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What is aluminium used for?

Aluminium is a versatile, widely used and abundant metal with a range of applications across various industries. We will not discuss the use of aluminium oxide, which is a compound of aluminium and oxygen found in minerals such as bauxite found in the earth’s crust and used in producing aluminium. Some of the most common uses of aluminium include:

Transportation:

Aluminium is used in the production of cars, trucks, trains, boats, and airplanes because of its strength, light weight, and corrosion resistance.

Aluminium has a low density, making it significantly lighter than steel. Using aluminium in transportation vehicles helps reduce overall weight, leading to improved fuel efficiency and reduced emissions. It is commonly used in car bodies, aircraft, and bicycles.

Aluminium naturally forms a protective oxide layer that helps resist corrosion. This makes it suitable for outdoor applications, especially in marine environments where exposure to moisture and saltwater is common.

Aluminium is highly malleable and can be easily formed into complex shapes, allowing for innovative designs and streamlined structures in vehicles. This flexibility in shaping is particularly beneficial in the aerospace industry.

Although aluminum is not as strong as steel, it offers a favorable strength-to-weight ratio. This means that aluminium structures can provide sufficient strength while keeping weight low. It contributes to improved performance and efficiency in transportation vehicles.

Aluminium is highly recyclable, and the recycling process consumes significantly less energy compared to primary production. This makes aluminium a sustainable choice for transportation, aligning with environmental goals.

In transportation, aluminium production is used in various components such as body panels, engine blocks, wheels, suspension systems, and aerospace structures. The use of aluminium helps manufacturers meet stringent regulations for fuel economy and emissions, while also enhancing vehicle performance and durability.

Packaging:

Aluminium is used extensively in the packaging industry because it is lightweight, easy to shape, and provides an effective barrier against moisture, air, and light.

Aluminium is commonly used in packaging for beverages, including cans for carbonated drinks and beer. It is also used for pharmaceutical packaging, cosmetics, food containers, and flexible packaging such as blister packs and aluminium foil wraps. The use of aluminium in packaging helps preserve product integrity, enhance shelf appeal, and contribute to sustainable packaging solutions.

Construction:

Aluminium is used in construction because it is lightweight, strong, and durable. It is commonly used in window frames, roofing, siding, and gutters.

Aluminium is used in various construction applications, including window frames, curtain walls, roofing, cladding, structural elements, and interior components. It offers a combination of durability, aesthetic appeal, and sustainability, making it a popular choice for modern construction projects.

Electrical and Electronics:

Aluminium is used in electrical transmission lines, electronic devices, and heat sinks because it is a good conductor of electricity and dissipates heat quickly.

Aluminium is used in various electrical applications, including power transmission lines, electrical cables, bus bars, switchgear, transformers, motors, and generators. While copper is still commonly used for many electrical applications, aluminium offers advantages in terms of weight, cost, and corrosion resistance, making it a viable alternative in certain scenarios. Proper design considerations and installation techniques are essential when using aluminium to ensure its effective and safe use in electrical systems.

Consumer Goods:

Aluminium is used in a wide range of consumer goods, including kitchen utensils, beverage cans, and foil.

Aluminum is used in a wide range of consumer goods, including electronic devices, kitchenware, furniture, sporting goods, packaging, automotive components, and personal accessories. Its combination of lightweight, durability, aesthetic appeal, and recyclability makes aluminum a popular choice for manufacturers aiming to create high-quality and sustainable consumer products.

Overall, aluminium’s unique combination of properties makes it a valuable material for a variety of applications across numerous industries.

What are the properties of aluminium?

