In this section of ‘Metals and their Properties’, we’re tooting our horns for brass. Brass alloy shares its name with the group of wind instruments, but we’re going to be looking at more than just its instrumental value. In this post, we’ll cover the history of the uses of brass, including its place in non-ferrous metal recycling.
WHAT IS BRASS?
Brass is not a chemical element but an alloy of copper and zinc that has a yellow colouration. If the brass is quite yellow in colour, this will be because it has a high amount of zinc in it. Brass with less zinc will retain more features of copper and will be more red as a result.
Brass is sometimes confused with bronze – another copper-alloy – but instead of copper alloyed with zinc, bronze is a mixture of copper and tin.
HISTORY OF BRASS
The Bronze Age followed the Copper Age, but although bronze and brass are both copper-alloys, the Brass Age never happened, because brass is typically quite hard to make without the correct tools. This is due to zinc’s melting point of 420 ºC, which made it difficult to form zinc-alloyed metal pre-18th century. Originally, brass was made from mixing ground zinc ore (calamine) into a crucible with copper. In the crucible, vapour from the zinc would permeate the copper, resulting in brass.
In the Ancient World, brass was used differently by different civilisations. The Romans, in particular, loved brass for its beautiful white-gold colour and often used it in the production of helmets. The Roman alloy of brass tended to be around 20% zinc, 80% copper, which is the same combination that is still in high demand today.
PROPERTIES OF BRASS
Brass has a comparatively low melting point of around 900 to 940 °C. It is fairly easy to cast, so it is often used to make intricate decorations, and by shifting the ratio of copper to zinc or the temperature, the properties of brass can be changed to allow for hard or soft brasses. There are three main types of brass:
This type of brass contains less than 37% zinc melted into the copper. Alpha brasses are soft and ductile, making them good for welding, rolling, drawing, bending and brazing.
Alpha brass is used in common items such as:
- Ammunition Cartridge Cases
Beta brass is not used nearly as commonly as the other types of brass. Beta brass contains above 45% zinc and is harder and stronger than the other categories. As a result, beta brass can only be hot-worked or cast.
Beta brass is used in common items such as:
- Sprinkler heads
- Window fittings
- Door fittings
These brasses are also sometimes known as ‘duplex brasses’ or ‘hot-working brasses’. Alpha-beta brass contains between 37% and 45% zinc and is harder and stronger than Alpha brass, but less so than Beta brass. It is also good for working at high temperatures as it resists cracking and is usually hot-worked by extrusion, stamping or die-casting.
Alpha-beta brass is used in common items such as:
- Engraved nameplates
- Appliance trim
- Clock components
- Gear meters
- Builders hardware
Brass is susceptible to corrosion; contact with amine (derived from ammonia) can cause dezincification, whereby the zinc is leached out of the alloy causing weakness and porosity in the metal. In order to combat this, alloying agents can be added to brass.
Although brass is already an alloy, other metals are sometimes used as ‘alloying agents’ to improve brass’ machinability, corrosion resistance, or colour. These alloying agents may include aluminium, lead, arsenic, manganese and nickel.
- Lead: Makes brass softer and more malleable
- Aluminium: Increases strength and hardness, protects against corrosion
- Manganese: 1% will turn brass brown in colour
- Nickel: Adding nickel will turn brass silver
- Arsenic: Reduces potential to corrode
WHAT IS BRASS USED FOR
Brass is used for numerous day-to-day items, including both decorative and practical applications such as door handles, lights, fans and jewellery. Due to its ductile quality, brass is also widely used for making the aforementioned wind instruments.
It is especially important to use brass for door fittings, as it is proven to reduce the spread of antibiotic resistance in bacteria. Usually, when bacteria dies, its DNA can still survive and be passed onto other bacteria. This is very dangerous when it comes to bacteria improving their antibiotic resistance. Brass and other copper alloys, however, have the ability to kill bacteria and destroy this important DNA. Wider use of brass fittings across the country could reduce the possibility of superbugs.
Brass is a part of our non-ferrous metal processing. Non-ferrous metals have quite extensive uses as their properties tend to be quite desirable: low weight, high conductivity, non-magnetic and corrosion resistance. Of the non-ferrous metals, copper is one of the most widely recycled, closely followed by zinc recycling.
Considering the high demand for zinc and copper recycling, it is no surprise that brass is also in high demand at recycling plants. Brass is particularly good in the recycling process too, as it does not lose any of its chemical or physical properties. The recycling process is not as energy-intensive as it is for other metals either, so recycling of brass is both an economical and an eco-friendly process.
If you’re interested in the properties of other recyclable metals, then you’ll be glad to know that we’ve also looked at copper, iron, aluminium, and steel. Brass is an important metal in today’s economy, so it is equally important to ensure that brass is recycled. By recycling brass, we can continue to use brass door handles and watches for decades to come.