Brass

Cols

Summary

Brass is an alloy of copper and zinc, usually about twice as much copper as zinc by weight, with small additions of lead, tin, aluminum, manganese, or silicon. 🟠Alloy choice sets machinability, color, and dezincification resistance, and lead content decides whether a brass can be used in potable water components.

Cols

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[!abstract] Contents

Terminology

Alpha brass: over 65 percent copper; malleable and cold-workable
Alpha-beta brass: about 55 to 65 percent copper; usually hot-worked
Beta brass: about 50 to 55 percent copper; harder, suited to casting
Free-cutting (leaded) brass: lead added for easier machining
Dezincification: loss of zinc from brass in seawater and aggressive water
DZR brass: dezincification-resistant brass for harsh conditions such as boiler systems
Season cracking: cracking of brass exposed to ammonia
Muntz metal / naval brass: 60 percent copper alloys; naval brass adds tin
Architectural bronze / commercial bronze: trade names for brasses (UNS C38500 and C22000)

History and demand

Discovery and early use

Used since prehistoric times, though its nature as a copper-zinc alloy was not understood until the post-medieval period
Romans made brass by cementation, heating copper with zinc ore; speltering with metallic zinc reached Europe in the 16th century
1738: William Champion patented an industrial method for distilling zinc

Use in construction

Furniture and door fittings (drawer pulls, hinges, doorknobs), locks, plumbing, valves, and hose couplings; architectural interior and exterior use in UNS C38500

Composition and production

Raw materials

Copper and zinc, with small amounts of arsenic, lead, tin, aluminum, manganese, silicon, or phosphorus
Higher copper gives a softer, more golden color; higher zinc gives a harder, more silvery metal

Manufacturing process

Melts at about 900 to 940°C, which makes it easy to cast; more malleable than bronze or zinc

Grades and types

Alloy	Nominal composition	Typical use
Cartridge brass (UNS C26000)	Cu 70, Zn 30	Radiators, hardware, electrical parts; good for cold working
Yellow (high) brass	Cu 65, Zn 35	Good corrosion resistance
Free-cutting brass	Cu 62, Zn 35.5, Pb 2.5	Screws, nuts, gears, keys
Muntz metal (UNS C28000)	Cu 60, Zn 40	Condenser tubes
Naval brass	Cu 60, Zn 39.25, Sn 0.75	Marine use; resists salt corrosion
Red brass (UNS C83300, C83600, C83800)	Cu 83 to 93, with Zn, Sn, Pb	Copper-rich brass; composition varies by grade
Commercial bronze (UNS C22000)	Cu 90, Zn 10	Decorative and architectural features; forms well
Architectural bronze (UNS C38500)	Cu 57, Pb 3, Zn 40	Building interiors and exteriors; free-machining, yellow-gold color

Properties

Physical

Density: 8.4 to 8.73 g/cm³ (about 524 to 545 lb/ft³); cartridge brass 8,530 kg/m³, red brass 8,746 kg/m³

Thermal and moisture

Thermal conductivity: cartridge brass (C26000) 120 W/(m·K), about 830 Btu·in./(h·ft²·°F); yellow brass (70 Cu, 30 Zn) 111 W/(m·K), about 770
Coefficient of thermal expansion: 18 to 19 × 10⁻⁶/°C, about 10.0 to 10.6 × 10⁻⁶ in./in./°F

Fire behavior

Melting range: about 900 to 940°C (1,650 to 1,720°F) by composition

Durability

Corrosion: attacked by moisture, chlorides, ammonia, and some acids; zinc leaches out in seawater (naval brass adds tin; DZR brass for harsh service)
Antimicrobial: kills bacteria, often within minutes to hours of contact

Standards

Material specifications

ASTM B36: brass plate, sheet, strip, and rolled bar (lists C28000 Muntz metal)
ASTM B455: listed as an equivalent specification for UNS C38500

Test methods

NSF/ANSI/CAN 372: lead content of drinking water system components
NSF/ANSI/CAN 61: drinking water system components

Uses in buildings

Building elements

Door Hardware: hinges, doorknobs, and locks
Domestic Water Piping: valves and fittings, with lead content controlled for drinking water
Terrazzo: divider strips
Architectural Metal Trim: architectural bronze (UNS C38500) and commercial bronze for interior and exterior trim

Pros and cons

Pros

Easy to cast and machine
Higher copper gives a golden color; conducts heat and electricity well
Antimicrobial surface
Almost 90 percent of brass alloys are recycled

Cons

Dezincification in aggressive water
Season cracking in ammonia
Leaded grades are restricted for drinking water components

Design considerations

Compatibility

Specify DZR or tin-bearing grades for seawater, boilers, and aggressive water; keep ammonia-bearing cleaners and atmospheres away from stressed brass

Movement

Expansion about 0.12 in. per 10 ft for a 100°F swing (calculated from 10.3 × 10⁻⁶ in./in./°F)

Sustainability

Recycled content and end of life

Almost 90 percent of brass alloys are recycled; ferrous scrap is removed magnetically because brass is not ferromagnetic

Health

Free-cutting brass contains lead; drinking water components are regulated by lead content on wetted surfaces (see the METALS Code reference)

Manufacturing and cost

Main manufacturers and suppliers

Trade association: Copper Development Association.

Sources

Wikipedia: Brass, https://en.wikipedia.org/wiki/Brass
Wikipedia: List of copper alloys, https://en.wikipedia.org/wiki/List_of_copper_alloys
AZoM: Architectural Bronze UNS C38500, https://www.azom.com/article.aspx?ArticleID=6382
Engineering ToolBox: density, thermal conductivity, and expansion of metals, https://www.engineeringtoolbox.com/metal-alloys-densities-d_50.html
ANSI Webstore: ASTM B36/B36M-23, https://webstore.ansi.org/standards/astm/astmb36b36m23