FEERITIC RING DEFECT- Dr Rao 1) Ferritic ring seen in Ductile iron microstructure on surface in shell Moulding. Reasons and remedial measure? 2) This phenomenon is observed in shell moulded CI also... 3) What grade of SG is that... 4) I do not have. But it is ferrite 5) What's the depth of skin? 6) For CI..Addition of a little Sn helps... 7) Why it comes? Tin we can not add in lower grades in SG iron 8) Thickness of ferrite rim or depth of rim will be 1.5mm. 9) Because faster cooling effect of shell 10) Yes. It is 0.5-1.0 mm. This is in unmachined area. 11) Customer do not want Ferrite on surface 12) This is a inherent properties of metal, you can not avoid surface decarb or ferrite rim on surface. It could be upto 1.5 mm depth. The same phenomenon would be observed in green sand castings as well as forgings too. I did not found any standards for permissible limit. However some times customer demands to maintain it within 0.8 mm. 12) Ferrite rim in shell mould specially could be due to slower cooling rate and heat generated at the metal mould interface due to resin burning. Metal remain hotter hence all the carbon gets free and gives ferritic rim. Need to see how faster heat can be extracted. 13) We used to pack the shell molds with second hand (scrap)steel balls of assorted size to enhance the cooling rate and coat certain areas with Tellurium paint. 14) Even GREEN sand can be tried. 15) We had seen some other practice, shell moulds were placed on high moisturised green sand and then poured.. 16) It's due to solid to solid transformation.... 17) Often...Tellurium wash is used for she'll water jackets...serves duel purpose...One ferrite rim and leakages ....Shell. ..
18) At Kulkarni engg Sangli- large production of shell mold CV Castings. Shells were embedded with only pouring cup protruding, covered with paper to avoid any sand falling in - embedded in floor in loose green sand. I think in Paranjape auto cast at shirwal same practice on trolley shell molds packrd in green sand & mold system like ARPA track trolley pushers & knock out . Sand collected like return sand system & back for filling via hopper. Faint memory of say about 30 years back 18) I have used Te- paste in Cast iron. Can be use in SG iron also? 19) % mixing please? 20) To add Shell thickness has to be minimal possible. (Core also and that too hollow) 21) In tappet production in shell molding I also used tellurium paint for chilling Soley Sb. 22) Also Hindustan Tractors - nke known as Gujarat Tractors Mahindra were using this paint for chilling to get good hardness was sourced from AFFCIL . 23) With what % do you mix the Te paste to 1.Graphite wash 2. Zircon wash 24) Dear Avinashji - we were buying ready to use - so formulation I have vno idea & in those days as beginner didn't have that much of quizzing ability - went with suppliers support'. 25) Foseco. Don't know %age 26) For tappets we used to cast directly onto m.s.plates. Even today same practice 27) Yes On M S plate too was cast & Cupola metal . 28) A mm or 2 on face on ms plate side in ht around . 29) Te paint..as made available by suppliers can not be used for castings being too potent a carbide promoter... It's applied as it is in CE cups and needs be diluted with..to a % suitable to the wall thickness of casting....