Kev Tshawb Fawb Thiab Kev Siv Txoj Kev Txhim Kho Ntawm Hlau Ua Npuas Ncauj

Hlau ua npuas ncauj yog cov khoom siv hlau ntxeem tau uas tsim ntau npuas hauv cov hlau matrix, tseem hu ua porous hlau ua npuas ncauj. Vim tias nws muaj ob qho khoom siv hlau thiab qee qhov tshwj xeeb lub cev ntawm cov hlau tsis yog hlau, nws tau txais kev saib xyuas thoob plaws hauv tsev thiab txawv teb chaws. Nyob rau hauv xyoo tas los no, kev vam meej tau ua tiav nyob rau hauv kev tshawb fawb theoretical ntawm kev txhim kho, kev siv thiab kev loj hlob ntawm cov hlau ua npuas ncauj thiab nws cov khoom siv.

1. Txheej txheem cej luam ntawm kev txhim kho ntawm cov hlau ua npuas ncauj hauv tsev thiab txawv teb chaws

Txij li thaum SOSNIK hauv Tebchaws Meskas thawj zaug ntxiv mercury rau txhuas los tsim foamed aluminium hauv xyoo 1948, cov kws tshawb fawb tau ua haujlwm ntau ntawm kev npaj, kev tshawb fawb kev ua haujlwm, thiab kev tsim cov hlau foamed. Cov txheej txheem feem ntau yog tsau, uas tuaj yeem muab faib ua txoj kev casting, hlau deposition txoj kev, hmoov metallurgy method, spray deposition method, etc. xyoo. Piv txwv li, lub tuam txhab American Roa thiab Tebchaws Meskas thiab Nyij Pooj tau ua tiav cov hlau lead alloy qib ntawm 7075 thiab ALMAG35 ua npuas ncauj aluminium profiles los ntawm txoj kev ncaj nraim foaming thiab peev casting txoj kev raws li.

Los ntawm cov tsos ntawm hlau ua npuas ncauj mus rau xyoo 1970 thiab 1980s, kev tshawb fawb tau tsom mus rau kev npaj cov hlau ua npuas ncauj. Piv txwv li, kev daws teeb meem ntawm viscosity nce hauv kev npaj ntawm txhuas ua npuas ncauj muaj lub zog loj rau kev npaj ntawm txhuas ua npuas ncauj; Tsis tas li ntawd, cov lus pom zoo thiab kev siv lub tshuab ua npuas ncauj yog qhov ua tau zoo hauv kev npaj ua npuas dej. Txoj kev xav zoo li ntxiv cov nucleating tus neeg sawv cev hauv cov txheej txheem solidification ntawm cov hlau, uas ua rau txoj kev ncaj nraim ntawm cov hlau ua npuas ncauj ua tau.

Tam sim no cov khoom ntawm foamed aluminium tau muaj peev xwm nqa tawm tas li ntau lawm los ntawm foaming mus rau txheej txheem.

(A) Rau kev tsim khoom loj ntawm txhuas; (B) Kev tsim khoom tas li ntawm daim hlau loj nrog qee qhov tuab; (c) Rau castings uas yuav siv tau los tsim ib tug tej yam zoo li; (D) Rau kev tsim khoom tas mus li ntawm qee yam duab casting. Txoj kev no yog kom tau txais ib qho ruaj khov molten hlau ua npuas ncauj raws li lub npuas tub ntxhais txoj kev xav, thiab tom qab ntawd kos nws tawm rau molding kom tau txais cov khoom tiav ntawm qhov xav tau.

Ntawm qhov tod tes, ntau lub teb chaws tau nqis peev ntau ntawm cov neeg ua haujlwm thiab cov khoom siv los txhim kho cov khoom ntawm cov hlau ua npuas ncauj, thiab cov ntsiab lus kev tshawb fawb feem ntau suav nrog kev sib tsoo, kev kho cua sov, kev siv fiber ntau lossis lwm yam kev txhawb nqa ntawm cov hlau ua npuas ncauj. Ntawm lawv, Gasser high-strength porous ua npuas ncauj khoom tsim los ntawm Ukrainian metallurgist Shapovalov yog cov feem ntau raug. Cov khoom siv no muaj qib siab ntawm cov qauv kev ntseeg siab thiab muaj zog ntau dua thiab nruj dua li cov khoom siv ua npuas dej ua ke.

