Method and device for predicting temperature profiles throughout the thickness of a polymer preform

A device for determining the temperature distribution throughout the thickness of a preform used in a container reheat stretch blow molding process from temperature measurements taken from the outside surface of the preform, comprising:

• a temperature measuring means for measuring the outside surface temperature of the preform at least two times during the period the preform is cooling down after exiting the heat station and before entering the blow molding station, wherein the temperature measuring means is coupled to a calculating means capable or receiving temperature data from the temperature measuring means;
• and
• a calculating means for calculating the temperature distribution throughout the thickness of the preform based upon the measured outside surface temperatures, wherein the calculating means receives outside surface temperature data from the temperature measuring means and calculates the preform temperature distribution using an algorithm comprising:
• curve fitting the measured outside surface temperatures to solve for An using an equation having the formula
• 12 T ⁡ ( 0 , t ) = T ⁢ ⁢ c + ∑ n = 1 ∞ ⁢ ⁢ A n ⁢ ⅇ - z n 2 ⁢ α ⁢ ⁢ t ⁡ ( z n ⁢ k / h )
• and using the An values to calculate the through-the-thickness temperature distribution for the preform using an equation having the formula
• 13 T ⁡ ( x , t ) = T ⁢ ⁢ c + ∑ n = 1 ∞ ⁢ ⁢ A n ⁢ ⅇ - z n 2 ⁢ α ⁢ ⁢ t ⁢ v n ⁡ ( x ) ,
• where T(x,t) is the through-the-thickness temperature distribution of the present invention, T(0,t) is the outside temperature as a function of time t which is curvefit to the experimental data to determine the unknown front factors An, Tc is the ambient air temperature, e is the exponential equal to 2.718, vn are the eigenvectors for the nth eigenvalue zn, k is conductivity, x is the depth of the preform from the outside surface, and a is the thermal diffusivity.

A method for manufacturing high quality containers using a reheat stretch blow molding process, comprising:

• determining the temperature distribution throughout the thickness of a preform used to manufacture containers using a method comprising:
• measuring the outside surface temperature of the preform at least two times during the period the preform is cooling down after exiting the heat station and before entering the blow molding station in the blow molding machine;
• calculating the temperature distribution throughout the thickness of the preform based upon the measured outside surface temperatures using an algorithm comprising:
• curve fitting the measured outside surface temperatures to solve for An using an equation having the formula
• 14 T ⁡ ( 0 , t ) = T ⁢ ⁢ c + ∑ n = 1 ∞ ⁢ ⁢ A n ⁢ ⅇ - z n 2 ⁢ α ⁢ ⁢ t ⁡ ( z n ⁢ k / h )
• and using the An values to calculate the through-the-thickness temperature distribution for the preform using an equation having the formula
• 15 T ⁡ ( x , t ) = T ⁢ ⁢ c + ∑ n = 1 ∞ ⁢ ⁢ A n ⁢ ⅇ - z n 2 ⁢ α ⁢ ⁢ t ⁢ v n ⁡ ( x ) ,
• where T(x,t) is the through-the-thickness temperature distribution of the present invention, T(0,t) is the outside temperature as a function of time t which is curvefit to the experimental data to determine the unknown front factors An, Tc is the ambient air temperature, e is the exponential equal to 2.718, vn are the eigenvectors for the nth eigenvalue zn, k is conductivity, x is the depth of the preform from the outside surface, and α is the thermal diffusivity;
• using the calculated temperature distribution to adjust the heating elements used to heat preforms in the heat station to obtain a desired preform temperature distribution;
• and
• blow molding the preforms into containers.

A reheat stretch blow molding machine, comprising:

• a heat station where preforms are heated;
• a blow molding station where the preforms are converted to containers;
• a means for transporting heated preforms from the heat station to the blow molding station at an essentially uniform rate;
• a temperature measuring means for measuring the outside surface temperature of a preform at least two times during the period the preform is cooling down after exiting the heat station and before entering the blow molding station, wherein the temperature measuring means is coupled to a calculating means capable or receiving temperature data from the temperature measuring means;
• and
• a calculating means for calculating the temperature distribution throughout the thickness of the preform based upon the measured outside surface temperatures, wherein the calculating means receives outside surface temperature data from the temperature measuring means and calculates the preform temperature distribution using an algorithm comprising:
• curve fitting the measured outside surface temperatures to solve for An using an equation having the formula
• 16 T ⁡ ( 0 , t ) = Tc + ∑ n = 1 ∞ ⁢ ⁢ A n ⁢ ⅇ - z n 2 ⁢ α ⁢ ⁢ t ⁡ ( z n ⁢ k / h )
• and using the An values to calculate the through-the-thickness temperature distribution for the preform using an equation having the formula
• 17 T ⁡ ( x , t ) = Tc + ∑ n = 1 ∞ ⁢ ⁢ A n ⁢ ⅇ - z n 2 ⁢ α ⁢ ⁢ t ⁢ v n ⁡ ( x ) ,
• where T(x,t) is the through-the-thickness temperature distribution of the present invention, T(0,t) is the outside temperature as a function of time t which is curvefit to the experimental data to determine the unknown front factors An, Tc is the ambient air temperature, e is the exponential equal to 2.718, vn are the eigenvectors for the nth eigenvalue zn, k is conductivity, x is the depth of the preform from the outside surface, and α is the thermal diffusivity, and
• wherein the calculating means is coupled to the heat station such that the calculating means can adjust the heat station heating elements based upon the calculated preform temperature distribution and control the temperature distribution throughout the thickness of a preform in the heat station.