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Re: [hobbicast] Re: Microwave Melting

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  • Ray Brandes
    Rick, Thanks for the link. Someone dumped a microwave down the street (dirt road) and I will score it this morning. Probably just a switch or some other
    Message 1 of 8 , Jan 1, 2004
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      Rick,
      Thanks for the link. Someone dumped a microwave down the street (dirt
      road) and I will score it this morning. Probably just a switch or some
      other mechanical thing wrong with it....(grin)
      Regards, Ray in FLA

      rick wrote:

      >>http://www.popsci.com/popsci/science/article/0,12543,473581,00.html
      >>
    • Daniel C. Postellon
      Try this: http://home.c2i.net/metaphor/mvpage.html ... From: rick To: Sent: Wednesday, December 31, 2003
      Message 2 of 8 , Jan 1, 2004
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        Try this:
        http://home.c2i.net/metaphor/mvpage.html
        ----- Original Message -----
        From: "rick" <rgbaileyrg@...>
        To: <hobbicast@yahoogroups.com>
        Sent: Wednesday, December 31, 2003 7:46 PM
        Subject: [hobbicast] Re: Microwave Melting


        > --- In hobbicast@yahoogroups.com, "nesenrik" <nesenrik@k...> wrote:
        > > We got a new microwave this Christmas, I'd like to try the microwave
        method if it is easier than
        > > the tiny furnace I built.
        > > Can any of you folks give me information on microwave melting for
        > > the hobby caster?
      • thenelsons
        My attempt at a first melt was a failure. I used what is now the shop microwave , an old 1400 watt Kenmore 1.5 cubic foot model. This unit was
        Message 3 of 8 , Jan 3, 2004
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          My attempt at a first melt was a failure. I used what is now the "shop
          microwave", an old 1400 watt Kenmore 1.5 cubic foot model. This unit was
          top-of-the-line in 1989, which is probably why it still works.
          I didn't really expect this attempt to work. I couldn't find silicon
          carbide stones, only aluminum oxide. I tried using those as a heat
          receptor, but a full power run for 20 minutes did not get hot enough to melt
          aluminum in a 2" tall by 1.5" wide stainless crucible (amazing resemblance
          to the stainless salt shakers sold at Wal-Mart).
          I made a second attempt using a stack of four silicon carbide 4" grinder
          disks that were in the shop. That didn't work either.
          Anyone have ideas on where I can find silicon carbide sharpening stones? I
          tried the local shops, wal-mart, Harbor Frieght, Home Depot, Lowes, ACE
          Hardware, but only aluminum oxide were available.

          Rick
        • Ed Paradis
          Rick, if I remember correctly, Silicon wheels are used for sharpening Carbide tipped lathe tool bits and the like. You may not be able to find them cheaply.
          Message 4 of 8 , Jan 3, 2004
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            Rick, if I remember correctly, Silicon wheels are used for
            sharpening Carbide tipped lathe tool bits and the like. You may not
            be able to find them cheaply. You may have to try some places such
            as McMaster Carr, Enco, MSC, or some of the industrial suppliers.
            You might even try on eBay for something like this. I had purchased
            a Silicon wheel for my grinder a while back for sharpening my
            carbide lathe bits and I was surprized at how much it cost compared
            to Aluminium wheels...

            Ed
            "Expiring minds want to know!"

