Emax Yellowing

[NathanNever]

I had the same problem. I only have on oven right now, and my PFM metal has some silver. I purge the oven before firing any Emax, and it does the trick. A separate tray for my emax is a good idea too. Also I quit using the wonder peg putty, and it seemed to help.

What do you use to purge the chamber? Unitek sentry carbon in EP3000 is ok? and what program?

 

[ps2thtec]

I was wondering if it was the wonder peg putty.

Here's one more to throw in the mix, vacalon has "fiber-free" tray liner. Suspend the liner on the pegs of the honeycomb tray and lay veneers on it, no peg putty!

 

[TheLabGuy]

That can get expensive.

Then get to work slacker!!!

 

[rkm rdt]

Then get to work slacker!!!

Some of us are still watching hockey

 

[TheLabGuy]

Some of us are still watching hockey

Ouch!!!
At least we still have baseball to soften that blow...good luck in the playoffs!!!

 

[Kurt Zubler]

When we talk about purge an oven never ever use carbon or other materials. Just purge empty at a high temperature round about 1150C for several minutes - it depends on the manufacturer round about 15min. and the oven is clean.

The so called materials (purge trays and so on) - like carbon or others, are destroying or shorten the live of the thermocuppler and heating elements.

Just purge your oven empty depending on usage once a month to once a quarter year.

So again don't use those helping devices believe me please. Just forget those

Kurt Zubler

 

[zvac]

I agree with you kurt. Have replaced many thermocouples shortly after using carbon and others purging.
My new Vacumat 6000M has purge program very similar to yours described above.

 

[charles007]

When we talk about purge an oven never ever use carbon or other materials. Just purge empty at a high temperature round about 1150C for several minutes - it depends on the manufacturer round about 15min. and the oven is clean.

The so called materials (purge trays and so on) - like carbon or others, are destroying or shorten the live of the thermocuppler and heating elements.

Just purge your oven empty depending on usage once a month to once a quarter year.

So again don't use those helping devices believe me please. Just forget those

Kurt Zubler

Kurt, I've use Purge All and Plus ,, fires to 700C 5 minute hold , no vac and its not carbon..... is this what you were talking about to not use ?
I've probably used it for 3 years now in both my ep5000 and P500,, no repairs on anything yet.. Power is on 24/7 .. never turned off.. bought both ovens Oct. 1008
No pfms fired in my ep5000..

 

[AaronR]

Sounds like the same thing you get on pfms with high silver content alloys, but you said it is only happening on pressed not milled?

Are you using your pressing furnace to fire pfms?

Al, i have heard of this as well, but not familiar with the metallurgy behind why silver alloys can react to porcelains and giving them a yellow / green tint. Could you fill me in for my own knowledge? thanks!

 

[paulg100]

you want yellowing, try working off silver plated models, then the fun really starts!

maybe im just lucky..oh no skint, but i have a dedicated oven for pressing, a dedicated oven for ceramics and a dedicated oven for de-oxing.
so thats under control.

i use the same metal pins and trays that i fire crappy non-precious on and have never had an issue with yellowing

the cause sounds more like its coming from contamination in the press oven during the higher temp press cycle.

its strongly advised to have a dedicated oven for pressing.

 

[rkm rdt]

"its strongly advised to have a dedicated oven for pressing.

Woops,there goes that per unit cost up again.

 

[karabear]

I had this happen today too, except this was a full contour zirconia crown. (It was liquid colored prior to sintering.) I added a little stain and fired. After glazing the color intensified considerably and displayed as a mad mustard yellow/green. I sandblasted three times, (supposedlly a Zirconia no-no),and 1) changed out glaze, 2) changed out stain 3) did not add any stain prior to glaze. Results were the same. I have all new elements in the sintering furnace with this batch, but the units look fine after sintering. I do not work on metal, although the furnace did at one time. I am working with the other Zirconia crowns from this batch today and may know more.

update-I noticed this on a previous Zirconia restoration from a week ago, prior to changing out all elements, but after changing one element in the sintering furnace.

 

[TheLabGuy]

Sintering furnaces have to have a decontamination cycle (because of the yellowing). It should be a specific cycle built into your sintering oven because they all do it. I think it has something to do with the heating elements, some of the milling center guys can be more descriptive but I'd run that cleaning cycle and you should be good to go.

 

[karabear]

I have changed elements on the sintering oven over 6 times previously, albeit not all four, with no deleterious effects, but I will look into your suggestion on a decontamination cycle. Thanks.

 

[charles007]

Kara, next fire to 1000c and hold for 5-15 minutes, this will burn off alot of the coloring.. no vac.. also used as a Regeneration firing ... hold 15 min.

 

[karabear]

Thanks Charles. Initially I was to create monolithic Zirconia crowns, but my boss, and the doctor, now wants the addition of layered Zirconia. Although a seasoned tech of sorts with a salty background, I am a porcelain virgin. I welcome any and all help in this arena. (Videos suggestions would be great too-and I think there is a posting on this very topic. I guess I find my CDT Navy manuals a bit dry for my taste. I'm visual all the way)

 

[TheLabGuy]

Were you Navy Kara???...and check into your sintering oven having a cleaning cycle, I'm almost positive it does just for the yellowing issue. Call the manufacturer of the sintering oven and ask them, or double check the manual. Hope that helps.

 

[karabear]

No, not Navy, just used their books to study for CDT exam. I would be a terrible recruit-too headstrong. Will check the sintering furnace manual. (Grrr, hate manuals)

 

[karabear]

To be specific, this yellowing to which you are referring is noticeable immediately after sintering?

 

[TheLabGuy]

Yep, sure is!!! Happens with all sintering ovens