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ABSTRACT
This review will discuss the mechanisms that are responsible for the adhesion between brass-coated steel tire cord and rubber. In particular, the role of cobalt as an adhesion promoter and how it influences the stability of the bond between the steel tire cord and rubber are examined. Some of the techniques by which the morphology of the interfacial layers has been investigated will be discussed, along with a brief review of the latest bonding mechanisms.
I. INTRODUCTION
Brass-coated steel cords1-3 are the principal strengthening elements in specific regions of a pneumatic tire such as the belt, carcass and bead. Since the development by Michelin in 1946 of the radial tire, steel cord has become a common form of reinforcement and is used in 98% of the world's passenger tires and 70% - 80% of truck tires. At present, passenger car tires contain about Ikg of steel and commercial vehicle tires contain 3kg - 7kg, depending on size. Steel cords, present in the belt region, allow the manufacturer to optimize many physical parameters of the tire, such as strength, stiffness, modulus, stability, and uniformity. Indeed, high stiffness of the belt region is essential for good tread wear, handling and low rolling resistance characteristics of the tire.4 It is worth noting that the reduction in the weight of steel and an increase in strength are important factors in the future developments of tire cord. The use of high tensile steel wire has meant that cord construction can be simplified and thereby reduce the weight of the tire. Such a reduction of weight will decrease the inertia of the tire and so improve fuel economy and lengthen tire life.
When forming a tire cord, copper and zinc are electro-deposited sequentially on to drawn steel wire and treated by a thermal diffusion process to produce a brass alloy coating. Further drawing of the wire eventually produces a steel cord filament coated with a brass layer, approximately 0.2μm thick. It has been demonstrated5 that for bonding to a natural rubber compound the optimum plating thickness is between 0.2 - 0.3μm. The method of drawing the wire through the forming die creates a surface texture as well as influencing the composition, distribution and thickness of the brass layer.6...