Optimization of weir and dam with drain holes in continuous casting slab

Optimization of Weir & Dam with Drain Holes inContinuous Casting Slab TundishChao Chen a, Guoguang Cheng b, Haibo Sun cXinchao Wang d and Jiaquan Zhang eState Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, No. 30 Xueyuan Road, Haidian District, Beijing, 100083, P.R.China.a chenchao8901@,b chengguoguang@,c sunmyseven@, d526535901@, e jqzhang@ Keywords: Water model, Mathematical model, Tundish, Weir & Dam, Drain hole.Abstract.The optimization of the location and height of weir & dam with drain holes in a single-strand continuous casting tundish was carried out from the view of fluid flow characteristics by physical modeling using a 0.4 scaled water model and mathematical modeling study. Considering simultaneously reducing the remaining melt, maximizing the plug flow and avoiding the short circuited flow, the dam with two upwardly inclined drain holes was optimized. The parameters such as location and height of weir & dam Lw/L, Ld/L, Hw/H and Hd/H are important to fluid flow in tundish. Among them, the location and height of dam were more critical to the overall fluid flow in tundish. The gap between weir and dam was also very important, the gap length that smaller than 0.266 will be preferred. The dead region behind the weir was enlarged and the tracer flow through the drain holes of dam was weakened as increasing the gap of weir and dam. In present study, the parameters of the optimized Case7 are Hw/H0.448 (162/362), Hd/H0.718 (260/362), Lw/L0.4 (480/1200) and Ld/L 0.667 (800/1200). For the fluid flow field, the near surface flow which beneficial to inclusions removal existed both above the dam and through the upwardly inclined drain holes. While the case of bottom grooved dam used may lead to short circuited flow through the grooves. IntroductionWeir & dam, which exhibit advantages on inclusion removal[1,2] even in large-capacity tundish[3] and special steel tundish[4], have been widely used in continuous casting slab tundish. J. Knoepke and J. Mastervich[5] reported that the order of dams and weirs from the ladle shroud to the tundish nozzle should be alternating pairs of weirs followed by dams. The weir that next to the ladle shroud plays a principal role in limiting the mixed zone to increase the plug volume, thereby promote the floatation of inclusions; on the other hand, the dam near the tundish nozzle plays a principal role in guiding the inclusions toward the slag layer and limiting the mixed zone near the bottom of tundish[6].The location of weir & dam is important in tundish. M.M. Collur et al.[7] reported that the efficiency of particle (simulate inclusions) flotation deteriorated significantly as weir & dam were located closer to the tundish exit. Then J.J. Kim et al.[8] further demonstrated that minimum residence time, mean residence time and plug flow volume decreased and dead flow volume increased with increasing the distance from the ladle shroud to weir. Similarly, S.K. Sinha et al.[9] found that the residence time increased with the dam move closer to the ladle shroud. In contrast, D. Bolger[10]reported that turbulence increased which contributed to slag entrapment as the weir move closer to the ladle shroud. In addition, S. Chakraborty and Y. Sahai[11] found that the incoming melt became cooler than that in the bulk of the tundish, as a result the melt sunk along the dam and started to flow along the bottom instead of the top free surface, the inverse flow pattern developed and continued over the remaining 25 min of the teeming period (for a typical 50 min casting period), their further report[2] stated this flow pattern will deterioated the inclusions removal. While this effect can not be avoided as weir & dam move closer to the ladle shroud.The height of dam and depth of weir are also important parameters on fluid flow in tundish [12,13], some papers [14,15] further reported the selection of dam height was more critical than that of weir. For the dam height selection, a lower dam that near the tundish nozzle was optimized both for the weir & dam design [16] and for only a dam case [17], on the contrary, a higher dam with a turbulence inhibitor were also reported [18,19].The location and height or depth of weir & dam can be described by these parameters as shown in Fig. 1, namely the distance of ladle shroud to tundish nozzle L , the distance of ladle shroud to weir (or dam) Lw (or Ld ), liquid height H , the height of weir bottom to