Raw materials including pigments, chemicals, and up to 30 kinds of rubber are mixed in giant blenders called Banbury machines, which operate under tremendous heat and pressure. They blend the ingredients together into a black, gummy compound that will be milled.
The cooled rubber is processed into slabs and transported to breakdown mills. These mills prepare the different compounds for the feed mills, where they are slit into strips to become sidewalls, treads etc.
Another kind of rubber also coats the fabric that will be used for the tyre’s body. Many kinds of fabrics are used: polyester, rayon and nylon.
Another component, shaped like a hoop, is called the bead. It will be added to fit against the vehicle’s wheel rim.
Next, two layers of ply fabric, the cords, are added. Then follows a pair of chafer strips, so called because they resist chafing from the wheel rim on a vehicle.
Now the tyre builder adds the steel belts that resist punctures and hugs the tread firmly to the road. The tread is the last part to go on the tyre. After automatic rollers press all the parts firmly together, the tyre, now called a green tyre, is ready for curing and inspection.
The curing press gives the tyres their final shape and tread pattern. Hot moulds shape and vulcanise the tyre. The moulds contain the tread pattern, the sidewall markings of the manufacturer and those required by law. Tyres are cured at over 300 degrees for 12 to 25 minutes, depending on their size.
If anything is wrong with the tyre – even the slightest blemish – it is rejected. Some flaws are caught by an inspector’s trained eyes and hands; others are found by specialised machines. Inspection doesn’t stop at the surface. Some tyres are pulled from the production line and X-rayed to detect any hidden weaknesses or internal failures. In addition, quality control engineers regularly cut apart randomly chosen tyres and study every detail of their construction.