Brian Joss – The tyre is a complex combination of components made from numerous ingredients. But how do we get from the rubber tree to the road?
Tyre production consists of six key stages in the manufacturing process: sourcing of materials, production of compounds, manufacturing of components, building the tyre, vulcanisation and, finally, quality control.
The first stage for tyre manufacturing is the sourcing of raw materials used to create the necessary compounds and components. Natural rubber is tapped from rubber trees grown in large plantations. The milky fluid (latex) extracted coagulates when acid is added to it. It is then cleaned and pressed into solid bales for easier transportation and storage.
Synthetic rubber and materials such as silica are used to reduce wear, increase grip and extend the life of the tyre, and are supplied by the chemical industry. The bales of natural and synthetic rubber are sectioned, cut to size, weighed and then mixed with other ingredients. Base materials such as rayon, nylon, polyester and aramid fibres that serve as reinforcement for the tyre construction are supplied by the textile industry.
High-strength steel serves as a starting material for the manufacture of steel belts (steel cord) and bead cores (steel wire). These give the tyre rigidity, which enhances shape retention and directional stability. Pre-treated steel cord is fed into a calender, where it is embedded in one or more layers of rubber that results in a continuous sheet of steel and rubber.
In the next stage, kneadable rubber material that has been blended in a mixer is now ready to be made into the tread. A screw-type extruder shapes the rubber into an endless tread strip. After extrusion, the tread is cooled by immersion and then cut to length in line with the size of the tyre.
A multitude of textile threads is then fed into the calender by a large roller device and embedded in a thin layer of rubber, which is then cut to the desired width. The core of the bead, which keeps the tyre firmly seated on the rim of the wheel, is made up of many ring-shaped steel wires, each with its own rubber coating. An extruder forms sidewall sections that are cut to suit the particular tyre size, and a calender produces a wide, thin layer of airtight inner liner.
Building the tyre brings the various semi-finished products together on a tyre building machine, producing what is known as a ‘green’ tyre. This is done in two stages; first the casing, then the tread/belt assembly.
This green tyre is then sprayed with special fluid and prepared for the next stage of development, vulcanisation. In this process, the tyre is placed in a curing press at a specific pressure and temperature, which gives the tyre its final shape. The vulcanisation results in the raw rubber becoming flexible, elastic rubber. Curing press moulds give the tyre its tread pattern and sidewall markings.
The typical breakdown of ingredients that make up a modern tyre, comprise approximately 41 percent natural and synthetic rubber, 30 percent fillers (carbon black, silica, carbon, chalk), 15 percent reinforcing materials (steel, polyester, rayon, nylon), 6 percent plasticisers (oils and resins), 6 percent chemicals for vulcanisation (sulphur, zinc oxide, and others), and 2 percent anti-ageing agents and other chemicals.
Each stage of production – from the inspection of raw materials to delivery of the finished tyres – is subjected to strict quality controls. Finished Continental tyres are subject to visual checks, Xray inspection, and are checked for uniformity.
Once the tyre has passed all checks and inspections, it is sent to the distribution warehouse for shipment.
CAPTION: Production line: making tyres at a Continental plant. Picture: Quickpic