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| awemawson:
OOPS - wrong picture - try again ! |
| awemawson:
I started drawing up a model in Fusion 360 of a label for our 'Bore Hole Taps' - it's 25 mm x 75 mm and needs refining as the detail is going to be too fine for the silver sand I am using with sodium silicate. The idea is to use 'lost PLA' - ie encase the model in silver sand with 4% sodium silicate mixed in, set it with Carbon Di-Oxide, then burn the PLA out in a pottery kiln set to 650 Centigrade. More work needed. But as an adjunct to this I cut some slices off that big lump of coppery brass that I produced on Friday, and to my surprise found that it was hugely porous. Now I've had this with aluminium castings where hydrogen gets entrapped and forms bubbles but not with brass. I strongly suspect that the metal was far too hot, and the bubbles are zinc vapour. Hard to prove but I'll make a conscious effort next time to pour at a lower temperature. It's all a (re) learning curve ! |
| tom osselton:
Interesting I wouldn’t have thought about the temperature vs zinc gas bubble formation. |
| pycoed:
Look on the bright side, Andrew: you've just invented Oilite : :clap: |
| mattinker:
--- Quote from: awemawson on July 19, 2020, 04:26:45 PM ---ded. But as an adjunct to this I cut some slices off that big lump of coppery brass that I produced on Friday, and to my surprise found that it was hugely porous. Now I've had this with aluminium castings where hydrogen gets entrapped and forms bubbles but not with brass. I strongly suspect that the metal was far too hot, and the bubbles are zinc vapour. Hard to prove but I'll make a conscious effort next time to pour at a lower temperature. It's all a (re) learning curve ! --- End quote --- Hi Andrew, It may be just air bubbles due to your casting in an open crucible. Have a look at Olfoundryman &t=0s He's casting in Al, but his sprue and risers are worth looking at! Cheers, Matthew |
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