Lub PTFE sheath yuav zoo tag nrho rau sab nraud, tab sis yog hais tias lub sab hauv tsis kam hlau yog overstressed thaum khoov, ib tug kub qhov chaw yog tsim nyob rau hauv. Qhov khoov yog ib qho chaw rau kev kub hnyiab ntxov ntxov, thiab cov hauv paus ntsiab lus feem ntau yog kev puas tsuaj rau cov hlau - puas tsuaj uas tsis muaj qhov kev tshuaj xyuas sab nraud tuaj yeem ntes tau. Nkag siab qhov cuam tshuam ntawm anruj khoov sab hauv kuj xaim PTFE rhaubkev ua haujlwm yog qhov tseem ceeb rau txhua tus neeg qhia lossis txhim kho zoo li lub tshuab tso cua sov hauv kev xav tau kev lag luam.
Yuav ua li cas Internal Resistance Wire teb rau dabtsi yog khoov
Nyob rau hauv txhua txhua PTFE immersion rhaub yog ib tug hlau tsis kam hlau, feem ntau yog ib tug npib tsib xee-chromium (NiCr) alloy xws li Nichrome. Cov hlau no yog lub plawv ua haujlwm ntawm lub tshuab cua sov: thaum muaj hluav taws xob tam sim no dhau los ntawm nws, cov cua sov tuaj yeem tshwm sim. Nyob rau hauv feem ntau cov qauv, cov hlau yog qhov txhab mus rau hauv ib tug meej helical kauj los yog nteg raws li ib tug ncaj, uniform strand raws li ntev ntawm PTFE sheath.
Thaum lub tshuab cua sov yog khoov rau ib qho duab tshwj xeeb, cov hlau tsis kam raug yuam kom ua raws li qhov nkhaus tib yam. Lub tshuab teb ntawm cov hlau nyob ntawm nws txoj hauj lwm txheeb ze rau qhov khoov:
Nyob rau sab nraud ntawm khoov- Cov xaim yog muab tso rau hauv kev ntxhov siab tensile. Yog hais tias lub vojvoog khoov yog dav dav, cov hlau stretches elastically thiab rov qab mus rau nws qhov qub ntev thaum lub zog khoov raug tshem tawm. Txawm li cas los xij, yog tias qhov khoov yog nruj heev, cov hlau hla nws txoj kev txwv elastic thiab dhau musyas deformation mus tas li, ua hauv zos thinner.
Nyob rau hauv qhov khoov- Cov hlau muaj kev ntxhov siab. Kev khoov nruj tuaj yeem ua rau cov hlau buckle, kink, lossissib koom ua keraws li lub puab ncig compresses. Nyob rau hauv ib tug coiled hlau tsim, uas nyob ib sab lem yuav tiv tauj ib leeg los yog ua irregularly spaced.
Cov Khoom Siv Hluav Taws Xob: Los ntawm cov hlau txuas mus rau qhov kub
A nruj khoov sab hauv kuj xaim PTFE rhaubtsim ob peb qhov txawv hluav taws xob ua txhaum, txhua yam uas degrades kev ua tau zoo thiab shortens lub neej kev pab cuam.
Localized nce nyob rau hauv Resistance
Thaum cov hlau tsis kam yog stretched thiab ua thinner ntawm qhov khoov sab nraud, nws qhov chaw hla ntu yog txo. Kev tiv thaiv hluav taws xob yog qhov sib npaug ntawm qhov sib npaug ntawm thaj chaw hla ntu: ib ntu nyias muaj qhov ua haujlwm siab dua rau ib chav tsev ntev. Qhov kev nce hauv cheeb tsam no txhais tau hais tias rau tib qhov tam sim no ntws los ntawm tag nrho lub tshuab cua sov, qhov khoov ntu ua kom muaj cua sov ntau dua (lub zog=I²R). Qhov no tsim ibkub qhov chaw- thaj chaw me me uas qhov kub thiab txias siab dua li ntawm lub tshuab cua sov.