Tsis tas li ntawd, nyob rau hauv xyoo tas los no, ib txoj kev tshawb fawb ntawm cov hlau foams kuj tau ua nyob rau hauv txoj kev xav. Ua ntej ntawm tag nrho cov, nyob rau hauv kev tshawb fawb ntawm cov yam ntxwv tsis xws li cov hlau ua npuas ncauj, cov neeg nce xav tias qhov tshwj xeeb ntawm hlau ua npuas ncauj nyob rau hauv lub cev qauv, nws tsis yog tsuas yog ib tug structural khoom, tab sis ib tug multifunctional cov ntaub ntawv uas muaj ntau lub cev muaj zog. Nws cov khoom tshwj xeeb tuaj yeem pom los ntawm nws cov qauv. Piv txwv li, kev ntsuas thiab kev tshawb fawb ntawm qhov qhib porosity thiab kaw porosity ntawm npaus hlau pores, statistical ntsuas ntawm pore loj, kev ntsuas ntawm qhov chaw tshwj xeeb thiab cov kev cuam tshuam ntawm cov tsis ua hauj lwm ntawm cov hlau ua npuas ncauj. Qhov thib ob, nws yog los kawm txog cov khoom ntawm cov hlau ua npuas ncauj, xws li cov yam ntxwv deformation, cov yam ntxwv ntawm lub suab nqus thiab damping sab hauv kev sib txhuam cov yam ntxwv ntawm cov hlau ua npuas ncauj. Cov kev tshawb fawb no muab lub hauv paus theoretical rau kev tshawb fawb siv.

Cov kev ua tiav zoo tau ua tiav hauv daim ntawv thov thiab kev tshawb fawb ntawm cov hlau ua npuas ncauj, thiab cov khoom me me thiab cov khoom loj tau npaj thiab nkag mus rau theem ntawm kev sim ntau lawm thiab daim ntawv thov. Piv txwv li, cov txhuas ua npuas dej ua los ntawm Nyiv Sumitomo Electric Co., Ltd. yog siv los tsim qee qhov kub-resistant thiab puas-resistant qhov chaw ntawm lub tsheb thiab qhov chaw ntawm cov neeg hais lus; ntawm txoj kev tsheb ciav hlau, txhuas ua npuas ncauj yog siv los ua cov phab ntsa tsis muaj suab nrov rau cov cua txias hauv chav tsim hluav taws xob. Tsis tas li ntawd, foamed aluminium kuj tseem siv los ua cov khoom siv hluav taws xob poob siab rau cov cuab yeej precision.

Kev tshawb fawb hauv tsev ntawm cov hlau ua npuas tsuas yog pib thaum xyoo 1980s. Tom qab ntau tshaj 10 xyoo ntawm kev tshawb nrhiav thiab kev tshawb fawb, qee qhov kev tshawb fawb xws li Southeast University, Guizhou Academy of Sciences, Dalian University of Technology, Southwest Aluminium Processing Factory tau pib mastered txoj kev tsim cov hlau ua npuas ncauj. Ntawm lawv, Southeast University thiab Guizhou Academy ntawm Sciences yog cov qib siab tshaj plaws. Tshwj xeeb, Guizhou Academy ntawm Kev Tshawb Fawb tau ua tiav ua tiav cov txheej txheem txhuas ua npuas ncauj los ntawm kev siv cov txheej txheem foaming ncaj qha nrog cov khoom pheej yig foaming. Tom qab kev soj ntsuam los ntawm lub koom haum ntawm Acoustics ntawm Suav Academy ntawm Sciences thiab lwm yam units, lub suab nqus, shielding, shock absorption thiab cuam tshuam tsis kam, tshwj xeeb lub ntiajteb txawj nqus thiab lwm yam Performance index, tau mus txog qhov ntsuas ntawm cov khoom txawv teb chaws zoo sib xws. Tam sim no, Lub Tsev Kawm Ntawv Qib Siab Sab Hnub Tuaj tau muaj zog heev hauv kev tshawb fawb txog kev npaj thiab cov khoom ntawm foamed hlau. Lawv tsuas yog tsom rau kev npaj ntawm foamed aluminium los ntawm txoj kev seepage, thiab tau ua simulation simulation ntawm txoj kev seepage thiab npaj cov foamed aluminium los ntawm txoj kev seepage. Polymer composite cov ntaub ntawv, Hebei University of Technology tau ua tiav kev npaj siab-melting hlau ua npuas ncauj los ntawm kev ntxiv cov pore-forming agents, thiab ua tiav cov txiaj ntsig zoo.

