Q We are using a 25mm diameter phosphor bronze alloy CC491K (LG2) to manufacture balustrade posts with a 'dog leg' at the top with a 50mm radius on each bend. We are annealing the bars to a dull read then bending them in a hydraulic press. We have bent two bars successfully and two bars have fractured. Could you advise please?
A LG2 is a casting alloy which is not designed to be bent. A wrought phosphor bronze could be used but make certain that it is in the annealed condition. Another possibility is to use brass bar which is easily bent and could be treated chemically (antiqued) to any colour.
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Q I have been asked to produce 22 valves in gunmetal from a drawing which originates from 1958. The company has been taken over and the patterns and casting drawings lost. Due to the small quantity that will have to be made from bar, what should I use?
A Suggest that you use continuously cast CC491K (LG2) bar or a wrought free-machining phosphor bronze.
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Q Our company currently uses a brass threading insert for a product which is screwed onto the top of golf flag sticks. Corrosion is a concern as the flag sticks are laid on the ground. This allows them to pick up moisture, chemicals (fertilisers) and debris that can cause corrosion. We also have the piece in use at areas that are close to the ocean, which makes for high humidity and 'salty air'. Can you recommend a brass with increased corrosion resistance?
A My first thought is to leave the brass alone; it will very slowly become darker with time but it will not rust away to nothing.
The second option would be to apply a lacquer to maintain the bright surface colour.
The third option is to have the inserts chemically antiqued; this gives a darkened attractive attractive surface.
I would not use a different brass, keep with the cheapest brass which is a leaded free-machining grade. Other brasses are more expensive and would not give much improvement in this application. But best of all leave them, let nature take its course.
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Q I am designing a rope guide in brass for a racing yacht. Which brass and manufacturing method should be used? Is chromium plating essential?
A To resist the bending stresses in service, a high-tensile brass such as CW721R (CZ114) should be used. There is no need to chromium plate since it will increase the cost by 50% and is in any case merely decorative. Depending on the numbers required hot stamping (forging) could be used to make the component to near net shape.
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Q I am looking at the design of a machine utilising copper/copper alloy sheet. The sheet must be capable of being deep drawn and have a minimum tensile strength of 70MN/m2s. It is to be situated in an industrial environment and must not suffer from stress corrosion cracking. The most important property is a very high electrical conductivity.
A Since high conductivity is essential use electrical grade copper CW004A (C101) or CW009A (C110). These grades may be deep drawn, have the required tensile strength and will not suffer from stress corrosion cracking.
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Q I am using a leaded gunmetal casting which is machined and then crimped onto a copper pipe. I have had a number of failures due to leakage. Can you explain this?
A Leaded Gunmetal is a cast alloy which is not designed to be cold worked. Crimping involves extreme deformation which will not usually be tolerated by the gunmetal without cracking. However, castings do not have a uniform structure and in the areas free from lead and possibly a smaller grain size some ductility is present. This will account for some of the castings surviving the crimping without cracking.
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Q I have been following the progress of the restoration of the Cutty Sark and am interested in the history of the metallic alloys used as cladding for early sailing ships.
A The ship was built in 1869 and the wooden hull was protected below the water line with sheets of Muntz Metal (a brass of 60% copper, 40% zinc) which was patented in 1832 by George Frederick Muntz. Prior to this date copper was used as a cladding material for sailing ships (e.g. Nelson's Victory) but Muntz metal was 2/3 the cost of copper and was easily hot rolled into sheets whilst maintaining the anti-fouling properties of copper.
Further information: Pub 121 Copper - The Vital Metal  www.oldcopper.org 
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Q I have been asked to produce bolting for use inside a van used to carry explosives. The material must be non-sparking. What should I use?
A Tiny particles can be detached from their parent object by the force of impact of a harder instrument or object in air. Elements like iron, when finely divided and hot, can ignite spontaneously as they oxidise, becoming even hotter. This results in dull red particles rapidly becoming bright white at a much higher temperature. At this temperature the particle is visible as a spark and can cause fire or explosion in a combustible environment. In common with most other copper base alloys, the particles detached from an aluminium bronze object due to impact against a ferrous or other harder objects, do not attain a dangerous temperature and are not visible as a spark. In view of their high strength, aluminium bronzes are the most favoured for applications where this is important. They may therefore be safely selected for non-sparking tools and equipment for handling combustible mixtures such as explosives.
