Despite the presence of synthetic rubber compounds, natural rubber tires are quite common in the world today.
High percentages are commonly used in tires that require a high degree of wear and heat resistance.
For example, airplane tires are almost always made out of 100% natural rubber.
Regular passenger car tires also have natural rubber in them. Therefore, almost 50% of the global production of natural rubber goes into the manufacturing of tires.
Why Is Natural Rubber Not Used In Automotive Tires?
Natural rubber is used in tires based on their applications. A regular passenger car tire will contain a lot less natural rubber than a truck tire. As explained earlier, natural rubber possesses certain features that are beneficial in high-load applications.
The tire in most passenger cars is a complex blend of different types of rubbers and additives.
Both natural and synthetic rubber are used in their construction.
However, since the invention of radial tires, the use of natural rubber has steadily decreased. Tire manufacturers have started replacing natural rubber with a whole host of other synthetic polymers and construction materials.
These include synthetic rubber, fillers, steel, kevlar, and nylon compounds.
What Materials Are Tires Made Of?
Natural Rubber:
For tire manufacturing rubber is produced from the latex of para rubber tree which originated in Brazil.
However these days most of the rubber comes from plantations in Southeast Asia.
General usage tires have less than 20% natural rubber in them, but it is still used because of their different properties. In recent years, a limited supply of natural rubber has forced manufacturers to look at synthetic polymers
Synthetic Polymers:
Synthetic polymers were first discovered as a substitute for natural rubber in the early 20th century.
However, its production drastically increased during World War II as USA was facing import shortfalls of natural rubber.
Since then synthetic polymers are used in conjunction with natural rubbers to form special mixes that are used to make various tire components.
The three major types of synthetic polymers used in tire manufacturing are Butyl Rubber, Butadiene Rubber, and Styrene-Butadiene Rubber.
These synthetic rubber compounds are highly pliable and can be mixed in different ways to get the desired amount of rolling resistance, traction, or grip.
Tire manufacturers have their own in-house blends that they use for different parts of the tire.
Fillers:
Various types of fillers are used as additives to create the final rubber compound of the tire.
These include carbon black to increase strength, sulfur for elasticity, oil for softness, and silica to improve wet weather grip and mileage.
Manufacturers also use antioxidants that inhibit oxidation and vulcanization accelerators that help build cross-links between rubber and sulfur during the curing process.
Constructions Materials:
A plethora of construction materials such as steel, nylon, rayon, and kevlar are used for various reinforcement structures on the tire.
Even fabric compounds such as polyester are used in making the body play of passenger tires.
White Car Tires: Are Rubber Tires Naturally White?
The answer to this question is Yes and No. Although the material sourced for rubber tires comes from a milky white sap, the end product is a black tire.
With the help of Carbon Black, which is the byproduct of the combustion of various petroleum products. Carbon black is added to rubber to help with fortifying the surfaces of the tires.
Due to the additive Carbon Black, any feature of a fully white tire eventually becomes black.
Properties Of Tires?
Over the years tire components have become increasingly layered and complex. These days the major parts of tires are as follows:
Tire Tread:
The outer surface of the tire, which comes in contact with the road.
It is generally made out of an abrasion-resistant natural rubber compound with additives. Some manufacturers may use proprietary synthetic rubber compounds as well to give their tires a higher grip.
Silica and carbon black are used as reinforcing agents to provide the tread with longevity.
The Belts:
The next layer down on which the tire tread is attached during the curing process.
The belt system’s main purpose is to provide strength to the tire tread helping with traction and wear.
Steel is the material of choice here, although some manufacturers have started using fiberglass as well. Their construction is usually two belts made out of steel chords, stacked on top of each other.
Tire Casing:
This is the rest of the tire, and it is made up of the sidewall, body ply, inner liner, bead filler, and bead.
This casing forms the structure of the tire to which the tread and the belts are bonded during the manufacturing process.
Sidewall:
The sidewall protects the tire casing from wear and tear. Natural rubber is used in its construction for its elasticity and weathering resistance properties.
Body Ply:
The body ply provides strength to the tire to withstand the inflation pressure.
Most tires these days have more than two plies to meet the safety regulations. These are made out of layers of polyester, nylon, or rayon chords mostly bonded together with synthetic rubber mixes.
Innerliner:
Inner liners are an integral part of a tire that helps seal the air inside.
They are bonded to the body ply layers and act as an inner tube.
Made out of butyl rubber compounds they are optimized to be maintenance-free with the lowest possible air-loss rates.
Bead & Bead Filler:
The inner liner functions in conjunction with the bead and the bead filler.
A tire bead holds the tire to the rim of the wheel. They are generally made out of copper, brass, or bronze-plated high tensile steel wires.
The bead filler is the rubber compound inside the beads, providing stability.
It is mostly made out of synthetic rubber and additives to be very rigid and maximize the strength of the tires.
How Is Rubber Made for Tires?
Natural Rubber is made by mixing various acids into the natural white latex gathered from the rubber trees.
After it solidifies, the rubber is passed through a number of presses to squeeze out the excess water.
It is then cured in tall smokehouses, after which it is shipped to tire manufacturers all over the world in sheet form. On the other hand, synthetic polymer rubber is made by mixing various chemicals together in massive industrial processes.
Both rubber compounds are sent to manufacturers, where they are reheated and mixed in specific ratios with other chemicals, fillers, and oils.
This step is carried out a few times to evenly distribute the chemicals throughout the final mix.
Each component of the tire has a specific ratio for its final mix, which is then milled into sheets or tubes according to the need of the component.
Manufacturing Process of Modern Tires?
After the final mix for each component is created.
Powerful rolling mills, wire wrapping machines, and extruders are all used to create the necessary shapes for the sidewall, body ply, treads, and beads.
These separate components are then glued and assembled by an expert technician over a tire rolling machine.
Once all the components are put together, the tire is placed inside a large mold for the curing process to begin.
The mold has an outer shell and an inner bladder on which the tire is cured at a temperature of 280 degrees Fahrenheit.
After the tire is cured, it is thoroughly checked for any manufacturing defects and sent to the warehouse for distribution.
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