GT Cong Nghe Va Tbi Luyen Thep

I HC NNG TRNG I HC BCH KHOA

HONG MINH CNG

Gio trnh CNG NGH V THIT B

LUYN THP

NNG - 2007

Li ni u

Cng vi s tin b vt bc trong khoa hc v cng ngh, c bit l trong

lnh vc vt liu, nhiu loi vt liu mi c nghin cu v ng dng trong sn

xut. Tuy nhin, cho n nay thp vn c coi l mt trong nhng vt liu ch yu

dng trong ch to my mc, thit b cng nh trong nhiu kt cu v cng trnh chu

lc khc. Hng nm, nc ta s dng mt lng ln thp xy dng trong cc cng

trnh xy dng, cng trnh giao thng vn ti v mt lng khng nh thp ch to

ch to my mc, thit b phc v ngnh c kh, ngnh ch to t, ngnh ha cht v

nhiu ngnh khc m mt phn ln trong s vn phi nhp ngoi. Trong nhng nm

ti, p ng nhu cu xy dng v sn xut trong nc, mt nhim v cp bch l

nhanh chng pht trin ngnh thp, trong vn luyn v c phi ng mt vai tr

ht sc quan trng. pht trin ngnh thp, song song vi vic u t i mi thit

b, i mi cng ngh th mt vn ht sc cn thit l pht trin i ng cn b k

thut chuyn ngnh c kin thc chuyn mn v c nng lc thc t vng.

Gio trnh Cng ngh v thit b luyn thp c bin son gm 8 chng,

trnh by nhng kin thc c bn v thit b v cng ngh luyn thp nh c s l

thuyt qu trnh luyn thp; nguyn, nhin vt liu dng trong luyn thp; thit b v

cng ngh luyn thp trong cc loi l khc nhau; thit b v cng ngh c phi

cn Gio trnh c dng lm ti hc tp cho sinh vin chuyn ngnh C kh Luyn

cn thp thuc Khoa C kh, trng i hc Bch Khoa - i hc Nng. Mt khc,

vi ni dung lin quan n nhiu vn thc t sn xut, gio trnh cng c th dng

lm ti liu tham kho b ch cho cc cn b k thut ang lm vic trong lnh vc sn

xut thp.

Do gio trnh c bin son ln u, mi dung bao qut rng, ti liu tham

kho hn ch, chc chn cn nhiu sai st. gio trnh c hon thin hn, rt

mong s gp ca bn b ng nghip, mi kin ng gp xin gi v khoa C kh,

trng i hc Bch Khoa - i hc Nng.

Tc gi

- 5 -

Chng I

KHI QUT CHUNG

1.1. Khi nim v phn loi thp 1.1.1. Khi nim

Thp l hp kim ca st vi cacbon v mt s nguyn t kim loi hay phi kim

khc, trong hm lng cacbon khng vt qu mt gii hn nht nh.

St l nguyn t c bn v cacbon l nguyn t tp cht chnh nh hng quyt

nh n t chc v tnh cht ca thp. Cc nguyn t khc c a vo thp do c

im ca cng ngh nu luyn hoc do hp kim ha c th l tp cht c li cng c

th l tp cht c hi. Trong thp cacbon, ngoi st v cacbon, thng cha mt lng

nht nh cc nguyn t khc nh Si, Mn, P, S trong Si, Mn l tp cht c li cn P,

S l tp cht c hi cn hn ch.

Cht lng ca thp c nh gi qua cc ch tiu:

+ Tnh dn t; + Tnh chng mi mn; + Tnh chu nhit; + Tnh chng r.

1.1.2. Phn loi thp a) Phn loi theo thnh phn ha hc

Theo thnh phn ha hc, thp c chia ra: thp cacbon v thp hp kim.

+ bn b (kG/mm2); + Gii hn chy s (kG/mm2); + gin di (%); + co tht (%); + dai va p ak (kj/mm2).

Ngoi ra cn c nhng tnh nng c

bit khc nh:

b

s

%

kG/mm2

0,2

Hnh 1.1 Gin ko ca thp

- 6 -

Thp cacbon: hm lng cacbon

- 7 -

+ Thp dng c: dng ch to cc loi dng c ct, dng c o, khun dp ...

thng l thp cacbon cao hoc thp hp kim. Yu cu c bn ca thp l cng cao,

bn tng i tt, chu mi mn.

+ Thp c bit: l thp c tnh cht l ha c bit nh: chu n mn (khng g),

chu nng, chu mi mn, chu axit...

d) Phn loi theo cng ngh nu luyn Theo thit b nu luyn, thp c chia ra:

+ Thp l mactanh;

+ Thp l thi;

+ Thp l in ...

Theo mc kh oxy khi nu luyn, thp c chia ra:

+ Thp si: kh oxy cha trit ;

+ Thp lng: kh oxy trit ;

+ Thp na lng: mc kh oxy nm gia thp lng v thp si.

1.1.3. K hiu ca thp Theo TCVN, thp c k hiu nh sau:

+ Thp cacbon thng dng: CT31; CT34; ...;CT51, trong CT ch loi thp

cacbon thng dng, con s tip theo ch bn ko ca thp tnh bng kG/mm2.

+ Thp cacbon kt cu: C08; C12; ...;C20; C15; ...; C50, trong C ch loi

thp cacbon kt cu, con s tip theo ch phn vn cacbon trong thp.

+ Thp dng c: CD70; CD80; ...; CD130, trong CD ch loi thp cacbon

dng c, con s tip theo ch phn vn cacbon trong thp.

+ Thp hp kim: 60Si2; 55Mn; 110Mn13; 30CrNiW; 20Cr18Ni12Mo3Ti ...

trong con s u tin ch phn vn cacbon c trong thp; cc k hiu tip theo l k

hiu tn nguyn t hp kim v ngay sau k hiu l con s ch phn trm nguyn t

c trong thp, trng hp nguyn t hp kim c hm lng xp x 1% th khng ghi

con s.

- 8 -

1.2. Lu trnh sn xut thp Tu thuc nguyn liu dng sn xut thp, c th s dng hai lu trnh trnh

khc nhau:

+ Lu trnh dng nguyn liu qung; + Lu trnh dng st thp ph;

Hnh 1.1 trnh by s lu trnh luyn thp.

Theo quy trnh ph bin hin nay, nguyn liu qung cng vi nhin liu v

cht tr dung c a vo l cao sn xut ra gang luyn thp. Gang luyn thp

c c thnh thi hoc chuyn trc tip th lng vo cc l luyn luyn thnh

thp v c phi cn.

Qung st: qung luyn thp gm qung st nguyn khai hm lng st 66%

hoc qung thiu kt dng cc.

Gang luyn thp

Hon nguyn trc tip

Ho

n ng

uyn

th

lng

Hon nguyn th rn

St thp ph x

y

Qung st

Kh

l c

ao

X Gang c

Khng kh

L thi L in

L tinh luyn

Thp c

c phi Cn

Hnh 1.1 S lu trnh sn xut thp

- 9 -

Nhin liu: luyn gang dng nhin liu chnh l than cc l nhin liu nhn

to c bn c v bn nhit cao, hm lng tro t.

Cht tr dung: to x khi luyn gang, thng dng vi.

Sn phm chnh ca l cao l gang luyn thp cha

- 10 -

Chng II

NGUYN VT LIU DNG LUYN THP 2.1. Nguyn vt liu 2.1.1. Nguyn vt liu kim loi

Nguyn vt liu kim loi dng trong sn xut thp gm cc loi: gang thi

(hoc gang lng) luyn thp; thp vn, hi liu v cc hp kim fer.

a) Gang thi luyn thp: gang thi luyn thp c sn xut t l cao, thnh

phn ph thuc vo loi l s dng. Bng 2.1 v 2.2 cho thnh phn ca mt s loi

gang thi luyn thp ca Nga (Lin X c) v Vit Nam. Gang thi M1, M2 (hoc

GM1, GM2) dng cho l mactanh, gang thi 1, 2 dng cho l Betsme, gang thi T

dng cho l Tmat

Bng 2.1 Thnh phn gang thi luyn thp (Lin X c)

Thnh phn ha hc (%)

Mn P S

Mc

gang

Si Nhm I

Nhm

II

Loi

A

Loi Loi

B

Loi

I

Loi

II

Loi

III

M1 0,761,25 1,0 1,011,75 0,15 0,20 0,30 0,03 0,05 0,07 M2 0,75 1,0 1,011,75 0,15 0,20 0,30 0,03 0,05 0,07 1 1,261,75 0,60 1,20 - 0,07 - - 0,04 - 2 0,071,25 0,5 0,80 - 0,07 - - 0,06 - T 0,200,60 0,8 0 1,30 - 1,52,0 0,08

Bng 2.2 Thnh phn gang thi luyn thp (Cng ty gang thp Thi Nguyn)

Thnh phn ha hc (%)

Mn P S

Mc

gang

Si I II III I II III I II III

GM1

GM2

0,75

0,761,25 1,0

1,01

n

1,75

1,76

n

2,50

0,03 0,05 0,07 0,15 0,20 0,30

- 11 -

b) Thp vn: thp vn (hay cn gi l thp ph) l cc chi tit my bng thp

hng, cc ro vn, u tha trong qu trnh gia cng c kh, rn dp... c thu mua

t ngoi v. Thp ph thng c chia thnh hai loi l thp vn cacbon v thp vn

hp kim.

Thp vn cacbon (cc ro vn t thp cacbon) c dng nu thp cacbon

v thp hp kim. Thp vn nn chn dng cc, dng tm kch thc nh hn kch

thc l (chiu dy nn 10 mm), khng nn chn dng ng bt kn, thp vn rt r

nhiu, dnh du m, axit, kim ...

Thp vn hp kim (cc ro vn t thp hp kim) c tn dng nu cc mc

thp hp kim. Thp vun hp kim c phn loi theo nhm nguyn t hp kim ph

hp vi thnh phn thp cn nu, vi cc ro vn thp hp kim cha nguyn t d b

oxy ha ch nn dng khi nu khng c giai on oxy ha.

c) Hi liu: l thp h thng rt, ngt, thp ri vi trong qu trnh c... c thu

hi nu li. Hi liu yu cu phi sch, t dnh t ct.

d) Hp kim fer: hp kim ca st vi mt hoc mt s nguyn t hp kim nh Si,

Mn, Cr ... c dng iu chnh thnh phn, hp kim ha v kh oxy. Thnh phn

mt s mc fer ph bin cho cc bng 2.3 n bng 2.7.

Bng 2.3 Thnh phn hp kim fermangan (Vit Nam)

Thnh phn ha hc (%) Loi

fermangan

K hiu Mn C Si P S

Cc bon

thp Mn 0 80 0,50 2,0 0,30 0,03

Mn 1 78 1,0 2,5 0,30 0,03 Cc bon

trung bnh Mn 2 75 1,5 2,5 0,35 0,03

Mn 3 78 7,0 2,5 0,38 0,03

Mn 4 75 7,0 2,5 0,45 0,03

Mn 5 70 7,0 3,0 0,45 0,03

Cc bon

cao

Mn 6 65 7,0 4,0 0,45 0,03

- 12 -

Bng 2.4 Thnh phn hp kim fersilic (Thi Nguyn)

Thnh phn ha hc (%) Loi fer K hiu

Si Mn Cr P S

Fersilic 45 Si 45 40 47 0,80 0,50 0,05 0,04 Fersilic 75 Si 75 7080 0,70 0,50 0,05 0,04 Fersilic 90 Si 90 8795 0,50 0,20 0,04 0,03

Bng 2.5 Thnh phn hp kim silicmangan (Thi Nguyn)

Thnh phn ha hc (%) Loi fer K hiu

Si Mn C P

Silicmangan 20 SiMn20 20 65 1,0 0,1

Silicmangan 17 SiMn17 17 65 1,7 0,1

Silicmangan 14 SiMn14 14 60 2,5 0,2

Bng 2.6 Thnh phn siliccan xi (Lin X c)

Thnh phn ha hc (%) Loi fer K hiu

Ca CaSi Al P S

KaCu0 31 90 1,5 0,05 0,04

KaCu1 28 90 2,0 0,05 0,04

Siliccanxi

KaCu2 23 85 3,0 0,05 0,07

Bng 2.7 Thnh phn fercrm (Lin X c)

Thnh phn ha hc (%) Loi fer K hiu

C Si P Cr S

Xp 0000 0,06 1,5 0,06 65 0,03

Xp 000 0,071,0 1,5 0,06 65 0,04 Xp 00 0,110,15 1,5 0,06 60 0,04

Fercrm

Xp 0 0,160,25 0,2 0,06 60 0,04

- 13 -

Xp 01 0,260,50 2,0 0,1 60 0,04 Xp 1 0,501,0 2,53,0 0,10 60 0,04 Xp 2 1,12,0 2,53,0 0,10 60 0,04 Xp 3 2,14,0 2,53,0 0,10 65 0,04 Xp 4 4,16,5 2,05,0 0,07 65 0,04

Fercrm

Xp 5 6,68,0 2,05,0 0,07 65 0,04

Ngoi cc nguyn liu trn, hin nay ngi ta cn dng st xp ln nguyn liu

luyn thp, l sn phm ca qu trnh hon nguyn trc tip qung st bng kh

thin nhin hoc bng than gy, hm lng st trn 90%.

2.1.2. Cht oxy ha Thng dng l qung st v oxy.

Qung st: thng dng loi c hm lng oxyt st cao v cc oxyt khc thp.

Yu cu k thut i vi qung st dng lm cht oxy ha khi luyn thp nu bng

2.8.

Bng 2.8 Yu cu k thut i vi qung st dng lm cht oxy ha

Thnh phn ha hc (%) Loi l

Fe SiO2 S P

m

(%)

C cc

(mm)

L Mactanh 50 10 0,2 - - 30250 L thi nh 50 10 0,2 - - 1050 L in 55 8 0,1 0,1 70

- 14 -

Oxy: dng oxy trong khng kh hoc oxy k thut hm lng oxy 98%. Yu

cu i vi oxy k thut dng trong luyn thp nu bng 2.10.

Bng 2.10 Yu cu i vi oxy k thut dng trong luyn thp

Loi l Hm lng O2

(%)

m

(g/m3)

p sut s

dng (kG/cm2)

L in > 98

- 15 -

Bng 2.12 Yu cu i vi hunh thc dng lm cht to x khi luyn thp

Thnh phn ha hc (%) Loi l

CaF2 SiO2 CaO < S <

m

(%)

C cc

(mm)

L mactanh 85 5 - 0,2 - 2050 L thi 85 5 - 0,2 - 550 L in 85 4 5 0,2 0,5 550

Sa thch: thnh phn chnh l SiO2, bng 2.13 nu thnh phn mt s loi sa

thch hay dng to x trong luyn thp nc ta.