            --- In hobbicast@yahoogroups.com, "thenelsons" <nesenrik@k...> wrote:
            > My attempt at a first melt was a failure. I used what is now
            the "shop
            > microwave", an old 1400 watt Kenmore 1.5 cubic foot model. This
            unit was
            > top-of-the-line in 1989, which is probably why it still works.
            > I didn't really expect this attempt to work. I couldn't find
            silicon
            > carbide stones, only aluminum oxide. I tried using those as a heat
            > receptor, but a full power run for 20 minutes did not get hot
            enough to melt
            > aluminum in a 2" tall by 1.5" wide stainless crucible (amazing
            resemblance
            > to the stainless salt shakers sold at Wal-Mart).
            > I made a second attempt using a stack of four silicon carbide 4"
            grinder
            > disks that were in the shop. That didn't work either.
            > Anyone have ideas on where I can find silicon carbide sharpening
            stones? I
            > tried the local shops, wal-mart, Harbor Frieght, Home Depot,
            Lowes, ACE
            > Hardware, but only aluminum oxide were available.
            >
            > Rick
          • Stone Tool
            I don t know where the idea that silicone carbide was a sufficient microwave absorber to accomplish a melt came from..... In the earlier experiments done
            Message 5 of 8 , Jan 4, 2004
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              I don't know where the idea that silicone carbide was a sufficient microwave absorber to accomplish a melt came from..... In the earlier experiments done with microwave melting a slurry of ferrite and magnetite was used on the outside of the crucible. Unfortunately the original page is not to be found..... I thought I had saved it but didn't. The current web page uses the "Reid Technique" which is slightly different than simply pouring molten metal into a mold, but of course the same considerations apply here. They mention using graphite and magnetite. The really interesting aspect of this is that the magnetite appears not to become a good receptor of microwave energy until the temperature is elevated, while the graphite varies little, but is never adequate by itself.... it does however appear to bring the temp of the magnetite up to a level where it is an efficient absorber. This little bit of insight is probably the most important discovery of the whole experiment.... It probably applies to many substances which do not appear to be absorbers at normal temperatures. In a perfect world silicone carbide would turn out to be an ideal absorber at elevated temperatures, and one would simply coat a silicone carbide crucible with carbon and magnetite "stucco" to get it started as they found that the magnetite would not withstand the temps necessary to deal with steel. I would suggest beginning where these folks left off..... There is little value in starting from scratch when much groundwork has already been done. Perhaps I missed a post where someone discovered that silicone carbide was the ideal receptor...... I don't always catch everything that goes by here. Here are some paragraphs from the current microwave melting page that pertain to my comments:

              <><><><><>< From Microwave Melting ( much left out ) ><><><><><>

              Trials were begun which simply aimed to melt metals such as silver and bronze in open crucibles. However, it soon became obvious that casting to shape could also be accomplished by adapting the Reid Technique (RT) - a simplified ceramic-shell procedure for the casting of non-ferrous metals, patented in 1990. RT was first developed to avoid the problem of heat loss, which makes the the pouring of small melts very difficult - these difficulties arise however the metal is heated, and while the microwave technique set out here can be used for heating small amounts of metal in open crucibles, its greatest potential lies in its use as a flameless furnace in processes such as the Reid Technique. The crucial discovery, made during extended tests with various susceptors - materials which heat up when exposed to microwaves - was that two substances, graphite and magnetite, working together were required to achieve the kind of heating we were looking for.

              Early experiments using carbon as a susceptor were discouraging. The uninsulated crucibles barely attained red-heat and after running for 5 or so minutes the machine shut off. Insulation around the crucible helped, as did the realisation that the cooling air from the fan could be redirected. But it was obvious that a more efficient absorber had to be found. The literature on absorbers mentioned both silicon carbide and ferrites as susceptors, so an SiC paste was mixed with clay and applied to a thickness of about 8 mm and dried on the inside of a ceramic shell crucible, which we knew from earlier tests to be non-absorbing. After drying, it still didn't show red heat after 10 minutes in the microwave field. Powdered ferrites proved very difficult to obtain until it was realised that they were just modified iron oxides. A quick visit to the Ceramics Department gave samples of red, yellow, black and granular iron oxides. Similar sized samples of these were similtaneously put in the oven and fired for a couple of minutes. They all showed warming, but the granular substance (magnetite) was hot enough to burn the finger.

              Another crucible was prepared, lined in the same way, but this time with a clay-ferrite paste. 50 g of sterling silver was added, and the crucible was capped with a carbon lined shell. Although it became very hot the silver had not melted after 10 minutes of firing. The carbon-lined cap was replaced by one lined with magnetite/clay and the test was re-run. After 15 minutes firing the silver was found to have melted. A very exciting moment! Although the methods were a bit crude, a temperature of 900 degrees Celcius had been reached. Using a similar crucible, with a small mould attached, the first castings were made soon after. However, the process was not efficient enough to be really useful. Some simple calorimetric calculations showed that very little of the energy entering the chamber was actually getting to the metal. Much of it was being absorbed by the crucible, and the walls of the chamber were getting quite hot, showing that less than perfect absorption was taking place around the metal. Closer examination of the absorbancy of various materials followed, and attempts were made to formulate more efficient ferrite susceptors.

              How thin could an absorbing layer of magnetite be made in order to reduce its thermal capacity but retain its heating qualities? The granularity of the magnetite suggested it could be applied as a stucco in a ceramic shell build-up. How many layers would be necessary? Two were tried for a start, then one. Both crucibles heated well when placed close to the wave-guide port, but the heating was by no means even. Small areas of the shell would 'light-up', getting hot enough to melt the refractory. Test shells, after cooling, that were replaced in the oven, sometimes fired up and sometimes did not. Again, much testing was undertaken to try and solve this problem.

