Agitating – Rubber or heavy plastic working – With specified feed means
Reexamination Certificate
2002-11-05
2004-11-16
Cooley, Charles E. (Department: 1723)
Agitating
Rubber or heavy plastic working
With specified feed means
C366S076700
Reexamination Certificate
active
06817748
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to a method for mixing polymer based compounds and mixtures and more specifically, to a method for controlling such a process in the manufacture of tires or the like through the calculation and control of mixing parameters, and to a method of simulating such a process with algorithms run on a computer.
BACKGROUND OF THE INVENTION
It is well known to employ a mixer and mixing process in the formulation of compounds necessary to the manufacture of sundry goods including tires. The mixer may be either continuous or discontinuous. In a continuous process, material is passed through a cylindrical chamber by operation of a screw mechanism. A discontinuous, or “batch” process, mixes the material within an enclosed chamber by operation of one or more mixing rotors.
A typical mixer suitable for the discontinuous mixing of compounds consists of a mixing chamber containing a pair of rotors that rotate in opposite directions and thereby process discrete batches of material within the chamber. Commercial mixers are available and are marketed under the “Banbury” or “Intermix” names
Component materials are combined in customized formulas within such mixers to create the various compounds necessary to the manufacture of tires. The component base materials and additive material, or “fillers”, are combined to create particular “blends”. Typically, a composition comprises a polymeric material to which one or more additive material is added to form a compound. The compound is then processed further or utilized directly in the manufacture of the finished product. In order to create a finished compound having the intended requisite performance characteristics, it is imperative that the composite materials are mixed homogeneously in a tightly controlled procedure. Control of the processing conditions in a mixer directly affects the quality of the mixture and mixture quality, in turn, affects the quality of the end product.
The mixing process must be controlled through the control of critical mixing parameters such as batch temperature, rotor speed and torque, and the extent of additive dispersion within the batch as a function of time. Controlling the process, as discussed above, is essential to minimize the possibility that compounds from one batch to another will prove non-uniform and result in an end product of uneven quality. A second consideration is that it is desirable to minimize the energy consumed throughout the mixing process to minimize costs.
Mixing kinetic, thermodynamic, and Theological principles, therefore, are of great interest to those engaged in the manufacture of products such as tires since mixing represents the first step in tire production. A fundamental understanding of mixing is necessary for optimizing Banbury processes, for assuring batch-to-batch consistency, and for relating mix parameters to material end properties. Despite the importance of kinetic, thermodynamic, and theological principles to the mixing process, the industry has not achieved a suitable methodology that integrates the control of such parameters into a generally applicable, continuous control process Part of the reason is the difficulty in obtaining reliable experimental data that can be directly related to the object principles. For example, approaches in the past have tried to link dispersion kinetics to power consumption or to changes in dispersion quality. The main drawback of the first approach is that power consumption is not solely a function of dispersion it also depends on compound viscosity, temperature and mixer parameters. The main drawback of the second approach is the subjectivity associated with assigning dispersion quality ratings.
Previously proposed attempts to achieve a suitable control system framework have proven less than optimal. U.S. Pat. No. 4,455,091 (Bamberger et al.) correlates temperature of the mixture with energy supplied to the rotors. Such a system, however, ignores the other factors set forth above (viscosity, mixer parameters, etc.) that can affect power consumption. WO 99/24230 (Hanna Rubber Compounding) likewise utilizes a reference curve to correct process temperature by varying rotor speed and suffers, therefore, from the same limitation. EP1201387 A1 divides the process into successive phases during which time a rectilinear approximation is used to determine the values of various process parameters. A temperature or power curve is followed over sequential but arbitrarily defined “mixing phase” intervals by linearizing the curves over each interval. The gradients (slopes) of the linearized segments are used to provide feedback to a controller that manipulates ram pressure or rotor speed to match the actual gradient to the expected gradient for any given mixing phase. Such an approximation does not directly link the cause and effect between the independent variables (mixer operating conditions of rotor speed and ram pressure) and the dependent variables (temperature, torque, energy, power, reaction extent).
Accordingly the need remains for a method for directly computing dispersion extent, batch temperature, and rotor torque in a mixer so as to maximize compound uniformity and performance attributes while minimizing energy consumption. The methodology should permit engineers and compounders to evaluate the efficiency of mixing protocols and to set mixing conditions to achieve optimal results. Such a process would allow for rapid comparison between alternative procedures, compounds or mixers in order to optimize mixing efficiency and minimize energy consumption.
SUMMARY OF THE INVENTION
The present invention provides a method for directly computing and controlling dispersion extent, reaction extent, batch temperature, rotor torque, and instantaneous power in a mixer based on fundamental kinetic, thermodynamic and Theological principles. The method uses a series of steps based on fundamental kinetic, thermodynamic and rheological equations to describe dispersion extent, reaction extent, mean batch temperature, and mean torque or instantaneous power in a mixer as functions of mixing time. The parameters required for solution of the model equations are either known a priori, can be determined empirically, or can be estimated from an appropriate database. Initial mixer conditions, compound characteristics, and necessary parameters are specified by the user and provided as input. The extent of dispersion and reaction (if reactive components are present) are then calculated over a user specified time interval. Once the dispersion and reaction rates are known, the energy balance around the mixer can be solved to give mean batch temperature over the same time interval. Once the temperature is known, mean batch viscosity is calculated based on models for the effect of temperature as well as filler incorporation, dispersion and fragmentation on the batch viscosity over the same time interval. The mean viscosity value is linked to the torque acting on the rotors, or to the power supplied to the rotors over the same time interval. The torque or power calculated pursuant to the method can then be used to obtain mixing energy, work, integrated torque or total power consumption, as desired. The procedure is repeated over subsequent time intervals generating dispersion extent, reaction extent, temperature, and torque or power profiles until a user-specified end-point is reached. The end-point may be time, temperature, dispersion extent, reaction extent, integrated torque, work, energy, power consumption or other process parameters or any combination of same.
The methodology describes the processes that occur in a mixer in order to predict batch properties in real time. The method thus is based on fundamental kinetic, thermodynamic, and rheological principles and directly links cause and effect between the independent mixing variables and the dependent variables. The subject method can be used as a process control and can also be applied to predict compound properties such as dispersion extent, reaction extent and viscosity, optimizat
Campanelli John Richard
Gurer Cigdem
Rose Terry Lee
Varner John Eugene
Cooley Charles E.
O'Planick Richard B.
The Goodyear Tire & Rubber Company
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