Sisebenzisa amakhukhi ukuthuthukisa ulwazi lwakho.Ngokuqhubeka nokuphequlula leli sayithi, uyavumelana nokusebenzisa kwethu amakhukhi.Ulwazi Olwengeziwe.
Ukukhiqiza okungeziwe (AM) kufaka phakathi ukudala izinto ezinezinhlangothi ezintathu, ungqimba olulodwa oluzacile kakhulu ngesikhathi, okulwenza lubize kakhulu kunomshini ovamile.Kodwa-ke, ingxenye encane kuphela yempushana efakwe phakathi nenqubo yomhlangano idayiswa engxenyeni.Okunye ke akuncibiliki, ngakho-ke kungasetshenziswa kabusha.Ngokuphambene, uma into idalwe ngokwejwayelekile, ukususwa kwezinto ngokugaya nomshini ngokuvamile kuyadingeka.
Izici ze-powder zinquma imingcele yomshini futhi kufanele zicatshangelwe kuqala.Izindleko ze-AM zizobe zingenamnotho uma kubhekwa ukuthi i-powder engancibilikisiwe ingcolile futhi ayikwazi ukuphinda isetshenziswe.Ukulimala kwezimpushana kubangela izenzakalo ezimbili: ukuguqulwa kwamakhemikhali omkhiqizo kanye nezinguquko ezimpahleni zemishini ezifana nokuma kwemvelo kanye nokusabalalisa usayizi wezinhlayiyana.
Esimweni sokuqala, umsebenzi oyinhloko ukudala izakhiwo eziqinile eziqukethe ama-alloys ahlanzekile, ngakho-ke sidinga ukugwema ukungcoliswa kwe-powder, isibonelo, ngama-oxides noma ama-nitrides.Esimweni sokugcina, le mingcele ihlotshaniswa ne-fluidity nokusabalala.Ngakho-ke, noma yikuphi ukuguqulwa kwezakhiwo ze-powder kungaholela ekusatshalalisweni okungeyona into efanayo yomkhiqizo.
Idatha evela ezincwadini zakamuva ibonisa ukuthi i-flowmeters ye-classical ayikwazi ukunikeza ulwazi olwanele mayelana nokugeleza kwe-powder ekukhiqizeni izithasiselo ze-powder bed.Mayelana nokubonakala kwezinto ezingavuthiwe (noma izimpushana), kunezindlela ezimbalwa zokulinganisa ezifanele emakethe ezinganelisa le mfuneko.Isimo sokucindezeleka kanye nenkambu yokugeleza kwe-powder kumele kube okufanayo esitokisini sokulinganisa kanye nenqubo.Ukuba khona kwemithwalo ecindezelayo akuhambisani nokugeleza kwendawo yamahhala esetshenziswa kumadivayisi we-AM kuma-shear cell testers nama-rheometer akudala.
I-GranuTools isungule ukugeleza komsebenzi kokuchazwa kwempushana ekukhiqizeni okungeziwe.Umgomo wethu oyinhloko kwakuwukuba nethuluzi elilodwa ngejometri ngayinye ukuze kwenziwe imodeli yenqubo enembile, futhi lokhu kuhamba komsebenzi kwasetshenziselwa ukuqonda nokulandelela ukuvela kwekhwalithi yempushana phezu kwamaphasi amaningi okuphrinta.Amaalloyi amaningana ajwayelekile e-aluminium (AlSi10Mg) akhethelwe ubude besikhathi obuhlukene emithwalweni ehlukene yokushisa (kusuka ku-100 kuya ku-200 °C).
Ukuwohloka kwe-thermal kungalawulwa ngokuhlaziya ikhono le-powder ukugcina icala.Ama-powders ahlaziywa ukugeleza (insimbi ye-GranuDrum), i-kinetics yokupakisha (insimbi ye-GranuPack) nokuziphatha kwe-electrostatic (insimbi ye-GranuCharge).Izilinganiso ze-kinetics zokuhlanganisa nokupakisha ziyatholakala kulezi zinqwaba ezilandelayo zempushana.
Ama-powder asakazeka kalula azothola inkomba ephansi yokuhlangana, kuyilapho ama-powder ane-dynamics yokugcwalisa ngokushesha azokhiqiza izingxenye zemishini ezine-porosity encane uma kuqhathaniswa nemikhiqizo okunzima ukuyigcwalisa.