tundish bottom Hw and the height of the dam Hd . However, these parameters are quiet different for each steelmaking plant, therefore the dimensionless distance of ladle shroud to weir (or dam) Lw/L (or Ld/L ), dimensionless height of weir bottom to tundish bottom Hw/H and dimensionless height of the dam Hd/H are defined to regulate theusing of weir & dam.Fig.1 Key parameters of location and height of weir & dam Fig. 2 Water model tundish configurations A summary of these parameters (Lw/L , Ld/L , Hw/H , Hd/H ) that published in papers are listed in Table 1, the inclination of tundish wall and the distance from ladle shroud (or tundish nozzle) to tundish wall are not involved, while the liquid height of pouring point is considered to be H for the raised floor tundish, besides the parameters of symmetrical half side in two-strand tundish are also involved. The literature review shows that Lw/L is changed from 0.06 to 0.463, Ld/L from 0.18 to 0.683, Hw/H from 0.115 to 0.6 and Hd/H from 0.153 to 0.735. These values varied within a large range may lead to difference of fluid flow characteristics and further inclusions removal efficiency. Table 1 Summary of the location and height parameters in weir &dam FCDInvestigators Year Lw/L Ld/L Hw/H Hd/Hremark D.J. Harris and J.D. Young [20] 1982 0.241 0.361 0.301 0.301 2 strand tundish T. Debroy and J.A. Sychterz [1] 1985 0.25 0.442 0.5 0.368 Y. Sahai and R. Ahuja [21] 1986 0.227 0.307 0.5 0.3 H. Nakajima et.al [22] 1986 0.163 0.244 0.305 0.305 Y. Sahai and S. Chakraborty [11] 1992 0.113 0.225 0.391 0.522 2 strand tundish S. Joo and R.I.L. Guthrie [23] 1993 0.411 0.5 0.273 0.409 J.L. Yeh, W.S. Hwang and C.L. Chou [24] 1993 0.194 0.66 0.222 0.289 2 strand tundish S. Singh and S.C. Koria [14] 1993 0.06 0.18 0.6 0.25 C.S. Damle and Y. Sahai [25] 1994 0.121 0.242 0.383 0.417 2 strand tundish M.M. Collur, D.B. Love and B.V. Patil [7] 1997 0.456 0.735 Dam with holes D.Y. Sheng et.al [26] 1998 0.249 0.325 S. Chakraborty [2] 1999 0.25 0.375 0.2 0.333 2 strand tundish W. Wu [13] 1999 0.191 0.415 0.2 0.463 J.J. Kim et.al [8] 2001 0.139 0.217 0.115 0.153 K.J. Craig et.al [27] 2001 0.132 0.605 0.231 0.577 Y.P. Bao et.al [28] 2002 0.149 0.398 0.209 0.209 C. M. Fan, R. J. Shie and W. S. Hwang [29] 2003 0.298 0.375 0.288 0.426 J. Liu et.al [30] 2007 0.463 0.683 0.45 0.575 M. Bensouici, A. Bellaouar and K. Talbi [6] 2009 0.105 0.226 0.247 0.351From Table 1, only limit paper [7] dealt with the dam with holes, although multi-hole baffle has been widely used in multi-strand tundish [31], little information is known about the effect of holes added in dams on the fluid flow characteristics.In this paper, the optimization of the location and height of weir & dam with drain holes in a single strand continuous casting tundish is carried out from the view of fluid flow characteristic by physical modeling using a 0.4 scaled water model and mathematical modeling study, the configuration of water modeling tundish is shown in Fig. 2. The parameters such as Lw/L, Ld/L, Hw/H and Hd/H are investigated. Besides different kinds of drain holes are involved.ExperimentsWater modeling. The ratio of geometrical similarity of model tundish to the prototype tundish was 0.4, and Froude similarity number was maintained to be equivalent. The residence time distribution (RTD) curve was obtained by stimulus-response technique. After steady-state flow condition was maintained, 125mL saturated potassium chloride (KCl) solution was injected into the 248L tundish from the ladle shroud. Instantaneous concentration of the tracer as a function of time was measured by conductivity probes installed below the tundish nozzle. The analysis model for RTD curve is listed in Table 2.the molten steel flow. The modeling of fluid flow consisted of solving simultaneously the continuity, momentum-transfer and mass-transfer equations under turbulent conditions, also the standard k-ε equations were employed to describe the turbulence phenomena. All the equations and boundary conditions are negligible here for they can be found in other paper[33].Criteria of optimization case. The case exhibits the lowest V d, that is to say with large active tundish volume, and the highest V dp for inclusions removal are considered firstly.Results and discussionIn this section, the location and height of weir & dam are studied based on an original case, the parameters of original case are Lw/L 0.317(380/1200), Ld/L 0.5(600/1200), Hw/H 0.448(162/362) and Hd/H 0.552(200/362). Firstly