Make the plastic processing, the difference between double screw extruder and a single screw extruder!

Twin screw extruder is the most common machine in the modified plastic industry and is widely used in polymer processing and other production and processing fields.There are many kinds of twin screw extruders, which can be divided into two types: meshing type and non-meshing type, and the meshing twin screw extruder can be divided into two categories: some rotation and different rotation.
1. The difference of the working principle of the twin screw extruder and a single screw extruder.
The structure and function of the twin screw extruder are similar to that of a single screw extruder, but there are great differences in the working principle.It is mainly manifested in the following aspects:
1) forced delivery.Meshing direction rotating twin-screw, two screw speed in meshing direction on the contrary, a screw to pull material into the meshing clearance, and another screw the material from the clearance, the result of material from a screw screw slot to another screw in the screw groove, the material along the screw is “up” form be forced to transfer in the direction of the nose.
2) homogenization and mixing.Synthetic rotating twin-screw in the meshing clearance is small, screw arris and the speed of the screw groove in the opposite direction, relative velocity is large, so the meshing area has the very high shear rate, shear stress is very big, mixing effect is far better than the single screw extruder and the rotating twin-screw extruder.
3) self-cleaning.Synthetic rotating twin-screw extruder, due to the meshing area screw arris and the speed of the screw groove in the opposite direction, relative velocity is large, so it is of high shear rate, can scrape adhesion in any screw on the product material, have very good self-cleaning effect, so that the material stay time is very short, not easily get partial degradation of metamorphism.
4) plasticization of materials.The size of the screw gap has great influence on the quality of material plasticizing.The smaller the gap is, the greater the shear force is, but the amount of material is cut.The larger the clearance, the more material increased, but the shear force decreased.
5) material compression.There are numerous ways to compress the material with the twin-screw extruder, and the comprehensive effect is good.
6) feeding method.The identical twin-screw extruder requires a uniform and quantitative feeding method.
7) exhaust.Because it is hungry feed, can use the thread conveying element of the big lead. Make the spiral groove is in unfilled state and be in zero pressure state, can set the exhaust section.
2. Application of a twin screw extruder.
The rotating direction of the twin screw extruder can be divided into two screw and two screw.
It is widely used in the physical and chemical modification of matrix resin, such as the filling, strengthening, toughening, reaction extrusion, etc.
Predominantly dispersion mixing all kinds of raw materials blending, should choose synthetic twin-screw extruder, and the same as in the above to the velocity vector of double screw into reverse, therefore a higher rotating twin-screw compared with differential rotating twin-screw, its role is much larger shear, mixing forming is not suitable for Pvc.
Commonly used in blending and filling plastic is powdery calcium carbonate, talcum powder, titanium dioxide, the general filling amount is 30%~60%, and the filling mother is up to 80%.Because the powder packing contains a large amount of air, when screw kneading zone of mixed air can be separated, and the material reverse flow into the spiral groove, effect of powder feed forward, decreasing the quantity finally.
Application examples of twin-screw extruder: fiberglass enhancement and resistance fuel granulation (such as PA6, PA66, PET, PBT, PP, PC enhanced flame retardant, etc.);High fill material granulation (such as PE, PP filling 75% CaCO3.);Heat sensitive material granulation (such as PVC, XLPE cable);Strong color masterbatch (e.g. fill 50% color powder);Antistatic mother grain, alloy, coloring, low filling blending granulation;Cable granulation (e.g. sheath, insulating material);XLPE pipe material granulation (for example, the mother grain used for hot water crosslinking);Thermosetting plastic mixing extrusion (e.g. phenolic resin, epoxy resin, powder coating);Hot melt adhesive, PU reactive extrusion granulation (such as EVA hot melt adhesive, polyurethane);K resin, SBS, and so on.
3. Advantages and disadvantages
Because of twin-screw extruder of the complexity of the structure design and processing, theory development is not perfect, but shaped design direction twin screw extrusion unit, a variety of geometric shapes can be threaded components and barrel components for permutation and combination, according to the theory of experience – – practice – test, which can be mixed according to different requirements, the optimization design to adapt to the needs of different technological formula, so that the same double screw extrusion machine has the very strong adaptability.It is mainly manifested in the following aspects:
1) mixing performance: as the two screw pitch, and can according to need to join all kinds of screw elements, such as reverse thread element, mesh plate element, toothed plate element, and so on, to precision adjusting shear/mix, so that the strength and the mix quality (whether distribution or dispersed mix) can be effectively controlled.This is out of reach of a single screw extruder.
2) processing flexibility: synthetic twin screw extruder USES measuring hunger feeding normally, production depends on the feed rate, independent of the screw rotation speed, is an independent controlled variables, thus it can be on one machine flexibility to deal with a variety of processing capabilities, such as melting and mixing, exhaust, and so on.
3) process parameter control, direction twin-screw extruder narrow residence time distribution, better convection heat transfer and a precisely controlled temperature curve, can be better in the extrusion of shear – time – temperature process, mechanical energy input in a wider scope, which can get a better product quality stability.
4) high efficiency of process production: the positive displacement transport of the screw can handle more varied raw materials and mixed formulation, and the downtime is short.
5) higher economy: because of the flexibility of high technology and productivity, can produce a wider range of end products, and can provide high consistency of product quality, can also through the screw speed adjustment to compensate for the wear and tear of the screw.