Foot rolls for continuous casting

Abstract: Foot rolls for continuous casting which consist of at least two successive layers of assemblies of rolls (13), each assembly of rolls (13) lying substantially on the same plane, the foot rolls (13) being positioned immediately downstream of an ingot mould and immediately upstream of a discharge conveyor (11), each assembly of rolls (13) defining a geometric figure conforming to the cross section of the ingot being formed, the rolls (13) containing a stationary, cooled supporting shaft (14) secured at its ends to vertical uprights (18), the rolls (13) being supported on bearings (15) keyed to their respective shafts (14), each shaft (14) being supported and positioned on the uprights (18) and containing a first inner conduit (21a) connected to first radial conduits (23a) opening out at one end of a cooling chamber (24) within the respective roll (13), the cooling chamber (24) cooperating at its other end with second radial conduits (23b) connected to a second inner conduit (21b), which opens out in a passage (25) machined in a housing (19) that supports the terminal portions of two consecutive shafts (14).

Description: This invention concerns the cooling of the foot rolls of a continuous casting device. To be more exact, the foot rolls of this invention are positioned immediately downstream of the ingot mould employed in continuous casting plants. Such ingot moulds are located downstream of a tundish and upstream of a discharge roller conveyor. Continuous casting ingot moulds contain a crystallizer, or downstream mould portion, of a pre-set section which upon start-up cooperates with a movable bottom, to which is fitted a pinetree-shaped element for attachment to the cast liquid metal. This movable bottom is connected to a starter bar that cooperates with a discharge roller conveyor positioned downstream of the mould so as to draw the ingot being formed. It is known that the ingots being formed and leaving the mould are additionally cooled by suitable cooling means that act directly on the ingot being formed. The skin of the ingot at the outlet of the crystallizer may be thin, and therefore the ingot has to be suitably contained by the foot rolls and conveyed to the discharge roller conveyor. These foot rolls form series of two, three, four or more succesive layers of assemblies of rolls cooperating together. Each assembly consists of idler rolls able to rotate about their respective supporting shafts. These idler rolls are positioned in such a way as to come into contact with the whole perimeter of the ingot being formed so as to prevent non-homogeneous pressures. The supporting shafts which bear the idler rolls are upheld by suitable uprights. The state of the art generally employs two solutions: bearings that bear the idler rolls, whereby the idler rolls rotate about their respective supporting shafts secured to the uprights; bearings that bear the supporting shaft, whereby the idler rolls are integrally secured to their respective supporting shafts able to rotate in relation to the uprights. The solution whereby the bearings bear the idler rolls is generally employed because it is safer and less expensive. From a dynamic point of view the foot rolls are little stressed but are heavily stressed from a thermal point of view; for this reason the cooling means spray the ingot being formed with water under high pressure and at the same time also bathe and cool the idler rolls and the respective supporting shafts. So as to reduce the thermal shock further, suitable inner conduits coaxial with the supporting shafts are included, and through these conduits a cooling liquid consisting of water is passed. In the state of the art each supporting shaft includes at the ends of each inner conduit an inlet and an outlet, the conduits being connected in series with flexible tubes. These flexible tubes are located in a zone in which a breakage of the skin of the ingot being formed brings the liquid metal into contact with the flexible tubes, thus causing wear of the tubes and impairing their functioning. Moreover, the cooling systems for the foot rolls of the state of the art do not ensure efficient cooling of the idler rolls, which thus become worn excessively. GB-A-2,029,742 discloses a system for the installation of a strand guide comprising a plurality of pairs of opposed rolls. This patent concerns the rolls which come after the foot rolls (that is to say, the rolls which follow the rolls positioned immediately below the outlet of the crystalliser) and which perform a containing task very different from that of the foot rolls. The rolls of GB-A-2,029,742 are positioned only on two opposite sides of the strand and are fitted at their ends to a pair of longitudinal carrier frames which extend along the whole length of the guide. GB-A-2,029,742 cannot be employed in containing and guide systems, such as the foot rolls, employed for the containing of products such as blooms which require to be contained on all four sides. According to the cooling arrangement of GB-A-2,029,742, if anomalies and/or even partial blockages take place in a hole and/or in a conduit performing circulation of the cooling fluid, then each roll is cooled with different conditions and parameters, as between the rolls forming part of the same pair of opposed rolls, or as between rolls belonging to different pairs, or even along the extent of the same roll. A difference in the conditions of circulation of the cooling fluid leads to a different action on the strand to be contained and to different wear on the rolls, and this situation causes incorrect working conditions of the whole device. Next, it should be noted that in GB-A-2,029,742 the arrangement of installation of the shafts of the rolls on the longitudinal carrier frame and the position of the conduits entails the need