Need help with the big cases!

[zuikis313]

Hello
I made a huge full monolith zirkonia case with layered Noritake CZR gingiva only. And after the last glaze it came like this. Furnace is Ivoclar EP3000. I think it was because of a cooling time?What cooling time it should be?

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[zero_zero]

You might had micro cracks to begin with...

 

[Patrick Coon]

Hello
I made a huge full monolith zirkonia case with layered Noritake CZR gingiva only. And after the last glaze it came like this. Furnace is Ivoclar EP3000. I think it was because of a cooling time?What cooling time it should be?

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Hi, here is my answer from your other thread:

Glad to hear it is a little better after calibration. I notice you said a couple things here that intrigue me and give me a couple ideas to try. You mention using CZR porcelain (which tells me you are working on Zirconia). You also mention big cases. With both of these things in mind, here are a few things that consider when programing for these cases.

1. Zirconia is an insulator. What this means is it takes a long time heat-up and a long time to cool-down.
2. Most manufacturer's standard programs are designed for single units or at most a 3 unit bridge. Not for large cases with a lot of mass

So keeping these in mind what I suggest to customers is to drop your heat rate to about 25-30 degrees C. This gives these larger cases a chance to heat evenly and fully. You could also adjust your high temp upwards, but this is less predictable, and can be problematic when working on cases with large and small units together.

I would also recommend setting your Long Term Cooling to about 450C for all your smaller units (4 units or below). If it is larger than 4 units(or has massive pontics),up to a large roundhouse or All-on-4 type restoration, Long Term Cooling should be set to 250C. Setting these temps will keep the oven hood closed until the inside temp hits these marks. I would then allow these units to cool to room temperature, before removing them from the furnace platform. This will help to avoid cracking of the porcelain or Zirconia due to thermal stresses.

As always, anyone is welcome to give me a call at 716-264-2148 , to discuss this or other issues, or just to shoot the breeze!

Let me know if any of this helps, or even makes sense.

 

[zuikis313]

You might had micro cracks to begin with...

Hello Zero_zero
you mean it comes with the micro cracks from sinter oven?

 

[zero_zero]

Hello Zero_zero
you mean it comes with the micro cracks from sinter oven?

It could be from the milling process as well, I'd go over the strats...it happened to me that the tool went too deep while finishing one of the holes and the shank hit the wall, putting a crack in it. It didn't show till it hit the furnace with the glaze on.

 

[JohnWilson]

Go back and look at your CAM and look where the bar was placed for the sinter brace. I have seen this come up when its put too near the proximity to the access hole. Also how the sinter brace is sectioned from the pattern can be an issue here as well.

Look at how I place my bars. They are always on the thickest area of the pattern. I also make the offset very large to eliminate any possibility of crash and I do not have to run 25 simulations to KNOW it will fully mill with out a minor crash.

 

[zuikis313]

Thanks for the information zero_zero and John!I added a photo of mill im using Roland DWX 51D and Identica Blue scaner.

 

[RCKSTR]

It has to be cooled SUPER slow coming out of the glazing oven. We only do 2 glazes a day on big cases, they have to be SLOWLY cooled to the touch

 

[cadfan]

Start temp for ceramic 300 degrees Celsius 8 minutes dry minimum up rate 25-30 deg per minute hold 2-3 minutes cooling minimum 15 minutes down to 300 deg. care with metal pins !!! use better zirkon pins

 

[grantoz]

that crack shows how good zirconia is even with that massive its still together sure it will eventually end up in 2 pieces but its does hang in there.this shows how zirconia inhibits the cracks progress .Slow cool is the only way to go on these jobs.

 

[zuikis313]

Hello again
im remaking that big case!Maybe someone have an Ivoclar Porgramat EP3000 furnace and could help with the programs?Im using Emax ceram gingiva for this case but it comes out to burn.What im doing wrong?thanks

 

[esamuelr]

View attachment 22943 Go back and look at your CAM and look where the bar was placed for the sinter brace. I have seen this come up when its put too near the proximity to the access hole. Also how the sinter brace is sectioned from the pattern can be an issue here as well.

Look at how I place my bars. They are always on the thickest area of the pattern. I also make the offset very large to eliminate any possibility of crash and I do not have to run 25 simulations to KNOW it will fully mill with out a minor crash.

Those are great pics. I see you are also using sinter pins on the occlusal for horizontal sintering. Do you have a preference to horizontal sintering or is it a limitation of oven height and space for sintering?

 

[JohnWilson]

All ovens have a sweet zone, I also use a cover and stack, my big oven I can stack two courses and fit 4 arches no problem and have them all sinter evenly.

The dimension of your oven, weather its a bottom loader or a tray loader oven, how the elements surround the chamber, the number of elements all effect the look of the product.

Singles are super easy you can make them look decent any which way you sinter with the right heat ramp and cooling. The bigger jobs I feel sintering the way I have outlined is a bit more predictable. Of course you ovens may be different and all I can share is my experience.