Ceramic-lined compound copper pipe prepared by SHS process

Vol.14 Special 2Trans. Nonferrous Met. Soc. ChinaOct. 2004Article ID: 1003 一6326(2004)S2 -0106 -05Ceramic-lined compound copper pipe prepared by SHS processFU Han guang' , JIANG Zhi-qiang ，ZHANG Xiao-hong'(1. Depatment of Mechanical Engieering, Tsinghua University, Beijing 10084,4 China; .2. Department of Industrial Engineering , Zhengzhou Institute of Aeronautics, Zhengzhou, China;3. Taiyuan Iron and Steel (Group) Company, Taiyuan, China)Abstract: Slrpoppring high temperature sytesis(SHS) is a new kind of materil synthesis technigue, andhas caracteristis with respect to low energy consumption, short syhetzing time, high production quantity, highand no environmental pllution. When SHS combines with centifugal cesting, cramic lined com-produet purity andCP) can be produced, the inner surfece of copper pipe can produce ceramic coatings havingpound copper pipe(CLCCP) can be produced,good wer and corrosion resistance. In order to increse the densifcation degreecombining strength and toughnessof ceramie layer, the efte of editives such as SiO,, CrO3，NarB,O, and 2rO2 are researched, adding SiO, andCrO, in thermite, the desification degree of ceramic layer icress, ading Naz B.O, in thermite can increase com-biring srengh, adin ZrO2 in termite can icre the toughness of ceramie layer. CL.CCP is used in tubuler blleing exellnt service efets and decreasing the production cost of tubular bllete.Key words: SHS; ceramic lining; compound copper pipe; crystallizerCLC number: TG174Document code: A1 INTRODUCTIONceramic-lined compound copper pipe(CLCCP) canbe produced, and on the inner surface of copperThe continuous casting has characteristicspipe ceramic coatings can be formed with goousuch as saving energy and high eficiency, and itwear and corrosion resistance. When CL.CCP ishas extensive application in the production of ironused in tubular billet crystallizer, the combinationand stl-]. Mould used in the continuous castingbetween cerarmnic layer and copper tube is veryproduction is the key spare part of continuous cast-well, ceramic layer is not easy to crack and flake,ing machine(CCM), and its quality has direct in-and the service life of CLCCP is two times longerfluence on the quality and production cost of con-than that of ordinary copper pipe.tinuous casting billet. With the development ofhigh efficiency continuous casting technology,2 PRINCIPLE OF SHS COMPOUND COPPERhigher requests have been put forward to the quali-PIPEty of mould. Not only there should be highstrength and good heat conductivity, but also there2.1 Principleshould be high wear and corrosion resistancel*. 5?.^he principle of SHS ceramic lined compoundThe surface treatment of mould is the importantcopper pipe bases on the follow thermite reaction:measures to improve wear and corrosion resist-3Cu0+ 2AI-→Al2O3 +3Cu+1 194. 4 kJ/molancefe,n. Mould plating nickel and nickel alloy hasthe shortcoming that the hardness of plating layerCuO powder and Al powder are evenly mixedis low and wear resistance is badiB. Mould platingand placed on the copper pipe, then copper pipe ischromium also has the shortcoming that the thick-ness of plating layer is thin, there is large stressfixed on the centrifuge. W hen the copper pipe TO-and plating chromium layer is easy to crack andtates around an axis, the powdery thermite mix-flake in the usagel9]. Moreover, electroplating yetture is pressed against the inward surface of thepipe by the centrifugal force to form a layer. Ther-pollutes the environment.Recently, thermal spray technology is appliedmit reactant is ignited and the reaction of Eqn. (1)to mould abroad, and better results have been ob-takes place. The reaction of Eqn. (1) emits enor-tained[I0], which is only adaptive to plate blankmous heat, and the temperature of the system im-mould and can not be used in tubular billet crystal-mediatelv increases tn 2 844 K[1]、 Therefore, aslizer. When self propagating high temperature syn-showr中国煤化工thermit reactionthesis (SHS) combines with centrifugal casting,inasurface of theYHCNMHG①Recelved date; 2004 -05 - 10, Accepled date: 2004 -07-15Correspondence: FU Han-guang, PhD; Tel; + 86-10-80614640; Fax: + 86-10 62770190; E -mail: fhg@ tsinghua. edu. cnVol. 14 Special 2Ceramic lined compound copper pipe prepared by SHS processgas, which can improve the densification degree ofceramics.2.2 Process characteristicSHSis a high and new technology that com-bines physics, chemistry, metallurgy and material用分用务，science, etc. SHS ceramic-lined compound copperpipe technology which is developed by combinationbetween SHS and centrifugal casting technologyFig. 1 Principle of centrifugal SHS processhas the following characteristics:1-Centrifuge; 2--Copper pipe; 3- Thermite;1) The process and equipment are simple, the4-Copper layer; 5-Ceramic layerprocess flow is short, the production efficiency ispipe melts and forms a composite with the reactionhigh and there is no pollution.products. The revolution speed of centrifuge is se-2) SHS has low energy consumption. It is alected according to KOHCTaHTHHOB formulal12]， andheat releasing course by itself, and reaction doesthe formula is as follows:not need to supplement energy and goes on sponta-n= 55200.