Bng 2.13 Thnh phn mt s loi sa thch dng to x khi luyn thp

Thnh phn ha hc (%) a danh khai thc

Fe S SiO2 Al2O3 CaO MgO

Thi Nguyn 1 0,08 93 4 0,2 0,1

Tnh Gia 1,2 - 88 10 0,1 0,2

Ph Cm Ngh An 1,8 - 93 4 0,7 0,1

2.1.4. Cht tng cacbon tng hm lng cacbon trong thp ngi ta s dng: vn than cc, vn in

cc hoc rt thm gang lng vo. Yu cu i vi mt s loi cht tng cacbon cho

bng 2.14.

Bng 2.14 Yu cu i vi mt s loi cht tng cacbon dng khi luyn thp

Thnh phnha hc (%) Vt liu

C S <

tro

(%)

m

(%)

ht

(%)

Vn than 95 0,1 2 0,5 0,51,0 Vn in cc 80 0,1 15 0,5 0,51,0

- 16 -

2.1.5. Vt liu chu la Trong luyn thp, xy l v cc thit b lm vic nhit cao, ngoi cc

vt liu thng dng nh st thp, btng ... ngi ta thng s dng mt lng ln

gch chu la, gch cch nhit v cc vt liu chu la dng bt. Di y gii thiu

mt s loi vt phm chu la thng dng dng trong xy dng thit b luyn thp.

a) Vt phm inat: l vt phm chu la cha khong cht thch anh SiO2 >93%.

+ chu nng t 1690 1710oC; + Nhit bin mm di ti trng 2 kG/cm2 l 1650oC; + Bn vi mi trng axit; + Gin n nhit ln; + bn nhit thp.

b) Vt phm samt: l vt phm chu la cha t 30 45 % Al2O3. + chu nng 1610 1730oC; + C tnh axit yu; + bn nhit tng i ln (10 50 ln); + Gin n nhit ln.

c) Vt phm alumin cao: l vt phm chu la c hm lng Al2O3 t 46 100%.

+ chu nng cao v ph thuc hm lng Al2O3; + Bn vi c mi trng kim v mi trng axit; + bn c v bn nhit cao (trn 100 ln).

d) Vt phm bn axit: l vt phm chu la cha 15 30 % Al2O3 v > 65 % SiO2.

+ chu nng 1610 1700oC; + Bn vi mi trng axit; + Bn nhit thp.

e) Vt phm manhdit: l vt phm chu la cha 90 96 % MgO. + chu nng cao, trn 2000oC;

- 17 -

+ Bn vi mi trng kim; + Bn nhit thp; + Gin n nhit ln; + Gim cht lng mnh khi b m.

f) Vt phm crmit: l vt phm chu la cha 80 90 % crmit, 10 12 % manhdit v 7 10 % dumit.

+ chu nng 1900oC; + C tnh trung ho, bn vi c mi trng axit v mi trng kim; + Bn nhit thp (3 5 ln).

g) Vt phm crmit - ma nhdit: l vt phm chu la cha 30 70 % crmit v 70 30 % manhdit. Tnh cht tng t manhdit nhng cht lng cao hn.

h) Vt phm cacbon: Gm cc loi: cacbrun, graphit, cacbon.

Vt phm cacbrun: vt phm sn xut t bt SiC c cht dnh kt l t st

chu la v silicat st.

+ chu nng cao, trn 2000oC; + bn nhit cao; + Tnh chng mi mn v bn c hc tt; + Dn in, dn nhit tt; + Khi nhit trn 1300oC d b oxy ha v b kim n mn.

Vt phm graphit: c sn xut t hn hp 20 60 % graphit, 30 40 % t st chu la v 10 40 % bt samt.

+ chu nng > 2000oC; + bn nhit tt; + H s gin n nhit nh; + Dn nhit tt; + Bn vi mi trng x v kim loi lng.

Vt phm cacbon: thnh phn ch yu l cac bon, cha 80 90 %C. + chu nng cao > 2500oC;

- 18 -

+ bn nhit tt; + Dn in v dn nhit tt; + H s gin n nhit nh.

i) Vt liu cch nhit: Vt liu cch nhit dng trong l luyn thp gm hai

nhm:

+ Vt liu cch nhit thin nhin: iatmit, inphurit, aming. + Vt liu cch nhit nhn to: vt phm chu la nh, x bng ...

Diatmit, inphurit c thnh phn ch yu l SiO2 nhng c xp rt ln do

dn nhit km, h s dn nhit 0,014 0,06 W/m.. Aming c thnh phn chnh l silicat manh ngm nc, h s dn nhit

khong 0,15 W/m..

Vt phm chu la nh c thnh phn tng t cc vt phm chu la cng loi

nhng c xp ln ( 50 80 %), do khi lng th tch b (0,27 1,3 kg/m3) v dn nhit km, h s dn nhit 0,11 0,81 W/m.. chu nng ca vt phm cch nhit thp hn chu nng ca vt phm chu la cng loi. X bng c sn

xut t x luyn kim dng si, c xp ln, cch nhit v chu nng tt.

j) Cc th gch xy xy cc thit b luyn thp, ngi ta s dng cc th gch chu la v cch

nhit sn xut theo hnh dng v kch thc tiu chun ha. Trn hnh 2.1 gii thiu

mt s th gch xy thng dng.

Gch thng: dng xy tng thng, y l hoc phi hp vi gch vt xy

vm v tng cong, kch thc ph bin l 230x113x65.

Gch vt nm: dng xy tng cong hoc vm l c chiu dy mng, kch

thc ph bin l 230x113x65/55 hoc 230x113x65/45

Gch vt ng: dng xy tng cong hoc vm l c chiu dy ln, kch

thc ph bin l 230x113x65/55 hoc 230x113x65/45.

Gch chn vm: dng xy chn vm cong, kch thc ph bin l

230x113x135/56/37.

- 19 -

Gch vm treo: dng xy vm l phng bng mc treo, kch thc ph bin

l 300x276x260/100/75/30.

Khi chn gch xy l nn dng cc loi gch tiu chun c ch to hng lot

v d kim. Trong trng hp cn dng cc loi gch phi tiu chun cng nn a v

gn vi dng gch tiu chun vic ch to d dng hn.

2.2. Tnh ton thnh phn phi liu khi c thp Vic tnh ton thnh phn phi liu khi luyn thp ph thuc rt ln vo thit b

nu v cng ngh nu luyn

i vi l thi, vn cn gii quyt l m bo thnh phn, nhit gang

lng a vo l v qu trnh cng ngh thi luyn, do vic tnh ton phi liu ch

yu l tnh ton thnh phn phi liu khi nu gang lng theo yu cu ca l chuyn.

a

b

c

d

c

a

b

d

c

b

a

e

d

c b

a

e

c

b d

f

a) b)

a

c

b

d

c)

d) e) g)

Hnh 2.1 Hnh dng v kch thc mt s loi gch quy chun a) Gch thng b) Gch vt nm c) Gch vt ng

d) Gch chn vm e) Gch vm cu g) Gch vm treo

a

- 20 -

i vi l Mactanh, l in h quang vic tnh ton phi liu ch yu l tnh

ton thnh phn kim loi trong phi liu. Cc bc tnh ton theo trnh t sau:

+ Chn phng php nu: c hai phng php nu l nu khng c giai on oxy ha v nu c giai on oxy ha. Vic la chn phng php nu cn c vo

ngun nguyn vt liu nu v c im ca thp cn nu. Chn phng php nu

khng c giai on oxy ha khi yu cu cht lng thp khng cao, kh P v S khng

trit , nguyn vt liu ch yu l vn thp ph. Chn phng php nu c giai on

oxy ha khi yu cu cht lng thp cao (lng vt ln phi kim trong thp nh, kh P

v S trit ), ngun nguyn vt liu c nhiu gang.

+ Tnh ton thnh phn nguyn liu kim loi: cn c tnh ton l thnh phn nguyn vt liu s dng, lng chy hao cc nguyn t trong qu trnh nu luyn

v thnh phn mc thp cn nu.

T l chy hao cc nguyn t khi nu trong l in h quang baz cho bng

2.15.

Bng 2.15 T l chy hao cc nguyn t khi nu trong l in h quang baz

Nguyn t Lng chy hao trong cc giai on (%)

Nu chy Oxy ha Hon nguyn

Fe 2 5 8 10 - Mn 50 70 10 15 - Si 50 75 80 - 50 15 20 Cr 10 5 10 20 3 2 P 50 60 30 40 - S - 15 20 75 80

Thnh phn mc thp cn nu tra theo cc s tay.

Khi tnh ton phi liu ch yu cn c vo thnh phn cacbon, cc nguyn t

khc tnh sau khi tnh xong thnh phn phi liu, da vo s chy hao ca chng trong

tng giai on m iu chnh vo cui giai on hon nguyn (i vi Mn, Si... ) hoc

- 21 -

tm cch kh cc giai on (i vi P, S). Thng tnh ton thnh phn phi liu

theo %C sau khi nu chy xong. i vi phng php nu khng c giai on oxy

ha, ta tnh ton sao cho khi nu chy xong %C nh hn gii hn dc ca mc thp

cn nu. i vi phng php nu c giai on oxy ha, ta tnh ton sao cho khi nu

chy xong %C phi ln hn gii hn dc ca mc thp cn nu khong 0,3 0,4 % . Trong trng hp nu thp cc bon cao th gim lng cc bon thp hn bnh thng

mt t d dng cho vic kh P.

Hm lng cacbon trong thnh phn phi liu bng tng lng cacbon trong

gang, thp vn, phoi thp, hi liu. Khi tnh ton thnh phn phi liu c th dng

phng php gii tch hoc phng php chn.

Khi dng phng php gii tch, dng h phng trnh bc nht tnh ton.

Cc phng trnh c lp da trn c s s nguyn t c chn lm cn c tnh

ton v tng lng m liu. Gi s chn hai nguyn t tnh ton th s phng trnh

lp c l ba phng trnh, do ch c chn ba n s l t l thnh phn ca ba

loi liu. Nu s loi vt liu ln hn ba th chn trc t l dng mt s loi. Sau khi

gii h phng trnh bc nht, xc nh c t l cc thnh phn, tin hnh kim tra

hm lng cc nguyn t khc theo hm lng c trong m liu, tnh ton lng cn

kh hoc a thm vo trong giai on oxy ha hoc giai on hon nguyn t

c hm lng yu cu.

Trong thc t luyn thp ngi ta hay dng phng php tnh ton thnh phn

phi liu theo phng php chn. Cn c vo tnh hnh nguyn vt liu sn c v kinh

nghim nu luyn, chn trc thnh phn m liu, thng ngi ta chn nh sau:

i vi thp cacbon, chn:

+ St thp vn (ro cn, ro rn dp, ro tn dy, ..) : 46 50 %; + Phoi thp (phoi tin, ro tn mng, ro vn ...) :15 30%; + Gang luyn thp (hoc gang c) t P v S : 35 20 %; Hoc:

+ St thp vn : 70 90 %; + Gang luyn P v S trung bnh : 35 20 %;

- 22 -

i vi thp hp kim, chn:

+ St thp vn : 70 90 %; + Gang t P v S : 10 %; Hoc:

+ St thp vn : 20 %; + Ph phm thp hp kim: 60 70%; + Ph phm thp cc bon : 10 20%; Sau khi chn xong thnh phn phi liu kim loi, ta tnh c thnh phn cc

nguyn t (C, Si, Mn, P, S ...) trong phi liu, c bit l cacbon. Cc nguyn t ny

thng cao hn yu cu. Nu lng cacbon qu cao c th tng t l thp vn, gim t

l gang v tnh ton li. Qu trnh kh C, Si, Mn v P ch yu bng oxyt st do m

liu a vo, do thp b oxy ha, hoc do oxyt st a vo trong giai on oxy ha.

+ Tnh ton lng qung cn thit t chy C v cc tp cht: khi nu c giai on oxy ha cn xc nh lng qung st a vo lm cht oxy ha. Trong

qung st ngoi oxyt st Fe2O3 l ch yu, cn cha mt lng nh Fe3O4, FeO v cc

tp cht. Khi tnh ton ngi ta quy i F3O4 v FeO v Fe2O3, do thnh phn

qung tnh ton ch cha Fe2O3 v tp cht.

Khi a qung st vo l s xy ra phn ng:

FeO3FeOFe 32 + Khi s xy ra phn ng t chy cc tp cht v cacbon:

Fe2SiOFeO2Si 2 ++ FeMnOFeOMn ++ Fe5OPFeO5P2 52 ++ ++ COFeFeOC Da vo lng oxy cn thit cho tng phn ng v lng cc nguyn t cn

kh ta tnh c lng oxy cn thit v tnh ra lng qung cn dng.

+ Tnh ton lng cc nguyn liu khc a vo l: m bo tnh cht ca x, kh c P, S v oxy ... ta cn tnh ton lng cht to x, cht kh oxy a vo

- 23 -

l. Mun tnh lng cht kh oxy cn dng, ta cn phi bit lng oxyt st cn li sau

giai on oxy ha, s phn b ca n trong x v kim loi, phng php kh v loi

cht kh a vo, lng nguyn t cn iu chnh... , do qu trnh tnh ton thng

phc tp v d sai st. Trong thc t, n gin ngi ta thng tnh ton gn ng

nh sau:

i vi cht to x, tnh theo trng lng phi liu kim loi:

Cht to x vi: 2 3% ; Samt: 0,2 0,15%; Hunh thch: 0,13%;

i vi cht kh v iu chnh thnh phn, tnh theo trng lng kim loi lng:

Nhm: 0,5 1,5 kg/tn; Siliccanxi hay silicmangan: 0,5 1 kg/tn; Fermangan: 13 15 kg/tn; Ferersilic: 7,5 10 kg/tn.

- 24 -

Chng III

L THUYT QU TRNH LUYN THP Qu trnh luyn thp xy ra trong iu kin nhit cao, l kt qu ca nhiu qu trnh tc dng ha l phc tp gia kim loi, x, mi trng kh l, nhin liu, vt

liu xy l ... trong qu trnh oxy ha v hon nguyn cc nguyn t ng mt vai

tr ht sc quan trng. Trong chng ny nghin cu mt s vn c bn lin quan

n cc qu trnh luyn kim trong luyn thp.

