Max Casting temp

[Edy]

I was told today that those bubbles in the porcelain could be caused by my torch ( too much time heating until the alloy melts for cast ) , or a second cause my be the max temp of the oven with the ring is 960 C , the friend is telling me that his putting only 900 C for the casting oven .
What could happen if i set my temp of the casting oven to 960 ? that could burn my alloy too ? i think the too much heating of the alloy with the torch is the main reason of my bubbles .

What torch u advice me to buy and what number of the Head ( Dizza ) u use ,i got number 6 , the flame from the torch is coming 2.5-3 centimeters in diameter .
What temp you got max temp in casting oven and (how much time u leave the ring at max temp if thats is any important).

 

[Elab]

Edy, 960 C sounds hot to me, I was having occasional bubble problems also, furnace temp was 870 C. I dropped it to 850 C and things cleared up. For 90+% ceramic alloy I used 760 C. Sounds like furnace temp may be your problem. Can't help with the torch I use induction.

 

[Edy]

but how 760 ? isnot that too low ? how the alloy would travel all the way on that low temp ? i am always under pressure when i open oven and put ring into the casting mashine so it wont cool too much from 960 C, and u do it at 760 C ? something here its not entering my head..

 

[Tayebdental]

I was told today that those bubbles in the porcelain could be caused by my torch ( too much time heating until the alloy melts for cast ) , or a second cause my be the max temp of the oven with the ring is 960 C , the friend is telling me that his putting only 900 C for the casting oven .
What could happen if i set my temp of the casting oven to 960 ? that could burn my alloy too ? i think the too much heating of the alloy with the torch is the main reason of my bubbles .

What torch u advice me to buy and what number of the Head ( Dizza ) u use ,i got number 6 , the flame from the torch is coming 2.5-3 centimeters in diameter .
What temp you got max temp in casting oven and (how much time u leave the ring at max temp if thats is any important).

When casting NP for Maryland bridges here and there, I heat the crusable and alloy in a circular motion to distribute heat evenly, as soon as the ingot start to change shape with the skin oxide layer should be intact and not broken I do the casting. And..And start always with Fresh ingots no used button for NP alloys!!!.

 

[adamb4321]

but how 760 ? isnot that too low ? how the alloy would travel all the way on that low temp ? i am always under pressure when i open oven and put ring into the casting mashine so it wont cool too much from 960 C, and u do it at 760 C ? something here its not entering my head..

To hot a ring can cause brittleness in the alloy especially the high noble ones. Most NP has a recommended burnout temp of 900'c and precious will range from 800'C to 850'c . The ring shouldn't cool down that much when loading into the casting machine and if you do feel that maybe you've had a problem and taken too long (maybe you dropped the ring or got tangled in the cradle) just put the ring back in the furnace for 20 mins and start again. I had to use an old nessor vertical machine a while ago that needs three hands to operate and because I was on my own I had to place the ring in the casting machine before I started melting the alloy, pretty much worked fine apart from a couple of units that missed.