Theoretical Analysis of TCS with a Comparison to HGS in Characteristics

74Journal of Dong Hua University ( Eng. Ed.) Vol. 18 No .4 (2001)Theoretical Analysis of TCS with a Comparison to HGS inCharacteristicsHou Peimin(侯培民)Sinope Shanghai Petrochemical Limited, Shconghai , 200540A theoretical analysis of TCS is provided to explain thegnadient along the x axis can be described asstructure evolution along the flament during processing.This amalysis based on the spinning process kinematics业。_ 2πRh(r- ro)+ AH d1)dx=- WC,Cp dxincorporates the constitutive equation of PET polymer, aconvection and radiation combining procedure in thewhere h is convective heat transfer coefficient correlated with thethermal channel， and taking into account thefilament running velocity V and coss-fIow cooling air speed V,nonisothermal crystallization kinetics. The characteristicsdeveloped by Kase and Matsuo2 asof the fiber so-produced are compared with thoseproduced by HGS.h = 0.473 x 10~4(VA).34[1 + (8VJ/V)2]0.167 (2)Keywords: Themal Channel Spinning; Hot Godet Spinning;In the themmal chanel, the nadiant heat transfer between filamentHigh speed spinningand themal channel will also play an important role as theNotwithstanding that the so-called super-high-speed spinningconvective heat transfer between flament surface and heated airat the take up speed above 6000 m/min and up to 10 000 m/minflow while the nning filament moves rapidly within the theralcan produce fully oriented yarm (FOY) by the spinline reactingchannel, thereby, the nning filament temperature T satisfies thesolely with air friction and inertia, it is still necessary for procsesfollowing diferential reltionship:running at about 4 000 m/min to draw the spun yam, which isdT_ 2πReC;2xRaOH业parially oriented (POY)， in a later stage to obtain desinabledx=~ WCp(TW- %) -WC(T-To)+Tdxtensile properties.3)Alemaively, the process of melt spinning PET flament atmedium high speeds can be modifed through the inclusion of awhere the radiation energy fllows Stefan-Bolumann's law.thermal channel enclosing the spinline wih air stream initally atn the spin path scction between the outlet of themnal channelroom temperature sucked into the channel by the high speedand the winding point, the heat transfer equation is identical l0 thatflament as a medium to create a contact-free recheating. Theof equation (1), but with a dfferent cofficient h{2] for spinningheated channel rdiates toward the filament, while the air streanwithout transverse air flows.exchanges the heat between them convcively. The commercialh= 6.85 x 10~*( V2/W)0.259(4)PET yams produced by the themal channel spinning (TCS)technology possess a high tenacity, high molecular orientation and2 Crystallization kinetic equationmid-level crsailiniy (about 30% ~ 40%) . Obviously, TCSThe generalized Avrami equation in previous papers-3J reads:offers a single step integated process with minimum machinemodification and cost.g=1-0p{- (*"(0nd)'}(5)Basic principlewith its diferenial fom as fllows:The basic principle to describe the TCS process in PET high-speed melt spinning is built upon the regular goverming equationstal想∞0气(。合山)“c(-(告0) (6)of the thin-theory and heat transfer equations with specific3 Force balance equationconsideratioms related to the themnal channel as well s theIt is well known that the differential relationship of tensilerheological and consitutive relations.force gradient distribution along the regular high-speed melt1 Heat transfer equations中国煤化工:The whole TCS spinline can be divided into three parts withdistinctive heat transfer mechanism. In the section betwen theTHCNMHG) + πRVpoCq(7)face of spinneret and the inlet of thermal channel, the temperaturedx\dx VReceivred Sep.20,2000Jourmal of Dong Hua University (Eng. Ed.) Vol. 18 No.4(200) 75where Cr is the skin- friction coffcient depending on the velocitydn = Aopd_ An(9)V of the running filament . However, the cequation (7) is onlydsuitable for the spin path sections outside the channel. In thechannel, due to the much stronger sin-rction a new equation (8)where τm is he relaxation time of PET polymer, the strain-opticalceffcient Aop was experimentally determined, and thus theis derived to describte the tensile force gradient along the x-axisobtained