NGHIEN ciiu-TRAODOI
/ N G H I E N c d u Sg CHUYEN DONG BOI L U U CUA DONG KIM LOAI LONG TRONG VUNG HAN KHI HAN PLASMA BOT
RESEARCH FOR CONVECTIVE MOVEMENTS OF LIQUID METAL FLOW IN THE WELD POOL DURING
POWDER PLASMA WELDING
Ngo Huu IVIanh', Bui Van Hanh', Nguyin Thiic Ha- 'Truong Dai hgc Sao Do
^Truong Dai hgc Bach khoa Ha Noi
TOM TAT
Trong qud trinh han, kim loai trong vung han & trang thdi long. Do do, no chiu tdc dong cua nhieu loai luc khac nhau vd co dac tinh giong nhir chdt long. Qud trinh dich chuyen ciia dong kim loai /ong quyet dinh den hinh ddng, kich thu&c vd chdt lucmg cita moi hdn. Trong bdi bdo ndy, tdc gid tap trung nghien cuu su dich chuyen cua kim loai long trong viing han vd cdc yeu to anh hu&ng khi hdn thep ei&
hon bdng cong nghe hdn Plasma bot.
Tir khoa: Su dich chuyen cda kim loai viing hdn; Su chuyen dich cita kim loai long.
ABSTRACT
During welding, metal of welding pool in the liquid state. Therefore, it is influenced by different many forces and characteristics similar as liquid. The process of move of liquid metal flow determine to shape, size and quality of the weld. In this paper, authors is researching focus convection movemenl of liquid metal in the weld pool and factors affecting during welding carbon steel by plasma powder transferred arc welding technology.
Keywords: Movement of metal pool flow; Convection movement of liquid metal.
TAP CHi CO KHi VIET NAIM, S6 3 nam 2014
NGHIEN CIIU - TRAO DOI
1. DAT VAN DE
Hd quang Plasma dugc hinh thanh trong mdi trudng khi bi ion hda giua dien cue khdng ndng chay va vat han. Ngudn nhiet Plasma cd cdng suat Idn nen lam ndng chay kim loai trong thdi gian ngan. Cdng suat ngudn nhiet hd quang plasma, hudng dich chuyen hd quang, khoang each giiia mieng phun plasma ddn vat ban,...
quyet dinh thdi gian chuyen tir trang thai rdn sang trang thai Idng cua kim loai, su chuydn ddng cua kim loai Idng viing ban, su khuech tan va hda tan kim loai, qua trinh luyen kim, su ket tinh cua kim loai mdi ban.
Trong qua trinh ban, kim loai viing ban tdn tai d trang thai Idng. Vi vay, nd chiu tac ddng cua nhieu loai luc va cd dac diem giong nhu chat Idng. Tuy nhien, thdi gian kim loai chuyen tir trang thai ran sang trang thai Idng va thdi gian ton tai d trang thai Idng la rat ngan. Cac qua trinh hda ly xay ra vdi tdc do rat nhanh, lam anh hudng dSn cku tnic, td chiic kim loai mdi ban va gay anh hudng true tiep den hinh dang, kich thudc, chat lugng mdi han.
2. NOI DUNG NGHIEN ClTU
2.1. Qua trinh hinh thanh hd quang Plasma d didu kien binh thudng, cac phan tu khi cd tinh trung tinh va khdng dSn dien. Trong vimg khi giQa dien cue va vat ban, cac phan tir khi bi ion hda nen cd nang lugng va van tdc Idn.
Cac nguyen tii mang dien tich duong, cac dien
;ii tu do mang dien tich am. Do bi ion hda nen :;ac nguyen tii va dien tii cd dgng nang rat Idn,
;huydn ddng va va cham vao nhau. Luc lien TAP
ket giiia cac nguyen tir va dien tir bi be gay, cac electron dugc giai phdng va tach khdi hat nhan nguyen tit tao ra ddng dich chuyen plasma. Nhu vay, hd quang plasma dugc hinh thanh trong mdi trudng khi bj ion hda giiia dien cue khdng ndng chay va vat han [2].
Hinh I: Qua irin/i chuyen ddng cua cdc ion vd dien tic trong cot hd quang Plasma [12].
2.2. Hieu irng Idng cua kim loai
Hd quang Plasma cd cdng suat nhiet Idn lam ndng chay vat lieu ban va vat lieu ca ban, tao ra hieu ling Idng cua kim loai. Hieu ling Idng phu thudc chii yeu vao cac thdng sd che do ban, su dan nhiet va su khuech tan nhiet cua vat lieu ban va vat lieu ca ban [4]. Su thay ddi che do ban se lam thay ddi cdng suat nhiet ciia hd quang plasma, anh hudng true tiep den qua trinh ban.