(2)neously once it is initiated, which can save energy.Vr.r P3) Main raw materials producing centrifugalSHS ceramic-lined compound copper pipe are abun-mote! ceramic density, kg/m'; r- copper pipe in-dant and their prices are low.ner radius, m; β - adjusting coefficient, and that ofSHS ceramic-lined compound copper pipe con-ceramic lined compound copper pipe is 1.0~1.5.，tains the combustion process of thermite, the sepa-Under the action of centrifugal force, the mol-ration of liquid phases and solidification process often products are separated according to their densi-ceramics. By controlling these three importantty differences. Since the density of Al2Oz (3 970courses rationally, the performance of CLCCP cankg/m') is smaller than that of copper (8 900be greatly improved.kg/m')，a thick ceramic layer is formed inward3 EXPERIMENTALnd product copper is formed in the intermediateregion between the pipe and the ceramic layer.With the intermediate metal layer, the producedThe experiment was carried on in the smallCLCCP has not only high strength, toughness,type centrifuger. The range of adjustment speed ishigh corrosion and wear resistance, but also high800~ 2500 r/min, and the copper pipe size is d90resistance against thermal and mechanical shocks.mm/d110 mmX 150 mm. In the thermite, CuOFig. 1 shows the principle drawing of centrifugalpowder size is 74 - 147 μm, and aluminium powderSHS compound copper pipe process.size is 74 - 147 μm. CuO powder and aluminiumStudies have shown that the action of centrifu-powder is evenly mixed and enclosed into the cop-gal force is as follows. .per pipe. Copper pipe containing CuO powder and1) It helps the delamination of Cu and Al2O3.aluminium powder is installed to the centrifuger.Under centrifugal function, the larger the densityWhen the centrifuger revolution speed reaches re-difference of products is, the easier the delamina-quired speed, sample materials are ignited with ox-tion of Cu and Al2O3 is. The greater the centrifu-ygen- acetylene flame, and Al reacts with CuO bygal force is, the more complete the delaminationEqn. (1) reaction. Combustion reaction lasts moreis. When the centrifugal force is too great, whichthan 10 s, after 15 min centrifuge stops and theresults in complete separation between deoxidizingperformance of CLCCP is measured.copper liquid and ceramic liquid film and producesThe ceramic thickness, porosity, strength,the interval between the products, the homogenei-hardness，fracture toughness, thermal and me-ty of the ceramic-lined layer is deteriorated, and chanical shocks of CLCCP are measured. Strengththe combining strength between copper and ceram-measurement is accomplished through crushingics also reduces.test and compression-shear test. Crushing test re-2) It helps to increase the densification degreepresents the compression strength of ceramics andof ceramics. ln the course of burning, because ofcompression shear test represents combiningthe volatilization of moisture and low melting pointstrength between ceramic layer and transition lay-of impurity in the reactant, a large amount of gas中国煤化工clculaled acor-was produced, which has obvious influence on theproperties of ceramics. Centrifugal force is favora-ble to the separation of liquid phase and gaseousFYHCNM HG+卡(D+)}此1TKJphase products and accelerates the transgression of(3)Trans. Nonferrous Met. Soc. ChinaOct.2004where L, t and D are the length, thickness andcan notably reduce the porosity and improve theaverage diameter of test pipe, respectively. P isdensification degree of ceramic layer. It is discov-turning point load deviating from straight line atered that the crystallization starting point of purethe compress load- displacement curve. k is aAl2O3 having no SiO2 is also erystallization encross section factor.point and its temperature is 2 054 C from binaryk=-1+元>x In(B()(4)phase diagram of SiO2- Al2O34]. SiO2 not only de-creases the primary crystallization temperature ofCompression-shear strength(o,) is calculatedAl2O3，but also decreases the crystallization endaccording to the following formula:。(5)π.L. Dnwhere D. is the diameter of primitive pipe, Pm isthe largest compression-shear load.04 RESULTS AND DISCUSSION4.1 Performances of CLCCP25The performances of CLCCP are shown in Ta-:二si,ble 1. Compared with common copper pipe, it hassuch characteristics as high hardness of ceramiclayer and excellent mechanical and thermal shocksAdditive amount%resistance. It also has such shortcomings as highporosity of ceramic layer, low densification degree，Fig.2 Effect of additive on porosity of ceramicslow combining strength between ceramic layer andtransition copper layer and large brittleness. It isdiffcult to apply CLCCP made in common method1 350directly to the tubular billet crystallizere.4.2 Influence of additive on performance ofs1300CLCCP4.2. 