              Parallel experiments going on in the foundry involved heating glasses of various compositions in a microwave oven. It was found that although these were transparent to the microwaves when cold, they would absorb microwave energy when just below red heat. Maybe magnetite had to be above a critical temperature to absorb well. The carbon coated shells, we already knew, would always heat from a cold start. A double susceptor - a carbon (graphite) loaded primary coat stuccoed with magnetite sand - was tried with some confidence. The crucible, with a mould attached was fired and the temperature climbed steadily from cold, to something sufficient to melt the silver which was then cast. Further experiments led to temperatures high enough to melt small amounts of cast iron. This proved to be a limit - any increase above it caused the magnetite to flux and destroyed the shell. The hunt is on for susceptors that can take the temperature of the crucible beyond the magnetite limit. It may then be possible to cast even higher melting point metals, such as steel, by the microwave method.





              *********** REPLY SEPARATOR ***********

              On 1/3/04 at 1:04 PM thenelsons wrote:

              >My attempt at a first melt was a failure. I used what is now the "shop
              >microwave", an old 1400 watt Kenmore 1.5 cubic foot model. This unit was
              >top-of-the-line in 1989, which is probably why it still works.
              >I didn't really expect this attempt to work. I couldn't find silicon
              >carbide stones, only aluminum oxide. I tried using those as a heat
              >receptor, but a full power run for 20 minutes did not get hot enough to
              >melt
              >aluminum in a 2" tall by 1.5" wide stainless crucible (amazing resemblance
              >to the stainless salt shakers sold at Wal-Mart).
              >I made a second attempt using a stack of four silicon carbide 4" grinder
              >disks that were in the shop. That didn't work either.
              >Anyone have ideas on where I can find silicon carbide sharpening stones? I
              >tried the local shops, wal-mart, Harbor Frieght, Home Depot, Lowes, ACE
              >Hardware, but only aluminum oxide were available.
              >
              >Rick
              >
              >
              >
              >
              >This list is for discussion of metal casting
              >and does not accept attachments. For off topic discussion and to share
              >photos and stuff: join Sandcrabs by sending a blank message to:
              >sandcrabs-subscribe@yahoogroups.com
              >http://groups.yahoo.com/group/sandcrabs
              >Please visit our sponsor: Budget Casting Supply
              >http://budgetcastingsupply.com/
              >
              >Files area and list services are at:
              >http://groups.yahoo.com/group/hobbicastFor problems that cannot be
              >otherwise solved contact the list owner by email:
              >owly@...
              >
              >blems that cannot be otherwise solved contact the list owner by email:
              >owly@...
              >
              >
              >
              >Yahoo! Groups Links
              >
              >To visit your group on the web, go to:
              > http://groups.yahoo.com/group/hobbicast/
              >
              >To unsubscribe from this group, send an email to:
              > hobbicast-unsubscribe@yahoogroups.com
              >
              >Your use of Yahoo! Groups is subject to:
              > http://docs.yahoo.com/info/terms/
            • John Greene
              Hi, Using a microwave is really interesting to me, I hope that this thread continues. I have two ideas to throw out: 1- If graphite is a good absorber why not
              Message 6 of 8 , Jan 5, 2004
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                Hi,
                Using a microwave is really interesting to me, I hope that this thread
                continues.

                I have two ideas to throw out:

                1- If graphite is a good absorber why not use a graphite crucible.

                2- I use a mixture of fire clay and water as a wash on my crucibles -
                works good on crucibles made from pipe and I have read that used on ceramic
                crucibles it cuts out the gases from the flame penetrating the crucible and
                contaminating the melt. Anyway, why not mix some magnetite with this wash
                and paint it on the inside of the graphite crucible. It should make the heat
                transfer very efficient as the magnetite will be almost in contact without
                he melt. By being on the inside, the crucible will become somewhat of an
                insulator. Of course, One would still need to insulate the crucible as well
                as the walls of the microwave.