Kukhethwe izimpushana ezintathu ze-aluminium alloy (AlSi10Mg) ezigcinwe elabhorethri yethu izinyanga ezimbalwa, ezinosayizi wezinhlayiyana ezihlukene, kanye nesampula eyodwa yensimbi engagqwali engu-316L, okubhekiselwa kuyo lapha njengamasampula A, B kanye no-C.Izici zamasampuli zingahluka kwezinye.abakhiqizi.Ukusabalalisa usayizi wezinhlayiyana zesampula kukalwe ngokuhlaziywa kwe-laser diffraction/ISO 13320.
Njengoba zilawula imingcele yomshini, izakhiwo ze-powder kufanele zicatshangelwe kuqala, futhi uma sicabangela ukuthi i-powder engancibilikisiwe ingcolile futhi ingenakuphinda isetshenziswe, izindleko zokukhiqiza okungeziwe ngeke zibe ukonga njengoba singathanda.Ngakho-ke, kuzophenywa imingcele emithathu: ukugeleza kwempushana, ukupakisha kinetics kanye ne-electrostatics.
Ukusabalala kuhlobene nokufana kanye "nobushelelezi" bongqimba lwempushana ngemva kokusebenza kabusha.Lokhu kubaluleke kakhulu njengoba izindawo ezibushelelezi kulula ukuziphrinta futhi zingahlolwa ngethuluzi le-GranuDrum elinesilinganiso senkomba yokunamathela.
Ngenxa yokuthi ama-pores angamaphuzu abuthakathaka entweni, angaholela ekuqhekekeni.I-Packing Dynamics iyipharamitha yesibili ebalulekile ngoba ama-powders apakisha ngokushesha ane-porosity ephansi.Lokhu kuziphatha kukalwe nge-GranuPack ngevelu elingu-n1/2.
Ukuba khona kokushaja kagesi ku-powder kudala amandla ahlangene aholela ekwakhiweni kwama-agglomerate.I-GranuCharge ikala ikhono lempushana lokukhiqiza ukushaja kwe-electrostatic lapho ithinta into ekhethiwe phakathi nokugeleza.
Ngesikhathi sokucubungula, i-GranuCharge ingabikezela ukuwohloka kokugeleza, njengokwakheka kongqimba ku-AM.Ngakho-ke, izilinganiso ezitholiwe zizwela kakhulu esimweni sokusanhlamvu (i-oxidation, ukungcola kanye nokuqina).Ukuguga kwempushana etholiwe bese kubalwa ngokunembile (± 0.5 nC).
I-GranuDrum isuselwe kumgomo wesigubhu esijikelezayo futhi iyindlela ehleliwe yokulinganisa ukugeleza kwempushana.Isilinda esivundlile esinezindonga eziseceleni ezibonisa ngale siqukethe ingxenye yesampula yempushana.Isigubhu sizungeza i-axis yayo ngesivinini esingu-2 kuya ku-60 rpm, futhi ikhamera ye-CCD ithatha izithombe (kusuka ku-30 kuya ku-100 izithombe ngezikhathi zesekhondi elingu-1).Isixhumi esibonakalayo somoya/impuphu sikhonjwa esithombeni ngasinye kusetshenziswa i-algorithm yokuthola unqenqema.
Bala indawo emaphakathi yesixhumi esibonakalayo kanye nama-oscillations azungeze lesi simo esimaphakathi.Ngesivinini ngasinye sokuzungezisa, i-engeli yokugeleza (noma “i-engeli eguquguqukayo yokuphumula”) i-αf ibalwa ukusuka endaweni yokusebenzelana emaphakathi, futhi inkomba yokunamathela eguquguqukayo engu-σf, ebhekisela ekubopheni kwezinhlayiyana, ihlaziywa ngokuguquguquka kwesixhumi esibonakalayo.
I-engeli yokugeleza ithonywa inani lamapharamitha: ukungqubuzana phakathi kwezinhlayiya, umumo nokuhlangana (van der Waals, electrostatic and capillary forces).Izimpushana ezihlangene ziphumela ekugelezeni kwezikhawu, kuyilapho izimpushana ezingahlangene ziphumela ekugelezeni okuvamile.Amanani amancane we-engeli yokugeleza αf ahambisana nezakhiwo ezinhle zokugeleza.Inkomba yokunamathela eguquguqukayo eduze ne-zero ihambisana ne-powder engahlangene, ngakho-ke, njengoba ukunamathela kwe-powder kwanda, inkomba yokunamathela iyanda ngokufanele.