Aluminium has several unique properties that make it useful for a variety of applications. Here are some of the key properties of aluminium:

1. LightweightAluminium has a low density, making it lightweight and easy to handle. It is about one-third the weight of steel, which makes it ideal for applications where weight is a critical factor.
2. Corrosion resistanceAluminium forms a natural oxide layer on its surface, which protects it from corrosion. This makes it an excellent choice for outdoor applications and in corrosive environments.
3. DuctilityAluminium is highly ductile, which means it can be easily formed into different shapes without cracking or breaking.
4. ConductivityAluminium is a good conductor of heat and electricity, which makes it ideal for use in electrical and electronic applications.
5. StrengthAlthough aluminium is lightweight, it is also strong and durable. It has a high strength-to-weight ratio, which makes it suitable for applications where both strength and weight are important.
6. ReflectivityAluminium is highly reflective, making it useful in applications where reflective surfaces are required, such as in mirrors or reflectors.

Overall, the unique combination of properties of aluminium makes it a valuable material for a wide range of applications across various industries.

Disadvantages of Aluminium

Whilst aluminium has many advantages over other material, it is important to understand some of its limitations:

1. SoftnessAluminum is a relatively soft metal compared to some others, which can make it susceptible to dents, scratches, and general wear and tear.
2. CorrosionAlthough aluminum has a natural oxide layer that provides some protection against corrosion, it is still susceptible to corrosion, especially in certain environments such as highly acidic or alkaline conditions.
3. Higher costAluminum production requires significant energy inputs, making it more expensive than some other materials. This higher cost can impact the affordability of aluminum-based products.
4. Lower strength compared to some metalsWhile aluminum has good strength-to-weight ratio, it is not as strong as some other metals such as steel. In applications where high strength is crucial, aluminum may not be the ideal choice.
5. Limited heat resistanceAluminum has a relatively low melting point compared to other metals, which limits its use in high-temperature applications. It can start to lose its structural integrity at elevated temperatures.
6. Electrical conductivityWhile aluminum is a good conductor of electricity, it is not as efficient as copper. In applications where high electrical conductivity is crucial, such as in some electrical wiring applications, copper may be preferred.

It’s important to note that many of these disadvantages can be mitigated or managed through proper design, surface treatments, alloying, and other techniques. Aluminum continues to be widely used in various industries due to its favorable properties and versatility.

What happens when aluminium is in contact with other metals?

When aluminium comes into contact with other metals, a process called galvanic corrosion can occur.

Galvanic corrosion happens when two dissimilar metals come into contact in the presence of an electrolyte, such as saltwater or acidic solution.

In this process, the aluminium acts as an anode, which means it will corrode faster than the other metal, which acts as a cathode. This is because the electrons will flow from the aluminium to the cathode metal, leading to the breakdown of the aluminium.

The severity of galvanic corrosion depends on several factors, including the type of metal, the amount of surface area in contact, and the type of electrolyte present.

In some cases, the corrosion can be relatively mild and have little effect on the structural integrity of the aluminium. In other cases, the corrosion can be severe and lead to the failure of the aluminium component.

To prevent galvanic corrosion, it is important to use appropriate materials and coatings to separate the dissimilar metals or to avoid exposing the aluminium to electrolytes that can cause corrosion.

What are the most common grades of aluminium?

Aluminium is available in various grades, each with different properties and suitable for different applications. Some of the most common grades of aluminium are:

1. 1000 series: This is a soft, low-strength aluminium alloy that is often used for chemical processing equipment, light reflectors, and heat exchangers.
2. 2000 series: This grade contains copper and is known for its high strength, toughness, and excellent fatigue resistance. It is often used in aircraft and aerospace applications.
3. 3000 series: This grade contains manganese and is often used for applications that require good formability, such as kitchen utensils, food and beverage packaging, and automotive parts.
4. 5000 series: This grade contains magnesium and has excellent corrosion resistance, making it ideal for marine and architectural applications.
5. 6000 series: This is the most commonly used aluminium alloy for structural applications, such as in construction and transportation. It has good formability, strength, and corrosion resistance.
6. 7000 series: This grade contains zinc and has the highest strength of all aluminium alloys. It is commonly used in aircraft and aerospace applications, as well as high-stress structural components.

These are just a few examples of the most common grades of aluminium. The choice of the right grade depends on the specific application requirements, such as strength, corrosion resistance, formability, and cost.

