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Lost wax problems

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  • rogers92026
    Hi, I m a newby at this. I m trying to cast aluminum with fine detail using lost wax. I m using paraffin wax in Plaster of Paris. After burning out the wax
    Message 1 of 9 , Jan 1, 2007
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      Hi, I'm a newby at this. I'm trying to cast aluminum with fine detail
      using lost wax. I'm using paraffin wax in Plaster of Paris. After
      burning out the wax I heated plaster to ~ 1000 F for 45 minutes. When
      I poured the aluminum (~ 1400-1450 F) into the fairly small mold I
      could see lots of bubbles (like boiling)before it solidified. My
      surface finish was a bit irregular and there wasn't enough detail. Is
      this "boiling" the result of water molecules that were bound by
      chemical reaction with the plaster and that are being released by the
      hot aluminum? Should I heat the mold higher and/or longer? Is there
      a better investment material to use than Plaster of Paris? One of the
      other problems of Plaster of Paris is that it is so weak. If I try to
      use a very thin-wall mold w. POP, it often cracks during burn out.
      Would I get finer detail with a zinc alloy?
      Bruce
    • Jeshua Lacock
      ... It sounds like it. ... Possibly... ... What are you mixing with it if anything? You should not use pure plaster of P - the plaster alone cannot tolerate
      Message 2 of 9 , Jan 1, 2007
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        On Jan 1, 2007, at 1:11 PM, rogers92026 wrote:

        > Hi, I'm a newby at this. I'm trying to cast aluminum with fine detail
        > using lost wax. I'm using paraffin wax in Plaster of Paris. After
        > burning out the wax I heated plaster to ~ 1000 F for 45 minutes. When
        > I poured the aluminum (~ 1400-1450 F) into the fairly small mold I
        > could see lots of bubbles (like boiling)before it solidified. My
        > surface finish was a bit irregular and there wasn't enough detail. Is
        > this "boiling" the result of water molecules that were bound by
        > chemical reaction with the plaster and that are being released by the
        > hot aluminum?

        It sounds like it.

        > Should I heat the mold higher and/or longer?

        Possibly...

        > Is there
        > a better investment material to use than Plaster of Paris? One of the
        > other problems of Plaster of Paris is that it is so weak. If I try to
        > use a very thin-wall mold w. POP, it often cracks during burn out.

        What are you mixing with it if anything? You should not use pure
        plaster of P - the plaster alone cannot tolerate the 1400F+ temp.
        Should be using about 50% #120 sand.

        Hint: try adding a drop of dish soap and whip the investment until it
        is frothy - this will help create interconnected micro bubbles that
        will increase the porosity. You can also add a small amount of
        sawdust which achieves a similar function when the pulp burns out...

        Do you have adequate amount of vents? Also, make sure you have a
        oversize (huge) riser for small parts.


        > Would I get finer detail with a zinc alloy?

        Not necessarily...


        Cheers,

        Jeshua Lacock, Owner
        <http://OpenOSX.com>
        phone: 877.240.1364
      • conwayde
        ... If you re interested in the Lost Wax casting method, I highly recommend Tuck Langdon s book, From Clay to Bronze (available at Amazon.com.) Langdon
        Message 3 of 9 , Jan 2, 2007
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          --- In hobbicast@yahoogroups.com, "rogers92026" <brogers1@...> wrote:
          >
          > Hi, I'm a newby at this. I'm trying to cast aluminum with fine detail
          > using lost wax. I'm using paraffin wax in Plaster of Paris. After
          > burning out the wax I heated plaster to ~ 1000 F for 45 minutes. When
          > I poured the aluminum (~ 1400-1450 F) into the fairly small mold I
          > could see lots of bubbles (like boiling)before it solidified. My
          > surface finish was a bit irregular and there wasn't enough detail. Is
          > this "boiling" the result of water molecules that were bound by
          > chemical reaction with the plaster and that are being released by the
          > hot aluminum? Should I heat the mold higher and/or longer? Is there
          > a better investment material to use than Plaster of Paris? One of the
          > other problems of Plaster of Paris is that it is so weak. If I try to
          > use a very thin-wall mold w. POP, it often cracks during burn out.
          > Would I get finer detail with a zinc alloy?
          > Bruce


          If you're interested in the Lost Wax casting method, I highly
          recommend Tuck Langdon's book, "From Clay to Bronze" (available at
          Amazon.com.) Langdon explains both investment and ceramic shell molds
          in detail. For investment molds, Langdon recommends Gypsum no. 1
          molding plaster and 80-grit silica sand, both readily available and
          cheap. His mix is one part water, one part plaster, and two parts
          sand (measured by volume.) An even finer first coat can be achieved
          by using silica flour.

