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Re: Master materials

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  • Doug McClure
    ... From: BEN8800@aol.com To: casting@onelist.com Date: Tuesday, August 31, 1999 6:08 PM Subject: Re: [casting] Master
    Message 1 of 29 , Sep 1, 1999
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      -----Original Message-----
      From: BEN8800@... <BEN8800@...>
      To: casting@onelist.com <casting@onelist.com>
      Date: Tuesday, August 31, 1999 6:08 PM
      Subject: Re: [casting] Master materials


      >From: BEN8800@...
      >
      >In a message dated 8/31/99 4:58:31 PM Eastern Daylight Time,
      dmclure@...
      >writes:
      >
      ><< Uh didja ever ASK them what type of molds they are going to be using?
      > >>
      >UHHH I know what kind of molds they are. That has nothing to do with my
      >original question.



      Yeah it does. If you knew it was going to be an RTV silicone mold then you
      could make your master from a less hard material.
    • BEN8800@xxx.xxx
      In a message dated 9/1/99 6:37:41 AM Eastern Daylight Time, dmclure@apk.net writes:
      Message 2 of 29 , Sep 1, 1999
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        In a message dated 9/1/99 6:37:41 AM Eastern Daylight Time, dmclure@...
        writes:

        << << Uh didja ever ASK them what type of molds they are going to be using?
        > >>
        >UHHH I know what kind of molds they are. That has nothing to do with my
        >original question.

        Yeah it does. If you knew it was going to be an RTV silicone mold then you
        could make your master from a less hard material.
        >>

        I guess what I am saying is, and from responses I have gotten, that RTV molds
        are not used by professional spin casters. The black rubber seems to be the
        norm. Since I really don't know what maold material could be used by a spin
        caster, my masters should be of a material that will take the high heat from
        a heat pressed black rubber mold. Right? You see, I may not know what the
        mold material is when I make a master. The company I make masters for often
        change casters to find the best price. Many of the castings are done in
        foreign countries.

        Ben
      • VRBass
        ... Sorry to complicate this even more, but no, not all professional casters use vulcanized molds. Spin-casters, yes. Investment casters, no. Investment
        Message 3 of 29 , Sep 1, 1999
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          > I guess what I am saying is, and from responses I have gotten, that RTV molds
          > are not used by professional spin casters. The black rubber seems to be the
          > norm.

          Sorry to complicate this even more, but no, not all professional
          casters use vulcanized molds. Spin-casters, yes. Investment
          casters, no.

          Investment casting can do much more complex shapes than mold
          casting. If it's a one-of-a-kind, the master pattern can be made of
          virtually anything from styrene to bread dough. The master will be
          destroyed by the casting process.

          If you're having more than one copy cast, the caster will make an
          RTV mold and from that will create wax sub-masters. This is
          subject to the limitations already mentioned regarding RTV molds.

          BUT there is yet another consideration. If you have tolerances you
          must work with, you have to know the mold shrinkage factors for
          each step you're going through. The metal and wax shrink
          somewhat while cooling, and the mold material may expand when
          hot metal is injected. (Also true for spin-casting.)

          Different materials have different expansion characteristics, so a
          precision casting job must be carefully calculated and the patterns
          made accordingly larger to account for mold shrinkage.

          Regarding sources for vulcanizing rubber for molds, any jewelry
          supply will have it. There's probably a source in your city, if you
          know whom to call. If not, the largest jewelry supply in the US is
          Rio Grande Jewelry Supply, 800-545-6566. You can also get the
          moldmaking frames from them, but you can easily bolt these up
          yourself from sheet metal. The traditional jeweler's technique is to
          form these in a specialized oven, but the jeweler's apprentice
          textbook I have advises you can do it the in kitchen oven, as well.

          regards,
          -vance-

          Vance Bass
          Albuquerque, New Mexico, USA
          Small-scale live steam resources: http://www.nmia.com/~vrbass
        • darney@xxx.xxx
          It is my understanding the pattern is to be used for thousands of britannia metal castings. If this is true RTV silicone is nor a suitable mold material and
          Message 4 of 29 , Sep 1, 1999
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            It is my understanding the pattern is to be used for thousands of britannia metal castings. If this is true RTV silicone is nor a suitable mold material and
            Investment castings is far to labor intensive and far to slow. There is few parts that can be done by investment casting that can't be done in a black or
            Silicone vulcanized mold.
            (9" or 12") Britannia metal is one of a large family of White metals that is cast at about 600-650 degrees. RTV won't stand these temperatures for more than
            a few casts. A plastic master could be Invested cast in brass, nickel or silver in order to arrive at a master that can be vulcanized, and I have done this,
            but it is one generation down the process and something is lost at each step. For large volume casting in white metal the Vulcanized mold is the only way.