3.1. L thuyt v s oxy ha v hon nguyn Trong qu trnh luyn thp, phn ng oxy ha - hon nguyn ph bin l theo

h oxy. Phng trnh tng qut ca phn ng c dng sau:

2OMe2 + MeO2 (3.1) XOMe + XMeO + (3.2)

Trong :

Me - nguyn t oxy ha;

X - nguyn t hon nguyn.

V d qu trnh hon nguyn st xy ra theo phn ng:

QCO3FeC3OFe 32 +++ Tt c phn ng trong luyn thp u xy ra th lng, trong Fe ng vai

tr dung mi, cc cht khc l cht tan.

c trng cho kh nng xy ra phn ng oxy ha - hon nguyn, ngi ta

thng xt gi tr thay i nng lng t do ca h thng Z. Trong iu kin tiu chun th:

p0T

0T

0T KlgT575,4STHZ == (3.3)

Do : 575,4S

T575,4HKlg

0T

0T

p

+= (3.4)

Trong : 0TZ - s thay i nng lng t do ca h thng; 0TH - s thay i nhit hm ca h thng (entanpi).

- 25 -

0TS - s thay i entrpi ca h thng;

T - nhit tuyt i;

Kp - hng s cn bng;

mi nhit , trong h thng kim loi - oxy - oxyt u c p sut ring phn

ca oxy tng ng trn kim loi v oxyt. p sut ring phn (2O

P ) ca oxy trong pha

kh khi n cn bng vi oxyt v kim loi th gi l p sut phn ly ca oxyt v ta c:

2Op

PK = p sut phn ly oxyt cng nh th nguyn t kim loi cng d b oxy ha. Bnh

thng, p sut ring phn ca oxy trong pha kh thng ln hn p sut phn ly ca

cc oxyt kim loi nn hu ht kim loi u b oxy ha. Khi tng nhit , p sut phn

ly ca oxyt tng rt nhanh, nn phn ng oxy ha ca nhiu nguyn t kim loi gim.

thy r kh nng oxy ha ca mt s kim loi thng thy trong qu trnh

luyn thp ta kho st 0TH v 0TZ ca mt s phn ng thng gp. Bng 3.1 Gi tr ca 0TH v 0TZ ca mt s phn ng thng gp

0298Z kj/mol O2 Phn ng ha hc

to ra oxyt 1000oC 1600oC

0298H

kj/mol O2

CaO2OCa2 2 =+ - 1068 - 942,11 - 1270,27

322 OAl32OAl

34 =+ - 895,75 - 781,47 - 497,78

22 SiOOSi =+ - 690,28 - 581,17 - 872,99 MnO2OMn2 2 =+ -624,67 - 535,91 - 779,58

FeO2OFe2 2 =+ - 399,10 - 313,13 - 540,10 NiO2ONi2 2 =+ - 306,27 -190,54 - 339,24

22 CuOOCu =+ -190,92 - 103,84 - 339,24

T bng (3.1) v cc phng trnh trn ta c nhn xt: thng 0Z0T

- 26 -

cng ln th phn ng tin hnh cng mnh. Do nguyn t no xp trn st (c 0TZ nh hn) th s b oxy ha, cn cc nguyn t xp di st (c 0TZ ln hn) th thc t kh b oxy ha.

phng trnh phn ng (3.2), phn ng ch xy ra theo chiu thun khi 0XO

0MeO ZZ phn ng s xy ra theo chiu ngc li.

Mt khc, p0T QH = , trong Qp l nhit phn ng, theo bng (3.1) th ni

chung cc phn ng c 0H0T tc l phn ng ta nhit. V vy, khi nhit ca h thng tng ln th Kp gim i, c ngha l phn ng tin dn ti cn

bng v chuyn sang chiu ngc li (hon nguyn). Trn thc t, trong khong nhit

nu luyn, tr s ca 0TH v TS thay i t chng t phn ng hon nguyn xy ra yu hoc kh xy ra.

Tc oxy ha cc nguyn t bn cnh ph thuc vo i lc ha hc ca

nguyn t vi oxy cn ph thuc nng , do khi cp oxy vo l st thng b oxy

ha ngay mc d i lc ca n vi oxy nh hn Si, Mn.

phn ng xy ra th 0Z 570oC).

+ Fe - Fe3O4 - Fe2O3 ( vng nhit < 570oC).

Ty thuc phng php cp oxy m c cu ca phn ng oxy ha st tin hnh

c th khc nhau. Thc t, ngi ta cung cp oxy cho qu trnh nu luyn theo ba

phng php:

- 27 -

+ Trc tip thi oxy vo l;

+ a qung st vo l;

+ Nh mi trng kh l.

Khi thi trc tip oxy (hay khng kh) vo thp lng, c cu phn ng xy ra

nh sau:

{ } [ ]O2O2 = (3.5) [ ] [ ] FeOOFe =+ (3.6) [ ] ( )FeOzFeOyxFeO += (3.7) Vi zyx += Khi a trc tip qung vo hp kim lng:

32OFe qung ( )32OFe (3.8) ( ) [ ] FeO.x3FexOFex 32 + (3.9) [ ] ( )FeOz3FeOy3FeO.x3 += (3.10)

Vi zyx += Khi cung cp oxy bng mi trng kh l: nu trong mi trng kh l c cha

cc kh oxy ha (hi nc, CO2, O2 ...) th kh ny s truyn oxy cho st qua x, qu

trnh c th m t nh sau:

+ b mt tip xc gia x v kh:

( ) { } ( )322 OFeO21FeO2 =+ (3.11)

+ ( )32OFe khuch tn qua x n b mt tip xc gia x v kim loi v xy ra phn ng:

( ) [ ] xFeO3FexOFex 32 + (3.12) [ ] ( )FeOz3FeOy3FeO.x3 += (3.13)

Vi zyx += Mun qu trnh ny tin hnh nhanh th mi trng phi l mi trng kh oxy

ha, x cha nhiu FeO v c tnh linh ng tt.

- 28 -

Phn ng oxy ha st l phn ng ta nhit nn khi nhit tng tc phn

ng s chm li.

Phn ng hon nguyn st trn thc t rt kh xy ra, trong nu luyn hon

nguyn st ngi ta a vo hp kim lng cc nguyn t c i lc ha hc vi oxy

mnh hn st. Cc nguyn t ny c th a vo trong kim loi (Mn, Si, Al ...) hoc

ri ln x (bt cc, bt fersilic)

3.2.2. S oxy ha v hon nguyn mangan Mn l nguyn t hp kim nh hng ln n c tnh ca thp. Mn lm tng

bn, cng ca thp, tng tnh chu mi mn. Tuy nhin hm lng Mn phi nm

trong mt phm vi nht nh, khi vt qu gii hn nht nh li c nh hng c hi.

Theo bng (3.1), phn ng oxy ha Mn c Z nh hn phn ng oxy ha st, do khi nu luyn Mn d b oxy ha.

Khi thi oxy trc tip vo kim loi lng th xy ra phn ng:

[ ] { } ( )MnOO21Mn 2 =+ (3.14)

Khi trong kim loi lng cha [ ]FeO hay kh oxy trc tip bng Mn th: [ ] [ ] ( ) [ ]FeMnOFeOMn +=+ (3.15) Khi trong x cha nhiu FeO th phn ng xy ra in hnh l:

[ ] ( ) ( ) [ ]FeMnOFeOMn +=+ (3.16) Phn ng c:

T4,14200.30Z += Hng s cn bng:

( )( ) [ ]Mn%.N

NK

FeO

MnOMn = (3.17)

V 16,3T600.6Klg Mn = (3.18)

Suy ra:

[ ] ( )( )FeOMnO

Mn NN

.K

1Mn% = (3.19)

- 29 -

Khi t s ( )( )FeOMnO

NN

khng i, nu tng nhit th lng Mn cn li trong kim

loi tng (do KMn gim), ngc li khi nhit khng i ( constK Mn = ), vi cng t

s ( )( )FeOMnO

NN

th [ ]Mn% di x baz cao hn di x axit. V vy, qu trnh l axit th Mn b oxy ha hon ton hn qu trnh l baz.

Do phn ng oxy ha Mn l phn ng ta nhit, nn khi nhit tng tc

phn ng s chm li.

Khi nhit rt cao, c th xy ra s hon nguyn Mn, qu trnh ny thng

km theo s oxy ha cacbon, do ta c th coi n l kt qu ca hai phn ng ng

thi:

( ) [ ] [ ] ( )FeOMnFeMnO +=+ (3.20) ( ) [ ] { } [ ]FeCOCFeO +=+ (3.21)

( ) [ ] [ ] { }COMnCMnO +=+ (3.22) Trong thc t nu luyn rt kh xy ra phn ng hon nguyn Mn trc tip

bng cacbon, nhng trong l axit Mn c th c hon nguyn bi Si:

( ) [ ] ( ) [ ]Mn2SiOSi)MnO2 2 +=+ (3.23) Trong luyn thp ngi ta thng s dng Mn t c mc ch:

+ m bo c tnh cho thp c;

+ Kh oxy s b cho nc thp.

Kh nng kh oxy ca Mn rt yu nhng ngi ta vn dng Mn kh oxy s

b nhm gim hm lng oxy trong thp trc khi kh bng Si v Al, mt khc khi

cho Mn vo thp cho php ta iu chnh s si ca thp trong khun, khi thp ng

c Mn ngn cho thp khng b oxy ha tip bi kh tri, trnh c hin tng si

khun.

3.2.3. S oxy ha v hon nguyn silic Si cng l mt nguyn t hp kim nh hng ln n c tnh ca thp. Si tng

kh nng chng r, i vi mt s thp Si c tc dng tng t tnh. Cng nh Mn, hm

- 30 -

lng Si trong thp phi nm trong mt phm vi nht nh, khi vt qu gii hn cn

thit li c nh hng c hi.

Phn ng oxy ha Si xy ra c khi nu chy, trong giai on oxy ha to thnh

( )2SiO hoc ( )SiO v h Si - O chuyn bin theo hai h thng: Si SiO siO2 ( nhit > 1500oC)

Si siO2 ( nhit < 1500oC)

Phn ng oxy ha Si cng ph thuc phng php cp oxy.

Nu thi oxy trc tip vo thp lng:

[ ] { } ( )SiO2OSi2 2 =+ (3.24) Hay [ ] { } ( )22 SiOOSi =+ (3.25) Khi kh oxy bng Si hay trong thp c nhiu [ ]FeO th xy ra phn ng:

[ ] [ ] ( ) [ ]Fe2SiOFeO2Si 2 +=+ (3.26) in hnh nht l phn ng khc pha xy ra mt phn cch gia x v kim

loi:

[ ] ( ) ( ) [ ]Fe2SiOFeO2Si 2 +=+ (3.27) Phn ng c: T7,50000.87Z += (3.28)

( )[ ] ( )2FeOSiO

Si N.Si%N

K 2= (3.29)

1,11T057.19Klg Si = (3.30)

T (3.29) suy ra:

[ ] ( )( )2FeOSiO

Si NN

.K1Si% 2= (3.31)

Phn ng (3.27) cn ph thuc vo tng quan gia p sut phn ly oxyt ca

oxyt silic v oxyt st. giai on u nu chy, )SiO(O)FeO(O 222 PP > nn Si b oxy ha, nhng cui giai on nu chy (l mctanh, l thi) th s khc nhau gia chng

khng ln lm do phn ng dn t ti trng thi cn bng.

- 31 -

T cc phn ng trn ta nhn thy phn ng oxy ha Si l phn ng ta nhit,

do khi nhit tng, tc phn ng chm li v c th dn ti t cn bng hoc

chuyn sang hon nguyn Si. Kh nng t cn bng hoc chuyn sang hon nguyn

Si ph thuc qu trnh luyn.

Trong l baz, u giai on nu, mt phn ( )2SiO to ra s lin kt vi ( )FeO v to thnh hp cht phaialit: ( ) ( ) ( )422 SiOFeFeO2SiO =+ (3.32)

V sau, ty thuc theo mc ha tan ca vi trong phaialit m oxyt st s

tch dn ra:

( ) ( ) ( ) ( )FeO2SiOCaCaO2SiOFe 4242 +=+ (3.33) Nh vy trong x baz, oxyt silic nm dng silicat v phn ng (3.27) ch t

cn bng khi nng Si trong thp rt thp, do phn ng hon nguyn Si rt t kh

nng xy ra.

Trong l in h quang, i khi c s hon nguyn Si ti 0,1 0,15% vo giai on kh oxy khuch tn.

Trong l in axit, do x bo ha (SiO2) v rt t oxyt st t do, do cui giai

on nu, Si b hon nguyn kh nhiu bng C v Fe.

Trong nu luyn thp, Si c s dng nhm mc ch:

+ m bo thnh phn ha hc ca hp kim, t c c tnh v cc tnh

cht khc theo yu cu;

+ Kh oxy cho nc thp.

Trong l in baz ngi ta cho trc tip fersilic vo nc thp kh oxy

theo phn ng:

[ ] [ ] ( ) [ ]Fe2SiOFeO2Si 2 +=+ (3.34) ( )[ ][ ]2

SiO'Si FeO.Si%

NK 2=

85,10T050.26Klg 'Si +=

- 32 -

Trong l in axit do nng oxyt st trong x nh, oxyt silic b bo ha v p

sut phn ly ca oxyt cacbon nh hn p sut phn ly ca oxyt silic, do Si c

hon nguyn nhiu bi Fe v C:

( ) [ ] [ ] { }CO2SiC2SiO2 +=+ (3.35) ( ) [ ] [ ] ( )FeO2SiFe2SiO2 +=+ (3.36) Si hon nguyn t cc phn ng (3.35) v (3.36) c th dng kh oxy theo

phn ng (3.34). Trong trng hp cn kh oxy nhanh ngi ta cng c th cho thm

fersilic vo thp lng.

V kh nng kh oxy, th Si kh oxy mnh hn Mn, khi nhit tng kh nng

kh oxy ca Si gim.

3.2.4. S oxy ha ca cacbon Hm lng cacbon trong thp ph thuc vo mc thp, nhim v ca luyn thp

l kh bt C khi d v b sung C khi thiu. Ring i vi thp khng r, khi luyn phi

kh C xung hm lng thp nht c th.

Phn ng oxy ha cacbon l phn ng ch yu trong qu trnh luyn thp v c

nh hng rt ln n thi gian nu luyn.

Tc oxy ha cacbon ph thuc hai qu trnh ch yu:

+ Qu trnh cung cp oxy;

+ Phn ng oxy ha cacbon.

