cracks in d.sign pfm bridge after glaze

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emh56

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I just completed an upper and lower 32(thats right,32) teeth monster case. The upper is fine but the lower has hairline cracks after glazing.Whats the cure?Ive fired it a couple of times on lower temps trying to get it to heal but they're still there.
 
rkm rdt

rkm rdt

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Try firing without vacuum.
 
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Where are the cracks? Depending...could be too much unsupported porcelain, or bridges with massive metal in the pontics... Dont know what your porcelain is but Id suggest slow cool. Are the cracks evident as soon as it comes out of the oven, or showing up after its been sitting a bit? Where does the CTE of your alloy fall into the recommended range for that porc.? It all matters, but for a 'fix-NOW', Id go with a slowww cool. Use thin metal pegs, not heavy refractory type. Sorry to hear this.
 
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Sorry, I hope its not due in the morning.
 
sixonice

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I just completed an upper and lower 32(thats right,32) teeth monster case. The upper is fine but the lower has hairline cracks after glazing.Whats the cure?Ive fired it a couple of times on lower temps trying to get it to heal but they're still there.

like others have mentioned, doing a slow cool should help this case. in order to help you more, knowing the alloy and its composition you used would be very helpful. again, undersupported frameworks can be problematic, set your slow cool for about 5 or 6 minutes to give that large mass of alloy to cool gently. could be just as simple as that. finally, firing it on lower temps trying to heal the cracks isn't working because your below the sinterization temperature of the glass. you will have to fire it at the temp or program your doing your dentin & incisal bakes on. remove the glaze before you attempt to heal and slow cool.
 
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charles007

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Sandblast the case first! use the dsign glaze paste-powder over those areas, to seal the cracks, or just use all over to get an even finish. Fire at you bisbake as sixonice recommended using a long slow cool, maybe 5 minutes, not sure how long with dsign. May want to try a lower low temp, hate to see the porcelain pop off as its climbing into your furnace.
Even though I stopped using dsign several weeks ago, I used their dsign alloys for the fear of having problems.......I never had any checking-cracking with dsign 59...and still using it today.....
I also learned years ago that some alloys with matching cte for dsign ,don't work for some reason. If you are using a dsign alloy, I bet money your porcelain is unsupported. If you aren't using the dsign alloys, either change to them, or change porcelains.
Good luck, and don't touch the porcelain until its room temp after its fired!

Charles
 
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charles007

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Since you are having problems, I wouldn't recommend using dsign53....... If my memory serves me correctly, the dsign67 has a better cte match than the 59 I use, and the 59 matches better than the dsign 53....Much easier to have problems with these high cte alloys when frames aren't waxed correctly.

What alloy are you using emh56......do you have a name,,,,,,I want tell anyone !

Charles
 
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emh, I have a few more questions for you, is this the first case to crack, how long have you used Design, all of these good questions put before you will get great answers and it will help othersand not just your self and narrow down to your problem much faster. One quick note stay away from any water while opaquing IE metal surface sandblasting,cleaning brush.
 
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emh56

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Thanks for the response!Ive used dsign for 20 yrs. When I do a large bridge(seldom) with multiple firings sometimes Ill get this.Dsign has worked well over the years but I'm changing to Noritakes EX-3 Super porcelain because of cost.I use Talladiums Tilite Omega NP metal.It has worked very well too.My name is Ed. Thanks again!
 
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charles007

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Welcome aboard Ed.....Please let us all know if you were able to repair your bridge....

I started using Noritake the first 6 months it was sold in the USA, about 18+ years ago..... Never seen it check, or crack, even on the largest of cases........If you use an Noble alloy with Noritake, keep it under 30% silver.

Charles
 

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