Spruing help

[cumino]

Have been casting the same alloy ( very high gold yellow bonding alloy) for many years without any problems

Cost of gold has led to change of alloy to a white lower gold content alloy

Problem is, the yellow alloy flowed like water whereas the white is not as flowable and I have had a few miscasts just with implant work around the metal collar

Have increased the heating temp to 900 centigrade...but need some ideas of spruing differently ...its the old story of one man lab...no one to ask!

Use a Hereaus IQ for casting...am spruing with 3mm diameter short sprue connecting to 5mm dia feeder bar with 3mm dia sprues for connection to the ring

I thicken up the main bar if needed and attach thinner (1mm dia) sprues from the main feeder bar to the area close to the metal collar..

Any help appreciated folks... photos/ diagrams would be good, I know its something simple I'm doing wrong!

Thanks

Pip

 

[Brett Hansen CDT]

Could you post any pics of your miscasts?

 

[cumino]

Will do ...but hopefully I wont get any!

 

[Al.]

Hi Cumino,
Mabey a few things.
Pd based metals are lighter and need a hotter flame and don't flow as well as high gold content.
Lighter so make sure you have enough metal to push it in the mold.
Gold tends to swirl when it's ready to sling, you have to go just a bit past that with higher pd content. I sling it when it first turns white. A little early and you may have holes late and you may burn it.
Also for pd based mtl I keep it .5 over all thinner spots and you may have holes ESP if they are on corners.
Also I thicken the margins more than gold or put a small band 360 and then thin it down in the esthetic zones.
The 40 % gold alloys I used were similar to the higher au content but the pd alloys are a bit different. The 40% au alloys still need to be cast hotter than higher au but not as hot as pd. I burn out everything at 1550 F. 4 turns on the casting arm.

 

[cumino]

Thanks Al...I do most of what you say..the alloy is 50% gold. I think its my spruing technique... next time you do a big case , if you get time, post a pic of your spruing before youn invest?

many thanks

Pip

 

[Al.]

I dont know about spruing. 40% is pretty forgiving. Mainly make sure you are using the trailing edge for putting your ring in, you know all margins facin the same direction and mark the on the former to place it in the furnace, and no sharp angles with the sprue meaniing I put the sprue mostly on the lingual and aim it towards the opposite B margin.

If your already doing that my guess is your not casting it hot enough or your wax is too thin in spots. For ucla abbutments I used to get incomplete castings at the margin area or base, all I did is make sure the wax was thick enough and havent had that problem since.
My casting temp for high pd 2% au alloy would be too hot for 40% au and my casting temp for 40% au is too hot for 80% au alloy. My casting temp for pd 2% au alloy would burn my 80% au alloy.

 

[cumino]

Yes, I do think its partly not enough wax around the margin area...have just started thickening that area up..its better

As for the trailing edge and marking the ring...have always done that

Doesnt help that the Hereaus IQ is not centrifugal,,,its a fantastic machine, but I dont like the fact that the alloy is melted, then you open the door, get the ring to put in place...close the door, reheat the alloy...can take up to a 45 secs... my old machine, you melted alloy, put in ring and cast straight away

But ...as usual, its easy to blame the machine!

Will chip away until I get to solve it...its just annoying after years of having no problem, but these things are meant to try us!

 

[disturbed]

sounds like maybe you are trying to cast too thin to me. like al said. MINIMUM 5 tenths.

 

[user name]

"But ...as usual, its easy to blame the machine!"

Appropriately placed blame. With Als described technique, executed in a succinct and expedicious manner, I wouldnt hessitate to cast .3-.35 patterns.

 

[Gdentallab]

in my opinion, i believe it's the temperature of the ring, maybe low temp, or short heat soaking time.that's where i start.

 

[EJADA]

i add 1/4 turn to my casting machine for lower gold higher pd alloy. just don't add much as you will get internal turbulence.

 

[adamb4321]

900c sounds high for Pd alloys, this can cause brittle castings so beware. How long are you heat soaking the rings for?

I haven't used the IQ machine only the older versions that were not induction, on those machines it was necessary to heat the alloy for a further minute or more after it had gone into a ball which can seem like a very long time. Any way like Al says maybe you need to heat the alloy a little longer

Doesn't the IQ tell you when to cast anyway?

Hereaus used to have pretty good info for sprueing, are you following what they say?

 

[cumino]

Its a 50% gold alloy..900 is ok as I asked the alloy supplier

And its the "older IQ" which is not automatic... have not asked Hereaus about spruing, but may try and get in touch with them

Did one UCLA yesterday which was fine

The older machines were great, had one for years!

 

[charles007]

Al nailed all the must do's to prevent miscast.. If your having good results with gold, I don't think spruing is your problem.. 1. Check alloy directions with your investment and raise temp to allow for you oven to being off,,, calibrate oven next ! 2. Make sure your investment is no more than 1/4 " over top of patterns, and scrap top of ring.. 3. Extra turn on casting machine, I also use 4 turns. 5. 45 sec to cast ? may not work ? never tried ? I probably spend no more than 15 seconds tops from oven to release of arm.
To put it in a nut shell using these alloys, higher heat in oven, hotter flame, more turns on casting arm, 10g or 8 g sprues, correct pressure on oxy and propane, and cast fast !

I've used pd ag alloys for 25 years without any issues.. I cast .3 - .35 and expect a single miscasts about every 3 to 4 or months, and ususally know when it will happen..No more than 4 miscasts per year.. I seal margins with the same color of wax so I want make margins to thick.. maybe just the opposite of others.. It is slightly thicker though.. I hate metal finishing with a passion, so I wax very thin.. (Back when I was foolish, I cast NP between .1 and .2 did I say I hate metal finishing. With np, its all about temp, sprues and casting fast.) ! On molar and bi's coping, I sprue on the mesial or distal marginal ridge to save in metal finishing and prevent gringing holes on buccal or lingual where it might be thin. On anteriors, I sprue on mesial or distal incisal edge to prevent grinding holes on the facial or lingual where its sooo thin.. Also tilt crowns to outside wall, out of thermal zone like emax..