valuel4) 0.53 is used here.within the channelBesides the above-mentioned equations from (1) to (9)，2ryk v.2(8)constiutive equation of PET polymer, continuity equaion andlxln( R./R)other material property relations are adequately considered.where kt is a empirical coefficient in the range of 1.2~ 2.2,Experimentalincreasing with the wind-up speed between 3 600 m/min ~ 4 400m/min, μ is the dynamic viscosity.The PET chips used in this study have an intinsic viscositySpinning orientation equation[IV] of 0.66 dl/g. In the spinning experiments, the round orifceAlthough the high degree of molecular orientation required forof spinneret plate is 0.02 cm in diameter and the thermal channe!good mechanical behavior of textile fibers is produced mainly inis 150 cm long and 1.65 cm in inner nadius. The PET flamnent wasthe course of drawing, the high molecular orientation can alsoprepared in TCS spining eaquiprnent made in Barmag Company,achieved by the themal channel spinning (TCS) technology, ancGermany under the various process conditions as listed in Table I,satisfies the requirements for textile processes.and its properties such as birefringence, diameter and crytallinityThe relationship between birefringence and flamentwere measured by means of Senammont Method and X-raydeformation in the spinline was suggested by Nishiuniltl asDifraction Method, respectively.Table 1 The themal channel spinning process conditionsSpinningCross air flowThemal channelTake-up velocity,1emperaturt,velocity, cm/stenperature, Cposition" . cntemperalure, 它km/min2804020110160/180/2003.6/4.0/4.4Themal channel position refters如the distance between he face of spinneret and the inle of themal channedlisted in Table 2. It is evident that they are in good agreement eachCalculation results and discussionother. The development of tensile force, temperaoure, molecularorientation ( itpresented by birefringence) and crysalinity alongThe simulation results calculated by the mathematical modelthe TCS spinline under the various process conditions are indicatedwith certain appropriate value chosen for kp in equation (8) to ftin Figures1~4.the experimental measurements of corresponding take-up yarns areTable 2 The experimental data /simuiation results of take-up yarms under various process conditionsThemnal channelTakeupCaysalinityBirefringenceDiametertemperatut, Cvelocity, m/ min%10-3H60400025./25.9141.7/140.511.2/11.68031.2/31.0170.6/170.111.2/11.5 .0036.0/36.5159.4/160.011.2/11.5360030.5/29.4159.6/156.111.2/11.34 40033.5/33.3163.3/167.611.2/11.4Figure 1 sbows the simulated tensile force profiles along thetakoup godet is quenched by the transverse air blowing to beTCS spinline at various speeds. Iitally there is a gradual increasebelow its glass transition temperature and solidified to formin the tensile force. At the position of inlet of thermnal channelfilament.中国煤化工ine，the flament is(namely at 1.1 m) in the TCS spinline, there is an“up-tum”heated aln:rease in temperature,point, and then the tensile force increases mapidly because of mucharising a“MHC N M H G dsincive value forstronger skin-frictio inside the themal channel than that outside.diferent speedl). Out of the themal channel, the flamnent isThe calculated temperature profles are shown in Figue 2.cooled down quickly.The PET melt jet extruded from the spinneret and drawn by theFigue 3 shows the computed profiles of brefringence in PET76Joumal of Dong Hua University (Eng. Ed.) Vol. 18 No .4 (2001)where the acceleration of birefringence increases getting smaller1.leading to subsequently slight increase in binefringence within the1.2thermal channel spinline. Out of the themnal channel, the nunningfilament is sil continuously drawn， and the birefringence、1.03600 m/mincontinues to increase rapidly to reach a constant value.z包08 4000 m/min.4 400 m/min.35。0.630& 0.44000m/min.