                Jack


                ----- Original Message -----
                From: "Stone Tool" <owly@...>
                To: <hobbicast@yahoogroups.com>
                Sent: Sunday, January 04, 2004 8:12 AM
                Subject: Re: [hobbicast] Microwave Melting


                > I don't know where the idea that silicone carbide was a sufficient
                microwave absorber to accomplish a melt came from..... In the earlier
                experiments done with microwave melting a slurry of ferrite and magnetite
                was used on the outside of the crucible. Unfortunately the original page is
                not to be found..... I thought I had saved it but didn't. The current web
                page uses the "Reid Technique" which is slightly different than simply
                pouring molten metal into a mold, but of course the same considerations
                apply here. They mention using graphite and magnetite. The really
                interesting aspect of this is that the magnetite appears not to become a
                good receptor of microwave energy until the temperature is elevated, while
                the graphite varies little, but is never adequate by itself.... it does
                however appear to bring the temp of the magnetite up to a level where it is
                an efficient absorber. This little bit of insight is probably the most
                important discovery of the whole experiment.... It probably applies to many
                substances which do not appear to be absorbers at normal temperatures. In a
                perfect world silicone carbide would turn out to be an ideal absorber at
                elevated temperatures, and one would simply coat a silicone carbide crucible
                with carbon and magnetite "stucco" to get it started as they found that the
                magnetite would not withstand the temps necessary to deal with steel. I
                would suggest beginning where these folks left off..... There is little
                value in starting from scratch when much groundwork has already been done.
                Perhaps I missed a post where someone discovered that silicone carbide was
                the ideal receptor...... I don't always catch everything that goes by
                here. Here are some paragraphs from the current microwave melting
                page that pertain to my comments:
                >
                > <><><><><>< From Microwave Melting ( much left
                out ) ><><><><><>
                >
                > Trials were begun which simply aimed to melt metals such as silver and
                bronze in open crucibles. However, it soon became obvious that casting to
                shape could also be accomplished by adapting the Reid Technique (RT) - a
                simplified ceramic-shell procedure for the casting of non-ferrous metals,
                patented in 1990. RT was first developed to avoid the problem of heat loss,
                which makes the the pouring of small melts very difficult - these
                difficulties arise however the metal is heated, and while the microwave
                technique set out here can be used for heating small amounts of metal in
                open crucibles, its greatest potential lies in its use as a flameless
                furnace in processes such as the Reid Technique. The crucial discovery, made
                during extended tests with various susceptors - materials which heat up when
                exposed to microwaves - was that two substances, graphite and magnetite,
                working together were required to achieve the kind of heating we were
                looking for.
                >
                > Early experiments using carbon as a susceptor were discouraging. The
                uninsulated crucibles barely attained red-heat and after running for 5 or so
                minutes the machine shut off. Insulation around the crucible helped, as did
                the realisation that the cooling air from the fan could be redirected. But
                it was obvious that a more efficient absorber had to be found. The
                literature on absorbers mentioned both silicon carbide and ferrites as
                susceptors, so an SiC paste was mixed with clay and applied to a thickness
                of about 8 mm and dried on the inside of a ceramic shell crucible, which we
                knew from earlier tests to be non-absorbing. After drying, it still didn't
                show red heat after 10 minutes in the microwave field. Powdered ferrites
                proved very difficult to obtain until it was realised that they were just
                modified iron oxides. A quick visit to the Ceramics Department gave samples
                of red, yellow, black and granular iron oxides. Similar sized samples of
                these were similtaneously put in the oven and fired for a couple of minutes.
                They all showed warming, but the granular substance (magnetite) was hot
                enough to burn the finger.
                >
                > Another crucible was prepared, lined in the same way, but this time with a
                clay-ferrite paste. 50 g of sterling silver was added, and the crucible was
                capped with a carbon lined shell. Although it became very hot the silver had
                not melted after 10 minutes of firing. The carbon-lined cap was replaced by
                one lined with magnetite/clay and the test was re-run. After 15 minutes
                firing the silver was found to have melted. A very exciting moment! Although
                the methods were a bit crude, a temperature of 900 degrees Celcius had been
                reached. Using a similar crucible, with a small mould attached, the first
                castings were made soon after. However, the process was not efficient enough
                to be really useful. Some simple calorimetric calculations showed that very
                little of the energy entering the chamber was actually getting to the metal.
                Much of it was being absorbed by the crucible, and the walls of the chamber
                were getting quite hot, showing that less than perfect absorption was taking
                place around the metal. Closer examination of the absorbancy of various
                materials followed, and attempts were made to formulate more efficient
                ferrite susceptors.
