Nyob rau hauv chav tsev kub, PTFE yog cov yas tawv, ruaj khov. Tab sis raws li qhov kub nce, nws cov khoom siv kho tshuab hloov pauv loj heev. Kev nkag siab txog cov kev hloov pauv no yog qhov tseem ceeb rau kev khiav hauj lwm PTFE immersion heaters kom nyab xeeb thiab hauv lawv lub hnab ntawv tsim. Lub plhaub ntawm lub tshuab hluav taws xob PTFE ua ntau dua li tsuas yog muab tshuaj lom neeg ua haujlwm xwb- nws yuav tsum tiv taus lub siab ntawm cov kua ib puag ncig, tiv thaiv deformation dhau sijhawm, thiab tswj nws cov duab. Tag nrho cov tshuab ua haujlwm no degrade thaum kub nce. CovPTFE mechanical zog kub nyhuvYog li ntawd yog ib qho tseem ceeb rau txhua tus neeg qhia, txhim kho, lossis ua haujlwm PTFE immersion heaters.
Yuav ua li cas Kub Hloov Molecular Structure ntawm PTFE
PTFE yog ib nrab -crystalline polymer. Nyob rau hauv chav tsev kub, nws cov saw hlau molecular yog nruj nreem ntim rau hauv crystalline cheeb tsam interspersed nrog amorphous (kev tsis sib haum xeeb) zones. Cov qauv no muab PTFE nws cov yam ntxwv lub zog, tsis muaj kev sib txhuam, thiab tshuaj inertness. Raws li qhov kub thiab txias, molecular vibrations nce, thiab cov cheeb tsam amorphous pib mos ua ntej cov cheeb tsam crystalline yaj.
Kev siv tas mus li txwv rau PTFE hauv kev siv lub tshuab rhaub dej yog dav txais raws li110 degree. Qhov kev txwv no tsis yog arbitrary. Saum toj no qhov kub thiab txias, peb txawv mechanical kev hloov pauv sai sai:
Txo lub zog tensile- Lub zog yuav tsum tau ncab lossis rhuav lub PTFE sheath txo qis.
Nce creep- Raws li kev thauj khoom tas li (xws li kua siab lossis kev ntxhov siab sab hauv los ntawm cov hlau tsis kam), PTFE deforms qeeb qeeb dhau sijhawm.
Tsawg siab tsis kam- Cov ntaub qhwv tau yooj yim dua rau kev sib tsoo lossis ballooning nyob rau hauv qhov sib txawv.
Nws tau pom tias thaum PTFE tsis yaj mus txog 327 degree, nws cov khoom siv tau zoo kawg nkaus hauv qab qhov taw tes. Rau immersion heater daim ntawv thov, 110℃sawv cev rau cov tswv yim sab sauv rau kev ua haujlwm tas mus li.
Tensile zog txo nrog nce kub
Lub zog tensile yog qhov siab tshaj plaws kev ntxhov siab uas cov khoom siv tuaj yeem tiv taus thaum ncab ua ntej tawg. Rau PTFE, cov cuab yeej no poob qis tsis tu ncua thaum kub nce. Cov lus hauv qab no qhia kwv yees qhov tseem ceeb raws li cov qauv kev xeem (ASTM D638).
| Kub (degree) | Kub (degree F) | Kwv yees Tensile Strength (MPa) | Kwv yees Tensile Strength (psi) | Qhov feem pua ntawm Chav -Tsub Tus Nqi |
|---|---|---|---|---|
| 23 | 73 | 21 – 28 | 3050 – 4060 | 100% |
| 50 | 122 | 16 – 22 | 2320 – 3190 | 75 – 80% |
| 80 | 176 | 12 – 16 | 1740 – 2320 | 55 – 60% |
| 100 | 212 | 9 – 13 | 1305 – 1885 | 45 – 50% |
| 110 | 230 | 7 – 11 | 1015 – 1595 | 35 – 45% |
| 120 | 248 | 5 – 8 | 725 – 1160 | 25 – 30% |
Nco tseg: Tus nqi yog tus sawv cev. Lub zog tensile tiag tiag nyob ntawm qib PTFE, crystallinity, thiab kuaj mob.
