Thaum tshav kub kub resistant cam khwb cia hlau ntawm valve khoom

Thaum tshav kub kub resistant cam khwb cia hlau ntawm valve cov ntaub ntawv no scale txhais cov kev cai, kev xeem txoj kev, txij nkawm txoj cai, cim thiab zoo ntawv pov thawj, xeb tiv thaiv, ntim thiab cia yuav tsum tau ntawm tshav kub resistant cam khwb cia hlau. Lub geometry thiab qhov loj ntawm qhov casting yuav tsum ua raws li qhov yuav tsum tau ua ntawm cov duab kos. Qhov ntev kam rau ua thiab machining pub yuav tsum tau ua raws li GB / T6414 thiab qhov sib txawv ntawm qhov hnyav yuav tsum ua raws li GB / T 11351. Cov qauv metallographic ntawm cov hlau tsis muaj cua sov yuav tsum tau txhais raws li GB / T 9441 thiab GB / T 7216, thiab cov ncauj lus kom ntxaws yuav tsum tau pom zoo los ntawm ob tog. Lub matrix qauv ntawm silicon tshav kub cam khwb cia hlau yog tsuas yog ferrite. 1 ntau yam Qhov ntsuas no txhais cov kev xav tau, kev sim, cov cai tswj xyuas, kos npe thiab daim ntawv pov thawj zoo, tiv thaiv xeb, ntim thiab khaws cia ntawm cov cua sov cam khwb cia hlau. Qhov ntsuas no yog tsim rau cov xuab zeb forging los yog kub resistant cam khwb cia hlau castings nrog kub conductivity zoo li cov xuab zeb pwm thiab ua hauj lwm hauv qab no 1100 ℃. 2 Normative reference files Cov nqe lus hauv cov ntaub ntawv hauv qab no dhau los ua cov ntsiab lus ntawm qhov ntsuas no los ntawm kev siv rau qhov ntsuas no. Rau cov ntawv sau hnub tim, tag nrho cov kev hloov kho tom ntej (tsis suav nrog kev ua yuam kev) lossis kev hloov kho yuav tsis siv rau qhov ntsuas no. Txawm li cas los xij, ob tog rau kev pom zoo raws li qhov ntsuas no tau txhawb kom tshawb xyuas qhov muaj *** versions ntawm cov ntaub ntawv no. Rau cov ntaub ntawv tsis raug txheeb xyuas, *** version muaj feem xyuam rau qhov ntsuas no. 3 Cov Kev Xav Tau 3. Qib thiab tshuaj lom neeg muaj pes tsawg leeg ntawm cov cua sov-resistant cam khwb cia hlau Cov txheej txheem ntawm cov cua sov-resistant cam khwb cia hlau ua raws li kev demarcation ntawm GB/T5612, uas muab faib ua 11 qib. Qib thiab tshuaj lom neeg muaj pes tsawg leeg ntawm cov cua sov-resistant cam khwb cia hlau yog qhia nyob rau hauv Table 1. Table 1. Qib thiab tshuaj muaj pes tsawg leeg ntawm tshav kub-resistant cam khwb cia hlau 3.2 Geometric qhov ntev, machining pub thiab hnyav kam rau ua Lub geometry thiab loj ntawm cov casting yuav tsum ua raws li cov kev xav tau ntawm kev kos duab. Qhov ntev kam rau ua thiab machining pub yuav tsum ua raws li GB / T6414 thiab qhov sib txawv ntawm qhov hnyav yuav tsum ua raws li GB / T 11351. 3.3 Nto Zoo 3.3.1 Casting nto roughness yuav tsum ua raws li qhov delineation ntawm GB / T6061.1, thiab qhov scale grade yuav tsum tau pom zoo los ntawm ob tog. 3.3.2 Cov castings yuav tsum tau muab ntxuav kom huv, cov seem seem yuav tsum tau muab tshem tawm, thiab cov seem ntawm pouring riser, core pob txha, av nplaum xuab zeb thiab puab kab noj hniav yuav tsum tau muab tshem tawm. Castings yuav tsum ua raws li qhov yuav tsum tau muaj ntawm tus neeg yuav khoom daim duab, cov kev cai los yog daim ntawv cog lus ntawm ob tog. 3.3.3 Daim ntawv, tus naj npawb, qhov loj thiab txoj hauj lwm ntawm