Screw extruder classification and selection


Extruding system includes a screw extruder, a cylinder, […]

Extruding system includes a screw extruder, a cylinder, a hopper, nose, and mold, plastic plasticized by extrusion system to form a homogeneous melt, and established in the process under pressure, the extrusion screw is continuously head.
  Screw: is the most important part of the extruder, it is directly related to the range of applications and the productivity of the extruder, made of a high strength corrosion resistant alloy steel.

The basic type of the screw and the main parameters
     That is generally divided into three sections screw feed section, the compression section, are of segment.
     Feed zone - the end by the smaller, the main role is to transport raw materials to the segment, so the main problem is the transmission capacity parameter (L1, h1), h1 = (0.12-0.14) D.
     Compression section - the end by the change, the main role is compacted, molten material, building up pressure. Parameter compression ratio ε = h1 / h3 and L2. Gradation degree of accuracy should be A = (h1-h3) / L2.
     Homogenizing section (metering zone) - the compressed material melting section has pushed the metered temperature of the foremost end of the screw, the parameters (L3, h3), h3 = (0.05-0.07) D.
     Of the whole screw, the parameter L / D- aspect ratio
     L / D pros: L / D and the rotational speed n, is an important factor and the ability to effect plasticizing screw, L / D large, the material in the long residence time in the barrel, beneficial plasticizing while the pressure flow, reduced leakage, plasticizing capacity increased, while the material is advantageously require a higher temperature profile, but then a large, but also the negative impact on the use of the manufacturing assembly, generally L / D of (18 ~ 20), but tended to increase.
     Other pitches S, helix angle φ = πDtgφ, typically D = S, then φ = 17 ° 40 '.
     φ affect the ability of plastics, in general φ bigger the faster transmission speed, therefore, different materials, shape, its φ also varies. Powder preferably about φ = 25 °, φ = approximately cylindrical material 17 °, φ = feed block about 15 °, but different [Phi], for processing, but also more difficult, it is generally taken [Phi] 17 ° 40 '.
     Edge width E, the viscosity of the material in terms of small, E try to get bigger, too easy to leakage, but too large increase in power consumption, can overheat, e = (0.08 ~ 0.12) D.
     All in all, in the present case, due to lack of the necessary testing methods, the design of the screw is not complete design means. Most have Depending on the nature of the material, empirically formulate parameters to meet different needs, the plant roughly the same.

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