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Re: different finish

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  • pietro_45
    Hi, I m new to the group, but would like to offer that I reconize this type of problem, as I ve made this kind of pour myself. Looks like porosity in the
    Message 1 of 14 , Dec 31, 2001
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      Hi, I'm new to the group, but would like to offer that I reconize
      this type of problem, as I've made this kind of pour myself.

      Looks like porosity in the swivel, probably the handle too if it
      broke so easily. This usually results from a combination of pouring
      too hot, and or too much moisture in the sand, and most importantly,
      insufficient venting, in combination with the above.

      So in a nutshell, too much gas (steam) which couldn't escape.

      Just my two-penneth.

      Peter
    • Joe and Betty Harralson
      Terry, After thinking about it for a while, I have the following comments/suggestions. First as you may know from other posts, Lyle and I don t agree on the
      Message 2 of 14 , Jan 1, 2002
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        Terry,

        After thinking about it for a while, I have the following
        comments/suggestions. First as you may know from other posts, Lyle and I
        don't agree on the use of flux and degasser tablets. He feels you don't
        need them and judging from his web posts and different stuff I have to say
        he certainly is one of the more knowledgeable people on hobbicast. The fact
        that he and Fred both say you don't need flux gave me reason to pause and
        think. However, I concluded that first, the flux may not be as important as
        I thought it was, and second if you are not careful with how you use it, you
        might do more harm than good. My reason for still thinking flux can be good
        if used correctly are as follows:

        1. There are sound technical reasons for it to work. In this case I am
        thinking of a cover flux that prevents the absorption of hydrogen. Since
        water is a product of combustion, any crucible furnace is going to have a
        fair amount of superheated water vapor in it. A cover flux will reduce the
        amount of hydrogen absorbed, but a film of oxide will also reduce the
        hydrogen if it isn't disturbed.

        A flux that also does some cleaning may also be helpful. Ideally our metal
        is clean to begin with but for many of us who melt mainly scrap that isn't
        always the real world. What you don't want to do is a lot of stirring and
        mixing, particularly mixing the flux into the melt.

        2. ALL of my technical books discuss flux at length and although to be
        honest they never say you have to use it, they also never say that you don't
        have to. My interpretation is that they simply assume that you will use it.

        3. All of the commercial foundries I have been in used flux as least as far
        as I can recall. We use it at school.

        4. All of the foundry supply places sell it and so I cannot be the only one
        who thinks it useful.

        5. I almost always use it and have good results. This is of course the same
        argument Lyle uses and I admit it's the weakest. The problem is what do we
        mean by good results? Few if any hobby casters are measuring the amount of
        hydrogen absorbed, although it's easy to do. Few if any hobby casters
        measure the mechanical properties of their castings, such as hardness,
        tensile strength, or elongation. So what we mean by good is that the
        castings are bright and clean, machine well, and don't have any obvious
        porosity.

        So, I concluded that flux and degassing are a good thing if done well but
        you can achieve acceptable results without it. I still plan to use them,
        although some day if time permits I might try a few experiments.

        Having said all that, what about your problem? First I am not sure it has
        anything to do with flux. I wonder if the larger casting is actually less
        brittle than the small ones? Since it's larger and stronger the fact that
        it might be brittle would be hard to establish without some kind of test.
        The poor surface finish on the small parts is something I want to think
        about more.

        Brittleness can come from many causes, but you might consider the following:

        Brittleness and coarse grain structure are often caused by iron
        contamination. Over heating the melt could make this problem worse.

        Magnesium contamination in aluminum- copper alloys will cause brittleness.

        Iron, silicon, and copper will cause brittleness in aluminum-magnesium
        alloys.

        Hydrogen porosity can be invisible to the naked eye. You might have a great
        deal of micro porosity. People often confuse shrinkage and porosity,
        although they are really two different problems. Hydrogen absorption is
        very temperature dependent, another reason to avoid overheating.

        So, my suggestions are to keep using flux and degas. I would sprinkle the
        cover flux over the melt and leave it alone until you are ready to pour.
        Pour as cold as you can and not get misruns. Degas by wrapping the degasser
        in aluminum foil and then plunge it in using a tool like that described on
        the BCS web site. Skim the top of the melt and pour. Try coating your
        tools and crucible with a wash. I have heard that a good wash can be made
        from limestone ground very fine mixed with water and a little sodium
        silicate. I haven't used it but it might be worth a try if you don't want
        to buy a wash.

