Puas yog Qib Hla-Kev sib txuas hauv PFA Polymer Chain cuam tshuam rau lub sijhawm ntev-Lub Sij Hawm Los Tiv Thaiv- Kev Ua Haujlwm tawg hauv qab cua sov?

Thaum cov engineers qhia PFA (perfluoroalkoxy alkane) immersion heaters rau cov txheej txheem uas rov ua cua sov thiab cua txias cycles -batch reactors, periodic clean-nyob rau hauv- qhov chaw (CIP) ua hauj lwm, los yog intermittently ua plating da dej, piv txwv li-lub molecular architecture tsis tshua muaj. Cov ntaub ntawv pov thawj ntawm cov khoom pov thawj muab cov dej ntws Performance index (MFI), lub zog tensile, elongation ntawm kev tawg, tab sis tsis yog qhov sib txawv ntawm tus ntoo khaub lig- txuas rau hauv lub polymer matrix. Qhov kev tsis tuaj no ua rau pom qhov txawv txav tseem ceeb: hla- txuas PFA muaj qhov sib txawv ntawm qhov pib tawg thiab kev nthuav tawm tus cwj pwm nyob rau hauv cyclic thermal stress dua li linear lossis tsis muaj zog hla-qib txuas. Thaum lub sij hawm thermal cycling qhov sib txawv ntawm qhov sib txawv ntawm PFA sheath thiab cov hlau cua sov tseem ceeb tshwm sim ntau pua lossis ntau txhiab zaus. Qhov no ua rau cov ntaub ntawv polymer rau rov ua tensile thiab compressive hom. Hla-kev sib txuas yog kev txhim kho cov kev sib txuas ntawm cov khoom sib txuas ntawm cov khoom siv polymer. Qhov no txwv tsis pub txav mus los ntawm cov molecule thiab txhim kho qhov nruj ntawm cov khoom tab sis txwv nws lub peev xwm los ua kom plastically deform thiab txo cov kev ntxhov siab hauv cheeb tsam. Txhawm rau kom nkag siab qhov kev lag luam no-tawm, qhov kev loj hlob ntawm kev tawg ntawm cov kab hluav taws xob yuav tsum tau tshawb xyuas.

Kev vam khom ntawm Polymer Chain Mobility ntawm Hla -Txuas Kev Sib Txuas
Linear PFA yog tsim los ntawm cov hlua polymer ntev nrog me me los yog tsis muaj ceg thiab tsis muaj covalent bonding ntawm chains. Thaum rhuab saum lub iav hloov kub (Tg ntawm PFA yog li ntawm -}15 degree), cov cheeb tsam amorphous ntawm cov polymer ua rubbery, tso cai rau cov chains glide dhau ib leeg thiab rov faib cov kev ntxhov siab. Cov saw hlau txav thaum lub sij hawm thermal cycling tso cai rau lub zos yielding nyob rau hauv lub ntsis ntawm microcracks los yog voids, uas blunts lub tawg thiab tiv thaiv sai propagation. Hla kev sib txuas tsim cov tshuaj txuas mus ntev ntawm cov neeg nyob sib ze. Cov kev sib txuas no ua rau muaj kev txwv lub cev tiv thaiv cov hlua khi. Qhov loj ntawm crosslinking feem ntau qhia raws li qhov sib txuam ntawm qhov nruab nrab molecular hnyav ntawm crosslinks (Mc). Qhov qis dua Mc, qhov siab dua tus ntoo khaub lig-link ceev. Virgin PFA rau cov cua sov sheaths feem ntau muaj tus ntoo khaub lig qis heev -txuas txuas nrog Mc tus nqi siab dua 20,000 g / mol . Thaum tshav kub kub los yog hluav taws xob{14}}induced cross- txuas tuaj yeem txo Mc mus rau 5,000–8,000 g / mol, hloov pauv tus cwj pwm txhua yam. Nyob rau hauv qhov tseeb, cross-txuas hauv PFA tsis yog lub hom phiaj thaum ua haujlwm hauv cov ntaub ntawv ntawm overheating lub polymer lossis stabilizers degradation. Qee cov qib tshwj xeeb ntawm PFA rau qhov kub kub rwb thaiv tsev hlau, ntawm qhov tod tes, tau lub hom phiaj hla-txuas los ntawm electron beam irradiation los txhim kho creep resistance. Kev mob siab rau tus ntoo khaub lig- kev sib txuas ntawm cov cua sov sheaths yog qhov txawv txav, txawm li cas los xij, thermal aging hauv kev pabcuam tuaj yeem maj mam nce qhov sib txuas ceev los ntawm cov txheej txheem dawb radical seem.

