bubble in pontic in pfm bridge

[jijimon]

we had a 11 unit bridge case today
14-13-12-11 21-22-23 24-25-26-27
3 pontics 24-25-26
as usual i connected sprue to all the teeth
also fixed some extensions which look like reservoirs to the buccal side of the pontics
invested
preheated 1050 degrees ( ring only)
flame casted using non precious alloy in semi automatic centrifugal casting machine:mad2:

casting looked fine
allowed to cool down in room temprature
devested using air chisel
sand blasted
and i found a small bubble between the connection 25-26
i tried to remove it with tc burs and finds the bubble is getting bigger


some how i managed to clean the bubble and soldered it
but this happens to us almost every time we did a long span bridge with more than three pontics
and we call it our trade mark bubble

please help

 

[araucaria]

Got photos of the casting or waxwork sprued up? seems like an issue with sprues, reservoirs and the immediate cooling of metal.

 

[Bastien]

Why did you connected all theeth to the "nourrice" ?

..... shhhh ... andreas sabbath method Bob ....

 

[Hary]

Check if your pontics are bigger than the reservoir and the sprues going to reservoir and from the reservoir to pontic has to be indirect.

 

[charles007]

Pictures will tell the story, and I think its going to be a ugly spruing story..
If you want help, post pictures of a waxed bridge and give size of sprues.

 

[disturbed]

Worked for a guy in cali who cast his bridges in a crucible full of carbon buildup..fugging nightmare with large cases...crucible clean?

But yea.. Pics of pre and post casting needed.

 

[MasterCeramist]

Could be sprue size or overheated metal.