1. Nickel 2.4675 yog dab tsi, thiab nws muaj pes tsawg leeg ua kom muaj kev ua haujlwm tshwj xeeb hauv qhov kub thiab txias li cas?
Teb:
Nickel 2.4675, sib xws rau UNS N10665 thiab feem ntau hu ua Hastelloy B-2, yog nickel-molybdenum alloy nrog Werkstoff Number 2.4675 hauv German cov ntaub ntawv txheej txheem txheej txheem. Qhov kev xaiv no yog siv dav hauv European thiab thoob ntiaj teb engineering specifications. Cov hlau yog tsim tshwj xeeb rau kev tiv thaiv tshwj xeeb los txo cov kua qaub, tshwj xeeb tshaj yog hydrochloric acid ntawm txhua qhov siab thiab kub mus txog qhov kub.
Chemical Composition (Rau DIN / EN Standards):
| Element | Qhov hnyav% |
|---|---|
| Nickel (Ni) | Qhov nyiaj tshuav (65% min) |
| Molybdenum (hli) | 26.0 - 30.0 |
| Hlau (Fe) | Tsawg dua lossis sib npaug li 2.0 |
| Chromium (Cr) | Tsawg dua los yog sib npaug rau 1.0 |
| Cobalt (zeeg) | Tsawg dua los yog sib npaug rau 1.0 |
| Cov pa roj carbon (C) | Tsawg dua los yog sib npaug li 0.02 |
| Silicon (Si) | Tsawg dua lossis sib npaug li 0.10 |
| Manganese (Mn) | Tsawg dua los yog sib npaug rau 1.0 |
Cov yam ntxwv tseem ceeb ntawm Compositional:
High Molybdenum (26-30%):
Muab qhov tshwj xeeb tiv thaiv kom tsis txhob muaj cov kua qaub, tshwj xeeb tshaj yog hydrochloric acid (HCl) ntawm tag nrho cov concentrations thiab kub txog rau boiling.
Tsim cov yeeb yaj kiab tiv thaiv ntawm molybdenum oxides thiab ntsev uas ruaj khov hauv kev txo qis ib puag ncig.
Qhov tseem ceeb contributor rau corrosion kuj nyob rau hauv uas tsis yog -oxidizing acids.
Cov ntsiab lus molybdenum siab kuj muab kev tiv thaiv rau sulfuric, phosphoric, thiab acetic acids hauv kev txo qis.
Cov pa roj carbon tsawg (tsawg dua lossis sib npaug li 0.02%):
Minimizes carbide nag lossis daus thaum vuam thiab thermal raug.
Qhov tseem ceeb rau kev tswj hwm intergranular corrosion kuj.
Txo qhov kev pheej hmoo ntawm kev hnov mob hauv tshav kub- thaj tsam cuam tshuam thaum vuam.
Tsawg Silicon (tsawg dua lossis sib npaug rau 0.10%):
Txo qhov tsim ntawm intermetallic theem (Ni-Mo xaj theem) uas tuaj yeem embrittle cov hlau.
Txhim kho thermal stability thaum vuam thiab fabrication.
Tsawg Chromium (tsawg dua lossis sib npaug li 1.0%):
Tsis zoo li ntau cov nickel alloys uas tso siab rau chromium rau corrosion kuj, 2.4675 txhob txwm txwv chromium.
Chromium yuav cuam tshuam nrog molybdenum-raws li kev tiv thaiv zaj duab xis hauv kev txo cov kua qaub.
Qhov kev txwv no txhais tau hais tias cov hlau tsis haum rau oxidizing ib puag ncig.
Werkstoff Number System:
Werkstoff (Material) Number system yog tus qauv German (DIN) uas muab cov lej tshwj xeeb rau cov ntaub ntawv:
2.xxxx: Tsis yog- ferrous hlau thiab alloys
2.4675: Tshwj xeeb tsim cov nickel no -molybdenum alloy
Tus lej no tau lees paub thoob plaws Tebchaws Europe thiab ntau lub khw thoob ntiaj teb, ua rau nws tseem ceeb rau kev yuav khoom thoob ntiaj teb thiab kev qhia tshwj xeeb.