Khi thi oxy trc tip vo thp lng (trong l chuyn) th phn ng oxy ha

cacbon xy ra nh sau:

[ ] { } { }COO21C 2 =+ (3.37)

Hoc theo h hai phng trnh c phn ng trung gian:

[ ] { } [ ]FeOO21Fe 2 =+

[ ] [ ] [ ] [ ]COFeCFeO +=+ (3.38) [ ] { }COCO =

- 33 -

{ } [ ] { }COCO21

2 =+ (3.39) Khi cung cp oxy t kh l qua x hoc oxy t x ni chung, th c cu ca phn

ng oxy ha cacbon s xy ra theo nhiu giai on:

+ Khuch tn oxyt st t x vo kim loi:

( ) [ ]FeOFeO + Khuch tn cacbon vo khu vc phn ng:

+ Phn ng gia [ ]FeO v [ ]C : [ ] [ ] [ ] [ ]COFeCFeO +=+ (3.40) + To kh { }CO : [ ] { }COCO = Do , phn ng chung s l:

( ) [ ] [ ] { }COFeCFeO +=+ (3.41) Trong cc phn ng trn, thc t do CO khng ha tan trong thp lng, cc

phn ng (3.38) v (3.40) khng pht trin nhiu c m ch yu ch xy ra trn b

mt cc bt kh theo phn ng khc pha. Trong l thi, qu trnh s xy ra trm mt

cc bt khi do gi thi vo v cc bt kh CO mi to thnh. Trong l mactanh, l in

th lc u phn ng pht trin t cc tm mm kh trn cc mt nhm ca tng l,

y l, liu ... sau cc phn ng tip tc pht trin t cc bt kh CO va mi to

thnh.

Thc t xc nhn rng: s hn ch qu trnh oxy ha cacbon khi cung cp oxy

t x khng phi do phn ng ha hc m ch yu do qu trnh khuch tn. Xt trng

hp l mactanh, quan h gia hm lng [ ]FeO v [ ]C trong kim loi c dng nh hnh 3.1. Qua th nhn ta thy vi p sut phn ly 1PCO = atm v nhit 1600oC th tch s 0112,0FeO.%C% = cao hn nhiu so vi l thuyt. S d c s chnh lch ny l do s khuch tn xy ra vi tc rt chm, nht l qu trnh khuch tn

( ) [ ]FeOFeO .

- 34 -

Trong qu trnh luyn thp, do cacbon b oxy ha sau khi oxy ha gn ht Si,

phn ln Mn v cc nguyn t c i lc ha hc vi oxy mnh hn cacbon. V vy, khi

luyn thp c giai on oxy ha, khng nn a cc nguyn t hp kim d b oxy ha

vo trc giai on oxy ha, nu khng s lm tn hao nguyn t hp kim v hn ch

tc oxy ha cacbon.

Tc oxy ha cacbon ch yu do qu trnh cung cp oxy (phng php cung

cp v s khuch tn ca oxy trong kim loi). Chnh v vy, tc oxy ha cacbon

trong cc l thng rt khc nhau, trong l thi tc oxy ha cacbon t ti

0,5%/pht, trong khi trong l mactanh ch khong 0,002 0,007%C/pht. Tc khuch tn v thot kh CO ph thuc rt ln vo st ca x v chiu

dy lp x. X long v chiu dy mng th tc khuch tn v thot kh nhanh.. Khi

nu luyn thp, nhn vo s ni ca bt kh c th d on c chiu dy ca lp x,

khi chiu dy lp x hp l, bt kh ch hi n trn mt lp x v khng nhn thy mt

thong nc thp.

3.2.5. Kh phtpho Phtpho l nguyn t c hi trong thp v n lm gim tnh do ca thp, gy ra

hin tng dn ngui, c bit l khi hm lng cacbon trong thp cao. Ch trong mt

0 0,1 0,2 0,3 0, 0,5 0,6 0,7 0, 0,9

0,1

0,2

0,3

0,4

0,5

%FeO

%C

1

2

3

Hnh 3.1 Quan h cn bng ca [ ]FeO v [ ]C trong l mactanh p sut PCO = 1,0 1,5 atm

1) Cn bng 2) trong l 3) lp kim loi st di x

- 35 -

s mc thp, khi yu cu b mt gia cng cn nhn cao hoc cn phoi d gy vn

to thun li cho qu trnh gia cng, mi dng thp c hm lng P cao.

Trong qu trnh luyn thp, s oxy ha P xy ra theo phn ng:

[ ] ( ) [ ] [ ] QFe5OPFeO5P2 52 ++=+ (3.42) [ ]52OP khuch tn vo x kt hp vi ( )FeO to thnh mui ( )52OP.FeO3 theo phn ng:

( ) ( ) ( )5252 OP.FeO3FeO3OP =+ Mui ( )52OP.FeO3 rt khng n nh khi nhit cao v mi trng x axit. Khi c mt ( )2SiO , mui ( )52OP.FeO3 tc dng vi ( )2SiO theo phn ng: ( ) ( ) ( ) ( )522252 OPSiO.FeO3SiO3OP.FeO3 +=+ ( )52OP tc dng vi [ ]C v hon nguyn P tr li kim loi: ( ) [ ] [ ] { }CO5P2C5OP 52 +=+

Nh vy, trong qu trnh axit khng c kh nng kh P. Trong trng hp ny,

luyn c thp tt phi s dng nguyn liu cha t P.

Trong mi trng x baz, x cha nhiu ( )CaO , nn ( )52OP tc dng vi ( )CaO theo phn ng: ( ) ( ) ( )5252 OP.CaO3CaO3OP =+ (3.43) Hoc ( ) ( ) ( )5252 OP.CaO4CaO4OP =+ (3.44)

V ( )52OP.CaO3 hoc ( )52OP.CaO4 l cc phc cht khng b phn hy nhit cao nn cc phn ng trn xy ra theo chiu oxy ha P. Phng trnh phn ng

chung c dng:

[ ] ( ) ( ) ( ) [ ] QFe5OP.CaO3CaO3FeO5P2 52 ++=++ (3.45) T phng trnh (3.45), ta nhn thy iu kin kh P tt l:

+ kim ca x ( )( )2SiOCaOB = phi cao, ng thi trong x phi cha nhiu

( )FeO ; + Nhit l thp, tt nht l trong khong 1300 1350oC;

- 36 -

+ Din tch tip xc gia thp lng v x phi ln (do phn ng xy ra gia hai

pha).

Trong thc t, khi nu thp trong l mactanh hoc l in h quang baz ngi

ta tin hnh kh P vo cui giai on nu chy v u giai on oxy ha v l thi

k c iu kin kh P tt nht do nhit l cn thp, nng oxyt st kh cao c th

nng baz ca x ti 2,5 3. Trong l thi baz, ngi ta thng tin hnh kh P vo giai on gia, khi thnh phn ca x cha khong: 6,4 9,4% SiO2; 2,9 9% Al2O3; 44,1 53,3% CaO; 36 12,4%MgO; 4,2 7,9%MnO; 15,0 23,93%FeO.

Ngoi phng php kh P bng x ngi ta cn dng cc nguyn t kim loi

nh Ca, Mg, RE (t him: cha Ce, La) kh P. Khi a cc kim loi trn vo thp

lng, chng kt hp vi P to thnh cc hp hp cht bn nhit cao (CaP, MgP,

(Ce + La)P ...) v i vo x.

Mt vn cn lu l khi dng cc kim loi trn kh P, trc ht cn phi

kh ht oxy v i lc ha hc vi oxy ca cc nguyn t ny ln hn rt nhiu so vi

P.

3.2.6. Kh lu hunh Lu hunh l tp cht c hi trong thp (gy ra hin tng b nng). Bi vy,

thp c cht lng cng cao th hm lng S trong thp yu cu cng thp, i vi

thp sch phi kh S hu nh trit .

Lu hunh ho tan c vo Fe, nhit cng cao th ha tan cng ln,

phng trnh kh S:

[FeS] + [CaO] [CaS] + [FeO] - Q (3.46) T phng trnh phn ng ta nhn thy iu kin kh S tt l:

+ CaO cao ( kim cao);

+ Nng ( )FeO thp; + Nhit cao.

Qu trnh kh S c th tin hnh bng x, kh ho v kh lng.

Khi kh S qua x, do FeS ha tan c trong x v kim loi, hng s phn b:

- 37 -

( )[ ]FeS%N

K FeSFeS =

mt iu kin nu luyn nht nh th KFeS l hng s, nu ta tm cch gim

( )FeSN ti mc [ ] ( )FeSFeS NFeS%.K > th [ ] ( )FeSFeS . gim ( )FeSN ngi ta thng dng cc bin php chuyn ( )FeS t dng d ha tan sang dng kh ha tan nh cc phn ng:

( ) ( ) ( ) ( )FeOMnSMnOFeS +=+ (3.47) ( ) ( ) ( ) ( )FeOCaSCaOFeS +=+ (3.48) Ngi ta thng kh S theo phn ng (3.48), v phn ng ny c hiu qu kh

S cao, phng php kh li n gin v rt kinh t.

Trong cc l luyn thp, ngi ta thng kh S vo lc nhit nc thp

cao, nng ( )FeO thp v nng baz n 2,8 3,2. V d, trong l in h quang baz, ngi ta tin hnh kh S vo cui giai on oxy ha v ch yu vo u giai

on hon nguyn.

Khi kh S trong mi trng kh ha, S b t chy theo phn ng:

S + O2 = SO2 (3.49) Khi kh lng, ngi ta a vo thp lng cc kim loi (chng hn nh: Ca, Mg,

RE) d kt hp vi S to thnh cc hp cht bn. Khi kh S bng phng php ny,

phi tin hnh kh ht oxy trong thp trc khi kh S.

3.2.7. Kh kh Kh ho tan vo thp c ngun gc t nguyn vt liu, khng kh... chng c th

lm gim c tnh ca thp, cng nh gy ra r kh khi c. Thng khi luyn thp cn

tin hnh kh cc kh [O], [N], [H].

a) Kh oxy Oxy c cp vo thp lng oxy ha cc nguyn t d tha nh C, Si, Mn...

sau khi oxy ha cc tp cht trong thp cn mt lng oxy d. kh oxy c th tin

hnh bng phng php kh lng hoc kh khuch tn.

- 38 -

Trong phng php kh lng ngi ta dng cc nguyn t kim loi c i lc

vi oxy ln hn so vi st:

[Mn] + [O] (MnO) (3.50) [Si] + 2[O] (SiO2) (3.51) [Al] + 3[O] (Al2O3) (3.52) Phng php kh lng c u im: tc phn ng nhanh nhng c nhc

im l cc oxyt to thnh ni ln khng trit lm bn thp.

Phng php kh khuch tn dng fero (fersilic, fermangan) cho vo thp

lng hoc cacbon ht vo x.

(FeO) + C = (Fe) + CO (3.53) (FeO) + Si = (Fe) + (SiO2) (3.54)

Do hng s phn b oxyt st trong x v trong kim loi lng

( )[ ] constFeOFeOK p == , nn khi (FeO) gim ko theo [FeO] gim theo. Phng php kh

lng khng lm bn nc thp nhng tc kh chm, ko di thi gian kh, do

thng dng khi luyn thp yu cu sch cao.

Ngoi ra i vi thp cht lng cao, ngi ta c th tin hnh kh oxy bng

phng php chn khng.

b) Kh [N] v [H]: N2 = 2[N] (3.56)

H2 = 2[H] (3.57)

Hng s phn ly: [ ]2N

2

p PNK = [ ]

2NpPKN =

[ ]2H

2'p P

HK = [ ]2H

'p PKH =

Phng php kh ch yu l kh khuch tn, do trong qu trnh kh phi to

nn s xo trn kim loi tt tng cng s ni ca bt kh. tng tc kh kh,

ngi ta c th dng kh tr sc vo thp lng.

- 39 -

3.2.8. Tp cht phi kim Tp cht phi kim l nhng cht ln khng ni ln c trong qu trnh luyn v

nm li trong thp, chng ch yu l cc oxyt. Tp cht phi kim trong thp hnh thnh

do ni sinh hoc t ngoi a vo. Tp cht ni sinh l sn phm ca s oxy ha, tp

cht t ngoi a vo do nguyn vt liu ln cht bn, do vt liu chu la b n mn,

do ln x v s ti oxy ha. Tp cht phi kim lm gim cht lng ca thp, do vy

trong qu trnh nu luyn cn c bin php hn ch ngun tp cht a t ngoi vo,

nh dng nguyn vt liu sch, s dng vt liu chu la ph hp gim s n mn,

s dng cht kh ph hp v lng dng hp l, hn ch s ti oxy ha ... hoc dng

cc bin php tinh luyn ngoi l.

3.3. X trong qu trnh luyn thp Trong qu trnh nu luyn hp kim, d mun hay khng bao gi cng c mt

lng tp cht t nhiu ngun khc nhau a vo l v tch ra trong qu trnh nu

luyn to thnh x. Trong l, do x tip xc trc tip vi kim loi nn tc ng rt ln

ti nhiu qu trnh ha l lin quan n tin trnh thc hin qu trnh cng ngh. Trong

mt s qu trnh nu luyn (nh nu gang chng hn) qu trnh to x l qu trnh

khng mong mun nhng trong luyn thp x li ng vai tr rt ln trong nhiu qu

trnh luyn kim xy ra trong l nh qu trnh truyn nhit, qu trnh kh tp cht, kh

kh ... Bi vy, ty thuc yu cu cng ngh, trong tng giai on nu ngi ta thng

xuyn phi iu chnh ch x ph hp m bo cho qu trnh luyn pht trin

theo hng cng ngh mong mun.

3.3.1. Ngun gc v thnh phn ca x luyn thp a) Ngun gc ca x

Khi lng v thnh phn ca x ph thuc vo phm cht ca nguyn, nhin

vt liu nu, vt liu xy l v ch nu luyn.

Trong qu trnh nu luyn, x c hnh thnh t cc ngun ch yu sau y:

+ Do cc cht ln trong nguyn, nhin vt liu (nh t ct, du m, nc...),

do nguyn liu kim loi b oxy ha mang vo;

+ Do kim loi v tp cht trong phi liu b oxy ha;

- 40 -

+ Do tng l b n mn: trong iu kin nhit cao, do tc dng c hc hoc

s n mn ha hc, lp lm vic ca tng l b bo mn v i vo x.

+ Do cc oxyt v tp cht a vo cng cht oxy ha, v d khi a qung st

vo oxy ha tp cht v cacbon, mt lng ln oxyt st v cc oxyt khc c a

vo l.