Nhiet do ciia cot hd quang Plasma nkm trong khoang 15000 20000"C, tiiy thudc vao dac tinh ngudn, loai khi va dien cue sir dung [10]. d gan dien cue trong cdt hd quang Plasma, nhiet do cd thd dat tdi 25000"C [II].' CHI CO KHI VIET NAM, So 3 nam 2014
www.cokhivietnam.vn
NGHIEN cuu-TRAODOI
Vdi nhiet dp nay, hd quang plasma cd the lam ndng chay hau hSt cac loai vat lieu trong mot thdi gian ngan.
Hinh 2: Suphdn bd nhiet trong cdt hd quang plastna [11].
Khi cdng suat nhiet hd quang Plasma tang len se lam giam thdi gian chuyen tir trang thai ran sang trang thai Idng cua bdt hgp kim; tang tinh chay loang cua kim loai viing ban; Su tang mire do chuyen ddng ciia kim loai Idng trong vung ban; Su khuech tan kim loai vao vat han, chieu sau ngau ciing tang len va ngugc lai.
Hinh 3. Su tan chay ciia bdt hgp kim trong cdt ho quang Plasma khi hdn PTA [15].
B i i TAP CHi CO KHI VIET NAM, S6 3 nam
Nhiet do tren bd mat viing ban udc tinh khoang 27000C [5]. Nhiet do tnmg binh ciia viing ban la khoang 1650"C ddn IVOO^'C [6].
2.3. Su- chuySn dong doi luu cua kim lo^i long
trong vung han ^ Ddng chay va chuyen ddng ddi luu la nhihig
khai niem thudng dugc sii dung cho chit khi va chat Idng. 6 trang thai long, kim loai viing ban ciing tao ra ddng chay, dich chuyen cd tinh chal ddi luu. Qua frinh dich chuyen cua ddng kim loai Idng chu ydu phu thudc vao ngoai luc. Su chuyen ddng va ddi luu ciia kim loai long trong viing tian anh hudng true tiep den hinh dang mdi han, si:
hda trdn, tinh ddng diu, su phan ly, c4u mic v^to chirc kim loai, sir bay hai cua cac nguyen to h{^
kim va su chuyen ddng cua kim loai vung han [9]
Dac biet, nd anh hudng den hinh dang va kicb thudc viing han va mdi ban [16],
Su chuyen ddng ddi luu cua ddng kim loai long dugc xac dinh bdi cac mat cat ngang cua mdi ban. Ddng kim loai Idng dich chuyen tir bien vao tam cua viing ban dugc ggi la ddng doi luu hdi tu. Ddng kim loai Idng dich chuyen ddi luu hdi tu khdng 6n dinh. Nd tao ra hien tugng xao trdn manh kim loai Idng trong viing han. Day la nguyen nhan gay ra cac vet Idm dgc theo ducmj tam tren bd mat ciia viing han [3, 9], Ngugcl?i.
ddng kim loai long djch chuyen tit tam ra bien ciia viing han dugc ggi la ddng ddi luu phan ky. Dong kim loai Idng ddi luu phan ky dich chuyen wonj ddi dn dinh. Tuy nhien, nd cd xu hudng lam giai"
chieu cao cua mdi han.
2014
NGHIEN CirU-TRAO DOI
Hinh 4: Su chuyen ddng ddi luu ciia kim loai long trong vung hdn khi hdn PTA.
Cac yeu td anh hudng true tiep den su chuyen ddng ddi luu cua kim loai Idng trong vung ban la
• luc dien tii' hay chinh la luc Lorentz (F^ J , luc day Acsimet (F^), luc cang be mat hay luc Marangoni , (F), luc va cham, luc ma sat, khi ddng luc hgc ,cua hd quang plasma (F^^^), luc dich chuyen hd
quang Plasma [9, 13].
Luc dien tir (F ) ciia ddng dien tac ddng true ti8p tdi ddng kim loai Idng. Luc nay chi xuat hien d viing hd quang trong qua trinh han [17].
Nd quydt dinh ddn hinh dang va do sau ngau ciia mdi ban. Su dich chuyen cua ddng kim loai Idng trong cdt hd quang va kim loai Idng trong viing 'han phu thudc vao hudng va do Idn ciia luc dien tir. Dd Idn ciia luc dien tiv se thay ddi khi cd su thay ddi mat do ddng dien cua hd quang, cudng 'do ddng dien ban. Hudng cua luc dien td thay ddi khi cd su thay ddi dac tinh cua hd quang.
