Screw profile

Single- and twin-screw extruders with customised screw profiles are used to produce low density PETP-PP foams in the presence of reactive compatibiliser and coagents. Low density PETP foam is also produced from... 

The quality of the axial bearings of the two shafts in the duo-gear as well as that of the rotation angle allocation leads to tolerances and clearances in the screw profile. 

Figure 5.1 Screw profiles with lines of symmetry...

A screw profile with Z threads can be divided into 2Z symmetrical parts, as illustrated in Fig. 5.1. A screw profile is composed of three parts within this symmetrical area tip, flank, and root. The tip comprises an arc whose diameter equals the external diameter of the screw profile and whose center point is the center of the circle. One edge of each tip passes over to the adjacent flank area. For screws that wipe the inside of the barrel tightly, the flank areas each comprise an arc whose radius equals the centerline distance. The flanks then pass tangentially over into the root areas, the diameters of which correspond to the diameter of the screw core and whose circle center is the center of the profile. The tip cleans the root of the opposite screw and vice versa. The corner of the profile between the tip and the flank cleans the flanks. 

Figure 5.8 Geometric variables of a double-flighted screw profile, cross-section Green fully wiped contour. Red actual contour. Blue barrel wall...

Calculation of a Screw Profile for Production According to Longitudinal Offset... 

In the case of the planar offset we take the planar section of the fully wiped profile and move this inwards by half the screw-screw clearance. To calculate a screw profile according to the planar offset, we proceed as follows ... 

From the specified geometry data DG, A, Z, s and 8 of the extruder according to Table 5.1 we obtain the values DE, R, DI, RI, KWO and KBO of the fully wiped screw profile, (x, y) are the coordinates of the fully wiped screw and xa> ya are the coordinates of the profile to be produced. The planar profile of the fully wiped screw is thus... 

Figure 5.12 Determining a point of the actual screw profile...

Two screw profiles that are described by the same geometric parameters are known as geometrically similar. They can be converted into one another by scaling. The pressure and power numbers are dependent only on the throughput number if the screws are geometrically similar. The relationships are linear in the case of fluids of constant viscosity ( Newtonian fluids ). The complete pressure and energy behavior of a class of geometrically similar screws can thus be traced back to a simple linear relationship. 

Eccentric Screw Profiles (Section 13.6-13.9) Elere, the screw profiles are arranged eccentrically on the shafts. These screw elements consume less energy because, except for one screw tip, all other tips feature an enlarged clearance to the barrel. The self-cleaning of the barrel is guaranteed by the one tightly intermeshing tip. 

General Screw Profiles (Section 13.10-13.15) Next to the traditional screw profiles, additional completely self-cleaning profiles have been developed in which the tip angles differ or which feature asymmetrical profiles. 

Transition Elements (Section 13.16-13.19) Generally, shims are inserted between elements with different numbers of flights to compensate for the axial clearance of the shafts. It is also possible to use transitional elements whose screw profiles alter continuously along the axis from o ne number of flights to another, while maintaining a complete self-cleaning function. 

This patent lays claim to eccentric screw profiles in the twin-screw extruder. Its eccentricity is arranged such that the barrel is cleaned by a single tip only. 

Unlike the previous patent, the eccentricity in this case is achieved by arranging the screw profiles within a significantly enlarged barrel clearance. 

This patent concerns a single-flighted, asymmetrical screw profile which is mainly composed of a circular disc with a small tip and a small root region. 

This patent relating to single-flighted screw profiles clearly shows that the tip angles of a pair of screws do not have to be the same size. 

This patent lays claim to n-flighted screw profiles exhibiting different tip and core diameters. The barrel is cleaned by at least one tip. 

Claim is laid to a self-cleaning triple-flighted screw profile with two or three different tip widths. The barrel is cleaned only by the widest tip. 

In this patent, the transition from an x-flighted to a y-flighted screw profile is claimed. Both screws exhibit different screw profiles in the transitional region. 

This patent contains a description of a transition from a single-flighted to a triple-flighted and back to a single-flighted screw profile. The barrel is not cleaned in the triple-flighted region. 

The screw profiles are asymmetrical in design and exhibit large uneven clearances. 

Moving from triple-flighted to double-flighted screw profiles... 

The two intercepts A1 and A2 are called profile parameters of a screw machine because their numerical values depend on the screw geometry ( screw profile ), for details see [5, 65]. 

The production of rigid PVC profiles is described with reference to state-of-the-art twin screw profile extruders and downstream equipment from Battenfeld. Features of the machinery are described, and particular details are given of the profile dies, calibration block, calibration table, haul off and profile saw. 

Figure 1-2 presents an illustration of several types of mixing screws. These show variations in thread pitch as different profiles or offsets in the diameter of the screws between the threaded lands. Screw profiles vary for the type of compound being mixed. In some cases, very high shear is required to assure proper dispersion of ingredients. For other compounds, aggressive shear will... 

Fig. 10 Screw profile for Conical Twin-screw. (Courtesy of Cincinnati Milacron.) fView this art in color at www.dekker.com.)...

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