Kev pib tawg nyob rau hauv cyclic tensile hom: linear tiv thaiv cross -linked PFA
Lub ntsiab lus tseem ceeb ntawm cov khoom siv hluav taws xob ntawm PFA lub thawv cua sov thaum lub caij txias yog tshwm sim los ntawm qhov sib txawv ntawm qhov sib txawv ntawm thermal expansion (CTE) ntawm cov tub ntxhais hlau (feem ntau Incoloy lossis titanium, CTE 14-17 ppm / degree) thiab PFA casing (CTE 100-120 ppm / degree). Raws li PFA txias los ntawm kev ua haujlwm kub mus rau ambient nws sim txo qis li xya zaus ntau dua li cov hlau. Cov tub ntxhais hlau tiv thaiv qhov kev cog lus no, ua rau muaj kev ntxhov siab hauv PFA. Rau ib tug raug 12 hli txoj kab uas hla lub rhaub nrog ib tug 1.5 hli PFA phab ntsa txias los ntawm 160℃mus rau 25 degree, lub hoop strain nyob rau hauv lub PFA yog nyob ib ncig ntawm 2.3–2.8%. Cov kab mob no kov yeej cov kev txwv elastic ntawm PFA thiab ua rau cov yas deformation. Cov kab mob no tuaj yeem ua raws li kab PFA los ntawm kev sib xyaw ua ke ntawm molecule orientation thiab cov duab txias hauv zos. Microscopy kev tshawb fawb ntawm cycled linear PFA sheaths qhia diffuse shear bands thoob plaws hauv tag nrho cov phab ntsa thickness, qhia lub zog dissipation nyob rau hauv ib tug dav ntim. Vim muaj qhov txwv tsis pub txav mus los ntawm tus ntoo khaub lig- txuas PFA, nws tsis tuaj yeem raug rau tib qib ntawm cov yas deformation. Cov kab mob imposed yog nyob rau hauv ib cheeb tsam me, feem ntau nyob rau hauv lub polymer-hlau interface los yog nyob rau hauv microscopic nto imperfections. Hla-txuas PFA nthuav qhia qhov pib tawg tom qab 500–1,500 lub voj voog cua sov nyob ntawm qhov loj ntawm lub voj voog. Raws li cov xwm txheej qub, linear PFA qhia thawj microcracks tom qab 5,000-8,000 cycles. Tus ntoo khaub lig- cov khoom txuas mus txog qhov kawg ntawm nws lub neej siv tau, piv txwv li tawg qhov tob tshaj 50% ntawm phab ntsa thickness, nyob ib ncig ntawm ib feem tsib ntawm lub voj voog suav ntawm linear PFA.

Tus nqi ntawm kev loj hlob ntawm qhov tawg: rub- tawm ntawm cov saw hlau los yog tawg ntawm daim ntawv cog lus?
Thaum pib tawg, txoj kev nthuav tawm yog qhov tseem ceeb sib txawv rau cov kab thiab hla PFA. Kev nthuav tawm Crack nyob rau hauv linear polymers yog dominated los ntawm saw rub - tawm. Polymer chains hla lub dav hlau tawg yog rub tawm ntawm amorphous matrix thiab nqus tau ntau lub zog. Cov txheej txheem no ua rau muaj qhov tshwm sim ntawm fibrillated fracture nto thiab tshwm sim ntawm tus nqi qis, feem ntau yog 0.1-0.5 µm ib lub voj voog kub ntawm qhov kev ntxhov siab me ntsis. Hauv cross- txuas PFA, cov kev sib txuas ntawm cov saw hlau tsis tso cai rub- tawm. Cov kab nrib pleb nthuav tawm los ntawm kev rhuav tshem cov kev sib txuas ntawm cov pob txha polymer. Txawm hais tias txhua daim ntawv cog lus- tawg yuav tsum muaj zog tsawg dua li rub- tawm ntawm cov saw txuas ua tiav, qhov tawg - lub taub hau loj dua thiab ua tau zoo dua hauv kev xa cov kev ntxhov siab. Cov pob txha pob txha ntawm tus ntoo khaub lig- txuas PFA yog du, iav, qhia tias qhov tawg tawg tau nrawm ntawm tus nqi ntawm 2-5 µm ib lub voj voog kub. Ib qho tawg uas pib tom qab 1000 cycles nyob rau hauv cross-txuas PFA yuav khiav los ntawm tag nrho 1.5 hli phab ntsa thickness nyob rau hauv lwm 300-500 cycles. Qhov zoo sib xws hauv kab PFA yuav siv sij hawm ntxiv 6000-8000 cycles kom ncav cuag phab ntsa tawg. Qhov kev cuam tshuam zoo yog tias rau kev sib txuas ntawm PFA sheaths lub sij hawm los ntawm kev txheeb xyuas qhov tawg ua ntej mus rau qhov kev puas tsuaj loj heev nyob rau hauv cov xwm txheej thermal cycling luv luv. Lub qhov rais me me ua rau kev tiv thaiv kev saib xyuas nyuaj. Thaum lub sij hawm tawg yog tshwm sim nyob rau saum npoo, lub rhaub yog feem ntau nyob ze tsis ua hauj lwm.

