Zirconia fractures and craze lines after removal from oven

[mjGCD]

We have a DOF Craft 5x mill purchased from Cad-Ray that we are using to mill Zirconia crowns and bridges. Specifically, we use Katana STML Zirconia pucks. We fire them in a Cad-ray zirconia oven for about 20min.

We are getting a lot of craze lines/fractures visible after removing crowns from the furnace. I am not sure if it is a prep and crown design problem, a program issue with the oven where it is heating or cooling too fast or if we are having a different issue. Any tips for diagnosing and correcting the problem? TIA

 

[FASTFNGR]

We have a DOF Craft 5x mill purchased from Cad-Ray that we are using to mill Zirconia crowns and bridges. Specifically, we use Katana STML Zirconia pucks. We fire them in a Cad-ray zirconia oven for about 20min.

We are getting a lot of craze lines/fractures visible after removing crowns from the furnace. I am not sure if it is a prep and crown design problem, a program issue with the oven where it is heating or cooling too fast or if we are having a different issue. Any tips for diagnosing and correcting the problem? TIA

Elaborate on firing for 20min! Is that fast sintering or glaze stage?

 

[grantoz]

i think you are sintering them too long try 10 mins then quench them in water

 

[sidesh0wb0b]

Elaborate on firing for 20min! Is that fast sintering or glaze stage?

that has to be a long glaze cycle. im not aware of any oven that can heat up and ramp down in 20min
but boy that would be fun to watch!

 

[TheLabGuy]

Your first phone call should of been to cad-ray, especially Frank DeLuca, he will have you all sorted out in no time. This is a lab site, our ovens are ten times your size and milling capacity is probably a 100 times bigger is why we are steering you to cad-ray and they are great at support.

 

[Dentalmike]

Saw a presentation at last ceramic symposium where the presenter said he was sintering zirconia with microwave technology in 1 minute. Think it was in a university research facility. I thought that’s nice. We’d all like to have that. He seemed pretty happy about it. I guess that kind of microwave oven is too big and expensive.

 

[2000markpeters]

20 minute sinter cycle is ridiculous. Why do you think labs sinter for 9 hours?! We dont have problems. You should never delve into stuff you do not understand. Just saying

 

[ztech]

that has to be a long glaze cycle. im not aware of any oven that can heat up and ramp down in 20min
but boy that would be fun to watch!

The Zubler S430 can do it but would you want to.

 

[tuyere]

Slow ramping up and down helps this not happen. I don't know how you have a 20 minute sintering program, I'm assuming this is just your soak duration? The absolute shortest we can do from beginning to end is 1:20, on an oven specifically designed for rapid cycles, and you can only use it on small, thin-walled parts if you have any hope of it sintering through. No more than maybe 5 crowns for this cycle or else everything underfires due to the thermal mass involved. And the rapid thermal cycling is hell on the furnace, the linings and elements break down very quickly, even though their total time at 1500C + is much lower than the furnaces we run 12-hour cycles on 5 days a week.
But yeah, accept that sintering will take a day (or overnight), and extend your firing programs to make use of that time. Rapid sintering should be a tool of last resort, for rush cases, that sort of thing. It will output a lot more unusable crap than a longer, slower-ramping program will.

 

[sidesh0wb0b]

The Zubler S430 can do it but would you want to.

in 20 minutes, serioulsy?
if so, that is an impressive furnace and i have no idea why someone would r&d that type of cycle. thats faster than any speed cycle i have heard of!

please post the cycle? i would love to see the ramp up time/temp and how it is able to cool back down in 20min.