Copper and copper alloy are amongst the most versatile materials available and are used for applications in every type of industry. World consumption of copper now exceeds 18 million tonnes per annum.
Copper, Brass & Bronze alloys explained
Copper is well known for it’s conductivity but it has other properties that have been exploited in a wide range of copper alloy. These alloys have been developed for a wide variety of applications and numerous fabrication processes employed to produce fished goods.
Suitable Fabrication Techniques
Fabrication techniques that copper alloy are largely suited to include machining, forming, stamping, joining, polishing and plating.
Machinability
The exceptional machinability of some copper alloy means that free machining brass sets the standard of machinability by which all other metals are judged.
Handling and Storage of Copper
The procedures for the handling and storage of copper and copper alloy are very similar to those used for aluminium and stainless steel.
Cleanliness
The most important factor is cleanliness. Contaminated copper can be the cause of cracking or porosity during heat treatment or welding. Corrosion resistance can also be adversely affected. Tooling and work surfaces should be dedicated to use with copper materials or thoroughly cleaned before use. If this is rule us not adhered to, cross contamination can occur.
Protective Packaging
Copper sheets should remain in their packaging until required and should be kept separated by protective material to avoid abrasion between the sheets.
Storage of Copper
Plates and sheets should be stored vertically in covered racks. All copper materials should never be walked upon.
Ductility and Malleability
The ductility and malleability of copper and copper alloy makes them ideally suited to fabrication methods that involve severe deformation such as:
- Tube forming
- Wire drawing
- Spinning
- Roll forming
- Deep drawing
These fabrication methods require specialised, heavy equipment and skilled operators. If fabrication by one of these methods is required, more information should be sought independently.
Fabrication of Copper
Cutting of Copper
Most copper alloy are relatively soft and can be readily cut using common hand tools and standard cutting methods.
Damage During Cutting
While the relative softness of copper makes it easy to cut, it is important to protect the component from unwanted damage during cutting. This damage may include, but not be limited to, bending, denting or scratching.
Cutting Pipe and Tube
Hacksaw
When cutting copper pipe, a fine toothed hacksaw may be used quite successfully. To ensure the cut is square to the pipe, a tube cutter should be used.
To hold material for cutting with a hacksaw use a mitre box or a jig consisting of a piece of wood containing a notch to hold the tube or pipe in place.
Pipe Cutters
When a pipe cutter is used, it is recommended to grip the copper tubing with a pipe vice or a similar holding device.
After cutting the any burrs need to be removed from the inside and outside of the tube. For this, use a half round file. Pipe cutters tend to cause more burrs than do hacksaws.
Cutting Copper Sheet and Plate
The method employed for cutting copper sheet or plate largely depends on two factors; the thickness of the material and the amount of cutting required.
Thin Gauge Material
For thin gauge material where only a minimal amount of cutting is to be done, tin snips or hand shears may be adequate.
Thick Gauge Material
Thicker material can be cut using a bandsaw or other mechanical saw fitted with a bimetallic blade suited to the cutting of copper alloy.
Industrial Cutting Methods
For large cutting runs or for thick material it may be necessary to utilise one of the common industrial cutting methods like:
- Shearing
- Electrical discharge machining (EDM)
- Laser cutting
- Water jet cutting
- Plasma cutting
- Slitting
- Guillotining
- Abrasive disc cutting
Bar and Flat Bending
Copper and copper alloy bar can be bent using standard bending methods.
Minimum Bending Radius
As a general rule, the minimum bending radius for copper bar is equal to the thickness of the bar.
Tube and Pipe Bending
Most copper pipe/ tube can be readily bent and two main methods are employed. The first uses bending springs and the second, a pipe bending machine.
Bending Springs
The simplest tool for bending pipe is the bending spring. Bending springs are normally used for thinner walls where the pipe can be bent by hand. Two types of spring are used: internal and external. Both types of spring serve the same function; to prevent the wall of the pipe from collapsing during bending.
External Bending Springs
External springs are used for smaller diameter copper piping (6 to 10mm external diameter). As the name suggests, the spring is fitted over the tube during the bending operation.
Internal Bending Springs
Internal springs are placed inside the pipe during bending. Each pipe size requires its own specific size of spring.
Bending Machines
All bending machines are different but the principal is the same.
The bending machine is fitted with a bending roller and former matched to the size of the pipe. The pipe is secured at one end and the lever handle of the machine moved to bend the pipe around the former.
Joining of Copper Components
Copper and copper alloy are more readily joined than most other materials used in engineering.
Although 90% of copper based components are assembled using conventional welding and brazing techniques, they can be successfully joined using every known joining process.
When welding, soldering or brazing copper the joint must be clean and free of dirt, grease or paint.
Soldering
Soldering can be divided into two methods:
- Soft soldering using alloys that melt below 350°C
- Hard soldering using stronger, high melting point alloys
In regard to soldering copper alloys, hard soldering is often referred to as Silver soldering.
Soft soldering normally uses Tin based solders for joining copper and brass when high mechanical strength is not required. The method is commonly used for joining copper in domestic electrical and plumbing applications.
Brazing
With the exception of alloys containing more than around 10 per cent aluminium or 3 per cent Lead, brazing can be used to join all copper alloys.
Brazing is particularly popular for joining copper components used in building, heating, ventilation, air-conditioning and the manufacturing of electronic products.
