Pigment Paste Viscosity in Coatings: Khaws Shear Hauv Kev Tswj Nrog Ceramic Rotary Lobe Twj
Nyob rau hauv ib tug coatings cog, tsiv pigment paste los ntawm ib lub tank mus rau lwm yam zoo li qhov tsawg tshaj plaws nthuav ib feem ntawm lub hnub. Nws kuj tuaj yeem yog vim li cas ib pawg tawm los nrog tsis muaj zog gloss, tsis zoo zais, lossis xim uas yuav tsis phim qhov kawg. Pigment paste viscosity hloov nrog shear, thiab lub twj tso kua mis feem ntau pib ua haujlwm. Hloov cov cuab yeej, hauv lwm lo lus, yog ib feem ntawm kev tsim txawm tias leej twg kho nws li ntawd lossis tsis ua. Nws ua batch - rau -batch xim, fineness stability, thiab thixotropy.
Pigment particles yuav tsum tau deagglomerated, dispersed, thiab taw qhia. Dispersants qhwv cov khoom thiab muab electrostatic repulsion los yog steric hindrance. Cov txheej ntawd ua rau lub paste ruaj khov. Nws tsis yog indestructible. Push shear tus nqi siab txaus-30,000 s⁻¹ yog ib qho kev lag luam uas muaj kab-thiab cov khoom uas twb tau muab cais tawm tuaj yeem sib sau ua ke, lossis cov txheej txheem dispersant tuaj yeem rub tawm. Dispersion zoo poob. Tsis muaj dab tsi zoo li ntawm lub twj tso kua mis. Cov txheej txheej qhia nws tom qab: tsawg dua gloss, tsis muaj zog zais, xim uas tau txav mus.
Cov twj centrifugal feem ntau yog qhov teeb meem pib. Lub nrawm- spinning impeller muaj qhov ceev ceev, thiab ua rau muaj zog shear rau hauv paste. Nyob rau tib lub ndlwg tus nqi, lub twj tso kua mis centrifugal feem ntau ua rau cov nqi qis tshaj 45,000 s⁻¹. Lub twj tso kua mis teb lobe tuaj yeem nyob ze ntawm 12,000 s⁻¹. Nrog rau qhov siab tshaj 5,000 mPa·s, lub twj tso kua mis centrifugal tsis yog ua haujlwm tsis zoo; nws tseem ntxiv zog shear uas muab tshuaj tsis tau. Lub iav twj tso kua mis tsis yog cov lus teb huv. Lub meshing clearance tsim localized shear uas muaj peev xwm tshaj qhov muab tshuaj txhuam qhov txwv.
Lub twj tso kua mis ceramic rotary lobe ua haujlwm ntawm lub hauv paus ntsiab lus sib txawv. Nws yog qhov zoo hloov chaw. Ob lub lobes tig nyob rau hauv sync thiab tsim kom muaj kev hloov pauv hauv lub chamber. Cov khoom yog thawb los ntawm, tsis flung. Lub lobes yeej tsis kov ib leeg los yog lub chamber phab ntsa. Clearances feem ntau khiav 0.1 mus rau 0.5 hli. Ntws los ntawm lub chamber yog maj mam, tsis muaj qhov turbulence ntawm lub impeller taub. Lobe ceev feem ntau yog 200 txog 500 rpm; Lub twj tso kua mis centrifugal yuav khiav ntawm 2,900 rpm. Cov khoom lag luam nyob ze rau laminar, thiab cov nqi txiav tuaj yeem tuav nyob ib ncig ntawm 10 txog 50 s⁻¹. Cov twj centrifugal feem ntau khiav 1,000 txog 10,000 s⁻¹.
Shear rate thiab shear force tsis zoo ib yam. Shear rate yog ceev npaum li cas qhov kev hloov gradient hloov hauv cov kua. Shear force yog dab tsi ua rau cov xim agglomerate. Tsawg ceev txo qis shear tus nqi, tab sis qhov kev tiv thaiv tiag tiag los ntawm lobe profile. Involute lossis cycloidal duab nyem cov khoom maj mam es tsis txhob tawm tsam nws. Agglomerates deform maj mam es tsis txhob tawg sai sai. Rau paste uas twb tau tawg lawm, qhov sib txawv tseem ceeb.
Ceramic pab lwm txoj kev. Pigment paste nrog titanium dioxide lossis hlau oxide yog abrasive. Cov twj hlau hlau hnav, lobes thiab chamber phab ntsa poob cov khoom, clearances qhib, thiab shear cwj pwm hloov. Ceramic liner tuaj yeem ncav cuag Vickers hardness saum 1,600 HV. Nws tiv taus hnav peb mus rau tsib npaug zoo dua li siab -chromium cam khwb cia hlau, thiab hauv kev pabcuam abrasive nws tuaj yeem kav plaub mus rau rau lub sijhawm ntev dua li lub twj tso kua mis hlau. Shear tsis nyob ruaj khov raws li lub twj tso kua mis muaj hnub nyoog. Ceramic kuj tsis tso cov hlau ions, uas tseem ceeb hauv cov txheej txheem siab -purity coatings qhov twg hlau paug tuaj yeem hloov xim xim lossis ua rau lub cev tsis muaj zog.
Kev pib thiab kev teeb tsa kev khiav hauj lwm tseem ceeb txawm tias qis -shear twj. Pigment paste feem ntau muaj qhov pom tseeb dua viscosity thaum tseem. Kev mus ncaj nraim mus rau qhov nrawm tuaj yeem ua rau muaj kev hloov pauv hauv lub chamber thiab luv luv hauv zos shear spike. Ib tug sib txawv zaus tsav nrog ib tug linear ramp coj ceev kom maj mam. Rau xim muab tshuaj txhuam saum toj 5,000 mPa·s, ua kom siab tshaj plaws nyob ze 200 rpm. Tshem tawm siab yuav tsum tau saib ib yam nkaus. Lub zog rov qab ntau dhau ua rau ntau dhau los ntawm lub lobe - mus rau -chamber clearance, thiab hauv zos shear zuj zus.
Piping tau overlooked. Muab tshuaj txhuam tsuas yog ntws los ntawm cov yeeb nkab. Lub luj tshib, reducers, thiab li qub tsim siab -shear aav los ntawm kev hloov ceev. Ib txoj kab tawm nyuaj tuaj yeem ntxiv shear txawm tias lub twj tso kua mis maj mam. Kev khiav ncaj thiab tsawg fittings txo qhov kev pheej hmoo.
Tsiv pigment paste tsis yog ib qho teeb meem ntawm "yog tias nws txav, nws ua haujlwm." Viscosity reacts rau shear, yog li hloov khoom siv los ua ib feem ntawm cov khoom kawg qhov kev ua tau zoo. Ceramic rotary lobe twj tso kua mis tsis tshem tawm shear. Nws khaws shear nyob rau hauv dab tsi muab tshuaj txhuam tau, thiab cov ntaub ntawv thiab geometry tuav tswj lub sij hawm.
