How It’s Made: Aluminium

Are you sitting comfortably? Good! But have you ever stopped to wonder how a lump of wood, a sheet of metal, a vat of melted plastic or or other raw material became a table, chair or sofa? In a series running over the next few weeks, we will look at furniture and how it’s made. In the process, there should be some interesting ideas plus a bit of guidance about the debates and dilemmas, plus what to think about when choosing a new piece.

A look at aluminium launches our How It’s Made series.

Where do you find Aluminium furniture?
Different Types of Aluminium
What Is Cast Aluminium Patio Furniture?
Disadvantages of Cast Furniture
Sand Cast vs Die Cast Aluminium
What Is Extruded Aluminium Patio Furniture
Cleaning Up the Final Product
Mixing and Matching
The Perfect Finish
Green Credentials of Aluminium Garden Furniture

Where do you find Aluminium furniture?

Furniture is furniture – right? Fundamentally, it is all the same?

Only up to a point. There are solid themes in common between all chairs and all tables, but just think about the different challenges facing an item destined to live its life outside compared with one that will stay indoors.

The outdoor variety will have to cope with changes in heat and humidity. It will need to handle everything from sunshine during the annual summer heatwave, the regular soakings and the bitter cold that sets in for most of the British winter and all weather conditions in between. Sometimes all of them in the same day. 

It is a challenge that the mollycoddled stuff you keep indoors never has to cope with. Regulated temperature, dry conditions, regular dusting and care. All strange ideas to the hardy stuff that lives in the garden.

It is also where aluminium comes into its own. When it comes to all-weather garden furniture that handles the worst the weather can throw at it, aluminium is in a class of its own.

How Different Types of Aluminium Are Made

Aluminium has a lot going for it. It is both light and strong, that’s why it has so many uses – aircraft manufacture, for example. That’s a perfect case where the manufacturers want to keep the weight down but cannot sacrifice strength. The same logic applies to garden furniture. It looks good and, thanks to an accident of chemistry, the natural finish is a close as any substance can get to self-healing. Scratch it and the oxide layer that seals the metal from corrosion comes back immediately. As long as it is not too deep, the damage is at least camouflaged.

If you’re buying garden furniture, aluminium is the obvious answer. Hold your horses, though. It’s not as straightforward as that. Surprisingly (or not), there are different types of aluminium. You can go for cast, extruded or a mixture of both. All have plus points and all have minus points. In the end the decision is going to depend on a number of factors. 

It starts with the manufacturing process. You can buy pieces that have been cast into shape or made from tubes of extruded aluminium. They can also be mixed to try to get the best of both worlds. 

How Is Cast Aluminium Patio Furniture Made?

We’ll start with cast aluminium patio furniture. When you are looking at how it’s made, this is the technique where the metal is heated to melting point and then shaped in a mould. The result is strong, and it can be easier to add fancy decoration in the casting process that makes the finished piece more ornamental. The manufacturer can make the whole piece in one go if they want, as you can see with the Desalto Sand Dining Chair, where the frame is a single cast. Usually, however, there is a limit to how big a piece it is practical to make. A chair is entirely possible, an aluminium garden sofa is tricker to cast all at once.

Disadvantages of Cast Furniture

So why think about doing it another way? The big concern is the weight. Furniture made this way is solid. That makes it heavy and, as a result, hard to move.

Sometimes, the weight may be an advantage. If you have cast aluminium furniture, there is no chance of having to call around the neighbours after a gale has swept through to ask for your chairs back and argue about whether the damage to their roses was caused by the wind or falling furniture. 

The weight can also make a table or chair feel more secure when you are using it. A cast seat gives plenty of support, and a cast table feels solid. 

On the other hand, of one of the advantages of aluminium is its lack of weight, so the heavier option is not always sensible, particularly if you aim to move things around a lot. Sitting out in the sun is meant to be enjoyable not the start of a weight training regime.

Sand Cast vs Die Cast Aluminium

Even if you decide to go for the greater solidity of cast aluminium, decision time is not over. There are different techniques of casting the metal, depending on what kind of material is used for the mould. 

Sand casting is the process where the shape is created in the sand and the metal is poured into it. It is cheap and simple. The problem is that sand is not smooth. It leaves a pockmarked surface, and that doesn’t look particularly attractive. The rough look can lend the item an antique appearance, if that is what you are after, but it has to be part of an overall theme.

