Editorial Feature

Automotive Tyre Recycling

A tyre (or tire) is a ring-shaped covering designed to fit around the rim of a wheel so as to provide protection and better vehicle performance. The earliest tyres had bands of iron or steel fitted on wooden wheels for use on wagons and carts.

Modern tyres are predominantly manufactured with natural rubber, synthetic rubber, fillers, reinforcing materials, plasticizers and wire, coupled with other compound chemicals and anti-ageing agents. The tyre consists of a tread for providing traction and a body for ensuring support. Manufacturers design tyres into two main categories- for summer use and for winter use.

Types of Tyres

The different types of tyres are listed below:

  • All season tyres are ideal for all road surfaces and can be adapted to all weather conditions
  • Run flat tyres enable smooth running of the vehicle even if the tyre is punctured
  • Eco-friendly tyres are designed to reduce fuel consumption
  • Spare tyres are used in place of a blow out or a flat tire, are smaller in size, has a lower speed rating and short life expectancy
  • All terrain tyres are used on SUVs and light trucks
  • Heavy-duty tyres are used for dump trucks, passenger buses
  • Agricultural tyres are used for farm vehicles
  • Racing tyres are specially designed to suit race track and vehicle conditions

Manufacturing Process of Tyres

The rubber tyre manufacturing process consists of several steps. Once all the raw materials are procured, they are combined in a mixing process to create a homogenous rubber compound that is sent to a drop mill. At the mill, warm pliable sheets are made, cooled and coated with an anti-tack solution. The sheets are then forced into a shaped slot in an extruder to form different shapes. The rubber sheets are coated with fibers of cloth or steel in a process called calendaring, which is followed by curing in an irradiation oven. Then a bevel cuts them to a desired length, width, and angle.

A bead making process is commenced to provide a seal between the tyre and the rim for the tyre is to be mounted and inflated on the rim. During the entire course of tyre production, cementing and marking processes are carried out using adhesives or solvents. Similarly all the tyre components are cooled from time to time with cool air or water. The tyre carcass buildup drum and the tread application drum are important components to the tyre production and are used to assemble the rubber plies, belts, sidewall, extruded tread, and beads into tyres. The assembling process consists of applying a thin layer of rubber compound to the innermost carcass ply. Each ply is placed on the drum to be fitted with beads. Then the belts and tread rubber are added.

The lubricating process involves preparing the uncured tyre for curing by coating it with a lubricant to ensure that the cured tyre does not stick to the curing mold when extraction of tyre is performed. At the curing stage, the drum is removed and the tyre is loaded into an automatic tyre press to be cured or vulcanized at high temperature and pressure. Vulcanization causes the rubber to be converted and bonds the various components of the tyre into an individual unit. Finally tyre the finishing process will comprise of trimming, buffing, balancing, white sidewall grinding, blemish painting, whitewall /raised letter protectant painting, and quality control inspections.

Applications of Virgin Tyres

Tyres are used mainly by the transportation industry. The following is a list of specialized tyres used in various transports:

  • Racing cars to suit vehicle model and race track conditions
  • Agricultural-based vehicles such as tractors
  • Heavy duty vehicles such as trucks/buses
  • Tyres with high floatation feature for use in swampy environments
  • For off-the-road usage especially construction vehicles
  • For use in all terrains (mainly for SUVs and light trucks).

Environmental Impacts of Tyres

The primary environmental issues relating to rubber tyre manufacturing are solid wastes, wastewater, fugitive air emissions, and hazardous wastes. However, with the growing awareness about environmental impacts, manufacturers are trying to curb emissions and recycle or sell all the solid waste.

Waste tyres are a cause for concern as they are hazardous to health and the environment. Rainwater accumulates in these tyres and become a suitable place for mosquitoes, which are known to be disease carriers. If waste tyres are burnt, they cause soil and air pollution, and are difficult to extinguish. These tyres also occupy space in landfills.

Consumers are encouraged to purchase the best quality tyres in order to prolong its service life and also because high-grade tyres use more of natural rubber. Proper tyre maintenance is also recommended to ensure longevity. Tyres can also be retread. These measures will ensure a decrease in the number of waste tyres.

Recycling Process

Reuse of old tyres (either as whole tyre or shreds/crumbs) is a recommended recycling option.

Rubber tyres are difficult to recycle as they have been vulcanized. Vulcanization process involves adding sulfur to rubber so as to create stronger bonds between the rubber polymers, thereby making it difficult to melt tyres. However, a mechanical process to break it down is available, wherein rugged machines shred the tyres into strips. The strips are then placed in grinding machines fitted with rotors to shred the strips and also remove steel fibers from it. Once steel is removed, the pieces are placed in granulators to be milled into assorted sizes of granules according to the demand of an end user.

Another recycling process is a freezing method which uses liquid nitrogen to freeze the tyres and then crush and mill them. A recycling technique referred to as pyrolysis is being researched, wherein tyres are decomposed in an oxygen-free environment.

Applications of Recycled Tyres

There is a huge market for scrap tyres. The following are some of the key uses of waste tyres:

  • Waste tyres can be made into tyre bales and used to construct retaining walls or erosion control structures in many parts of the world
  • Artificial reefs have been constructed in the marine environment using scrap tyres so as to mimic conditions that enhance concentration of fishes and invertebrates on natural reefs
  • Rubber modifiers have been added to asphalt in the form of crumb rubber (from waste tyres) to improve certain properties of asphalt binders
  • Rubber modified asphalt concrete (RUMAC) is produced using a dry manufacturing process in which ground tyre pieces are used as a part-replacement of aggregate in the asphalt concrete mix
  • Tyre chips about 4 to 6 inch is used as lightweight fill material in road construction
  • Tyre derived fuel (TDF) is used in industrial kilns
  • Scrap tyres are used for shoreline protection

Sources and Further Reading

G.P. Thomas

Written by

G.P. Thomas

Gary graduated from the University of Manchester with a first-class honours degree in Geochemistry and a Masters in Earth Sciences. After working in the Australian mining industry, Gary decided to hang up his geology boots and turn his hand to writing. When he isn't developing topical and informative content, Gary can usually be found playing his beloved guitar, or watching Aston Villa FC snatch defeat from the jaws of victory.

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