Nyob rau hauv cov nqe lus ntawm kev npaj ua npuas ncauj hlau, muaj ntau yam domestic kev tshawb fawb ntawm foaming txoj kev, metallurgical txoj kev thiab percolation txoj kev, thiab lawv tau pib ntes tau nrog cov theem ntawm txawv teb chaws tsim lub teb chaws, tab sis cov kev tshawb fawb ntawm nruam ntau lawm txoj kev yog tseem dawb paug, thiab yuav tsum tau tsim kho kom haum rau cov xwm txheej hauv tsev. Nruam ntau lawm txoj kev.

Nyob rau hauv cov nqe lus ntawm kev kawm theoretical, kev tshawb fawb hauv tsev yog qhov ntxov, thiab kev tshawb fawb teb yog qhov tseem ceeb ntawm kev ua haujlwm thoob ntiaj teb, xws li kev ntsuas cov qauv ntawm cov hlau ua npuas dej, suab nrov txo kev ua haujlwm, kev ua haujlwm hauv qab dej suab nrov, kev ua haujlwm damping, thiab lwm yam. ntau qhov kev tshawb fawb tau ua tiav, thiab tau txais txiaj ntsig zoo heev. Tus naj npawb ntawm cov pores hauv cov hlau ua npuas ncauj yog qhov loj thiab qhov ntau thiab tsawg sib txawv. Nws yog ib qho nyuaj heev rau manually ntsuas cov txheej txheem tsis. Nyob rau hauv cov ntaub ntawv, cov ntaub ntawv nraaj ntawm cov hlau ua npuas ncauj yog nkag mus rau hauv lub computer thiab cov ntaub ntawv ua tau ua los ntsuas qhov nruab nrab txoj kab uas hla thiab qhov pore loj faib ntawm lub pores. Nws daws qhov teeb meem ntawm kev ntsuas cov txheej txheem ntawm cov hlau ua npuas ncauj. Hlau ua npuas ncauj yog ib yam ntawm lub teeb yuag thiab siab damping khoom nrog siab zog nqus cov noob. Nws cov yam ntxwv damping yog nonlinear internal kev sib txhuam uas yog ze ze rau lub strain amplitude, tab sis tsis muaj kev sib raug zoo nrog lub strain zaus. Kev tshawb fawb hauv cheeb tsam no tsuas yog tshaj tawm txawv teb chaws hauv xyoo 1998.

Nyob rau hauv cov nqe lus ntawm daim ntawv thov, muaj ob peb domestic kev tshawb fawb. Txawm hais tias kev tshawb fawb txog kev ua haujlwm theoretical tau npaj ntau qhov kev siv tau, nws yog decoupled los ntawm daim ntawv thov kev loj hlob, thiab tsis muaj ntawv qhia txog kev siv cov hlau ua npuas ncauj.

2. Kev npaj ntawm cov hlau foamed

Txawm hais tias hlau ua npuas ncauj muaj keeb kwm ze li ntawm 50 xyoo, kev tshawb fawb thiab kev loj hlob ntawm cov hlau ua npuas ncauj feem ntau yog ua los ntawm cov hlau nplaum, tshwj xeeb tshaj yog kev tshawb fawb ntawm foamed aluminium yog qhov dav tshaj plaws. Qhov no yog vim qhov tsawg melting point ntawm aluminium thiab nws cov alloys, zoo casting zog, thiab yooj yim tuav ntawm molten hlau. Tsis tas li ntawd, cov ntaub ntawv uas tuaj yeem siv los ua cov hlau ua npuas dej muaj xws li cov hlau uas tsis tshua muaj melting point xws li cu, Zn thiab lawv cov alloys, tab sis cov ntaub ntawv no tsis tshua muaj ntau dua li kev tshawb fawb thiab kev loj hlob ntawm foam aluminium.

Rau kev tshawb fawb ntawm high melting point hlau ua npuas ncauj, muaj mas Ni-raws li, Ti-raws li thiab D-raws li alloys, thiab ntau lawm txoj kev yog mas hmoov metallurgy sintering. Cov ntawv ceeb toom hais txog qhov no tsuas yog tshwm sim nyob rau xyoo tas los no, xws li kev siv Ni-raws li alloys los tsim nyias nyias cov electrodes.