        Be careful what you melt. Try to keep the melt all the same thing, that is
        don't mix a lot of different kinds of scrap together. Avoid remelting the
        metal again and again, don't use too much material like sprues and risers
        from previous castings. Keep your scrap clean and dry, and preheat it
        before it goes into the melt.

        Above all, keep at it. There are lots of little details that affect how
        your castings come out, and they all matter. Consider keeping a notebook
        and taking notes on every pour. In time you will learn what works best for
        you.

        Good Luck

        Joe
        ----- Original Message -----
        From: Terry Alexander <mercdogxx@...>
        To: <hobbicast@yahoogroups.com>
        Sent: Sunday, December 30, 2001 11:33 PM
        Subject: [hobbicast] different finish


        > Hello All,
        > I poured my bed (24"x1.5"x1.5" x.25" wall ), a handle and swivel base for
        my
        > Gingery lathe this morning. The bed came out good with the finish I
        > expected, the same all my parts have, but the other two (which were in a
        > single flask) have a rougher finish, and are more brittle and weak. While
        > cutting off the runners I noticed how brittle they are, and the handle I
        can
        > break with my hands, and I've poured two or three of the same handle, and
        > can't break them. The runners, gates and spru spout were rough, but the
        top
        > of the spru was smoother.
        > I poured all parts from one crucible fill (6lbs total Al), the bed then
        the
        > other two. I use 90 mesh green sand, a steel crucible, 356 Aluminum, and
        > use flux and degasser.
        > I've posted a few pictures, not sure if you'll be able to see the
        difference
        > or not. They're in the photos section under Terry's Albums->bed and
        swivel
        > castings.
        > -Terry A
        >
        >
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        >
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      • Terry Alexander
        I think overheating is the biggest cause. And fact the two molds were different is because of the sizes, and how they were fed. And as Joe pointed out,
        Message 3 of 14 , Jan 2, 2002
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          I think overheating is the biggest cause. And fact the two molds were
          different is because of the sizes, and how they were fed. And as Joe
          pointed out, without realing testing the parts I don't know how different
          they really are. Looking through my notes... and this pour's superheating
          time was 2min. longer then other "good" pours.
          Anyway thanks for the replies. I'll try and to do experiments with usage of
          flux and degass, it would be nice to have a better undersanding of what they
          are or arn't doing for me.
          -Terry A

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        • Joe and Betty Harralson
          Terry, I recall there were some earlier discussions on surface finish with lots of good ideas about what causes rough finish. You might want to go back and
          Message 4 of 14 , Jan 2, 2002
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            Terry, I recall there were some earlier discussions on surface finish with
            lots of good ideas about what causes rough finish. You might want to go
            back and check these out.

            My muller is almost done. I have tested it and there were a few problems
            that I needed to fix. It is now working very well. I still need to make a
            chute for the sand as it doesn't quite fall into the tub like I had
            expected. Painting will have to wait until it warms up/dries up around
            here. Almost constant rain for the last month.

            Joe
            ----- Original Message -----
            From: Terry Alexander <mercdogxx@...>
            To: <hobbicast@yahoogroups.com>
            Sent: Wednesday, January 02, 2002 1:09 PM
            Subject: Re: [hobbicast] Re: different finish