含254 400 m/min20000315 ,Spinline (m)Fig.l The development of tensile fores along the TCSspinline30050Fig.4 The development of crsalnitis in PET filamentalong the TCS spinine0o.4 400 m/minFigure 4 depicts the crstallinit profles. We can find easily4000 m/minthat crsallizaion in TCS spinline occurs in an exremely narrowregionss. Intilly, there is no appreciable crslization taking00 Iplace in PET filament, but around 2.22 m, dramatic crysallizationprocess begins, and acomplishes within several mliseconds,5oamiving at a constant value equals w hat of the take-up fib. 3600 m/minComparing to Figure 3, the orientation is evidently revealed in leadof the crytallization as a prerequisite for the orientation inducedcrystallization under a dynamic tensile stess state.Spinlinc (m)Fig.2 The development of filameat tempraures alongthe TCS spinline200200 r150 |50 t100- 3600 m/min4 000 m/min-4 400 m/min-一. 4000 m/min.4400 m/min00 t旨50-°04Fig.5 The development of filamnent diameers along theTCS spinine中国煤化工4，we can find the commonFig.3 The develpment of breringences in PETjlament temperature at the sameflament along the TCS spinlineMHC N M H Gs place rmpidly. It is because offilament Before the filament uns into the themal channel, thethe heal of arystallization released in such a critical zone thatbirefringence increases very slighdly. However, the birefringencecauses the temperatue jump. Figure 5 dermonstrates a suddenincreasesvery quickly and arises a“turm point” around 2.22 mdiameler contract in this critical zone， often refered to asJourmal of Dong Hua University (Eng. Ed.) Vol. 18 No .4(200) 77“eking" .velocity ratio aboul 2.8. The necking is much more pronouncedthan in TCS. Conceivably, the physical propertics of the fibersComparison with Hot Godet Spinningmade by TCS and HGS should be different as a result of the sharpdistinction of necking, which gives rise to the variation of super-Both TCS and HGS, when manufacturing FDY, have to gomolecular structure of the fiber， such as orientation andthrough two stages of drawing. The drawing ratio R, from thecrstallization, Table 3 provides a comparison.spinneret to the first hot cylinder/godet in HGS， which isTable 3Quality indexes of FDY fibers produced by twoanalogous to the drawing effect encountered by the filament beforetechunologieseatering the hot channel in TCS, is followed by the seconddrawing ratio R2 between the first and second hot cylinders inIndexTCSHGSHGS, which amounts to the drawing efect within the hot channelin TCS. In HGS, R can be solely controlled by the velocity oftenacity, cNVdtex4.0-4.24.1-4.4.the first godet, while the ratio of velocities of the first and theelongation, %32~3830~ 36.second determines R2. This way， an outright division ofdyability (gay card, grade)4.5-5.04.Stechnological adjustment into sections is applied in HGS,sigifying to control the integral process by local regulations. Inbilig waler shrinkage, %5.0~ 6.07.5-9.5TCS, from the spinneret through thermnal channel to the take-up,there is no contact drawing available, but the tensile stessFrom the above discussion and comparison， it may bedevelops according to the given operation parameters, as theconcluded that TCS has is special theoretical background lcanalysis depicts afore, automaically fnding the R and Rz in forceexplain the spinning performance, of which many advantagesbalance. Needless to adjust separately the velocities of the hoshould be fully employed in fiber processing.godets, TCS is easier to control its operation conditions than HGS,realizing the entire process adjustment by integral control.ReferencesIn TCS the thread lines of a bundle ane more even heated anddrawed than in HGS, where the thread lines adhering the godet are1] Ziabicki A. and Kawai H. , High-speed Fiber Spinning Science andheated more strongly by contact beating than those not adhering it.Engineering Aspects, John. Wiley & Sons, Inc. New York, 1985This can lead to the conclusion that TCS is better suitable for fine2] Kase s. and MasuoT., J. Polym. Scdi., 1965, A-3, 2541denier fiber produced with multi-bole (large number) spinneret.3] Nakamura K., Katayama K., and Amano T., J. Appl. Polym,The pbcnormenon of instant crysallization, accompanied bSer., 1973, 17, 1031necking, is constent with the observations of PET regular high-4] Shimizu., Okui N, and Kandko A., Anw. Moet. Fiber Sci.Japan, June 1979sped meltsining process at the speed below 4000 m's with hot{5] Haberkom, H，Hahn, K, Breuer, H，Dorrer, H.D., andgodets quipped. The necking happens between the first and theMathics, P., J. Appl. Polym. Sci., 1993, 47,1551 ~ 1579second godets with temperature difference around 40C and中国煤化工MYHCNMHG