Types of copper roofs

There is no doubt that copper is the premium roofing material, along with zinc cladding, as the best cladding products. It’s distinctive look attracts immediate attention meet most design requirements. There are several types of copper roofs, each with their own unique characteristics and benefits. Here are a few examples:

1. Standing seam copper roof cladding: The standing seam is is the most common type of copper cladding and is known for its durability and resistance to weathering. It consists of copper panels that are joined together with standing seams, which are raised seams that connect the panels and help to prevent water from seeping through.
2. Copper shingle roof cladding: This type of roof is made up of individual copper shingles that are installed in an overlapping pattern. It has a distinctive appearance and can be used to create intricate designs and patterns.
3. Copper tile roof cladding: This type of copper cladding is made up of individual copper tiles that are installed in a similar way to traditional ceramic or clay tiles. Copper tiles are lightweight and durable, making them an excellent choice for roofing.
4. Copper flat seam roof cladding: This type of roof is made up of copper panels that are soldered together along their flat edges. It is commonly used on flat or low-pitch roofs and is known for its sleek appearance.

Each of these types of copper roofs has unique benefits and can be customized to fit the specific needs of the building or structure. Copper roofs are known for their longevity, durability, and resistance to corrosion, making them a popular choice for high-end residential and commercial properties.

What grade of copper roofing sheet is used?

The most commonly used grade for copper cladding and roofing in Australia is C12200, Phosphorus Deoxidized (DHP) copper, which is a high-quality, commercial-grade copper that is specifically designed for architectural applications. C12200 copper is a pure copper that contains at least 99.9% copper and has a small amount of other trace elements, namely phosphorus. The phosphorus dioxides(removes) the oxygen, making this grade of copper roofing suitable for welding and brazing. It is also not subject to hydrogen embrittlement. The phosphorus also raises the softening point of work hardened tempers and promotes fine grain size.

C12200 copper is known for its excellent corrosion resistance, thermal conductivity, and ductility. It is also highly malleable, which makes it easy to form into complex shapes and details.

When choosing a grade of copper cladding for roofing, it is important to consider factors such as the environment, the design and style of the roof, and the budget. It is also important to work with a qualified roofing contractor who has experience working with copper roofing to ensure that the installation is done properly and to the highest standards.

Copper roofing coil and sheets

Austral Wright Metals stocks a range of copper for roofing applications.

Most common sizes for copper roofing sheet are:

0.55 x 1000 coil

0.55 x 1200 coil

0.70 x 1000 coil

0.70 x 1200 coil

0.7 x 1200 coil

A full range of sizes can be found at here.

FAQ

What are the advantages of copper roofing sheet?

Copper roofs and cladding offer a number of advantages over other roofing materials. Here are some of the key advantages of a copper roof:

1. Longevity: Copper roofs are incredibly durable and can last for centuries with proper maintenance. Unlike other roofing materials that may need to be replaced every few decades, a copper roof can last for generations if installed correctly. Examples of standing seam copper roofing can be seem all around the world.
2. Low maintenance: Copper roofs require very little maintenance, which makes them a popular choice for homeowners and property owners. They do not need to be painted or sealed and can be easily cleaned with soap and water.
3. Sustainability: Copper is a highly sustainable material that can be recycled indefinitely without losing its properties. This means that a copper roof can be recycled at the end of its useful life and turned into new products.
4. Resistance to corrosion: Copper is highly resistant to corrosion and can withstand harsh weather conditions, including heavy rain, snow, and wind. It is also resistant to fire and does not burn or emit toxic gases.
5. Aesthetic appeal: Copper roofs have a distinctive appearance and can add a unique and elegant touch to any building or property. They can be customized to fit a wide range of architectural styles and designs, and can even develop a natural patina over time that adds to their beauty. The standing seam gives lines that enhance any building.

Overall, copper roofs are a highly durable, low-maintenance, sustainable, and visually appealing choice for any building or property.