          Most foundries use a casting wax for burnout (available at any
          sculpture supply house.). It will give you better detail than
          paraffin. As far as burning out the wax goes, you can ask 10
          different artisans and get 10 different answers on how to complete
          burnout. Langdon recommends 1,000 F. for 36 to 48 hours, depending on
          size. Some recommend ramping the temperature over a few days, others
          insist 950 F. is sufficient. Your 45-minute burnout time was
          obviously too short to remove the water still in your mold, hence the
          reaction you got. The book gives hints and suggestions on how to
          determine if your mold is ready.

          There are so many variables in casting, but the book does a good job
          of tackling many problems and answering questions. The book also
          goes into much more detail than I can here. Although the book is
          written for the sculptor who wants to cast his own sculptures, his
          ideas have many casting applications. There is no reason that you
          cannot achieve fine detail with aluminum following the correct
          principals. Another good book is "Methods for Modern Sculptors", by
          Young and Fennell.(also available at Amazon.) – but this book deals
          primarily with ceramic shell casting, not investment molds. Another
          excellent book, but long out of print is "Studio Bronze Casting: Lost
          Wax Method", by Mills and Gillespie, c. 1969 (I found a copy through
          my library, but abebooks.com has several copies for sale.) This book
          recommends "small jeweler's molds" can be baked between 900 and 1000
          F. for 2 to 3 hours. As you can see, everyone has his own formula.

          Hope this helps.

          Dave
        • keeebird
          ... detail ... When ... Is ... the ... there ... the ... to ... Well Bruce, your aluminum pouring temp is on the high side. 1250-1350 F. should help with the
          Message 4 of 9 , Jan 2, 2007
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            --- In hobbicast@yahoogroups.com, "rogers92026" <brogers1@...> wrote:
            >
            > Hi, I'm a newby at this. I'm trying to cast aluminum with fine
            detail
            > using lost wax. I'm using paraffin wax in Plaster of Paris. After
            > burning out the wax I heated plaster to ~ 1000 F for 45 minutes.
            When
            > I poured the aluminum (~ 1400-1450 F) into the fairly small mold I
            > could see lots of bubbles (like boiling)before it solidified. My
            > surface finish was a bit irregular and there wasn't enough detail.
            Is
            > this "boiling" the result of water molecules that were bound by
            > chemical reaction with the plaster and that are being released by
            the
            > hot aluminum? Should I heat the mold higher and/or longer? Is
            there
            > a better investment material to use than Plaster of Paris? One of
            the
            > other problems of Plaster of Paris is that it is so weak. If I try
            to
            > use a very thin-wall mold w. POP, it often cracks during burn out.
            > Would I get finer detail with a zinc alloy?
            > Bruce
            >

            Well Bruce, your aluminum pouring temp is on the high side. 1250-1350
            F. should help with the porosity. And, you will have better results
            using jewelers or dental investment. It has silica with the gypsum to
            give it strength.

            Do a Google search for Kerr, Ransom & Randolph and Westcast.
            Westcast's DuraLok also has fine fibers to give added strength. To
            prevent bubbles on the surface of your casting, investment should be
            vacuum degassed.

            To completely vaporize the wax the invested mold is heated to 1300-
            1350 F in steps. Depending on the size of your wax, this burn out
            time will be in the 5 - 12 hour range. Waxes designed for investment
            casting will give you better results than paraffin. Sprue wax added
            to the pattern also helps insure a better casting, since it melts at
            a lower temperature and prevents any pressure buildup in the mold.

            Steam dewaxing before burnout greatly reduces the odors from the
            melting wax.

            You didn't mention whether you are using vacuum or centrifugal.
            Either should work, but centrifual should give you better detail on
            the small elements.

            Vacuum may reqire a much larger sprue and button. Your flask pouring
            temperature should be in the 700 - 900 degrees F. for aluminum
            and 500 - 700 degrees F. for zinc depending on the alloy.

            Good luck.

