be replaced very easily by removing the nozzle clamping plate 26.

[0059] FIG. 4 shows an enlarged exploded perspective rear view of the mold of FIG. 1. Insert 20 has been introduced from the front side, and nozzle plate 25 is inserted from the rear side, abutting against the insert 20; the back plate 29 is then pressed against nozzle plate 25 using said fixation means 22.

[0060] This can be seen from FIG. 5 which shows a cross section of a mold cavity 2 similar to that shown on FIGS. 1 to 4. Said nozzle plate 25 has an opening acting as the liquid metal inlet 3, delimited by a perimeter wall 27, and a substantially flat bottom portion 37, the front surface 35 of which abuts against the rear surface 36 of the insert 20. One or more O-rings 40 can be used to ensure tightness of this abutment.

[0061] According to the invention, the mold 1 is provided with cooling means. Said cooling means are of at least two kinds: the mold itself is cooled by a cooling fluid that circulates in cooling channels 39 (so-called primary cooling means), and a plurality of spray nozzles 19 are provided in the protective insert 20 at the mold outlet 4 for spraying a cooling fluid onto the emerging metal strand are provided (so-called secondary cooling means). This will now be explained in more detail.

[0062] Said primary and secondary cooling means are provided in the form of at least one cooling fluid circuit. A circuit for cooling fluid is provided in the mold body 8, said circuit comprising cooling fluid channels 39 and/or a cooling fluid box 30 (as in the embodiment of FIG. 1). An appropriate connection interface 18 is provided to connect said cooling fluid circuit to an external supply of cooling fluid. Said cooling circuit carries the cooling fluid through channels 39 arranged in the mold body 8, and in particular in the outlet part of the mold, in order to cool said mold body 8 and in particular said outlet part. As the most frequently used cooling fluid is water, the cooling circuit will here also be called a water circuit and the cooling fluid box 30 will here also be called a water box, which does however not imply that other fluids cannot be used (such as water-glycol mixtures).

[0063] FIG. 5 shows the water box circuit 39, which ensures primary cooling of the mold. Said cooling fluid channel 39 (called here also water channel) is provided in vicinity of the mold body 8 and preferably, as in FIG. 5, adjacent to the mold body 8, so as to ensure excellent thermal contact with the perimeter wall 32, said perimeter wall 32 being itself in thermal contact with the hot metal being cast. The cooling fluid circulating in said fluid channel 39 is therefore a means to cool the liquid metal during casting, as it passes through the insert 20: in contact with the perimeter wall the liquid metal will solidify at least in a certain thickness from its surface, said thickness in a given portion of metal being increasing as said metal portion is passing through the insert 20.

[0064] The length of said perimeter wall 32 in the direction of advancement of the metal during casting is advantageously comprised between about 10 mm and about 60 mm, preferably at least 15 mm, more preferably at least 20 mm, and still more preferably at least 25 mm. If the length is too small, the cooling effect is insufficient. If the length is too high, lubrication of the interface between the metal strand and the perimeter wall 32 may become unstable, leading to an insufficient surface quality of the cast metal strand.

[0065] In the embodiment of FIG. 5, said cooling fluid box 30 is defined by the front plate 28 of the mold 1, by the mold body 8, and by the outer perimeter wall 32 of metallic insert 20. Cooling fluid enters and leaves the mold 1 through appropriate connection interfaces 18. One or more O-rings 40 can be used to ensure tightness of the various conduits of the waterbox circuit. As these O-rings are inserted in a cooled zone of the mold, they can be made of elastomeric materials such as synthetic rubber.

[0066] In other embodiments (not shown on the figures) the water box 30 can be defined also by the back plate 29 of the mold 1, and/or the water channel 39 can be provided in the mold body 8.

[0067] In addition to primary cooling of the mold itself, and in particular of its perimeter wall, means for secondary cooling of the solid surface of the solidifying metal strand are provided by a set of spray nozzles 19 provided in an annular zone around the outlet of the insert 20. They are configured such as to spray cooling fluid in an annular zone over the surface of the metal strand as it emerges from the mold outlet.

[0068] Typically, one single cooling circuit is provided for both primary and secondary cooling means, as in the figures, and the cooling fluid used for cooling the mold will leave the mold through the spray nozzles 19 which are provided in the insert 20. In the embodiment of FIGS. 1 to 4, the waterbox circuit 39 as well as said spray nozzles 19 are in fluid connection with the connection interfaces 18 for the fluid circuit. It would however be within the scope of the invention to use separate cooling fluid circuits for the primary cooling means and the secondary cooling means; in this case said cooling fluids can be identical or different.

