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Lab talk, the good, the bad, and the ugly
Metal
spruing FGC techniques
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<blockquote data-quote="ztech" data-source="post: 97684" data-attributes="member: 3022"><p>The best advice ever given to me in casting alloy is that the last area to cool <u>will</u> have porosity. Using this axiom you view the patterns in two ways. Thick areas will tend to stay hot longer and the center of the ring will stay hot longer. Thick crowns usually have porosity in and around the sprue area. This is caused because the mass of alloy in the crown moves the heat center toward it and away from the reservoir and into the area of the sprue. The way to stop this is to increase the reservoir size larger than the mass of the crown to be cast. I have cut my sprues into the different segments and weighed them. Knowing the weight of the unaltered reservoir portion I then weight the wax pattern. I make the reservoir 20-30% larger by weight and when I place it in the ring I make sure that the reservoir is closest to the center of the ring. If the porosity is not localized to the sprue area but is all throughout the casting then you have a different porosity problem and it is probably in the melting techniques.</p></blockquote><p></p>
[QUOTE="ztech, post: 97684, member: 3022"] The best advice ever given to me in casting alloy is that the last area to cool [U]will[/U] have porosity. Using this axiom you view the patterns in two ways. Thick areas will tend to stay hot longer and the center of the ring will stay hot longer. Thick crowns usually have porosity in and around the sprue area. This is caused because the mass of alloy in the crown moves the heat center toward it and away from the reservoir and into the area of the sprue. The way to stop this is to increase the reservoir size larger than the mass of the crown to be cast. I have cut my sprues into the different segments and weighed them. Knowing the weight of the unaltered reservoir portion I then weight the wax pattern. I make the reservoir 20-30% larger by weight and when I place it in the ring I make sure that the reservoir is closest to the center of the ring. If the porosity is not localized to the sprue area but is all throughout the casting then you have a different porosity problem and it is probably in the melting techniques. [/QUOTE]
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Lab talk, the good, the bad, and the ugly
Metal
spruing FGC techniques
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