High Noble Gold Porosity.

[DMC]

Nice looking bridge. My old-skool Dad preps that stuff all the time.


ps, I never weigh any wax. Type IV gold has more copper and looks pretty, but it often turns into a crappy button when the alloy breaks down. I like both type IV and type III.

To rejuviinate a button, I just melt it in a crucible with a dash of white flux powder, let cool, then grind off the top and bottom skin. You'll see heavy crap sink to the bottom and lighter garbage float to the top, major discoloration and various grain sizes on the surface. Inside in the good stuff.

 

[charles007]

***
The way I rejuvinate my metal is to sprinkle on borax just before I cast, the molten metal clears up as you sprinkle...... very old technique,
I don't weight my metal, but I should when you have very large cases. Sometimes I end up with a good casting and sprues and no button, very scary when your devesting.

Charles

 

[aidihra]

The button is too large. It is acting as a "heat sink" cooling last, and counter-acting the job the reservoirs on the primary sprues are supposed to be doing.

You are correct, but TheLabGuy's casting looks like one of mine. The only difference is that he didn't use any chill vents. I normally don't have problems with porosity.

 

[Al.]

Rob this is the min reservior I use on a reg size crn. The heaver the crn the larger the reservior I use. All my porosity stays on the sprue connecting the reservior to the former. I use 10 ga sprue on the crn and 8 ga on the bottom connecting the reservior to the former.

I fit max of 3 crns per 100 gm ring.

For a cant pontic like yours I would have used a reservior the same size as the pontic, no vents and no porosity.

 

[TheLabGuy]

That's just sexy brother........nice work.

 

[Pronto]

I never use a resevoir on single castings. I use a 6 guage Kerr gate and throw a chill vent on. I keep the button about the same size of the crown or smaller, not bigger. FGC is a 2 turn of the armer for me. I have never used borax or fluxes on the molten gold. Replace the crucibles often and sand blast the button well to get rid of any hidden investment.

 

[Captek09]

Porpsity

Rob,....I am Al fillastre..using Captek's account...was looking at the "Communicator" pics & saw this. my email: [email protected]

From what i see there are a few issues going on simultaneously:

1. TOO much metal!!!....by having an exposed button bottom, it is exposed to the air, cooling faster than anything else and efectively sucking the reservoir back into the button!!! (which makes it worthless)...It is not available to feed the crown. SOLUTION: Weigh your wax-up (with sprue) in grams, multiply that by the specific gravity of the metal (probably in the 14.0 to 14.5 range) and cast only what you need. A proper casting should have no visible button! Youre going to have a problem if you have a bunch of big buttons from previous castings...try getting them really hot (almost but not melted) & using a screw driver to break them apart so you can use a smaller quantity of metal

2. Overheating metal is a possibility

3. If the wax-up is over about .2 grams or so, use a chill on the crown. 6 ga wax works nice..and it needs to be atleast 1 inch long..but I make it as long as I can...If the crown has a really thick side I put the sprue there & chill it nearby and on opposite or thinner side

 

[Al.]

Rob,....I am Al fillastre..using Captek's account...was looking at the "Communicator" pics & saw this. my email: [email protected]

From what i see there are a few issues going on simultaneously:

1. TOO much metal!!!....by having an exposed button bottom, it is exposed to the air, cooling faster than anything else and efectively sucking the reservoir back into the button!!! (which makes it worthless)...It is not available to feed the crown. SOLUTION: Weigh your wax-up (with sprue) in grams, multiply that by the specific gravity of the metal (probably in the 14.0 to 14.5 range) and cast only what you need. A proper casting should have no visible button! Youre going to have a problem if you have a bunch of big buttons from previous castings...try getting them really hot (almost but not melted) & using a screw driver to break them apart so you can use a smaller quantity of metal

2. Overheating metal is a possibility

3. If the wax-up is over about .2 grams or so, use a chill on the crown. 6 ga wax works nice..and it needs to be atleast 1 inch long..but I make it as long as I can...If the crown has a really thick side I put the sprue there & chill it nearby and on opposite or thinner side

Thats instresting, no visible button, that makes alot of sense.