qhov pom zoo tsis xws luag ntawm lub casting, kho thiab kho txoj kev yuav tsum tau pom zoo los ntawm ob tog. 3.4 Mechanical function Cov khoom siv ntawm castings ntawm chav tsev kub yuav tsum ua raws li qhov delineation nyob rau hauv Table 2, thiab lub sij hawm luv luv kub kub tensile zog muaj nyob rau hauv Appendix A 3.5 Thaum tshav kub kub kev kho mob feem ntau, kev kho cua sov yuav tsum tau nqa tawm kom tshem tawm cov residual kev nyuaj siab rau. Thaum tshav kub kub-resistant ductile hlau ntawm silicon thiab aluminium series. Txawm li cas los xij, thaum cov ntsiab lus pearlite ntawm tshav kub-resistant ductile hlau ntawm silicon tseem ceeb series yog qis dua 15%, kev kho cua sov tsis tuaj yeem nqa tawm. Rau lwm hom, yog tias xav tau los ntawm tus neeg xav tau, kev kho cua sov kom tshem tawm cov kev ntxhov siab seem yuav tsum tau ua raws li qhov chaw ntawm kev txiav txim. Cov txheej txheem ua ntej rau kev siv cov khoom siv hluav taws xob kub-resistant cam khwb cia hlau yog qhia nyob rau hauv Daim Ntawv Ntxiv B 3.6 Metallographic qauv Cov qauv metallographic ntawm cov hlau tsis muaj cua sov yuav tsum raug txiav txim siab raws li GB / T 9441 thiab GB / T 7216, thiab cov ncauj lus kom ntxaws yuav tsum tau pom zoo. los ntawm ob tog. Lub matrix qauv ntawm silicon kub resistant cam khwb cia hlau yog tsuas yog ferrite. 3.7 Anti-oxidation, tiv thaiv kev loj hlob muaj nuj nqi thiab coefficient ntawm thermal expansion Nyob rau ntawm qhov kev pab cuam kub, lub uniform oxidation hnyav nce tus nqi ntawm tshav kub-resistant cam khwb cia hlau yog tsis ntau tshaj 0.5 g / m2 ·h, thiab kev loj hlob tus nqi yog tsis ntau tshaj. 0.2%. Kev tiv thaiv oxidation thiab tiv thaiv kev loj hlob ntawm cov cua sov-resistant cam khwb cia hlau thiab cov coefficient ntawm thermal expansion tsis yog siv los ua lub hauv paus rau kev txais. 3.8 Cov Kev Xav Tau Tshwj Xeeb Yog tias tus neeg xav tau muaj qhov yuav tsum tau kuaj cov khoom sib nqus, kuaj ultrasonic, kuaj X-ray, thiab lwm yam, tus neeg thov thiab tus neeg thov yuav tsum sib tham thiab ua raws li GB / T 9494, GB / T 7233 thiab GB / T 5677 raws li. . 4 Test method 4.1 Chemical composition analysis 4.1.1 Chemical composition analysis can be carry out by pa chemical analysis or photoelectric direct reading spectroscopic tsom xam. 4.1.2 Cov qauv coj mus kuaj rau cov pa tshuaj ntsuam xyuas yuav tsum tau teev tseg hauv GB/T 20066. 4.1.3 Spectrum sampling method yuav tsum ua raws li GB/T 5678 thiab GB/T 14203. Txoj kev tsom xam spectral yuav tsum tau ua raws li qhov specification GB/T 20125. 4.1.4 Arbitrate tsom xam ntawm carbon, silicon, manganese, sulfur thiab phosphorus nyob rau hauv tshuaj muaj pes tsawg leeg yog GB / T 20123 los yog GB / T223.69, GB / T223.60 thiab GB / T raws li ua raws li demarcations ntawm 223.58 lossis GB / T223.64, GB / T223.3 lossis GB / T223.59 lossis GB / T223.61, GB / T223.68; Chromium, txhuas, txhuas arbitration tsom xam raws li GB / T223.11 los yog GB / T223.12, GB / T223.26, GB / T223.28 delimit lub txim. 4.2 Mechanical function test 4.2.1 Chav ntsuas kub ntawm cov tshuab ua haujlwm ntawm HTRCr, HTRCr2, HTRSi5 thiab lwm qib, suav nrog kev npaj cov qauv, yuav tsum tau ua raws li cov lus qhia ntawm GB / T228. 