The manufacture of a tyre
Despite appearances, the tyre is a high-technology product, and not just a moulded object.
On the same topic
The tyre is a complex assembly of numerous components: up to 200! Its manufacture required a wide variety of raw materials: natural and synthetic rubbers, metal cables, textile fibres and various additives.
The rubber compound
The manufacture of a tyre uses more than 30 various sorts of natural and synthetic rubber each with their own properties. They are mixed in huge mixing machines to obtain a smooth, homogenous paste. The assembly of the various rubber compounds will determine the tyre’s qualities in terms of flexibility, grip or resistance.
Assembling the components
The assembly phase is carried out on a rotating drum which receives the various layers of materials. Here are the main stages.
Laying of the liner
The first component applied to the drum is an airtight sheet of synthetic rubber. It replaces the tube in modern tyres.
Laying of the casing ply
A layer of textile or metal rubber-coated wires is then added. This will form a frame surrounding the tyre. It is called the radial carcass.
Placing of beads
Two hoops of metal wire are placed on either side of the tyre. These are the bead wires. They hold the tyre firmly on the rim and ensure that it is airtight. The casing ply is then folded up around the bead wires to hold them in place.
Other plies are added. In particular the sidewalls, made of flexible, durable rubber, that absorbs tyre deformations and protect it from side-on impacts. They also carry the markings.
Shaping the tyre
The tyre is then given its shape by inflating the central part of the drum.
Strengthening the crown
Two plies are then applied to the tyre crown. Reinforced with crosswise metal cords, with the casing ply they form a network of shape-retaining triangles.
Laying of the tread rubber
Finally the tread is laid down, the part of the tyre in contact with the ground.
The green tyre is then placed in a curing mould, whose walls are engraved to reproduce the tread pattern and the markings on the tyre. In the centre of the mould, a membrane filled with hot pressurized water pushes the still-supple tyre against the walls. Under the effect of the heat the curing starts. The rise in temperature of 150° causes the rubber to vulcanize: the sulphur in the rubber compound, forms chemical bonds between chains of polymers. It thus passes from a plastic to an elastic state.
After coming out the curing mould, the tyre is inspected. Faults are detected either by inspectors, or by means of a special machine. Tyres are also sampled at random from the production line and x-rayed. If a tyre shows any signs of faults, even a slight imperfection, it is rejected.
Source: Michelin film "How tyres are made"
The tyre in figures
1.1 billion: world production of “touring” tyres (2008).
127 billion: dollar value of the worldwide tyre market (2007).
72%: replacement market share.
49%: consolidated market share of the 3 leaders – Michelin, Bridgestone and Goodyear.
(Sources: Tire Business, Michelin Factbook)