            By the way; the silicon vulcanized molds can be used to spin cast plastics, with no demolding problems. It also can be used to spin cast silver and zinc.
            Dale Darney

            VRBass wrote:

            > From: "VRBass" <VRBass@...>
            >
            > > I guess what I am saying is, and from responses I have gotten, that RTV molds
            > > are not used by professional spin casters. The black rubber seems to be the
            > > norm.
            >
            > Sorry to complicate this even more, but no, not all professional
            > casters use vulcanized molds. Spin-casters, yes. Investment
            > casters, no.
            >
          • John Grant
            ... Vance is talking about the sheet rubber used in making molds for lost wax casting. The rubber for spin casting is quite different. John Grant
            Message 5 of 29 , Sep 1, 1999
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              VRBass wrote:
              >
              > Regarding sources for vulcanizing rubber for molds, any jewelry
              > supply will have it.

              Vance is talking about the sheet rubber used in making molds for lost
              wax casting. The rubber for spin casting is quite different.

              John Grant
            • Doug McClure
              ... From: BEN8800@aol.com To: casting@onelist.com Date: Wednesday, September 01, 1999 11:21 AM Subject: Re: [casting]
              Message 6 of 29 , Sep 1, 1999
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                -----Original Message-----
                From: BEN8800@... <BEN8800@...>
                To: casting@onelist.com <casting@onelist.com>
                Date: Wednesday, September 01, 1999 11:21 AM
                Subject: Re: [casting] Master materials


                >From: BEN8800@...
                >
                >
                >I guess what I am saying is, and from responses I have gotten, that RTV
                molds
                >are not used by professional spin casters.
                The black rubber seems to be the
                >norm.
                I agree.

                Since I really don't know what maold material could be used by a spin
                >caster, my masters should be of a material that will take the high heat
                from
                >a heat pressed black rubber mold. Right? You see, I may not know what the
                >mold material is when I make a master.

                Then your original question is moot as you already know the answer.
              • John Grant
                ... ??Silver?? John Grant
                Message 7 of 29 , Sep 1, 1999
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                  darney@... wrote:

                  >
                  > By the way; the silicon vulcanized molds can be used to spin cast plastics, with no demolding problems. It also can be used to spin cast silver and zinc.

                  ??Silver??

                  John Grant
                • darney@xxx.xxx
                  YES! Conquest s catalogue has a silicone mold blank that will handle silver check it out. Dale Darney ******************
                  Message 8 of 29 , Sep 1, 1999
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                    YES! Conquest's catalogue has a silicone mold blank that will handle silver check it out.
                    Dale Darney
                    ******************

                    John Grant wrote:

                    > From: John Grant <grantjoh@...>
                    >
                    > darney@... wrote:
                    >
                    > >
                    > > By the way; the silicon vulcanized molds can be used to spin cast plastics, with no demolding problems. It also can be used to spin cast silver and zinc.
                    >
                    > ??Silver??
                    >
                    > John Grant
                    >
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                  • John Grant
                    ... Did you misread it? With ZincSil the Sil stands for silicon not silver. Silver melts around 1,600 degrees F. The silicon rubber molds do not last
                    Message 9 of 29 , Sep 1, 1999
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                      darney@... wrote:
                      >
                      > From: darney@...
                      >
                      > YES! Conquest's catalogue has a silicone mold blank that will handle silver check it out.
                      > Dale Darney
                      > ******************

                      Did you misread it? With "ZincSil" the "Sil" stands for silicon not
                      silver.

                      Silver melts around 1,600 degrees F. The silicon rubber molds do not
                      last long with 800 degree zinc..

                      John Grant
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