The vulcanization of rubber makes it stiff and enormously resilient against external forces. The reason behind this is a phenomenon known as cross-linking is that it strengthens individual tyre components. For example, the sulphur mixed into the tyre compound cross-links with rubber molecules resulting in a hardened rubber with enhanced strength and improved elastic properties. Usually, for a passenger car tyre, the vulcanization time varies from 8 to 10 minutes.
So, how’s a tyre moulded into a final shape? The operator places green tyre inside the mould machine where the segments around the tread and sidewall are pushed inward by the curing press, providing the tread its outer shape. Simultaneously, a large rubber bladder (replicating an inner tube, albeit filled with high-pressure steam) inflates the tyre so that it fits snugly against the mould. Different tread-pattern tyres are produced using different mould design. Depending on the type of tyre to be produced, the moulds are replaced from time to time. At Apollo, they have over 160 different moulds to produce different tread-patterns.
During the moulding process, the manufacturer branding, marking, tyre size lettering etc., are engraved on the tyre sidewall as well.
The final process includes inspecting the tyre visually for any defects. Post which, a tyre further undergoes a uniformity test where an automated machine checks balancing, concentricity, run-out, etc., of the tyre. Once through all that, the freshly prepared tyres are dispatched to various locations