Ntawm 100 degree, lub zog tensile ntawm PTFE yog kwv yees li ib nrab ntawm nws cov nqi ntawm 23 degree. Ntawm 110 degree, nws poob rau kwv yees li 40% ntawm chav tsev -tus nqi kub. Qhov kev txo qis no txhais tau hais tias txhua yam kev ntxhov siab ntawm txhua yam-txawm yog los ntawm cov kua siab, thermal expansion, lossis tuav- feem ntau yuav ua rau muaj kev puas tsuaj ntawm qhov kub siab.
Creep thiab Deformation nyob rau hauv Load
Ib qho kev txwv tseem ceeb ntawm PTFE ntawm qhov kub siab yog nws qhov kev nkag mus rau nkag. Creep yog lub sij hawm- nyob ntawm deformation ntawm cov khoom nyob rau hauv ib tug tas li load. Tsis zoo li cov hlau, uas muaj qhov tsawg tsawg nkag hauv qab ib qho chaw pib, PTFE creeps ntawm txhua qhov kub siab tshaj ambient. Tus nqi ntawm creep nce exponentially nrog kub.
Rau PTFE lub tshuab rhaub cua sov, cov khoom muaj feem cuam tshuam suav nrog:
Sab nraud kua siab- Hauv cov tso tsheb hlau luam sib sib zog nqus, lub siab hydrostatic tuaj yeem ncav cuag 0.1 bar ib meter ntawm qhov tob. Nyob rau ntawm 2-3 meters, qhov siab yog me me, tab sis ua ke nrog qhov kub thiab txias, nws tuaj yeem ua rau lub plhaub maj mam vau lossis dimple.
Internal stresses los ntawm cov hlau tsis kam- Cov khoom cua sov hlau yog kos rau hauv PTFE. Qhov sib txawv ntawm thermal expansion ntawm hlau thiab PTFE tsim kev ntxhov siab sab hauv. Ntawm qhov kub thiab txias, PTFE txo cov kev ntxhov siab los ntawm kev nkag mus, uas tuaj yeem hloov pauv cov duab ntawm lub hnab.
Clamping los yog mounting quab yuam- Txhua yam kev txwv tsis pub siv rau lub tshuab cua sov (xws li, brackets, flanges, lossis kev txhawb nqa) tsim kom muaj kev ntxhov siab hauv zos. Creep tuaj yeem ua rau PTFE ntws tawm ntawm qhov siab - cov ntsiab lus siab, ua rau xoob lossis foob tsis ua haujlwm.
Hauv kev xyaum, creep tsis tshua muaj kev puas tsuaj nyob rau lub sijhawm luv. Lub tshuab cua sov ua haujlwm ntawm 105℃yuav tsis pom qhov deformation rau lub hlis lossis ntau xyoo. Txawm li cas los xij, dhau sijhawm, kev nkag tuaj yeem ua rau cov ntaub qhwv nyias nyias hauv qee qhov chaw, txo cov dielectric zog thiab kev tiv thaiv txhua yam. Qhov tseem ceeb tshaj, nkag mus rau ntawm qhov sib cuam tshuam ntawm PTFE sheath thiab lub davhlau ya nyob twg foob tuaj yeem qhib txoj hauv kev rau ya raws lossis corrosive vapors nkag mus rau lub rhaub.
Siab Resistance thiab Risk of Collapse los yog Ballooning
PTFE rhaub sheaths tsis yog cov hlab ntsha siab. Lawv tau tsim los ua haujlwm ntawm lossis ze atmospheric siab ntawm ob sab hauv thiab sab nraud. Cov kab noj hniav sab hauv uas muaj cov hlau tsis muaj zog; nws tau ntim nrog PTFE lossis cua ntawm ambient siab. Txawm li cas los xij, ob lub siab- ntsig txog kev ua tsis tiav muaj nyob:
Sab nraud siab poob- Yog hais tias cov kua sab nraud siab tshaj lub siab sab hauv los ntawm ib tug txaus margin, lub sheath tuaj yeem tawg sab hauv. Qhov no muaj feem ntau ntawm qhov kub siab vim tias PTFE's elastic modulus (stiffness) txo qis. Collapse feem ntau pom tau tias yog ib qho flattened los yog dimpled seem ntawm lub sheath.