Sib piv rau Lwm Lub Npe:
| Qhov System | Lub npe |
|---|---|
| Werkstoff Number | 2.4675 |
| UNS | N10665 |
| Common Trade Name | Hastelloy B-2 |
| EN Txuj | NiMo 28 |
| ASTM / ASME | B335 / SWB-335 |
2. Dab tsi yog cov ntawv thov tseem ceeb rau Nickel 2.4675 round bars hauv European thiab thoob ntiaj teb tshuaj ua lag luam?
Teb:
Nickel 2.4675 round bars tau teev tseg rau cov ntawv thov tshwj xeeb los txo cov kua qaub, tshwj xeeb tshaj yog nyob rau hauv European chemical processing industries uas DIN / EN cov qauv tswj kev xaiv cov khoom. Daim ntawv puag ncig bar yog machined rau hauv cov khoom tseem ceeb rau qhov kev ua phem tshaj plaws.
Kev Siv Tshuaj Siv Tshuaj:
Hydrochloric Acid (HCl) Kev Pabcuam:
Muaj nuj nqi: Cov khoom xyaw hauv HCl ntau lawm, tuav, thiab khaws cia.
Vim li cas 2.4675 Bars: Tsis sib haum xeeb tiv thaiv HCl ntawm tag nrho cov concentrations thiab kub txog rau boiling. Siv rau:
Pump Shafts: Rau cov twj centrifugal ncig HCl hauv cov nroj tsuag tshuaj European.
Valve Stems: Rau li qub tswj HCl ntws raws li DIN / EN valve qauv.
Fasteners: Bolts, studs, thiab ceev rau flanged kev sib txuas hauv HCl systems.
Kev ntsuas: Thermowells, sensor vaj tsev ntsib DIN 43772 specifications.
Sulfuric Acid (H₂SO₄) Kev Pabcuam:
Muaj nuj nqi: Cheebtsam hauv sulfuric acid cov nroj tsuag thiab tuav cov tshuab.
Vim li cas 2.4675 Bars: Kev tiv thaiv zoo heev rau sulfuric acid hauv kev txo cov concentrations (txog 60%) ntawm qhov kub nruab nrab.
Cov khoom xyaw nquag: Agitator shafts, valve stems, twj tso kua mis shafts.
Phosphoric Acid (H₃PO₄) Kev Pabcuam:
Muaj nuj nqi: Cov khoom xyaw hauv phosphoric acid ntau lawm (qhov twg fluorides tsis tuaj).
Vim li cas 2.4675 Bars: Zoo ua haujlwm rau cov ntshiab phosphoric acid.
Kev Pabcuam Acetic Acid thiab Organic Acid:
Muaj nuj nqi: Cov khoom xyaw hauv acetic acid ntau lawm thiab tuav.
Vim li cas 2.4675 Bars: Kev tiv thaiv zoo rau tag nrho cov ntsiab lus ntawm acetic acid, txawm tias thaum boiling.
Pharmaceutical Industry Applications:
API Synthesis Reactor Cheebtsam:
Muaj nuj nqi: Agitator shafts, baffle kev txhawb nqa, thiab ntsuas hauv reactors rau cov khoom siv tshuaj nquag (API) synthesis.
Vim li cas 2.4675 Bars: Tiv thaiv cov hlau tsis huv; ua tau raws li GMP (Good Manufacturing Practice) cov cai.
High -Purity Water Systems:
Muaj nuj nqi: Cheebtsam hauv WFI (Dej rau Txhaj) tshuab.
Vim li cas 2.4675 Bars: Tiv thaiv corrosion los ntawm siab - dej huv thiab tshuaj tua kab mob.
