Vim li cas PFA Rhaub Rhaub nrog Smooth Outer Surface Resistant Cracking nyob rau hauv siab -Purity Ammonia Vapor Zoo dua li Textured Ib?
Tso lus
PFA yog qhov nruab nrab rau kev ua phem heev rau ammonia vapor (NH3) purity ntawm 50-100 degree, inducing ib puag ncig kev nyuaj siab tawg (ESC) ntawm cov polymer nyob rau hauv tensile kev nyuaj siab. Cov txheej txheej du (Ra < 0.2 µm) yog 3-5 × tawg tiv taus ntau dua li cov ntaub ntawv zoo nkauj (Ra> 0.8 µm) ntawm tib qhov kev ntxhov siab thiab ammonia raug. Cov txheej txheem yog kev nyuaj siab concentration: textured nto muaj microscopic peaks thiab kwj uas yog kev ntxhov siab raisers. Nrog rau kev siv cov loads (thermal expansion, siab, residual stress) lub hav hauv qab yuav muaj kev ntxhov siab concentrators nrog Kt qhov tseem ceeb ntawm 2-5x. Hauv cov chaw muaj kev ntxhov siab no, ammonia vapor nyiam adsorbs, txo qis lub zog ntawm lub cev tsim nyog rau kev pib tawg. Ib tug du nto tsis muaj kev ntxhov siab concentrators; Cov kev ntxhov siab uas siv yog qhov sib xws thiab qis dua qhov kev ntxhov siab tseem ceeb rau ESC. Rau ammonia vapor kev pab cuam muab ib tug du PFA nto, polished los yog li-extruded.
Ammonia Induced Environmental Stress Cracking
Ammonia tsis hnov tsw tshuaj nrog PFA (tsis muaj saw hlau los yog oxidation ntawm qhov kub hauv qab 120 degree). Nws yog tiag tiag tus neeg saib xyuas kev ntxhov siab tawg. Ammonia molecules yog me me (0.26 nm kinetic txoj kab uas hla) thiab polar heev. Lawv tawg mus rau hauv cov cheeb tsam amorphous ntawm PFA thiab rhuav tshem van der Waals kev sib cuam tshuam ntawm cov saw hlau. Cov ammonia-plasticized cheeb tsam yields hauv zos nyob rau hauv tensile stress (tsawg li 2-3 MPa) thiab ua ib tug frenzy. Txoj kev npau suav yuav tawg. Kev ntxhov siab nyob rau saum npoo nta txo qhov kev ntxhov siab tseem ceeb rau ESC hauv ammonia los ntawm 3-5 MPa rau PFA du mus rau 1-2 MPa rau textured PFA. Lub tshuab cua sov uas muaj kev ntxhov siab ntawm 4 MPa (los ntawm extrusion txias) tuaj yeem muaj sia nyob hauv ammonia yog tias du, tab sis tawg hauv lub lis piam yog tias textured.
Qhov saum npoo roughness ua cov ntawv notches. Rau V-zoo li tus zawj ntawm qhov tob d thiab lub hauv paus vojvoog r, qhov kev ntxhov siab concentration Kt ≈ 1+2√ dr . Rau ib tug raug textured nto (Ra=0.8 µm, r ≈ 0.5 µm, d ≈ 2 µm) peb tau Kt ≈ 1 + 2√(2/0.5)=1 + 2√4=1 + 4=5. Lub nominal kev nyuaj siab ntawm 4 MPa yog nce mus rau 20 MPa groove ntawm lub hauv paus yield zog. Kev tawg pib hauv ib teev.
Cracking Resistance vs Surface Roughness NH3 vapor (80 degree, 1 bar)
Surface Condition Ra (µm) Kt (max) 4 MPa Kev nyuaj siab 1st Crack (teev) Critical Stress ESC (MPa) Hom Ua Tsis Tau
Polished (mirror finish) 0.05–0.1 1.1–1.2 >10,000 (tsis muaj kab nrib pleb) 5–6 Tsis muaj (tsis pub dhau qhov txwv)
Extruded (nqus) 0.2 rau 0.3 1.3 rau 1.5 5,000 rau 8,000 4 rau 5Crazing, nplua
Raws li extruded (ib txwm) 0.4-0.6 1.8-2.2 1,500-3,000 3-4 Ntau cov kab nrib pleb zoo
Sandblasted (zoo) 0.8–1.2 3–5 200–500 1.5–2.5 Ib qho tseem ceeb tawg
Sandblasted ( ntxhib) 1.5–2.5 5–8 50–150 1.0–1.5 Kev tawg sai
Machined (cov cim cim) 0.5–1.5 (kev taw qhia) 4–10 20–100 0.5–1.0 Kev tawg raws cov cim cim
Chemically etched 0.6–{1}}–4 300–800 2–3 Nruab nrab tawg
Smooth Surfaces: Vim Li Cas Lawv Tseem Ceeb rau Ammonia Service
Dhau li ntawm kev ntxhov siab, cov chaw tiaj tus muaj tsawg qhov chaw ntawm ammonia adsorption. Ammonia molecules nyiam condense nyob rau hauv me me fissures (capillary condensation). Lub condensed ammonia muaj ib tug loj concentration thiab ib tug ntev kev sib cuag, uas accelerates lub plasticization. Qhov du, crevice-dawb nto yuav txo tau qhov nqus ntawm ammonia thiab yog li cov polymer nto tseem qhuav qhuav.
Cov npoo du kuj ua rau nws tuaj yeem pom cov kab nrib pleb uas tsim ua ntej. Ntawm qhov ntxhib saum npoo, me me tawg yog faus rau hauv qhov roughness; thaum lawv pom tias lawv tob tob. Ib qho tawg me me li 0.1 hli tuaj yeem pom hauv lub teeb zoo ntawm qhov chaw du kom nws tuaj yeem hloov ua ntej tsis ua haujlwm.
Ammonia Service Surface Npaj
Rau PFA rhaub rau ammonia vapor kev pab qhia:
Nto tiav: Ra 0.3 µm txiav txim los ntawm profileometer raws li ISO 4287.
Tsis muaj xuab zeb los yog beading tom qab extrusion.
Kev Tshawb Fawb: Nug kom pom qhov roughness pov thawj rau txhua qhov ntau lawm.
Polishing tshem tawm 0.05-0.1 hli ntawm PFA, yog li txo cov phab ntsa thickness. Polishing tuaj yeem ua rau cov ntaub nyias nyias rau 1.5 hli phab ntsa. Zoo dua los txhais tus du hauv thawj qhov chaw.
Piv txwv teb