Digu nay dl nhan bidt nh^t khi ban hd quang xung [7, 8, 9, 13, 14], Luc dien hi dugc xac dinh qua cong thiic sau day:
Kn^-^cd-^.„f(l)
Trong do; J^^ la vector mat do ddng dien;
B^(. la vector tir thdng.
Luc day Acsimet (F^^) sinh ra khi cd sir chenh lech ve nhiet do trong vung kim loai viing ban. C) nhiet do cao, ty trgng ciia kim loai se giam xudng. Luc day Acsimet se day kim loai Idng d vimg cd nhiet do cao, kim loai cd tl trgng thap ban, di chuyen len phia tren be mat cita vung ban. Cdn kim loai Idng d viing nhiet thap hon, kim loai cd ti trgng cao ban, se di chuyen xudng phia dudi ciia viing ban. Qua trinh dich chuyen nay dien ra lien tuc, tao ra sy chuyen ddng phan ky cua ddng kim loai Idng trong viing ban. Luc day dugc xac dinh bang phuang trinh sau [8, 9].
/=;,=-p„„-P,-g-(r„„-r„,,)r2;
Trong dd: p,^ la ti trgng ciia kim loai Idng;
p^ la he sd gian nd nhiet cua kim loai long;
g la gia tdc trgng trudng;
T la nhiet do cua viing han;
Tg, ^p la nhiet do ndng chay cua kim loai.
Luc cang be mat (F ) xuit hien tren bl mat thoang cua vung kim loai long khi cd su thay "^
TAP CHI CO KHi VIET NAM, So 3 nam 2014 www.cokhivietnam.vn
NGHIEN ciiu-TRAO DOI
ddi nhiet do. 6 nhiet do cao, nang lutmg nhiet Idn, Icim loai chuy6n sang trang thai long, hen kk giua cac nguyen tu kim loai giam xuong, qua trinh chuySn dong va va hao d6i nhiet tang len, hen ket kim loai hi pha vS. Khi do, hieu ling Marangoni tao ra dong dich chuyen tten toan ho be mat viing kim loai long va tao ra lire cang tren he mat ciia viing han. Luc cang bS mat cua kim loai long tren bk mat vung han thay doi khi co su thay d6i nhiet do. Dp 1cm ciia lire cang be mat ti le nghjch vol nhiet do. No se tang len khi nhiet do giam xuong va ngtrpc iai, giam xuong khi nhiet dp tang len. Dilu nay gay ra sir biSn dang hk mat va lam thay doi hinh dang ciia vung han.
Luc cang bk mat duoc xac dinh bSng phuang trinh sau [1,8, 13].
P-,y^T (3)
Trong do:Y la sure cang be mat ciia kim loai long;
AT la sir chenh lech nhiet dp tren be mat vung han.
Luc va cham la ket qua ciia su va cham giua cac nguyen tu kim loai trong viing han. Ci nhiet dp cao, cac electron va ion trong cot h6 quang Plasma, cac nguyen tir kim loai trong viing han co toe dp cap va cham vai nhau. Luc va cham tap ra nang luang rat Ion duai dang dpng nang cua cac hat. Toe dp djch chuyin cua cac hat ty le thuan vai nhiet dp. Lire va cham tap ra sir xao trpn Ion ciia kim loai long trong viing han va gay ra hien tuong lom tren be mat moi han sau khi kk tinh. Day la kit
qua ciia sir chuyen dpng doi liru lien tuc voi hudng chuyin dich hoi tu ciia dong kim loai long trong viing ban [9].
Nhu vay, su dich chuyen ciia kim loai long trong cpt h6 quang va sir chuyin dpng doi luu cua kim loai long trong vung ban la do su tac dgng cua cac loai luc sinh ra trong qua trinh ban.
3. KET LUAN
Nhiet do ciia cot ho quang plasma la khoang 15000 - 20000°C, tiiy thupc vao dac tinh ngtiSn, loai khi va dien cue su dung. Nhiet do tren be m|t viing han la khoiing 2700°C. Nhiet dp ttung bink cua viing ban la khoang leSCC din IVOffC.
Kim loai long trong viing ban chuyen dpng doi luu lien tuc theo hai hudng hoi tu va phan ky, Luc day Acsimet va luc cang be mat kim loai long tao ra dong chuyen dong phan ky ciia kim loai long ciing ban.