to have sealing packings inasmuch as there is a very great risk of seepage of the cooling liquid. The present applicant has designed, tested and embodied this invention so as to obviate such shortcomings and achieve further advantages. This invention is set forth and characterized in the independent claim, while the dependent claims describe variants of the idea of the main embodiment. The purpose of this invention is to provide foot rolls which ensure efficient cooling of the idler rolls, supporting shafts and relative bearings. This is achieved owing to a suitable system of inner conduits for the passage of a cooling liquid. These inner conduits are coaxial with the supporting shafts and cooperate with a cooling chamber within the relative idler roll. This cooling chamber cooperates directly with the sidewalls of the idler roll. Thus an efficient cooling of the idler rolls and supporting shafts is achieved and the thermal shock which affects them is reduced Therefore the idler rolls according to the invention last longer and the downtimes due to their replacement are limited and output is increased. Furthermore, the invention arranges to reduce to a minimum or, even better, to eliminate the flexible tubes so as to prevent problems of defective functioning when there are leakages of the liquid metal. According to one embodiment the layers of assemblies of foot rolls according to the invention are connected together in series. When the foot rolls according to the invention are connected together in series, the foot rolls comprise, at least for the two upper assemblies, only one outer tube for the entry of cooling liquid and one outer tube for the discharge of the same from the second assembly. According to a preferred embodiment of the invention, whereby a plurality of assemblies of foot rolls are connected in series, the inlet conduit cooperates with the first upper assembly of foot rolls, while the discharge conduit cooperates with the lowest assembly of the foot rolls. According to a variant the assemblies of foot rolls according to the invention are connected together in parallel. In this case the foot rolls include one outer tube for the entry of cooling liquid for each assembly and also include one single discharge conduit for all the assemblies. According to a further variant which is suitable in the case of a great number of assemblies of foot rolls, the assemblies of foot rolls are connected in a combined manner, both in series and in parallel. The foot rolls according to the invention provide the further advantage of eliminating the outer flexible connecting tubes, at least for the first two assemblies, so as to restrict the risks of damage of such outer flexible connecting tubes. According to the invention each assembly of foot rolls consists of idler rolls able to rotate about their respective supporting shafts and lying substantially on the same plane as each other and positioned in a coordinated sequence. The end portions of two successive shafts are supported and positioned in uprights having a hollow section. According to a variant these uprights having a hollow section act also as conduits for the cooling liquid. This solution enables an efficient cooling of the frame too upholding the idler rolls to be achieved. Suitable connecting holes connect together the inner conduits in successive shafts. According to a variant the shafts of all the idler rolls are standardized and the same as each other so as to reduce the spare parts. According to another variant the shafts protrude at one of their ends from one of the two uprights with which they cooperate and are clamped and secured at that end. According to another variant the supporting shafts have an eccentric seating so that the distance between the idler rolls can be adjusted. Let us now see a preferred embodiment of the invention with the help of the attached figures, which are given as a non-restrictive example and in which:- Fig.1 is a side view of foot rolls according to the invention; Figs.2 and 3 show the sections A-A and B-B respectively of Fig.1; Fig.4 shows a variant of Fig.1. Fig.5 shows the section C-C of Fig.4; Figs.6 and 7 show possible paths of the cooling liquid according to the invention. In the figures the reference number 10 indicates generally the foot rolls according to the invention. The foot rolls 10 according to the invention are located immediately downstream of an ingot mould of the state of the art, which is not shown here. A discharge roller conveyor 11 to draw the ingot being formed cooperates downstream of the foot rolls 10. In this case the discharge roller conveyor 11 is of a curved type but could be of any other type. Moreover, the example shown provides for an ingot of a substantially square section, but the ingot could have any other section. Figs.1 and 4 show sprayers 12 of the state of the art, which spray the ingot being formed with cooling water. In this case the foot rolls 10 consist of three layers of assemblies cooperating with each other. Each assembly comprises four idler rolls 13 supported on bearings 15 borne on respective supporting shafts 14, all of which lie on the same plane. The four idler rolls 13 are arranged along the four sides of the ingot and are substantially in contact with the whole perimeter of the ingot being formed. The bearings 15 are shielded against infiltrations of water or other substances by suitable outer 16 and inner 17 annular packings positioned between the supporting shaft 14 and the idler roll 13. The end portions of the supporting shaft 14 cooperate with housings 19 integrally secured to four uprights 18 having a hollow section. A first supporting shaft 14a has one end wholly inserted into and solidly secured to a first housing 19a included in a first upright 18a, whereas its other end is anchored in a hole 31 in a second housing 19b solidly