European Industry Standards Ua raws li:
| Kev xav tau | Siv tau Standard |
|---|---|
| Cov Lus Qhia Txog Cov Khoom Siv Siab (PED) | 2014/68/EU |
| EN Khoom Specification | EN 10095 (rau cov khoom siv) |
| AD 2000 | German technical cai rau cov hlab ntsha siab |
| DIN Standards | Ntau yam rau cov khoom tshwj xeeb |
Yam Cheebtsam Machined los ntawm 2.4675 Bars:
| Cheebtsam | Bar Size Range | Cov Qauv Txheej Txheem |
|---|---|---|
| Pump Shafts | 20mm - 200mm txoj kab uas hla | DIN 24960 (cov khoom siv foob) |
| Valve Stems | 12mm - 100mm txoj kab uas hla | DIN 3352 (tus qauv valve) |
| Fasteners | M6 - M64 | DIN 931/933 (Ntev cov qauv) |
| Thermowells | 12mm - 50mm txoj kab uas hla | TIAB SA 43772 |
| Flanges | Machined los ntawm bar | TS EN 1092-1 |
Case Study: German Chemical Plant HCl Pump Shafts
Ib lub tuam txhab tshuaj German uas tsim HCl tau ntsib kev ua tsis tiav ntawm 1.4571 (316Ti) stainless hlau twj tso kua mis hauv 32% HCl kev pabcuam. Ncej lub neej nruab nrab tsuas yog 4-5 lub hlis vim muaj kev xeb sai. Hloov shafts machined los ntawm Nickel 2.4675 round tuav ib DIN EN 10095 ncua kev pab cuam lub neej tshaj 6 xyoo, tsis muaj kev ntsuas corrosion. Cov khoom xaiv tau ua raws li PED cov cai thiab tau sau nrog EN 10204 3.1 ntawv pov thawj.
3. Dab tsi machining yam ntxwv tshwj xeeb rau Nickel 2.4675 puag ncig tuav, thiab cov khw muag khoom European ua haujlwm zoo li cas?
Teb:
Machining Nickel 2.4675 round bars nthuav tawm cov teeb meem tseem ceeb zoo ib yam li lwm cov npib tsib xee-molybdenum alloys, tab sis cov khw muag khoom nyob sab Europe tau tsim cov tswv yim zoo rau kev tsim khoom kom zoo thaum tswj xyuas qhov ntev ntev uas yuav tsum tau ua los ntawm DIN cov qauv.
Kev txiav txim siab txog kev coj tus cwj pwm:
Siab zog:
Annealed tensile zog: 760 MPa (110 ksi) yam tsawg kawg nkaus.
Yuav tsum muaj cov cuab yeej siv tshuab nruj thiab siab dua txiav quab yuam.
Rapid Work Hardening:
Ua hauj lwm hardens ceev heev thaum lub sij hawm machining.
Qhov cuam tshuam: Yuav tsum txiav hauv qab ua haujlwm- txheej tawv tawv; zam kev txiav lub teeb.
Tsawg Thermal conductivity:
Thaum tshav kub kub concentrates ntawm tej cheeb tsam.
Qhov cuam tshuam: Yuav tsum tau ua kom txias thiab cua sov- cov ntaub ntawv tiv taus.
Gummy Chips:
Ua kom tawv, stringy chips.
Qhov cuam tshuam: Yuav tsum tau chip breakers thiab nti tswj cov tswv yim.
European Machining Practices:
Machinery Requirements:
Rigid CNC lathes nrog siab torque muaj peev xwm.
Siab -cov tshuab cua txias txias (50-100 bar ib txwm).
Chip conveyors rau kev ua haujlwm tas mus li.
Kev xaiv cuab yeej (ISO Standards):
| Kev ua haujlwm | ISO Code | Geometry |
|---|---|---|
| Tig (rough) | CNMG 120408-MM | Zoo rake, chip breaker |
| Tig (tiav) | DNMG 150404-F | Wiper geometry |
| Drilling | TIAB SA 6539 | Carbide, coolant los ntawm |
| Xov | TIAB SA 1835 | Daim ntawv profile |
Txiav Parameters (Metric Units):
| Kev ua haujlwm | Ceev (m / min) | Pub (mm / rev) | Qhov tob ntawm qhov txiav (mm) |
|---|---|---|---|
| Tig (rough) | 12-20 | 0.25-0.45 | 1.5-4.0 |
| Tig (tiav) | 15-25 | 0.08-0.20 | 0.3-0.8 |
| Drilling | 6-12 | 0.03-0.10 hli / rev | Peck lub voj voog |
| Xov | 8-15 | Xov xov | Ntau dhau |
Coolant thiab Lubrication:
Flood coolant nrog EP additives tseem ceeb.
Siab -siab los ntawm- cov cuab yeej coolant (50-100 bar) rau drilling.
Rau tapping, tshwj xeeb tapping pastes (chlorine - xaiv dawb muaj).
Kev ua haujlwm:
Hydraulic expansion chucks rau precision.
Nthuav so rau cov ncej ntev (DIN 24960 twj tso kua mis ncej).
