Extrusion

Component design using thermal and fluid mechanical simulation methods

Coperion uses complex simulation methods to develop new components and aggregates. Thermal calculations relating to the component come together with fluid mechanical calculations for the flow channel to facilitate reliable designs and predictions.

For example, in our newly developed SK 92 die head for throughput rates of up to 5 t/h, the flow channel geometry and heating were optimized to give uniform product flow along the entire width of the die plate.

Transient two-phase simulation for calculating partially filled screw sections

Calculations for completely filled sections of the screw channel, e.g. in the pressure build-up zone, are already state of the art, but Coperion is also able to use a transient two-phase simulation to further adjust the flow in those parts of the process section where the screw elements are only partially filled. This approach gives us a better understanding of the flow processes in partially filled screw sections. The results are used to develop new screw elements and screw configurations.

Transient multiphase simulation for calculating distributive mixing quality

Coperion can use transient multi-phase simulation to simulate the mixing quality of various screw elements in the process section of the extruder. This simulation takes into account the continuous inflow and outflow of the mixing components in the model space so that it corresponds to the actual conditions in the process section of the extruder. The model uses the specified initial and boundary conditions to calculate a stationary condition corresponding to continuous operation of the twin screw extruder.

An appropriate evaluation makes it possible to determine the mixing quality of the compound at the exit from the model space, so that we can then compare the mixing effects of various mixing elements and combinations of elements for different process conditions (screw speed, throughput rate).

Distributive mixing effect of different screw elements

A transient simulation of the velocity field can be used to trace the paths of massless particles flowing through the screw element in the process section. This comparison between kneading blocks with offset angles of 45° and 90° clearly shows the various particle paths. The 45° kneading block has a markedly better conveying effect, but this results in a poorer mixing effect. Conversely, the 90° kneading block has a much better mixing effect, but makes no contribution to conveying the melt. Results of this kind are used in our development of special elements and their geometry.

Pressure build-up in fully filled screw sections

One ongoing development goal is to optimize the pressure build-up capacity of co-rotating twin screw extruders. Coperion uses appropriate transitory simulation methods to characterize the individual elements as regards pressure build-up. This then enables us to investigate the effects of various element geometries.

An optimized pressure build-up zone can not only contribute to energy savings in the compounding process but also to better product quality. And these simulation methods can also be used to make statements about the wear of the various screw configurations.

Pressure loss optimization for discharge units

For its further development of discharge units Coperion relies on CFD methods for calculating flow conditions. This makes it possible to very accurately predict the pressure loss for specific applications and compare different variants.

Product stress caused by screw elements

A quasi-stationary simulation of screw elements enables us to clearly illustrate the shear rate for different process parameters. Thanks to Coperion’s optimal screw geometry, average product stress remains at a low level even at high screw speeds.

Such considerations enable us to optimally match screw elements and mixing elements to their specific field of application.

Optimized aggregate design thanks to a detailed understanding of the flow processes

The CFD methods used at Coperion give us a view of the smallest details of our machines – such as the screen layers of our SWZ screen pack changer. Modeling and calculating the individual screen layers facilitates targeted optimization of the components.

We compile a pressure loss evaluation for every single screen layer by simulating the actual screen geometries. This enables us to precisely calculate changes to the pressure loss caused by changing the mesh width or wire diameter. Considering main flows and cross flows when designing the screen changer enables us to achieve minimum pressure loss.