Cov ntaub ntawv tshawb fawb ntawm cov hlau foamed yog qhov tsawg dua, tsuas yog ob peb cov ntaub ntawv hais txog cov hlau uas muaj Taiwan kub ua npuas hlau tau pom, ib qho yog Cu-Fe. Kev tsim cov sn ua npuas ncauj hlau, uas cov ntsiab lus Fe (feem feem ntau) yog 60 feem pua ​​​​rau 80 feem pua, thiab cov cu yog 10 feem pua ​​​​rau 30 feem pua, uas yog tau los ntawm cov hmoov metallurgy sintering, thiab nws cov porosity yog 10 feem pua ​​​​rau 35 feem pua. [3U]; Lwm Fe-Cr-AI. RE Taijin, Fe suav rau 70 feem pua ​​​​~ 8O feem pua, kuj tsim los ntawm sintering txoj kev, Fe muaj nyob rau hauv daim ntawv ntawm fibers "; kuj tseem muaj Fe hmoov thiab lwm cov hmoov hlau ua raws li cov nplaum nplaum nplaum, thiab ces sintered kom tau ib daim ntawv nyias hlau ua npuas ncauj, uas yog siv los ua ib qho electrode, tsis tas li ntawd, muaj cov ntaub ntawv qhia txog kev npaj cov hlau ua npuas ncauj los ntawm txoj kev seepage, thiab qhia txog kev npaj cov hlau ua npuas ncauj los ntawm txoj kev hollow pob, tab sis lawv tsis tau nrov. .

Nyob rau hauv ib lo lus, kev npaj thiab daim ntawv thov ntawm high-melting hlau ua npuas ncauj tsuas yog nyob rau hauv nws cov me nyuam mos, thiab txoj kev yog kuj complex thiab yooj yim. Yog li ntawd, nws yog ib qho tsim nyog los tshawb nrhiav thiab tsim cov txheej txheem kev npaj rau cov hlau melting hlau ua npuas ncauj thiab lwm yam high-melting-point hlau thiab lawv cov alloys, thiaj li yuav siv tau sai li sai tau Cov khoom siv no muaj ntau yam khoom tshwj xeeb pab rau noob neej.

3. Cov yam ntxwv thiab kev siv ntawm cov hlau ua npuas ncauj

Txij li thaum muaj ntau qhov hauv cov hlau ua npuas dej, qhov loj, tus naj npawb, qhov sib xws, kev sib txuas thiab kev kaw ntawm lub qhov yuav cuam tshuam rau nws qhov kev ua tau zoo.

3.1 Cov yam ntxwv thiab cov yam ntxwv

1) Pore loj: Pore loj feem ntau yog hais txog qhov nruab nrab txoj kab uas hla ntawm pores, uas yog qhov tseem ceeb parameter ntawm ua npuas ncauj hlau. Qhov pore loj ntawm cov hlau ua npuas ncauj yog feem ntau loj dua, O. 1-10mm lossis ntau dua (feem ntau, qhov aperture ntawm hmoov metallurgy hlau tsis ntau tshaj 0.3mm).

2) Tag nrho cov porosity, zoo porosity: Tag nrho cov porosity yog hais txog qhov piv ntawm qhov ntim ntawm qhov pores mus rau tag nrho cov ntim (uas tuaj yeem tau txais los ntawm txoj kev hnyav). Txij li tsis yog txhua qhov pores txuas nrog ib leeg, qhov piv ntawm cov pores txuas nrog rau tag nrho cov ntim yog hu ua qhov zoo porosity. Tsuas yog thaum tag nrho cov pores txuas nrog, tag nrho L porosity yog sib npaug rau qhov zoo L porosity. Lub porosity ntawm hlau ua npuas ncauj yog qhov siab, thiab nws cov porosity yog nyob nruab nrab ntawm 40 feem pua ​​thiab 90 feem pua.

3) Los ntawm porosity: qhov piv ntawm qhov nruab nrab pore channel txoj kab uas hla mus rau qhov nruab nrab pore txoj kab uas hla ntawm txhua seem yog los ntawm porosity.