            KB
          • philbattenburg
            Out of interest, I ve just been through the lost wax process to cast something large in ciment fondue rather than in metal. I made a one-piece plaster mold
            Message 5 of 9 , Jan 3, 2007
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              Out of interest, I've just been through the lost wax process to cast something large in
              ciment fondue rather than in metal. I made a one-piece plaster mold around the hollow
              wax model of a dog and then used a steam cleaner to remove all the wax from inside the
              plaster mold. The recovery of wax was 100% and I was able to remove every trace of wax
              from the inside of the mold, even from very delicate details with intricate tunnels within
              the mold. If I were to cast in metal using the lost wax process, I think that I would use a
              steam cleaner to remove all the wax before heating up the mould to the required
              temperature for metal pouring. Likewise, I'd make my mould using part sand mixed in
              with the plaster after a wash coat of plaster and graphite (for detail) had been poured over
              the original wax pattern. Does anyone see a problem in this?
              John

              --- In hobbicast@yahoogroups.com, Jeshua Lacock <jeshua@...> wrote:
              >
              >
              > On Jan 1, 2007, at 1:11 PM, rogers92026 wrote:
              >
              > > Hi, I'm a newby at this. I'm trying to cast aluminum with fine detail
              > > using lost wax. I'm using paraffin wax in Plaster of Paris. After
              > > burning out the wax I heated plaster to ~ 1000 F for 45 minutes. When
              > > I poured the aluminum (~ 1400-1450 F) into the fairly small mold I
              > > could see lots of bubbles (like boiling)before it solidified. My
              > > surface finish was a bit irregular and there wasn't enough detail. Is
              > > this "boiling" the result of water molecules that were bound by
              > > chemical reaction with the plaster and that are being released by the
              > > hot aluminum?
              >
              > It sounds like it.
              >
              > > Should I heat the mold higher and/or longer?
              >
              > Possibly...
              >
              > > Is there
              > > a better investment material to use than Plaster of Paris? One of the
              > > other problems of Plaster of Paris is that it is so weak. If I try to
              > > use a very thin-wall mold w. POP, it often cracks during burn out.
              >
              > What are you mixing with it if anything? You should not use pure
              > plaster of P - the plaster alone cannot tolerate the 1400F+ temp.
              > Should be using about 50% #120 sand.
              >
              > Hint: try adding a drop of dish soap and whip the investment until it
              > is frothy - this will help create interconnected micro bubbles that
              > will increase the porosity. You can also add a small amount of
              > sawdust which achieves a similar function when the pulp burns out...
              >
              > Do you have adequate amount of vents? Also, make sure you have a
              > oversize (huge) riser for small parts.
              >
              >
              > > Would I get finer detail with a zinc alloy?
              >
              > Not necessarily...
              >
              >
              > Cheers,
              >
              > Jeshua Lacock, Owner
              > <http://OpenOSX.com>
              > phone: 877.240.1364
              >
            • Stone Tool
              John: It probably would work very well......... however the moisture of course would need to be baked out of the investment. It s critical that the investment
              Message 6 of 9 , Jan 3, 2007
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                John:
                It probably would work very well......... however the moisture of
                course would need to be baked out of the investment. It's critical that
                the investment be completely dry. I've seen many bronze castings end up
                with inclusions due to small pockets of moisture in the
                investment....... The investment in this case being quite thin as it was
                built up by the dip method. The heavier the investment, the more
                difficult it is going to be to dry it completely. I've often thought
                that using a vacuum chamber to dehydrate the investment prior to pouring
                would be an excellent addition to the process.

                H.W.