[0069] According to an advantageous feature of the invention, the surface of the perimeter wall 5 of the mold is lubricated during casting. To this end, the mold 1 comprises a dedicated circuit (called here oil circuit) that carries a separating agent, said circuit comprising at least one channel. This separating agent (also called lubrication agent or simply oil) has has two functions: it lubricates the interface between said metal surface and the inner perimeter wall 5 of the insert 20, and it contributes (as a so-called tertiary cooling means) to cooling the emerging metal surface of the cast strand. Lubrication should be permanent and stable, in order to avoid ripples and other defects on the surface of the metal strand. To this end, openings are provided in the insert 20 and/or the mold body 8, allowing oil to penetrate and to access to the surface of the emerging metal strand. Said separating agent can be an oil or an oily liquid such as an oil-water mixture. For example, said oil can be selected from the group formed by vegetable oil(s), refined vegetable oil(s), refined mineral oil(s), synthetic oil(s), mixtures of the mentioned oils.

[0070] More precisely, as can be seen from FIG. 5, the mold body 8 is provided with conduits 38 which extend into the insert 20, until close to the perimeter wall 5. Said conduits 38, which are in fluid connection with a specific connection interface 31, extend until close to the edge 40 or interface between the mold body 8 and the nozzle plate 25; a small opening (not shown on the figures) may be provided to allow oil to penetrate until the edge 40 or close to said edge of the perimeter wall 5, where it can access to the surface of the emerging metal strand. Said opening advantageously has a diameter comprised between 0.1 mm and 1.0 mm, preferably between 0.25 mm et 0.75 mm. There may be provided more than one of such conduits 38 for each mold cavity 2, preferably on each of the sides of the cross section. This system of conduits is used to inject oil at a remote position of the perimeter wall 5, namely close to, or at, said edge 40. Said oil will form a continuous and homogeneous thin film on the whole surface of the emerging metal strand, as soon as it will solidify in contact with the perimeter wall 5. This continuous and homogeneous lubrication leads to an excellent surface quality of the as-cast metal strands.

[0071] Said oil circuit is in fluid connection with an oil pump (not shown on the figures). One single oil pump can be used for the mold. According to an advantageous embodiment of the invention, each mold cavity 2 has its own means of adjustment (not shown on the figures) for the oil pressure and/or the oil throughput. This single strand lubrication approach allows to adjust the lubrication individually for each mold cavity, taking into account in particular the surface aspect of the emerging metal strands. Said adjustment can be carried manually or automatically. A camera coupled with appropriately configured image analysis software run on a control computer can be used to identify any significant surface defects that could be avoided by improving lubrication; a feed-back loop can be provided between the camera and the means of adjustment for oil pressure and/or oil throughput.

[0072] In a variant of the invention, air cooling can be provided as an additional cooling means, as an additional air circuit (not shown on the figures) for supplying compressed air blown on the mold and/or on the emerging metal strand. This air circuit is optional.

[0073] The protective insert 20 is made from a material that is relatively inert with respect to the liquid metal and which does not stick to the liquid metal. Graphite can be used as a material for said protective insert 20, as it is chemically inert and self-lubricating. According to a particularly advantageous embodiment of the invention, the insert 20 is a metallic insert. An insert made in aluminium or copper is preferred for molds intended to be used for casting aluminium. Although metallic materials based on aluminium or copper are not auto-lubricating like graphite, they have significant advantages over graphite: their thermal conductivity is much higher than that of graphite, they have a significantly longer lifetime, they are less expensive, and can be recycled. Said metallic inserts can be manufactured by casting and/or by machining, or by additive techniques (so-called 3D printing). Cast perimeter surfaces need to be machined prior to their first use. All machined perimeter surfaces are advantageously polished, preferably after each use. After removal of the insert from the mold, the insert can be inspected and repaired if needed, or discarded for recycling if repair is not possible. Discarded metal inserts can be recycled (usually by remelting), which is hardly possible with graphite.

[0074] The lifetime of perimeter walls made from graphite is usually of the order of 250 h to 500 h. The inventors have found that perimeter walls made from aluminium alloys have a lifetime that is significantly higher than that of graphite, and in particular the lifetime of the metallic insert 20 can be in excess of 1 000 hours. The nozzle plate 25 needs to be changed typically after 60 h to 80 h.

