An introduction to metal casting
Updated: April 18, 2011
Metal Casting is a useful skill if you want to repair tools, make jewelry or make all sorts of useful things that will last a lifetime. Metal casting can be very easy and there are almost endless applications once you know how. Outlined here is one simple safe method for making quick castings using easy to melt zinc or other metals like aluminum if you crank the heat up a bit.
- Fabricating parts
- Decorative weights and sinkers
- Making metal stamps for wood burning
- Candle holders
- Tool handles
- Jewelry making
- If you are Zinc casting you need a source of Zinc metal. The first step is to get zinc metal from a scrap dealer, dealer in bullion or online such as eBay. The smaller one or two pound ingots are fairly easy to work with. Larger ingots require cutting with a torch or melting in a larger container and pouring smaller easy to work with ingots. Post 1981 pennies used to be an easy source of zinc for small scale castors but in 2006 there were laws passed against melting pennies. And this is actually a good thing too from a quality perspective. It doesn’t take much effort to get Zinc in bar form and these ingots tend to have very few impurities making for better quality castings.
- If you are Aluminum casting, aluminum wire or most any small scrap that will fit into your “melt can” will work. But aluminum casting requires a hand torch and much higher temperatures then casting with zinc.
- If you are casting with other metals like silver, the clay molds described in the next section work fine with high temperature molten metals.
- If you are casting Zinc you can use a small propane stove.
- If you are casting aluminum you will want a propane torch or a map gas torch or a blower and charcoal to get the melt can hot enough. I use a propane torch.
- You will need a steel tuna can with a rounded unsoldered bottom.
- Pliers for moving the hot tuna can.
- Clay dug from near a river works well.
- Optional - Flour to mix with the clay to make a better molding material.
- A shell, stamp or something to make an impression in the clay.
- An Altoids tin or second tuna can. You put your clay mold into the can so extra metal that spills out of your mold doesn’t spill onto the ground. I often use an old metal baking tray.
- A bucket or water to cool your casting quickly and for safety if you need water.
- Optional - A file and little steel wool for polishing your casting.
- Optional - An old metal fork for clearing out slag in your melt.
- Optional - An old metal spoon for measuring out liquid metal. But I usually just pour right from the can.
- Step 1 - Get the materials you need together.
- Step 2 - Make a mold. There are many ways to make a mold for metals. Sand, clay and oil works, Salt and sand molds work, I've heard plaster of paris works, and high temp silicone molds can work with zinc. But for a quick demonstration I like clay molds.
You can just put some clay into a second tuna can. Make an imprint in the clay using a shell, stamp or something you would like to copy. Now you have a mold. To make a better clay mold I mix clay and maybe 5% by weight of flour and a little cotton fiber. The cotton fiber is optional. But flour clay mixes take imprints much better then clay alone and can be dried very fast. Just an hour in a conventional oven @ 250-300 and the mold is dry. The drying is optional, but it yields better results and these molds are reusable.
Also my clay/flour molds smoke a little when I use them. The problem with smoking is it can create bubbles in your casting. If you find that to be a problem, they are clay and can be fired in a charcoal fire, campfire or by using a hand torch. Also if you are firing a mold, if you put the mold inside a larger tin in the fire it will heat and cool the mold more evenly and it will be less likely to crack during the firing process.
- Set up a bucket of water outside where you want to do your metal casting.
- Pinch your tuna can with the pliers so it makes a spout.
- Start up a stove and melt the metal in your can. (5-10 minutes for Zinc)
- Shake the can a little using the pliers so any slag settles (or use a fork).
- A wind guard made from a coffee-can helps speed things up if it’s a cold or windy day.
- Using the pliers carefully pour the metal into your mold.
- I sometimes give the mold a tap or little shake so the metal spreads out better.
- The metal will be solid in about 30 seconds or faster if you blow on it. At this point you can flip the casting over and pop the metal out if you are wearing welding gloves (that's what I do). Or you can use pliers to drop the mold into the bucket of water if you don't mind losing the mold. After a second in the water, your cast should be cool enough to touch.
- Dry off, file and polish your casting as needed (Usually you won't need to polish).
- Zinc is safe to handle and plenty strong for all sorts of castings. However for a stronger alloy on par with cast iron, mix in 20-30% aluminum.
- A map gas torch or oxyacetylene torch is great for speeding up the melting process.