Sand casting can, however, be cheaper than die casting, which is the alternative. That is a technique that uses a mould made from solid steel and uses it over and over again. Molten metal is forced into the mould. In the past, this was mainly done under relatively low pressure but these days high-pressure casting is normal. Not only does this harden the metal, it gives the finished product a much better appearance. The downside is that you need heavy machinery, and the mould is expensive so it really only pays its way if there is big production run.

How Is Extruded Aluminium Patio Furniture Made?

This the rival technique for how it’s made. The metal is heated until it is soft and then forced through a shaped hole or die. This produces a hollow round or square tube that is then cut up and assembled into the item of furniture.

The extruded aluminium tubes are usually used to make a frame and the flat areas are made from something else. Cast aluminium is one answer but it makes sense to go for something lighter. Canvas, cloth or vinyl strips strung across the gaps are one answer, solid plastic or sheet wood is another.

It is a great technique for designers as you can see in the Eos range from Matthew Hilton. They mix the different sizes and shapes to get creative with the look of the finished piece. 

It uses less metal, so is usually cheaper, and is a lot lighter. That makes it easy to move while still being strong enough to handle most demands. The thinner surfaces also mean that if you are lucky enough to see some sun, the metal won’t hold as much heat as the more solid cast metal style.

On the downside, it is unlikely to last as long as cast aluminium. While the surface may resist scratches, the thinner metal is more easily dented. As with all tubes, a lot of the strength comes from the shape, so dents also raise the risk of it breaking. 

Finally extruded aluminium furniture is likely to be welded or bolted together. Water can get into these joints and can loosen them if the weather turns icy. It is a good idea to keep extruded aluminium furniture in a shelter during the winter months. 

Cleaning Up the Final Product

On the whole, the more expensive options are also likely to be finished to a superior standard. That is also important. If you look at how a table, chair or sun lounger is made and see the joints have been or roughly welded then it is not a good sign. It is probable the manufacturer was more worried about speed than quality and they would be better avoided. 

Make sure the welds go all the way round. Some cheaper manufacturers try to spot-weld the visible sides of the joints but without the complete weld, the joint is less secure. 

Seamless welds are an indication that you are looking at a high-quality item. If it has been carefully finished by hand, there may also be areas where a filler has been used. Don’t worry about this. It is just a sign of how much care has been put into making sure there are no gaps and no way of water getting in. 

Mixing and Matching

There is a lot to be said for the joys of trying to get the best of both worlds with modular aluminium garden furniture. Use cast aluminium for the bits that need solidity and strength but save weight where you can with extruded tubes. So, when deciding how it’s made, you’ll find the body, the arms and the back of the chair may come from a single casting but extruded tubes are used for the legs. 

How the Perfect Finish is Made

The final decision for how it’s made is over the finish. In its natural state aluminium is a classy silvery colour but that may not suit everyone and there are other options. The standard way of colouring aluminium is with a powder coated finish. This is a technique that uses an electrostatic paint gun to spray charged particles of paint onto the aluminium surface. The piece is then heated so that the colour melts into a uniform film all round the item. 

This is a tough finish that resists scratches, peeling and chipping. Because there are no solvents in the coloured powder, it is also environmentally friendly. 

Other colouring techniques used less frequently for furniture include anodising – using electrolysis to deepen the oxide finish to create a porous surface that paint can sink into – and painting. Both have issues that make them less effective – anodising is less efficient when it comes to furniture while paint is prone to peeling, chipping and scratching. 

The final thing to think about is the joints. Often they will be simple bolts or welds but some designers make a feature out of them by using brass or steel to create a different look. There are arguments for that but well-finished welded joints are stronger. 

Green Credentials of Aluminium Garden Furniture

This is another area where aluminium scores high. It doesn’t rust so a well-made piece will last for a long time. When the time for a change comes, however, aluminium is one of the most easily recycled materials around. The energy savings are considerable. Experts reckon it takes about five percent of the energy to recycle aluminium compared to the energy needed to refine it. If you send it away for recycling, don’t worry, it won’t end out on a foreign landfill. It will get used. 

With a little care and an examination of how it’s made, your garden furniture will look great, will last for years and, when the time comes, is sought after as material for recycling. It’s hard to go wrong.

Verpan Spiegel Wall & Ceiling Lamp by Verner Panton Brushed Aluminium life 1 Olson and Baker - Designer & Contemporary Sofas, Furniture - Olson and Baker showcases original designs from authentic, designer brands. Buy contemporary furniture, lighting, storage, sofas & chairs at Olson + Baker.

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