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Potmetal homebrew casting question

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  • Potmetal homebrew casting question

    Zamac has got a certain reputation.
    Has anyone ever tried to cast something out of this stuff.
    It should be fairly easy melting all sorts of broken things and make a crude cast. Not much heat required.
    The reason is that i like the apearance of a crude casting much better than a bolted on cold rolled welded hotrolled gadget for the workshop.
    Now i have got my heat treat oven i can start with melting the casings of those two nv divices
    From what i have seen on some home casting pages casting brass takes to much shop space to even think about starting.
    Someone got any experience with this?

  • #2
    I have limited understanding of foundry practice os here's my inexpert take on the topic. Zinc aluminum sand casting is certanly possible but there are a few factors that get in the way of satisfactory results.

    One is cooling rate. Cool die casting alloys too slowly and you get segregation and huge grain growth. Too much superheat and you get good mold filling at the expence of shrinking tears and distortion. Too little and you have trouble with filling and cold shuts.

    Another is using miscelaneous scrap as melt material. Zinc Aluminum die cast metals are carefully balanced/ Mixed scrap upsets the balance almost always to the detrement of the product properties and success in the foundry.

    There are zinc casting alloys available that work quite well in sand molding and if you care to take on the manufacture of metal molds, good gravity castings are possible there too. So the problem as I see it isn't so much "can you" but "will it work". I submit that given a good mold flask and the right alloy, success is almost unavoidable.

    OTH, misc pot metal scrap melted down and poured even in a good mold may produce unsatisfactory results. Here its metallurgy that's kicking your butt, not process.

    Comment


    • #3
      There was an article in one of the old (black & white?) HSM magazines where the author did Zamac casting. He claimed that one of the Zamac alloys was nearly as strong as cast iron.

      McMaster sells Zamac ingots, and it melts at ~ 700° -- low enough to do on an industrial hot plate (mine goes up to 1,000° F). I don't know if the Zinc fumes would be toxic though...

      Zinc Alloy Ingot

      Excellent retention of molded dimensions combined with good corrosion resistance make this an ideal casting alloy. Composition is approximately 95% zinc, alloyed with 3.9 to 4.3% aluminum, .10% copper, and other elements. Melting temperature range is 718° to 728° F. Ingots are approximately 6" x 2 1/2" x 1 3/4" and weigh approximately 6 lbs.
      9069K2 Each $41.00
      "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

      Comment


      • #4
        ZAMAK is good stuff, if used properly. I don't understand why people belittle it. My change gears are 75 years old, fully toothed, and not corroded. Would I prefer steel? Of course. But you pay more for that.

        ZAMAK is made of zinc, aluminum, magnesium, and copper. If you can melt all those and get them mixed then you got it goin' on.

        Copper's melting point is just under 2000 deg F. Aluminum and Magnesium melt at about 1200 deg F. Zinc melts at about 800 deg F. The latter 3 are easily within the reach of the home foundry. I'm not too sure about the copper...

        Abuse of ZAMAK is seen statistically by the quantity of broken gear cover brackets and apron traversal housings on Atlas/Craftsman lathes ;-)

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        • #5
          Tony
          "...as mechanical as a cornflake"
          Tony a guy got caught round here for shooting hundreds of corn flakes,he got life.






          Well he was England's biggest cereal killer in many years.
          Please excuse my typing as I have a form of parkinsons disease

          Comment


          • #6
            I got into this zany hobby by finding Dave Gingerys series of books, and ole unca Dave had kind words for Zamac/potmetal and pointed out places in his projects where it could be beneficial.

            So, I have used it on several occasions with good success. I just go to the scrap yard and ask for it, they have a bin for separating it out...its probably the cheapest of the scrap. I've got an old propane fish cooker and a plumbers lead pot that I'll just pile full, light it up and go about making up my mold and within 30min to an hour itll be melted. I go about this as I do a lot of things, just by the seat of the pants! ... I dont know about proper temperature, metal content, etc, --- "its melted and there aint no lumps, pour it up"

            I got one of the generic, no name import, 16" band saws and the the casting that held the top axle and allowed tracking of the wheel cracked. Knowing that a replacement part was non-existent, --- I cast a new one out of "pot".... It had cracked, not broken, so I carefully drove the steel axle out of the casting and used it as the mold in green sand, separated the casks and set the axle in the sand, closed up and poured the "headlight trim, washing machine trim, sign facia, etc" in and got a perfectly good casting! I was quite pleased to not have to scrap that saw!
            If everything seems to be going well, you have obviously overlooked something........