Tailstock chaw txhawb nqa.
Surface Finish Capabilities (DIN Standards):
| DIN Specification | Yuav tsum tau ua tiav | Hom Achievable |
|---|---|---|
| DIN 24960 (Lub ntsej muag foob) | Tsawg dua lossis sib npaug li 0.8 μm Ra | Sib tsoo yuav tsum tau |
| DIN 3352 (Valve qia) | Tsawg dua lossis sib npaug li 1.6 μm Ra | Precision tig |
| General machining | Tsawg dua lossis sib npaug li 3.2 μm Ra | Txheem tig |
Kev Tswjhwm Zoo rau DIN EN ISO 9001:
| Tshawb xyuas | Khoom siv | Ntau zaus |
|---|---|---|
| Dimensional | Micrometers, calipers | Hauv - txheej txheem thiab zaum kawg |
| Nto tiav | Profilometer | Rau batch |
| Hardness | Rockwell tester | Rau cua sov |
| Kev ncaj | Ncaj nraim | 100% ntawm cov khoom tseem ceeb |
Common Challenges thiab Solutions:
| Kev sib tw | Kev daws |
|---|---|
| Cov cuab yeej siv ceev ceev | Txo ceev, coated carbides (TiAlN) |
| Qhov chaw tsis zoo | Wiper inserts, txo pub |
| Chip tswj | High -paj coolant, chip breakers |
| Ua hauj lwm hardening | Khaws nruj pub |
| Kev vibration | Rigid teeb, txo overhang |
4. Dab tsi yog kev tswj hwm thiab ntawv pov thawj uas yuav tsum tau siv rau Nickel 2.4675 round bars raws li European qauv?
Teb:
Nickel 2.4675 round bars rau cov ntawv thov European tseem ceeb yuav tsum muaj kev tswj xyuas kom zoo thiab ua tiav cov ntawv pov thawj raws li EN cov qauv thiab Cov Lus Qhia Cov Khoom Siv Siab (PED). Cov kev cai no ua kom muaj kev ncaj ncees ntawm cov khoom, traceability, thiab ua raws li European cov cai.
Tswj Specifications:
| Txuj | Title | Daim ntawv thov |
|---|---|---|
| TS EN 10095 | Thaum tshav kub kub resisting steels thiab npib tsib xee alloys | General specification |
| TS EN 10204 | Cov khoom siv hlau - Cov ntaub ntawv tshuaj xyuas | Hom ntawv pov thawj |
| AD 2000 | German technical cai rau cov hlab ntsha siab | Cov cuab yeej siv siab |
| PEB 2014/68/EU | Cov Lus Qhia Cov Khoom Siv Siab | Kev ua raws li European |
Cov ntaub ntawv pov thawj (EN 10204):
Hom 2.2 (Test Report):
Tsis yog -cov ntaub ntawv tshuaj xyuas tshwj xeeb.
Haum rau cov ntawv thov tsis yog - tseem ceeb.
Hom 3.1 (Kev Tshuaj Xyuas Daim Ntawv Pov Thawj 3.1):
Tshaj tawm los ntawm cov chaw tsim khoom, ywj pheej ntawm kev tshuaj xyuas sab nraud.
Daim ntawv pov thawj tias cov khoom ua tau raws li cov kev xav tau tshwj xeeb.
Yuav tsum tau rau siab tshaj -muaj cov khoom.
Hom 3.2 (Kev Tshuaj Xyuas Daim Ntawv Pov Thawj 3.2):
Tshaj tawm los ntawm cov chaw tsim khoom thiab tshawb xyuas los ntawm tus neeg sab nrauv sab nrauv (lub cev ceeb toom lossis tus neeg soj ntsuam tau tso cai).
Yuav tsum tau muaj kev nyab xeeb siab tshaj plaws (PED Qeb IV).
