charles hallam cdt
Active Member
Full Member
- Messages
- 106
- Reaction score
- 13
Have you been using this alloy and porc/opaque combo for long time?
Its how its been sand blasted ,particles are staying on the surface or burnishing the surface. If you notice your np is fine look at your grit size and who is doing it . My feeling is they are blasting at 90 deg to the surface and not along the surface . Also the semi precious is a different heat conductor to np so if your using hot pegs under the copings you can be boiling the opaque liquid and causing voids between the metal and the opaque. Ive had techs tell me before that they are doing nothing different before, but when you go through the whole process yourself and nothing goes wrong you know its them and not the material which is what they want to blame ......I tell them they are sounding like a dentist then they listen.
At least 1 year but like I said the bubbles are inconsistent. One thing I did notice is that a whole ring seemed to get contaminated while another ring of copings was safe. The contaminated ring was one where I reused a button that had been recycled 3 times already (and yes I add at least % 50 new metal)Have you been using this alloy and porc/opaque combo for long time?
Question: what's ur procedure of treating the metal? Do u sandblast before degas and after degas? Do u use distilled water to rinse or do u just steam/air dry?I had the same exact issue last summer for about 3 or 4 months before I figured out what was wrong.. It was just the semi precious (I use Inline) and a few times it happened on my high noble, NEVER on the NP. I tried tons of things, spent a lot of time on the phone with Ivoclar etc... Changed my air filters, went over casting techniques, crucibles even bought a new air compressor. In the end I found it was one of two things.. I changed to a high quality aluminum oxide and also lowered the pressure i was blasting the metal copings down to around 3.5 bars and made darn sure it was an even dull gray surfrace when I was done blasting. This did the trick and I havent seen any bubbling for a year now.
Question: what's ur procedure of treating the metal? Do u sandblast before degas and after degas? Do u use distilled water to rinse or do u just steam/air dry?
I would look to casting techniques and blasting/cleaning techniques. A miscalibrated torch can cause it. Maybe just ditch the metal and try a different kind if you can't figure this out.
Good news for today - i got a new sandblasters renfert and used their sample beads as well. No bubbles whatsoever. I also tried re trimming and re doing the opaque on one's that showed bubbles from the day before and those came out good as well.
Mohammad I think the better oven has helped some of the problem. And I do think the metal I'm currently using is more sensitive then another semi we use as well. I'm gonna keep tracking it and figuring out what the main culprit was. I think it was a combination of a few things and all the little fixes are helping.