As regards production, tyre manufacturing may be initially considered as being comprised of two principal phases:

  • creation of the rubber part, the compound, the tread and the sidewalls;
  • construction of the base structure, an actual rubber “framework” that supports all the components.

The rubber part of the tyre (tread, sides and fabric) is a special mix, more commonly referred to as a “compound,” which is mainly composed of rubber (both natural and synthetic), plasticizers (petroleum derivatives) and binders (mainly carbon black and silica), whose percentages are about 30% each, even if the exact value depends on the type of compound that is desired. The remaining 10% or so is comprised of other mineral binding agents and products (e.g. accelerating agents, anti-decomposition agents, vulcanizing agents…).

The plasticizers and carbon black are stored in dedicated silos and sent to a closed mixer (“banbury”), in which the compound undergoes initial processing. A computer controls and manages the quantities of ingredients, both those in storage and those sent to the mixer.

Instead, the rubber (both natural and synthetic) is cut into pieces and added manually, after being weighed in order to obtain the desired composition. Then, the compound sheets are transferred to an open mixer (“calender”), comprised of two big rollers. After passing through these rollers, the composition and density of the mixture becomes more uniform. This particular step in the process involves continuous torsion and simultaneous stretching. At the end of the cycle, special chemicals are added, such as vulcanizing agents and accelerants, which are necessary for the following phases.

Then, the compound sheet is sliced into strips and plunged into a vat (“batchoff”) for final cooling. At this point, the compound is used to fabricate the tyre tread or sidewalls. It is then extruded into the appropriate form for the subsequent steps. The heart of the tyre structure is represented by the fabrics, which are formed by longitudinal threads (weft) and transverse threads (warp), and may be composed of various materials. The fabrics are then cut at a certain angle with respect to the longitudinal direction (the direction of movement, of rolling or of the weft).

Another fundamental part of the tyre is the sidewall, and specifically the area close to the metal wire, which is called the “bead.” The base is supported by the ring, comprised of a series of brass-coated steel wires, which stiffens the part touching the wheel rim.

056-1_redux_e.gifThe components described thus far must be assembled together to make the finished tyre. This assembly process is carried out by using devices that are called “building machines.

” The resulting tyre (called a “raw tyre”) is then sent to be vulcanized, which involves a genuine solid state chemical reaction. Before being vulcanized, the tyre must first be “grouted,” a treatment that prevents it from sticking to the mould or the vulcanization chamber.

After being cooled, the vulcanized tyre is deburred to remove any imperfections that might alter its appearance. Then it undergoes an initial visual inspection (both internal and external, to check that there are no obvious fabrication defects), which is then followed – in the case of truck tyres – by an X-ray inspection in specially shielded areas.