the effect of drain hole on the fluid flow characteristics will be discussed, and then the effect of location and height of weir & dam on fluid flow will be investigated. Each parameter (Lw/L, Ld/L, Hw/H and Hd/H) is studied as the other three fixed the same with the original case, the combined optimize of these four parameters will be studied finally.Drain holes design. The original purpose of holes added in dams were promoting drain of steel and reducing the remaining melt[8,20], besides optimizing the start of continuous casting process[13] and maximizing the plug flow[34] were reported. On the contrary, the drain holes in dams could lead to short circuited flow[29], moreover exacerbated the tundish nozzle plugging[18].Considering simultaneously reducing the remaining melt, maximizing the plug flow and avoiding the short circuited flow are critical for drain holes design. Two upwardly inclined drain holes were designed as schematically shown in Fig. 3, also bottom grooved dams of rectangular shape (R1, R2) and semi-round shape (SR1, SR2) were also investigated as shown in Fig. 4. The cases of R1 (groove dimensions 110×18 mm) and R2 (groove dimensions 132×15 mm) were sharing the same area of rectangular groove, besides the design of SR1 was similar to the study of J.J. Kim et al.[8], while thedesign of SR2 was from the view of avoiding the ladle pouring point, tundish nozzle and drain holes located in a straight line. The dead and dispersed plug volume fraction of different cases is shown in Fig. 5, the dam without drain holes are also involved.Fig. 3 Inclined drain holes in the dam Fig. 4 Bottom grooved dams (a) Rectangular groove1 (b) Rectangulargroove2 (c) Semi-Round groove1 (d) Semi-Round groove2Fig. 5 The dead and dispersed plug volume fraction with drain holes variedFrom the results in Fig. 5, the V d increases greatly and V dp decreases significantly of all the drain hole added cases compared with the case without drain holes, however the drain holes will be beneficial for reducing remaining melt especially for high-alloyed grades. The V d of all the drain hole added cases showing little difference except the case SR2 is bigger than that of the others. On the other hand, the V dp of the inclined drain holes case is larger than that of the bottom grooved cases R1,R2, SR1 and SR2.(a) Without drain holes (b) Inclined drain holes (c) Rectangular groove1(d) Rectangular groove2 (e) Semi-round groove1 (f) Semi-round groove2 Fig. 6 Photograph of black ink tracking in water model at 80s of different drain hole casesFig. 6 describes the fluid flow field of the drain holes cases, the fluid flow near the surface of the cases without and inclined drain holes, this kind of flow is beneficial to inclusions removal [2]. However, the short circuited fluid flow through the grooves occurred of the bottom grooved cases. The groove area of SR2 was bigger than that of R1, R2 and SR1, therefore the short circuited flow was improved and measured mean residence time was reduced, finally V d increased. Hence, the dam with inclined drain holes will be utilized for further study.Optimization of height of weir & dam . The dead and dispersed plug volume fraction as functions of height parameters Hw/H and Hd/H are shown in Fig. 7. From Fig. 7(a), the RTD data V d and V dp increase slightly with increasing Hw/H from 0.171 to 0.503, while in Fig. 7(b) V d decreases and V dp increases greatly with increasing Hd/H from 0.331 to 0.773.The depth of weir can only influenced the mixing behavior of ladle pouring chamber, the height of dam was more critical to the overall fluid flow in tundish. A relative larger Hw/H is preferred considering the refractory erosion; also a higher dam with inclined drain holes plays a principal role inguiding the inclusions toward the tundish cover layer.Fig. 7 The dead and dispersed plug volume fraction as functions of height of weir & dam (a)Hw/H (b)Hd/HOptimization of location of weir & dam . The dead and dispersed plug volume fraction as functions of location parameters Lw/L and Ld/L are shown in Fig. 8. For the location of weir changed as shown in Fig. 8(a), V d decreases greatly and V dp changes slightly with increasing Lw/L from 0.283 to 0.367. This variation is opposite to the results of J.J. Kim et al.