Kev Ua Haujlwm Keeb Kwm thiab Kev Pabcuam Uas Hla -Txuas: Ncua Kev Sib Tw
Ib tus kws tshaj lij tsis tuaj yeem thov "tsawg hla- txuas" PFA los ntawm tus neeg xa khoom yam tsis tau qhia meej txog kev ua haujlwm. Tus ntoo khaub lig-link ntom ntom yog cuam tshuam los ntawm peb yam: cov khoom siv hluavtaws (tswj los ntawm cov chaw tsim khoom), qhov chaw extrusion lossis molding (tswj los ntawm lub tshuab cua sov fabricator), thiab hauv - kev pabcuam thermal aging (nyob ntawm daim ntawv thov). Thaum lub sij hawm extrusion ntawm PFA mus rau ib tug hlau core, kub ntawm 350{10}}400℃yuav ua rau ib co degradation ntawm stabilizers thiab induce chain branching. Ntawm cov kab extrusion tsis zoo, linear resin ua rau tsis zoo ib yam khoom sib txuas. Lub tshuab cua sov ua haujlwm los ntawm tib pawg ntawm cov resin tab sis ntawm cov cuab yeej tswj tau zoo, ntawm qhov tod tes, tswj cov linearity rau lub sijhawm ntev dua. Thermal aging tshaj 180℃thaum lub sij hawm kev pab txhawb nqa hla-txuas. Tus ntoo khaub lig{17}}link ceev ntawm cov pa PFA loj hlob los ntawm ~ 15-20% ib 1000 teev ntawm 200 degree, trending cov khoom mus rau nkig cwj pwm. Hauv cov ntawv thov nrog ntau lub voj voog thermal, qhov kev sib txuas ua ke no ua rau lub voj voog tsis zoo uas txhua lub voj voog ua rau cov khoom siv thiab ua rau me ntsis nce tus ntoo khaub lig- txuas ceev rau lub voj voog hauv qab no. Qhov pib ntawm kev tawg pib qis dua nrog lub neej ntawm lub rhaub. Teb cov txiaj ntsig ntawm 150-160oC semiconductors cov rooj zaum ntub dej nrog txhua hnub kev caij tsheb kauj vab qhia tias lub neej tsis ua haujlwm ntawm PFA cov cua sov, los ntawm tib lub chaw tsim khoom thiab batch, yog 8,000 txog 25,000 cycles. Fabrication overheating ua rau kom tsis tu ncua pib qhov sib txuas ntawm qhov ntom ntom hauv cov chav nyob luv.

Thermal Cycle Tolerance Guide by Hla -Txuas Qib thiab Qhov hnyav ntawm daim ntawv thov
The estimated thermal cycle life expectancy of PFA heater sheaths is presented in the following table as a function of cross-link density, cycle delta temperature and availability of crack detection monitoring. Cov nqi xa mus rau phab ntsa tuab ntawm 1.5-2.0 hli thiab tsis muaj kev ntxhov siab ntxiv los ntawm kev co lossis kev sib txuas tsis raug.