Chemical Composition Verification (Raws li EN 10095):
| Element | Kev xav tau (%) |
|---|---|
| Nickel | Qhov nyiaj tshuav (65% min) |
| Molybdenum | 26.0 - 30.0 |
| Hlau | Tsawg dua lossis sib npaug li 2.0 |
| Chromium | Tsawg dua los yog sib npaug rau 1.0 |
| Cov pa roj carbon | Tsawg dua los yog sib npaug li 0.02 |
| Silicon | Tsawg dua lossis sib npaug li 0.10 |
Mechanical Property Verification:
| Khoom | Qhov yuav tsum tau muaj (Room Kub) |
|---|---|
| Tensile zog (Rm) | Ntau dua lossis sib npaug li 760 MPa |
| Yield zog (Rp0.2) | Ntau dua lossis sib npaug li 350 MPa |
| Elongation (A5) | Ntau dua lossis sib npaug li 40% |
Tsis yog -Kev Tshawb Fawb Txog Kev Ua Phem (Rau EN Standards):
| Txoj kev | EN Txuj | Daim ntawv thov |
|---|---|---|
| Kev kuaj Ultrasonic | TS EN 10308 | Sab hauv suab |
| Kua Penetrant | TS EN 571-1 | Kev tshuaj xyuas saum npoo |
| Visual Examination | TS EN 10228-1 | Nto zoo |
Dimensional Inspection (Metric Units):
| Parameter | Kev kam rau siab (rau EN 10060) | Kev ntsuas ntsuas |
|---|---|---|
| Txoj kab uas hla (h9) | 0-0.036mm (rau 20mm bar) | Micrometer |
| Txoj kab uas hla (h11) | 0-0.090mm (rau 20mm bar) | Micrometer |
| Ntev | +2mm, -0mm | Daim kab xev ntsuas |
| Kev ncaj | Tsawg dua los yog sib npaug li 1mm / m | Ncaj nraim |
| Nto tiav | Raws li tau teev tseg | Profilometer |
Kev kuaj Corrosion:
TS EN ISO 3651-2:
Kev txheeb xyuas ntawm intergranular corrosion susceptibility.
Zoo ib yam li ASTM G28 Txoj Kev A.
Kev lees txais:
Corrosion tus nqi Tsawg dua los yog sib npaug rau 0.5 hli / xyoo raug.
Tshawb xyuas los ntawm lub chaw kuaj mob uas tau lees paub.
Cov ntaub ntawv pob (rau Kev Pabcuam Tseem Ceeb):
| Cov ntaub ntawv | Cov ntsiab lus |
|---|---|
| EN 10204 3.1 Daim ntawv pov thawj | Chemistry, mechanicals, kho cua sov |
| NDE Reports | UT, PT cov qhab nia |
| Daim Ntawv Qhia Dimensional | Ntsuas qhov ntev |
| Cov ntaub ntawv Traceability | Thaum tshav kub kub rau bar daim ntawv qhia |
| PED Tshaj Tawm | Ua raws li Cov Lus Qhia Cov Khoom Siv Siab |
| REACH Ua Raws Cai | Nqe lus hais txog kev ua raws li EU cov cai tswj hwm tshuaj |
Cov Lus Cog Tseg:
TS EN 10095
2.4675
Loj (hli hauv mm)
Kub naj npawb
Tus neeg tsim khoom lub npe lossis lub logo
CE cim (yog tias muaj rau PED)
Ntim thiab Kev Tiv Thaiv:
Tus kheej lub tes tsho yas.
Cov kaus mom kawg (yas lossis hlau).
Ntoo crating rau export.
Kev tiv thaiv noo noo rau kev xa khoom hiav txwv.
5. Cov kev xav txog kev kho cua sov dab tsi yog qhov tshwj xeeb rau Nickel 2.4675 round bars, thiab European cov qauv ntsuas thermal stability li cas?
Teb:
Kev kho cua sov ntawm Nickel 2.4675 puag ncig tuav yuav tsum muaj kev tswj xyuas kom ua tiav qhov kev pom zoo corrosion thiab cov khoom siv kho tshuab. Lub alloy qhov rhiab heev rau qhov txias txias yog qhov zoo- tau lees paub hauv European cov qauv, uas qhia meej cov cai nruj rau kev daws teeb meem annealing thiab quenching.
Kev kho cua sov Specifications (Raws li EN Standards):
Kev daws Annealing:
Kub: 1060℃- 1120℃(1940℃F - 2050℃F).
Sijhawm: Txaus kom ua tiav cov kev daws teeb meem (feem ntau 30-60 feeb ib 25mm thickness).
Cua txias: ceev ceev quench yuav tsum tau (dej quench nyiam).
Lub hom phiaj:
Dissolve precipitated theem.
Ua tiav homogeneous microstructure.