I-GranuDrum ikuvumela ukuthi ulinganise i-engeli ye-avalanche yokuqala kanye ne-aeration yempushana ngesikhathi sokugeleza, kanye nokukala inkomba yokunamathela engu-σf kanye ne-engeli yokugeleza engu-αf kuye ngesivinini sokujikeleza.
Ukuminyana kwenqwaba ye-GranuPack, ukuminyana kokuthepha kanye nezilinganiso zesilinganiso se-Hausner (ebizwa nangokuthi “izivivinyo zokuthinta”) zidume kakhulu ekufanekisweni kwempushana ngenxa yokulula nesivinini sokulinganisa.Ubuningi be-powder kanye nekhono lokwandisa ukuminyana kwayo yimingcele ebalulekile ngesikhathi sokugcina, ukuthutha, i-agglomeration, njll. Inqubo ephakanyisiwe ichazwe ku-Pharmacopoeia.
Lesi sivivinyo esilula sinezinkinga ezintathu ezinkulu.Izilinganiso zincike ku-opharetha futhi indlela yokugcwalisa ithinta ivolumu yokuqala ye-powder.Izilinganiso ezibonakalayo zevolumu zingaholela emaphutheni amakhulu emiphumeleni.Ngenxa yobulula bokuhlolwa, sidebesele ukuhlangana kwe-dynamics phakathi kobukhulu bokuqala nobokugcina.
Ukuziphatha kwempushana efakwe esitokisini esiqhubekayo kwahlaziywa kusetshenziswa okokusebenza okuzenzakalelayo.Linganisa ngokunembile i-coefficient ye-Hausner Hr, ukuminyana kokuqala ρ(0) kanye nokuminyana kokugcina ρ(n) ngemva kokuchofoza kuka-n.
Inombolo yompompi ivamise ukumiswa kokuthi n=500.I-GranuPack iyisilinganiso sokuminyana sokuthepha esizenzakalelayo nesithuthukisiwe esisekelwe ocwaningweni lwakamuva oluguquguqukayo.
Ezinye izinkomba zingasetshenziswa, kodwa azibaliwe lapha.Impushana ifakwa kumashubhu ensimbi futhi idlule kunqubo eqinile yokuqalisa okuzenzakalelayo.I-extrapolation yepharamitha engu-n1/2 kanye nokuminyana okukhulu ρ(∞) kuthathwa ejini lokucinana.
Isilinda esingenalutho esingasindi sihlala phezu kombhede oyimpushana ukuze kugcinwe ileveli yokusebenzelana kwempushana/yomoya ngesikhathi sokuminyana.Ishubhu eliqukethe isampula yempushana liyakhuphuka lifinyelele ekuphakameni okungaguquki ∆Z bese liwela ngokukhululekile lifinyelele ekuphakameni, ngokuvamile okugxilwe kokuthi ∆Z = 1 mm noma ∆Z = 3 mm, likalwa ngokuzenzakalelayo ngemva komthelela ngamunye.Ngokuphakama, ungakwazi ukubala ivolumu V yenqwaba.
Ukuminyana isilinganiso sesisindo m kuya kuvolumu V yongqimba lwempushana.I-powder mass m iyaziwa, ukuminyana ρ kusetshenziswa ngemva kokukhululwa ngakunye.
I-Coefficient ye-Hausner Hr ihlobene nezinga lokuhlanganisa futhi ihlaziywa ngesibalo Hr = ρ(500) / ρ(0), lapho ρ(0) kuwukuminyana kwenqwaba kokuqala kanye no-ρ(500) ukuminyana kompompi okubaliwe ngemva kuka-500. ompompi.Imiphumela ikhiqizwa kabusha ngenani elincane lempushana (imvamisa engu-35 ml) kusetshenziswa indlela ye-GranuPack.
Izakhiwo ze-powder kanye nemvelo yezinto ezibonakalayo lapho idivayisi yenziwe khona yimingcele eyinhloko.Ngesikhathi sokugeleza, amashaji e-electrostatic akhiqizwa ngaphakathi kwempushana, futhi lezi zindleko zibangelwa umphumela we-triboelectric, ukushintshaniswa kwezindleko lapho okuqinile kuhlangana.
