A Computational Cure for Radial Tires
By Christophe Waucquez and Antoine Dozolme, Fluent Benelux
Curing is the final step in tire manufacturing whereby a “green” tire built from layers of rubber compounds is formed to the desired shape in a press. Heat is transferred to the tire from the surroundings, which are maintained at a higher temperature. The added heat causes a curing reaction(vulcanization) of the rubber compounds to begin,converting the layers of compounds into a strong elastic material and binding them with internal rein-forcing cords.
The temperature on the mold, compounds, and bladder at the start of the problem, along with the mesh |
The curing process is energy-consuming and has a strong impact on the final tire properties. Given the temperature history, the cure cycle may be optimized to minimize capital and energy expenditures.The conventional method is to directly measure profiles of the temperature as a function of time using thermocouples inserted into various parts of the tire, and then to use the measured profiles to predict the quality of the final product. This method is costly and time-consuming however, so computer simulations are now being performed by engineers in this industry as an effective alternative. The ample data provided by numerical simulations can be used to assess the structural characteristics of the finished tire and to optimize the process.
In this example, POLYFLOW is used to simulate the curing process using a simplified model of a tire. A Passenger car radial tire typically consists of 15 or more layers of rubber compounds, but in this example, only two layers are used. The layers are assembled in a mold with sidewalls and a flexible bladder on the inside surface. Steam and hot water are the major sources of heat used for curing reactions. Steam circulates in the mold and pressurized hot water circulates through the bladder.
    
The temperature distribution (lower half) and state of cure (upper half) for the tire and it surroundings from 1 to 12 minutes (top to bottom), at which time a |
In addition to the transient boundary conditions, temperature-dependent properties, and a geometrical description of the tire, bladder, and mold, a cure calculation also requires an accurate kinetic model for the reactions that take place inside the rubber compounds. For the two component case considered here, a fairly general model is used that accounts for both an induction period, before any changes to the rubber properties are measurable,and a curing stage, during which these changes take place. A dimensionless variable is used to characterize the state of cure (SOC) during the process. One popular way to compute the SOC is through rheometry. The torque required to maintain a given strain on a rubber specimen changes as the material properties change. The torque is constant and the SOC is 0 during the induction period; both quantities change during the curing process; and when the curing process is complete, the torque is again constant but the SOC has a value of 1.
The histories of temperature and the state of cure are among the most important predictions of such a calculation. The state of cure predictions, in particular,can be used to ensure that the time required to complete the curing process is not over-estimated.
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