Yuav Ua Li Cas Magnesium Oxide Compaction Density Hauv 316 Stainless Steel Sheathed Rhaub Correlate nrog Dielectric Strength thiab Kub Hloov Uniformity

Dual -Function Performance Variable: Internal Ceramic Packing

Magnesium oxide (MgO) hmoov sau qhov chaw nyob nruab nrab ntawm cov hlau tsis sib haum thiab cov phab ntsa sab hauv ntawm 316 stainless hlau sheathed hluav taws xob cua sov raj tsis yog tsuas yog hluav taws xob rwb thaiv tsev xwb tab sis kuj tseem yog ib qho tseem ceeb ntawm kev ua haujlwm nrog nws cov compaction ntom ib txhij tswj ob yam ntxwv kev ua tau zoo. Raws li qhov compaction ceev loj hlob, hluav taws xob rwb thaiv tsev tsis kam (hauv megohms) nce. Nrog compacted MgO crystals, tsis muaj qhov chaw huab cua rau ionisation to tam sim no. Thermal conductivity thoob plaws MgO txheej kuj nce nrog compaction ceev raws li cov khoom - mus rau - cov khoom sib cuag ntawm cov muaju uas nyob ib sab ua kom kub tau zoo dua li kev sib txuas ntawm huab cua. Tab sis ntau heev compaction ceev yog ib qho kev hem thawj rau kev puas tsuaj ntawm cov hlau tsis kam los yog sheath nyob rau hauv cov txheej txheem swaging. Daim ntawv no ntsuas kev sib raug zoo ntawm MgO packing ceev thiab kev ua haujlwm ntawm lub rhaub thiab muab cov txheej txheem tshwj xeeb uas ua kom muaj kev nyab xeeb ntawm hluav taws xob thiab thermal efficiency rau 316 sheathed heaters hauv kev xav tau kev ua haujlwm.

Lub cev lub hauv paus rau Compaction ntom thiab nws ntsuas

The magnesium oxide powder, which is first put into a straight or coiled sheath assembly, has a bulk density of around 1.6-1.8 g/cm 3 , filling about 50-55 % of the annular volume, the balance being interstitial air. The MgO crystals are mechanically compressed to a final density of 2.8‐3.2 g/cm3, i.e. 85‐95 % of the theoretical crystal density of 3.58 g/cm3, in a swaging or rolling process reducing the sheath outer diameter by 10‐25 %. The basic quality parameter is the compaction density ratio – actual density to theoretical density. At compaction densities below 2.6 g/cm3 (around 73% of theoretical) the MgO matrix possesses interconnecting gaps which allow for the absorption of moisture from the atmosphere. Absorbed water causes a substantial reduction in electrical resistivity, from >1000 megohms ntawm ambient kub rau<1 megohm, triggering ground fault circuit disruption or nuisance tripping. Crushing force applied to MgO crystals surpasses their fracture strength at compaction densities above 3.2 g/cm3 (89 % of theoretical) and microcracks are generated that increase the void volume and impair long-term insulating stability. For 316 sheathed heaters, the best compaction density range is 2.9-3.1 g/cm3, achieved by a controlled swaging reduction of 15-18 % and verified by density measurement on randomly chosen heaters (usually by weighing a known volume of MgO taken from a destructively tested unit).

Hluav taws xob rwb thaiv tsev Resistance raws li ib tug Function ntawm Compaction Condition

Kev sib raug zoo ntawm MgO compaction ceev thiab hluav taws xob rwb thaiv tsev tiv thaiv yog ib qho nkhaus exponential. Hom insulating tsis kam ntawm qhov txias (25 degree) 316 sheath yog 50-200 megohms ntawm 2.6 g / cm^3, NW nyuam qhuav zam tau rau ntau qhov kev siv, tab sis rhiab heev rau cov av noo. Txias rwb thaiv tsev tsis kam nce mus rau 500-2000 megohms ntawm 2.9 g / cm3, muab qhov tsis zoo rau cov xwm txheej ntub dej. Rwb thaiv tsev tsis kam yog feem ntau ntau dua 5000 megohms ntawm 3.1 g / cm3 uas yog cov khoom tsim tau zoo heev. Tsis muaj qhov tseem ceeb tsawg dua yog qhov kev cia siab ntawm qhov kub thiab txias: qhov kev tiv thaiv insulating txo qis los ntawm peb mus rau plaub qhov kev txiav txim loj thaum lub rhaub ua haujlwm ntawm qhov kub ntawm 400-600℃(sab hauv MgO kub). Lub tshuab ua kom zoo zoo (3.0 g / cm³) muaj 5-10 megohms ntawm 500 degree, txaus los tiv thaiv cov xau tam sim no tshaj 0.5 mA ntawm 240 VAC. Lub tshuab hluav taws xob tsis muaj zog (2.7 g / cm3) tuaj yeem poob qis dua 0.1 megohm ntawm qhov kub thiab txias nrog rau cov dej ntws tam sim no ntawm ob peb milliamperes, uas yuav ua rau cov khoom siv tiv thaiv hauv av los yog, hauv cov tshuab tsis siv neeg, tsim hluav taws xob txaus ntshai. Kuj tseem ceeb yog rhiab heev rau cov dej noo. Lub tshuab cua sov compacted rau 2.8 g / cm3 thiab raug rau 80 feem pua ​​​​ntawm cov av noo nyob rau 48 teev tuaj yeem siv los ntawm 0.5 mus rau 1.0 feem pua ​​​​ntawm cov dej noo los ntawm qhov hnyav, uas txo cov rwb thaiv tsev kom qis dua 10 megohms. Tib lub rhaub ntawm 3.0 g / cm^3 absorbs tsuas yog 0.1-0.2% noo noo thiab muaj> 100 megohms. Rau 316 sheathed heaters rau sab nraum zoov lossis kev siv ntxhua khaub ncaws, kaw qhov xaus nrog qhov tsawg kawg nkaus compaction ntom ntawm 3.0 g / cm3.

