18: Copper, Bronze, and Brass

Copper ore generally contains between ______ and _____ % copper, with an average of _______%

.2/3/.7

How is copper created?

1. The copper ore must be refined through a long and complex process. The ore is first crushed into very fine powder. The powder is with mixed water and chemicals so the part of the ore containing copper (copper concentrate) floats to the surface. the copper concentrate is skimmed off the top of the solution. This process is called ore benefaction. 2. The copper concentrate is heated in a reverberatory furnace, where some of the impurities are driven off. The product that emerges from the furnace is called copper matte. The matte is converted to blister copper in another furnace. Blister copper is 97-99% pure. 3. If the blister copper does not contain gold or silver and is not going to be used for electrical applications, it can be heated in a fire-refining furnace to burn off most remaining impurities. If, however, the copper is to be used as an electrical conductor, it must be refined using an electrolytic refining stage called solution extraction, or electrowinning. Large flat plates are cast from molten blister copper. These plates, called anodes, are suspended in an electrolytic cell that contains a solution of copper sulfate and sulfuric acid. These sheets of pure copper are placed between the anodes. These sheets are called the cathodes, or starter plates. 4. Electrons pass through the solution from the cathode plates to the anode plates. At the same time, the copper atoms from the anodes dissolve into the solution and are deposited on the cathodes. At the end of the electrolytic process, the cathodes are nearly pure copper. During this electrolytic refining stage, small amounts of silver and gold in the copper drop down to form a sludge in the electrolytic tank. This sludge is a major source of gold and sliver metal. This concentration of these metals in the sludge is much higher than in their natural ores. 5. To make sheet, wire, tubing, and other useful semifinished products, the copper from the electrolytic cathode is charge in a melting furnace. Suitable clean scrap may also be added. For metal to be used in nonelectrical applications, fire-refined metal may be used. Selected alloying elements such as zinc, alumnium, or phosphorous, may be added as needed to achieve a desired alloy. 6. The liquid copper or copper alloy is then sent to a holding furnace. From the holding furnace, the metal is poured into a mold. Modern molds for casting copper are semi-continuous, like the molds for aluminum. Typical ingots are 5" thick, 32" wide, and up to 25' long. Some casting operations produce a continuous strip in a horizontal caster. 7. The finished ingot is ready for reheating and hot rolling or extrusion. All copper alloys intended for sheet to strip are milled after the first hot roll reduction. This guarantees that the final surface finish will be uniform and clean.

Aluminum bronze contains from _____ to ______% aluminum, plus small quantities of _______, and sometimes _________ or _____________.

5/10/iron/nickel/manganese

What are two common copper alloys?

Brass and bronze

Describe how cold working can be used to strengthen copper.

Cold working is the repeated application of force to harden or strengthen metal. Cold working techniques such as extruding a thick-walled copper tube through a die to its final size.

What are the most useful properties of pure copper?

Excellent electrical and thermal conductivity, as well as high ductility and malleability. The electrical conductivity of copper is second only to that of silver. Copper and copper alloys can be easily soldered and brazed. Copper wire and other electrical applications account for 60% of all copper produced. Copper also has excellent corrosion resistance.

Describe Bronze

It is an alloy of copper and tin and was the first metal alloy discovered. Typically, bronze is mixture of copper and another element, but people usually use the word bronze when referring to the copper-tin alloy. The development of Bronze launched the "Bronze Age" of human development in about 3000 BC.

Describe Brass

It is an alloy of copper and zinc. When 5-30% zinc is added to copper, brass is created. The zinc increases the strength of the copper through solid solution hardening. Ductility and formability are also increased. For these reasons, brass alloys are used wherever very high formability is needed. Typical applications for brass include electrical fixtures, hardware, jewelry, and musical instruments.

What is naval brass?

It is an alloy originally developed for the British Navy. It is an alloy of 60% copper, 39.2% zinc, and 0.8% tin. Naval brass resists corrosion very well and can be cast easily to make cannon barrels for use on ships. Today, naval brass is called C46400.

What does tin do for copper?

It lowers the melting point of copper and improves its strength. The addition of tin to copper increases strength by formation of a fine, hard, second phase.

Describe the first interactions that humans had with copper.

It was one of the first metals used by man. Lumps of pure copper, or native copper were sometimes

____________ copper rarely occurs in nature, and the majority of its reserves have been __________.

Native/exhausted

What methods are used for hardening copper?

Same as aluminum: 1. Alloying 2. Cold Working 3. Precipitation hardening

Describe copper alloys that have silver as an alloy.

The silver improves the strength of the alloy through solution hardening without hurting electrical conductivity. The addition of silver also helps prevent the alloy from undergoing stress relaxation over time. Copper-silver alloys are generally used for electrical motors and large generator windings.

Describe the main benefits of bronze alloys

They offer corrosion resistance equal to that of copper, are easier to cast than copper, and are stronger than copper. Most bearing blocks are made from bronzes because of these superior properties.

Describe the earliest bronzes

They were arsenical bronzes (Cu-4%As), but it was discovered that adding 5-10% tin to copper worked better. Tin bronze was also less toxic for the people casting it.

Copper and copper alloys are identified by what system? Who maintains this system? Describe how the numbering system works.

UNS (Unified Number System)/American Society for Testing Materials (ASTM) and the Society of Automobile Engineers (SAE). Each designation contains a five digit number and is proceeded by the letter "C." The number designations are based on the alloying elements added to copper.

Describe how precipitation hardening can be used to strengthen copper

When extreme strength and good conductivity are needed, C68800 or C17200 may be used. C68800 is a complex alloy of copper that uses zinc, aluminum, and cobalt to form the fine precipitates that produce high strength. It is usually shipped in the as-quenched and aged condition due to the complexity of the heat treatment. Either way, precipitation hardening works similarly with copper alloys as it does with aluminum alloys.

Bronze flows into a ________ better than pure copper and is able to fill what?

mold/smaller spaces

Today, most copper comes from copper ore mined where?

the western Unite States, the Andes Mountains of South America, Central Africa, and Russia.

Today, what types of bronze metals are used as both cast and wrought alloys?

tin bronze (copper and tin) and aluminum bronze (copper and aluminum).

If superior corrosion resistance is needed, _______ and _______ can be added to brass as alloys.

tin/nickel

Bronze also _________ hardens better than pure copper.

work