+ Do cc tp cht ln trong cc cht to x;

+ Do tro ca nhin liu: trong nhin liu c bit l nhin liu rn thng cha

mt lng tro nht nh, khi nu luyn mt phn cun theo kh l, mt phn nm li

trong l v i vo x.

b) Thnh phn ha hc ca x Thnh phn ch yu ca x luyn thp l cc oxyt, theo tnh cht ha hc ca

chng c th chia lm ba nhm: nhm c tnh cht baz, nhm c tnh cht axit v

nhm c tnh cht lng tnh.

Nhm cc oxyt c tnh baoz gm: CaO, MgO, MnO, FeO, NiO, ...

Nhm cc oxyt c tnh axit gm: SiO2, P2O5, TiO,V2O5, ...

Nhm cc oxyt c tnh cht lng tnh gm: Al2O3, Fe2O3, Cr2O3, V2O3, ...

Trong cc cc oxyt c tnh cht lng tnh, ch c Al2O3 l th hin tnh cht

lng tnh r rt cn Fe2O3 v Cr2O3 thng mang tnh axit yu.

Ngoi cc oxyt trn, trong x cn cha cc hp cht khc nh: CaS, FeS, CaS2...

Cc oxyt trn khi dng t do phn ln c nhit chy rt cao, tuy nhin

trong x ngoi cc oxyt t do, cn c cc hp cht ca nhiu oxyt vi nhau m thng

c nhit chy gim mnh. Chnh v vy, trong iu kin nu luyn x thng

trng thi lng.

Cc hp cht thng gp trong x luyn thp c nhiu loi nhng c th chia

thnh bn nhm chnh:

Nhm silicat:

( ) 2x SiO.FeO (x = 1; 2) 2SiO.MnO

( ) 2x SiO.CaO (x = 1; 2)

- 41 -

2SiO.MgO

232 SiO.OAl ....

Nhm phtphat:

( ) 523 OP.FeO 52OP.MnO

( ) 52x OP.CaO (x = 3; 4) ( ) 523 OP.MgO ... Nhm aluminat:

32OAl.FeO

32OAl.CaO

32OAl.MgO ...

Nhm pherit:

32OFe.FeO

( ) 32x OFe.CaO (x = 1; 3) ( ) ( )y32x OFe.CaO ... Ngoi cc hp cht trn, x cn cha mt s hp cht phc tp khc nh:

2SiO.MeO.CaO (Me = Fe, Mn, Mg ...)

252 SiO.OP.CaO5 ...

Trong thnh phn ca x th cc oxyt t do quyt nh hot tnh ha hc ca x,

cc hp cht nhiu oxyt lm nhit chy ca x gim thp, m bo cho x c st,

chy long v mt s tnh cht khc cn thit theo yu cu cng ngh.

Trong luyn thp, ngi ta c bit ch ba loi oxyt: ( )CaO , ( )2SiO v ( )FeO . Cc oxyt ( )CaO v ( )2SiO quyt nh baz ca x, cn ( )FeO quyt nh kh nng oxy ha ca x.

3.3.2. Cc tnh cht ca x luyn thp a) baz ca x: baz ca x xc nh bi t s gia t l phn trm theo

trng lng ( hoc t l phn t gam) ca hai oxyt ( )CaO v ( )2SiO :

- 42 -

( )( )2SiO%

CaO%B = hoc ( )( )2SiOCaO

NN

B = (3.58)

Khi lng ( )52OP trong x cao, ngi ta tnh baz ca x theo cng thc sau: ( )( ) ( )522

'

OP%SiO%CaO%B += hoc

( ) ( )( )2

52'

SiO%OP%18,1CaO%B =

Cn c vo baz ca x ngi ta chia ra:

+ X c baz thp : 5,13,1B = (35 40 %CaO, 25 30 %SiO2); + X c baz trung bnh : 2,28,1B = (40 45 %CaO, 20 25 %SiO2) + X c baz cao : 5,2B = (45 48 %CaO, 12 20 %SiO2)

Trong l luyn thp axit, ngi ta cn dng axit thay cho baz, xc nh

theo cng thc:

( )( )CaO%SiO%R 2=

baz ca x c ngha rt ln trong vic kh P, S v m bo cho nhiu tin

trnh cng ngh tin hnh thun li. baz nh hng ln n chy long ca x,

do nh hng ln n hot tnh ca x, kh nng ht kh hoc thot kh ca kim loi

v kh nng kh tp cht. V vy, ty theo nhit trong l v yu cu cng ngh, khi

nu luyn cn phi thng xuyn kim tra v iu chnh baz ca x.

b) Cc tnh cht vt l ca x st ca x: c trng cho linh ng ca x, st cng cao th linh

ng ca x cng thp. n v o st l poa (g/s), mt poa bng 100 ln st ca

nc 20oC. Bng 3.2 cho st ca thp v x cc nhit nht nh.

Bng 3.2 st ca thp v x ph thuc nhit

Cht Nhit (oC) st (poa)

Thp 1595 0,025

X lng 1595 0,02

X lng va 1595 0,20

X c 1595 2,0

- 43 -

Hai yu t nh hng n st ca x l:

+ Thnh phn ha hc ca x;

+ Nhit ca x.

X axit d chy hn x baz nn khi nhit thp c st nh hn x baz.

Khi nhit tng, st ca x axit v x baz u gim nhng st ca x baz

gim mnh hn nn khi nhit cao st ca x baz li thp hn st ca x axit.

thy r nh hng ca thnh phn n st ca x, ta xt gin ba

nguyn ca x nhit 1600oC (hnh 3.2).

T gin ta nhn thy, nhit 1600oC, nhiu thnh phn x c th m bo

chy long ( st ca x thp), nht l nhng loi cha t 48 55 %CaO, khi %CaO < 45% th st ca x ch ph thuc vo %CaO m t ph thuc vo t s SiO2

: Al2O3.

Trng lng ring ca x: trng lng ring ca x cng thp th x cng nh v

cng d tch ra khi kim loi. Trng lng ring ca x ph thuc thnh phn ca x,

trong c nh hng ln nht l cc oxyt FeO, Fe2O3, MnO. Bng 3.3 cho trng

lng ring v nhit chy ca mt s oxyt v hp cht trong x.

%CaO

%Al2O3

%SiO2

20 30 40 50 60

40

50

60 30 40

50

60

70

30

2 3

4 5

4 6

10 8

Hnh 3.2 Gin st ca x 1600oC

15

35

- 44 -

Bng 3.3 Trng lng ring v nhit nng chy ca mt s hp cht

Hp cht Trng lng ring

(g/cm3)

Nhit chy

(oC)

FeO 5,7 1420

Fe3O4 5,1 5,2 1538 phn hy

Fe2O3 5,24 1560 phn hy

MnO 5,45 1785

MgO 3,65 > 2800

CaO 3,40 2572

SiO2 2,20 1713

Al2O3 2,65 2050

P2O5 2,39 -

MnS 4,00 1620

(CaO)3.P2O5 3,14 1670

CaO.SiO2 2,405 1540

Nhit hm ca x: l lng nhit cn cung cp cho 1 kg x nung nng n n

nhit nng chy, nng chy hon ton v qu nhit n nhit yu cu. Nhit hm

ca x c th tnh theo cng thc gn ng sau:

50t28,0q += (kj/kg) Trong t l nhit lm vic ca x.

dn in ca x: dn in ca x c ngha ln trong mt s qu trnh

nu luyn, c bit l khi luyn thp trong l h quang hoc l in x. dn in

ca x tng khi tng nhit v trong thnh phn ca x cha nhiu cc oxyt baz,

cacbit canxi.

Sc cng b mt ca x: sc cng b mt ca x nh hng rt ln n vic tch

chng khi kim loi. X c sc cng b mt ln th t dnh vo kim loi v d tch ra

trong qu trnh nu luyn.

- 45 -

3.4. Cn bng nhit trong qu trnh luyn thp 3.4.1. Ngun nhit cung

Ngun nhit cung cp cho l trong qu trnh luyn thp c th chia lm hai

dng:

+ Nhit ha hc.

+ Nhit vt l.

a) Nhit ha hc: Nhit ha hc l nhit c cung cp do t chy nhin liu

hoc do phn ng oxy ha khi kh tp cht sinh ra.

Ty thuc qu trnh luyn, ngi ta c th dng cc ngun nhin liu sau:

+ Nhin liu rn: than cc, than gy, ci hoc g;

+ Nhin liu lng: du t;

+ Nhin liu kh: kh thin nhin, kh l cc, kh l cao.

Nhit do phn ng oxy ho khi t chy tp cht: phn ng chy C, Si, Mn, P ...

V d trong l betsme nhit ha hc ch yu do t chy Si, trong l tmat ch

yu l do t chy P.

b) Nhit vt l: nhit vt l do gang lng, nhit tch ca tng l hoc do khng

kh, nhin liu... c nung nng mang vo. Trong cc l in ngun nhit vt l l do

bin i in nng thnh nhit nng: nhit ca h quang in, nhit tr hoc nhit sinh

ra do hin tng cm ng in t...

3.4.2. Ngun nhit chi Nhit cung cp cho l, mt phn c dng nung nng, nu chy v qu

nhit kim loi, x n nhit yu cu, cung cp cho cc phn ng thu nhit xy ra

trong qu trnh nu luyn... gi l lng nhit c ch, mt phn b mt mt trong qu

trnh nu luyn do truyn nhit cho l, truyn nhit ra ngoi, do kh thi mang theo ...

phn nhit ny c gi l nhit tn tht.

Trong qu trnh nu luyn cn m bo s cn bng ngun nhit cung v ngun

nhit chi trong l.

- 46 -

Chng IV

LUYN THP TRONG L IN H QUANG 4.1. c im v phn loi 4.1.1. c im

L in h quang l loi l c dng rt ph bin nc ta. u im ca l

in l:

+ Nu c nhiu loi nguyn vt liu (gang, thp vn ...);

+ Chy hao kim loi t;

+ D dng iu chnh nhit nc thp;

+ Nu c nhiu loi thp, cht lng thp tt;

Hn ch ca l in h quang l in nng t.

4.1.2. Phn loi Da vo cng sut bin p v dung tch cha thp, ngi ta phn ra:

+ L in h quang cng sut thng: 400kVA/tn. + L in h quang cng sut cao: 600 800kVA/tn. + L in h quang siu cng sut: > 800kVA/tn.

Da vo ngun in, phn ra:

+ L in h quang xoay chiu: dng ngun in xoay chiu, l c ba in cc.

+ L in h quang mt chiu: dng ngun in mt chiu, l ch dng mt

in cc.

4.2. Thit b 4.2.1. Cu to chung v nguyn l lm vic

Hnh 4.1 trnh by cu to chung ca l in h quang, l gm cc b phn c

bn sau:

+ Bung l;

+ Thit b nghing l;

+ Thit b nng h in cc;

+ Thit b in (my bin th v mng in).

- 47 -

L in h quang s dng ngun nhit l ngn la h quang sinh ra gia cc

in cc v kim loi nu. Khi nu, in cc c h xung chm vo kim loi gy ra

hin tng ngn mch, sau nng in cc ln cch mt kim loi mt khong cch

nht nh, gia in cc v kim loi pht sinh ngn la h quang. Do h quang gy ra

trc tip gia in cc v kim loi nu nn c gi l h quang trc tip, nhit

ngn la h quang rt cao v nhit tp trung nn nhit truyn cho kim loi rt ln v

Hnh 4.1. Cu to tng th ca l in h quang 1) Vi phun oxy 2) in cc grafit 3) ng ht khi bi 4) Np l 5) V l bng thp

6) Ca thao tc 7) Thit b dch chuyn v l 9) B phn dn ng quay l 10) ta b phn dch l 11) Thit b quay np l 13) B phn quay khung l 14) Qut thng kh

15) B phn lm ngui in cc 16) Thit b nng h in cc 17) Dy cp in

- 48 -

ch yu l truyn nhit bc x. Theo mc nng chy ca kim loi trong bung l,

in cc c iu chnh gi khong cch gia in cc v kim loi n nh, nh

h quang chy n nh.

4.2.2. Bung l Bung l gm ba phn: y l, thn l v nc l (hnh 4.2).

y l: lm nhim v cha kim loi v x. Phn trn y l c dng hnh cn,

gc nghing 45o, phn di c dng chm cu. Chiu dy th xy y l thng t

650 700 mm, gm: + Lp manhdit thiu kt dy 180 200 mm; + Lp gch manhdit dy 295 mm;

+ Lp gch samt dy 130 mm;

+ Lp vn samt dy 30 mm;

+ Lp ba aming dy 10 mm.

Ngoi cng l v l bng thp tm dy 20 mm.

Tng l: to khng gian cha liu, ng thi chu lc tc dng ca nc l.

Chiu dy tng l thng t 350 700 mm, gm cc lp:

D2 D1 d

h3

h1

h2

H1

10 0 a

b

Hnh 4.2 S cu to bung l in h quang

D3

- 49 -

+ Lp gch manhdit dy 285 mm.

+ Lp gch samt dy 130 mm.

Nc l: c dng hnh chm cu, xy bng gch crm-manhdit hoc bng gch

dinat, chiu dy khong 300 mm. nc l, khi xy cha ba l trng t ba in

cc.

Th xy y v tng l in h quang baz trnh by trn hnh 4.3.

.

Cc kch thc c bn ca bung l: thng khi thit k l, s liu cho ban u

l cng sut l (T/h), t c th tnh c khi lng ca m kim loi nu, th tch

ca kim loi v x. Trn c s , xc nh dung tch ni l v cc kch thc c bn

ca bung l.

Da vo hnh 4.2 ta c th tnh nh c th tch ni l:

( )2222121 rRR3h.6h8rh.V +++

+= (4.1)

Trong : 2dr = v

2DR 1= .

1

2

6 4

5

3

Hnh 4.3 Th xy tng v y l h quang baz 1) Lp manhdit thiu kt 2) Lp gch manhdit 3)Lp gch samt

4) Lp vn samt 5) Lp ba aming 6) V thp

- 50 -

Cc kch thc ca ni l thng c chn theo chiu cao ni l H:

H5D1 = H25

2DR 1 ==

H.51h1 =

H.54hHh 12 ==

H5

17h2Dd 21 ==

H7,1d21r ==

Thay cc gi tr trn vo cng thc (4.1) ta tnh c:

3H6,11V =

Suy ra: 36,11

VH = (4.2)

Cc kch thc khc ca tng l c chn theo chiu cao ni l H nh sau:

200H5200DD 12 +=+= [mm] ( )H2,21,2H1 = [mm] ( ) 200H44,542,5D3 += [mm] Chiu cao nc l:

33 D81

71h

= [mm]

Chiu rng ca l:

3D3,0a = Chiu cao ca l:

a8,0b = . Dung tch l mi thit k thng nh hn 30 40% so vi sau khi nu, do c

th nu qu t 15 20% (bng 4.1).

