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Casting molten metals? Answered

What mold materials are suggested for making cast duplicates of metal objects Metals that may be used in some of my planned projects may include aluminum, brass, bronze, mild steel, and the like. (Jewelry, belt buckles, as well as similar items are planed)

I realize that the high temperature may be a problem in material choice for the molding material(s). I think mild steel is the highest melting temperature of all the metals I've considered, and it's about 2700°F (1482°C). (Suggestions for easier to work with metals or hard casting materials would be happily accepted, considering I'm looking to make a set of reusable hard positives to make casting negatives for larger numbers of final product.)

The choices I make for FINAL material will also include how well they can be plated, so steel may be for an intermediate mold positive, and something more easily plated (with yellow gold) like brass would be a final choice. Though, I may go for highly polishing the brass and then covering it with a corrosion inhibitor to avoid the high cost of gold.

4 Replies

Paige RussellBest Answer (author)2017-04-06

HI John,


I'm afraid aluminum, silver, and copper have melting temperatures that are too high for silicone molds to withstand.

There are several types of RTV silicone rubber that you can use for casting low-temperature metal/alloys like tin and pewter (SmoothOn's Mold Max 60 has the highest heat resistance that I know of at 560° F / 294° C), but RTV silicone is NOT recommended for higher melting temperature metals.

To cast silver or copper, you'll need to do lost wax casting in a plaster mold. Here are two instructables and an online example that go over the lost wax casting process:




I've never cast steel, so I'm afraid you and Google are on your own for that one. :)

Hope this was helpful!


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ithica2012 (author)Paige Russell2017-05-28

Plaster works for aluminum lead and metal that melt at lower temps higher temps you will need to look in to sand casting or lost wax methods.

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GaryV50 (author)ithica20122018-01-13

I once cleaned up a dental office and held on to an old box of dental investment casting material used along with the lost wax method. The item is first made in a hard wax like carnauba, then is sunk into the investment slurry made of investment casting powder and water, which looks like smooth mortar mix or hydraulic cement, with a cylinder poking into the investment until it reaches the wax, like a small dowel or unsharpened pencil. When fully dried, the investment is brought up to the temperature where the wax melts and can freely be poured out the investment. Then your molten metal can be poured into the cylinder and into the mold. Many times there are either multiple pour points or one pour point and another for removing floating dross or air pockets. After cooling the mold is broken and the part remains with the stem(s) that you poured into, (kind of like the stems that protrude from plastic hobby model parts). You cut off the stems, file, grind or de-burr with a Dremel tool with appropriate grinding stones, and polish out.

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mwinegardner (author)2017-04-14

For casting metals you may want to look into the sand casting process. Its commonly used for aluminum, brass, bronze, and iron. Steel is usually investment cast, i.e. lost wax.

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