Control for batch mixers

A process for mixing a composition comprising polymeric material and additive materials in an internal mixer having two mixing rotors mounted for rotation in a mixing chamber, a ram mounted for sliding movement in a passage opening into the mixing chamber by which pressure can be applied to material in the mixing chamber and means for controlling the temperature of the mixer, the process comprising:

• (a) introducing each of the polymeric and additive materials to be mixed into the mixing chamber at appropriate points of the mixing operation;
• and
• (b) after introduction of all the materials, initiating a control stage, the control stage comprising:
• (1) selecting defined ultimate targets from at least some monitorable mixing variables at which mixing is deemed satisfactory, said mixing variables being selected from composition temperature, total energy input to the composition by the rotors during mixing, mixing cycle time, torque of the rotors at a preselected mixing cycle time and position of the ram;
• (2) monitoring at least three mixing variables from which the quality of mixing can be determined;
• and
• (3) dependent on the values of the mixing variables monitored, adjusting at least one of the speed of rotation of the rotors and the pressure applied by the ram so that the mixing process continues towards the previously defined target values of the monitored mixing variables, and
• (4) terminating mixing when the defined target value of the torque of the rotor at a preselected mixing cycle time is achieved, with the proviso that if the defined target value of the torque is not achievable, then terminating mixing when the most significant defined set of target values selected from mixing cycle time and composition temperature or mixing cycle time and total energy input to the composition by the rotors has been achieved.

A process for mixing a composition comprising polymeric material and additive materials in an internal mixer having two mixing rotors mounted for rotation in a mixing chamber, a ram mounted for sliding movement in a passage opening into the mixing chamber by which pressure can be applied to material in the mixing chamber and means for controlling the temperature of the mixer, the process comprising:

• (a) mixing a selected number of experimental batches of the composition;
• (b) during mixing of the experimental batches monitoring and storing data for at least three mixing variables from which the quality of mixing can be determined;
• (c) using the data stored from mixing of the experimental batches and deriving a number of equations, each equation relating at least one of the mixing variables with at least one of the speed of rotation of the rotors and the pressure applied by the ram;
• and
• (d) mixing a batch of the composition subsequent to the experimental batches using automatic control comprising:
• (1) selecting defined ultimate targets from at least some monitorable mixing variables at which mixing is deemed satisfactory, said mixing variables being selected from composition temperature, total energy input to the composition by the rotors during mixing, mixing cycle time, torque of the rotors at a preselected mixing cycle time and position of the ram;
• (2) monitoring the mixing variables of the subsequent batch and applying the derived relations to adjust at least one of rotor speed and ram pressure to achieve the predefined target values of the monitored mixing variables, and terminating mixing when the predefined target values are achieved, with the proviso that if all the target values are not simultaneously achievable, then terminating mixing when the most significant predefined target values have been achieved.

A process for mixing a composition comprising polymeric material and additive materials in an internal mixer having two mixing rotors mounted for rotation in a mixing chamber, a ram mounted for sliding movement in a passage opening into the mixing chamber by which pressure applied to material in the chamber can be adjusted and means for controlling the temperature of the mixer, the process comprising:

• (a) storing a first series of equations relating increase of total energy supplied to the composition to be mixed with at least one of rotor speed and ram pressure, each equation of the series being valid to predict energy input increase over a particular interval of time within a finite period in an automatically controlled stage of a mixing cycle subsequent to a material feeding stage,
• (b) storing a second series of equations relating change in temperature of the composition to at least one of rotor speed and ram pressure, each equation of the series being valid to predict temperature increase over the corresponding increments of time applicable to the first series of equations;
• (c) deriving from the first and second series of equations first and second relationships relating change in total energy input supplied to the composition and change in temperature of the composition, respectively, with at least one of mixing cycle time, rotor speed and ram pressure continuously over a desired operating range of mixing time;
• (d) storing desired target values for target total energy to be supplied by the rotors to the composition in a mixing cycle, target composition temperature to be achieved by the composition at the end of the mixing cycle and target length of time of the mixing cycle;
• (e) at intervals during the automatically controlled stage:
• (1) comparing total energy input to the composition with the stored target total energy input to the composition;
• (2) comparing actual composition temperature with the stored target composition temperature;
• (3) comparing the time elapsed during the mixing cycle with the target length of time of the mixing cycle;
• and
• (4) calculating a remaining total energy to be supplied to the composition, a remaining temperature increase of the composition and a remaining time of the mixing cycle necessary to achieve the respective target values;
• (f) if the remaining time of the mixing cycle necessary exceeds said finite period:
• (5) calculating the finite period as a proportion of the remaining mixing cycle time;
• (6) calculating the same proportion of a remaining total energy input to be supplied;
• (7) calculating the same proportion of a remaining composition temperature increase to be achieved;
• (8) applying the equations from the first and second series appropriate to said finite period and calculating an adjustment in at least one of rotor speed and ram pressure necessary to most closely achieve the calculated proportion of total energy increase to be supplied and the calculated proportion of composition temperature increase at the end of said finite period;
• and
• (9) causing at least one of rotor speed and ram pressure to be adjusted to the calculated rotor speed and ram pressure adjustment;
• and
• (g) when the remaining time necessary to achieve the target mixing cycle time is less than said finite period
• (10) applying the first and second relationships calculating the rotor speed and ram pressure adjustment values necessary to most closely achieve the target total energy input to the composition and target composition temperature at the target mixing cycle time, and
• (11) causing at least one of the rotor speed and ram pressure to be adjusted to the calculated rotor speed and ram pressure adjustment values.