Zirconia Opaqueness & Shade Issues

[kristian]

We've run things relatively unchanged as far as our processes, machines and materials are considered, for the last 4 years. In the last few weeks we've got opaque and dead pontics (and other thick areas),and shades coming out too light.

I'm looking for ideas as to what to investigate next. We've looked into following so far:

• Zirconia type is the same (ArgenZ Esthetic),problem cases come from different lot #s
• Green stage cleaning and handling is the same (air, brush, gloves)
• Stain type is the same (ZZ Acid based),we've tried different batches (new bottles) too
• Brushes are the same (metal free)
• Drying times and equipment is the same
• Furnaces are the same (2 x Dekema μSic),Heating elements and Thermocouples get changed before hitting recommended hours
• Beads get changed every other week
• No new sintering trays, no ancient ones
• Sintering programs are unchanged and manufacturer recommended
• Furnaces think things are fine (no errors, no current fluctuations, logs look fine)
• Calibration (single tray, 1500°C program, one PTCR ring, correct chart) is within +-6°C

Not every unit in every load is showing issues. There's no differences between success rate between the two furnaces.

Any other ideas where to look at?

 

[CoolHandLuke]

remove your eyes.

maybe its your perception. did you recently change techs? are they being wierd?

 

[JMN]

We've run things relatively unchanged as far as our processes, machines and materials are considered, for the last 4 years. In the last few weeks we've got opaque and dead pontics (and other thick areas),and shades coming out too light.

I'm looking for ideas as to what to investigate next. We've looked into following so far:

• Zirconia type is the same (ArgenZ Esthetic),problem cases come from different lot #s
• Green stage cleaning and handling is the same (air, brush, gloves)
• Stain type is the same (ZZ Acid based),we've tried different batches (new bottles) too
• Brushes are the same (metal free)
• Drying times and equipment is the same
• Furnaces are the same (2 x Dekema μSic),Heating elements and Thermocouples get changed before hitting recommended hours
• Beads get changed every other week
• No new sintering trays, no ancient ones
• Sintering programs are unchanged and manufacturer recommended
• Furnaces think things are fine (no errors, no current fluctuations, logs look fine)
• Calibration (single tray, 1500°C program, one PTCR ring, correct chart) is within +-6°C

Not every unit in every load is showing issues. There's no differences between success rate between the two furnaces.

Any other ideas where to look at?

No easy answer, but just want to ensure you know that PCTR rings are a start, but do not give the whole picture. It just means your ovens temp was at that point and no higher. Not for how long, or if ramping and staging was accurate.

 

[kristian]

remove your eyes.

maybe its your perception. did you recently change techs? are they being wierd?

No new techs involved the processes, although all of them are weird as usual. "Opaque" and "dead looking" are bit subjective but two shades lighter is at least somewhat objective.

PTCR calibration should at least be comparable in a circular reference; if the same calibration program gives me 19.55 mm in January and everything is fine, running the same program in September and getting 19.55mm should indicate we're at least in the same neighbourhood. I think.

 

[grantoz]

put a thick bit of zirconia in the furnace no stain.if it comes out trans looking and completely fired you know its your staining technique not your furnace. hope this helps. also if you are using acid stains they dont look great unless you completely dry them this could be a problem its why we changed to water based stains this is also better for your furnace.

 

[Getoothachopper]

Have you tried Decontaminating the furnaces and trays ?. I use 'Purge Sinter' by Vision USA . Something else for you to try

 

[CoolHandLuke]

put a thick bit of zirconia in the furnace no stain.if it comes out trans looking and completely fired you know its your staining technique not your furnace. hope this helps. also if you are using acid stains they dont look great unless you completely dry them this could be a problem its why we changed to water based stains this is also better for your furnace.

you do know the "water" based ones are still highly acidic, right?

 

[grantoz]

ive seen what the acid based stains did to my drying lamp compared to the water based aquarell the acid based are far more corrosive so even if the h20 stains are acidic its nothing like the old acid based ones.so coolhand laugh all you like i can only go by my experience and ive seen that unless you dry out the acid stains properly you get colours just like the ones described in the thread. so how about we get back to helping the techo that started the thread i hope this helps kristian.

 

[JMN]

No new techs involved the processes, although all of them are weird as usual. "Opaque" and "dead looking" are bit subjective but two shades lighter is at least somewhat objective.