How energy efficient are copper roofs?

Copper roofs are known to be energy efficient due to their ability to reflect sunlight and reduce heat absorption. When compared to other roofing materials such as asphalt shingles or clay tiles, copper roofs have a higher solar reflectance and lower heat absorption, which helps to keep the building cooler and reduce the amount of energy needed to cool it.

Copper roofs also have a high thermal conductivity, which means that they can transfer heat effectively. This can help to reduce heat loss during the winter months, which can result in lower heating costs and improved energy efficiency.

In addition to their energy-saving properties, copper roofs are also a sustainable roofing option. Copper is a highly durable material that can last for centuries with proper maintenance, which means that a copper roof can reduce the need for frequent roof replacements and conserve natural resources over the long term.

Overall, copper roofs are an energy-efficient and sustainable roofing option that can help to improve the energy performance of a building while also providing a beautiful and durable roofing solution.

How long do copper roofs last?

Copper roofs are known for their longevity and durability, and can last for centuries with proper maintenance. The lifespan of a copper roof depends on a variety of factors, including the quality of the installation, the design and construction of the roof, and the local climate and weather conditions. Examples of standing seam copper roofing dates back for centuries.

In general, a well-installed copper roof can be expected to last for 50 to 100 years or more. Over time, the copper will develop a natural patina that can protect it from corrosion and give it a distinctive greenish-gray color.

With proper maintenance, a copper roof can last even longer. Regular cleaning and inspection can help to prevent damage and ensure that the roof is in good condition. It is also important to address any issues such as leaks or damage promptly to prevent further damage to the roof.

In summary, a copper roof is a long-lasting and durable roofing solution that can provide reliable protection for a building for many decades or even centuries.

How do you choose the right copper roof?

Choosing the right copper roof involves considering a number of factors, including the design and style of the building, the local climate and weather conditions, and your budget. Here are some tips to help you choose the right copper roof:

1. Determine the appropriate thickness: Copper roofs come in different thicknesses, or gauges, which can impact their durability and longevity. Thicker copper is generally more durable and longer-lasting, but it is also more expensive. The appropriate thickness for your copper roof will depend on the design and style of your roof, as well as your budget.
2. Choose the appropriate profile: Copper roofs come in a variety of profiles, including standing seam, flat seam, and shingle. The profile you choose will depend on the style and design of your roof, as well as your personal preferences.
3. Consider the local climate: The local climate and weather conditions can impact the performance and longevity of your copper roof. In areas with heavy rainfall, for example, it may be beneficial to choose a copper roof with a steeper slope to help facilitate water runoff.
4. Determine the appropriate finish: Copper roofs can be finished with a variety of coatings and finishes, including natural, pre-weathered, and painted finishes. The appropriate finish will depend on your aesthetic preferences and the design of your building.
5. Choose a qualified roofing contractor: Installing a copper roof requires specialized knowledge and expertise. It is important to choose a qualified roofing contractor with experience working with copper to ensure that the installation is done properly and to the highest standards.

In summary, choosing the right copper roof involves considering a number of factors and working with a qualified roofing contractor to ensure that the installation is done properly and to your satisfaction.

“Stainless Steel Doesn’t Rust”

“All Stainless Steel is the same”

Actually, stainless steels are a family of alloys, which can have a great range of properties, depending on what they are to be used for. Stainless steels are often used for their appearance or corrosion resistance, but they are also used for heat resistance, strength or toughness, and for their magnetic properties. The best grade of stainless steel is chosen to suit the application. The grades fit into branches of the family, called austenitic, ferritic, duplex, martensitic or precipitation hardening, depending on their crystal structure.

“Stainless Steel is not Magnetic”

Some types of stainless steel, including the most common ones, the austenitics, aren’t magnetic. But most types – the ferritics, martensitics, duplexes and most of the precipitation hardening grades – are magnetic. The corrosion resistance is not affected in any way by whether the grade of stainless steel is magnetic or not – corrosion resistance depends on how much of the key alloying elements you have, especially chromium and molybdenum.

