Tire Groove Research Articles

A One-Dimensional Numerical Model of Heat Transfer in the Process of Tire Vulcanization

Abstract A one-dimensional heat flow model based on the Crank-Nicolson system of nodes is described. Conventional cooling theory has been incorporated into the model which may then be entirely represented in matrix form as a generalized theory. A considerable amount of investigation of the tire shoulder region has shown that by simulation, one-dimensional heat transfer theory is applicable to the molding process of tire vulcanization. The problem is one in which a unique set of thermal constants may specify the basic process. In heating, these constants are the apparent thermal diffusivity and equivalent tire shoulder thickness and, in cooling, the so-called surface heat transfer coefficients are used to define the material. The tire curvature and groove geometries may be considered to perturb the linear model but are accounted for by adjustments of the equivalent tire thickness which is determined empirically. Generally, agreement between theory and experiment is very good, and hence, such a model paves the way for on-line computer control of the production press.

Truck Tire Groove Cracking Theory and Practice

Abstract The work described has aimed at clarifying the mechanism of groove cracking in tires. Basic studies of the fracture mechanics of rubber have shown that the rate of growth of a crack is independent of sample shape and type of deformation when it is expressed in terms of the available elastic energy. An empirical method is described which enables the energy to be estimated for a tire groove from measurement of the amount by which a crack opens under stress. The method also enables the strain to be determined and can, in principle, be applied to any stressed article. Using this approach and the crack growth characteristics of the tread rubber, the rate of growth of groove cracks in a tire can be predicted. Satisfactory quantitative agreement is found between observed and predicted behavior suggesting that the mechanism has been correctly identified. The work indicates relevant design factors and material properties and enables an appropriate laboratory test for groove cracking resistance to be defined.

Tread Cracking of Natural and Synthetic Rubber Stocks

Abstract The development of cracks in the base of the tread grooves of tires has long been recognized as a major factor governing their useful life. A number of laboratory tests have been employed in an effort to evaluate crack initiation and growth. Dumbbell strips, rings, and grooved blocks have been flexed through various tension cycles. Grooved belts and tire treads have been flexed by weaving over pulleys and thereby producing a cycle which involves both tension and compression. Tires themselves have been flexed under load on rotating drums. The strains which produce cracking along the length of a tire groove are complex. They occur on and near the surface in the base of the groove. For the purpose of this discussion, they are defined as the strains at right angles to the groove length and in the plane of the groove base. To devise a flexing machine which reproduces these strains qualitatively, one must consider the forces acting to produce them. The force acting upward on the ribs of the tire tread in the contact region bends the tread to an extent which is determined primarily by the load on the tire, the inflation pressure, the moulded tire shape, and the fabric structure. This bending is concentrated to a large extent in the groove base, with its magnitude substantially independent of the speed of the tire and of the tread stock used; and a compression strain of constant amplitude is produced. This upward force also deforms the ribs and thus contributes a slight additional compression strain of the constant force type. This produces little difference in the compression strain between different stocks, especially since all normal tire treads have moduli in the same general range. Compression strains of the order of 30 per cent have been found in the base of the grooves of passenger tires under static load by means of cement casts of the grooves in which wire brads were embedded as markers.