Porosity in bulky 60% gold implant, help.

R

richuk

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Usually not a problem when it comes to casting. Positioning in the ring etc is how it should be yet, a full gold crown for an implant keeps going porous. pre formed sprues has a reservoir. Now at my forth attempt.
Wondering if there was any tips to avoid this. I'm thinking make the reservoir bigger?

498B0A9B-8076-4CF8-8989-72222A308C49_1_201_a.jpeg
 
JMN

JMN

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Usually not a problem when it comes to casting. Positioning in the ring etc is how it should be yet, a full gold crown for an implant keeps going porous. pre formed sprues has a reservoir. Now at my forth attempt.
Wondering if there was any tips to avoid this. I'm thinking make the reservoir bigger?

View attachment 36180
larger sprue to bar/button connection if not 2 sprues.

Larger reservoir ball/bar-thicken it, but make sure it os smooth or cavitation may be caused.

Add a 'tail' of wire wax to the opposite side of the metal's entrance. An air evacuation channel to reduce/prevent 'vapor lock'.

Verify your gas and o2 flowrate/pressures/psi are where they should be for this blend, they're not all the same and yiu can get away with a lot until you find an edge case.

I'm assuming you are using a broken arm casting machine, check the counterweight, it may not be set right for the large amount of metal.

A bit longer heatsoak may help.



These are what gave me headaches when casting 5-8g 74%Au implant crowns, and I hope they help you.

Either way, let it be known. Especiallly if it doesn't help.
 
JMN

JMN

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Also, use more metal to push it through. If you are not used to large castings, they need more metal overall, not just in the result. Needs more mass to 'push it through'.
 
CatamountRob

CatamountRob

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I’d use a direct sprue, make sure it’s thicker than the thickest part of your crown. Make sure the direct sprue reservoir is in the center of the ring. I burnout at 1300 F or so but let the oven and ring cool to 900 before I cast. You want the reservoir to cast fully and no button. Add a vent if it makes you feel better but I rarely use them.
 
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user name

user name

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Id use a reservoir equal in mass to the crown, locate the res at the heat center of the ring.
Angle crown with margins to the trailing edge as the casting machine spins.
I burn out at 850, then let it cool to 540 before casting (centigrade). Looking inside the ring it should just still have an orange glow, but not bright.
Smooth edges on all wax connections to avoid turbulence.
Dont over heat the alloy.
Make sure alloy is CLEAN! When its just about ready to cast, sprinkle some borax on it to pull any slag so clean metal enters the ring first.
Minimum force on casting. Broken arm machine, no more than 1.5 turns.
As @CatamountRob said...use the correct amount of alloy. You want the res feeding the crown, not being drawn back by the button.

@JMN and I were discussing earlier this weekend...I gave up all metal work. If forced, Id send designs to be milled in metal.
 
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doug

doug

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Id use a reservoir equal in mass to the crown, locate the res at the heat center of the ring.
Angle crown with margins to the trailing edge as the casting machine spins.
I burn out at 850, then let it cool to 540 before casting (centigrade). Looking inside the ring it should just still have an orange glow, but not bright.
Smooth edges on all wax connections to avoid turbulence.
Dont over heat the alloy.
Make sure alloy is CLEAN! When its just about ready to cast, sprinkle some borax on it to pull any slag so clean metal enters the ring first.
Minimum force on casting. Broken arm machine, no more than 1.5 turns.
As @CatamountRob said...use the correct amount of alloy. You want the res feeding the crown, not being drawn back by the button.

@JMN and I were discussing earlier this weekend...I gave up all metal work. If forced, Id send designs to be milled in metal.
 
C

charles007

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Richuk, you wrote "Usually not a problem when it comes to casting" having said that all bets off on all of your casting techniques. I will go back to basic casting techniques as posted above by other members.
Follow everything posted above and I will share in more detail what I did for years. First of all its practically impossible to miscast gold, so go on the lower end in with any temps used.
Use 8 or 6g sprues with reservoirs. Since this will be your forth attempt use 2 sprues. Correct angle attaching sprues to pattern so alloy flows straight into the pattern. Place pattern outside the thermal zone in the casting ring, closer to the outside wall rather than center of the ring. Check alloy for correct burnout temp and use the lower temp. As user name posted, 1.5 turns is all that's needed casting gold, higher turns creates turbulence. Critical your oxy and propane is adjusted correctly or you will see porosity for sure ! Heat up your metal until its clear after using a sprinkle of borax and quickly cast. Don't continue heating up alloy with torch, not necessary. Push off the casting arm as you let go to have a smooth release. If your hearing your casting machine or feel it shaking, your arm is not balanced. If the machine is not balanced you will notice this on higher arm turns, not at 1.5 turns casting gold.
How can you create porosity easily ? 1. incorrect sprue size, to small/ and spruing. 2. high oxy/prop setting. These are the 2 most likely reasons to see porosity.
One tip that can make a difference in not getting porosity is adding a little extra wax to sprue connected down the wax pattern. This creates a wider connection of the sprue to the pattern. In other words the opposite of having a tapper connection to your wax pattern. After using sticky wax to hold the sprue in place I had a little soft rope wax around the wax pattern. If you don't use to much soft wax it can help prevent the pattern from falling off later because of the hard brittle sticky wax used.
Two of my favorite sprues for gold alloys are the pear shaped reservoir sprue by Renfert and Ivoclar 6g red reservoir sprue. Straight 8g wax spruing ceramic single unit crowns. Also used same reservoir sprues for spruing ceramic alloy bridges, and not using a sprue bar. Almost forgot the one rule you must always follow, sprue from the bulkiest part of the pattern and correct angle.