Thermal conductivity ntawm Compacted MgO Txheej

Qhov zoo thermal conductivity ntawm compacted MgO hmoov yog qhov tseem ceeb ntawm kev ceev thiab kev ua haujlwm ntawm qhov kub thiab txias. Thermal conductivity ntawm 400℃yog hais txog 2.5-3.0 W/m·K ntawm 2.6 g/cm³-nqi qis dua cov khoom MgO (kwv yees li 40 W/m·K) vim cov huab cua qhov chaw (thermal conductivity 0.03 W/m·K) muaj nuj nqi raws li thermal insulators g/cm3 conductivity: 6.5–7.5 W/m·K Qhov sib txawv no ncaj qha cuam tshuam qhov sib txawv ntawm qhov kub thiab txias ntawm MgO txheej. Rau ib tug raug 316 sheath nrog ib tug internal kuj hlau ntawm 750℃qhov poob nyob rau hauv kub nyob rau hauv ib tug MgO txheej 2 hli tuab ntawm 2.6 g / cm^3 ceev yog ~ 180-220 degree, lub puab sheath phab ntsa kub yog 530-570 degree. Tib lub tshav kub flux ntawm 3.1 g / cm3 tshwm sim nyob rau hauv ib tug kub sib txawv nyob rau hauv lub puab sheath phab ntsa ntawm tsuas yog 80-100℃(650-670 degree) ntawm tib hlau kub. Lub phab ntsa txias txias retards tus nqi ntawm oxidation, prolonging lub cua sov lub neej. Xwb, nrog rau qee qhov kev tso cai los ntawm qhov kub thiab txias (piv txwv li, 550℃siab tshaj plaws los tiv thaiv scaling nyob rau hauv ib qho dej), ib qho kev sib txuas ntau dua tso cai rau lub hwj chim ntau dua lossis lub hnab ntawv me me. Cov lus hauv qab no qhia txog kev sib raug zoo ntawm MgO compacted ntom, qhov ua tau zoo thermal thiab kev cia siab ntawm hluav taws xob.

Compaction Density (g/cm3) % of Theoretical Density MgOInsulation Resistance (txias) (megohms, qhuav) Thermal Conductivity at 400 C (W/mK) Moisture Absorption Rate (mass % after 48h, 80% RH) Pom zoo siv<2.6 <73 10-50 2.0-2.8 >1.5 Tsis tsim nyog rau txhua qhov kev pabcuam ntub lossis ntub dej
2.6-2.8 73-78 50-200 2.8-3.8 0.8-1.5 Kev siv hauv qhov chaw qhuav, hauv cov av qis
2.8-2.9 78-81 200-500 3.8-4.5 0.4-0.8 Kev lag luam dav dav; txais tau nrog kaw terminals
2.9-3.0 81-{2}}-2000 4.5-5.5 0.2-0.4 Pom zoo rau kev pabcuam dej thiab sab nraum zoov feem ntau
3.0-3.1 84-86 2000-5000 5.5-6.5 0.1-0.2 Kev ntseeg siab heev; ntxuav, marine los yog high humidity
3.1-3.2 86-89 >5000 6.5-7.5 <0.1 Premium quality Maximum life duration and electrical safety3.2 >89 Variable (tej zaum yuav txo qis vim tawg) 7.0-8.0 Unpredictable Over-compacted; txaus ntshai ntawm cov hlau puas; zam cov txheej txheem Manufacturing Control thiab Verification Methods