Hot Spot Consequences
Qhov chaw kub ceev nrawm ntau yam tsis ua haujlwm:
Oxidation ntawm cov hlau tsis kam- Qhov kub siab ua rau NiCr alloy oxidize sai dua. Oxidation ua rau muaj kev tiv thaiv ntxiv, tsim kom muaj lub tswv yim zoo uas nws thiaj li ua rau lub melt-los ntawm los yog qhib Circuit Court.
Degradation ntawm ib puag ncig PTFE sheath- Txawm hais tias PTFE tuaj yeem ua haujlwm tsis tu ncua ntawm 110 degree, qhov chaw kub hauv zos tuaj yeem tshaj 200℃lossis ntau dua. Ntawm cov kub no, PTFE pib degrade, poob dielectric zog, thiab muaj peev xwm tso tawm corrosive byproducts. Lub sheath yuav soften, deform, los yog tawg ntawm overstressed khoov.
Shortened Hlau Lub Neej Vim Kev Nyuaj Siab
Txawm hais tias cov xov hlau tsis tawg tam sim ntawd thaum khoov, cov yas deformation ua rau muaj kev ntxhov siab ntau. Nyob rau hauv kev rov ua dua thermal cycling (cua sov rau kev khiav hauj lwm kub thiab txias rov qab rau ambient), cov xaim nthuav dav thiab cog lus. Lub cheeb tsam kev ntxhov siab ntawm qhov khoov tau ntsib cyclic mechanical strain, ua rauqaug zog tsis ua hauj lwm. Ib lub xaim uas yuav kav ntev rau xyoo hauv kev teeb tsa ncaj tuaj yeem ua tsis tiav hauv lub hlis ntawm kev khoov nruj.
Teeb meem ntawm Bunching thiab Tig-rau-Tig Sib cuag
Nyob rau hauv coiled-xaim cua sov cov ntsiab lus, ib tug nruj khoov rau sab hauv ntawm lub nkhaus yuav compress lub kauj, yuam nyob ib sab tig mus kov. Thaum tig kov, cov hluav taws xob tam sim no tuaj yeem hla txoj kev npaj helical, ua kom luv luv ntawm cov hlau nyob hauv cheeb tsam ntawd. Qhov no txo cov kev tiv thaiv hauv zos (tsis sib haum nrog cov nyhuv stretched-xaim) tab sis tsim ib qho teeb meem sib txawv: tam sim no muaj neeg coob coob thiab tsis sib xws. Qhov chaw tiv tauj yuav arc lossis overheat hauv zos, rov ua qhov chaw kub.
Hauv kev xyaum, kev ntsuas hluav taws xob tiv thaiv tau coj los ntawm lub tshuab hluav taws xob hauv lub tshuab hluav taws xob tuaj yeem pib qhia qhov tseem ceeb. Lub multimeter tsis tuaj yeem ntes qhov kub me me vim tias qhov kev tiv thaiv tag nrho ntawm cov hlau tseem nyob hauv qhov tshwj xeeb. Qhov tsis ua haujlwm feem ntau tshwm sim tom qab qee lub sijhawm hauv kev pabcuam- qee zaum ntau pua teev, qee zaum tsuas yog hnub- thaum qhov chaw kub kub thaum kawg melts los ntawm cov xaim lossis cov PTFE degraded tso cai rau luv luv rau hauv av.