            > I think overheating is the biggest cause. And fact the two molds were
            > different is because of the sizes, and how they were fed. And as Joe
            > pointed out, without realing testing the parts I don't know how different
            > they really are. Looking through my notes... and this pour's superheating
            > time was 2min. longer then other "good" pours.
            > Anyway thanks for the replies. I'll try and to do experiments with usage
            of
            > flux and degass, it would be nice to have a better undersanding of what
            they
            > are or arn't doing for me.
            > -Terry A
            >
            > _________________________________________________________________
            > Send and receive Hotmail on your mobile device: http://mobile.msn.com
            >
            >
            > Please visit our sponsor: Budget Casting Supply
            > http://budgetcastingsupply.com/
            >
            > The Home Foundrymen's Association website may be found here:
            http://members.nbci.com/HWilkinson/
            > It includes member project pages & links
            >
            > To unsubscribe from this group, send an email to:
            > hobbicast-unsubscribe@egroups.com
            >
            >
            >
            > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
            >
            >
          • Terry Alexander
            Joe, Have an photo of your muller yet? Ya, the rain is awful, I had all least week off and couldn t pour cause of it. I have a few patterns finished and am
            Message 5 of 14 , Jan 2, 2002
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              Joe,
              Have an photo of your muller yet? Ya, the rain is awful, I had all least
              week off and couldn't pour 'cause of it. I have a few patterns finished and
              am just waiting for the rain to stop.
              I got Ed Hamiltons book "Patternmaking Guide", per your suggestion. Great
              book lots of good detail and neat tricks of the trade (I'm have way through
              it thanks to all the rain). A lot of thinks that once he explains them are
              so simple and ingenious you think "du, why didn't I think of that".

              -Terry A


              >From: "Joe and Betty Harralson" <jbharr@...>
              >Reply-To: hobbicast@yahoogroups.com
              >To: <hobbicast@yahoogroups.com>
              >Subject: Re: [hobbicast] Re: different finish
              >Date: Wed, 2 Jan 2002 14:15:12 -0800
              >
              >Terry, I recall there were some earlier discussions on surface finish with
              >lots of good ideas about what causes rough finish. You might want to go
              >back and check these out.
              >
              >My muller is almost done. I have tested it and there were a few problems
              >that I needed to fix. It is now working very well. I still need to make a
              >chute for the sand as it doesn't quite fall into the tub like I had
              >expected. Painting will have to wait until it warms up/dries up around
              >here. Almost constant rain for the last month.
              >
              >Joe
              >----- Original Message -----
              >From: Terry Alexander <mercdogxx@...>
              >To: <hobbicast@yahoogroups.com>
              >Sent: Wednesday, January 02, 2002 1:09 PM
              >Subject: Re: [hobbicast] Re: different finish
              >
              >
              > > I think overheating is the biggest cause. And fact the two molds were
              > > different is because of the sizes, and how they were fed. And as Joe
              > > pointed out, without realing testing the parts I don't know how
              >different
              > > they really are. Looking through my notes... and this pour's
              >superheating
              > > time was 2min. longer then other "good" pours.
              > > Anyway thanks for the replies. I'll try and to do experiments with
              >usage
              >of
              > > flux and degass, it would be nice to have a better undersanding of what
              >they
              > > are or arn't doing for me.
              > > -Terry A
              > >
              > > _________________________________________________________________
              > > Send and receive Hotmail on your mobile device: http://mobile.msn.com
              > >
              > >
              > > Please visit our sponsor: Budget Casting Supply
              > > http://budgetcastingsupply.com/
              > >
              > > The Home Foundrymen's Association website may be found here:
              >http://members.nbci.com/HWilkinson/
              > > It includes member project pages & links
              > >
              > > To unsubscribe from this group, send an email to:
              > > hobbicast-unsubscribe@egroups.com
              > >
              > >
              > >
              > > Your use of Yahoo! Groups is subject to
              >http://docs.yahoo.com/info/terms/
              > >
              > >
              >
              >
              >Please visit our sponsor: Budget Casting Supply
              >http://budgetcastingsupply.com/
              >
              >The Home Foundrymen's Association website may be found here:
              >http://members.nbci.com/HWilkinson/
              >It includes member project pages & links
              >
              >To unsubscribe from this group, send an email to:
              >hobbicast-unsubscribe@egroups.com
              >
              >
              >
              >Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
              >
              >




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            • Joe and Betty Harralson
              Terry, I wanted to paint it before I post a picture of it, and I also have to borrow a digital camera or else have my prints made into digital. There is a
              Message 6 of 14 , Jan 3, 2002
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                Terry, I wanted to paint it before I post a picture of it, and I also have
                to borrow a digital camera or else have my prints made into digital. There
                is a picture of it partially finished in my stuff on the files area of
                hobbicast.

