Function and Role of Twin Screw Thread Elements for Extruders

Model code: For example, K45°/5/56 (KB45/5/56) belongs to the shear block. "K" refers to the sliced shearing block, "45°" refers to the angle formed by the pieces, "5" means a total of 5 pieces, "56" means the length is 56MM, and the width of screw flight is 56/5=11.2mm).

Main Parameters:

Direction: forward and reverse. Reverse (left-handed), hinders the conveying of materials, prolongs the time, increases the filling pressure, and greatly improves the mixing effect.

Angle: it is generally divided into "30 °, 45 °, 60 °, 90 °".

Function and Effect:

In the positive direction, increasing the stagger angle will reduce the conveying capacity, prolong the residence time, and improve the mixing effect, but it will be easier to flow over. For distributive mixing and dispersive mixing, distributive mixing is more effective as the angle increases, and dispersive mixing is the best at an angle of 45° followed by 30°. 60° is the last.

In the reverse direction, increasing the angle will reduce the effective confinement of the polymer, but it's more likely to flow over.

Width of Screw Flight: it's generally sorted with 7mm, 11mm, 11.2mm, 14mm, 19mm, etc., which is among one of the most important parameters to measure the shear force and mixing force. The larger the width, the larger the shear and the smaller the mixing; the smaller the width, the smaller the shear, the greater the mixing. For distributive mixing and dispersive mixing, the effectiveness of distributive mixing decreases as the width increases, and the effectiveness of dispersive mixing increases as the width increases; the smaller the width, the greater the ratio between the effective axial flow and the effective radial flow of the material.

The number of screw lobes is generally divided into single head, double head and triple head.

Effect:

In the positive direction, the smaller the number of heads, the greater the extrusion conveying capacity, the greater the torque, and the better the mixing characteristics, but the less the shearing effect.

In the reverse direction, the smaller the number of heads, the smaller the extrusion conveying capacity and the better the mixing characteristics.

The two-lobe thread features uniform and quick heat. It has a good self-cleaning performance and is popularly used for extruders.

The three-lobe thread can flexibly select the pressure and temperature distribution of the material in the machine corner. The exhaust effect is good, but the output is low.