Cord tension, tire

Typical inflated cord tension plots for a truck tire are shown in Figure 14.13. In an unloaded state the cord tension for the belts tends to be at the tire centerline, and the ply tension is greatest at the point corresponding to the sidewall location however, on application of a load to the inflated tire and consequent deflection, the cord tensions increase at the belt edges away from the centerline and in the bead zone. As reviewed earlier, these two regions tend to be the failure zones in a tire construction (Figure 14.14). 

The most critical stage in preparing a cord or fabric for use in tires is fabric treatment, which consists of applying an adhesive under controlled conditions of time, temperature, and tension. This process gives the fabric the following properties ... 

Thermomechanical analysis in the tension mode can be employed in the production of films and fibers to follow the consistency of the product during manufacturing, and to characterize properties of the product, such as CLTE, thermal shrinkage and shrinkage force, and physical properties like Tg and T. All these properties are important, and they determine the end-use possibilities. For example, matching fiber-matrix expansion properties is necessary to avoid delamination of components, such as in tire cords. Shrinkage (i.e., irreversible contraction) is important to avoid in textiles for safe ironing, and it is also an important property in heat-shrink films (Jaffe et al. 1997). 

Flat Spotting n A characteristic of certain tire cords. It occurs with all materials but is more noticeable with nylon cord and is associated with nylon cord by users. Nylon exerts a shrinkage force as it becomes heated in tire operation. When the tire is stopped under load, the cord in the road-contact portion of the tire is under less tension than that in other portions of the tire, and it shrinks to conform to the flat surfece of the road. When cooled in this position, the cord maintains the flat spot until it again reaches its glass transition temperature in use. 

A special variation of SBR latex containing terpolymerized vinyl pyridine is used in the tire industry to provide adhesion of organic fiber tire cords to rubber stock. The vinyl pyridine SBR latex is combined with resins and coated on the fiber by a dipping process, followed by a controlled temperature and tension process to set the adhesive as well as to control the shrinkage properties of the cord. 

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