fixed to a second upright 18b. The second housing 19b bears one end portion of a second supporting shaft 14b, which has its other end portion secured in a third housing 19c solidly fixed to a third upright 18c. The same situation applies to the other supporting shafts 14. In this example the four uprights 18a-18b-18c-18d are located at the four corners of a square, while the four supporting shafts 14a-14b-14c-14d form the sides of that square. The first supporting shaft 14a contains a first inner coaxial conduit 21a fed by a flexible tube 22 that delivers water. In correspondence with the first idler roll 13a there are included in the first inner conduit 21a first radial conduits 23a which cooperate with the frontal part of a cooling chamber 24 machined within the first idler roll 13a, so that the cooling liquid passing through comes into contact with the inside of the first idler roll 13a and cools the same. In correspondence with the rear part of the cooling chamber 24 the first supporting shaft 14a contains second radial conduits 23b cooperating with a second inner conduit 21b, which cooperates with the hole 31 contained in the second housing 19b. The second idler roll 13b and the other idler rolls 13c-13d are conformed internally like the first idler roll 13a, so that the path of the cooling liquid is the same therein. Second 19b, third 19c and fourth 19d housings comprise closure means 30 to prevent escape of the cooling liquid. The first housing 19a in cooperation with a passage 25 provided between the inner wall of the first housing 19a and a narrowed portion of the first supporting shaft 14a includes a connecting hole 26, which connects the passage 25 to a vertical cavity 27 in the first upright 18a. This vertical cavity 27 enables the cooling liquid to pass from the first assembly of foot rolls 10 according to the invention to the second assembly of the same 10. The second assembly is exactly the same as the first assembly, but the cooling liquid circulates in the opposite direction to the circulation in the first assembly (see Figs.3 and 6). The movement of the cooling liquid from the second assembly to the third assembly is achieved owing to an auxiliary inner conduit 32, which is obtained by securing a suitable vertical connecting element 33 of the relative first housing 19a of the second assembly of foot rolls 10 to the relative corresponding first housing 19a of the third assembly of foot rolls 10. Fig.6 shows the path followed by the cooling liquid in the above case of three assemblies of idler rolls 13 connected in series. The horizontal segments show the movement of the liquid through the inner conduits 21, radial conduits 23 and cooling chamber 24, while the vertical segments show the movement of the liquid through the vertical cavity 27 of the first upright 18a and through the auxiliary inner conduit 32. In this example only one outer tube for the entry of cooling liquid and one outer tube for the discharge of the liquid are comprised. According to the variant shown in Fig.7 the connection between the second and third assemblies of idler rolls 13 is provided by a connection consisting of an outer flexible tube 28. In the event of foot rolls 10 forming four assemblies of idler rolls 13, the connection between the first three assemblies of idler rolls 13 remains the same as that described above (Figs.6 and 7), whereas the connection between the third and fourth assemblies of idler rolls 13 is exactly like that between the first and second assemblies of rolls 13. Likewise, the concepts disclosed can be applied to a greater number of assemblies of rolls 13. The variant shown in Fig.8 represents the path followed by the cooling liquid when three assemblies of idler rolls 13 are connected in parallel. In this case the vertical segments show the movement of the liquid through the continuous inner cavity of the first upright 18a. In this example an outer tube is provided for the entry of cooling liquid into each assembly of rolls 13, but only one discharge tube is provided for discharge from all the assemblies. According to a variant shown in Figs.4 and 5 all the supporting shafts 14 are substantially the same as each other. The first supporting shaft 14a has one end solidly fixed, owing to suitable fixture means 20, to the first housing 19a in the first upright 18a, whereas the other end of that shaft 14a is secured in the hole 31 contained in the second housing 19b. As in the case described above, the first supporting shaft 14a contains a first inner conduit 21a, a cooling chamber 24 and a second inner conduit 21b. The second inner conduit 21b cooperates with a second passage 25 machined between the inner wall of the second housing 19b and a corresponding narrowed portion of the second supporting shaft 14b. In this example the second supporting shaft 14b in cooperation with the second passage 25 comprises at least one connecting conduit 29, which has a substantially radial axis and connects the second passage 25 to the first inner conduit 21a. The successive rolls of one and the same assembly have a circulation of cooling liquid substantially the same as that of the first roll 13a. In the example of Fig.4 the second assembly of rolls 13 has the cooling liquid outlet corresponding with the first inner conduit 21a, which is connected by flexible tubes to the third assembly of rolls 13 (see the drawing of Fig.7). The third and possible fourth assemblies of rolls 13 work like the first and second assemblies. According to a variant the supporting shafts 14 have an eccentric seating 34 (see the dotted lines within the roll 13d in Figs.1 and 4), so that the axes of rotation of the rolls 13 are eccentric in relation to the axes of the relative supporting shafts 14. In this way, when the supporting shafts 14 rotate, the rolls 13 approach, or become distanced from, each other.