 

[kcdt]

1. TOO much metal!!!....by having an exposed button bottom, it is exposed to the air, cooling faster than anything else and efectively sucking the reservoir back into the button!!! (which makes it worthless)...It is not available to feed the crown. SOLUTION: Weigh your wax-up (with sprue) in grams, multiply that by the specific gravity of the metal (probably in the 14.0 to 14.5 range) and cast only what you need. A proper casting should have no visible button! Youre going to have a problem if you have a bunch of big buttons from previous castings...try getting them really hot (almost but not melted) & using a screw driver to break them apart so you can use a smaller quantity of metal

I missed that, but it's correct, in effect, if you're using indirect reservoirs close to the pattern, then having a button is like an enormous chill going the wrong way... it'll suck alloy away from the pattern. The only time you leave a button is in direct spruing where you run without a reservoir.

 

[rgkbmk]

Al and Russ give some good advice. Russ has helped me with my gold castings over the years and it has been appreciated. What I can tell you that I have learned was:
Minimal turn on the casting machine
Proper placement of the sprue and chill sprill makes all the differance.
A well centered casting arm is needed so as to not shock the metal when casting. If it bangs and doesn't sound smooth then it's not centered properly.
proper resevors in the right space.
proper gas oxygen mixture ( i do around 2lbs gas and 2 oxygen) for a cool flame.
Sorry this was a bit late.
Rick

 

[charles007]

To get a smoother release of the arm when you cast, I release the arm, hold for a split second, then push off with the arm, rather than just release.......which can be jerky sometimes, try it, you will hear the difference. This gives a smoother release of the arm........Also like Rick said, when you release the arm, it shouldn't be noisy. It should be a very quiet sound and very smooth. I think a lot of labs kind of get use to the sound of the casting machine and forget that we should keep the arm balanced.. Mark the arm once you learn where the weights should for the different size rings........ If you aren't sure if your machine is balanced, move the weights after you cast your case. You will hear and feel the difference......This turbulence from the casting can be completely eliminated with a little trial and error.

Charles

 

[Al.]

Al and Russ give some good advice. Russ has helped me with my gold castings over the years and it has been appreciated. What I can tell you that I have learned was:
Minimal turn on the casting machine
Proper placement of the sprue and chill sprill makes all the differance.
A well centered casting arm is needed so as to not shock the metal when casting. If it bangs and doesn't sound smooth then it's not centered properly.
proper resevors in the right space.
proper gas oxygen mixture ( i do around 2lbs gas and 2 oxygen) for a cool flame.
Sorry this was a bit late.
Rick

Rick is a detective. A private eye.
BMK must be your bride.

 

[Stirling Ross]

. General biocompatibility–On this most basic level, we have to look at how the material reacts generally with human tissue. In other words, how toxic the material is at a cellular level. Does it poison cells? This toxicity tends to be an inherent property of the material, and all people will react to it in a similar manner. Using a toxic material such as mercury or nickel would always be a mistake.

 

[zahnartz]

Works for all castings - Its a method to determine the amount of alloy regardless of type.
All castings will have porosity because of the shrinkage that occurs during cooling. All you can do is control where the porosity finally ends up at.
The alloy amount is just one of those control factors.

Just curious - When you cast the final one, did you still have a button?

Casting multiple units was a thorn in my side for a long time
I eventually went back to basics
I use an 8 gauge runner bar
10 gauge feeds (around 6mm in length) to each pattern
and on a thick pontic I run another sprue lead from the pontic down to the runner (18 gauge)
Oh - and all my type III castings I still use a gypsum bound investment
The castings are spot on every time.

Everyone I work with laughs at me - says they have quicker methods -
Heat it and it will cast, all for one investments etc...
Im all for change and new methods when it works- but sometimes I just chuckle as they are 'RE'waxing that bridge due tomorrow morning

I would like talk to you if you have some time, Michael Noriega 706-631-0005 cell