Welding
Copper alloys are readily welded using all common welding techniques including:
- Arc welding
- Gas-shielded arc welding
- Tungsten inert gas (TIG) welding
- Metal inert gas (MIG) welding
- Plasma arc welding
- Pulsed-current MIG welding
- Electron Beam welding
- Laser welding
- Friction welding
- Ultrasonic welding
Bolting and Riveting
Copper and all copper alloys can be successfully bolted or riveted. However consideration must be given to the material used in the bolts or rivets. As copper is often chosen for its corrosion resistance, the material used in the bolts and rivets should be made from the same or similar material to that being joined.
For roofing applications, copper nails are preferred but brass or stainless steels can be substituted.
Localised Stress Through Mechanical Joining
Mechanical joining like bolting and riveting may induce localised areas of high stress, which could induce failure in the component. Replacing the mechanical joint with adhesive bonding can eliminate this. Adhesive bonding can also be used in conjunction with mechanical bonding.
Adhesive Bonding
With consideration given to joint design so there is an adequate overlap on the joint area, copper and copper alloys can be successfully joined using adhesive bonding.
As copper and copper alloys form a protective surface oxide layer, the surfaces must be cleaned before the adhesive is applied.
Casting of Copper
Copper and many copper alloys are ideally suited to fabrication of components by casting.
Sand Moulds
The most flexible casting technique utilises sand moulds. Sand moulds can be used for production runs from simple one-off items to long casting runs. These items can also range in size from a few grams to many tonnes.
Iron Moulds – Die Casting
The other popular casting technique uses iron moulds and is called die casting. Die casting is suited to long casting runs.
Both die casting and sand casting can be used for the low cost production complex near net-shape components. This minimises expensive post casting machining.
Continuous Casting
Bars, sections and hollows that require tight dimensional control are often produced by continuous casting.
Centrifugal Casting
Rings, discs and other symmetrical shapes tend to be produced using centrifugal casting.
Machining
All copper and copper alloys can be machined accurately, cheaply, with a good tolerance standard and good surface finish. Some copper alloys are specifically formulated to have excellent machinability.
If machinability is the paramount consideration for the material, the material of choice is high speed machining brass.
Machinability Rating
The relative machinability of metals is demonstrated by a percentage rating. This rating system is based on the original free machining brass (CZ121) which has a rating of 100.
Descaling
The surface oxide films that form on copper alloys can prove to be quite tenacious. Often these films need to be removed before some fabrication processes can be performed.
Abrasive Descaling
Very fine abrasive belts or discs can be used to remove oxides and discolouration adjacent to welds.
Pickling
Pickling might be necessary by using a hot 5-10% sulphuric acid solution containing 0.35g/l potassium dichromate. Before commencing pickling, oxides can be broken up by a grit blast. Components that have been pickled should be rinsed thoroughly in hot, fresh water and finally dried in hot air.
Finishing
Copper components can be finished in a vast variety of ways. The finish used for any given copper component is dependent upon function and/or aesthetics.
Oxide Layer
Copper naturally forms a protective oxide layer on exposure to the elements. This layer is normally blue – green and may or may not be desirable.
The blue – green patina develops over time but its development can be enhanced and accelerated by the use of commercially available oxidising agents.
Lacquer Coating
If the tarnished patina of copper is not desirable, the material can be protected using a lacquer coating.
Acrylic Coating
An acrylic coating with benzotriazole as an additive will last several years under most outdoor, abrasion-free conditions.
Painting
In most instances copper and copper alloys do not require painting. The inherent properties of copper resist corrosion and biofouling. Painting of copper is occasionally done for aesthetic reasons. It is also done to reduce the incidence of metal to metal contact of bimetallic couples where galvanic corrosion might be a problem.
Surface Preparation
Before painting copper, the surface of the material should be roughened by grit or sand blasting. Other specific procedures will depend upon the type of paint being used. Please consult the paint manufacturer for details.
Cleaning and Polishing Copper
The best way to keep copper clean is to not allow it to get dirty in the first place.
Where possible, decorative items should be kept clean and free of dust. Many decorative copper items are coated with lacquer to protect the finish. Other than dusting, for these items occasional washing with luke warm, soapy water may be required. They should never be polished as this may remove the protective lacquer.
Cleaning Copper Cookware
To remove tarnish from copper cookware, simply rub with lemon halves dipped in salt.
Cleaning Industrial Copper
Tarnish can be removed from copper in industrial applications using commercial copper polishes. These polishes should be applied following the manufacturers instructions.
Brushed Finishes
If a brushed finish is required on copper or copper alloy, stainless steels brushes must be used to eliminate cross contamination.
Recycling of Copper
Copper alloy are highly suited to recycling. Around 40% of the annual consumption of Copper alloy comes from recycled copper materials. Both process scrap and the component, at the end of its working life, can be readily recycled.
DISCLAIMER
This Data is indicative only and must not be seen as a substitute for the full specification from which it is drawn. In particular, the mechanical property requirements vary widely with temper, product and product dimensions. The information is based on our present knowledge and is given in good faith. However, no liability will be accepted by the Company is respect of any action taken by any third party in reliance thereon.
As the products detailed may be used for a wide variety of purposes and as the Company has no control over their use; the Company specifically excludes all conditions or warranties expressed or implied by statute or otherwise as to dimensions, properties and/or fitness for any particular purpose.
Any advice given by the Company to any third party is given for that party’s assistance only and without liability on the part of the Company. Any contract between the Company and a customer will be subject to the company’s Conditions of Sale. The extent of the Company’s liabilities to any customer is clearly set out in those Conditions; a copy of which is available on request.
This information has been sourced, reviewed and adapted from materials provided by Aalco - Ferrous and Non-Ferrous Metals Stockist.
For more information on this source, please visit Aalco - Ferrous and Non-Ferrous Metals Stockist.