PTCR calibration should at least be comparable in a circular reference; if the same calibration program gives me 19.55 mm in January and everything is fine, running the same program in September and getting 19.55mm should indicate we're at least in the same neighbourhood. I think.

Have you been making observations that the affected zirconia came from all areas of the sinter furnace, or could the 'bad' ones be coming from the same region of the chamber.

 

[JMN]

Does it happen with any pre-shaded materials?

Does it happen with every shade, or only certain shades?

If multiple techs are staining, is there a shared source for all materials, or per bench/per tech.

Since it happens independant of lot #, it will have to be either caused by (or during usage of)
an oven issue,
a tech/station/bench specific issue,
a brush issue,
a brushed on material issue
a transport issue
an environment issue - mill(impurities in airline?new airline/trap/contaminamts in moisture trap. Burrs handled with contaminated hands(unlikely or most would have problems unless it is only ones using a specific burr)) furnace(new doesn't mean known good),or lab ambient.

I know some techs will use their mouths to repoint the brush bristles, if that is done there, even a change of lipstick or use of chapstick/lipbalm/cold sore ointment or something similar may be a culprit. Not necessarily by itself, but posssibly in combination with something else that may or may not have changed.


You did great investigations to determine what was not the problem, and @grantoz had it right with firing untouched materials to see what happens.

New gloves?
new bottle of commonly used stain?
new brush package opened?

Something changed, and as you've shown in your dilligence, finding that something is a labourious process sometimes. I know you]ve racked your brain, and I'm hitting you with lots of options, but just keep detailed records of what was handled by who and had what used on it and was where in which furnace for a few days and the answer will reveal itself eventually.

Wish you well. And I'm really curious as towhat's happening too.

 

[Joon Hong]

check your electricity voltage stability
few years ago I had same problem with new sintering machine my lap purchased
old machine had no problem, but on new one only
so the new one my lab purchsed (it was cheap one by the way) required 220V to 240V
my boss hired cheap electrician, and he did poor job
so the voltage was not stable, and was lower than 220V most of the time
sintering manufacture tech support told me the machine would try to compensate shortage of voltage for (higher temperature or longer program) (don't remember this part well)
after we fixed electricity issue, everything was good

hope this helps

English is not my 1st language as you can see, excuse me on that and let me know if something is not clear

 

[deadhead]

We have had the same issue in the past, and it took us a while to figure out what was going on because just like you our process didnt change(meaning our material, staining technique, oven and even the technician working on green state and staining never changed) After doing intensive investigating we found out that our issue was dirty heating elements and the brush that was being used for pre-staining had some old dry stain on the brush which was causing off coloring. Once we started cleaning our heating elements on a regular bases and started using new brushes every few weeks(well now we use pre shaded blanks so no more pre shading) our issue stopped and we started getting our normal results again. So basically it can come down to not the process itself but maybe the tools used for each step. From our experience we noticed that dirty brushes, hands, heating elements, and tools are usually the cause of most mis colors. Also your heating times play an important role because if your hold times or even how fast your temp rises and cools can play a role especially if the furnace is dirty the elements wont heat up properly causing issues with color or even cause cracking.

 

[Patrick Coon]

you do know the "water" based ones are still highly acidic, right?

Hey, CHL!

When companies say that there infiltration liquids are no longer "Acid" based, they are referring to the fact that they no longer contain chlorine or hydrochloric acid, which is what caused the majority of the problems with heating elements and muffles.

Yes all the water based or "organic" liquids I've looked at are on the acidic side of the pH scale, but as long as dried completely, they should not damage your furnaces excessively. If worried about it still, you can use a cover for sintering tray, but you should raise your temps by about 50C to make up for the additional mass and shielding the cover presents.

 

[kristian]

Thanks everyone. It'll take me a while to get through all that.

