Page 14 - RB-82-17-3

TECHNICAL REPORT
Retreading Materials and Quality By Joseph Kurian
In modern times, retreading tyres is perceived as a 'twice blessed' activity: it bestows economic benefits to consumers and an environmental bonus to our planet. In developed countries, retreads are considered to be as safe as new tyres, permitting extended use of the investment made in expensive tyres. Unfortunately, these lofty ideals go missing, when some of our tread rubber manufacturers produce and supply sub-standard material to retreaders in the guise of compulsions from market forces. Retreaders and consumers are initially pleased to pay a lower price for such products, unaware of the pitfalls and the eventual tragic budgetary loss. The objective of this article is to shed light on the dark side of this surreptitious practice and to reveal the inherent deficiencies of sub- standard treads which result in economically counter-productive consequences.
The quality and life cycle of retreaded tyres have been improving every day, every year, over the last three decades. Better quality keeps coming on the horizon due to continuous effort from tread rubber manufacturers, demand from customers and technological innovations in tyres and the process of retreading. India has since been a forerunner in this business and has been exporting a large quantity across the world, with a major share to the Middle East and African Countries.
In the recent past the business of retreading has been affected largely due to the following factors
• Invasion of the market by low priced Chinese tyres with doubtful quality. The Indian Automotive Tire Manufacturers Association made the critical revelation that the per unit import cost of tyres from China is lower than the input raw materials that go into its production. Now, this is not to say that all Chinese tyres are of low quality. Many customers have a tendency to buy new low cost tyres rather than retreading without a precise understanding of the total life cycle achievable, if casings are strong enough to undergo retreading operations.
• This irrational situation shall have its consequential end only when the end user (the fleet owner) faces implied setbacks like shorter service life and insufficient
tyre casing strength, making his tyres unfit for retreading.
• Lastly, based on the above, certain producers have compromised beyond limits the quality of tread rubber itself!
To remedy this situation the retreading fraternity needs to take concrete steps to prove that retreads, properly made, are matching and prudent substitutes for new tyres irrespective of their origin. The service life of good retreads depends solely on the quality of tread rubber and inputs used, and the deployment of the right workmanship on retreading machines of mechanical sophistication.
Awash with tyre retreading material suppliers from India, retreading firms in the Middle East and African countries are in a dilemma as to how to select a good product (tread rubber). The best option suggested is selection by assessing the measurable mechanical properties.
In the pursuit of assessing the quality of various grades of tread rubber available in India and also in the Middle East and African countries, the evaluation of physical properties undertaken on samples collected and tested has shown that many suppliers market their products in very poor quality, in sharp contrast to the desired/required quality parameters.
A cursory glance into the following charts shall reveal the authenticity of the above statement.
The major characteristics assessed are tensile strength, modulus at 300% elongation, percentage of elongation at break, hardness, and specific gravity, which are indicators of a performing tread rubber providing good mileage, lower wear with minimal cost per kilometer run. (Samples mentioned as S1 to S6 represents those collected from Middle East/ Gulf and Africa and that mentioned as domestic pertains to supplies within India. STD represents properties of a Standard Tread Compound)
Tensile strength, Modulus and Elongation
These physical properties have high relevancy in predicting service performance of retreaded tyres, albeit, there are limitations to the scope of physical tests; that is, almost no physical test gives a direct correlation to service
Modulus of 100kg/cm2 along with Elongation above 550% predicts a performing tread compound with good mileage, resistant to chipping/chunking ensuring long life. From the graphs shown below one can see that many supplies are of poor quality. Needless to mention that supplies within India are of better quality.
14 Retreading Business
performance. This aspect notwithstanding, evaluation of physical properties does help in identifying rubber compounds with desired service properties and of consistent quality.
Tensile strength is the major indicator of the quality of a good tread material, required level being
190 to 225 kg/cm2. This range is preferable considering a good blend of natural and synthetic rubber. From this chart, it can be seen that many supplies are of low quality ranging between 84 to 131 kg/cm2.