4.2.2 Mechanical tests of heat-resistant ductile iron and HTRCr16 at room temperature yuav tsum tau ua raws li GB/T228. 4.2.3 Lub hardness ntawm tshav kub cam khwb cia hlau yuav tsum tau txiav txim raws li GB / T231.1. 4.2.4 Lub sij hawm luv luv kub siab tensile lub zog ntawm tshav kub-resistant cam khwb cia hlau yuav tsum tau txiav txim raws li GB / T4338. 4. 3 Test block, qauv 4.3.1 Cov duab thiab qhov loj ntawm Y-zoo li ib leeg cam khwb cia siv nyob rau hauv lub tensile xeem ntawm QTRSi4, QTRSi5, QTR5i4Mo, QTRSi4Mo1, QTRA14Si4, QTRA15Si5 yog qhia nyob rau hauv FIG.1 thiab Table 3 (the oblique kab hauv FIG.1 yog qhov chaw ntawm cov qauv txiav). Hom B feem ntau xaiv. Cov kev sim thaiv hauv Cov Ntawv Ntxiv C kuj tseem siv tau. Cov duab thiab qhov loj ntawm ib qho yooj yim cam khwb cia txiav sim block rau QTRA122 thiab HTRCr16 4.3.2 Cov duab thiab qhov ntau thiab tsawg ntawm cov qauv tensile siv los ntawm cov khoom siv hluav taws xob kub-resistant ductile hlau hom thiab HTRCr16 hom muaj nyob rau hauv FIG.3 thiab Table 4. 4.3.3 Test blocks yuav tsum tau ntim nrog cov kua hlau tib yam li cov casting thiab nchuav thaum kawg ntawm cov txheej txheem, thiab cov cua txias yuav tsum zoo ib yam li cov casting. 4.3.4 Qhov ntsuas kub ntawm cov khoom ntsuas yuav tsum tsis pub tshaj 500 ° C 4.3.5 Nws tau pom zoo kom coj cov qauv txuas nrog rau lub nrum casting los yog ncaj qha rau ntawm qhov casting, thiab qhov kev lees txais yuav tsum tau pom zoo los ntawm ob tog. 4.4 Oxidation Resistance and Growth Resistance Test Thermal Expansion Test Thermal Expansion Test Thermal Extension Test Thermal Expansion Test Thermal Extension Test Thermal Expansion Test Thermal Expansion Test method of Thermal Expansion Test Txoj kev ntsuam xyuas coefficient ntawm thermal expansion yog ua nyob rau hauv Daim Ntawv Ntxiv F. 4.6 Kev kho cua sov Ntxiv nrog rau kev tshem tawm cov kev ntxhov siab sab hauv ntawm cov castings, yog tias muaj lwm yam kev kho cua sov ua rau ntawm cov castings, cov blocks yuav tsum tau txais kev kho cua sov hauv tib lub cub tawg lossis txheej txheem. Chav tsev: millimeter 5 Kev lees txais Txoj Cai 5.1 Cov qauv ntawm cov qauv batch 5.1.1 Cov castings uas tsim los ntawm cov pwm sib koom ua ke yuav tsum yog ib pawg sampling. 5.1.2 Qhov hnyav ntawm txhua tus qauv ntau yog 2000 kg ntawm castings tom qab ntxuav. Cov qauv batch tuaj yeem hloov tau raws li kev pom zoo los ntawm ob tog. 5.1.3 Yog hais tias qhov hnyav ntawm lub casting yog ntau tshaj 2000 kg, yuav tsum tau tsim ib tug cais sampling batch. 5.1.4 Nyob rau hauv qhov kev tshwm sim ntawm ib tug kev hloov nyob rau hauv tus nqi, kev hloov nyob rau hauv cov txheej txheem premise los yog ib qho kev hloov nyob rau hauv cov tshuaj muaj pes tsawg leeg yuav tsum tau nyob rau hauv ib tug tej lub sij hawm, tag nrho cov castings poured nrog molten hlau tsis tu ncua melted nyob rau hauv lub sij hawm ntawd, tsis hais lub sij hawm luv luv. lub sijhawm, yuav tsum suav tias yog ib qho qauv ntau. 5.1.5 Thaum muaj ntau cov hlau molten ntawm ib qib zoo ib yam tsis tu ncua, cov txheeb ze ntawm txhua tus qauv yuav tsum tsis pub tshaj qhov hnyav ntawm castings poured li ntawm 2 teev. 5. 