Mar. 07, 2022
Aluminum is known as the "wonder metal". Found primarily in bauxite, it is the third most common element in the earth's crust and the most abundant metal on earth. But what makes it perfect for windows, doors and curtain walls?
Well, the chemical, physical and mechanical properties of modern aluminum alloys have led to a dramatic increase in their global use at a rate of more than 5% per year. Here are 8 reasons why the aluminum framing market in the glass world continues to grow, now dominating the commercial market and making PVC-U an instant hit in the residential sector.
If you're looking for low-maintenance windows, then aluminum is the way to go. That's because when aluminum comes in contact with air, a protective layer of aluminum oxide immediately forms on the surface. This layer is extremely resistant to corrosion that can be caused by any weather, including acid rain, and will not be damaged by cleaning products. Unlike wood or PVC-U frames, aluminum window frames will not swell, crack, split or warp over the years, regardless of the weather. Corrosion protection can be further enhanced by anodizing or painting the surface (usually by powder coating).
Aluminum is a very light metal, with a specific gravity of only 2.7 g/cm 3, about one-third that of steel or copper. In fact, it is one of the lightest commercially available metals. This makes it ideal for window and door frames, but for curtain walls, it is especially important to use lightweight frames. Curtain walls are not structural and can only carry their own weight, so the lighter they are, the better.
Aluminum is ductile and malleable - and in case you forgot the GCSE chemistry, that means it can be bent or pressed into shape or drawn into thin wires without losing its toughness and without breaking or cracking. In other words, it's pliable and not brittle. In fact, aluminum is the second most ductile metal and the sixth most ductile metal. This is good news for anyone who wants to bend curtain walls or windows, because aluminum framing profiles can be easily bent or pressed into the desired shape without any risk of breakage.
As we have already seen, aluminum is often alloyed with other elements to improve its physical properties. For example, the strength of pure commercial aluminum can be increased by 20% with the addition of only manganese. Aluminum also readily forms alloys with silicon, copper, zinc, iron and magnesium. This means that a range of alloys can be produced with properties tailored to specific applications. Aluminum Glass Company uses alloys of aluminum with silicon and magnesium, which are excellent choices for extruded aluminum profiles. They are versatile, heat treatable, highly formable, weldable, and offer high strength and excellent corrosion resistance.
Aluminum window frames are manufactured using the extrusion process, which involves forcing preheated aluminum alloys through a die to create aluminum profiles. These profiles are then joined together to form the frame. It is the design of these profiles that gives the window frame its unique characteristics. They can be complex designs, but fortunately, these intricate shapes can be achieved using a single extruded section, so the profiles are both strong and durable. Aluminum also has excellent machinability, making it easy to fabricate aluminum profiles into finished window frames with precision.
Aluminum is used in the manufacture of window, door and curtain wall frames. That's because pure aluminum itself does not have a high tensile strength. However, once it is alloyed with other elements such as manganese, silicon, copper and magnesium, it becomes much stronger. Pure aluminum has a tensile strength of about 90 MPa, but as an alloy it can increase to over 690 MPa. In fact, as we have already seen, aluminum is one of the lightest engineered metals, and when used as an alloy, its strength-to-weight ratio is far superior to that of steel. Even more impressively, unlike steel, aluminum's strength increases as the temperature decreases, whereas steel does at low temperatures (below 0 oC). This means that aluminum windows, doors and curtain walls can handle the most extreme winter temperatures in the UK. The lowest temperature recorded in the UK was -27.2°C in Scotland.
Aluminium is unique when it comes to recycled metal. It is 100% recyclable and recycled aluminum has the same quality as virgin aluminum. This means it can be recycled time and time again. In fact, nearly 75% of the aluminum ever produced is still in use today. That's good news for the aluminum supply, especially considering that global demand for aluminum has grown to about 29 million tons per year since the first industrial aluminum production about 100 years ago. But it's even better news for the environment, because while it takes 14,000 kWh to produce 1 ton of new aluminum, it takes only 5-10% to remelt and recycle the same amount of aluminum. This means a smaller carbon footprint and lower costs.
Aluminum can be easily anodized or powder coated to give it a decorative smooth or textured finish. This means that aluminum windows, doors and curtain walls not only perform well, they look great too. Anodizing is performed by immersing aluminum in an acidic electrolyte bath and passing an electric current through it. This transforms the metal surface into a decorative, durable, corrosion-resistant aluminum oxide finish. The aluminum oxide is completely bonded to the underlying aluminum and therefore will not chip or flake, making it very durable. Aluminum oxide has a porous structure and therefore needs to be sealed to make it corrosion resistant. Sealers can be clear or contain special dyes, so anodized aluminum is available in a variety of colors. Another method is to apply paint to the aluminum. The aluminum is pre-treated by anodizing or by chemical reaction to create a corrosion resistant barrier and can then be coated with any RAL color powder. At Skyland Door & Window, we have a state-of-the-art powder coating facility. The pretreated aluminum strip is grounded and the paint powder is electrostatically charged as it leaves the gun. This helps the powder molecules adhere to the bar by electrostatic charge, just like dust particles adhere to a TV due to the electrostatic charge on the screen! The bar is then cured in an oven where the powder melts and forms a uniform, pliable and smooth finish that will resist weathering for 25 years.
With all this effort, it's no wonder that more and more people are choosing aluminum windows, doors and curtain walls for commercial and residential buildings.
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