To start melting copper you need to obtain some of the shiny stuff! This can be from scrapping or by purchasing copper from scrapyards or copper dealers.
Copper melts at 1084°C (1983°F). To pour molten copper the temperature needs to be 50-100 degrees Celsius higher than the melting point, as to prevent the copper solidifying mid pour. 1150°C is a common pouring temperature for copper ingots.
For an average ingot that weighs 1kg (2.2lbs) you may need about 1.050kgs to account for impurities that burn off and for slag. This will vary depending on the quality of copper used. For bright and shiny copper there will be minimal slag, but for motor windings and dirty copper that have varnish and other contaminant coatings there will be slightly more waste.
Items Required to Melt Copper.
- Furnace. This can be induction, oil fired, propane/gas, solid fuel. I use a gas furnace but had previously built a solid fired one for aluminium. This used a standard BBQ gas cylinder with a gas burner attachment.
- Crucible. Crucibles are what hold scrap metal while it heats up, ultimately into a liquid form. They are generally clay and graphite in construction, but can be made from pure graphite, silicon carbide/graphite mixes etc.
- Ingot Mould. This is what makes the ingot shape and they vary depending required ingot size requirements. When the liquid copper is at temperate for pouring, you can remove the crucible from the furnace and then pour the molten copper into the mould where it will solidify. Commonly made of pure graphite.
- Crucible Tongs. Used to remove the hot crucible from the furnace. Typically made from cast iron, but many are also made from mild steel with the rise of DIY tongs.
- Pouring Tongs. For holding and tilting the crucible to opur out the molten copper.
- Slag Remover/Skimmer. Used to remove dross (slag) from the surface of the melt, and also to stir.
- Quenching Container. Suitable container full of water to quench hot ingots if wanting to cool quickly.
- Multigrips/Smith Tongs. General work, for holding ingots etc.
- Fire bricks or smelting area. Used to place hot crucible and ingots on.
- Heat Gun/Foundry Crucible Thermometer. To measure the temperature of the copper inside the crucible.
Safety Equipment
Safety is the most important consideration, as nobody wants to hurt themselves!
As a minimum these are some items of safety you should have, but it is by no means all safety items - so you need to do your own research to keep safe.
Safety equipment is only one control measure - maintaining a safe workplace and eliminating hazards before starting needs to also be considered.
Underneath any PPE (Personal Protective Equipment)it is a good idea to wear fire retardant clothing.
- Leather Apron/Jacket/Pants. Heavy duty preferred. Aluminized clothing is a good first choice to protect your body from molten metal splash and radiant heat.
- Heat Resistant or foundry industrial work boots.
- Heavy duty face shield/goggles.
- Respirator with adequate filters for foundry work.
- Welding or Foundry gloves, usually heavy leather or heat resistant kevlar.
- Water Supply. Having one close by as a precaution.
- Fire extinguisher. Suitable type for foundry work close by as a precaution.
Basic Copper Melting Process
For more information I highly recommend buying foundry books. There is a wealth of highly detailed information online to assist if you are interested in giving foundry work a go. This is only a basic process below.
1. Temper (heat treat) your crucible if it is new. This can be looked up online as it depends on your crucible type.
2. Prepare copper for melting by cutting it to a size that fits in the crucible. You do not want copper going above the height of the crucible, as air will hit the copper as it melts, causing impurities to be absorbed like oxygen and hydrogen. This causes pitting and bubbles in the melt which cool as cavities.
3. Clean copper by removing dirt and contaminants and then pack into the crucible, being careful not to pack too tightly.
4. Place crucible into furnace. Make sure the furnace is in a safe place on foundry sand/bricks if possible. Avoid working over concrete or any surfaces which contain water as molten metals will explode on contact with concrete and water.
5. Ignite your furnace, depending on the type of fuel this will change. For gas you will need to turn the gas supply on and ignite the torch in the furnace.
6. Inspect copper as it gets up to temperature. Use a heat gun or thermometer to get an accurate temperate reading. When up to 1150°C the molten copper is ready to pour.
7. Before turning off the fuel supply or removing the crucible from the furnace, first preheat your ingot moulds to ensure no moisture is present. Pouring into cold ingot moulds where moisture may be can cause an explosion.
8. Preheat ends of crucible and lifting tongs. Remove crucible from the furnace using lifting/crucible tongs and place on foundry sand/fire bricks or adequate surface.
9. Skim the top of the molten copper to remove and slag.
10. Using pouring tongs, carefully pour the molten copper into your pre-heated ingot mould. When the ingot has been poured, leave to cool down. When cool enough it is possible to use tongs to shake the ingot free of the mould, and then quench in water. Do this away from the furnace work area.
11. Clean up and allow equipment to cool.
12. Buff or polish ingots to get a shiny metal appearance and then coat with a clear lacquer to protect against corrosion (green) coloured oxide for copper.
Impurities
Copper is considered a half noble metal but with a high solubility for oxygen in the liquid state. This causes it to absorb oxygen and hydrogen as impurities. Degassing and Deoxidisation are two common methods to improve the quality of the finished copper product. Phosphorous and charcoal are common foundry items used to degass molten copper, while Argon or Nitrogen gas pumped into the molten copper is used to deoxidise.
The nature of your furnace type, and foundry equipment will dictate if and how you go about removing unwanted contaminants.