                >
                > How thin could an absorbing layer of magnetite be made in order to reduce
                its thermal capacity but retain its heating qualities? The granularity of
                the magnetite suggested it could be applied as a stucco in a ceramic shell
                build-up. How many layers would be necessary? Two were tried for a start,
                then one. Both crucibles heated well when placed close to the wave-guide
                port, but the heating was by no means even. Small areas of the shell would
                'light-up', getting hot enough to melt the refractory. Test shells, after
                cooling, that were replaced in the oven, sometimes fired up and sometimes
                did not. Again, much testing was undertaken to try and solve this problem.
                >
                > Parallel experiments going on in the foundry involved heating glasses of
                various compositions in a microwave oven. It was found that although these
                were transparent to the microwaves when cold, they would absorb microwave
                energy when just below red heat. Maybe magnetite had to be above a critical
                temperature to absorb well. The carbon coated shells, we already knew, would
                always heat from a cold start. A double susceptor - a carbon (graphite)
                loaded primary coat stuccoed with magnetite sand - was tried with some
                confidence. The crucible, with a mould attached was fired and the
                temperature climbed steadily from cold, to something sufficient to melt the
                silver which was then cast. Further experiments led to temperatures high
                enough to melt small amounts of cast iron. This proved to be a limit - any
                increase above it caused the magnetite to flux and destroyed the shell. The
                hunt is on for susceptors that can take the temperature of the crucible
                beyond the magnetite limit. It may then be possible to cast even higher
                melting point metals, such as steel, by the microwave method.
                >
                >
                >
                >
                >
                > *********** REPLY SEPARATOR ***********
                >
                > On 1/3/04 at 1:04 PM thenelsons wrote:
                >
                > >My attempt at a first melt was a failure. I used what is now the "shop
                > >microwave", an old 1400 watt Kenmore 1.5 cubic foot model. This unit was
                > >top-of-the-line in 1989, which is probably why it still works.
                > >I didn't really expect this attempt to work. I couldn't find silicon
                > >carbide stones, only aluminum oxide. I tried using those as a heat
                > >receptor, but a full power run for 20 minutes did not get hot enough to
                > >melt
                > >aluminum in a 2" tall by 1.5" wide stainless crucible (amazing
                resemblance
                > >to the stainless salt shakers sold at Wal-Mart).
                > >I made a second attempt using a stack of four silicon carbide 4" grinder
                > >disks that were in the shop. That didn't work either.
                > >Anyone have ideas on where I can find silicon carbide sharpening stones?
                I
                > >tried the local shops, wal-mart, Harbor Frieght, Home Depot, Lowes, ACE
                > >Hardware, but only aluminum oxide were available.
                > >
                > >Rick
                > >
                > >
                > >
                > >
                > >This list is for discussion of metal casting
                > >and does not accept attachments. For off topic discussion and to share
                > >photos and stuff: join Sandcrabs by sending a blank message to:
                > >sandcrabs-subscribe@yahoogroups.com
                > >http://groups.yahoo.com/group/sandcrabs
                > >Please visit our sponsor: Budget Casting Supply
                > >http://budgetcastingsupply.com/
                > >
                > >Files area and list services are at:
                > >http://groups.yahoo.com/group/hobbicastFor problems that cannot be
                > >otherwise solved contact the list owner by email:
                > >owly@...
                > >
                > >blems that cannot be otherwise solved contact the list owner by email:
                > >owly@...
                > >
                > >
                > >
                > >Yahoo! Groups Links
                > >
                > >To visit your group on the web, go to:
                > > http://groups.yahoo.com/group/hobbicast/
                > >
                > >To unsubscribe from this group, send an email to:
                > > hobbicast-unsubscribe@yahoogroups.com
                > >
                > >Your use of Yahoo! Groups is subject to:
                > > http://docs.yahoo.com/info/terms/
                >
                >
                >
                >
                > This list is for discussion of metal casting
                > and does not accept attachments. For off topic discussion and to share
                photos and stuff: join Sandcrabs by sending a blank message to:
                sandcrabs-subscribe@yahoogroups.com
                > http://groups.yahoo.com/group/sandcrabs
                > Please visit our sponsor: Budget Casting Supply
                > http://budgetcastingsupply.com/
                >
                > Files area and list services are at:
                > http://groups.yahoo.com/group/hobbicastFor problems that cannot be
                otherwise solved contact the list owner by email:
                > owly@...
                >
                > blems that cannot be otherwise solved contact the list owner by email:
                > owly@...
                >
                >
                >
                > Yahoo! Groups Links
                >
                > To visit your group on the web, go to:
                > http://groups.yahoo.com/group/hobbicast/
                >
                > To unsubscribe from this group, send an email to:
                > hobbicast-unsubscribe@yahoogroups.com
                >
                > Your use of Yahoo! Groups is subject to:
                > http://docs.yahoo.com/info/terms/
                >
                >
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