4) Lub ntiajteb txawj nqus tshwj xeeb thiab thaj chaw tshwj xeeb: lub ntiajteb txawj nqus ntawm cov hlau ua npuas ncauj yog lub teeb. Feem ntau tsuas yog 1/10-3/5 ntawm tib lub ntim ntawm cov hlau. Nws thaj chaw tshwj xeeb yog loj dua, uas yog lO-40cm²/cm³

3.2 Cov yam ntxwv ua haujlwm

3.2.1 Lub teeb yuag thiab lub ntiajteb txawj nqus me me

Vim tias muaj ntau qhov loj thiab me hauv cov hlau matrix, cov khoom siv no pom tseeb lub teeb hauv qhov hnyav. Lub ntiajteb txawj nqus yog me me. Qhov tshwj xeeb lub ntiajteb txawj nqus ntawm foamed aluminium ranges ntawm {{0}}.2 mus rau 0.5 g / cm, thiab nws tus nqi nruab nrab tsuas yog 1/10 ntawm cov txhuas.

3.2.2 Mechanical Properties

Lub zog tensile ntawm ua npuas ncauj hlau yog qhov tsawg. Lub zog tshwj xeeb kuj tseem qis, tab sis lub zog compressive thiab flexural zog yog siab. Lub zog tensile ntawm foamed aluminium tsuas yog hais txog 1/100 ntawm txhuas, thiab lub zog tshwj xeeb yog li 1/10 ntawm txhuas. Foamed aluminium muaj tsawg severability. Piv txwv li, txhuas ua npuas ncauj tsis muaj ductility ntawm hlau txhuas, thiab yuav luag tsis muaj yas deformation tshwm sim nyob rau hauv siab. Lub elastic modulus ntawm foamed aluminium ntsuas los ntawm dabtsi yog khoov kuaj yog hais txog 1/50-1/100 ntawm cov aluminium alloy.

3.2.3 Kev poob siab lub zog nqus cov yam ntxwv

Cov khoom siv hlau ua npuas dej muaj qhov sib txawv tshwj xeeb, tsis muaj kev taw qhia ntxeem tau, thiab tsis muaj qhov cuam tshuam. Los ntawm kev ntsuam xyuas kev ntxhov siab ntawm cov khoom siv no, nws pom tau tias nws txoj kev nyuaj siab poob qab qhov kev ntxhov siab, thiab nyob rau hauv lub compressive stress-strain curve E kab uas muaj ib tug ntev toj siab, hlau ua npuas ncauj yog ib yam khoom uas muaj feem xyuam rau lub zog nqus zog.

3.2.4 Thermophysical zog

Foamed hlau feem ntau muaj kev kub ntxhov, txawm tias qhov kub mus txog qhov melting point ntawm lub hauv paus alloy, nws yuav tsis yaj. Piv txwv li, ALMAG alloys muaj qhov kub thiab txias ntawm 560-640. C, tab sis ALMAG alloy ua npuas ncauj alloy yog rhuab mus rau 1400 nyob rau hauv qhov chaw. C tsis yaj thiab.

3.2.5 kis tau tus mob

Permeability yog rab rawg-tus yam ntxwv ntawm cov xov tooj ntawm tes ua npuas ncauj. Los ntawm kev hloov kho ntawm cov hlau ua npuas ncauj pore qauv (xws li porosity, pore loj, los ntawm porosity, thiab lwm yam). Foamed hlau cov ntaub ntawv nrog txawv permeability yuav tsum tau.

3.2.6 Acoustics thiab Hluav Taws Xob

Rau lub qhov taub hlau ua npuas ncauj, thaum lub suab yoj kov cov hlau nto, nws nkag mus rau hauv lub qhov ntawm cov hlau ua npuas ncauj los ntawm diffuse reflection, thiab sab hauv vibration ntawm cov hlau converts lub suab zog rau hauv lub tshav kub zog, uas plays lub luag hauj lwm nyob rau hauv lub suab nrov txo. . Electromagnetic nthwv dej tau siv los ntsuas cov hlau ua npuas ncauj, thiab nws tau pom tias cov hlau ua npuas dej kuj muaj qhov cuam tshuam ntawm cov khoom siv hluav taws xob, yog li cov hlau ua npuas dej kuj muaj kev tiv thaiv ntawm cov hluav taws xob tsis zoo.

