Bridges Gassing

[desertfox384]

I thought it was just a fluke..maybe overheated metal or something. Let me back up, 5 unit NP bridge, Rex CC (Chromium, Cobalt) Everything went fine with it, opaqued, then I packed dentin layer and had about 5 bubbles... mostly small and one BIG one. Stripped it, refinished and re-packed.. same results. Ok stripped it again finished with new stones very well, checked all my opaque temps etc.. same results. Big gassing all the way to the metal..its blowing 1.5mm holes thru my opaque and porcelain. Rewaxed the bridge. At this point im thinking it was overheated or something. Re opaqued and packed today and same exact results. 7 or 8 tiny holes and one big bubble probably 1mm in diameter.

Any ideas? I realize it could be a plethora of things. I have done plenty of single units with no gassing, only bridges. I also had a 6 unit semi precious bridge gas (callisto 75)... mostly on the lingual. Previously the bridges ive done with this metal did not gas, but they were smaller 3 unit bridges.

We blast metal at 3 bars and steam clean really well.. I degas and the surface looks good to me.
Called metal supplier and left a message but have not gotten a call back yet

 

[charles007]

How many minutes do you dry your opaque... is it paste ? and low temp. The rare times I've had glassing, it always leads back to paste opaque and blistering/ to thick on pontics...I now dry at 8 minutes. The last time I had gassing, I opaqued in an older oven that the vacuum doesn't run no stop, then fired my bis-bake in my Ivoclar with the vac that does run no stop......I finally realized the gassing problem after stripping off twice. I almost rewaxed when I thought about the vac differences in both ovens.

 

[desertfox384]

Charles im using Ex-3 and yes paste opaque. I go by the book on their settings and i think it is an 8 minute dry time. They suggest for a cr/co metal to use a higher temp for the first base opaque, it runs up to 1000 deg. c. so i do that. I do notice my opaque on this bridge has a few areas that are cracking. I opened a new bottle of opaque and its very runny so I did 2 base opaques on it then a 3rd shade opaque, but it still cracked in a few spots.

 

[charles007]

I used a lower low temp than manual, I used 500C on opaque and bis-bake with higher temp on vac start . As a precaution, if you ever seen blisters- bubbles on opaque, smooth off to check. If metal appears, refinish metal again or you will have gassing. Make use your opaque is thin on pontics, if its to thick, it can cause bubbling/blisters and lead to gassing.
Most obvious questions, what is you gas and oxy setting?. Check with the alloy company.. What stones- disks to metal finish, carbides better, grinding in the same direction . Any oil from handpiece and air lines can cause problems. Use clean crucible's...... These are the most likely problems.

 

[user name]

Steam cleaner contamination.

 

[maxi]

Steam cleaner contamination.[/QUOTE

Or; may be dirty air line on your micro blater

 

[TheLabGuy]

Are you steam cleaning your metal work before you degas?

 

[designasmile]

Gassing with EX-3

I've been using EX-3 paste opaque for years and have dealt with the
gassing/blow-out problems and trying to solve the problem with all of
the regular recommendations of casting, finishing, and contamination.
The gassing problem completely disappeared a few months a ago when
I stopped mixing the EX-3 paste opaque with the liquid in the jar. The
oily liquid that covers the paste opaque is used to keep the paste from
drying out. Do not mix the liquid and paste together. Tilt the jar and allow the liquid to run off to the side, then scoop out enough paste with an instrument for your copings. Transfer the scoop of paste to a glass slab. If you need to thin out the paste use only the special EX-3 paste opaque liquid sold separately, not the liquid from the jar. No more gassing!
This is also the technique recommended by Pentron/Zahn.

 

[designasmile]

With EX-3 paste opaque, I start the low temp at 400C
and a dry time of 10 minutes. Hope it helps.

 

[desertfox384]

I've been using EX-3 paste opaque for years and have dealt with the
gassing/blow-out problems and trying to solve the problem with all of
the regular recommendations of casting, finishing, and contamination.
The gassing problem completely disappeared a few months a ago when
I stopped mixing the EX-3 paste opaque with the liquid in the jar. The
oily liquid that covers the paste opaque is used to keep the paste from
drying out. Do not mix the liquid and paste together. Tilt the jar and allow the liquid to run off to the side, then scoop out enough paste with an instrument for your copings. Transfer the scoop of paste to a glass slab. If you need to thin out the paste use only the special EX-3 paste opaque liquid sold separately, not the liquid from the jar. No more gassing!
This is also the technique recommended by Pentron/Zahn.

