The substance used to harden the rubber for tyre manufacture is: (a) \(\mathrm{CaC}_{2}\) (b) Wax (c) Carbon black (d) 1,3 -butadiene

When it comes to the manufacturing of tires, the fundamental factor that ensures durability and efficiency is the hardening of rubber. The hardening process is achieved through a critical procedure known as vulcanization. This process utilizes a rubber hardening agent, which fundamentally transforms the properties of natural rubber from a sticky, pliable material to one that is robust and elastic, capable of withstanding the harsh conditions of the road.

Vulcanization involves heating the raw rubber with the hardening agent, which often includes sulfur. This chemical reaction creates cross-links between the rubber molecules, leading to enhanced strength and resistance to temperature variations, abrasion, and deformation. While there are various potential hardening agents, the addition of carbon black has prevailed as a choice in tire manufacturing, not only due to its ability to harden the rubber but also to improve other characteristics such as resistance to UV light and conductivity.

The process of tyre manufacturing is intricate and requires precision. It starts with the preparation of raw materials, where rubber is mixed with specific compounds, like carbon black, to enhance its attributes. The rubber compound is then shaped into the form of a tyre through a process called extrusion. For tyre components like treads and sidewalls, this is a critical step as it dictates the performance features of the final product.

After extrusion, the tyre parts are assembled together in a process known as building. The assembled tyre is then ready for vulcanization, where it is placed in a mold and subjected to high temperatures and pressure. This is where the hardening agent plays its part, solidifying all components together and forming a unified and resilient structure, perfect for withstanding the diverse stresses encountered during vehicular movement.

Carbon black is a formidably versatile additive in rubber manufacturing, particularly in the tyre industry. Its distinct black color is recognizable, but its importance extends far beyond mere pigmentation. Carbon black enhances the overall performance of tyres, providing increased tensile strength, durability, and improved wear characteristics.

As a reinforcing filler, carbon black effectively fills voids in the rubber compound, contributing to its rigidity while maintaining flexibility—a necessary balance for tyres that must adapt to varying road surfaces. In addition, it's instrumental in preserving the longevity of the tyre by conducting heat away from critical tread and belt areas, reducing thermal damage during long driving sessions. Overall, carbon black elevates the tyre quality and safety, making it an indispensable component in the rubber hardening process.