{"id":8585,"date":"2020-01-06T16:41:40","date_gmt":"2020-01-06T15:41:40","guid":{"rendered":"https:\/\/www.hawkins.biz\/?post_type=insight&p=8585"},"modified":"2025-08-06T17:04:07","modified_gmt":"2025-08-06T16:04:07","slug":"as-bold-as-brass","status":"publish","type":"insight","link":"https:\/\/www.hawkins.biz\/insight\/as-bold-as-brass\/","title":{"rendered":"As Bold As Brass"},"content":{"rendered":"\t\t
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Brasses have been used for many thousands of years and can be used for decorative structures such as the Benin \u2018Bronzes\u2019 (actually made of brass) or, more recently, for architectural uses and for plumbing applications, to name a few (Photograph 1<\/strong>).<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Photograph 1: Uses of Brass<\/b>

Left - cladding at 10 Weymouth Street[1]<\/a>, London<\/p>

Right - Benin \u2018Bronzes\u2019 dated 1100-onwards[2]<\/a><\/p><\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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The term \u2018brass\u2019 can be used to described a wide range of copper (Cu) – zinc (Zn) alloys, with small additions of other alloying elements, e.g. lead, arsenic, tin, etc. Generally, brasses can be manufactured cheaply, in large volumes, and provide a range of useful mechanical properties: hardness, strength, ductility, wear resistance, ease of machinability, corrosion resistance, etc. The properties of brass can be altered by the addition or removal of chemical elements, or by heat treatment.<\/p>

It follows that the performance of brass components often relies on correct property specification and manufacture. If, for instance, a brass application requires exemplary corrosion resistance, but the brass component has been incorrectly manufactured or specified, it will be unlikely to perform effectively and may fail prematurely.<\/p>

This article will concentrate on the use of brass in plumbing applications, such as water or oil supply systems. In these applications, brasses are often used to form compression joints
(e.g.\u00a0Photograph 2<\/strong>). In order to make a joint like this, a pipe is inserted through the back nut, through a metal olive and to the shoulder stop of the fitting body. The back nut is then screwed onto the fitting body and tightened using a spanner to the number of turns specified by the manufacturer (if that information is provided).<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Photograph 2:<\/b> Exploded view of a compression joint as labelled.<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Figure 1<\/strong>\u00a0provides a partial phase diagram for a Cu-Zn binary system. Depending on the composition, brass can be divided into three categories (each with a different crystal or grain structure):\u00a0\u03b1 brass<\/strong>,\u00a0\u03b1 + \u03b2 brass\u00a0<\/strong>and\u00a0\u03b2 brass<\/strong>\u00a0as indicated on the phase diagram.<\/p>

\u03b1 brasses<\/strong>\u00a0are soft and ductile, which makes them easy to deform by rolling, bending, drawing spinning, etc., into various functional shapes. Generally, \u03b1 brasses are hardened by cold or hot working, and then annealed to relieve excessive stress.<\/p>

Brasses with both \u03b1 and \u03b2 phase in their microstructure are termed as\u00a0\u03b1 + \u03b2 brass<\/strong>\u00a0or \u2018duplex brass<\/strong>\u2019, and the volume ratio of the two phases depends on the zinc content. Although \u03b2 phase has a higher hardness, and therefore reduces cold ductility in \u03b1 + \u03b2 brass compared to \u03b1 brass, it greatly increases the brass\u2019 amenability to hot working by extrusion or stamping, and also enables die casting without hot cracking[3]<\/a>\u00a0.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Figure 1:<\/b> Copper-zinc partial phase diagram showing the hot working, recrystallization, and stress-relieving temperature ranges for \u03b1, \u03b1 + \u03b2, and \u03b2 brasses. Taken from Callcut, V. (2000). Introduction to Brasses (Part II). Copper Development Association.<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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For hot stamping, the ideal alloys (such as duplex brass) need to have maximum ductility at elevated temperature and can be extruded into bars of complex section, while strength and reasonable ductility should be guaranteed at room temperature to ensure structural integrity.<\/p>

Generally, compression joints are made by either casting molten brass into a shaped die or by hot stamping ingots into shaped components. During processing or fabrication of brass components by cold or hot working, plastic strain increases strength and hardness of the materials, but also results in high residual stresses. A sufficient magnitude of residual tensile stress can lead to unpredictable distortion during cutting or machining, to hot cracking, or to a phenomenon known as stress corrosion cracking (SCC) in storage or service.<\/p>

SCC requires three conditions in order to occur:<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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