Hla -Txuas Qib Ib Yam Mc Tus Nqi Cycle Delta Kub Ciav Ciav mus rau qhov pib ntawm CrackingCycles mus txog ntawm - Phab Ntsa Failure (Predicted) yam ntxwv ntawm hom tsis ua haujlwm
Very low (virgin, well-extruded) >20,000 g/mol 50–80°C 20,000–30,000 >50,000Diffuse microcracking; sluggish kis tau
Very low (virgin, well-extruded) >20,000 g/mol 100–140℃8,000–15,000 25,000–40,000 Ntau cov kab nrib pleb maj mam to
Nruab nrab (nruab nrab hnub nyoog lossis tus qauv extrusion) 10,000–15,000 g/mol 50–80℃8,000–12,000 15,000–20,000 Tsawg tawg; nce los ntawm - phab ntsa nce qib
Txheem (txheej txheem kev laus los yog txheej txheem extrusion) 10,000-15,000 g / mol 100-140℃2,500-5, 000 6,000-10,000Single dominant crack Smooth fracture deg 12.
Siab (irradiated los yog overheated thaum fabrication) 5,000–8,000 g/mol 50–80℃1,500–2,500 3,000–4,500 ceev nrooj tawg; glassy tawg zoo li
Siab (irradiated lossis overheated thaum lub sij hawm tsim khoom) 5,000–8,000 g / mol 100–140℃300–{7}}–1,500Detection window luv; kev puas tsuaj loj
Very high (degraded, >2,000 hours at >190 degree)<5,000 g/mol Any >50 degree<200 <500 Brittle fracture; multiple site failure
Tswv yim Specification & Cov txheej txheem tswj kom zoo
Engineers can prevent the accidental purchase of cross-linked PFA sheaths for thermal cycle applications by adding three conditions to procurement specifications. First, the heater manufacturer should be required to give MFI measurements before and after the extrusion or welding process. A MFI decrease of >15%. Qhov thib ob, nug txog qhov sib txawv scanning calorimetry (DSC) kev ntsuas uas ua rau pom qhov kub ntawm fusion thiab melting tus cwj pwm. Crosslinked PFA qhia tau hais tias lub melting endotherm yog dav dua thiab ib qho kev txo qis hauv crystallinity (feem ntau 5-10% qis dua cov khoom siv linear). Thib peb, rau cov ntawv thov tseem ceeb nrog ntau dua 500 lub voj voog thermal hauv ib xyoos, suav nrog kev tshaj tawm -fab anneal kauj ruam ntawm 180℃rau plaub teev. Annealing tshem tawm qhov nro, tab sis tsis thim rov qab - txuas. Qhov tseem ceeb tshaj, cov txheej txheem annealing yog lub lim dej zoo tswj -- cov khoom siv tsis zoo uas muaj kev sib txuas ntau dhau thaum extrusion tuaj yeem tsim cov kab nrib pleb thaum lub sij hawm annealing, tso cai rau kev tsis lees paub ua ntej xa khoom. Cov cua sov uas twb muaj lawm yuav tsum tau ua pov thawj hauv teb los ntawm kev sim ua kom puas tsuaj ntawm chav tsev fij. Txiav PFA sheath thiab txheeb xyuas qhov chaw sab hauv (hlau kov) ntawm 50x magnification. Linear PFA muaj qhov du, matte tiav nrog tsis muaj kev tawg tom qab kev caij tsheb kauj vab. Hla-txuas PFA nthuav tawm cov qauv ntawm cov microcracks circumferential, nrog qhov sib nrug ntawm 0.5-2 hli, feem ntau nrog cov xim dawb ntawm cov polymer vim cavitation.

Xaus: Ua Kom Paub Txog Molecular Architecture nrog Dimensions
Tab sis qhov cuam tshuam ntawm crosslinking hauv PFA cuam tshuam nws cov tshuaj tiv thaiv rau thermal cycling, txawm hais tias nws tsis tau pom los ntawm cov kev cai ntawm lub tshuab cua sov uas tsuas yog xav txog phab ntsa tuab thiab cov tshuaj sib xyaw ua ke. Thaum phav phav lub voj voog txhim khu kev qha ntawm ambient thiab kev ua haujlwm kub yuav tsum tau ua, lub voj voog lub neej ntawm linear PFA nrog tus ntoo khaub lig tsawg tshaj plaws -kev sib txuas tshaj qhov nruab nrab ntawm tus ntoo khaub lig- cov khoom txuas los ntawm ib qho ntawm tsib mus rau kaum. Nws tau pom tias qhov kawg ntawm tus ntoo khaub lig-link ceev yog nyob ntawm cov txheej txheem fabrication (tshwj xeeb tshaj yog lub tshav kub keeb kwm thaum extrusion thiab vuam) dua li ntawm cov qib qub ntawm resin. Cov cua sov uas twb muaj lawm uas tawg ntxov thaum lub caij cua sov uas tsis muaj tshuaj tua kab mob lossis kub dhau tuaj yeem muaj kev sib tw siab -txoj kev sib txuas vim yog dhau- cua sov thaum tsim khoom. Hauv kev pabcuam kev caij tsheb kauj vab hnyav, kev pabcuam lub neej ntawm lub rhaub hauv ib puag ncig yog qee zaum txuas ntxiv los ntawm lub hlis mus rau xyoo thaum hloov nrog chav tsev los ntawm cov chaw tsim khoom uas tswj qhov kub ntawm extrusion hauv ± 5℃thiab siv tsuas yog nkauj xwb, tsis ruaj khov PFA resin. Rau cov ntawv thov nrog delta kub tshaj 120℃txhua lub voj voog, xav txog lwm cov khoom siv hluav taws xob xws li qis-CTE cov ntaub ntawv tseem ceeb lossis cov khoom siv hluav taws xob decoupled sheaths, txawm tias qhov zoo tshaj plaws linear PFA yuav ncav cuag nws qhov pib tawg.