April 22, 2015
There is no component of a vehicle that is more important than its tires. Arguably, they are the most critical safety components on the vehicle – the only part of it that touches the road and the medium through which all of the driver's control is exercised.
But have you ever stopped to consider how a tire is made? It's far from a simple process. It's not just made, it's built. Every tire is assembled, a piece at a time, from multiple components.
There are more than 450 factories around the world producing one-billion tires each year. Let’s take a look behind the scenes at what is involved in producing them.
To do so, it's important to understand the key parts of the tire's construction. They are:
1. BEAD – woven bands of high-tensile-strength steel, coated with special alloys of bronze or brass and wrapped in rubber to help prevent corrosion. The beads provide the basic structure of a tire. They are the point at which the tire contacts the wheel or rim. Incredibly strong, they must endure the forces of tire mounting machines when the tires are installed.
2. PLIES – the layers of steel or polyester cords that make up the body, carcass or casing of the tire – the foundation upon which it is built. These layers are connected to the beads. Each ply is coated with rubber to not only provide a seal against air leakage but to help them bond with the other components.The number of plies typically is rated to the strength or load carrying ability of the tire. Car tires typically have two plies; those beneath a large commercial airliner can have 30 or more.
3. BELTS – usually made of woven steel strands that wrap around the tire on top of the casing to reinforce the area under the tread, help keep the tire flat on the ground and provide impact and puncture protection. Here again, tires with higher speed ratings will have an extra belt, usually nylon, wrapped around the steel belts. At higher speeds and temperatures nylon shrinks, preventing expansion.
4. TREAD – this is where the biggest advances have been made, where science, computers and chemistry have combined to create not only vast improvements in all tires but also a new generation winter and all-weather tires. The tread surrounds the tire carcass. It is composed of both natural and synthetic rubber along with a variety of compounds and other materials – a special recipe for each specific application or function of the tire. The chemistry involved is a closely guarded secret within each tire company
The process begins with preparation of the individual components.
To form the tread and sidewall coverings, there are as many as 200 different materials involved, including: natural rubber, or polyisoprene; styrene-butadiene co-polymer or synthetic rubber; polybutadiene, halobutyl, bromobutyl or chlorobutyl rubber; carbon black, silica, sulphur, vulcanizing accelerators and activators like zinc oxide, antioxidants, antiozonants, colour pigments and other unpronounceable stuff. You get the idea.
Those components are mixed together, according to the recipe established for the particular type of tire, in what amounts to a giant mix-master called a Banbury mixer. The resulting rubber compound is then extruded into a cross-sectional shape that will form the tread and sidewall and cut to just the right length for the tire size.
At the same time, the steel strands and fibres that will be used to form the structural components of the tire go through a series of rollers in a process called calendering, to transform them into the precise components needed to build the tire. Then, like the tread material, they will be cut to exact length.
All of those components are then fed sequentially into a machine that ensures they are all properly aligned and combined into the form that will become the completed tire. At that stage it is known as a “green” tire. It has no tread patterns or other markings.
From there it's into the mold and the curing machine where it is inflated, pressing the outside edge to the mold and heated to about 150-degrees C. The heat bonds all the components together, and like a waffle iron, the mold creates the tread and sidewall markings. This process is known as vulcanizing.
Once suitably cured and cooled, the finished tire passes on through a series of inspections and quality checks and on its way to a vehicle manufacturer or aftermarket distributor and ultimately onto the wheels of your car.
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