Zirkonzahn Prettau and Zr problems

[MrSae]

We are working with Prettau for about 2 years, and we experienced few times that the material broke after sintering, zircon and prettau also. Did you ever experience that kind of problem? We can't find where the problem occurs. We are using exclusively Zirkonzahn products. Our furnace is also Zirkonzahn, and we were thinking maybe something isn't right with temperatures when sintering. Would you please tell at what temperature do you sintering Prettau and zircon? We are glazing in ceramic furnace at 831 Celsius.

 

[Marcusthegladiator CDT]

DLN will need to see photos of these failed frameworks to make any educated guess as to what the problem may be.

 

[MrSae]

Okay, I uploaded photos of one work that broke. It is Prettau. The crack happened when the work was in ceramic furnace. Also, the crack wasn't that big, we broke it totally. We think the it was thick enough not to broke.

What you think?

 

[MrSae]

Okay, I uploaded photos of one work that broke. It is Prettau. The crack happened when the work was in ceramic furnace. Also, the crack wasn't that big, we broke it totally. We think the it was thick enough not to broke.

What you think?

 

[Marcusthegladiator CDT]

Okay, I uploaded photos of one work that broke. It is Prettau. The crack happened when the work was in ceramic furnace. Also, the crack wasn't that big, we broke it totally. We think the it was thick enough not to broke.

What you think?

It's definitely thick. Are you letting your furnace cool at 45c/min or do you crank things down to 25c/min when your baking bridges?

 

[primus]

Probably already cracked before you even sinter.

Spruing issues perhaps?

Too much chatter/vibrations during milling? Throw some fresh tools in yo'mill?

Thicker sprues, more sprues?

I'd look at this type of stuff first.

Maybe the tools you use and the way you are cutting out the frame from the disk?

Again, vibration and chatter will set-up a crack that you will NOT see until it comes out of furnace.

I seriously doubt it is sintering temps.

 

[cadfan]

these parts must be slowly cooled down no metal pins thin parts with big surface near thick part with half surface ( crown outside inside surface , pontic only outside surface but 4 times more volume ) 25- 30 degrees up per minute and 8 minutes down to open the furnace the rest like Scotty said. Maybe not long enough dried before sintering

 

[KentPWalton]

I would probably have to agree with Primus. It was probably already cracked before sintering. It looks as if it were plenty thick to me.

Or I can bet what happened...and this is a big one. You MUST do your embrasures in the GREEN state!!! DO NOT use a disk in them after it's been fired. You cause micro-fractures in the ZR when you do that. I've had bridges break on us time and time again when we thinned the embrasures after it was sintered. After it's milled, take the diamond disk and then them down a bit to where you want them, then clean it up and fire it.

 

[Adigitalsmile]

Looks to me like they may have been in the zirconia prior to sintering or happened during the cooling. We also have the Prettau material and have experienced similar issues.

 

[CoolHandLuke]

is that pink porcelain over the frame? do you not think that the porcelain shrinkage had torn the zirc at its thinnest point ?

 

[settimius]

We are working with Prettau for about 2 years, and we experienced few times that the material broke after sintering, zircon and prettau also. Did you ever experience that kind of problem? We can't find where the problem occurs. We are using exclusively Zirkonzahn products. Our furnace is also Zirkonzahn, and we were thinking maybe something isn't right with temperatures when sintering. Would you please tell at what temperature do you sintering Prettau and zircon? We are glazing in ceramic furnace at 831 Celsius.

your problem is before sintering, do not use red lamp, dried in a Pyrex pot furnace for casting it to 450 C degrees with a speed 'rise of 3 degrees per minute, then you can sinters and your problems will be over!!

 

[grantoz]

I think you are opening the furnace too quickly my p95 doesn't open until 650c and on thick jobs I don't touch the job until its cooled right down even at 100 200 degrees in the middle the job can be 5-600degrees ,slow cooling and heating are very important. also your porcelain is looking under fired which may mean you are also heating it too quickly.The other main reason could be vibration in milling or cutting out particularly if you are hand milling with the zirkograph

 

[MrSae]

It's definitely thick. Are you letting your furnace cool at 45c/min or do you crank things down to 25c/min when your baking bridges?

The cooling temperature is at 45c/min. Do you think its too high?

 

[MrSae]

Probably already cracked before you even sinter.

Spruing issues perhaps?

Too much chatter/vibrations during milling? Throw some fresh tools in yo'mill?

Thicker sprues, more sprues?

I'd look at this type of stuff first.

Maybe the tools you use and the way you are cutting out the frame from the disk?

Again, vibration and chatter will set-up a crack that you will NOT see until it comes out of furnace.

I seriously doubt it is sintering temps.

The CAD CAM works very nice, no vibrations noticed. Also, we really pay attention to often change heads for milling in CAD CAM, and other tools also.

 

[MrSae]

Looks to me like they may have been in the zirconia prior to sintering or happened during the cooling. We also have the Prettau material and have experienced similar issues.

Did you resolve the problem somehow?

 

[MrSae]

is that pink porcelain over the frame? do you not think that the porcelain shrinkage had torn the zirc at its thinnest point ?

Yes it is porcelain. We really doubt it happened because of that. But interesting approach.

 

[DMC]

no way.....

 

[MrSae]

Here are photo of settings we use when baking glaze in Gemini 2 furnace.

 

[primus]

It was cracked before you did the proc.

Crack just grew.

Porc. is more than 10x weaker than Zr!!

 

[MrSae]

It was cracked before you did the proc.

Crack just grew.

Porc. is more than 10x weaker than Zr!!

We are trying to find the solution how to avoid cracks like this. Is there a possibility that that crack was in raw block before milling?
I mean, things like this not happening so often. But still, it would be good to know why. It would be very unpleasant to happen after cementing.

We are promoting 100% zirconia as best of best. The strongest material possible for restoration. We can't just let things like this to happen. We will risk our prestige.

By the way. Do you think Prettau is worth to continue investing in? Do you prefer other brands to work with? We are seriously thinking about trying Sagemax NexxZr