Even the austenitics can become somewhat magnetic when they are deformed. Try putting a magnet in the corner of a stainless steel sink – some magnetism can usually be detected. The amazing ability of austenitic stainless steel to deform without breaking is used to deep draw sinks in one piece – without heating!

“Stainless Steel is Expensive”

Stainless steel do cost more than carbon steels, in dollars per tonne. With the extra alloys, they are bound to. But the extra performance of stainless steels more than pays for the difference, and stainless steel often works out as the cheapest way to do the job. Carbon steels usually need to be painted for corrosion protection, and even if their first installed cost is lowest, their advantage disappears on the day they have to be repainted. The cost of stainless in dollars per day for the life of the job will be much lower.

“18/10 Stainless Steel is better than 18/8 Stainless Steel”

Actually they are both the same. The common austenitic grades contain about 18 to 20% of chromium, and 8 to 10% of nickel. Europeans often refer to them as 18/10 stainless, while the English speaking world – Australia, USA, UK – call them 18/8 stainless steel. There are minor differences between the standard stainless steel compositions in different parts of the world, but the performance of the grades are effectively the same wherever in the world they are made.

“All Stainless Steels have the same Corrosion Resistance”

The corrosion resistance of stainless steels mostly depends on their content of the alloying elements chromium and molybdenum, plus a few other factors, depending on the specific application. The surface finish and fabrication practice can have a major effect.

I would like to buy a stainless steel appliance for my kitchen. But isn’t its beautiful surface difficult to clean?

No, stainless steels are easy to clean. For this reason, they are the normal choice of material in catering and food manufacturing industries. The smooth and non-porous surface makes it difficult for bacteria and other micro-organisms to adhere and survive.

Of course, no material is totally maintenance-free, and stainless steel is no exception to this rule. Stainless steel can be cleaned easily, leaving sanitised surfaces with a high standard of hygiene.

The excellent corrosion resistance of stainless steels used in the kitchen means that they resist attack or staining from foods like tomatoes, beetroot and capsicums, which can affect the surfaces of other materials.

How can I remove fingerprints from stainless steel?

Slightly damp microfibre cloth is efficient in removing finger marks from decorative finishes mirror-polished stainless steel surfaces, chloride-free glass cleaners may perform well.		On mirror-like stainless steel surfaces, glass cleaners perform well.

Avoid abrasive products as they will leave scratches. On brushed and polished stainless steel surfaces, wipe along the polish and not across it. This will produce the best results when you clean your stainless steel appliances.

Finger marking on the surfaces of stainless steel is more of a problem on new appliances. After only a few weeks in the kitchen, fingerprints do not show up as much as when the surface was “brand new”.

How can I handle more tenacious deposits, e.g. on my kitchen sink?

For more stubborn dirt, e.g. grease or tea stains, a normal cream cleanser (e.g. Jif) will generally do the job.

Cream cleansers are particularly suitable for stainless steel kitchen sinks. Especially in areas with hard water, wipe the surfaces dry and remove the wet cloth or sponge to avoid water marks and limescale.

Is there any way I can remove limescale from stainless steel?

If cream cleanser is not enough, treat scale with a 25% vinegar solution (acetic acid) and give it some time to dissolve. Then clean, rinse and wipe dry as usual.

What can I do about burnt-on food in pots and pans?

You can reduce the cleaning effort substantially by soaking the burnt-on deposits on stainless steel pots and pans. Simply fill the pot with hot water and a drop of dishwashing liquid and leave it for 15 minutes. After this, the deposit can generally be removed with a sponge or a nylon scouring pad without particular effort.

Never use non-stainless steel wool scouring pads. Ordinary steel wool pads can leave rusty stains after cleaning, which may permanently damage the corrosion resistance of the stainless steel.

For pots and pans, special stainless steel scouring pads are available.		Never use “ordinary” steel wool!

