Extruder Screw Surface Speed Calculator

Convert screw diameter and rpm into screw outside-diameter peripheral speed for setup comparison.

Formula and method

Surface speed (m/min) = π × screw diameter (mm) ÷ 1,000 × screw speed (rpm).

Inputs and units

Use the actual screw outside diameter and the controller or tachometer rpm for the defined operating point. Keep screw design, material, torque, melt temperature, and pressure with the record.

Worked example

A 90 mm screw at 100 rpm has a surface speed of 28.27 m/min.

When to use it

Use when comparing operating points across screw diameters or translating an equipment or scale-up record into a common kinematic quantity.

How to interpret the result

Surface speed is one comparison coordinate. Review it alongside specific output, torque, melt temperature, pressure, residence-time behavior, and the equipment maker limit.

Assumptions and limitations

This tool does not calculate shear rate, motor load, torque demand, melt temperature, mixing quality, or a safe maximum. Flight geometry and material rheology are not represented.

Validation guidance

Confirm actual rpm and screw diameter from machine documentation. Use OEM limits and measured melt/process results before changing speed.

FAQ

Does the same surface speed reproduce the same process on another extruder?

No. It preserves one kinematic relationship only; geometry, L/D, specific output, torque, thermal history, and residence-time distribution also matter.

Sources

Davis-Standard Extruder Specifications · Thermo Fisher: Residence-Time Distribution in Extrusion