[Jewelry making - Article 00437] - [Orchid] Bronze casting porosity

[Carlos]

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    I am having a real issue with porosity. I am casting in bronze. Here
    is my process. I use a vacuum casting machine to de-bubble my flasks
    and for the casting as well. I use a electro melt furnace to melt my
    metal. 

	Burnout cycle:
	2 hours at 300
	2 hours at 700
	3 hours at 1350 
	1 hour at casting temp( I have varied this from
	700-800-900 degrees)

    melting temp of the metal is 950 degrees, I am casting it at just
    under 1000 C. I am using 100% new metal. 

    I usually give it about 15 minutes and I quench the flask in water. 

    Several of the parts I cast look like the surface has a type of
    crystalisation. That is when I look at the surface under a magifying
    glass it appears like many lines that have spaces between them
    overlapping each other. Kind of like fiberglass. I hope I am clear
    what I am trying to explain. And the porosity is strongest in the
    center of the object. I have a link to a couple photos below so you
    can see what I am trying to describe: 

    http://www.geocities.com/vovinit/porosity.htm 

    These pics are worst case scenarios. But I still get it to some
    degree in all my casts. But not alway's this bad. 

    Sorry for the poor pics but I can only get so close to the object
    with my digital camera before it losses focus. 



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