Luc dien tir, luc ma sat, lire va cham va khi dpng luc hoc tao ra dong chuyen dpng hoi tu cua kim loai long trong viing ban.
Cdng suat ngudn nhiet hd quang Plasma, hudng dich chuyen hd quang, khoang each giiia mieng phun Plasma din vat han se quylt dinl thdi gian chuyen tit trang thai tin sang trjng thai long cua kim loai, su chuyen dpng cua kim loai Idng vung ban, su kbulch tan va hoa tan kim loai, qua trinh luyen kim, sir kit tinh ciiJ kim loai mdi ban. Cac ylu td nay anh hucmg den hinh dang, kich thudc, chit lupng moi ha«
khi ban PTA.*:*
TAP CHi CO KHI VIET NAM, So 3 nam 2014
NGHIEN CirU-TRAO DOI
Ngay nhan bai: 12/01/2014 Ngay phan bien: 25/02/2014
Tai lieu tham khao:
[1]. Burgardt and Heiple, 1986, Interaction between Impurities and Welding Variables in Determining GTA Weld Shape. Welding Journal, 65 (6), pp. 150-155.
: [2]. Craig, 1988, The Plasma Arc Process. Welding Joumal, Vol. 2"'', pp. 19-25.
[3]. David and Vitek, 1989, Correlation between Solidification Parameters and Weld Micros trucUires. International Materials Reviews, 34 (5), pp. 213-245.
[4]. DuPont and Marder, 1996, Dilution in Single Pass Arc Welds, Metallurgical and Materials Transactions B, 278 (3), pp. 481-489.
[5]. Feng, White, Willis and Solomon, \'^99, Development of Compressive Residual Stresses in Underwater PTA Welds, Technical Information Series, GE Research & Development Center, August 1999, p.8.
[6]. Gladky and Pavlenko, 1990, Development of Physical Concepts about the Plasma Transferred Arc Surfacing.
In: Machida (Ed.). Advanced Technology in Welding, Materials Processing and Evaluation, Proceedings, 5th Intemational Symposium of the Japan Welding Society, Tokyo, Japan, 17-19 April 1990, pp. 399-404.
[7]. Ishizaki, Okada and Yokoya, 1994, Electromagnetic Force near the Anode Boundary and Double Convention in a TIG Arc Weldpool, Welding Intemational, 8 (10), pp. 790-197.
[8]. Kou and Wang, 1986, Weld Pool Convection and Its Effect, Welding Joumal, 65 (3), pp. 63-70.
[9]. Messier, 1999, Weld Pool Convection. Oscillation and Evaporation, In: Principles of Welding, Processes, Physics, Chemistry, and Metallurgy, Chapter 10, John Wiley and Sons, Inc., New York, USA, pp. 291-312.
[10]. Nguyen Van Thong, 2012, So tay cdng nghe han. tap 1, Trang 234, NXB. Khoa hgc Ky thuat.
[W]. Tom Glynn (2007), Plasma transferred Arc and HVOFhardfacing process. Stellit,AWS.
[12]. Sumio Noda, Satonu Zenltani, Yoshikazu Yamada, Tomoyoshi Sasaki (2004), Improved Technologies of Steam Turbine for Long Term Continuous Operation, Mitsubishi Heavy Industries., Ltd, Technical review, Vol.41, No.3,pp.l-5.
[13]. Ushio, 1991, Mathematical Modelling of Flow in the Weld Pool-Fart 11. Welding Intemational, 5 (8), pp.
593-597.
[14]. Yokoya, Okada and Matsunawa, 1994, Penetration Shape in Carbon Steel Welds Produced by a Stationary TIG Arc, Welding Intemational, 8 (10), pp. 781-789.
[15]. www.castolin.com
[16]. T. Debroy, H. Zhao, W.Hang and G. G. Roy, 2002, Weld pool heat and fluid flow in probing weldment characteristic. Methematical modelling of weld phenomena 6, pp. 21-41, Edited by H. Cerjak, Series editor H, K. D. H. Bhadesshia.
[17]. Michael Hughes, Koulis Pencleous andNadia Strusevich, 2002, Modelling the fluid dynamics and coupled ohenomena in arc weld pools. Methematical modelling of weld phenomena 6, pp. 63-81, Edited by H. Cerjak, Series editor H. K. D. H. Bhadesshia.
TAP CHI CO KHI VIET NAM, Sd 3 nam 2014 www.cokhivietnam.vn
