While defining Kneading blocks a few aspects are to be considered: - In order to define kneading blocks completely, the Number of discs of one kneading block is to determine in addition to Length and Diameter. - Furthermore, the Staggering angle has to be entered. The staggering angle is only permitted in the range of

$$-\frac{180°}{z} \leq \text{Staggering angle} \leq \frac{180°}{z}$$

with i as Number of flights of the element. A negative angle identifies a reconveying kneading block, in contrast positive angle characterizes a conveying kneading block. Neutral kneading blocks are indicated by a Staggering angle of 180°/i.

Figure: Input mask eccentrical kneading block

In practice, eccentric kneading discs are often used in co-rotating twin-screw extruders to increase the melting capacity.

It is known that in a profile only one comb is scraped off with the housing. If the comb angle is zero, the eccentric profile can be generated by a displacement. The displacement is called eccentricity e. This generated eccentric profile is also tightly intermeshing. The shapes of the contours are not changed after the displacement. The following figure shows the displacement of the profiles.

Figure: Displacement of profiles with eccentricity

If the comb angle is zero, the diameter ratio of the three-course profile is at the maximum point.

Maximum diameter ratio of three-way profile (i=3)

Equation 3-13

Outer diameter of three-course profile

Equation 3-14

Eccentricity e

Equation 3-15

Inside diameter of three-course profile

Equation 3-16

The graph below shows the standard profile and the eccentric profile. The black profile is centered and symmetrical over the rotation center O point. It is also symmetrical over 3 axes: AD, BE and CF. On the other hand, the red profile is symmetrical only over x-axis.

Illustration: Profile geometry with Dv=1.366. Black: standard profile; red: eccentric profile.

This profile shows that the comb angles are zero. Therefore the flank angles of the standard profile are the same:

Comb angle: Equation 3-17 Flank angle: Equation 3-18 Outside radius: Equation 3-19 Inside radius: Equation 3-20

The coordinates of the points in the three-course standard profile can be calculated by these geometry sizes. Because the profile is symmetrical, only half the contour is selected as the calculation object.