Internal siab ballooning- Yog hais tias cov kab noj hniav nyob rau hauv lub pressurized vim muaj gas expansion los yog outgassing, qhov kub, softened PTFE tuaj yeem tso tawm sab nraud. Qhov no tsis tshua muaj tshwm sim tab sis tuaj yeem tshwm sim yog tias ya raws hauv lub rhaub dej hloov mus rau chav.
CovPTFE mechanical zog kub nyhuvncaj qha tswj hwm ob hom kev ua tsis tiav. Ntawm 23 degree, PTFE tuaj yeem tiv taus qhov sib txawv ntawm ntau qhov bar yam tsis muaj deformation mus tas li. Ntawm 110 degree, qhov sib txawv ntawm qhov sib txawv tuaj yeem ua rau tam sim ntawd tawg lossis ballooning. Vim li no, PTFE cov cua sov yuav tsum tsis txhob ua haujlwm nyob rau hauv siab - ib puag ncig siab lossis raug hloov siab ceev.
Qhov tshwm sim ntawm Kev Tshaj Tawm 110℃Nruam Limit
luv- lub sij hawm mus ncig ua si me ntsis siab dua 110℃tej zaum yuav zam tau yam tsis ua tiav tam sim ntawd. Txawm li cas los xij, rov ua haujlwm lossis ua haujlwm ntev tshaj qhov kev txwv no yuav muaj kev puas tsuaj mus tas li. Pom qhov tshwm sim muaj xws li:
Sheath thinning thiab localized hotspots- Creep tso cai rau PTFE ntws tawm ntawm qhov chaw kub tshaj plaws, txo cov sheath thickness. Cov cheeb tsam nyias nyias muaj cov thermal conductivity ntau dua, tsim kom muaj kev tawm tswv yim zoo uas ua kom cov cua sov hauv zos.
Kev poob ntawm lub zog dielectric- Thinned sheath seem txo cov hluav taws xob rwb thaiv tsev, ua rau muaj kev pheej hmoo ntawm kev tawg.
Permanent deformation- Thaum PTFE tau crept lossis deformed, txias tsis rov qab zoo li qub. Ib qho kev sib tsoo los yog ballooned sheath tsis tuaj yeem kho.
foob tsis ua hauj lwm- Qhov chaw txias txias nyob ntawm qhov sib haum xeeb ntawm PTFE sheath thiab lub davhlau ya nyob twg los ua ke. Creep tuaj yeem cuam tshuam qhov haum, tso kua lossis vapor ingress.
Nws yog ib qho tseem ceeb uas yuav tsum nco ntsoov tias 110℃txwv siv rau PTFE sheath kub, tsis tas yuav ua rau cov kua kub ntau. Nyob rau hauv lub qhov dej-tsim lub rhaub, lub plhaub kub tsuas yog siab dua li cov kua kub me ntsis vim tias cov cua sov hloov tau zoo los ntawm cov hlau tsis kam mus rau cov kua. Txawm li cas los xij, yog tias watt ntom ntom (lub zog ntawm ib cheeb tsam hauv cheeb tsam) siab dhau lawm, lossis yog tias cov kua dej poob qis hauv qab qhov cua sov, qhov kub ntawm lub plhaub tuaj yeem nce siab tshaj cov kua kub txawm tias cov kua nws tus kheej qis dua 110 degree.
Watt Density Derating rau siab -Tsev Kev Pabcuam
VimPTFE mechanical zog kub nyhuvtxo cov khoom muaj peev xwm tiv taus kev ntxhov siab, cov khoom siv hluav taws xob tso rau hauv qhov chaw ua haujlwm ze 110℃yuav tsum ua haujlwm ntawm qis watt densities dua li cov cua sov siv hauv qhov kub qis. Watt ceev yog lub zog tso tawm rau ib chav tsev ntawm cov cua sov saum npoo, feem ntau qhia hauv watts ib square inch (W / in²) lossis watts ib square centimeter (W / cm²).
Cov lus qhia dav dav rau PTFE immersion heaters yog:
Mus txog 60℃(140℃F)- Watt ceev txog li 25-30 W / in² (3.9-4.7 W / cm²) tau txais.
60-90 ° F (140-194 ° F)- Watt ceev yuav tsum raug txo kom 15-20 W / in² (2.3–3.1 W / cm²).