                Joe
                ----- Original Message -----
                From: Terry Alexander <mercdogxx@...>
                To: <hobbicast@yahoogroups.com>
                Sent: Wednesday, January 02, 2002 11:49 PM
                Subject: Re: [hobbicast] Re: different finish


                > Joe,
                > Have an photo of your muller yet? Ya, the rain is awful, I had all least
                > week off and couldn't pour 'cause of it. I have a few patterns finished
                and
                > am just waiting for the rain to stop.
                > I got Ed Hamiltons book "Patternmaking Guide", per your suggestion. Great
                > book lots of good detail and neat tricks of the trade (I'm have way
                through
                > it thanks to all the rain). A lot of thinks that once he explains them
                are
                > so simple and ingenious you think "du, why didn't I think of that".
                >
                > -Terry A
                >
                >
                > >From: "Joe and Betty Harralson" <jbharr@...>
                > >Reply-To: hobbicast@yahoogroups.com
                > >To: <hobbicast@yahoogroups.com>
                > >Subject: Re: [hobbicast] Re: different finish
                > >Date: Wed, 2 Jan 2002 14:15:12 -0800
                > >
                > >Terry, I recall there were some earlier discussions on surface finish
                with
                > >lots of good ideas about what causes rough finish. You might want to go
                > >back and check these out.
                > >
                > >My muller is almost done. I have tested it and there were a few problems
                > >that I needed to fix. It is now working very well. I still need to make
                a
                > >chute for the sand as it doesn't quite fall into the tub like I had
                > >expected. Painting will have to wait until it warms up/dries up around
                > >here. Almost constant rain for the last month.
                > >
                > >Joe
                > >----- Original Message -----
                > >From: Terry Alexander <mercdogxx@...>
                > >To: <hobbicast@yahoogroups.com>
                > >Sent: Wednesday, January 02, 2002 1:09 PM
                > >Subject: Re: [hobbicast] Re: different finish
                > >
                > >
                > > > I think overheating is the biggest cause. And fact the two molds were
                > > > different is because of the sizes, and how they were fed. And as Joe
                > > > pointed out, without realing testing the parts I don't know how
                > >different
                > > > they really are. Looking through my notes... and this pour's
                > >superheating
                > > > time was 2min. longer then other "good" pours.
                > > > Anyway thanks for the replies. I'll try and to do experiments with
                > >usage
                > >of
                > > > flux and degass, it would be nice to have a better undersanding of
                what
                > >they
                > > > are or arn't doing for me.
                > > > -Terry A
                > > >
                > > > _________________________________________________________________
                > > > Send and receive Hotmail on your mobile device: http://mobile.msn.com
                > > >
                > > >
                > > > Please visit our sponsor: Budget Casting Supply
                > > > http://budgetcastingsupply.com/
                > > >
                > > > The Home Foundrymen's Association website may be found here:
                > >http://members.nbci.com/HWilkinson/
                > > > It includes member project pages & links
                > > >
                > > > To unsubscribe from this group, send an email to:
                > > > hobbicast-unsubscribe@egroups.com
                > > >
                > > >
                > > >
                > > > Your use of Yahoo! Groups is subject to
                > >http://docs.yahoo.com/info/terms/
                > > >
                > > >
                > >
                > >
                > >Please visit our sponsor: Budget Casting Supply
                > >http://budgetcastingsupply.com/
                > >
                > >The Home Foundrymen's Association website may be found here:
                > >http://members.nbci.com/HWilkinson/
                > >It includes member project pages & links
                > >
                > >To unsubscribe from this group, send an email to:
                > >hobbicast-unsubscribe@egroups.com
                > >
                > >
                > >
                > >Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
                > >
                > >
                >
                >
                >
                >
                > _________________________________________________________________
                > Join the world's largest e-mail service with MSN Hotmail.
                > http://www.hotmail.com
                >
                >
                > Please visit our sponsor: Budget Casting Supply
                > http://budgetcastingsupply.com/
                >
                > The Home Foundrymen's Association website may be found here:
                http://members.nbci.com/HWilkinson/
                > It includes member project pages & links
                >
                > To unsubscribe from this group, send an email to:
                > hobbicast-unsubscribe@egroups.com
                >
                >
                >
                > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
                >
                >
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