Non-meshing and Meshing, Open and Closed Twin Screw Extruder

There are many types of twin screw extruders, which can be classified from different angles, such as whether they have meshed or not, whether the grooves of the two screws are open or closed in the meshing area, whether the rotation directions of the two screws are the same or different. The screws are cylindrical. The shape is still conical, or whether the axes of the two screws are parallel or intersecting, etc. Next, let's take a look at some common ones.

Ⅰ. Non-intermeshing and intermeshing twin screw extruder

1. Non-intermeshing twin screw extruder

Also known as outer diameter contact or tangential twin screw extruder, the shaft distance of the two screws is equal to the sum of the outer radii of the two screws. To a certain extent, it can be regarded as two single-screw extruders that influence each other. Their working principle is the same as that of a single-screw extruder. The friction characteristic of the material is the main factor to control the conveying, and this type of extruder is rarely used in food processing.

2. Intermeshing twin screw extruder

The shaft distance between the two screws is less than the sum of the two screws' outer radii, and the spiral edge of one screw extends into the groove of the other screw. It is classified into two types based on the degree of meshing: full meshing and partial meshing. The full-meshing type has no gap between the top of one screw's ridge and the root of the groove of another screw; the partial-meshing type has a gap between the top of one screw's ridge and the root of the groove of another screw. Leave space for materials to flow through.

It is called meshing type because the ridge of one screw is inserted into the groove of the other screw. It is classified into three types based on the degree of meshing: full meshing, partial meshing, and no meshing. The so-called full meshing type means that there is no gap between the top of the ridge of one screw and the root of the groove of the other screw. It means that there is a geometric gap between the top of the spiral edge of one screw and the root of the groove of the other screw.

Ⅱ. Open and closed dual screw extruder

For the meshing type, according to whether the screw groove in the meshing area is designed with possible passages along the screw groove or across the screw groove, it is divided into longitudinal open or closed and horizontal open or closed.

1. Longitudinal open or closed dual screw extruder

If the material can flow from the groove of one screw to the groove of another screw, it is called longitudinally open; otherwise, it is called longitudinally closed.

2. Horizontally open or closed dual screw extruder

In the meshing area of two screws, if the material can enter the adjacent groove of the same screw through the screw edge, or one screw, the material in the groove can flow into the adjacent groove of the other screw, it is called For horizontal opening. A horizontal opening must also be a vertical opening.

Open and closed refer to the situation of the groove in the engagement area, that is, whether the material has a possible passage along the groove or across the groove in the engagement area of the two screws. This can be divided into several situations, such as vertical opening or closing and horizontal opening or closing.

If a material has a channel from the inlet to the outlet, and the material can flow from one screw to another, it is called longitudinally open; otherwise, it is called longitudinally closed. Longitudinal closure means that the two screws each form several chambers that are not communicated with each other, and the screw groove of one screw is completely blocked by the screw edge of the other screw.

In the meshing area of the two screws, if there is a passage for the material across the screw, the material can flow from one groove of the same screw to another adjacent groove. Or the material in one groove of one screw can flow into two adjacent grooves of another screw, which is called a horizontal opening. Otherwise, it is called horizontal closing. Horizontal opening and vertical opening are not in isolation. There are two things: it is not difficult to imagine that if the horizontal opening is open, then vertical opening must also be done.