Claims: Foot rolls for continuous casting which define at least a first and a second successive assemblies of rolls (13), each assembly of rolls (13) comprising rolls lying substantially in the same plane, the foot rolls (13) being positioned immediately downstream of a mould and immediately upstream of a discharge conveyor (11), each assembly of rolls (13) defining a geometric figure conforming to the cross-section of the ingot being formed and cooperating by contact with the perimeter of that ingot, each roll (13) containing a stationary, cooled supporting shaft (14) secured at its ends to vertical uprights (18), the rolls (13) being supported on bearings (15) keyed to their respective shafts (14), each shaft (14) being supported and positioned in a respective housing (19) on the uprights (18), each shaft (14) containing a first inner conduit (21a) connected to first radial conduits (23a) opening out at one longitudinal end of a cooling chamber (24) within the respective roll (13), the cooling chamber (24) cooperating at its other longitudinal end with second radial conduits (23b) connected to a second inner conduit (21b), which opens out in a passage (25), wherein the respective inner conduits (21a, 21b) of the shafts (14) of the rolls (13) of one and the same assembly of rolls are all in hydraulic communication in series with each other through the passages (25) located in the supporting housings (19) so as to define a circuit of circulation of the cooling liquid having a preferred direction of circulation, there being defined a first shaft (14a), the first inner conduit (21a) of which is associated with a flexible tube (22) introducing cooling liquid, and a last shaft (14d), the second inner conduit (21b) of which is associated with a tube that discharges the cooling liquid, the passages (25) being provided in the housings (19) supporting the terminal parts of two adjacent shafts (14). Foot rolls as in Claim 1, whereby the passages (25) include at least one connecting conduit (29) able to put the second inner conduit (21b) of one shaft (14) in communication with the first inner conduit (21a) of the adjacent shaft (14). Foot rolls as in Claim 1 or 2, whereby the passages (25) include hydraulic seal-engagement closure means (30). Foot rolls as in any preceding claim, whereby at least the last shaft (14d) of a first assembly of rolls is in hydraulic communication with the first shaft (14a) of a second assembly of rolls through an upright (18a). Foot rolls as in any preceding claim, whereby in correspondence with the passage (25) upstream of the first shaft (14a) there is included a hole (26) which connects the passage (25) to a vertical cavity (27) contained in the first upright (18a), this vertical cavity (27) being in hydraulic communication with the underlying passage (25) in the second assembly of rolls (13) by means of a respective connecting hole (26). Foot rolls as in any preceding claim, whereby the first inner conduit (21a) in the first shaft (14a) of the second assembly of rolls (13) opens out into an auxiliary inner conduit (32) that connects the second assembly of rolls (13) hydraulically to a third assembly of rolls (13). Foot rolls as in any of Claims 1 to 5 inclusive, whereby the first inner conduit (21a) in the first shaft (14a) of the second assembly of rolls (13) opens out into a flexible tube (28) which connects the first shaft (14a) of the third assembly of rolls (13) hydraulically. Foot rolls as in any preceding claim, whereby at least two assemblies of rolls (13) are connected hydraulically in parallel through the first upright (18a). Foot rolls as in any preceding claim, whereby the supporting shafts (14) have an eccentric seating (34) for their adjustment.

Inventors: MARCHESAN GUIDO, SOBAN ALESSANDRO, MARCHESAN, GUIDO, SOBAN, ALESSANDRO
Applicants: DANIELI OFF MECC, DANIELI & C. OFFICINE MECCANICHE S.P.A.
Application year: 1992
Main classification: B22D11
IPC codes: B22D11