Lapho impushana igeleza ngaphakathi kwedivayisi, imiphumela ye-triboelectric ivela lapho kuthintana phakathi kwezinhlayiya kanye nasekuxhumaneni phakathi kwezinhlayiya nedivayisi.
Lapho ithintana nezinto ezikhethiwe, i-GranuCharge ikala ngokuzenzakalelayo inani le-electrostatic charge elakhiwe ngaphakathi kwempushana ngesikhathi sokugeleza.Isampula yempushana igeleza ku-V-tube edlidlizayo futhi iwela enkomishini ye-Faraday exhunywe kumshini wokulinganisa ugesi okala inkokhiso etholwa yimpushana njengoba ihamba ngeshubhu le-V.Ukuze uthole imiphumela ephindaphindekayo, phakela ishubhu ye-V njalo ngedivayisi ezungezayo noma edlidlizayo.
Umphumela we-triboelectric ubangela into eyodwa ukuthi ithole ama-electron ebusweni bayo futhi ngaleyo ndlela ishajwe kabi, kuyilapho enye into ilahlekelwa ama-electron ngakho ishajwa kahle.Ezinye izinto zithola ama-electron kalula kunezinye, futhi ngokufanayo, ezinye izinto zilahlekelwa ama-electron kalula.
Iyiphi impahla eba yinegethivu futhi ehle incike ekuthambekeleni okuhlobene kwezinto ezihilelekile ekuzuzeni noma ekulahlekelweni kwama-electron.Ukumela lezi zitayela, uchungechunge lwe-triboelectric oluboniswe kuThebula 1 lwakhiwe.Izinto ezivame ukukhokhiswa kahle nezinye ezivame ukukhokhiswa kabi zibaliwe, kuyilapho izinto ezingabonisi ukuthambekela kokuziphatha zibalwe maphakathi nethebula.
Ngakolunye uhlangothi, leli thebula linikeza kuphela ulwazi mayelana nomkhuba wokuziphatha kokushaja okubalulekile, ngakho-ke i-GranuCharge yadalwa ukuze inikeze amanani anembile okuziphatha kwe-powder.
Kwenziwa izivivinyo eziningana ukuze kuhlaziywe ukubola kokushisa.Amasampula ashiywe ku-200 ° C ihora elilodwa kuya kwamabili.Impushana ibe isihlaziywa ngokushesha ngeGranuDrum (igama elishisayo).Impushana ibe isifakwa esitsheni ize ifinyelele izinga lokushisa elizungezile bese ihlaziywa kusetshenziswa i-GranuDrum, i-GranuPack ne-GranuCharge (okungukuthi “kubanda”).
Amasampula aluhlaza ahlaziywa kusetshenziswa i-GranuPack, i-GranuDrum ne-GranuCharge endaweni efanayo yomswakama/izinga lokushisa legumbi, okungukuthi umswakama ohlobene no-35.0 ± 1.5% kanye nezinga lokushisa elingu-21.0 ± 1.0 °C.
Inkomba yokuhlangana ibala ukugeleza kwempushana bese ihambisana nezinguquko endaweni yesixhumi esibonakalayo (impushana/umoya), ebonisa amandla amathathu kuphela okuxhumana (van der Waals, capillary kanye ne-electrostatic).Ngaphambi kokuhlola, rekhoda umswakama ohlobene (RH, %) nezinga lokushisa (°C).Bese uthela impushana esitsheni sesigubhu bese uqala ukuhlola.
Siphethe ngokuthi le mikhiqizo ibingazweli ku-caking uma sicabangela amapharamitha we-thixotropic.Kuyathakazelisa ukuthi ukucindezeleka okushisayo kwashintsha ukuziphatha kwe-rheological kwezimpushana zamasampula A no-B kusukela ekuqinisweni kwe-shear kuya ekunciphiseni ukugunda.Ngakolunye uhlangothi, amasampuli C kanye ne-SS 316L awazange athintwe izinga lokushisa futhi abonise ukujiya kokugunda kuphela.Impushana ngayinye ibonise ukusabalala okungcono (okungukuthi inkomba yokuhlangana ephansi) ngemva kokushisisa nokupholisa.