[0075] We will describe now in relation with FIG. 4 a method for changing the nozzle plate 25. In a first step the fixation means 22 of the nozzle clamping plate 26 are unlocked. In a second step the nozzle clamping plate 26 is removed. In a third step the nozzle plate 25 is removed. In a fourth step a new or renovated nozzle plate 25 is put in place. In a fifth step the nozzle clamping plate 26 is reinstalled. In a sixth step the nozzle clamping plate 26 is fixed by fastening the fixation means 22. During nozzle plate change all other components of the mold can remain mounted, only the nozzle clamping plate 26 and the fixation means 22 have to be dismounted to allow change of the nozzle plate 25. The surfaces of the removed nozzle clamping plate 26 are cleaned before it is put in place in the third step, or another cleaned, new or renovated nozzle clamping plate is used. The visible surface of the back plate 29 is cleaned between the second and the fourth step, as well as all accessible surfaces of the mold cavity.

[0076] We will describe now in relation with FIG. 2 a method for changing the mold insert 20. In a first step the fixation means of the insert clamping plate 24 are unlocked. In a second step the insert clamping plate 24 is removed. In a third step all accessible surfaces of the mold cavity are cleaned. In a fourth step a new (or renovated) mold insert 20, and preferably a new O-ring, are installed. In a fifth step the insert clamping plate 24 is reinstalled. In a sixth step the insert clamping plate 24 is fixed by fastening the fixation means. During insert plate change all other components of the mold can remain mounted, only the insert clamping plate 24 and the fixation means have to be dismounted.

[0077] The invention has many advantages. One of the advantages of the invention is that the body 8 is not subject to wear, but only the insert 20 and the nozzle plate 25, both of which can be exchanged individually if necessary, using a simple and fast method. The insert 20 and the nozzle plates 25 are metallic parts that can be manufactured easily, and which are rather inexpensive; moreover, they can be recycled easily after having been discarded. The perimeter wall 5 is made from metal, such as aluminium alloy, which has a higher thermal conductivity than graphite, thereby allowing better cooling of the whole surface of the perimeter wall 5. Lubrication is efficient and is limited to the part of the interface where it is absolutely necessary; this allows to use a small amount of lubrication agent (such as oil) only. The lubrication agent is used in a mixture with water, which acts as coolant. The quantity coolant (water-lubrication agent mixture) and/or lubrication agent can be adjusted for each individual mold cavity, according to what is needed to ensure sufficient lubrication.

[0078] The mould 1 coding to the invention can have one single mold cavity, or preferably a plurality of mold cavities. FIGS. 1 and 3 show a typical embodiment with ten identical mold cavities 2 arranged in a row. The mold cavities 2 can be different, although this would not be a preferred embodiment of the invention.

EXAMPLES

[0079] The mold and casting process according to the invention has been used for horizontal casting of foundry ingots (so-called HDC ingots or Horizontal Direct Chilled ingots) in various aluminium alloys, with a width of about 55 mm and a height of about 75 mm or 90 mm, which can be used for remelting in various casting processes, such as die casting. During these industrial casting tests, the temperature range of the cooling water was between about 5 C. and about 50 C., the volume of cooling water per cast mass of aluminium was between about 5 Nm.sup.3/t and about 40 Nm.sup.3/t, the volume of cooling water per strand and hour was comprised between about 2.3 Nm.sup.3/h and 18.2 Nm.sup.3/h, the volume of lubrication agent per cast mass of aluminium was comprised between 10 mL/t and 400 mL/t, the volume of lubrication agent per strand and hour was comprised between about 0.5 mL/h and 18.5 mL/h, and the casting speed was between about 0.1 mm/s and about 15 mm/s. Said lubrication agent can typically be used in a concentration of about 0.2 L/m.sup.3 of water.

LIST OF REFERENCE SYMBOLS

[0080] The following reference numbers are used on the figures and in the description: [0081] 1 Mold according to the invention [0082] 2 Mold cavity [0083] 3 Liquid metal inlet [0084] 4 Mold outlet [0085] 5 Inner surface of the perimeter wall of the mold [0086] 6 Solidified metal strand [0087] 8 Mold body [0088] 9 Assembling or fixation means [0089] 18 Connection interface for water circuit [0090] 19 Spray nozzles for cooling fluid [0091] 20 Protective insert [0092] 22 Assembly or fixation means [0093] 24 Insert clamping plate [0094] 25 Nozzle plate [0095] 26 Nozzle clamping plate [0096] 27 Perimeter wall of 3 [0097] 28 Front plate [0098] 29 Back plate [0099] 30 Water box [0100] 31 Connection interface for oil circuit [0101] 32 Outer perimeter wall of insert 20 [0102] 35 Front surface of 25 [0103] 36 Rear surface of 20 [0104] 37 Bottom portion of 25 [0105] 38 Conduit [0106] 39 Channel for cooling fluid [0107] 40 O-ring