1.6 Cov batch ntawm molten hlau castings no yuav siv tau raws li ib tug batch sampling thaum lub luj ntawm molten hlau yog tsawg tshaj li 2000 kg. 5.1.7 Raws li kev pom zoo los ntawm ob tog, ob peb pawg ntawm castings kuj tuaj yeem lees txais hauv ib pawg. Nyob rau hauv cov ntaub ntawv no, yuav tsum muaj lwm yam zoo tswj txoj kev nyob rau hauv cov txheej txheem ntau lawm, xws li ceev ceev cov tshuaj muaj pes tsawg leeg tsom xam, metallographic txij nkawm, kev ntsuam xyuas nondestructive, kev tu pob txha, thiab lwm yam, thiab muaj tseeb proved hais tias qhov nodulation kev kho mob tsis chaotic, nyob rau hauv txoj kab nrog rau cov kev kho mob ntawm cov pob qij txha, thiab lwm yam. cov txheej txheem xav tau. Lus Cim: Rau cov castings uas tau raug kho cua sov, cov qauv batch yuav tsum tau coj mus kuaj uniformly, tshwj tsis yog tias cov castings nyob rau hauv lub batch txawv heev nyob rau hauv cov qauv. Nyob rau hauv cov ntaub ntawv no, cov dissimilar castings yog ib tug qauv batch. 5.2 Sampling of Chemical Composition Txhua batch sampling yuav tsum tau soj ntsuam cov tshuaj muaj pes tsawg leeg, thiab cov kev soj ntsuam xyuas yuav tsum tau raws li qhov yuav tsum tau muaj nyob rau hauv Table 1. Yog hais tias cov tshuaj muaj pes tsawg leeg sib txawv, cia ob npaug rau tus naj npawb ntawm cov qauv yuav tsum reanalyzed ib zaug, tus qauv yog tsim nyog tsuas yog thaum nws tsim nyog tag nrho. 5.3 Casting size sampling Qhov loj me, geometry thiab nto roughness ntawm thawj castings thiab tseem ceeb castings yuav tsum tau kuaj xyuas ntawm txhua daim. Cov txheej txheem ntawm qhov chaw kuaj xyuas yuav tsum pom zoo los ntawm ob tog. 5.4 Kev kuaj xyuas qhov zoo ntawm qhov zoo li qhov zoo ntawm cov castings yuav tsum raug kuaj pom los ntawm ib qho. 5.5 Sampling thiab kev ntsuam xyuas ntawm cov khoom siv kho tshuab, metallography, kev loj hlob tsis kam Cov khoom siv hluav taws xob ntawm cov cua sov ductile hlau ntawm chav tsev kub yuav tsum tau kuaj xyuas los ntawm batch. Cov khoom siv hluav taws xob ntawm lwm cov hluav taws kub-resistant cam khwb cia hlau ntawm chav tsev kub nrog rau cov qauv metallurgical, oxidation tsis kam thiab kev loj hlob tsis kam ntawm txhua hom yuav tsum raug kuaj raws li qhov chaw ntawm kev txiav txim. Cov cuab yeej cuab tam ntawm chav tsev kub tau txais raws li lub zog tensile. Yog tias yuav tsum tau kuaj xyuas qhov hardness ua ntej xaj, nws yuav tsum ua kom tau raws li qhov yuav tsum tau ua ntawm Table 2. Txhawm rau kom ntseeg tau tias lub tshuab hluav taws xob lossis cov pob ntawm cov casting yog tib yam li cov pas ntsuas, lub cub tawg lossis cov naj npawb pob yuav tsum tau muab cim kom meej rau qhov tsis tseem ceeb nto ntawm cov qauv thiab cov casting. 