Umphumela wokushisa nawo uncike endaweni ethile yezinhlayiya.Uma kukhulu ukuqhutshwa kwe-thermal kwempahla, umphumela uba mkhulu kuzinga lokushisa (okungukuthi ???225°?=250?.?-1.?-1) kanye no-?316?225°?=19?.?-1.?-1), uma izinhlayiya zincane, umphumela wokushisa ubaluleke kakhulu.Ukusebenza emazingeni okushisa aphakeme kuwukukhetha okuhle kwezimpushana ze-aluminium ingxubevange ngenxa yokwanda kokusabalala kwazo, futhi amasampuli apholisiwe afinyelela ukugeleza okungcono nakakhulu uma kuqhathaniswa nezimpushana ezihlanzekile.
Ocwaningweni ngalunye lwe-GranuPack, isisindo sempushana sarekhodwa ngaphambi kokuhlolwa ngakunye, futhi isampula yaba ngaphansi kwemithelela engu-500 nemvamisa yomthelela engu-1 Hz ngokuwa kwamahhala kweseli yokulinganisa engu-1 mm (amandla omthelela ∝).Amasampuli asakazwa kumaseli wokulinganisa ngokuya ngemiyalelo yesofthiwe ngaphandle komsebenzisi.Izilinganiso bese ziphindaphindwa kabili ukuze kuhlolwe ukukhiqizwa kabusha nokuhlola incazelo kanye nokuchezuka okujwayelekile.
Ngemva kokuqedwa kokuhlaziywa kwe-GranuPack, ukuminyana kokuqala kokupakisha (ρ(0)), ukuminyana kokugcina kokupakisha (ngokuchofoza okumbalwa, n = 500, okungukuthi ρ(500)), isilinganiso se-Hausner/Carr index (Hr/Cr) , nokubili okurekhodiwe. amapharamitha (n1/2 kanye no-τ) ahlobene namandla okuhlanganisa.Ukuminyana okuhle kakhulu ρ(∞) nakho kuyaboniswa (bona iSithasiselo 1).Ithebula elingezansi lihlela kabusha idatha yokuhlola.
Amanani 6 kanye no-7 abonisa amajika okucinana esewonke (ukuminyana ngobuningi uma kuqhathaniswa nenani lemithelela) kanye nesilinganiso sepharamitha ye-n1/2/Hausner.Amabha amaphutha abalwe kusetshenziswa okumaphakathi aboniswa kwikhevu ngayinye, futhi ukuchezuka okujwayelekile kubalwe kusukela ekuhlolweni kokuphindaphinda.
Umkhiqizo wensimbi engu-316L ubuwumkhiqizo osinda kakhulu (ρ(0) = 4.554 g/mL).Mayelana nokuminyana kokuthepha, i-SS 316L kuseyimpushana enzima kakhulu (ρ(n) = 5.044 g/mL), ilandelwa Isampula A (ρ(n) = 1.668 g/mL), ilandelwe Isampula B (ρ (n) = 1.668 g/ml) (n) = 1.645 g/ml).Isampula C beliphansi kakhulu (ρ(n) = 1.581 g/mL).Ngokobuningi benqwaba yempushana yokuqala, sibona ukuthi isampula A ilula kakhulu, futhi kucatshangelwa iphutha (1.380 g/ml), amasampula B no-C anenani elicishe lilingane.
Uma i-powder ishisa, isilinganiso sayo se-Hausner siyancipha, okwenzeka kuphela kumasampula B, C kanye ne-SS 316L.Kusampula A, lokhu akunakwenziwa ngenxa yobukhulu bamabha wephutha.Ku-n1/2, amathrendi epharamitha anzima kakhulu ukuwakhomba.Ngesampula A kanye ne-SS 316L, inani le-n1/2 lehla ngemva kwamahora angu-2 ngo-200 ° C, kuyilapho kuma-powder B no-C lenyuka ngemva kokulayisha okushisayo.
Isiphakeli esidlidlizayo sisetshenziswe ekuhloleni ngakunye kwe-GranuCharge (bona Umfanekiso 8).Sebenzisa ipayipi lensimbi engu-316L.Izilinganiso ziphindwe izikhathi ezingu-3 ukuze kuhlolwe ukukhiqizwa kabusha.Isisindo somkhiqizo osetshenziswe esilinganisweni ngasinye sasicishe sibe ngu-40 ml futhi ayikho impushana etholakele ngemva kokulinganisa.