Further information:
Cast and Wrought Aluminium Bronzes -
Properties, Processes and Structure
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Q I am designing a power lead connector for a large earth moving vehicle. The connector is crimped to copper wires to make electrical contact. I propose to machine this component from brass CW606N (CZ131) bar followed by tin plating. Any advice please?
A The brass selected is free machining with good ductility and is an excellent choice for this application. I suggest that the component is annealed in the range 400 to 600oC to give maximum ductility to ensure that the crimping will be successful. There is no need for tin plating; in this environment the brass will darken with time with no loss of properties.
It is important that the lead content (1.6 to 2.5%) of this brass is maintained at the specification level in all of the connectors since higher lead levels may lead to cracking on crimping. With this in mind I suggest that the source of the brass is from the UK or Europe where full certification will be available.
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Q We fabricate by cold forming radiator header tanks from half hard (121-124HV), 1.2mm thick CZ108 (CW 508L) sheet. The tanks are annealed after fabrication. A small number (5 out of 4,000) of tanks have failed in service by cracking on a 90o bend. These failures have occurred in Hong Kong where the cooling water is from a recycled source which contains nitrates. Any advice on how to prevent failure would be welcome.
A The grade of brass (63/37) is suitable for this application but the hardness (121 to 124HV) is at the top end of the half hard range. It would be better to anneal before cold fabrication and stress relieve after fabrication since it is possible that the nitrates in the water in Hong Kong may lead to ammonia release and the possibility of stress corrosion cracking.
Always ensure that the bending takes place so that the grain runs with the long bend since brasses have better ductility longitudinally in line with the rolling direction rather than in the transverse direction.
A grain size range of 0.08 to 0.01 mm is recommended for cold working brass sheet.
Ensure that the brass has full certification, particularly with respect to the lead content (0.1% max.).
Further information: Pub 117 The Brasses - Properties & Applications
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Q What are the dimensional changes which take place on heat treating the age-hardenable copper alloys? What allowances should I make?
A CuCr - this alloy is solution treated at 1000oC quenched and aged at about 470oC . The shrinkage on ageing is about 0.1 to 0.3%. However, the alloy is supplied fully heat treated (hard) so no further dimensional change will take place.
CuBe - this alloy is supplied solution treated (soft). It is machined first, then aged so the resultant shrinkage (0.1 to 0.3%) must be allowed for in design.
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Q I wish to produce components by carrying out simple forming operations on brass sheet. Should I use the 70/30 Cartridge Brass (CW505L)?
A CW505L is the most ductile brass, but for simple forming the more economical 63/37 Common Brass (CW508L) should be used.
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Q I am a designer using brass for new lock mechanisms. Some parts are subject to high stress. What should I use?
A The high tensile brasses CW721R & CW705R would be suitable.
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Q What manufacturing methods would be suitable for lock parts made in high tensile brass?
A Either extrusion, if the shape is regular, or hot stamping for more complicated shapes.
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Q Which copper alloys may be used for the design of springs?
A Copper strip and wire may be produced with a combination of high elastic limit and good corrosion resistance making them an ideal choice for springs. The main groups of alloys are:
1. Phosphor bronzes-typically PB102 (CW451K) with a yield strength of about 500N/mm2.
2. Nickel silvers-typically NS106 (CW409J) this is white coloured and has excellent corrosion resistance.
3. Copper beryllium CB101 (CW100C) - these alloys are used where very high yield strength is required (greater than 1000N/mm2).These alloys are expensive and usually phosphor bronzes will be adequate for most engineering applications. Useful standards are BS 1654 Copper and Copper Alloys- Strip for Springs and Connectors, and BS2B 33 Copper Beryllium Springs for Aerospace.
Further information: TN12 Copper Alloy Spring Materials
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Q I make shear rings from CZ121 (CW614N). The rings, up to 6.5 inches dia. are notched to ensure fracture when overloaded, thus ensuring protection from damage of expensive sub sea tools. The problem is that the rings are showing variation in shear stress values on testing even within the same batch. Can you suggest a possible solution to this problem?
A The strength of CZ121 in the specification is quoted as a minimum value and is achieved by cold working. What is preferable for this application is a maximum value of strength with a narrow min to max range. It may be that a heat treatable alloy such as a copper nickel silicon (BS B25) would meet these requirements. However this would be much more expensive than CZ121and testing would have to be carried out on the rings made from this alloy before being put into service.
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