5.6 Kev ntsuam xyuas cov txiaj ntsig ntawm kev ntsuas kev ua haujlwm thaum kuaj xyuas lub zog tensile, yog tias qhov kev soj ntsuam ntawm cov qauv tensile tsis ua raws li qhov yuav tsum tau ua, thiab nws tsis tshwm sim los ntawm cov laj thawj uas tau teev tseg hauv 5.7, lwm ob qhov piv txwv los ntawm kev sib koom ua ke tuaj yeem coj mus rau rov xyuas dua. Yog tias qhov kev tshuaj xyuas rov qab ua tau raws li qhov yuav tsum tau ua, cov khoom siv ntawm cov khoom siv no tseem tsim nyog. Yog tias qhov kev tshuaj ntsuam xyuas tseem ua tsis tau raws li qhov yuav tsum tau ua, batch ntawm castings yuav raug txiav txim ua ntej raws li kev faib khoom. Lub sijhawm no, ib qho ntawm cov castings tuaj yeem raug coj los ntawm cov batch, thiab cov qauv ntawm lub cev tuaj yeem raug txiav ntawm txoj haujlwm tau pom zoo los ntawm ob tog rau kev kuaj tshuab. Yog tias qhov ntsuas tau ua tau raws li qhov yuav tsum tau ua, cov khoom siv casting tseem tuaj yeem txiav txim siab kom tsim nyog; Yog tias qhov ntsuas ntawm lub cev qauv tseem ua tsis tau raws li qhov yuav tsum tau ua, ** thaum kawg txiav txim siab tias cov khoom siv casting ntawm cov khoom siv no yog cais cov lattice. 5. 7 Kev siv tau ntawm qhov kev xeem Yog tias qhov kev xeem tsis tau raws li qhov yuav tsum tau ua, tsis yog vim qhov zoo ntawm qhov casting nws tus kheej, tab sis vim yog ib qho ntawm cov laj thawj hauv qab no, qhov kev xeem tsis raug. a) Kev thauj khoom tsis raug ntawm cov qauv ntawm lub tshuab kuaj lossis kev ua haujlwm tsis raug ntawm lub tshuab kuaj. b) Muaj forging tsis xws luag nyob rau saum npoo ntawm cov qauv los yog kev txiav tsis raug ntawm cov qauv (xws li tus qauv loj, hloov fillet, roughness tsis ua raws li qhov yuav tsum tau, thiab lwm yam). c) Tensile specimen lov sab nraum tus qauv nyob deb. d) Muaj qhov cuam tshuam loj heev ntawm kev puas tsuaj ntawm cov qauv tensile. Nyob rau hauv tas li ntawd, ib tug tshiab qauv yuav tsum tau ua los ntawm lub uniform test block los yog cov qauv yuav tsum tau reprocessed los ntawm lub uniform batch ntawm poured test block rau retesting, thiab qhov tshwm sim ntawm lub retesting yuav tsum tau hloov qhov tshwm sim ntawm qhov kev xeem tsis raug. 5.8 Thaum tshav kub kub kev kho mob ntawm cov kev sim blocks thiab castings Tshwj tsis yog tias muaj tshwj xeeb yuav tsum tau, yog hais tias cov castings muab raws li cam khwb cia thiab cov neeg kho tshuab kev ua hauj lwm ntawm cov castings tsis ua raws li qhov ntsuas no, tus neeg muag khoom yuav, nrog rau kev tso cai ntawm Demander, tshav kub kho cov castings. ua ke nrog cov kev sim blocks thiab tom qab ntawd rov sim dua. Yog hais tias cov castings tau raug tshav kub-kho thiab cov neeg kho tshuab kev ua haujlwm tau muab faib, tus neeg muag khoom tuaj yeem rov ua kom sov cov castings thiab cov kev sim blocks ntawm castings ua ke. Thiab xa rov qab rau kev lees txais. Yog tias cov qauv ua tiav los ntawm cov khoom siv hluav taws xob kho cua sov yog tsim nyog, cov batch raug txiav txim siab tias yuav tsum tau rov ua kom sov kho Qhov ua haujlwm raws li qhov ntsuas no. Kev kho cua sov rov qab rau kev tshuaj xyuas yuav tsum tsis pub tshaj ob zaug. Yog tias tsis muaj qhov yuav tsum tau ua kom pom tseeb ntawm txoj haujlwm, qhov loj me (qhov loj me, qhov siab, convex thiab concave) thiab cov qauv ntawm lub cim, tus neeg muag khoom thiab tus neeg muag khoom yuav tsum pom zoo. Txawm li cas los xij, kev kos npe yuav tsum tsis txhob ua rau qhov zoo ntawm casting. Tom qab cov castings dhau kev tshuaj