• The metal free brushes we use are disposable kind. I'm not sure if we've started a new box of those around the time things went south, but I'll check on that. Gloves.. no idea. I'll give them a new box.
• We use pre-shaded discs (ArgenZ also) for C shades. None of those have been affected by the issues.
• We did some dipping with ZZ "Water Based" liquids, and they were subject to same problems (some coming out too light, some very opaque). Some came out extremely dark, but it turned out they accidentally dipped crowns from pre-shaded discs
• I'm not sure if the electrical current logging that the furnace does is accurate, or should I be measuring that at the wall, but when plotted on a graph from the furnace log, it looks pretty stable with no dips or spikes.
• We usually stack 2 or 3 trays in the furnace, I don't think we've tracked which layer the problem ones came out of. I know there's been good ones and bad ones in a single tray.
• I just ran a fat bridge stained and unstained, waiting for oven to cool down to see how it turned out.
• Airline impurities are interesting thing to look at. I know we've occasionally ran into condensation moisture in the lines issue.
• We tracked the mills that were used - no single one popped out in that list as more or less likely to cause issues

 

[kristian]

We do some sort of decontamination run weekly (quick heatup with some sort of kibble in the tray).

We had issues sort of like this in 2013 for a couple months, we never figured out what exactly was causing it, and in the end we tried the new ArgenZ, everything worked fine on that so we just moved on and didn't research it any further. A lab needs to push out units


We got the unstained test bridge out with its stained buddy, it doesn't seem like stain hinders the sintering process, although in this specific case the pontic wasn't super heavy.

 

[JMN]

Thanks everyone. It'll take me a while to get through all that.

• The metal free brushes we use are disposable kind. I'm not sure if we've started a new box of those around the time things went south, but I'll check on that. Gloves.. no idea. I'll give them a new box.
• We use pre-shaded discs (ArgenZ also) for C shades. None of those have been affected by the issues.
• We did some dipping with ZZ "Water Based" liquids, and they were subject to same problems (some coming out too light, some very opaque). Some came out extremely dark, but it turned out they accidentally dipped crowns from pre-shaded discs
• I'm not sure if the electrical current logging that the furnace does is accurate, or should I be measuring that at the wall, but when plotted on a graph from the furnace log, it looks pretty stable with no dips or spikes.
• We usually stack 2 or 3 trays in the furnace, I don't think we've tracked which layer the problem ones came out of. I know there's been good ones and bad ones in a single tray.
• I just ran a fat bridge stained and unstained, waiting for oven to cool down to see how it turned out.
• Airline impurities are interesting thing to look at. I know we've occasionally ran into condensation moisture in the lines issue.
• We tracked the mills that were used - no single one popped out in that list as more or less likely to cause issues

If it happened in both mills, it could be still be air unless you have separate compressors and air feeds.

With position in the furnace, look. not at just which stack layer but also at if they are always or more often in the back half, right, left, or front half etc.

 

[kristian]

I did the recommended furnace updates (from 3.01f to 5.01) and was running calibration rings. With 3 layers stacked, I get 20-30°C cooler results in the bottom layer and 20-30°C warmer results in the top layer, (Edit: not reproducable results; see below) compared to the middle one. I assume this is normal, but up to 60°C difference depending on tray choice sounds like a lot.

 

[JMN]

Waitaminute. Just re read. Never has any preshaded/unstained zirconia had an issue? Never ever never? There's a big arrow pointing at what happens different between preshaded/unstained and the rest. Unless you do so relativly few preshaded that the odds are possible they just got lucky and didn't go pear shaped because of an insufficient volume of sintered preshades.

But that's where I'd look. What steps, processes, materials, locations, are different for stained zirc.

 

[kristian]

Waitaminute. Just re read. Never has any preshaded/unstained zirconia had an issue? Never ever never? There's a big arrow pointing at what happens different between preshaded/unstained and the rest. Unless you do so relativly few preshaded that the odds are possible they just got lucky and didn't go pear shaped because of an insufficient volume of sintered preshades.

But that's where I'd look. What steps, processes, materials, locations, are different for stained zirc.

Yep, never ever. Preshaded is pretty low amount, but I think we're approaching a point where not getting any messed up might be statistically unlikely.

I'm guessing I could have similar success with other brand white Zirconia - I have some Ceramill ones coming in on Monday.

 

[user name]

60 degree variance from one area in your oven to the other is huge, and unacceptable. If you really know your zirconia, a 10 degree swing can be noticed in a shift in value and chroma.

You started by saying its the pontics and other thick areas. That sounds like under firing. If the other areas look nice, then increase your hold time. Are you holding a full 2 hours? When you stack your trays, are they vented?

How are you powering the Dekemas? 110 or 220? If youre doing more than one tray it needs to be running on 220. (it should be 220 regardless)