too tight crowns for PFMs

[Baker]

Need to know what the labs are using as far as investment for PFM's. We are getting to tight of fit. Looking for an investment that is stable and that will fit. We use ringless, fastfire investment, and up to 4 wax patterns per ring (90gram rings). Please inform me what investment you use, How many wax patterns you use in a 90gram ring , fast burn out or slow? And what is a good noble metal and investment?
Thanx for your help.

[clearH2O]

Hi Baker, I use Bego investment. Tight fit may start from die, from wax, from burn out technique, from investment or metal. To my opinion, check your die stone expension first then check your water/powder ratio. You may add die spacer to loosing the fit. Check your metal expension too. For investment, water will do the trick to expension. More water>>>less expension and less water >>>more expension. I use both techniques fast and slow and follow strickly to manufacturer directions. Depend on its sizes I can add or reduce the number of wax paterns in 90gr ringless mould. Jensen Nobble metal I use giving me good result for my PFMs and that is all I can say to response to your question. I hope its help.

[Malcolm Graham]

Hi Baker, I use Fuji-vest 2 investment which is a ringless system and fast burnout. I presume the problem is when you are fitting the casting to the die.
Adjustment of the expansion of the investment is done with the ratio of water to expansion liquid.
Remember that as the alloy cools it shrinks onto the form of the coping in the investment and different alloys will shrink at a different amount, that is why we need different water-liquid ratio's for differnt alloys.
For non precious alloys I use 15ml liquid to 6ml of water for a 90 gram ring. For the 52% AU alloy I use mainly for PFM's I use a 50/50 mix, The same for high noble > 80% AU.
For the alloy I use for AU crowns ( 60% AU)I use 5ml liquid-16ml water and mix it for two minutes instead of the normal one minute to help improve the strength of the investment as any ratio with less than 50% liquid reduces the stenght of the investment and the ring may crack.
I will put up to 5 copings into a 90g ring or 3 gold crowns.
Hope this is of some help. Cheers Malcolm

[Al.]

I use CB 30 and I had the same problem with NP. Iwas not getting enough expansion with Rexillium 111.
They sell a high expansion liquid to be used with alloys that need more expansion. I use 13 cc of the regular liquid and 3 cc of the special exp. liquid.

[Byron]

Hello Baker, I have been using Microstar HS for the last several months with great success. I use it with all my alloys plus pressing techniques with absolutley no problems. I also use ringless, which I have done for over twenty five years. I will say that any investment you use you will need to adjust the water to liquid ratio for each type of alloy or pressing type. But saying this I have found the Microstar to be the most accurate once you get your ratios dialed in. The chart that is sent with the investment is VERY close. I also check all my castings under forty power magnification and I am not seeing a problem. One thing I also want to mention is a lot of manufactors are having trouble with getting a consistent quality of base material that goes into investment. This is a by product of the plaster board industry, sheet rock. The reason I mention this is I have been running into problems with other investment breaking or blowing up in the burn out furnace. Man what a waste this can be!! I have used several investments and the Microstar is the only one I have not had this problem with. Good Luck, Byron

[Al.]

Originally Posted by Byron

Hello Baker, I have been using Microstar HS for the last several months with great success. I use it with all my alloys plus pressing techniques with absolutley no problems. I also use ringless, which I have done for over twenty five years. I will say that any investment you use you will need to adjust the water to liquid ratio for each type of alloy or pressing type. But saying this I have found the Microstar to be the most accurate once you get your ratios dialed in. The chart that is sent with the investment is VERY close. I also check all my castings under forty power magnification and I am not seeing a problem. One thing I also want to mention is a lot of manufactors are having trouble with getting a consistent quality of base material that goes into investment. This is a by product of the plaster board industry, sheet rock. The reason I mention this is I have been running into problems with other investment breaking or blowing up in the burn out furnace. Man what a waste this can be!! I have used several investments and the Microstar is the only one I have not had this problem with. Good Luck, Byron

Byron what does HS stand for? High Strength, High Speed?
I have been thinking about switching from CB 30. I have been using it forever but it is not consistant anymore. Mabey its their liquid I dont know. I never have had a blowout but the fits change at times. I always had adjustments with season changes from summer to winter but sometimes Ill have 3 or 4+ cc
fit changes regardless of weather. I had a few boxes where they put some kind of musk perfume in the powder.
Also since Ive bought the emax system, their investment is so nice and smooth and bubble free that my fitting time is 0 on pressed crns.
I figure that there is a C&B investment equally as good as emax investment.
Ive always heard very good things about Microstar. Mabey Ill order a box.
Al

[Byron]

Hello Al, sorry it took me a while to respond back. HS stands for high speed . Trust me this stuff is fast! From investing to casting generally takes an hour. Every day I use this stuff I get more and more happy with it. Byron Call me if I can be of any help. ph. 1-870-741-7752

[dentcre]

Originally Posted by Al.

I use CB 30 and I had the same problem with NP. Iwas not getting enough expansion with Rexillium 111.
They sell a high expansion liquid to be used with alloys that need more expansion. I use 13 cc of the regular liquid and 3 cc of the special exp. liquid.

I use straight liquid on the cb 30 ,,works wonderfull.