Sorry for the long posts guys and gals. When your seeing porosity its just a matter of getting back on track to basic c&b techniques that's easy to drift away from over years of changing alloys, techniques, materials and equipment.
Btw....I stopped casting several years ago, and not looking back... only CAD designed using Argen until metal ceramics die an opaqued oxide death..... lol
 
Y

Yuugen

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Was told by my Boss/Teacher about porosity in gold crown, Many things to consider about positioning, reservoir, and the temp burnout @ 600 degree Celsius for gold crowns and 750 degree Celsius for copings and most of all is to rapidly cool down that thick metal by attaching the piece of same metal your casting on the thickest part of the crown to cool it right away,
 
JMN

JMN

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[...]and most of all is to rapidly cool down that thick metal by attaching the piece of same metal your casting on the thickest part of the crown to cool it right away,
Sorry but I get a solid "HUH?" out of that.
can you please try saying that differently?
 
kimba

kimba

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I think whatbhe is talking about is a technique I where an ingot of the same alloy as the crown is waxed to the crown and postioned toward the outside of the ring furthest away from the heatcentre
the theory is that it acts like a radiator and cools the crown quicker than it would nomally , therfore drawing alloy away from the still solidifying reservoir which is postioned in the heat centre of the ring.
 
Tayebdental

Tayebdental

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Casting torch setting is too hot, proper reservoir and thinner venting sprues if not mentioned previously
 
rkm rdt

rkm rdt

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Any chance some of that dirt could have made it's way into the alloy?
 
WENDY

WENDY

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I had the same problem years ago. Turns out, my alloy was contaminated. Used brand new alloy and problem was fixed. Also added some chill vents on thicker areas to avoid bubbling.
 
OP
R

richuk

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Thanks for the response everyone. Good news following everyones advice i managed to avoid the dreaded porosity. I increased the size of the reservoir, and added a plastic stick to act as a chimney to allow the air/gases to escape. We no longer cast with a flame/torch anymore, we've been using an induction casting machine for a good 8 years now.

Alloys we aways sandblast the old and add fresh alloy to each casting. I used about 17 grams of metal on this one following on from what was advised above.


0B7C6A8A-F739-4D43-BB27-071E7857FFC9_1_201_a.jpeg 6409C7AC-F6EC-4CC6-8160-F7134B67A2B7_1_201_a.jpeg C3216339-3153-4484-9410-C72E2FF0B5A9_1_201_a.jpeg

Edit: nope, not a clue how to put the pictures in order🤦‍♂️
 
JMN

JMN

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Time to break out the marshmellows and dance around the bunsen burner.

Glad it worked out for you.
 
user name

user name

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Surface still looks iffy.
Reservoir needs to be in the heat center of the ring, not off to the side.
Your vent should be attached near the other end and looped back
 
user name

user name

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@richuk
I want to be clear, Im not picking on you.
'Whew, it finally worked' isnt a plan for success. I beat my head on the bench many times trying to figure this stuff out.
Im glad you got it done. Now, tell us about this thug wannabe that got your gold tooth. :p

Im kidding, everybody. Could just be a Jew. Ahhhhh
 
OP
R

richuk

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@richuk
I want to be clear, Im not picking on you.
'Whew, it finally worked' isnt a plan for success. I beat my head on the bench many times trying to figure this stuff out.
Im glad you got it done. Now, tell us about this thug wannabe that got your gold tooth. :p

Im kidding, everybody. Could just be a Jew. Ahhhhh
Not at allBeer, I appreciate the advice. There has been many a time i've also banged my head against the bench trying to figure stuff out, its nice to be able to sleep well afterwards😅.

All i know is the person already has a few gold teeth. Each to their own 🤪
 
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