[8] while in their study Lw/L wasaround 0.139.Fig. 8 The dead and dispersed plug volume fraction as functions of location of weir & dam (a)Lw/L (b)Ld/LFor the location of dam varied as shown in Fig. 8(b), V d decreases and V dp increases significantly with increasing Ld/L from 0.483 to 0.733. Fig. 9 describes the fluid flow field of the cases that location of dam varied, the dead region behind the weir was enlarged and the tracer flow through the holes of dam was weaken as the gap of weir and dam was increased. In summary, the location of dam is critical than weir to the fluid flow in tundish, however the location of weir & dam should be considered simultaneously.(a) (b) (c)(d) (e) (f)(g) (h) (i)Fig. 9 Photograph of black ink tracking in water model at 70s with Ld/L varied(a) 0.483 (b) 0.5 (c) 0.517 (d) 0.533 (e) 0.583 (f) 0.625 (g) 0.667 (h) 0.7 (i) 0.733 Optimized location and height of weir & dam. From the previous discussion, the location of weir & dam and dam height are key parameters to the fluid flow in tundish. Besides, the gap between weir and dam is also very important as Fig. 9 indicated. The gap length that smaller than 0.266 (0.583 minus 0.317, namely the gap as shown in Fig. 9(e)) will be preferred. The combined varying results of Hw/H , Hd/H , Lw/L and Ld/L are shown in Fig. 10.Fig. 10 The dead and dispersed plug volume fraction with Hw/H , Hd/H , Lw/L and Ld/L variedFirstly, the gap of weir and dam was fixed at 0.15, the location of weir & dam was changed as Case1 to Case3, besides the parameters Hw/H and Hd/H were chosen from previous study. Case3, as weir & dam move closer to tundish exit, showing a relative lower V d and a higher V dp than the other two cases.Secondly, the height of weir and dam were changed based on Case3, as Case4 and Case5, respectively. Compared with Case3 and Case4, V d increases greatly and V dp decreases slightly as the immersion depth of weir increased. Similarly, V d decreases and V dp increases slightly as the height of dam increased (Case5). So Case5 is used for further optimization. 298New Materials and ProcessesThirdly, the gap length of Case6 was increased to 0.267 by moving the weir closer to ladle shroud and keeping the location of dam same with Case5. It was noteworthy that V d decreased and V dp increased significantly as increasing the gap length.Finally, based on Case6 and fixed the gap length at 0.267, moving the weir & dam to ladle shroud was studied as Case7 and Case8. The dead volume fraction first decreases and then increases as moving weir & dam closer to ladle shroud.As a result, Case7 which exhibits the lowest V d(0.14) and relatively higher V dp(0.25) is the optimized case in this study, the parameters of Case7 are Hw/H0.448 (162/362), Hd/H0.718 (260/362), Lw/L 0.4 (480/1200) and Ld/L 0.667 (800/1200). The fluid flow field of Case7 is shown in Fig. 11, the near surface flow exists both above the dam and through the drain holes.Fig. 11 Calculated velocity profiles at the symmetric plane of tundish(y=0mm) and drain hole(y=200mm) for Case7ConclusionsThe optimization of the location and height of weir & dam with drain holes in a single-strand continuous casting tundish is carried out from the view of fluid flow characteristics by physical modeling and mathematical modeling study, the findings are concluded as follows:(1) Considering simultaneously reducing the remaining melt, maximizing the plug flow and avoiding the short circuited flow, the dam with two upwardly inclined drain holes was the optimized case. The case of bottom grooved dam used may lead to short circuited flow through the grooves, while the fluid flows through the upwardly inclined holes will promote the near-surface flow for inclusions removal.(2) The parameters such as location and height of weir & dam Lw/L, Ld/L, Hw/H and Hd/H are important to fluid flow in tundish. Among them, the location and height of dam were more critical to the overall fluid flow in tundish. The dead volume fraction decreases and dispersed plug volume fraction increases with increasing the height of dam or moving the dam closer to the tundish nozzle.(3) The gap between weir and dam was also very important. The gap length that smaller than 0.266 will be preferred. The dead region behind the weir was enlarged and the tracer flow through the drain holes of dam was weakened as increasing the gap of weir and dam.