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too tight crowns for PFMs

Discussion in 'Misc' started by Baker, Feb 7, 2008.

  1. Baker

    Baker New Member

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    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.
  2. clearH2O

    clearH2O Member

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    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.
  3. Malcolm Graham

    Malcolm Graham New Member

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    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
  4. Al.

    Al. Well-Known Member

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    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.
  5. Byron

    Byron New Member

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    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
  6. Al.

    Al. Well-Known Member

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    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
  7. Byron

    Byron New Member

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    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
  8. dentcre

    dentcre Member

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

    zena New Member

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    i also use FF15 and we use it in 90gram packages which in total amount of volume whether its water or liquid should equal 24ml as it states in the instruction. We also had the same problem with pfm's fitting to tight even at full expansion of 24 Liquid : 0 water So I called Whip Mix they told me to decrease 1ml.
    So this is how I do it now, First thing in the morning I place my liquid bottle in a hydro bath of warm water so that around lunch when I'm ready to invest my bottle has been warmed up afew hours prior. My measurement ratio is for every 90g pack I mix straight liquid only 23ml, hand mix 20-30seconds then whip mix for 1min and I only let in bench set 10mins even though they say it should be 15min and I also use ringless most of the time make sure to trim off the tops of your moulds I just take it to the trimmer. This works for me.
  10. Travis
    Paranoid

    Travis Administrator Staff Member

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    My newest box of Microstar HS investment doesn't seem right. I tried using the same liquid water ratios and it came out really thick. Now I have 12 crowns that I am unsure if they will fit properly. I will call them later today if I get a chance but I am pretty upset about it.
  11. zena

    zena New Member

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    I never had much luck with Microstar HS for metal castings try fastfire15 but for the past year I have been using Mircostar HS for all my IPS empress/emax only because the investment from ivoclar was not working for us. We had a ivoclar tech come to our lab for afew days to see if we were doing something wronge and we weren't, so I suggested to try a different investment and bingo problem sloved. We must of had a bad batch from ivoclar.
  12. Travis
    Paranoid

    Travis Administrator Staff Member

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    I cant do anything right now with the weather. Does the (fastfire) liquid need to stay above freezing?
  13. Pronto

    Pronto Member

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    Baker, what brand are you using? Is it a new batch or old? Bags or bulk? Liquid fresh? Frozen? Lots of possibilities. I've been using Triumph formally it was Dental Ventures. It seems to be pretty consistant as long as I am with my measurements of the liquids.;)
  14. zena

    zena New Member

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    I keep my FF15 liquid warmed in a hydrobath.
  15. DMC
    No Mood

    DMC wheeeeeeeee!!! Donator Sponsors

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    For NP metal try the following if too tight

    Invest using full special liquid of course.
    Right after pouring the investment into ring, place ring into hot water bath.
    Around 140F (I just use the sink, and plug the bottom. I let it fill up while investing, and the temp stays high for a while, due to volume of water)

    I would NOT heat the liquid before mixing the investment, as I thought someone stated earlier. That's not right IMO. Investment should be room temp when mixing/pouring, or you risk opening a worm-hole sucking everything to another dimention right in your lab!
  16. Pronto

    Pronto Member

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    Or warping the waxups.
  17. aidihra
    Stressed

    aidihra Member Donator

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    I've been using Quickfire investment for about 9 years now. I use it for PFM crowns and pressing. I did have to play with the special liquid/water ratios until I got satisfied with the results when I first used it. I let it set for 20 minutes and then I put it in the burnout furnace at 1600 F for 30 minutes. If I'm casting a NP or a full gold crown, I simply adjust the liquid ratios.
  18. pit-stain

    pit-stain New Member

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    I use mircostar for empress/emax rings works great. But for PFM rings not much luck the castings come out rough looking weather we use debublizer or not. Any ideas why?
  19. Bobby Orr ceramics

    Bobby Orr ceramics Member

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    First......insure you've blocked out any micro-undercuts at the base of the preps. They're subtle, but a lot of times there. We scan all our dies and mill copings in wax. Scanning does the best block out and cement spacer......no human can be that consistent and accurate.

    Second.....we use exclusively Talladium's Galaxy investment for ALL alloy castings and pressings. Their cheat sheet for controlling expansions for investing various materials is awesome since they test the expansions on each batch tumbled and therefore the ratios could be a little different from box to box. When we started eMax, we noticed a very significantly less reaction layer upon divesting. Saves labour time a bunch.

    Start with that block out first !!! Cheers, James
  20. charles007

    charles007 Well-Known Member

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    This thread was started in Feb 08

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