Txheeb xyuas Internal Wire Integrity tom qab khoov
Vim tias PTFE sheath yog opaque, kev soj ntsuam pom ntawm cov hlau sab hauv yog tsis yooj yim sua. Cov neeg tsim khoom lag luam uas tseem ceeb rau kev siv zooX-ray kuajtxhawm rau tshuaj xyuas cov kab teeb tsa hauv lub tshuab ua kom tiav khoov. X-ray duab qhia:
Uniform sib nrug ntawm kauj tig (tsis muaj bunching lossis sib cais)
Tsis muaj kinks, ntse khoov, los yog thinning nyob rau hauv cov hlau
Txoj hauj lwm zoo ib yam ntawm cov ntaub ntawv txuas mus rau sheath centerline
Txoj kev khoov tsim kom zoo- ua tiav los ntawm kev ua kom sov mandrel dabtsi yog khoov thiab tom qab khoov annealing- khaws cia qhov qub hlau geometry. Cov hlau nyob rau sab nraud ntawm qhov khoov tsis ncav cuag nws qhov kev txwv elastic, thiab cov xaim ntawm sab hauv tsis buckle. Qhov sib txawv ntawm cov xov hlau tseem tsis sib xws, kom ntseeg tau tias muaj cua sov faib thoob plaws txhua qhov ntev ntawm lub rhaub.
Vim li cas Thermal Cycling Magnifies Hloov Kho Khoov puas
Lub tshuab cua sov uas muaj qhov khoov dhau me ntsis tuaj yeem muaj sia nyob pib lub zog thiab txawm tias ob peb hnub ua haujlwm tas mus li. Txawm li cas los xij, thermal cycling (cua sov thiab txias) exacerbates qhov kev puas tsuaj nyob rau hauv ob txoj kev:
Differential expansion- Cov hlau thiab PTFE sheath muaj cov coefficients sib txawv ntawm thermal expansion. Txhua lub voj voog tsim shear stresses ntawm lub xaim-sheath interface, uas yog concentrated ntawm qhov khoov qhov twg cov hlau twb stressed.
Progressive oxidation- Txhua lub sij hawm qhov chaw kub nce mus txog qhov kub siab, ib txheej nyias ntawm oxide daim ntawv ntawm cov hlau. Cov oxide txheej no tsis tshua muaj hluav taws xob thiab nkig ntau dua. Thaum kawg, cov hlau yuav nyias nyias thiab oxidized uas nws tsis qhib.
Cov kev paub dhau los qhia tau tias cov cua sov khoov qis dua qhov pom zoo 5–6 × OD vojvoog feem ntau ua tsis tiav hauv 3 mus rau 12 lub hlis raws li kev caij tsheb kauj vab ib txwm muaj, thaum cov cua sov zoo ib yam nrog cov khoov zoo txuas ntxiv ua haujlwm rau 5 xyoo lossis ntau dua.
Xaus: Mechanical Precision raws li hluav taws xob kev ntseeg tau
Tiv thaiv cov hlau tsis muaj zog sab hauv los ntawm overstressing thaum lub sij hawm khoov yog qhov tseem ceeb rau kev cia siab rau hluav taws xob mus sij hawm ntev. Kev khoov nruj nreem ncab los yog bunches cov hlau, tsim cov chaw kub kub uas ua rau oxidation, degrade lub PTFE sheath, thiab ua rau burnout ntxov ntxov. Kev ntsuam xyuas hluav taws xob pib yuav dhau mus, tab sis qhov kev puas tsuaj zais inevitably tshwm sim hauv kev pabcuam.
Qhov kev nkag siab no ua rau kev txiav txim siab dav dav: lub rhaub dej kub yog qhov sib xyaw ntawm cov khoom siv hluav taws xob thiab kev ua haujlwm hluav taws xob. Tib cov txheej txheem tsim khoom uas tsim kom muaj kev ntxhov siab tsis muaj dabtsi yog khoov-kub mandrel dabtsi yog khoov, tom qab khoov annealing, thiab X-ray pov thawj-tseem khaws cov kev ncaj ncees ntawm cov hlau hauv lub cev. Kev qhia qhov qis qis qis qis tsis txaus; kom ntseeg tau tias qhov khoov tau ua kom raug tiv thaiv cov xaim, tshem tawm cov chaw kub, thiab muab lub neej ntev kev pab cuam uas cov ntawv thov kev lag luam xav tau.