                philbattenburg wrote:
                > Out of interest, I've just been through the lost wax process to cast something large in
                > ciment fondue rather than in metal. I made a one-piece plaster mold around the hollow
                > wax model of a dog and then used a steam cleaner to remove all the wax from inside the
                > plaster mold. The recovery of wax was 100% and I was able to remove every trace of wax
                > from the inside of the mold, even from very delicate details with intricate tunnels within
                > the mold. If I were to cast in metal using the lost wax process, I think that I would use a
                > steam cleaner to remove all the wax before heating up the mould to the required
                > temperature for metal pouring. Likewise, I'd make my mould using part sand mixed in
                > with the plaster after a wash coat of plaster and graphite (for detail) had been poured over
                > the original wax pattern. Does anyone see a problem in this?
                > John
                >
                > --- In hobbicast@yahoogroups.com, Jeshua Lacock <jeshua@...> wrote:
                >>
                >> On Jan 1, 2007, at 1:11 PM, rogers92026 wrote:
                >>
                >>> Hi, I'm a newby at this. I'm trying to cast aluminum with fine detail
                >>> using lost wax. I'm using paraffin wax in Plaster of Paris. After
                >>> burning out the wax I heated plaster to ~ 1000 F for 45 minutes. When
                >>> I poured the aluminum (~ 1400-1450 F) into the fairly small mold I
                >>> could see lots of bubbles (like boiling)before it solidified. My
                >>> surface finish was a bit irregular and there wasn't enough detail. Is
                >>> this "boiling" the result of water molecules that were bound by
                >>> chemical reaction with the plaster and that are being released by the
                >>> hot aluminum?
                >> It sounds like it.
                >>
                >>> Should I heat the mold higher and/or longer?
                >> Possibly...
                >>
                >>> Is there
                >>> a better investment material to use than Plaster of Paris? One of the
                >>> other problems of Plaster of Paris is that it is so weak. If I try to
                >>> use a very thin-wall mold w. POP, it often cracks during burn out.
                >> What are you mixing with it if anything? You should not use pure
                >> plaster of P - the plaster alone cannot tolerate the 1400F+ temp.
                >> Should be using about 50% #120 sand.
                >>
                >> Hint: try adding a drop of dish soap and whip the investment until it
                >> is frothy - this will help create interconnected micro bubbles that
                >> will increase the porosity. You can also add a small amount of
                >> sawdust which achieves a similar function when the pulp burns out...
                >>
                >> Do you have adequate amount of vents? Also, make sure you have a
                >> oversize (huge) riser for small parts.
                >>
                >>
                >>> Would I get finer detail with a zinc alloy?
                >> Not necessarily...
                >>
                >>
                >> Cheers,
                >>
                >> Jeshua Lacock, Owner
                >> <http://OpenOSX.com>
                >> phone: 877.240.1364
                >>
                >
                >
                >
                >
                > For discussion of Metal Casting and related issues
                > this list does not accept attachments.
                >
                > Files area and list services are at:
                > http://groups.yahoo.com/group/hobbicast
                >
                > For additional files and photos and off topic discussions
                > check out these two affiliated sites:
                > http://groups.yahoo.com/group/sandcrabs
                > http://groups.yahoo.com/group/Hobbicast1
                >
                > Please visit our sponsor: Budget Casting Supply
                > http://budgetcastingsupply.com/
                >
                > List Owner:
                > owly@...
                >
                >
                > Yahoo! Groups Links
                >
                >
                >
                >
              • philbattenburg
                HW I would think that some form of sealed cabinet with a dehumidifier or vacuum pump would considerably help in removing most of the moisture from a plaster
                Message 7 of 9 , Jan 4, 2007
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                  HW

                  I would think that some form of sealed cabinet with a dehumidifier or vacuum pump would
                  considerably help in removing most of the moisture from a plaster based mold, prior to
                  heating the mold before pouring. Alternatively, if there is no time pressure to do the
                  casting, then a mold could be left up-turned in the sun for several days in dry weather to
                  partially bake it.

                  --- In hobbicast@yahoogroups.com, Stone Tool <owly@...> wrote:
                  >
                  > John:
                  > It probably would work very well......... however the moisture of
                  > course would need to be baked out of the investment. It's critical that
                  > the investment be completely dry. I've seen many bronze castings end up
                  > with inclusions due to small pockets of moisture in the
                  > investment....... The investment in this case being quite thin as it was
                  > built up by the dip method. The heavier the investment, the more
                  > difficult it is going to be to dry it completely. I've often thought
                  > that using a vacuum chamber to dehydrate the investment prior to pouring
                  > would be an excellent addition to the process.
                  >
                  > H.W.
                • Rupert Wenig
                  Hi Guys, It s time I put in my $0.02. Plaster based molds are too dense if your using only plaster. It has been suggested to add about 50% sand to plaster to
                  Message 8 of 9 , Jan 4, 2007
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                    Hi Guys,
                    It's time I put in my $0.02.