If stainless steel wool scouring pads are used, where the deposits are very difficult to remove, then the scratches left will not damage the corrosion resistance of the surface. The scratches left however, cannot be removed by further cleaning and so this form of “aggressive” cleaning is not suitable for delicate, decorative surfaces.

Tea stains can be difficult to remove. Is there any particular recommendation?

Washing soda (sodium carbonate) is very efficient in removing tea (tannin) stains from stainless steels. Tea pots can be immersed completely in a hot washing soda solution, on larger surfaces it can be applied with a cloth or sponge. Then rinse with clear water and dry as usual.

Tea stains can be removed with a solution of washing soda

Does the same procedure apply to coffee deposits?

Coffee deposits are oily, and they only occur if coffee urns are not cleaned regularly. In such a case, baking powder (sodium bicarbonate) is the answer. Mix a solution of boiling water and baking powder, allow the solution to work for 15 minutes, and then rinse and dry the stainless steel as usual.

Are there any cleaning practises that should be avoided when cleaning stainless steel

Disinfectants containing bleach (sodium hypochlorite) can damage stainless steel if concentrated or allowed to be in contact with surfaces for too long. Salt or other cleaners shown as containing chlorides can also cause damage. Look on the side of the packaging for the ingredients. Always dilute these “sanitising” products, if used, keeping the contact times to a minimum and ensuring that the surfaces are thoroughly rinsed with clean water afterwards.

Hard abrasive scouring powders (e.g. Bon Ami) will leave scratch marks.

Wire wool pads made of “ordinary” steel (e.g. Bly’s, Brillo pads) are totally unsuitable for stainless steel as they will impair the self-healing capability of the stainless steel surfaces. Fragments of steel wool breaking off the pad will rust on the stainless steel, staining the surface.

Silver dip cleaners may contain chlorides and strong acids and are not suitable for stainless steel.

There are special protective sprays and pastes for metals. What are they for?

Most spray cleansers for metallic surfaces (e.g. by 3M, Henkel) contain silicone oil. These products, often made specifically for stainless steel, can make cleaning a lot easier. However, although removing old finger marks, these sprays will not prevent new finger marks from being visible. The effect of the spray generally lasts between a few days in heavily exposed areas to several weeks. The silicone oil can be removed again completely with soapy water.

Polishing pastes produce a microscopic, but very resistant wax layer that make metallic surfaces particularly easy to clean. Being resistant to detergents, these layers may last several months. They can be removed with alcohol.

Both these treatments are used for decorative parts, not for food contact articles.

I have seen ‘stainless steel cleaner’ for pots and pans at the local hardware store

How does it work?

There are white powder stainless steel cleaners, which are applied with a clean damp cloth or sponge. They are very effective cleaners to remove contamination and will brighten the stainless steel surface slightly. They can be used with most stainless steel articles except knives – follow the instructions on the package.

Be sure to rinse the stainless steel surface thoroughly after use.

Introduction to Copper Coatings

The distinctive colours of copper and copper alloys make them prized for architectural and consumer items and objects of art. Their natural metallic tones range from reddish to silvery. A number of other colours can be obtained by chemical or electrochemical processing.

Copper and its alloys are extremely resistant to corrosion, but a superficial discolouring tarnish eventually forms with exposure to the atmosphere or handling. The appearance of these metals can be preserved by applying thin clear protective coatings to their surfaces. These layer coatings are organic chemicals that harden at room temperature or with baking and are usually applied in a solvent.

There are hundreds of useful clear copper coating products on the market, formulated from numerous polymers, solvents, and additives. The user selects from these a coating based upon economics, intended life, desired transparency, and the expected service conditions. The effectiveness of a finish also depends on the procedures used when coating.

Serviceability

Coatings are available which can protect copper-base metals for many years under ideal conditions. However, handling, humidity, air pollution, sunlight, and abrasion all work to reduce the life of a coating. For example, copper coating life is usually short in exterior applications in cities with severe air pollution.