Ngaphambi kokuhlolwa, isisindo sempushana (mp, g), umswakama womoya ohlobene (RH, %), nezinga lokushisa (°C) kuyarekhodwa.Ekuqaleni kokuhlolwa, linganisa ukuminyana kokushaja kwempushana eyinhloko (q0 ku-µC/kg) ngokwethula impushana enkomishini ye-Faraday.Okokugcina, rekhoda isisindo sempushana bese ubala ukuminyana kokugcina kweshaji (qf, µC/kg) kanye no-Δq (Δq = qf – q0) ekupheleni kokuhlolwa.
Idatha ye-GranuCharge eluhlaza iboniswa kuThebula 2 nakuMfanekiso 9 (σ ukuchezuka okujwayelekile okubalwe kusukela kumiphumela yokuhlolwa kokukhiqiza kabusha), futhi imiphumela yethulwa njengama-histogram (kuboniswa kuphela u-q0 no-Δq).I-SS 316L yayinezindleko zokuqala eziphansi kakhulu;lokhu kungase kube ngenxa yokuthi lo mkhiqizo une-PSD ephakeme kakhulu.Ngokuphathelene nenani lenkokhelo yokuqala ye-aluminium alloy powder eyinhloko, azikho iziphetho ezingafinyelelwa ngenxa yobukhulu bamaphutha.
Ngemva kokuxhumana nepayipi lensimbi engagqwali elingu-316L, isampula A ithole inani elincane lenkokhiso uma liqhathaniswa nezimpushana B no-C, okugqamisa ukuthambekela okufanayo, lapho i-SS 316L powder ihlikihlwa nge-SS 316L, kutholakala ukuminyana kokushaja okusondele ku-0 (bona i-triboelectric uchungechunge).Umkhiqizo B usakhokhiswa kakhulu kuno-A. Kusampula C, ithrendi iyaqhubeka (inkokhiso yokuqala evumayo kanye nenkokhiso yokugcina ngemva kokuvuza), kodwa inani lezindleko liyakhuphuka ngemva kokuwohloka kokushisa.
Ngemva kwamahora angu-2 okucindezeleka okushisayo ku-200 ° C, ukuziphatha kwempushana kuba okumangalisayo.Kumasampuli A no-B, inkokhiso yokuqala iyehla futhi inkokhiso yokugcina iyashintsha isuke ekubeni inegethivu iye kokuphozithivu.I-SS 316L powder yayinecala eliphakeme kakhulu lokuqala futhi ukuguqulwa kwayo kwe-charge density kwaba kuhle kodwa kwahlala kuphansi (okungukuthi 0.033 nC/g).
Siphenye umthelela wokuwohloka kwe-thermal ekuziphatheni okuhlanganisiwe kwe-aluminium alloy (AlSi10Mg) kanye nezimpushana zensimbi engagqwali ezingu-316L ngenkathi sihlaziya izimpushana zangempela emoyeni ozungezile ngemva kwamahora angu-2 ku-200°C.
Ukusetshenziswa kwama-powders ekushiseni okuphezulu kungathuthukisa ukusabalala komkhiqizo, futhi lo mphumela ubonakala ubaluleke kakhulu kuma-powders anendawo ethile ephezulu kanye nezinto ezine-conductivity ephezulu yokushisa.I-GranuDrum yasetshenziselwa ukuhlola ukugeleza, i-GranuPack yasetshenziselwa ukuhlaziywa kokugcwalisa okuguquguqukayo, futhi i-GranuCharge yasetshenziselwa ukuhlaziya i-triboelectricity ye-powder ethintana ne-316L yensimbi engenasici.
Le miphumela yasungulwa kusetshenziswa i-GranuPack, ebonisa ukuthuthukiswa kwe-Coefficient ye-Hausner ye-powder ngayinye (ngaphandle kwesampula A ngenxa yephutha lesayizi) ngemva kwenqubo yokucindezeleka okushisayo.Uma ubheka amapharamitha okupakisha (n1/2), awekho amathrendi acacile njengoba eminye imikhiqizo ikhombisa ukwenyuka kwejubane lokupakisha kanti eminye ibe nomthelela ohlukile (isb. Amasampula B no-C).
Isikhathi sokuthumela: Jan-10-2023