Raws li MgO compaction ntom yog ua tiav los ntawm kev tswj hwm ntawm peb qhov kev tsim khoom: pib MgO particle loj faib, feem pua ​​​​ntawm kev txo qis thaum lub sij hawm swaging, thiab tus naj npawb ntawm swaging hla. Lub bimodal particle loj faib (70-80% coarse crystals ntawm 200-400 µm thiab 20-30 % zoo crystals ntawm 20-50 µm) ua rau ntau dua li - ntim ntim ua ntej swaging thiab xav tau tsawg dua kom tau raws li lub hom phiaj ntom. Qhov kev txo qis yog (initial OD rho tawm kawg OD) / pib OD Qhov txo qis ntawm 12 hli OD sheath rau 10.2 hli yog 15%, feem ntau nce MgO ntom ntawm 1.7 txog 2.9-3.0 g / cm3. Kev siv ob lossis peb lub viav vias viav vias nrog inter-theem anneals muab qhov sib npaug sib npaug ntawm qhov ntev ntawm lub hnab dua li ib qho hnyav dua. Cov txheej txheem pov thawj suav nrog tsis yog -kev ntsuas kev puas tsuaj (qhov dielectric tas li ntawm compacted MgO ntawm 1 kHz correlates linearly nrog ntom) thiab kev puas tsuaj ntawm cov qauv tso cua sov los ntawm txhua qhov ntau lawm. Cov neeg yuav khoom hais txog 316 sheathed heaters rau cov ntawv thov tseem ceeb yuav xav tau daim ntawv pov thawj MgO qhov ntsuas qhov ceev raws li ASTM E12 (lossis zoo sib xws) nrog rau kev lees paub ntawm 2.90-3.10 g / cm³ rau kev lees paub zoo. The terminal sealing method also interacts with compaction density, because an open or badly sealed terminal permits moisture intrusion that overcomes even well-compacted MgO, whereas a well sealed terminal (epoxy, silicone or glass) keeps the initial dry insulating resistance permanently.

Kev khiav hauj lwm cua sov & Cov cim qhia tsis zoo ntawm Compaction + Failure Analysis

Muaj peb qhov chaw - pom cov tsos mob ntawm qhov tsis txaus MgO compaction ceev hauv cov cua sov uas twb tau siv lawm . 1. Kev sib tshuam hauv av Fault Tripping uas tau mob zuj zus thaum lub sij hawm muaj av noo los yog thaum lub rhaub tau tawm thaum hmo ntuj (kom tso cai rau cov dej noo nyob rau hauv MgO), tab sis tshem tawm tom qab lub rhaub dej tawm (piv txwv li ib teev). Qhov thib ob yog qhov kawg corrosion los yog ntsuab discoloration ntawm 316 sheath ze ntawm qhov kev txiav. Qhov no yog ib qho qhia tias electrolytic to tam sim no tau ntws los ntawm txoj kev damp MgO. Qhov thib peb, nws muaj qhov chaw kub kub, uas yuav pom tau tias yog cov pob zeb ntawm cov xim tsis sib xws ntawm cov ntaub qhwv tsis sib xws ua rau tsis muaj -cov thermal conductivity, uas tso cai rau cov hlau tsis muaj zog kom kub hauv qhov chaw ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom. Kev tshawb nrhiav kev puas tsuaj ntawm lub tshuab hluav taws xob tsis ua haujlwm los ntawm kev tshem tawm MgO ntawm ntau lub ntsiab lus thiab ntsuas qhov ntom ntom pom tseeb tias lub hauv paus ua rau. Qhov sib txawv ceev ntau dua ± 0.15 g / cm3 raws li qhov ntev yog qhov qhia txog kev tsim khoom tsis zoo. Nyob rau hauv cov xwm txheej no cov lus teb tsis yog kho lub rhaub hauv lub tshav pob tab sis hloov nws nrog ib qho los ntawm ib tus neeg muab kev pabcuam uas qhia meej thiab siv tau qhov kev sib khi ntom ntom raws li cov txheej txheem tswj xyuas.

Xaus: MgO Compaction Density li Core Quality Attribute

Lub compaction ceev ntawm sab hauv MgO hmoov tsis yog ib qho kev tsim me me rau 316 stainless hlau clad hluav taws xob cua sov raj - nws yog qhov tseem ceeb ntawm ob qho tib si hluav taws xob kev nyab xeeb thiab kev ua haujlwm thermal. Nyob rau hauv -compacted MgO absorbs ya raws, rwb thaiv tsev tiv thaiv te thiab hluav taws xob kev txhawj xeeb tshwm sim. Qhov no ua rau nyob rau hauv -compaction thiab tsis zoo thermal conduction, ua rau cov hlau khiav kub rau tib lub tshav kub tso tawm, ua rau oxidation sai dua thiab txo cov cua sov lub neej. Qhov zoo tshaj plaws ceev ntawm compaction 2.9-3.1 g / cm3 yog ib qho kev cuam tshuam ntawm qhov siab tshaj plaws hluav taws xob kev cia siab thiab kev thauj mus los tau zoo. Cov kws tsim hluav taws xob xaiv cov cua sov rau txhua daim ntawv thov uas xav tau cov av noo, aqueous immersion, los yog sab nraum zoov yuav tsum tau qhia qhov tsawg kawg nkaus qhov yuav tsum tau muaj (piv txwv li, 3.0 g / cm³ validated los ntawm kev puas tsuaj ntawm ib chav tsev ib tug ntau) thiab ib tug terminal sealing yuav tsum tau. Lub ntsiab lus piav qhia ntawm no muaj peev xwm txheeb xyuas MgO compaction ntom rau ntsuas kev ua tau zoo, tso cai rau cov neeg yuav khoom los txheeb xyuas cov cua sov uas tsim los kom nyob rau hauv qhov chaw hnyav tiv thaiv cov uas yuav ua tsis tau sai vim kev puas tsuaj ntawm cov rwb thaiv tsev sab hauv.