What is tire shredding? A recycling guide
Recycling has become critical for the tire industry to limit the volume of tire waste and the problems it creates. The 1.5 billion tires discarded each year need 80 to 100 years to decompose. Tire shredding is a crucial part of tire recycling and is instrumental in reducing tire waste by 96 per cent in Europe and 76 per cent in the USA.
But what is tire shredding, and how does it help tire recycling?
What is tire shredding?
Tire shredding is a size reduction technology where end-of-life tires (ELTs) are cut to produce rubber chips. Shredding, along with grinding, is the most widespread recycling method and processes 87.5 per cent of ELTs.
Though tires can be reused whole, shredding them into chips segregates their physical components, making recycling easier. There are more recycling possibilities for shredded ELTs, since tires are built to withstand extreme climatic conditions and don’t degrade fast.
Shredding also prepares ELTs for disposal. 75 per cent of a tire’s volume is empty space, making it extremely inefficient to landfill them in a single piece. Shredding ELTs to reduce their volumes before disposal is a better use of landfill space.
Tire shredding and recycling technologies are well developed and can treat tires of all vehicles, even off-road or mining tires, economically.
Tires are considered “end-of-life” and replaced when their tread depth is less than 1.6 cm (or 2/32 inches). Despite lifetime wear and tear, ELTs still have all their essential components.
Due to the composition of tires, the ELTs from various vehicles like cars, trucks, and earthmovers (EM) will yield varying proportions of recovered rubber, steel, and fabrics; see Table 1.
Stages of tire shredding
The varying size and composition of tires can pose challenges that tire shredding machines must be able to tackle. ELTs come from passenger, light and medium-heavy trucks, and offroad vehicles used for mining, agriculture, and logging.
Offroad vehicle tires are large and heavy with thick treads. Offroad and truck tires have a high steel content, so the shredding process needs high-quality, robust machines to handle wear and tear.
Contec recycles both pre-sale rejects from a major tire producer and ELTs. Their network of tire collectors only picks up tires that meet certain hygiene standards, free from mud and dirt, to ensure high-quality recycled products.
Tire shredding has two objectives:
- Separating steel and fabrics from the rubber
- Reducing the size of the rubber into a fixed particle size
These objectives are met by the following tire shredding process.
Debeading: This preprocessing stage removes the steel bead from truck tires and significantly reduces wear and tear on the shredder and subsequent machines. The steel bead is only 10-15 per cent of the weight of a truck tire but causes 70 per cent of the wear and tear on the machines.
Primary shredding: Here, the rubber is cut into large bits, but in the absence of debeading, this stage has also to cut the steel ring and wires. The machines commonly used for primary shredding are rotary shears with one or two counter-rotating shafts. Shreds from single shafts are uniform in size, while those from double shafts are irregular. These machines can work at low and high speeds of 20 to 40 RPM to handle light and heavy-duty tires.
Secondary shredding: These machines are also called graters and reduce the size of the shreds into chips. Standard equipment includes bobcats and front-end loaders. The engines run on electricity, and most tire shredders and grinding machines process 2 -6 tons of tires per hour. Screening controls chip size and separates steel wires.
Shredding produces chips ranging in size from 25 mm to 450 mm. Chip size results from machine type, cutting mechanism, and the number of shredding used.
Besides shredding, magnetic separation to remove steel and dust collection also form part of the operation.
To reduce the size of the rubber chips further, grinding machines come into play. The application for which the recycled rubber is used determines the size of chips and granulates.
- Granulators take 50 mm chips and produce ten mm-sized smaller granules free of steel and fabrics.
- Cracker mills take this rubber crumb to produce rubber powder with particles as small as 0.2 mm.
Tire shredding equipment can be expensive and high-quality chips have to be produced in large amounts to be economical. Therefore, historically, due to the availability of low-cost synthetic rubber, people tended to dispose of ELTs.
Tire shredding in the circular economy
To encourage tire recycling and reduce waste, landfilling entire ELTs was banned in the EU and the USA. Many landfills charge a tipping fee for whole tires because ELTs are difficult to compact and “float” on the waste, damaging landfill cover.
Tire shreds are more suitable for landfilling as they are compressible due to the high proportion of flexible rubber, which is free of steel and fabrics, and have only a quarter of the volume of whole tires.
Monofilling or storing only entire tires is also prohibited as it can cause fire hazards or become a source of health problems. So recycling businesses shred ELTs into chips to avoid paying to dump entire ELTs.
Besides saving money, shredding also makes the tire industry more environmentally and socially sustainable.
Shredding is instrumental in decreasing the environmental impact of the tire industry. The process increases recycling possibilities to reduce rubber waste. It closes the material loop, helping the tire industry join the circular economy. Recycled fabrics and steel from ELTs are products ready for direct reuse after shredding without further processing. The recycled rubber undergoes more processing to recover energy or materials.
The ELTs’ shredding, recycling, and recovery activities create local and regional jobs. Moreover, tire shredding and recycling allow the vehicle industry to generate income from ELTs instead of paying to landfill them.
Contec helps in rubber recycling by shredding tires and recovering products through pyrolysis to reduce landfilling, as shown in Figure 1.
The company uses a mechanical shredding method improved by its innovations. A primary tire shredder produces chips of 250 mm, and the secondary shredder reduces the size to 25-30 mm. Magnetic separation of steel also contributes to the quality of steel and rubber chips. The chips are used in civil engineering applications and as feedstock for pyrolysis.
Contec chooses to produce moderate-sized chips to limit the energy use required to make smaller chips and increase the sustainability of the process. The recovered steel and rubber from Contec go into the supply chain and have many applications.
According to ETRMA, steel recovery is possible from all types of tires to produce high-quality metal. Recovered steel scrap after cleaning is in great demand by the steel industry to make steel. The more efficient the separation of steel from rubber is, the better the quality of both products. And the cleaner the metal is, the higher its value. The concrete industry also uses recovered steel wires for reinforcement.
Recovered rubber granulates
Prices of polymers and natural rubber are currently high. Therefore, rubber recovery has become an economic necessity and not just an alternative. Rubber granulates have several direct uses and can also be further processed.
Rubber chips from shredding are used in highway construction as non-structural sound barrier fills, edge drains, embankment fills, and retaining wall refills.
Rubber crumbs make rubber-modified asphalt, playgrounds, athletic fields, and railroad ties. Small-sized rubber crumb is also helpful as a filler for manufacturing virgin rubber compounds as its properties after vulcanization gives it several advantages.
It’s standard practice for tire manufacturers to use 5-15 per cent recycled rubber crumb in tire treads. Crumbs are also the raw material for producing moulded products like urban furniture, dustbins, wheelbarrows, livestock mats, and athletic mats.
Rubber granulates are also used for devulcanization, and the resultant rubber regenerates are suitable for making rubber mixtures and producing mats, rubber slabs, footwear, washers, and cables.
Rubber chips and granulates are used as feedstock for pyrolysis, a thermo-chemical recycling technique that recovers Carbon Black, steel, oil, and gas.
Tire Shredding at Contec
Contec not only invests in pyrolysis technology but also in high-quality tire shredding.
However, partnerships and collaborations among all the stakeholders in the tire industry like manufacturers, end tire users, public institutions, and treatment facilities are crucial for the industry to achieve circularity and benefit from options like pyrolysis. For more information about tire shredding, subscribe to our LinkedIn newsletter to receive industry-related information about the circular economy in manufacturing.
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