Output is a main indicator to measure the performance of the extruder screw. However, it is of little significance to only emphasize the percentage increase in the output of the improved screw over the original screw, because the benchmark for comparison is not clear.
From the theory of fluid dynamics, we know that if a screw with a smaller screw edge clearance is used to replace the worn screw, the output will also be greatly improved. In order to accurately reflect the performance of the extruder screw in this aspect, it generally can be compared from the following four aspects.
That is to compare the output of different extruder screws per unit speed on the premise of qualified quality. Since the actual output Q (kg, Hr) and speed n (rpm) can be measured, the specific flow rate Q/n is easy to calculate, and its unit is (kg/Hr)/rpm, that is, hourly output of each extruder screw.
If the Q/n value is too small, then other comparisons are meaningless, because it means that the extruder screw design is unreasonable, or the process operating conditions are unreasonable.
The ratio of actual output Q to theoretical output Q1. η=Q/Q1 The actual output can be measured, but there are many calculation methods and formulas for the theoretical output Q1. When the extruder screw parameters and density are known, the denominator is constant, so the specific flow rate Q/n is related to the conveying efficiency η, and it is obviously proportional.
That is, the greater the specific flow rate, the higher the delivery efficiency. Therefore, we can simply compare the transmission efficiency by measuring the specific flow rate. For the extruder screw design, the concept of conveying efficiency is a very important concept, which reflects the comprehensive performance of the screw extrusion system.
The main goal pursued by the extruder screw designer is to obtain the highest possible output under the premise of ensuring quality. When comparing the maximum output Qmax of two screws, a formula can be used to calculate the maximum output of each screw.
The so-called "hardness" of the extruder screw characteristics refers to the decrease in output when the head pressure increases.
Forward kneading elements provide a balance between conveying and mixing, with adjustable shear depending on stagger angle and disc width.
Best suited for:
Plastication zones
General compounding
Controlled mixing processes
SSK conveying elements combine the strong conveying ability of single flight elements with increased free volume.
Best suited for:
Difficult-to-feed materials
Low-density powders and fillers
Neutral kneading elements provide strong mixing with minimal conveying effect, ensuring stable residence time and high mixing efficiency.
Best suited for:
High mixing zones
Sensitive formulations
Residence time control
Double flight conveying elements are the most widely used design in twin screw compounding. They provide the best balance between free volume and torque transmission.
Best suited for:
Feeding sections
Venting zones
Pressure control sections
Six-sided geometry enabling uniform torque transfer and rapid screw element replacement.
Best suited for:
Powder coating
Frequent material changes
Fast screw configuration changes
Reverse kneading elements introduce backflow and pressure build-up, increasing residence time and enhancing mixing intensity.
Best suited for:
Before venting zones
Degassing preparation
High mixing demand sections
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