Recycling tyres has become and will remain a big issue. With the increase in vehicles, waste issues and environmental directives work is set to continue into what to do with the used tyre mountain.
Used tyres, known as casings, are mostly sorted for use in one of four options: retreading; re-use; material recycling; and energy recovery.
The first line recovery option since it is considered to make the best use of the waste tyre resource. The first stage of retreading is a primary inspection, from which as few as 15% proceed to stage two. In the second stage, the old tread of the tyre is mechanically removed by a process called buffing.
Application of new tread follows, using one of two methods: pre-cure or mould-cure. In the pre-cure process, the tread rubber has already been vulcanised with the new tread design prior to application. In the mould-cure process, unvulcanised rubber is applied to the buffed tyre before the tread is vulcanised.
The new tyre is then inspected again, before being trimmed (to remove any excess rubber) and painted. Retreads have to be marked according to the British Standard BS AU144f:1988.
Re-use of tyres
Some used tyres are perfectly suitable for further use on vehicles. Tyre Safety Regulations apply to the sale of part-worns. The Tyre Industry Council (TIC) has developed a voluntary code of practice for so-called ‘part-worns' under its Responsible Recycler scheme. Regulations also apply to partworns. These require that tyres have at least 2 mm of tread across the breadth of the tyre and that tyres are clearly marked as a part-worn at the point of sale.
Around 10 000 tonnes of tyres are exported to other countries for use as part-worns or in overseas retread operations.
Tyre Material Recycling
The number of companies shredding and recycling tyres is increasing although the available market for the shredded material remains relatively stable.
The most widespread material recovery process in the UK, ambient grinding, produces a range of crumb sizes through a progressive size reduction process. The energy used to break up the tyres increases as the particle size decreases. Uses for rubber crumb include surfacing for sports, playgrounds, carpet underlay, street furniture and acoustic barriers, as well as incorporation into new tyres. A trial stretch of road surface containing rubber crumb has also been performing well.
Energy Recovery from tyres
Innovative processes such as pyrolysis can be used within recovery. Pyrolysis is the thermal degradation of a material in the absence of oxygen which in the case of tyres generates gas, oil, carbon char and steel. A proportion of the resultant gas and oil can be used to fuel the process.
Used tyres can beneficially replace some of the fossil fuels traditionally used in the cement making process. Doing this produces environmental benefits, reducing the overall environmental impact of cement works, and commercial benefits helping reduce the high energy bills involved in cement making.
It is believed that the cement business will be key to achieving tyre recovery targets for 2006.
Main source www.dti.gov.uk