Double screw extruderThe composition of the components is basically similar to that of a single screw extruder. There are two screws inside the barrel of a twin-screw extruder, and the feeding part uses a screw to force feeding into the barrel. The specifications and layout of the screw bearings are relatively complex.
Double screw extruderThere are many types of screws that can be classified from different perspectives, such as whether they are engaged or not, whether the two screws have open or closed grooves in the engagement area, whether the rotation direction of the two screws is in the same or opposite direction, whether the screws are cylindrical or conical, or whether the axes of the two screws are parallel or intersecting.
The application selection of twin-screw extruders should be determined based on the following conditions.
① The selection of which type of twin-screw extruder to use should be based on the performance of the raw materials used in the production of the product.
② Consider the purpose of choosing a twin-screw extruder: whether it is used for mixing plastic pellets or for extruding molded profiles. Use this condition to select the type of twin-screw extruder.
③ Considering the required output of the twin-screw extruder and the size specifications of the product cross-section, the diameter size of the twin-screw extruder is chosen.
choiceDouble screw extruderThe general rule is that when extruding and producing profiled materials, meshing type counter rotating conical screw or cylindrical screw extruders are often used, and meshing type co rotating twin-screw extruders can also be used. When the meshing type counter rotating twin-screw extruder is used for producing profiles, it has a strong plasticizing and shearing effect on the raw materials, and the plasticizing, melting, and mixing of the raw materials are uniform, making it more suitable for the molding and extrusion of PVC materials. For the mixing and plasticization of raw materials, a meshing type co rotating high-speed twin-screw extruder is generally used for granulation, and the number of screw threads can be two or three.
Dismantling and maintenance screw of twin-screw extruder
1. Confirm that the material in the barrel is melted, remove the machine head, and extract the screw.
2. Extract materials and carbon deposits from the surface of the screw. Pay attention to the tools used during the cleaning process, such as copper plates, copper rods, and copper wire brushes. It is not allowed to use steel rods to strike.
The difference between parallel and conical twin-screw extruders
1. Diameter: The diameter of parallel twin-screw is the same, while the small end diameter of conical twin-screw is different from the large end diameter.
2. Concentric distance: The center distance of the flat twin-screw is the same, while the two axes of the conical twin-screw form an angle, and the size of the center distance varies along the axis.
3. Length to diameter ratio: Parallel twin-screw (L/D) refers to the ratio of the effective length of the screw to the outer circumference of the screw, while conical twin-screw (L/D) refers to the ratio of the effective length of the screw to the average of the large and small end diameters.
From the above, we can clearly see that the most significant difference between parallel and conical twin-screw extruders is the geometric shape of the screw barrel, which leads to many differences in structure and performance. Although the two have different characteristics, they have their own advantages.