(4) In present study, Case7 which exhibited the lowest V d(0.14) and relatively higher V dp(0.25) is the optimized case, the parameters of Case7 are Hw/H 0.448 (162/362), Hd/H 0.718 (260/362), Lw/L 0.4 (480/1200) and Ld/L 0.667 (800/1200). For the fluid flow field, the near surface flow existed both above the dam and through the drain holes.References[1] T. Debroy and J.A. Sychterz: Metallurgical Transactions B Vol. 16B. (1985), p. 497[2] S. Chakraborty: Revisiting Tundish Flow Modeling for Clean Steel Practices. Steelmaking Conference Proceedings 1999, p. 175[3] C. Zhang, L. Wang, K. Cai, W. Yuan, Z. Yu and Y. Zou: Journal of University of Science and Technology Beijing Vol. 9. (2002), p. 412[4] D.S. Kim, J.J. Park, H.S. Song, Y.K. Shin, B.H. Choi and S.S. Yim: “Improvement of cleanness in continuously cast slab of titanium containing stainless steel”, 76th Steelmaking Conference, 291-297, Dallas U.S.A, March 1993, Iron & Steel Society.[5] J. Knoepke and J. Mastervich: Water Modeling Inland Steel’s No.3 Combination Caster Tundish. Steelmaking Conference Proceedings 1986, p.777[6] M. Bensouici, A. Bellaouar and K. Talbi: Journal of Iron and Steel Research International Vol. 16. (2009), p. 22[7] M.M. Collur, D.B. Love and B.V. Patil: Use of Flow Modifiers to Improve Performance of a Tundish. Steelmaking Conference Proceedings 1997, p. 313[8] J.J. Kim, S.K. Kim, J.W. Kim, S.D. Shim, Y.D. Lee: Numerical and Experimental Study of Tundish Flow during Continuous casting of Stainless Steel. Proceedings of Electric Furnace Conference 2001, p. 395[9] S.K. Sinha, K.M. Godiwalla and C.S. Sivaramakrishnan: Ironmaking and Steelmaking Vol. 20. (1993), p. 485[10] D. Bolger: Development of a Turbulence Inhibiting Pouring PAD/Flow Control Device for the Tundish. Steelmaking Conference Proceedings 1994, p. 225[11] S. Chakraborty and Y. Sahai: ISIJ International Vol. 31. (1991), p. 960[12] S.X. Liu, X.M. Yang, L. Du, L. Li and C.Z. Liu: ISIJ International Vol. 48. (2008), p. 1712[13] W. Wu. A research on controlling of flow state inside tundish of continuous casting and its metallurgical effects. Ph.D thesis. 1999. University of Science and Technology, Beijing. (in chinese)[14] S. Singh and S.C. Koria: Ironmaking and Steelmaking Vol. 20. (1993), p. 221[15] D. Mazumdar, G. Yamanoglu and R.I.L. Guthrie: Steel Research International Vol. 68. (1997), p. 293[16] H. Solhed, L. Jonsson and P. Jönsson: Metallurgical and Materials Transactions B Vol. 33B. (2002), p. 173[17] A. Cwudziński: Steel Research International. Vol. 81. No. 2. (2010), p. 123[18] M.A. Schueren and J. Schade: Quality and Productivity Improvements with a Revised Tundish Flow System at AK Steel Middletown Works. Steelmaking Conference Proceedings 2001, p. 445[19] T.A. Zimmerman and M. Schmidt: A dynamic mathematical model for grade-mixing in tundish and strand. ISSTech Conference Proceedings 2003, p. 1173[20] D.J. Harris and J.D. Young: Water modeling-a viable production tool. Steelmaking Conference Proceedings 1982, p. 3[21] Y. Sahai and R. Ahuja: Ironmaking and Steelmaking Vol. 13. (1986), p. 241[22] H. Nakajima, F. Sebo, S. Tanaka, L. Dumitru, D.J. Harris and R.I.L. Guthrie: On the separation of non-metallic inclusions from tundishes in continuous casting operations-a water model study. Steelmaking Conference Proceedings 1986, p. 705[23] S. Joo and R.I.L. Guthrie: Metallurgical Transactions B Vol. 24B. (1993), p. 755[24] J.L. Yeh, W.S. Hwang and C.L. Chou: ISIJ International Vol. 33. (1993), p. 588[25] C.S. Damle and Y. Sahai: Modeling of Grade Change Operations During Continuous Casting of Steel. Steelmaking Conference Proceedings 1994, p. 235[26] D.Y. Sheng, C.S. Kim, J.K. Yoon et al: ISIJ International Vol. 38. (1998), p. 843[27] K.J. Craig, D.J. Kock, K.W. Makgata and G.J. Wet: ISIJ International Vol. 41. (2001), p. 1194[28] Y.P. Bao, W. Jiang, B. Xu and H. Zhang: Journal of University of Science and Technology Beijing Vol. 9. (2002), p. 13[29] C.M. Fan, R.J. Shie and W.S. Hwang: Ironmaking and Steelmaking Vol. 30. (2003), p. 341[30] J. Liu, H. Yan, L. Liu and X. Wang: Journal of Iron and Steel Research International Vol. 14. (2007), p. 13[31] C. Chen, G.G. Cheng, H.K. Yang and Z.B. Hou: Advanced Materials Research Vols. 284-286. (2011), p. 1071[32] Y. Sahai and T. Emi: ISIJ International. Vol. 36. (1996), p. 667[33] S. López-Ramírez, J. De J. Barreto, J. Palafox-Ramos, R.D. Morales and D. Zacharias: Metallurgical and Materials Transactions B Vol. 32B. (2001), p. 615[34] M.C. Tsai and M.J. Green: A three dimensional concurrent numerical simulation of molten steel behavior and chemical transition at inland steel’s No.2 caster tundish. Steelmaking Conference Proceedings 1991, p. 501New Materials and Processes10.4028//AMR.476-478Optimization of Weir & Dam with Drain Holes in Continuous Casting Slab Tundish 10.4028//AMR.476-478.293。