xyuas thiab kev saib xyuas, kev tiv thaiv xeb, ntim thiab khaws cia yuav tsum tau pom zoo los ntawm ob tog. Muaj qhov sib txawv txaus ntawm cov qauv muab tso rau hauv lub cub tawg kom ntseeg tau tias muaj kev sib cuag zoo ntawm cov huab cua hauv qhov cub thiab cov qauv saum npoo. Ob lub ntsuas ntsuas tuaj yeem ntsia tau rau ntawm ob qho kawg ntawm cov qauv, qhov ntev ntawm qhov uas tau pom hauv daim duab D.2. (Yog tias tsis muaj qhov ntsuas ntsuas, lub ntsej muag kawg ntawm tus qauv tuaj yeem plated nrog chromium lossis npib tsib xee... Daim ntawv pov thawj ntawm cov cim thiab qhov zoo 6. 1 Cov khoom siv casting yuav tsum raug cim los ntawm tus neeg muag khoom. 6. 2 Yog tias tsis muaj qhov xav tau meej ntawm txoj hauj lwm, qhov loj me (qhov loj me, qhov siab, convex thiab concave) thiab txoj kev ntawm lub cim, ob tog yuav tsum pom zoo, txawm li cas los xij, lub cim yuav tsum tsis txhob ua kom puas lub casting zoo mus rau casting ua ntej xa khoom, thiab cov ntsiab lus ntawm daim ntawv pov thawj yuav tsum muaj cov ntsiab lus hauv qab no: a) Lub npe lossis lub logo ntawm tus neeg muag khoom; b) Tus naj npawb lossis xaj daim ntawv cog lus; C) Khoom siv hom; d) Cov txiaj ntsig kev saib xyuas; e) Tus lej ntsuas. Kev tiv thaiv xeb, ntim thiab khaws cia 7.1 Kev tiv thaiv xeb, ntim thiab khaws cov txheej txheem ntawm cov castings yuav tsum tau pom zoo los ntawm ob tog tom qab cov castings raug kuaj xyuas thiab tsim nyog. 7.2 Rau castings thauj mus los ntev, ob tog yuav tsum pom zoo rau kev ntim khoom thiab kev thauj mus los raws li cov kev cai thauj mus los. Kev tiv thaiv ib puag ncig, kev nyab xeeb thiab kev cai lij choj thiab kev tswj hwm Ob tog yuav tsum ua raws li kev tiv thaiv ib puag ncig, kev nyab xeeb thiab kev cai lij choj ntawm cov teb chaws cuam tshuam thaum tsim khoom, txais tos, khaws cia thiab kev thauj mus los. Kev sim txoj kev loj hlob ntawm cov cua sov resistant cam khwb cia hlau Txoj kev no yuav siv tau los ntsuam xyuas qhov kev loj hlob tsis kam ntawm ntau yam kub resistant cam khwb cia hlau nyob rau hauv high kub huab cua nruab nrab. D.1 Cov kev cai tseem ceeb rau kev ntsuas cov cuab yeej thiab thaj chaw tiv thaiv kev loj hlob D.1.1 Lub qhov cub tiv thaiv kev loj hlob yuav tsum ua raws li cov cai hauv qab no: a) Muaj cov cuab yeej hloov kho qhov kub thiab txias, qhov tseeb yog 5 ℃; b) Qhov kub ntawm qhov sib txawv ntawm txhua qhov chaw nyob rau hauv qhov piv txwv faib cheeb tsam nyob rau hauv lub cub tawg yuav tsum tsis txhob ntau tshaj 5 ℃; c) Tswj kom txaus oxidation cua nyob rau hauv lub cub tawg. D.1.2 Muaj kev tshem tawm txaus ntawm cov qauv muab tso rau hauv lub cub tawg kom ntseeg tau tias muaj kev sib cuag zoo ntawm huab cua hauv qhov cub thiab qhov chaw ntawm cov qauv. D.1.3 Tom qab cov qauv thauj khoom mus rau hauv lub cub tawg, lub sij hawm thaum qhov kub ntawm lub cub tawg mus txog qhov ntsuas kub yuav tsum raug suav hais tias yog qhov pib ntawm qhov kev sim, thiab lub sij hawm thaum lub sij hawm ntsuas qhov ntsuas tau dhau los thiab lub cub tawg tsis ua haujlwm ( los yog tshem tawm cov qauv) yuav tsum suav tias yog qhov kawg ntawm qhov kev xeem. D.2 Sab nraum tus qauv