- 51 -

Bng 4.1 Dung tch l h quang luyn thp

Ti trng cht (tn)

L baz

Dung tch

danh ngha

(tn) Nu bnh thng Nu cng bc L axit

0,5 0,7 0,8 0,8 0,9 1,0 1,1 1,5 2,0 2,2 2,3 2,5 2,6 2,8 3,0 3,8 4,2 4,5 5,0 5,2 5,5 5,0 6,0 7,0 7,4 7,8 8,0 8,5 10,0 12,0 13,0 14,0 16,0 -

4.2.3. Thit b nng h in cc Trong qu trnh nu luyn, mc kim loi di in cc thay i, in cc b

mn dn... duy duy tr h quang chy n nh, ba in cc ca l cn phi chuyn

ng ln xung ph hp. Thit b nng h in cc lm nhim v iu chnh in cc

trong sut qu trnh nu luyn, m bo khong cch gia in cc v kim loi hoc x

duy tr ng theo yu cu.

Thit b nng h in cc gm:

+ Gi lp in cc;

Hnh 4.4 Thit b nng h in cc 1) Gi lp in cc 2) Tr dn hng

3) H thng dn ng 4) Kp in cc 5) i trng

5

1

2

4

3

- 52 -

+ H thng dn ng;

+ Tr dn hng.

Gi lp in cc dng kp in cc, c cu kp c lm ngui bng nc.

Dn ng c cu iu chnh nng h in cc thc hin bng h thng c kh hoc h

thng thy lc. Chuyn ng iu chnh c t ng ha.

4.2.4. C cu nghing l i vi l in h quang ra thp qua mng ra thp bn hng khi ra thp phi

nghing l. nghing l c th dng c cu c kh hoc thy lc.

4.2.5. Thit b in S mng in v bin p ca l in h quang trnh by trn hnh 4.5.

Dng in cao th t ng dy (1) qua cu dao khng kh (2), cu dao du

chnh (3), cun cm (7), my bin p (9) ti in cc (12) v sinh ra h quang gia

in cc v kim loi (13). Cu dao khng kh (2) dng ng m thit b in ca l,

n ch c ng m khi cu dao du chnh (3) m. Cu dao du chnh dng ngt

mch in. V y c dng cao th chy qua, nn phi dng cu dao ny m bo

an ton (cu dao u chnh trit tiu c tia la in pht ra khi ngn mch).

m bo an ton cho mch in ca l, ngi ta phi dng h thng ng h

o v r le bo v (6), khi dng in hay in p tng qu t ngt, n c kh nng t

ng ngt mch. Cun cm (7) ca my bin th c kh nng to ra sc in ng cm

ng bin h quang gin on thnh h quang lin tc, do h quang v dng in

n nh, liu s chng chy, nhng khi c cun cm th s tng tiu hao in, khng s

dng ht cng sut ca my bin p, h s cos gim. V vy khi nu chy xong, h quang v dng in n nh th phi ct cun cm khi mch, thc hin vic

dng cu dao u in cm (8).

Bin p (9) ch yu i dng in h th ph hp vi tng giai on nu

luyn. Yu cu ca bin p l h quang l cch in rt tt, c kh nng qu ti ln

chu c on mch v qu ti thng xuyn.

- 53 -

1

2

3

4

6

5

7 8

9

10

11

12

13

Hnh 4.5 S thit b in ca l in h quang 1) ng dy cao th 2) Cu dao khng kh 3) Cu dao du chnh 4) B phn o dng 5) B phn o p my bin p 6) ng h o v r le bo v 7) Cun cm

8) Cu dao du cun cm 9) My bin p 10) Cu dao i in p 11) ng h o, thit b bo v v t ng iu chnh in cc 12) in cc 13) Kim loi

- 54 -

Ty theo tng giai on nu, ngi ta yu cu nhng cp in p khc nhau. Do

, my bin p cn c nhiu cp in p, thng l su cp in p ty theo cch mc

hnh sao ( ) hay tam gic ().

Th d su cp in p ca my bin p l:

Khi mc tam gic: 260 V - 220 V - 180 V.

Khi mc hnh sao: 150 V - 127 V - 104 V.

Ty theo tng giai on nu, ta s dng in p thch hp, thng thng:

Giai on nu chy: 240 380 V. Giai on oxy ha: 160 200 V. Giai on hon nguyn: 140 115 V.

Cng sut my bin p xc nh theo cng thc:

= cos.I.U.3P Trong :

P - cng sut my bin p;

U, I - in p v cng dng in.

Theo yu cu nu luyn, cng sut gim dn t giai on nu chy sang oxy

ha n hon nguyn (hnh 4.7).

Hnh 4.6 Cc phng php ni cun dy my bin p a) Mc hnh sao b) Mc tam gic

a) b)

- 55 -

gim cng sut c th gim U hoc I. Khi in p vng h th c nh,

gim I th phi tng chiu di h quang (tng in tr). Ngc li khi gim U th chiu

di h quang phi ngn li.

Bng 4.2 in p ti thiu sinh h quang ph thuc vt liu ch to in cc

in cc in p sinh h quang (V)

in cc than - than 17

in cc than - kim loi 26

in cc than - x baz 9

in cc than - x axit 30

Do , khi bt u chy l, nhit l cn thp, h quang pht sinh gia cc

than v kim loi khng vng, n nh h quang ngi ta cho thm cc mnh in

cc ln trn kim loi. Khi trong l c x baz th h quang d n nh nn ta c th

ct cun cm ra khi mch in.

4.2.6. in cc: lm nhim v gy h quang in, c ba loi: + in cc t thiu;

+ in cc cacbon;

+ in cc grafit.

1000

2000

8000

7000

6000

5000

4000

3000

0 1 2 3 4 5 6

1600

1500

1700

210V

267V

210V210V

210V157V 157V

121V121V

Hnh 4.7 Ch in cho m luyn thp l h quang 30 tn

- 56 -

in cc t thiu chuyn dng cho sn xut fer. in cc dng cho luyn thp

thng dng in cc grafit. in cc cacbon hin nay t dng.

Theo cng sut l, in cc grafit c phn ra:

+ in cc grafit thng;

+ in cc grafit cng sut cao;

+ in cc grafit siu cng sut.

in cc c ch to dng hnh tr, u cui c phn lp u ni hnh tr hoc

hnh cn c ren (hnh 4.8).

Cc ch tiu ha l ca in cc grafit thng dng trnh by bng 4.3.

Bng 4.3 Cc ch tiu ha l ca in cc grafit thng dng

ng knh in cc (mm)

75 130 150 200 250 350 400 500

Ch tiu

cp

cao

cp

1

cp

cao

cp

1

cp

cao

cp

1

cp

cao

cp

1

Thn 8,5 10 9,0 11 9,0 11 9,0 11 in tr sut

min (.mm2/m) ni 8,5 8,5 8,5 8,5 Thn 7,85 7,85 6,37 6,37 Cng b gy

min (Mpa) ni 11,3 11,3 9,81 9,81

Thnh phn tro

max (%) Thn 0,5 0,5 0,5 0,5

Hnh 4.8 Cu to in cc 1) Thn in cc 2) u ni

1

2

- 57 -

Mt thc

min (g/cm3) Thn 2,18 2,.18 2,18 2,18

Thn 19,6 19,6 17,7 17,7 bn nn

min (MPa) ni 29,4 29,4 29,4 29,4

Cng dng in cho php ph thuc ng knh in cc (bng 4.4).

Bng 4.4 Cng dng in cho php

ng knh

in cc

Cng

dng in

cho php (A)

ng knh

in cc

Cng

dng in

cho php (A)

75 1000 1400 300 10000 13000 100 1500 2400 350 13000 18000 125 2200 3400 400 18000 23000 150 3500 4200 450 22000 30000 200 5000 6900 500 25000 34000 250 7000 10000

Ch tiu ha l ca in cc grafit siu cng cng sut cho bng (4.5)

Bng 4.5 Ch tiu ha l ca in cc grafit siu cng cng sut

ng knh in cc (mm)

225 400 400 600

Ch tiu

Thn u Thn u

Hm lng C (%) 99,3 99,3 99,3 99,3

Tro (%) 0,2 0,2 0,2 0,2 Xp (%) 20 24 20 24 20 23 20 23

Mt (g/cm3) 1,65 1,72 1,74 1,80 1,66 1,73 1,74 1,81 in tr sut

(mm2/m) 5,0 6,5 4,5 5,5 4,5 5,75 4,0 5,0

- 58 -

Un (MPa) 9,0 14,0 - 8,5 13,5 - Nn (MPa) 6,6 10,0 14,0 20,0 6,0 9,5,0 13,0 19,0

M un n hi

(GPa) 6,5 11,0 12,5 18,0 6,0 11,0 12,0 17,0

H s dn nhit

(w/m.oC) 175 260 240 260 210 280 250 320

H s gin n nhit

(10-6/oC) 0,5 1,0 0,4 0,9 0,3 0,6 0,75 0,6

i vi in cc grafit cn lu :

+ Khi bo qun in cc grafit cn trnh ma gi lm m in cc, trong qu

trnh vn chuyn phi ht sc cn thn trnh va p, trc lc s dng cn sy kh

nhit 100oC. + Khi ni in cc cn vn cht trnh to khe h, dn n sinh h quang

mi ni khi dng in i qua.

+ Khi np liu trnh liu va p vo in cc.

4.3. Cng ngh nu luyn 4.3.1. Nguyn vt liu

Nguyn vt liu dng luyn thp trong l h quang gm:

+ Nguyn liu kim loi: thp ph, gang, phe-r hp kim, st xp.

+ Liu to x: gm vi, hunh thch ...

+ Liu oxy ha: qung st, kh oxy ...

4.3.2. Cng ngh luyn thp thp trong l in h quang baz a) Giai on nng chy

Trong giai on ny liu c nung nng n nhit nng chy v chuyn

sang th lng. y l giai on quan trng trong qu trnh luyn thp, chim ti 60%

thi gian nu luyn.

- 59 -

u tin cht mt lp thp ph m di y l trnh va p gy hng y

l khi cho liu thi ln vo. Tip theo cho gang thi vo khong 50%, sau cht mt

lp thp ph ln trn.

Khi bt u nu luyn, liu cht gn y l, h quang nm gn nc l, ch dng

khong 50% cng sut trnh lm hng nc l. Sau khi liu di in cc nng

chy, kim loi lng tp trung xung y l, xung quanh in cc to thnh h (ta gi

giai on ny l giai on o h), tng cng sut l ln cc i (Wmax) v tip tc iu

chnh in cc i xung duy tr h quang. Khi nc thp tp trung y l dn dn

dng ln v in cc xung gn mt nc thp, iu chnh in cc i ln theo tc

dng ca mt nc thp. Trong qu trnh nu chy, liu st thnh l kh nng chy

v xa h quang, tng qu trnh nng chy ngi ta c th thi kh oxy vo qua cc

vi phun b tr quanh thn l.

Khi liu rn nng chy ch cn cc nh nm trong thp lng, cho thp ph vo

v tip tc nu chy, khng nn cho thp ph vo khi liu nng chy hon ton, v

nh vy d gy bn te kim loi lng gy nguy him.

Trong giai on ny, nhit tiu tn ln, nu chy nhanh cn phi dng cng

sut l ln, kt hp thi thm oxy. Cui giai on nu chy ly mu phn tch thnh

phn ha hc (ch yu l phn tch cacbon v phtpho).

b) Giai on oxy ha Trong giai on ny xy ra cc phn ng oxy ha cc nguyn t C, Si, Mn, P, S,

ng thi tin hnh kh kh v tp cht phi kim. Do cc phn ng oxy ha to nhit

nn cng sut l giai on ny khng cn ln (ch cn khong 50% Wmax). Trong giai

on ny Si b kh u tin, khi Si ch cn 0,02% th Mn bt u b kh. Trong giai on nu chy, Mn b t chy khong 50%, sau giai on oxy ha tip tc b t chy

cn li 0,2%. kh P kim (B) phi cao, hm lng (FeO) cao v nhit (T) thp. Khi

kh S kim phi cao, nhng hm lng FeO trong x cng thp cng tt v nhit

phi cao.

- 60 -

Trong giai on oxy ho cm m bo [C], [P] v nhit t yu cu. i vi

[S] trong giai on ny t quan tm nhng cui giai on cng phi xc nh [S]

chun b cho giai on x l tip theo.

c) Giai on hon nguyn Giai on hon nguyn ch duy nht luyn trong l in h quang mi c cn

trong cc l khc khng c. Mc ch ca giai on ny l kh [S] nu cn, sau kh

[O] v hp kim ho, ng thi nng nhit thp lng.

Kh oxy bng phng php khuch tn: u tin tin hnh co b x oxy ha,

sau tin hnh to x hon nguyn, thnh phn gm vi (CaO) v cht tr dung

(CaF2) v bt than, khi kim ca x tng, hm lng (FeO) gim xung, lng

dng cht to x khong 4 7%. Vi lm tng kim ca x.

Cht tr dung CaF2 lm gim nhit nng chy ca CaO.

Bt than: ( ) ( ) { }+=+ COFeCFeO Lc ny kh [S] rt tt v B tng, (FeO) gim v nhit cao.

Thc t trong giai on ny, hm lng kh [H], [N] vn cn do dng h quang

a vo.

Khi a bt than vo cn trnh ch dng h quang, v khi gp dng h quang:

++ COCaCC2CaO Tcao ++=+ CO(CaO)(Fe)CaCFeO

Cui giai on hon nguyn cho Si v Mn vo t hm lng yu cu ca

mc thp.

[ ]( )MnFeMn%

CCQP 21MnFe

=

Trong :

C1 : hm lng cn c trong thp.

C2: hm lng cn li trong thp lng trc khi cho fer vo.

Sau khi ra thp, ch lng 3 5 pht, ng thi tp cht ni ln v tng s ng u thnh phn mi tin hnh rt khun.

