Normally, four major kinds of rubber are put in use during a tyre’s production, namely, natural rubber, styrene-butadiene rubber (SBR), polybutadiene rubber (BR), and butyl rubber (halogenated). If you were to distinguish these based on their functioning, the first three make the tread and sidewall compounds while the butyl rubber forms the inner liner that holds the compressed air inside the tyre, thanks to its low-permeable characteristics.
Rubber in its raw state, be it natural or synthetic, comes in a white latex form. However, the reason tyres, almost all, are black in color is due to the addition of a chemical called carbon black. In addition to that, specific chemicals like silica and sulphur are also mixed with rubber so as to provide different characteristics such as high friction (high grip) or high mileage (low friction) for a passenger car tyre. Other ingredients that are added during compounding and mixing of a tyre include anti-oxidants, anti-ozonants, and anti-aging agents.
In order to prepare a desired tyre compound, a mixing mill with two counter-rotating rollers is used. Pre-calculated amount of a particular compound is dropped off at the rollers where raw materials are mixed with each other at a temperature of approximately 120 degree Celsius. Once the mixing process is completed, the batch for a particular compound type is stored in form of continuous rubber sheets. It is then sent to the next processes like bead-wire assembly preparation, inner-liner calendering, steel/fabric belt/ply cord calendering, etc.
2. Material Manufacturing Process:
Tyre material manufacturing includes three parallelly run processes that comprises building the carcass- body of the tyre; belt- to reinforce the carcass; the bead- that holds the tyre against the rim, and the tread- the part that comes in direct contact with the road.
The carcass & belt are produced by Calendering, i.e, coating the steel cords with rubber. This is done by incorporating a giant machine in place. The Calendering machine pulls strands of bronze-coated steel wires from a stack and mixes it into rubber compound at a uniform rate of 60 meters per minute. The freshly prepared carcass is subsequently cut according to the required size of the tyre using an automated cutting tool on flat bench.