Rubber Powder from Waste Tyres: An Approach to Tyre Recycling

Published on 01/11/2011

Since the wheel got invented, it has been redesigned and recreated according to convenience of humans. Today, we can see there is a heavy load of traffic on roads. This load is more in the case of urban areas as compared to rural areas due to difference in life style and infrastructure. The number of vehicles (cars, buses, trucks, motorcycle) are increasing exponentially with time. These vehicles run on the road through wheels by means of tyres.

A lot of waste is generated from automobiles and one of these wastes is used tyres. The powder of these used tyres can be used as a substitute of raw material for the production of rubber. With the increasing number of cars and trucks all over the world, used tires are also available in large quantities and are extremely cheap for the production of rubber powder. This is a recycling process of vehicles tyres that are no longer suitable for use on vehicles due to wear or irreparable damage such as punctures. Granules of rubber and iron can be obtained in various final grain sizes. This has become meaningful because processed rubber is becoming more and more acceptable on the market due to increasing raw material prices. Waste tyre rubber powder is widely used to build the playground, highway road, etc. It is also material of rubber product. The sales profit depends naturally on the quality of the output material and the pricing structure depends on processing that is as efficient as possible.

The process of manufacturing of rubber powder

Manufacturing of rubber powder from used tyres is a three-stage processing primarily shredding, after that granulation and lastly fine grinding through which high-quality materials for recycling are ultimately produced.

1. Shredding: The very first step involved in the recycling of tyres is shredding. Shredding means separation of wire and mesh from tyre and breaking them into pieces. This can be obtained by a machine with moving parts in which used tyres are put and steel or iron made wires are separated out from the tyre after this tyre is torn to pieces.  The machine is very versatile which can also be used for shredding of all kinds of input materials and is well suited for different industries. The diameter of rotors ranges from 457 mm -850mm to 2000 mm width which are driven by either one or two oversized gearboxes. There is a well integrated hydraulic power pack into the machine housing which is used to save space and protect it from damage but is still easy to access or remove for maintenance. In this machine shredders are usually designed for a wide range of applications and which can also be used in industries such as in-house and general recycling, electronic waste and post consumer waste handling. Apart from the tyre waste input materials can be all types and forms of plastics such as lumps, pipes, film, bales, woven bags, electronic waste like cables and ICBs, paper, wood and other organic materials. In some cases where the raw material or waste is of small size, can be sent directly to the next step granulation.
2. Granulation: The granulators are used in the next step of this recycling process in which pieces of waste tyres are grinded in the large sized granulators to produce large quantity of granules. Granulators are developed as slow-running grinders for applications in the injection and blow molding sector.  The material which has to be granulated is fed via a sound-absorbing feed hopper which is available in a wide range to suit the application.  The slow-speed granulators which are designed of this range are commonly mounted on either low or high level base frames. With these numerous options, the slow speed granulators can be tailored to an extremely wide range of applications. P
3. Pulverizer: The last step involved in the production of rubber powder from tyre waste is to convert the granulated material into the fine powder. This is done by means of pulverizes. Pulverizes are high speed, precision grinders which are used for the processing of medium hard, impact resistant and friable materials. The granulated material is introduced through the centre of a vertically fixed grinding disc which is mounted concentrically with an identical high speed rotating disc to make the fine powder of it. Some typical applications are the pulverizing of plastic products, tube, edge trim materials, film waste. The waste generated from the food, chemical and pharmaceutical industry can also be pulverized in order to make the fine powder.  The material to be pulverized is. Inside the pulverizer the centrifugal force acts on the material to be pulverized and carries the material through the grinding area and the resulting powder is collected with a blower and cyclone system which is fine rubber powder or the other product of which waste material used.

Uses of waste/recycled tyres

Tyre which is not useful for us can be reused in many different ways. Up to some extent it can be used in a steel mill to use the tires as a carbon source which replaces coal or coke in steel manufacturing. This eliminates mining of coal from the ground and then burying tires in landfills, the tires are used directly. Tires can also be used together as different types of barriers such as: collision reduction, erosion control, rainwater runoff, wave action that protects piers and marshes, and sound barriers between roadways and residences. This is practiced through binding of tyres together. In some cases it is seen that entire homes can be built with whole tires by ramming them full of earth and covering them with concrete, known as Earth ships.

Some Artificial reefs are made up of used tires that are bonded together in groups. There is some controversy on the effectiveness of tires as an artificial reef system for which an example is The Osborne Reef Project.

• Tires are used in the process of stamping and cutting some apparel products, such as sandals and as a road sub-base. This is done by connecting together the cut sidewalls to form a flexible net.
• Chipped and shredded tires are used as Tire Derived Fuel (TDF). This can’t be considered as recycling, although TDF helps to eliminate tires from our waste stream and produces a fuel source. These are used in applications of civil engineering such as sub grade fill and embankments, backfill for walls and bridge abutments, sub grade insulation for roads, landfill projects, and septic system drain fields.
• Shredded tires, known as Tire Derived Aggregate (TDA) can also be used in civil engineering applications. TDA can be used as a backfill for retaining walls, fill for landfill gas trench collection wells, backfill for roadway landslide repair projects as well as a vibration damping material for railway lines.
• A size-reduced, recycled rubber which is known as Ground and crumb rubber, can be used in both paving type projects and in moldable products. These types of paving are: Rubber Modified Asphalt (RMA), Rubber Modified Concrete, and as a substitution for an aggregate. Examples of rubber-molded products are carpet padding or underlay, flooring materials, dock bumpers, patio decks, railroad crossing blocks, livestock mats, sidewalks, rubber tiles and bricks, moveable speed bumps, and curbing/edging. The rubber can be molded with plastic for products like pallets and railroad ties. Athletic and recreational areas can also be paved with the shock absorbing rubber-molded material.
• Sometimes rubber from tires is ground into medium-sized chunks which can be used as rubber mulch. Rubber crumb can also be used as an infill, alone or blended with coarse sand, as in infill for grass-like synthetic turf products such as Field Turf.

Environmental concerns of tyre recyling

Tyre basically consists of heavy metals and other pollutants so there is a potential risk for the (leaching) of toxins into the soil and groundwater when placed in wet soils leading to contamination of ground water and pollution of soil. The solubility of theses toxins varies with the variation in the pH of soil and conditions of local water. Research has proven that very little leaching occurs when shredded tires are used as land fill material. In some cases however, there are limitations on use of this material. For its safe disposal each site should be individually assessed for determining if this product is appropriate for given conditions.

Sometimes eco-toxicity may be a bigger problem than first thought. Studies show that host of vulcanization and rubber chemicals such as zinc, heavy metals leach into water from tires. Shredded tire pieces leach much more, creating a bigger concern, due to the increased surface area on the shredded pieces. Many organisms are sensitive, and without dilution, contaminated tire water has been shown to kill some organisms.

Burning of tyres also produces many harmful gases. In winters, for the purpose of heat poor people burn used tyres which are precursor of air pollution and produces harmful and toxic gases and particulate matters. One can fell seriously ill with the inhalation of these contaminants due to suffocation. So it is better to recycle these tyres to promote secondary raw material for the manufacturing of mew rubber goods. This can also be considered as an efficient drive for the better and safe environment. More economic activity can be obtained from new products derived from waste tires than combustion or other low multiplier production, while reducing waste stream without generating excessive pollution and emissions from recycling operations.