Comparison study of three tractor tyre tread compounds
Keywords:Retreading / Tackfying agent, Fillers, Buffing dust, Specific gravity
This project was carried out to develop a low cost rubber compound for retreading tractor wheels, while maintaining standard physical properties or perhaps with improved physical properties of the retread.
The first formulate tried out was with the rubber content in the standard formula reduced by 10 phr and by increasing the filler load with the help of a tackyfying agent to obtain the expected volume. DPG 2phr was used as the booster accelerator to impart the vulcanization of the compound. The reason for adding tackyfing agent in the formula was to enhance the tackiness of the compound to facilitate more filler loading. When tackyfying agent is added, the dosage of ball clay and buffing dust and reclaim rubber addition up to 5 phr to the compound can be done conveniently.
Physical properties of the vulcanizates of each of these compounds tried out were determined using ISO test methods. A marked increase in the specific gravity and the hardness of the compounds was observed with the substitution of fillers replacing rubber in the formule.
Hence, the second lab scale trial (TR TEST-2) was carried out with the intention of reducing the specific gravity of the vulcanizate while improving physical properties. Reducing ball clay load by 5 phr and introducing the semi EV vulcanizing system it was possible to achieve physical properties comparable to the control. However, from this exercise it was not possible to significantly reduce the cost of the compound.
In order to reduce the cost of the compound third lab scale trial (TR TEST-3) was conducted; in which the level of scrap crepe, aromatic oil and antioxidant were reduced by 10, 1 and 3 phr respectively. Physical properties of vulcanizates of TR TEST-3 trial were within the acceptable limit for tyre retreads. Further, the cost of the resulting compound was below the cost of the earlier compound used for the purpose by 7.95% thereby making it more economical to be used as the compound for retreading tractor tyres.
In TR TEST 1 SG and hardness is higher due to addition of excess ball clay. In TR TEST2 and TR TEST3 the elongation value reached 300% due to excess reclaim rubber in their formulation. TR TEST 4 did not reach 300% elongation, because of the very high shear action on rubber exert on Banbury mill mixing.