Twin Screw Extruder Special structure
In the late 1930s, the twin-screw extruder developed by the Italians was the first twin-screw extruder used to process polymers. In the initial stage, the working mechanism of the twin-screw extruder was not well understood, and some problems encountered in the design and manufacture of the machine were difficult to solve until the late 1960s, The special thrust bearing of the machine, which solves the problem of bearing capacity in the axial and radial directions of the bearing in the smaller space between the two screws makes the twin screw extruder very reliable in the mechanical structure. At present, twin screw extruders have been used in the polymer processing industry is very common.
The two main applications of twin screw extruders are: extrusion molding of heat-sensitive materials such as P V C pipes and profiles; special polymer processing such as blending, exhaust, chemical reactions and the like. The twin screw for the extrusion of the profile has intermeshed ribs, grooves, and operates at a lower speed of about 10r / min. Compared with single screw, twin screw extruder feed and delivery performance is much better, especially those difficult to feed and easy to slip, such as fibrous, powder and grease materials. Material retention time is short and relatively uniform, better mixing and a larger heat transfer area, so that the temperature control is good, which is particularly important for the processing of heat-sensitive materials.
Since the twin screw extruder is also designed as a number of special structural elements, can be any combination and replacement, it is particularly suitable for some special polymer processing. The intermeshing co-rotating twin-screw extruder can be used for blending, continuous chemical reactions, and exhaust extrusion. This type of extruder running at high speed, the maximum screw speed range of 300 ~ 600r / min. Different engagement types, different steering forms, different combinations of components of the twin screw, the working mechanism is different. For details, please refer to the technical center of a twin screw and barrel damage reasons
1, the screw rotation in the barrel, the material and the friction between the two, so that the screw and the barrel of the working surface gradually wear: screw diameter gradually reduced, the barrel of the hole diameter gradually increased. In this way, the screw and the barrel with the diameter of the gap, with the gradual wear and tear of the two slightly increased. However, since the resistance of the front head and the manifold of the barrel does not change, this increases the leakage flow at the time of the extruded material, i.e., the flow of material from the diameter gap to the feed direction. As a result, the extruder production is reduced. This phenomenon also makes the material in the barrel to increase the residence time, resulting in material decomposition. If it is polyethylene, the decomposition of hydrogen chloride gas to strengthen the corrosion of the screw and barrel.
2, if the material such as calcium carbonate and glass fiber filler, can speed up the screw and barrel wear.
3, because the material is not plasticized evenly, or a metal foreign body mixed with the material, so that the screw torque torque suddenly increased, this torque exceeds the screw strength limit, so that the screw off. This is an unconventional accident damage.
Second, the twin screw extruder manufacturers screw repair
1, the screw is broken according to the actual diameter of the barrel to consider, according to the normal gap with the barrel to give the new screw diameter deviation manufacturing.
2, the wear screw diameter reduced thread surface after treatment, thermal spraying wear-resistant alloy, and then by grinding to the size. This method is generally a professional spray processing plant repair, the cost is still relatively low.
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