- 61 -

i vi quy trnh luyn thp hin i trong l in siu cng sut v c lin

tc, giai on nu luyn thng rt xung di mt gi, l in ch lm hai nhim v

nu chy v oxy ha, cn tinh luyn, kh [O], kh tp cht, kh kh v hp kim ho

tin hnh ngoi l.

4.3.3. Tinh luyn ngoi l Tinh luyn ngoi l c th tin hnh bng phng php chn khng x hoc thi

kh (xo trn). Di y trnh by phng php tinh luyn bng thi kh l phng

php ph bin trong cng ngh luyn thp hin i, l tinh luyn bng l LF (Ladle

Furnace).

S cu to l LF trnh by trn hnh 4.9.

Np l c cu to tng t l in h quang cng sut thng. Tng l gm 4

lp (mt ct A) tnh t ngoi vo gm: v l bng thp, lp aming, lp gch xp cch

Hnh 4.9 S cu to l LF 1) Np l 2) Tng l 3) y l 4) Gch xp 5) L rt

6) Tm chn 7) ng dn kh acgng 8) Ca quan st 9) Ca vo liu

2

5 3

6 7 4

B

A

C D

B C D A

1

Gch manhedit Gch xp thu kh Gch ZrO.C

Tm chn chuyn ng

8 9

- 62 -

nhit v lp gch lm vic. Phn tng l ngang mc cha x (mt ct B), lp lm vic

xy bng gch manhedit. phn y l c b tr cc vin gch xp thu kh (mt ct

C) v l thi kh (mt ct D). Bn di l thi kh t hai tm chn c l cho kh i

qua, mt tm t c nh, mt tm chuyn ng qua li khi lm vic.

tinh luyn v kh kh, sau khi cho thp lng vo l, tin hnh to x hon

nguyn, gy h quang chm trong x v thi kh acgng vo l. Khi sc kh acgng vo

l, cc bt kh to ra s xo trn mnh thp lng lm tng qu trnh ni ca cc ht ln

rn, ng thi kh [H], [N] khuch tn vo cc bt kh v b cun ra ngoi. Nh s xo

trn mnh ca thp lng s kh [S] cng tng ng k.

Qu trnh tinh luyn tng t nh giai on hon nguyn trong l in h

quang.

- 63 -

Chng V

LUYN THP TRONG L IN CM NG

V MT S L IN KHC 5.1. c im v phn loi 5.1.1. c im

L in cm ng s dng in nng bin thnh nhit nng nh hiu ng cm

ng in t.

L in cm ng c nhiu u im hn so vi l h quang:

+ C th luyn c thp C rt thp (khng c s tng C do in cc);

+ Thnh phn kim loi ng u hn (nh s khuy trn kim loi tt di tc

ng ca lc in t);

+ Nng sut l cao, ct chy hao cc nguyn t hp kim;

+ D khng ch thnh phn v nhit kim loi;

Nhc im:

+ Nhit ca x thp nu khng c bin php x l thm;

+ bn lp o l baz thp.

5.1.2. Phn loi Theo cu to, l in cm ng c chia thnh hai loi: loi c li st v loi

khng c li st, luyn thp thng dng loi khng c li st.

Theo c tnh ca dng in ngun cung cp, l in cm ng c chia ra:

+ L cao tn: lm vic vi tn s my pht khong 100 200 kHz. + L trung tn: lm vic vi tn s my pht khong 500 1.000 Hz. + L thp tn: lm vic vi tn s 50 60 Hz.

5.2. Thit b 5.2.1. S cu to v nguyn l lm vic

L in cm ng khng c li st (hnh 5.1) lm vic ging nh mt bin th

khng kh m cun s cp l cc vng cm ng v cun th cp l lp mt ngoi ca

kim loi nu.

- 64 -

Khi c dng in tn s cao chy qua cun s cp, th trong m liu kim loi

sinh ra sc in ng cm ng:

n.f.44,4E2 = [vn] (5.1) Trong :

- t thng; f - tn s dng in;

n - s vng dy cm ng.

Sc in ng cm ng E2 sinh ra dng in cm ng I2, ch yu tp trung

lp mt ngoi cc liu, lm kim loi b nung nng v chy lng. Chiu su lp b mt

cc liu, ni m mt dng in cm ng t gi tr ln c gi l chiu su thm

t c th xc nh theo cng thc sau:

f.

10.03,5 3 =

Trong :

- in tr sut ca vt liu [.cm]; - t thm ca vt liu; f - tn s dng in [Hz].

Nhit nng to ra c th xc nh theo cng thc:

Hnh 5.1 S cu to l in cm ng khng c li st 1) Ni l 2) Vng cm ng 3) Kim loi nu

1 3

2

- 65 -

92

22222 10.f...h

d..n.I.2W = [W] (5.2)

Trong :

I - cng dng in (A);

N - s vng cm ng;

- in tr sut vt liu (.cm); - t thm; f - tn s (Hz);

d2 - ng kinh trung bnh ca liu (cm);

h2 - chiu cao ca kim loi trong ni l (cm);

T phng trnh (5.1) v (5.2) ta thy tng E2 v W2 cn tng n v f, thng

thng ngi ta tng f. Tn s ti thiu i vi mt kim loi nu xc nh theo cng

thc:

29

min de10.5,2f

e - khe h gia vng cm ng v m liu (cm);

d - ng knh trung bnh ca ni l (cm).

i vi l cm ng khng c li st, khe h gia vng cm ng v m liu ln,

t thng r rt ln nn h s cng sut thng khng vt qu 15%.

Dng in trong vng cm ng v thp lng ngc chiu nhau, hai vt dn ny

li ng tm nn y nhau lm cho thp lng c xo trn tt.

5.2.2. Cc b phn c bn ca l L in cm ng c nhiu b phn, song ta c th chia ra hai phn chnh:

+ Mng in l;

+ L nu.

a) Mng in l cm ng: gm c ng c xoay chiu, my pht tng tn s, my in kch thch mt chiu t in, cun cm ng.

- 66 -

ng c in: thng dng ng c in khng ng b vi rto ni ngn

mch (hiu in th ti 500V, s vng quay c 300 vng/pht, c cung cp bi

ngun in tn s cng nghip.

My pht tng tn: thng dng ba loi: my pht quay, my pht n in t

v my pht phng tia la. My pht quay c tn s 100 10.000 Hz, cng sut my pht cn khong 0,3 1 kw/kg liu. Loi ny thng dng cho l th nghim dung tch c 8 10 kg. My pht n in t v my pht phng tia la c tn s 200 1.000 kHz, thng dng cho cc l dung tch nh trong cng nghip v th nghim.

Cun cm ng: thng lm bng ng ng c tit din ngang l hnh trn, ch

nht hoc bu dc. Vt liu ch to l ng k thut in c dn in cao, kch

thc c tnh ton sao cho va m bo yu cu v dn in, va phi m bo lu

lng nc lm ngui vng cm ng. t tn hao in nht th chiu dy thnh ng

phi m bo iu kin:

> .3,1t Trong : - chiu su thm t.

S vng cm ng cng tng th lng nng lng in chuyn thnh nhit nng

trong m liu cng ln, nn cng tng s vng th tn tht cng gim, tuy nhin vn

phi m bo t l:

3,11,1hH =

Trong :

H - chiu cao cun cm ng;

h - chiu cao kim loi trong ni l.

Vng cm ng c lm ngui bng nc, p sut nc 1atm, nhit nc ra khong 35 - 45o.

T in cun cm ng: gim cng sut my pht in cung cp cho l v

nng h s cos (thng khng qu 0,15) ngi ta thng mc song vi cun cm mt h thng t in (gi l t b). Khi mc t b, gc lch pha gia dng in v in

p s gim, h s cos tng v dn ti 1.

- 67 -

Hnh 5.2 S h thng in ca l cm ng 1) B chnh lu ant 2) My pht cao tn 3) Chnh lu ph 4) Mch l nu

BA

1

2

3

4

5

6

7 L 1

8

L 2

L 3

C2

C1

C1

C2

C3

C4

L 4

L 2

L 2

R2

R2

1

2

3

4

- 68 -

iu kin t 1cos = l:

Lf4

1C 22= Trong :

C - in dung ca t b;

f - tn s dng in;

L - t cm ca cun cm.

Hnh 5.2 trnh by s mch in vi my pht n in t ca mt l in

cm ng.

Mch in gm: bin p ant BA, b chnh lu ant (1), my pht cao tn (2),

b chnh lu ph (3) v mch l nu (4). B chnh lu ant dng su n gadotron

(D1D6), bin p cao tn gm hai cun dy L3 v L4.. b) B phn l: gm ni l, khung l v thit b nghing l. B phn quan trng nht l ni l, n c ngha rt ln v kinh t v k thut. Ngoi cc yu cu chung, ni l

cm ng cn phi m bo yu cu thnh mng, khng dn in gim bt tn tht

in, d ch to, sa cha.

Ni l axit: c m bng ct thch anh, thnh phn: SiO2: 99 99,5%, Fe2O3: 0,5%, CaO: 0,25%, Al2O3: 0,2%, m: 0,5%. ht v t l trn nh sau:

Thch anh c ht 5 6 mm : 25%. Thch anh c ht 2 3 mm : 20%. Thch anh c ht 0,5 1 mm : 30%. Thch anh bt : 25%.

Axit boric k thut :1,72 %. bn ni l axit tng i cao, vi l dung tch 1,4 tn c th dng c 150

m.

Ni l baz: c m bng hn hp ct manhdit hm lng MgO 85%, 4% SiO2, 0,1% CaO, 1% Al2O3, 2% Fe2O3. Cht dnh l axit boric, t st hoc nc thy tinh. Thnh phn hn hp kh:

Ct manhdit : 90 94,5%.

- 69 -

t st chu la : 5 9%. Axit boric : 1 1,5%. Lng nc : 5 7% (so vi khi lng kh). bn ni l baz thp hn l axit, thng ch vo khong 10 100 m, l

cng ln tui th cng thp.

Ni l c th m trc tip hoc m ngoi sau a vo. Khi m trc

tip, u tin t lp cch nhit aming vo pha trong cun cm ng v y, ph lp

hn hp p y ni dy khong 20 40 mm xung y ri m cht. Tip tc t khun p ni vo v cho hn hp vo tng lp v m cht. Khun p ni ch to

bng thp tm c khoan l ng knh 3 mm, v ni l bng thp dy 5 7 mm. Sau khi m xong c th sy s b bng ci hoc than sau sy bng in trc

tip trong l. Qu trnh sy v thiu kt l gm cc giai on:

+ Sy kh: lm bc hi m, nhit sy 100 150oC. + Lm bc hi nc hydrad: nhit nung 600 800oC, thi gian 30 pht. + Thiu kt: nhit bng nhit nng chy ca kim loi, thi gian 30 pht.

Sau khi nu ln u, ni l c thiu kt cn v l chy lun. Sau hai ba ln

nu th ni l c thiu kt hon ton.

Kch thc cun cm v ni l ca l cm ng khng li cho bng 5.1.

Bng 5.1 Kch thc cun cm v ni l ph thuc dung tch l.

Kch thc cun

cm (mm) Kch thc l (mm)

Chiu dy thnh

Cng

sut my

pht

(kw)

Dung

tch l

(kg) Cao ng

Knh trong

Chiu

su

Chiu

dy y Trn Di

1400 8000 1300 1380 1200 200 110 150

1400 5000 1170 1180 1100 140 100 130

1200 4000 1100 970 970 500 90 125

680 1400 830 720 720 200 90 130

150 250 650 560 560 304 30 48

- 70 -

5.3. Cng ngh luyn thp trong l cm ng Khi nu thp trong l in cm ng, yu cu phi bit thnh phn ha hc ca

nguyn liu em nu cng nh phi liu m liu chnh xc, v thi gian nu nhanh ch

c th phn tch kp C v Mn hoc C v Si.

Kch thc liu cn ph hp vi dung tch l v tn s dng in, l cng ln

v tn s dng in cng b yu cu kch thc liu cng ln. Kch thc liu nh nht

nh sau: l tn s 500Hz kch thc liu 20 mm, l tn s 1.000 Hz kch thc liu 10 mm, l tn s 10.000 Hz kch thc liu 5 mm.

Khi cht liu, xp liu cng cht cng tt, liu c sy trc th nu chy s

nhanh hn v t 750oC tr ln thp thm t tt hn.

Trong giai on nu chy, nhit vng st thnh ni cao hn gia l, gia l

cao hn vng y, cn nhit vng trn st vi x thp nht. Do nhit vng di

cao hn vng trn nn khi liu vng di chy lng, vng trn cha chy lng c

th gy ra hin tng treo liu, khc phc hin tng ny c th dng kh oxy thi

vo mt trn.

Trong l cm ng, sau khi nu chy xong thng tin hnh iu chnh thnh

phn, kh oxy v ra thp.

5.4. Thit b v cng ngh nu thp trong mt s l in khc 5.4.1. Nu thp trong l in x

L in x dng luyn li nhm nng cao sch ca thp, s nguyn l

cu to ca l trnh by trn hnh 5.3.

L gm y l (1) c lm ngui bng nc, tng l (2) xy bng gch chu

la. in cc kim loi (3) l kim loi cn nu li c th nng ln h xung nh c cu

nng h in cc (4). Ngun in (9) c ni vi y l v in cc.

Nguyn l lm vic: sau khi np cht to x vo l, gy h quang, nhit ca h

quang lm nng chy x to ra lp x lng, khi in cc tip xc vi x lng h quang

tt, dng in tip tc chy qua lp x lng c in tr ln lm pht sinh nhit, tip tc

lm nng chy in cc kim loi. Cc git kim loi lng i qua lp x s c kh tp

cht v tp trung xung y. Do c lm ngui nhanh t y, kim loi kt tinh nh

- 71 -

hng t di ln trn lm cho tp cht tip tc b y ln pha trn, nh thu c

thi kim loi c sch cao.

5.4.2. Nu thp trong l in h quang chn khng S cu to tng t l in x nhng khng dng x tinh luyn m dng

mi trng chn khng.

~

Hnh 5.3 S nguyn l l in x 1) y l 2) Tng l 3) in cc 4) C cu h in cc 5) X

6) Kim loi lng 7) Kim loi kt tinh 8) Nc lm ngui 9) Ngun in

2

4 3

1

5

6

7 9

8

~

Hnh 5.4 S nguyn l l in x 2) y l 2) Tng l 3) Chp chn khng 4) C cu h in cc 5) in cc

6) Kim loi lng 7) Kim loi kt tinh 8) Nc lm ngui 9) Ngun in

2

4

3

1

5

6

7 9

8

- 72 -

Tng l (2) trc y xy bng gch chu la nhng hin nay thng c

thay th bng hp nc. in cc kim loi b nng chy do nhit ca h quang. Kim

loi nng chy trong mi trng l l chn khng, trnh c ho tan kh, ng thi

vic tch kh ho tan trit hn, kt hp vi kt tinh nh hng, tp cht b dn ln

phn trn ca thi, ta thu c kim loi phn di c sch rt cao.