Optimize corrosion kuj.
Stress Relieving:
Feem ntau TSIS pom zoo rau 2.4675.
Qhov ntau ntawm 650℃- 870℃(1200℃F - 1600}℃F) txhawb kev cuam tshuam rau theem nag lossis daus.
Yog tias xav tau, sab laj nrog tus muag khoom thiab tshawb xyuas los ntawm kev kuaj corrosion.
Qhov tseem ceeb ntawm Rapid Quenching:
2.4675 yog raug rau tsim ntawm intermetallic theem (Ni-Mo xaj theem, tshwj xeeb tshaj yog theem) thaum raug kub nyob rau hauv thaj tsam ntawm 650℃- 870℃(1200℃F - 1600}℃F). Thaum lub sij hawm txias los ntawm annealing kub, lub bar yuav tsum dhau los ntawm no ntau yam. Yog tias qhov txias txias qeeb dhau, cov theem no los nag, ua rau:
Embrittlement: Kev poob hnyav ntawm ductility thiab cuam tshuam tsis kam.
Poob ntawm Corrosion Resistance: Kev nyiam nres ntawm theem ciam teb.
Risk of Cracking: Thaum lub sij hawm tom qab tuav, machining, los yog kev pab cuam.
European Standards Requirements:
| Txuj | Kev xav tau |
|---|---|
| TS EN 10095 | Qhia meej cov tshuaj annealed mob |
| AD 2000 Merkblatt W2 | Yuav tsum muaj ntaub ntawv kho cua sov |
| SIB 1925 | Ultrasonic kuaj rau lub suab sab hauv |
Cooling Rate Requirements:
| Txoj kab uas hla | Txoj kev txias |
|---|---|
| Tsawg dua los yog sib npaug li 12 hli | Dej quench los yog ceev roj cua txias |
| 12mm - 50 hli | Kev ywg dej yog qhov tseem ceeb |
| >50 hli | Dej quench nrog kev ntxhov siab; txaus ntshai |
Kev txheeb xyuas qhov kev kho cua sov kom zoo:
Kev kuaj corrosion (EN ISO 3651-2):
Txoj kev tshawb xyuas qhov tseem ceeb.
Corrosion rate Tsawg dua lossis sib npaug li 0.5 mm / xyoo qhia tias kev kho cua sov kom raug.
Microstructural Examination:
Txheeb xyuas qhov ciam teb ntawm cov qoob loo.
Ua los ntawm kev tsim nyog metallurgist.
Kev kuaj Hardness:
Txheeb xyuas qhov sib npaug ntawm ntu.
Feem ntau 90-100 HRB.
Sib piv nrog Txhim Kho Alloys:
| Yam | 2.4675 (B-2) | 2.4600 (B-3) |
|---|---|---|
| Thermal stability | txwv | Txhim kho |
| Qhov Loj tshaj plaws | Txwv los ntawm tus nqi cua txias | Qhov loj dua tuaj yeem ua tau |
| Kev Nyuaj Siab Ua Tau | Tsis muaj | Nrog kev txheeb xyuas |
| Weldability | Yuav tsum tau saib xyuas | Kev zam txim ntxiv |
European Kev Lag Luam Kev Ua Haujlwm:
Rau cov ntawv thov tseem ceeb uas xav tau qhov loj me me los yog kev ntxhov siab, cov neeg ua haujlwm nyob sab Europe feem ntau qhia cov kev txhim kho (2.4600 / B-3) kom tsis txhob muaj kev txwv thermal stability ntawm 2.4675.
Cov ntaub ntawv kho cua sov:
Qhov cub lub sij hawm- cov kab kos ntsuas kub.
Quenching cov ntaub ntawv (kub, agitation).
Daim ntawv pov thawj rau EN 10204 3.1.
Cov lus qhia rau kev kho cua sov:
Tiv thaiv saum npoo thaum kho (argon, nqus tsev, lossis txheej tiv thaiv).
Tsis txhob kis kab mob los ntawm cua sov cua (sulfur, halogens).
Txhawb nqa tuav kom tiv thaiv sagging.
Tam sim ntawd hloov mus rau quench nruab nrab.
Agitated dej quench rau qhov siab tshaj plaws cua txias.
Tshawb xyuas nrog kev kuaj corrosion tom qab kho.
