October, 2010
The Ludovic v5.3 proposes new mathematical tools to analyse the link between the operating parameters, the screw geometry and the behaviour of the material during the twin screw extrusion process
Twin Screw modelling
The Ludovic software is dedicated to the modelling of corotating twin screw. It brings :
- information on the material and process behaviour at a given instant by the one shot simulation(see Pict1.)
- energy balance and functioning state of the twin screw by global results
- information on a whole functioning domain with the Sequencer
The new functionality is based on a mathematical model analysing the correlation between parameters, results and material behaviour.
An example about the usefulness and the application of this new tool will be more efficient than a classic description.
Impact of the wear of a kneading block on mixing efficiency
In this example, we'd like to observe the impact of the wear of kneading blocks on the mixing capability of the extruder.
In Ludovic, the wear is modeled by the evolution of the leakage (space between the edge of the block and the barrel) of the kneading block. We used a classic screw configuration as presented on the Picture1.
In a first time, we have created a sequence of simulations to change the value of the leakage in the range [0,1 ; 2]mm. It means that all kneading blocks of the screw have known the same evolutions.
After a sequence of 150 simulations, Ludovic proposed a 3D curve to analyze the impact of the leakage evolution (see Pict2.)
This curve shows that bigger the leakage is, less important the torque becomes.
Correlation between wear and mixing
We chose to observe the torque because this value is easy to get and to control (more than the mixing quality).
To go further, we used the Ludovic Correlation tool. The 150 simulations were loaded to get the opposite curve (see Pict3.). The correlation between the Torque and the leakage of the kneading blocks is very strong. The correlation coefficient is 0.998. It also confirms that more important the leakage is, less important the value of the torque is.
To have an idea about the impact on the mixing efficiency, we chose the mean of the RTD (Residence Time Distribution) as tag and we used the same procedure. The results is the correlation curve between the kneading block leakage and the RTD mean (see Pict4.). Once again, the correlation between these two values is very strong (correlation coefficient=0.949): the leakage of the kneading blocks has a direct impact of the RTD mean.
Conclusion of this experience
From those results, we can see that the wear of kneading blocks (modeled by the increase of the leakage) has a direct impact on the mixing efficiency of the twin screw extruder. The decrease of the torque is a signal of this loss of efficiency.
Usefulness of the correlation tool
After this study, we can notice that some parameters are more easy to observe than other ones (torque vs. mixing efficiency).
The correlation tool allows to connect parameters and results values to control and anticipate phenomenon and impact which are not necessary easy to measure (the mixing efficiency as an example).
The Ludovic V5.3 is available from October 15, 2010.
Pict1. Screw configuration used for this study. The kneading blocks are represented by the red, orange and green colors.
Pict2. Impact of the wear of kneading block on the torque.
The red axis represents the evolution of the leakage, the green axis is the torque and the blue axis is the evolution of the screw rotation speed.
Pict3. Correlation between Torque (y axis) and kneading block leakage (x axis)
Pict4. Correlation between Torque (y axis) and kneading block leakage (x axis)