1Influence of additive on densification de-The ceramic layer of centrifugal SHS ceramiclined compound copper pipe has more holes that se-1 200:-Si02riously influence the corrosion resistance, heat re-sistance and wear resistance of CLCCP. In order toimprove the density of ceramic layer, the influ-1150ences of adding SiO2, CrO3 in Al-CuO thermite on8the ceramic layer have been researched, and the rtesults are shown in Fig.2 and Fig. 3. SiO2 and CrO3Fig.3 Effect of additive on hardness of ceramicsTable 1 Properties of CLCCPCeramic thicknessPorosityCrushing strength, Conpression shear strength,Material/ mm/%o/MPa0./MPaCopper pipe3744.213. 236614.3Fracture toughnessMechanical shockThermal shockHardnessKre/(MPa. m12)resistance/ time*HB62-HV1 356中国煤化工22* Mechancal shock resistance is impact times that ceramic layer preMH* #Thermal shock resistance is thermal cycle times that ceramie layeCNMH Gedsm nderhecondition of 20 C←→800 C cyeling heating and cooling.Vol. 14 Special 2Ceramic lined compound copper pipe prepared by SHS process●109●point that is only 1 828 C, which lengthens liquidstate time of reaction product Al2O, and favors theescape of gas and improves the densification degree380of ceramics. SiO2 obviously reduces the micro-hardness of ceramnics. The more the adding amountof SiO2 is, the larger the influence is. CrO, also20 f360obviously improves the densification degree of ceramics and does not reduce the hardness of ceram-B340ics. The main reason that CrO, raises the densifi-16 tcation degree is that the reaction between CrO, and:二8;Al can take place such as Eqn. (6), whose reaction320temperature reaches 5 800 K[5]. Adding CrO, in AIand CuO powders can greatly raise the reaction125temperature of system, lengthen escaping time ofw(NarB40>)/%gas and promote densification of ceramics.CrO3+2A1-→Al2O3 +Cr+1094 kJ/mol (6Fig.4 Effect of additive on crushing strength(o,)4.2.2Influence of additive on combiningand compression-shear strength(o, )strengthThe ability that CLCCP endures resistance aobtained. Adding ZrO2 in thermite can refine thegainst thermal and mechanical shocks has some-crystal grain of ceramics and obviously improve thething to do with combining strength of ceramic lay-toughness of ceramics, the results are shown iner. Usually, compression shear strength repre-Fig. 5. When the adding amount of ZrO2 is lesssents combining strength between ceramics andthan 2%，the increase of fracture toughness is nottransition layer-1)]. Adding Naz B,O, in thermiteobvious. When the adding amount of ZrO2 is 2%-can improve compression-shear strength of7%, the increase of fracture toughness is very ob-CLCCP, but it has litle influence on crushingvious. When the adding amount of ZrO2 is 7%, thestrength.' The results are shown in Fig. 4. Thefracture toughness is the highest, which is onecompression shear strength increases with the in-time higher than that of the primitive ceramic lay-crease of Na:B.O，when the adding amount ofer. When the adding amount of ZrO2 exceeds 7%，Naz B,Oz exceeds 4% , and the increase of compres-the fracture toughness presents downward tenden-sion-shear strength is slow. The main reason iscy. The main reason is that a number of ZrOr ente-that the molten products Al2Oz and Cu after thering SHS reaction system absorbs heat and causesthermite reaction separate under the action of cen- the decrease of SHS reaction system temperature,trifugal force, and the combination situation of which will decrease the densification degree of ce-Al2O, and Cu depends on the wettability of tweramics and then influence the toughness of ceram-phases. Because ceramic layer and copper combineby means of mechanical coherence, it helps to in-crease the combining strength of two phases to im-.5tprove the wettability between Al2O, and Cu. Thewettability between AlL2Os and Cu is poor, and or-r 3.dinary CLCCP has low combining strength. Aferadding Na2 BO, in thermite, Na; B,O, decomposesand turns into BO, at high temperature. The sur-2.5 tface tension of B2O3 is only 0. 08 N/m. It can nota-bly reduce the surface tension between Al2O, andCu, and it also improves the wettability betweenseparate solid state Al2Os and liquid Cu, thereforeit increases the combining strength.284.2.3 Influence of additive on toughnessw(ZrO2)%Ceramic layer of CLCCP has large britlenessFig.5 Effect of ZrO2 onand does not endure large impact, which seriouslyfracture toughness of ceramicsinfluences the application of CLCCP in the tubularbillet crysalizer. The increase of ceramic tough-ness can improve the dependability of CLCCP. Re-中国煤化工ing SHS and cen-cently, sientistsl4a) pay great atention to theMHCN M H Gditis used in tuprocess that improves the toughness of ceramics bybular bilet crystallizer. Result indicates that themeans of adding ZrO2, and excellent results areceramic layer of CLCCP has high hardness and ex-●110●Trans. Nonferrous Met. Soc. 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Optimizing the hydraulic characteristics and ther-中国煤化工MYHCNMHG