In selecting a copper coating it must be realised that maximising resistance to one type of service condition may reduce resistance to others. Also, if the life of the article is expected to be longer than any reasonably attainable coating life, a coating that can be stripped off with a solvent must be selected so that the article may be restored when the coating and appearance have degraded to an unacceptable level.

Some examples of coating performance on copper metal indicate the range of serviceability of organic finishes and their alloys:

• Air-drying acrylic lacquers with a tarnish inhibitor (benzotriazole) have protected bronze nameplates outdoors for years. The same coating indoors on metal handrails and other objects subjected to wear could fail in less than one year.
• A combination of a silicone primer and an acrylic top coat displayed an excellent appearance after more than six years of service in interior applications with moderate or no abrasion. The same system darkened significantly in one year of open exterior exposure but indicated good performance for more than three years in sheltered doors of office buildings and churches.
• Silicone thermoset coatings for copper retained good protective qualities after 62 days at 93ºC.
• Antiqued brass automotive interior trim has been protected with a thermosetting epoxy clear coating.
• The copper roof of the Sports Palace in Mexico City is covered with an air drying acrylic lacquer formulated with an inhibitor and organic ultraviolet absorbers.
• Bathroom fixtures of brass have been satisfactorily protected for more than five years with a baked epoxy coating.

Basic Clear Coating Systems

Nitrocellulose

Nitrocellulose coatings are the least expensive and most common air-drying coatings for interior service. They are modified with alkyd or acrylic resins. Nitrocellulose coatings are used in exterior applications; however, they are usually stripped and replaced at intervals of less than one year. They do not have high resistance to chemicals, but they are fast drying and easy to use.

Acrylic

Available as air drying or thermosetting, these are relatively high-cost materials. The air drying modifications are popular for exterior applications, while the thermosetting types are useful for interior applications requiring high resistance to heat and abrasion. Since the thermosetting coatings are not conveniently stripped, they are unsuitable for major architectural applications.

Epoxy Coatings

Epoxy coatings have excellent resistance to wear and chemicals. They are relatively expensive and are only available in thermosetting or two-part (catalyst activated) compositions with relatively short pot lives. They are good for severe indoor applications, but they degrade rapidly and darken in a few months of exterior service.

Silicone Coatings

Silicones provide the best potential for coatings which must operate at elevated temperatures. When the films of these high-cost coatings are used, protection by a second coat of a more durable abrasion resistant lacquer may be necessary. Ultraviolet absorbing compounds are added to prevent darkening of the silicone during exterior exposures.

Alkyd Coatings

Slow drying or baking is required when applying the alkyd coatings. Modifications with melamine resins, these coatings are low cost and durable enough for exterior applications. Resistance to chemicals is usually good.

Urethane Coatings

Colour degradation on exterior exposure has been a problem with urethane coatings. Resistance to chemicals and abrasion are good even for the air drying coatings.

Cellulose Acetate Butyrate

Usually used for interior applications, cellulose acetate butyrate coatings are air drying and have moderate cost and properties. They have a tendency to darken in exterior applications.

Vinyl

Vinyls are usually soft and flexible and require stabilization against ultraviolet degradation.

Additives

Among the common coating additives for copper are the following types:-

Ultraviolet Absorbers

Ultraviolet absorbers are organic compounds which are sometimes added to coatings for exterior applications in order to prevent darkening and degradation of the coating. In some cases they may also interact with the substrate and prevent tarnishing.

Levelling Agents

Levelling improve the flow properties of coatings and thereby provide better surface appearance. In addition, the likelihood of pinholing or other defects is reduced.

Chelating Agents

Benzotriazole and other chelating agents interact with copper and its alloys to prevent tarnishing. Chelating agents are preferentially absorbed on the surface of the metals and act as an invisible barrier to elements or compounds which might cause corrosion. In this way they protect the metal… against oxidants permeating through the coating and continue to protect even after a minor defect has been formed in the coating. Chelating agents may be included in the coating formulation or applied as part of a pre-treatment procedure.