90-110 ° F (194-230 ° F)- Watt qhov ceev yuav tsum tau txo qis ntxiv mus rau 10-15 W / in² (1.6-2.3 W / cm²).
Tshaj 110℃(230℃F)- PTFE immersion heaters feem ntau tsis pom zoo rau kev ua haujlwm tas mus li.
Hauv kev xyaum, cov txiaj ntsig no yuav tsum tau hloov kho raws li kev thov tshwj xeeb. Agitated da dej nrog lub siab hloov pauv coefficients tuaj yeem ua rau siab dua watt ntom ntom. Cov kua dej khov los yog cov kua nplaum yuav tsum tau qis dua watt ntom ntom. Lub hom phiaj yog los xyuas kom meej tias PTFE sheath kub tsis tshaj 110℃ntawm txhua qhov chaw, suav nrog cov chaw kub tshaj plaws nyob ze ntawm cov xaim sab hauv.
Temperature Control raws li kev ntsuas kev tiv thaiv
Ua raws li 110℃txwv yuav tsum ntsuas qhov ntsuas kub kom raug thiab tswj xyuas kom ntseeg tau. Immersion heaters yuav tsum tau nruab nrog lub ntsuas kub (thermocouple lossis RTD) muab tso rau ze li sai tau rau cov cua sov lossis hauv PTFE sheath. Tus maub los yuav tsum tau teeb tsa nrog qhov ntsuas kub siab tshaj plaws, thiab qhov siab - txwv kev nyab xeeb yuav tsum tau muab ua thaub qab.
Nws tau pom tias ntau lub sijhawm ua ntej PTFE lub rhaub tsis ua haujlwm tshwm sim tsis yog vim qhov ntsuas kub siab dhau, tab sis vim tias muaj cua sov hauv cheeb tsam. Cov laj thawj uas ua rau muaj kev kub ntxhov hauv zos muaj xws li:
Cov kua dej qis nthuav tawm ib feem ntawm cov rhuab sheath rau cua.
Scale los yog fouling ntawm sheath nto txo tshav kub hloov.
Kev ncig tsis zoo ua rau thaj chaw nyob ib puag ncig ntawm lub rhaub.
High watt ceev tsim kom muaj qhov kub thiab txias gradient nruab nrab ntawm cov hlau sab hauv thiab cov sheath nto.
Txhua yam ntawm cov khoom no tuaj yeem nce qhov kub thiab txias kom ua rau muaj kev puas tsuaj txawm tias qhov kub ntawm cov kua dej tseem qis dua 110 degree.
Xaus
Kev khiav hauj lwm kub ncaj qha cuam tshuam cov neeg kho tshuab kev ncaj ncees ntawm PTFE sheath. CovPTFE mechanical zog kub nyhuvua rau cov khoom tsis muaj zog tensile, ua rau muaj kev nkag siab ntau dua, thiab txo nws txoj kev ua haujlwm siab thaum kub nce siab tshaj ambient. Ntawm qhov kev pab cuam tas mus li ntawm 110 degree, PTFE khaws cia tsuas yog li 40% ntawm nws chav- qhov kub thiab txias tensile zog, thiab tus nqi nkag los ua qhov tseem ceeb txaus ua rau lub sij hawm ntev - deformation.
Qhov kev txwv 110℃yuav tsum raug hwm tsis yog qhov kev paub daws teeb meem tab sis yog qhov tsim nyog rau kev siv tshuab. Tshaj qhov kev txwv no yuav ua rau lub plhaub tawg, lub zais pa, thinning, foob tsis ua haujlwm, thiab qhov kawg ntawm hluav taws xob tawg. Kev tswj qhov kub thiab txias kom raug watt ceev yog li ntawd yog qhov tseem ceeb rau kev txuag lub cua sov lub neej. Los ntawm kev ua haujlwm nyob rau hauv lub hnab ntawv ntsuas kub tsim thiab ua kom muaj kev hloov pauv kom zoo, PTFE sheath tuaj yeem tuav nws lub zog txhua yam thiab txuas ntxiv tiv thaiv cov cua sov sab hauv rau xyoo ntawm kev pabcuam txhim khu kev qha.
