Comparing plastic and metal is not entirely fair, but not for the reasons you’d think. It’s not that plastic comes off looking bad – quite the opposite, actually! Instead, the two classes are very different and should be considered for very different reasons.
Still, the question of choosing between plastic and metal comes up often, because plastic has expanded to offer far more uses. Where in the past certain jobs were only reserved for metal, today plastic can often solve the same problem faster, better and cheaper.
But for the best fit, let’s look at the strengths of either side:
Plastic is easier to fashion. Molding metal requires very high temperatures to achieve melting point. Even when you reach this stage, the viscosity – that being how easily the liquid flows – is much higher. This is a concern when trying to fill molds. Plastic melts at lower temperatures and flows more readily. It is also easier to cut and manipulate.
Plastic offers wider property manipulation. There is more than one type of metal, as you can see with the many alloys that are available. Each has properties that work better for some purposes. But plastic offers an even wider range of property choices. The type of resin and additives used for a plastic can change many things, including heat and chemical resistance. Plastic features often in high-demand environments, such as car engines and aircraft.
Plastic requires fewer post treatments. Once a metal product has been created, it still needs a lot of work before being ready. This can include polishing and painting because those properties cannot be introduced before the metal is cast. But plastic works the opposite way: many of its final properties are determined when the original ingredients are mixed together. When a plastic product pops out of the mold, it is very often ready to go.
Plastic weighs a lot less. It almost goes without saying: plastic weighs less than metal. This is one reason why we see more plastic in cars: the plastic not only can endure the harsh environments traditionally reserved for metals but does so while adding much less weight. Weight is also a leading consideration when choosing pipes and when you want to save on transportation costs.
Plastic has better chemical resistance. This last point may give you pause. Surely metal is more resistant to chemicals? Not really. While it is true that you can easily damage plastic with chemicals and heat, this is not true for all plastics. If treated with the right additives, plastic can resist chemical and heat corrosion, as well as UV damage. Metal can be treated or mixed to resist corrosion such as rust, but usually at a greater cost. Water, the great enemy of metal, doesn’t react with plastic.
Metal has better structural integrity. Plastic is wonderful, but metal can hold a lot of weight. This is why it’s still more popular to create support structures out of metal. That being said, the right plastic also has a lot of structural integrity, such as with water tanks.
Metal offers more fabrication choices. Most plastic fabrication uses heat and molding. Metal offers a bit more, including casting, soldering, welding, forging, chipping and deep drawing. These can be an advantage, depending on the product you want to make.
Metal has a very high heat resistance. Some plastics can handle a lot of heat, but creating such products can be expensive. Metal has very high melting points but at a reasonable price. So you’ll never consider using plastic for a braai grid when metal will do.