                    Plaster based molds are too dense if your using only plaster. It has
                    been suggested to add about 50% sand to plaster to make it porous. The
                    best is to use a proper ready mixed investment.
                    You have to deal with two types of moisture in investment casting- free
                    water that you can see and calcinated (not sure of the right word)
                    water. Plaster of Paris and the proper investment are hydroscopic so you
                    might say you have to remove three types of moisture. All forms will
                    cause problems. the free water can be seen and will evaporate by itself.
                    The "hydroscopic water" will boil off if the mold is warmed to above the
                    boiling point of water. The hydroscopic water is another matter. The
                    instructions I have for the investment I have on hand says to slowly
                    bring the temperature up to 1200F and hold for 1 hour to start the
                    chemical reaction to remove the hydroscopic water (thus, the term-
                    "calcinating"). Then, lower the temp of the flask/mold to the required
                    pouring temp and do the pour.
                    I understand that the flask must be reheated if you let the flask cool
                    right down mainly to drive out any absorbed water as the investment will
                    absorb moisture from the air quickly.
                    Check past posts on this. There have been discussions on investment
                    casting in the past both on this group and on the castinghobby group.


                    Rupert

                    philbattenburg wrote:
                    > HW
                    >
                    > I would think that some form of sealed cabinet with a dehumidifier or vacuum pump would
                    > considerably help in removing most of the moisture from a plaster based mold, prior to
                    > heating the mold before pouring. Alternatively, if there is no time pressure to do the
                    > casting, then a mold could be left up-turned in the sun for several days in dry weather to
                    > partially bake it.
                    >
                    > --- In hobbicast@yahoogroups.com, Stone Tool <owly@...> wrote:
                    >> John:
                    >> It probably would work very well......... however the moisture of
                    >> course would need to be baked out of the investment. It's critical that
                    >> the investment be completely dry. I've seen many bronze castings end up
                    >> with inclusions due to small pockets of moisture in the
                    >> investment....... The investment in this case being quite thin as it was
                    >> built up by the dip method. The heavier the investment, the more
                    >> difficult it is going to be to dry it completely. I've often thought
                    >> that using a vacuum chamber to dehydrate the investment prior to pouring
                    >> would be an excellent addition to the process.
                    >>
                    >> H.W.
                    >
                    >
                    >
                    >
                    > For discussion of Metal Casting and related issues
                    > this list does not accept attachments.
                    >
                    > Files area and list services are at:
                    > http://groups.yahoo.com/group/hobbicast
                    >
                    > For additional files and photos and off topic discussions
                    > check out these two affiliated sites:
                    > http://groups.yahoo.com/group/sandcrabs
                    > http://groups.yahoo.com/group/Hobbicast1
                    >
                    > Please visit our sponsor: Budget Casting Supply
                    > http://budgetcastingsupply.com/
                    >
                    > List Owner:
                    > owly@...
                    >
                    >
                    > Yahoo! Groups Links
                    >
                    >
                    >
                    >
                    >

                    --
                    --
                    yvt

                    Rupert Wenig
                    Camrose, Alberta, Canada.

                    http://www3.telus.net/public/rwenig/
                  • Jack
                    Drying only removes water not used in the chemical reaction that causes plaster to solidify. Dry plaster actually contains quite a lot of water, which will
                    Message 9 of 9 , Jan 4, 2007
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                      Drying only removes water not used in the chemical reaction that
                      causes plaster to solidify. 'Dry' plaster actually contains quite a
                      lot of water, which will be driven off by the heat of melted
                      aluminium, causing the plaster to de-compose and lose strength, no
                      matter what fillers (such as sand) are used.
                      Jack



                      --- In hobbicast@yahoogroups.com, "philbattenburg" <exdos@...> wrote:
                      >
                      > HW
                      >
                      > I would think that some form of sealed cabinet with a dehumidifier
                      or vacuum pump would
                      > considerably help in removing most of the moisture from a plaster
                      based mold, prior to
                      > heating the mold before pouring. Alternatively, if there is no time
                      pressure to do the
                      > casting, then a mold could be left up-turned in the sun for several
                      days in dry weather to
                      > partially bake it.
                      >
                      > --- In hobbicast@yahoogroups.com, Stone Tool <owly@> wrote:
                      > >
                      > > John:
                      > > It probably would work very well......... however the
                      moisture of
                      > > course would need to be baked out of the investment. It's
                      critical that
                      > > the investment be completely dry. I've seen many bronze castings
                      end up
                      > > with inclusions due to small pockets of moisture in the
                      > > investment....... The investment in this case being quite thin as
                      it was
                      > > built up by the dip method. The heavier the investment, the more
                      > > difficult it is going to be to dry it completely. I've often
                      thought
                      > > that using a vacuum chamber to dehydrate the investment prior to
                      pouring
                      > > would be an excellent addition to the process.
                      > >
                      > > H.W.
                      >
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