3.3 Kev siv ua npuas ncauj hlau

Nyob rau hauv kev saib ntawm ntau yam ua npuas ncauj hlau hais saum toj no, muaj ntau yam ntaub ntawv thov teb ntawm ua npuas ncauj hlau. Qhov kev xav tau ntawm daim ntawv thov kuj yog qhov tseem ceeb ntawm kev tsim cov khoom siv tshiab no.

3.3.1 Siv cov khoom siv thermophysical zoo heev

Foamed hlau muaj thaj chaw loj tshwj xeeb, thiab tuaj yeem siv los ua cov khoom siv hluav taws xob thiab cov hluav taws xob rau cov xov tooj ntawm tes foamed; rau kaw-cell foamed hlau, nws tuaj yeem siv los ua cov khoom siv thermal rwb thaiv tsev.

3.3.2 Siv cov kev poob siab lub zog nqus cov yam ntxwv

Nws yog ib qho tseem ceeb ntawm kev siv cov hlau ua npuas ncauj rau kev tsim cov buffers thiab shock absorbers. Nws cov ntawv thov muaj xws li los ntawm qhov cuam tshuam ntawm lub tsheb mus rau qhov tsaws iav ntawm lub dav hlau, thiab nws tau ua tiav zoo siv hauv elevators, conveyor kev nyab xeeb pads, thiab lub zog nqus cov ntaub thaiv rau kev kub ceev grinder shields.

3.3.3 Siv permeability

Siv cov permeability ntawm hlau ua npuas ncauj, nws tuaj yeem siv los ua cov khoom tseem ceeb rau kev npaj cov lim dej. Piv nrog cov hmoov metallurgy ntxeem tau hlau, nws muaj cov yam ntxwv ntawm cov pore loj thiab siab porosity, thiab cov lim ua nrog nws muaj ntau yam kev siv, uas tuaj yeem siv los lim tawm cov khoom ntawm cov kua, cua lossis lwm yam airflows.

3.3.4 Siv cov khoom acoustic thiab electromagnetic

Siv lub suab-absorbing zog ntawm cov hlau ua npuas ncauj, nws yog tsuas yog siv rau kev txo suab nrov thiab txo suab nrov, xws li attenuation mufflers rau chav fais fab nroj tsuag, pneumatic cov cuab yeej, tsheb, thiab lwm yam. Nyob rau hauv Nyiv, cov txiaj ntsig tau txais txiaj ntsig tau txais hauv kev kub ceev tsheb ciav hlau. chav tshuab hluav taws xob, xov tooj cua kaw studios, thiab Shinkansen suab nqus.

3.3.5 Lwm yam kev siv

Bubble hlau kuj tseem siv tau rau hauv kev tsim kho kev lag luam, xws li sab hauv thiab sab nrauv kho kom zoo nkauj ntawm cov tsev, ntaub thaiv phab ntsa, phab ntsa, thiab lwm yam; nws kuj tseem siv tau los ua lub computer sawv ntsug; ntau lub thawv ntim khoom, thiab lwm yam ... Siv cov hluav taws kub ua haujlwm ntawm cov hlau ua npuas dej, nws tuaj yeem siv rau cov khoom siv refractory hauv kev lag luam xws li kev tsim kho; los yog los ntawm kev ua nws qhov, nws tuaj yeem siv rau cov khoom siv hluav taws xob. Hauv kev lag luam chemical, nws tuaj yeem siv los ua cov khoom thauj khoom catalyst. Tsis tas li ntawd, hlau ua npuas ncauj kuj tseem siv tau los ua ib qho ntxeem tau electrode.

Raws li qhov tshwm sim, daim ntawv thov ntawm cov hlau ua npuas ncauj yog qhov dav heev, nws tuaj yeem siv rau hauv ntau qhov chaw xws li kev tsim kho kev lag luam, kev lag luam aviation, kev lag luam hauv computer, kev thauj mus los thiab ntim kev lag luam, thiab nrog kev txhim kho txuas ntxiv ntawm cov txheej txheem ua npuas hlau thiab nws cov kev tshawb fawb thiab txoj kev loj hlob nrog rau qhov txuas ntxiv mus tob zuj zus, daim ntawv thov ua npuas hlau tseem nthuav dav. Yog li ntawd, kev tshawb fawb thiab kev loj hlob ntawm cov hlau ua npuas ncauj muaj txiaj ntsig zoo rau kev siv.