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            • #7
              Bill, are the fumes overwhelming when you heat-up the Zamac?

              In other words, is it something I could do in the garage?
              "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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              • #8
                Alistair,have you already been sniffing the fumes?
                Hans

                Comment


                • #9
                  Zamak-3 (Zn-4Al-0.04Mg) and Zamak-5 (Zn-4Al-1Cu-0.04Mg) are liquid at 728F. Zinc boils at 1660F. If you hold your melting temperature to a resonable level like below 750F, there is very little zinc fume. This is also sufficiently hot for the copper to dissolve readily, no need to come even close to molten copper temperatures.

                  Zamak-5 has a typical die cast strength of 47 ksi per Metals Handbook, about 2/3rds of what a good cast iron would provide.

                  Comment


                  • #10
                    Originally posted by lazlo
                    Bill, are the fumes overwhelming when you heat-up the Zamac?

                    In other words, is it something I could do in the garage?
                    Hmmm Laz.... I had to dust off some memory cobwebs to pull that story out of the archives, --- was some years ago. I dont remember noticing fumes ... and I did do it with the fish cooker sitting over to the side of the shop .... dang, it might've been summertime and I had the doors flung open!

                    2-4 years ago I was working on a little hit-n-miss that called for a 5" flywheel out of Al .... so I cast one up... little engine just wouldnt run...finally decided flywheel was just too light. Using the same pattern, I fired up the fish cooker and cast one up in 'pot', MUCH heavier--- it got the engine to running, (though not very well!!)

                    And, I am well aware of the fumes, I've been put into a few situations of HAVING to weld up some galvanized and that can be POTENT!
                    If everything seems to be going well, you have obviously overlooked something........

                    Comment


                    • #11
                      Thanks Bill -- I never thought to try the junk yard. McMaster is selling it for $7/lb, but if I can find some scrap Zamac at the junkyard, I'll try to melt some it on my industrial hotpot, and see what it does.
                      "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                      Comment


                      • #12
                        "Zamak" and "pot metal" are not synonyms, in the same way that "AISI 1020" and "mystery metal" are not synonyms.

                        Zamak is a series of alloys with definite compositions and well-documented mechanical properties.

                        Pot metal is crap with unknown but not particularly good properties. It is useful because die-casting is easy (read: cheap) and it will sort-of hold its shape after it's cast.

                        Comment


                        • #13
                          Originally posted by lbender
                          Zamak-3 (Zn-4Al-0.04Mg) and Zamak-5 (Zn-4Al-1Cu-0.04Mg) are liquid at 728F. Zinc boils at 1660F. If you hold your melting temperature to a resonable level like below 750F, there is very little zinc fume.
                          lbender, thanks for that -- somehow I missed your post earlier. So that tells me that it should be safe to melt on an industrial hot plate, and that I won't kill everyone with Zinc fumes

                          Sounds like you really want the real Zamak-5 alloy. Does anyone know of a source cheaper than McMaster?
                          "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                          Comment


                          • #14
                            It's about $0.60/pound if you buy it by the standards or ingots in minimum orders. A standard is about 8lbs and an ingot is about 16lbs. The minimum will vary by supplier but few will deal with less than a $250 order (plus freight). You might want to check current prices since copper has gone up so much.

                            Zamak is a trademark name for specific blends of die-cast alloys. It's like Kleenex is to facial tissue. There are other "die-cast" alloys. The term "pot-metal" is a slang label given to all die-cast alloys including Zamak.

                            If you want to make your own, you'll need to get the copper higher than 750* and add a flux, aluminum then zinc or you'll be stirring for days. Don't try to melt it an iron pot! Borax works good for a flux. If you try to remelt a die-cast alloy (scrap), you'll need to add a chlorinated metal salt to pull the impurities out to dross. Zinc chloride, magnesium chloride or potassium chloride should work.

                            Aluminum engine blocks and pistons are a good source for aluminum in the die-cast alloy. They already contain silicon, magnesium and copper. You can get zinc in the form of sacrificial anodes in most plumbing or boat shops. Make sure they are zinc. Magnesium has been used lately in some.

                            Comment


                            • #15
                              Forgot to mention:
                              To tell the difference between anodes, zinc will oxidize and have a white or very light grey chalky coating. Magnesium turns dark. The oxide will look dark grey similar to lead.

                              Also - A good source for scrap die-cast is old lawn mower engines. In particular, Briggs & Stratton. They seem to be plentiful in the scrap yards. Strip the blocks down, clean, heat to 400 until they stop smoking, cool then clean again (or use an etch dip). Bust into pieces, add your metal salt and melt. Great stuff.

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