Application

No coating can perform to expectations if applied to a poorly prepared copper surface. The metal surface must be free of contaminants such as dirt, oil, dust, old finishes and fingerprints. Coating should be done with a minimum of delay after cleaning the metal surface and precautions should be taken to prevent recontamination. Precautions include working in a low dust environment, handling with white gloves, and apply tarnish inhibitors (chelating agents) to the surface.

Ordinary steel wool should not be used in cleaning as the pads may contain chemicals that stain copper metals. Suitable abrasives are silicon carbide (Scotch-brite) pads or wheels, stainless steel pads, and powdered pumice stone. The pumice powder is slurried in a 5% oxalic acid solution and rubbed on with a cloth. All residues must be removed and the surface wiped dry with a clean cloth. Abrasives should not be used in polishing prior to coating, parts should be degreased or otherwise cleaned to remove any residue.

Degreasing is normally done with solvents such as butyl cellosolve and trichloroethylene. To prevent streaking and staining, it may be necessary to wipe-dry large areas with lint-free wipers. Freshly plated parts must be thoroughly neutralized and rinsed in hot water prior to coatings.

The spraying area should be free of dust and dirt and at moderate temperature (between 10 and 33ºC), at low humidity (certainly less than 80% when organic vehicles are used), and well ventilated.

Usually enough coats are applied to achieve a total dry layer thickness of 13 to 40 micrometres. Greater thicknesses tend to become obvious and the metal takes on a varnished appearance. However, the coating manufacturer may recommend thinner coatings for certain application.

Incralac

A system called Incralac developed as a result of research by the International Copper Research Association has given good performance since its release.

Intended primarily for use on outdoor architectural metal work, it preserves the natural colours of copper and its alloys for long periods. It can also be used on copper and its alloys indoors.

Incralac contains an acrylic ester resin dissolved in a solvent such as toluene. Benzotriazole is added as a corrosion inhibitor, and epoxidized soya bean oil as a levelling agent. Incralac-coated test panels exposed in many cities and towns in Australia have remained untarnished for several years.

The inhibitor effectively combats tarnishing beneath lacquer films. This mode of failure is due primarily to peroxides formed during the early stages of degradation of the lacquer film and residual solvent under the influence of ultraviolet radiation. Greatly increased protection is afforded by the incorporation of suitable ultraviolet absorbers, anti-oxidants and copper complexing agents.

Careful cleaning and spraying are essential. Wiping with an inhibitor-cleaner (40 grams benzotriazole in a 4.5 litres of water) is recommended as the last cleaning step before the coating is applied.

Incralac is available in 500 ml cans and 300g aerosol spray packs from stockists of Wattyl products, or contact Wattyl Australia Pty Ltd at 48 Walker St, Canada Bay, NSW 2046. Phone (02) 9621 9208, or visit http://www.wattyl.com.au/.

Additional Considerations

A lustrous metallic surface acts as an excellent backdrop to view coating defects and tarnished spots. Therefore the tolerance for defects is low and clear coatings must have a high degree of effectiveness in order to perform satisfactorily.

This is less of a problem on antiques or coloured metals.

Of concern on copper alloys is that darkening of the substance can occur even under a coating that is intact due to interaction of the copper with residual solvents. This is a special problem during outdoor exposures when ultraviolet radiation can stimulate the breakdown of solvents.

By proper choice of solvents and additives this problem can be minimized. Ethyl alcohol and isopropyl alcohol cause considerable tarnishing. Benzene, toluene, xylene, butyl acetate, and ethyl acetate are much better.

Discolouration of copper and its alloys also may occur at the curing temperatures normally recommended for thermoset coatings. It is wise to use low curing temperatures and short curing schedules to avoid such in-process discolouration. Catalytic activity of copper sometimes allows lower temperatures or shorter curing schedules to be used.

This Product Data Sheet is based on information provided by the Copper Development Association. Further information is available from Austral Wright Metals.