The following screw elements are implemented in SIGMA: - Threaded elements - Pushing flight elements - Threaded mixing elements (conveying/ reconveying) - V-Mixing elements - Kneading blocks - Shouldered kneading blocks - Eccentrical kneading blocks - Distance elements - Blister elements - Tooth mixing elements
To define a new screw element, choose the New element button in the Machine configuration (see figure) and select the kind of element you would like to define. Then the dialog box for entering the values will open up.
It is possible to edit already existing screw elements in the same manner as the barrel elements by double-clicking the element to be edited in the Machine configuration and entering the changes in the belonging window which will open up.
Seven out of ten input masks offer the possibility to enter Additional data to define the exact geometry. Instead of entering a Volume correction factor you enter Real diameter and Flight or Base angle; the other one will be calculated.
Metering in litres:
The „Metering in litres“ function is used to calculate the volume correction factor, which is a ratio of the actual channel volume and the theoretical tightly intermeshing channel volume.
In terms of the illustration, the „Metering in litres“ function involves placing a screw element in a measuring cylinder and then filling the cylinder with liquid up to the upper edge of the screw element. The volume of liquid in the measuring cylinder is then used to determine how large the free channel volume of the element is. The additional liquid volume created by the clearance between the screw element and the cylinder is deducted when calculating the channel volume.
The ratio to the channel volume that results from a theoretically tightly intermeshing screw profile is then the volume correction factor.
With the „Metering in litres“ function, you can select whether a single element or a pair of elements are measured. If a single element is selected, a measuring cylinder with a round base is assumed.
$$A_{cylinder} = \frac{1}{4} \pi D_{cylinder}^2$$
If the measurement of a pair of elements is selected, a measuring cylinder with the base area of a cylinder element belonging to the screw elements is assumed.
$$A_{cylinder} = \frac{1}{4} (2\pi - \theta) D_s^2 + \frac{1}{2} a D_s \cdot \sin\left(\frac{\theta}{2}\right)$$
Additional data:
If the „Additional data“ function is selected, the diameter entered in this input field is used in the simulations instead of the diameter entered above.