L in h quang chn khng dng luyn thp siu sch, thp cht lng

cao.

- 73 -

Chng VI

LUYN THP TRONG L THI 6.1. c im v phn loi

Luyn thp trong l thi (cn gi l l chuyn) l phng php luyn thp ra i

sm nht, qua nhiu giai on pht trin, hin nay vn c coi l mt phng php

luyn thp quan trng trong lnh vc sn xut thp. L thi s dng nguyn liu kim

loi l gang lng t l cao hoc l c chuyn n, bng cch thi khng kh hoc oxy

vo gang lng t chy bt cc tp cht ch yu trong gang chuyn gang thnh

thp.

Nhit cp cho l gm hai ngun chnh:

+ Nhit vt l: do gang lng mang vo, nhit tch ca th xy l;

+ Nhit ha hc: sinh ra do t chy cc tp cht trong qu trnh luyn.

Theo phng php thi, l c phn ra ba loi chnh:

- L thi y: thi khng kh t y, gm:

+ L Betsme: tng l axit (l thi y axit).

+ L Tmat: tng l baz (l thi y baz)

- L thi sn: thi khng kh t bn hng, gm:

+ L chuyn thi sn axit.

+ L chuyn thi sn baz.

- L thi nh bng oxy (l LD): thi oxy t nh

Mt vn ht sc quan trng trong luyn thp l thi l gii quyt nhit

nc thp. Lng nhit vt l trong cc trng hp chnh lch t, nhng lng nhit

ha hc th rt khc nhau ph thuc vo phng php thi v tnh cht tng l.

Trong l thi y axit (l Betsme) v l thi sn axit ngun nhit ha hc ch

yu l do t chy Si, trong l thi y baz (l Tmat) l P, trong l thi sn baz l

Si v P. Mt khc, khi thi y ton b khng kh lnh i qua kim loi lng nn tn

hao nhit ln hn khi thi sn. Nhit l thi y thp, cht lng thp khng tt

nn hin nay t c s dng, tr l thi y baz cn c s dng nhng vng c

gang nhiu P.

- 74 -

L thi nh bng oxy (l LD: vit tt Lintz Donawit ni u tin xy dng l

LD) l phng php luyn thp ra i sau nhng tc pht trin rt nhanh v tr

thnh mt trong nhng phng php luyn thp ch yu hin nay trn th gii.

u im ca l LD:

+ Phm vi s dng nguyn vt liu rng: s dng c mi loi gang lng

luyn thp, ngoi gang lng c th dng c thp vn (c th dng ti 30% trong m

liu) hoc qung st.

+ Nu c nhiu loi thp: thp C, thp hp kim thp, mt s mc thp hp

kim cao, cht lng thp khng thua km thp l mactanh.

+ Hiu sut sn xut cao: thi gian nu luyn ngn, nng sut cao (2 l LD 40

tn c sn lng tng ng 4 l Mactanh 250 tn).

+ Vn u t xy dng v chi ph sn xut thp (vn u t xy dng ch bng

40 50 % , chi ph sn xut ch bng 55% so vi l mactanh cng sn lng). Nhc im ca l LD l bi khi v chy hao nhiu, mt khc luyn thp t

gang c Si >1,5% hoc P cao, luyn thp C > 0,6% c nhiu kh khn.

Hnh 6.1 S nguyn l cc loi l chuyn a) L thi y b) L thi sn c) L thi nh bng oxy

a) b) c)

Nc

O2

- 75 -

Hin nay, l thi y, nht l l thi y axt t c s dng, bi vy trong

chng ny ch yu gii thiu thit b v cng ngh luyn thp trong l thi sn v l

thi nh bng oxy .

6.2. Luyn thp trong l thi sn 6.2.1. Cu to l

L thi sn c hai dng: dng hnh ng (hnh 6.2a) v dng hnh tang trng

(hnh 6.2b).

L dng hnh tang trng c u im:

+ Hnh dng pha trong ph hp vi s chuyn ng ca kh nn tng l mn

u hn;

+ Mt gi di bng nhau v cch u tng l i din nn gi phn b u n

hn;

+ Hnh dng ni l ph hp vi chuyn ng ca cht lng, thun tin cho

chuyn ng i lu, tng tc oxy ha tp cht;

Hnh 6.2 S nguyn l cc loi l chuyn a) Dng hnh ng b) Dng tang trng

a) b)

- 76 -

+ Din tch b mt ln, chiu su cn, thun tin cho s tip xc v phn ng

gia thp lng v x.

Tuy nhin l hnh tang trng c cu to phc tp, nng n, ch thch hp vi l

dung tch ln, cn cc loi l dung tch di 5 tn thng hay dng l dng hnh ng.

6.2.2. Cng ngh luyn thp trong l chuyn thi sn baz a) c im

u im ca phng php luyn thp trong l chuyn thi sn baz:

+ Hm lng P trong gang lng cho php thay i trong phm vi rng (0,1 1,0%);

+ C kh nng kh S;

+ Khng cn giai on thi sau kh P;

+ Thit b n gin, vn u t thp, thi gian xy dng nhanh;

Nhc im:

+ Nhit ha hc thp, din tch ta nhit ca l kh ln do m bo nhit

thao tc cn dng gang lng c nhit cao;

+ bn tng l thp;

+ Hao tn gang ln do chy hao v bn te;

+ Cht lng thp thng khng n nh.

b) Ch thi luyn: gm ch gi, ch nghing l v ch x.

Ch gi: ch gi ph thuc dung tch l, thnh phn nc gang, nu chn

gi c lu lng ln v p sut cao th thi gian nu luyn ngn, nhng nu chn qu

cao th gy bn te kim loi v x. Lu lng gi hp l xc nh theo cng thc:

=WQ [m3/pht]

Trong :

W - lng khng kh cn thit trn mt tn gang lng, i vi gang phtpho thp

W = 500 m3/tn.

- thi gian thi (pht), thng thng 2218= pht.

- 77 -

p sut gi cn khuy trn c kim loi, nu qu thp khu vc phn ng

tp trung trn b mt gn mt gi lm tm thc mt gi, nu qu cao li ph hy o l.

p sut gi ph thuc dung tch l tham kho bng 6.1.

Bng 6.1 p sut gi khi thi luyn

Dung tch l (tn) p sut gi (atm)

0,5 0,15 0,2 1,0 1,5 0,2 0,25

3,0 0,30

6,0 0,40

10 0,60

Ch nghing l: mt c im quan trng ca luyn thp trong l thi sn l

l c th dng ch quay nghing l trong qu trnh thi luyn thay i su

thi luyn (khong cch t mt gi n mt thong nc thp trong l).

Ty thuc su thi luyn ngi ta chia ra:

+ Thi treo: mt gi nm trn mt thong nc thp, khong cc t mp di

mt gi n mt thong nc thp > 20 mm.

+ Thi mt: mt gi nm trn mt thong nc thp, khong cc t mp di mt

gi n mt thong nc thp t 0 20 mm. Thi nng: mt gi nm di mt thong nc thp, khong cc t mp trn mt

gi n mt thong nc thp t 0 60 mm. Thi su: mt gi nm di mt thong nc thp, khong cc t mp trn mt

gi n mt thong nc thp t > 60 mm.

Khi thi treo, mt gi nm trn mt thong nc thp v cch xa mt thong

nc thp, kh nng khuy trn nc thp ca dng kh km, vi b thi dt v pha

tng i din mt gi, dn n kh to x khng li cho vic kh P v S, ng thi

lm tng s n mn tng l, Fe b oxy ha nhiu v d gy bn te kim loi.

Khi thi mt, mt gi nm trn mt thong nc thp v gn mt thong nc

thp, do kh nng khuy trn nc thp ca dng kh ln, phn ng chy ca

- 78 -

cacbon hon ton hn, lng FeO thch hp cho to x nn x c to nhanh, thun

li cho vic kh P v S, thi gian nu rt ngn nn gim [N] trong thp. Thi mt l

thao tc c bn ca l chuyn.

Khi thi nng, mt gi nm di mt thong nc thp, t to ra FeO. V vy khi

x cha chy lng khng nn thi nng, khi x chy trnh x qu long gy bn

te c th thi nng.

Khi thi su, mt gi nm su di mt thong nc thp, lng FeO trong x

thp nn x kh chy, lm tng tn hao nhit do nung khng kh v tng s ha tan kh,

do vy khi thi luyn nn trnh thi su.

Trong qu trnh thi luyn, do kim loi b chy hao, mt thong nc thp h

thp lin tc, duy tr ch thi mt cn phi c ch nghing l chnh xc. Hnh

6.3 trnh by s thay i gc nghing l ti ba thi im khc nhau.

dm bo cui qu trnh thi, mp di mt gi v mt nc thp cng v tr

nm ngang th phi m bo xc nh chnh xc gc cht liu (gc gia trc mt gi v

mt nc gang khi cht liu xong). Bng 6.2 cho gc cht liu thch hp i vi mt

s l thng dng.

Hnh 6.3 S thay i gc nghin l duy tr ch thi mt a) Lc bt u thi b) Gia qu trnh thi c) Cui qu trnh thi

max

max

= 0

- 79 -

Bng 6.2 Gc cht liu thch hp khi nu thp trong l thi sn

Gc cht liu max () Dung lng l (tn/m)

L thi hnh ng L thi hnh tang trng

3 14 22 8 14 6 14 20 6 12

Ch x: c ba ch x: x n, x kp v x lu. X n l x ch to mt ln

trong sut m nu bng cch cho vo cng mt lc hay tng t nhng sut qu trnh

thi luyn khng co x.

u im ca to x n l thao tc n gin, tit kim thi gian v gim nh

cng lao ng. to x n ngi ta cho vo l vi, vi lng dng tng

cng khong 50 80 kg cho mt tn thp, lng x khong 10 15% khi lng thp, baz lc ra thp B 3.

X n c s dng khi luyn thp cacbon thp t gang lng c %P thp (%P

- 80 -

X lu thng c dng khi gang c hm lng P va v cao.

c) Qu trnh thi luyn Thnh phn nc gang dng cho l chuyn thi sn c thnh phn nh sau:

%C %Si %Mn %P %S

3,3 4,2 0,5 1,2 0,5 1,0 0,15 1,2 < 0,08 L chuyn trc khi nu c sy k. u tin than cc n 2/3 chiu cao l,

t than nung l n sng trng, sau co ht than ra, nc gang vo l, thi gi,

dng l v v tr thi v bt u qu trnh thi luyn. Qu trnh bin i thnh phn

nc gang thanh thp th hin trn hnh 6.4.

Qu trnh thi luyn c th chia ra hai thi k:

+ Thi k u: Fe, sau l Si, Mn b oxy ha, i khi P cng b oxy ha. Cc

phn ng:

0,4 0,8 1,2 1,6 2,0 2,4 2,8 3,2 3,4

2 4 6 8 10 12 14 16 2018 24220,2

0,6 0,4

1,0 0,8

1,2 1,4

0,1 0,2

0,5

0,3

0,6

0,4

0

10 5

20 15

30 25

35 40

2

0

4

1

5

3

Gc

thi

CaO

, SiO

2, M

nO, M

gO,

P2O

5, F

eO (%

) C(

%)

Mn,

Si(%

)

P, S

. 10

-2(%

)

Ch

t li

u

Co

x

i

m c

ui

Ra

thp

K

h o

xy

Hnh 6.4 Thay i thnh phn kim loi v x trong l chuyn thi sn bazzic

C

S

P Si Mn

SiO2

FeO CaO

P2O5 MgO MnO

- 81 -

[ ] [ ] [ ] 800.128FeO2O2Fe2 +=+ kcal [ ] [ ] [ ] ( ) 900.78SiOFe2SiFeO2 2 ++=+ kcal

Kt hp hai phn ng trn ta c phn ng:

[ ] [ ] ( ) 850.207SiOO2Si 2 +=+ kcal Mi kilgam Si chy cho ta 7.420 kcal, lng nhit ny c th tng nhit 100

kg liu t 1300oC ln thm 172oC nn nhit nc thp tng rt nhanh.

Phn ng t chy Mn:

[ ] [ ] [ ] ( ) 290.31MnOeFFeOMn ++=+ kcal Hiu ng nhit ca phn ng oxy ha Mn tng i nh ch b lng nhit

do gi mang i nn t nh hng n nhit nc thp.

Cc oxyt cng tham gia phn ng to x:

( ) ( ) ( ) 130.1SiO.FeO2SiOFeO2 22 +=+ kcal ( ) ( ) ( ) 900.5SiO.FeOSiOFeo 22 +=+ kcal 000.7SiO.MnOSiOMnO 22 +++ kcal

Trong giai on ny sau t pht ta thy khi nu bay ra, sau l nng ht mu

xm (ht x cha SiO2).

Do hiu ng nhit ch yu ca phn ng oxy ha Si v mt phn ca cc phn

ng khc nhit ca l tng nhanh, khi nhit l > 1470oC th c ngn la sng

(cacbon bt u chy), th nghing l, ngng gi tin hnh co x c v to x mi

ri chuyn sang giai on th 2.

+ Thi k th 2: trong giai on ny C v P ng thi b oxy ha, phn ng oxy

ha P v C nh sau:

[ ] ( ) ( ) ( ) [ ] 000.130Fe9OP.CaO4CaO4FeO5PFe2 522 ++=++ kcal Phn ng oxy ha P ta ra lng nhit kh ln c tc dng lm tng nhanh nhit

nc thp. Ni chung trong giai on ny P b kh ti mc yu cu, thng khng

phi thi thm kh P.

Phn ng ch yu trong giai on ny l phn ng chy C:

[ ] { } { } 650.97COOC 22 +=+ kcal

- 82 -

[ ] { } { } 970.29COO21C 2 +=+ kcal

{ } { } { } 630.67COO21CO 22 +=+ kcal

[ ] [ ] [ ] { } 460.34COFeCFeO +=+ kcal Do c phn ng chy cacbon to thnh CO ri tip theo chy thnh CO2 m

ming l ta thy c ngn la di v sng.

Thng ngi ta cn c vo ngn la v tnh hnh phun bn x phn on v

iu chnh qu trnh thi luyn. Nu ngn la d