Slag Entrainment Mechanisms

Transcription

1 ANNUAL REPORT 010 UIUC, Agst 1, 010 Review of Slag Entrainment Mecanisms Lance C. Hibbeler (P.D. Stdent) Department of Mecanical Science and Engineering University of Illinois at Urbana-Campaign 9 Families of Mold Slag Entrainment Mecanisms Meniscs level flctations Meniscs freezing / ooks Argon bbble interactions Slag crawling down te SEN ortex formation near te SEN Top srface instability Sear-layer instability Impinging g flow pon te meniscs Top srface balding University of Illinois at Urbana-Campaign Metals Processing Simlation Lab Lance C. Hibbeler

2 Meniscs Level Flctations Early work related flctations wit F vale 1 sinθcoll F = ρ Qcoll δ 3F 35 4 srface coll coll θ coll coll 3 F 5N/m 0. srface 0.4m/s Tesima et al., 1988 Kbota et al., 1991 Sdden drop in liqid pool level can expose sell to Ojeda et al., 007 slag, entrapping slag in dendrites Sengpta et al., 009 University of Illinois at Urbana-Campaign Metals Processing Simlation Lab Lance C. Hibbeler 3 Meniscs Level Flctations Slag can get entrapped in dendrites dring level flctation Severe case: powder entrapment Oscillation mark (OM) is te frozen sape of te meniscs OM redce eat transfer locally, ll leading to wavy appearance on sell inside OMs are deepened wen combined wit termal-stress bending of sell

3 Meniscs Freezing / Hooks Insfficient eat delivered to meniscs area will lead to ook formation, wic can trap particles and bbbles in te melt Mst be balanced wit flctations and impinging flow mecanisms Electromagnetic flow control elps Kbota et al., 1991 Wang, 1990 Sengpta et al., 006 Lee et al., 007 University of Illinois at Urbana-Campaign Metals Processing Simlation Lab Lance C. Hibbeler 5 Meniscs Freezing / Hooks Hooks can captre rising particles Slag can also get stck on dendrites on te back of te ook Sengpta et al., 006

4 Argon Bbble Interactions Argon mixing wit slag can form a foam tat easily becomes entrained in te jet Emling et al., 1994 Argon rising into te slag layer can case entrainment t by breaking te interface Yamasita et al., 001 Watanabe et al., 009 University of Illinois at Urbana-Campaign Metals Processing Simlation Lab Lance C. Hibbeler 7 Mold Slag Entrainment Mecanism: Slag Crawling Down te SEN Flow past blff bodies cases a pressre drop in te wake Slag is entrained if immersion dept is less tan te penetration ti dept C ρ + C ρ p = 1.9 g p,max p,min ( ρ ρ ) Yosida et al., 005 Circlar SEN pressre coefficients i C = 1.0 C =.5 p,max p,min Elliptical SEN pressre coefficients p Cp,max Cp,min = a D major a = D = a minor ln ( ) Ueda et al., 004 University of Illinois at Urbana-Campaign Metals Processing Simlation Lab Lance C. Hibbeler 8

5 ortex Formation Near te SEN Flow past a cylinder (from asymmetric flow) can lead to vortex formation in te wake of te SEN Exacerbated by te downward d momentm were reversing flows meet in a continos caster Critical port velocity to avoid vortices: Gpta and Lairi, 1996 μ ρ ρ port, crit = gwslab c1+ c μ ρ ortex dept (> immersion dept): mc ρ s ρ Δ v = g ρ ρ g ρ ρ 0.55 Kasai and Igci, 007 v Low Asymmetry Hig Asymmetry y University of Illinois at Urbana-Campaign Metals Processing Simlation Lab Lance C. Hibbeler 9 Mold Slag Entrainment Mecanism: Top Srface Wave Instability Standing at srface crases if too steep: ρ = λ crit ρ Predict maximm port velocity wit one of: D = g Lc port Dport = 0.1 g L c = 0.41 port g port port port D port ρ = g Lc ρ ρ D 0.31 port port ρ + ρ = g L ρ ρ c Rottman, 198 Gpta and Lairi, 1994 Mogaddam et al., 005 Panaras et al., 1998 Gpta and Lairi, 1996 Teodorakakos and Bergeles, 1998 λ SEN φ wslab Crest Trog discarge L c φ jet ( ) L = + w tan φ φ 1 1 c SEN slab discarge jet University of Illinois at Urbana-Campaign Metals Processing Simlation Lab Lance C. Hibbeler 10

6 Sear-Layer Instability Interface between two parallel-flowing, density-stratified flids will become nstable at critical velocity difference: 1 1 Δ 4 crit,min = 4g( ρ ρ ) Γ + ρ ρ Helmoltz, 1868 Kelvin, 1871 Δ crit = g( ρ ρ ) + ρ ρ Milne-Tomson, 1968 Igci et al., 000 LC 4 g ( ρ ρ ) ( μ + μ ) 4 Δ crit,min = 4 Γ ρμ + ρμ ( ) Fnada and Josep, 001 Magnetic field applied parallel to flow stabilizes interface like srface tension Candrasekar, 1961 Ca and Yoon, 000 University of Illinois at Urbana-Campaign Metals Processing Simlation Lab Lance C. Hibbeler 11 Mold Slag Entrainment Mecanism: Flow Impinging on te Meniscs Upward spot along narrow faces in dobleroll flow patterns can case entrainment by searing or ctting a flx finger crit ( ) 0.15 Γ ρ ρ 0.31 g μ g Γ ρ g Γ ρ = crit = 4 crit = 8 1 ρ μ ρ ρ ρ ρ Harman and Cramb, 1996 Xiao et al., 1987 Nakato et al., 1987 Searing Emling et al., 1994 Ctting Harman & Cramb, 1996 Savolainen et al., 009 University of Illinois at Urbana-Campaign Metals Processing Simlation Lab Lance C. Hibbeler 1

7 Top Srface Balding Excessive argon or narrow face spot can ps away liqid slag & expose te steel to powder or atmospere Creates inclsion particles Gpta and Lairi, 1996 Harris and Yong, 198 University of Illinois at Urbana-Campaign Metals Processing Simlation Lab Lance C. Hibbeler 13 Conclsions Nine families of mecanisms for mold slag entrainment ave been identified Mc work remains to be done to better qantitatively nderstand, predict, and control te mecanisms University of Illinois at Urbana-Campaign Metals Processing Simlation Lab Lance C. Hibbeler 14

8 Acknowledgements Continos Casting Consortim Members (ABB, Arcelor-Mittal, Baosteel, Cors, LWB Refractories, Ncor Steel, Nippon Steel, Postec, Posco, ANSYS-Flent) Keit Tomas University of Illinois at Urbana-Campaign Metals Processing Simlation Lab Lance C. Hibbeler 15