You are exactly right and I thought about that today. I will try it tomorrow.

Charles, i start my opaque cycle 50 deg. c. lower than manual at 450. Tech support told me today to get a hot plate and dry my opaqued bridges on it for 10 minutes before placing into the oven. Ill try that tomorrow as well.

Rob, yes I steam clean very well and finish metal VERY carefully, one direction with stones and no unfinished metal anywhere.

 

[Al.]

It may be best for you to treat your first bake as a bond bake or coat. Apply your opaque thin and fire it high. Then treat your second bake like your first bake. That's what I do with bridges. Also for larger bridges after I degass the frame I inspect it for pits or porosity or discoloration. If I find anything I grind the area again sandblast, back in the ultrasonic and degass again.

 

[Al.]

Rob, yes I steam clean very well and finish metal VERY carefully, one direction with stones and no unfinished metal anywhere.

Rob will tell you a story about using a steam cleaner before degassing.

 

[TheLabGuy]

Rob will tell you a story about using a steam cleaner before degassing.

Yep, I don't use it anymore. The new steam cleaners with the internal heating elements are coated with something that contaminates the water. It makes the heating element last longer which is great, but it'll make your metal look like Al's face when he hit puberty if you put porcelain on it.

 

[charles007]

I told you wrong, I used a 9 min. dry with paste.. On larger bridges, I placed on firing tray in oven and let dry a couple minutes before pressing start . This would come close to using a hot plate until you buy one. I think the gas is coming from blistering that you may or may not see..
I call BS on the liquid in paste jars. All brands of paste have that liquid to floats to the top. I mixed that liquid on top without issues, and the same with paste in syringes. True, the liquid is why it gasses, just need to dry longer and use a lower start temp. I always used a lower temp than their manual.
Another tip that's not in the Noritake manual, mix one part clear margin powder with 3 parts margin.. This will prevent your shoulder margins from looking so opaque.
Good luck

 

[Al.]

it'll make your metal look like Al's face when he hit puberty if you put porcelain on it.

What it looks like is a coon I trap in my sweet corn after it meets the barral of my shot gun.

I trapped 5 of those rat bastards last week and still I got up this morning and had almost 20 stalks down from their feeding orgy last night.

So I put out three traps tonight loaded with sardines.

 

[Travis]

How do you guys clean your metal then? I dont think my steamer has any heating elements in it.

 

[Alistar]

How old is your furnace and have you purged it lately? We do a "bonding" layer like Al recommended and fire it 30 degrees F higher than the shade layers. 7 min dry + 5 min pre heat. I've had all the same issues you're talking about. Fixed with running purge-all/purge-all plus and doing a high bonding layer. Have not had a bubble/tear in a long time. We do use a high silver alloy for singles, Np for 3 and 4 unit bridges, and milled CrCo for 5 or larger.

 

[Al.]

How do you guys clean your metal then? I dont think my steamer has any heating elements in it.

Ultrasonic in distilled water for a couple of minutes for me. I dont know why but Ive never owned a steam cleaner.

 

[desertfox384]

You need to get a couple hounds Al and let them sleep outside at night. Problem solved . My shorthair pointer would do the rounds every night around my house growing up, never had a coon or woodchuck problem.

 

[TheLabGuy]

What I do Travis is sandblast, then from the sandblaster they go directly into a glass of fresh distilled water. Then I place them on a new piece of paper towel to air dry. Once they are air dried I degas them. Once degassed, the first layer of opaque is my wash or scrub layer. I scrub it in, usually B1 shade, not a thick coat all, then fire. Also, this wash layer is about 30 degrees higher like someone else mentioned above me. Then apply the next coats evenly and thicker until you get that egg look. The only difference between Al and me, is he places them into the ultrasonic cleaner (good idea) before the paper towel. I still like the steamer to clean my models before I stack porcelain on them.